Veterinary · Clinical · also MSVE VMD-421
The production diseases of high-yielding animals and the mineral and vitamin deficiencies: milk fever, ketosis, grass tetany, downer cow and their relatives.
In the exams: ICAR AICE-JRF core group 07 (Medicine); China comprehensive paper cattle; a recurring topic across Indian PG, PhD and state PSC syllabi
Production diseases are the diseases a farm creates when the demand it places on an animal outruns the animal's ability to adapt. Milk fever, ketosis, fatty liver, hypomagnesaemic tetany, post-parturient haemoglobinuria and the downer cow are the price of failed adaptation. Mineral and vitamin deficiencies are their slower cousins: diseases of soil, forage and diet that show up as wasting, lameness, infertility, anaemia or dead newborns.
Each disease is followed from aetiology (cause) and pathogenesis (mechanism) through signs and diagnosis to treatment and prevention. Because the curriculum is built around the transition dairy cow, chapter 1 sets out the physiology of that period, herd monitoring with metabolic profiles, and two diseases that ride alongside the metabolic ones: subacute ruminal acidosis and displaced abomasum. Chapter 12 covers the endocrine disorders of dogs and cats, which share the logic of failed hormonal control.
Worldwide, this subject is examined in two ways. Indian postgraduate, PhD and state public service papers (ICAR AIEEA-PG, AICE-JRF core group 07, RPSC, TNPSC, ASRB) ask for definitions, synonyms, causal agents, characteristic signs and the biochemistry of each disease. Licensing examinations such as the NAVLE, RCVS SME, Australasian AVE and China's national examination use case vignettes, which reward understanding the mechanism.
Doses are given only where a value is standard across textbooks, and always with a reminder to check the product label and national formulary. Reference ranges and herd alarm thresholds differ between laboratories, analysers and countries; where they do, this manual says so and gives the commonly cited value as a guide, not a rule.
The transition period is usually defined as the three weeks before to three weeks after calving. In those six weeks a dairy cow moves from a low-demand dry state to lactation, and three pressures arrive at once. First, calcium: colostrum and milk draw calcium out of the blood faster than intestinal absorption and bone resorption can be switched on. Second, energy: milk yield rises faster than dry matter intake (DMI), which falls in the last days before calving and recovers only over several weeks, so the cow is in negative energy balance (NEB). Third, immunity: neutrophil and lymphocyte function is depressed around calving, which is why retained placenta, metritis and mastitis cluster here. These problems are linked: hypocalcaemia reduces gut motility and intake, which deepens NEB; NEB mobilises body fat as non-esterified fatty acids (NEFA), which load the liver. A cow with one transition disease is at higher risk of the others, and a herd with one problem usually has several.
A metabolic profile is the measurement of selected blood (or milk and urine) analytes in a group of animals to judge whether the group's nutrition and metabolism are adequate before disease appears. The approach was formalised in the Compton metabolic profile test developed in England by Payne and colleagues around 1970, which compared blood values of dry, early-lactation and mid-lactation groups. The analytes are chosen by the question asked. Energy status is judged from glucose, NEFA and beta-hydroxybutyrate (BHB). Protein status is judged from blood or milk urea nitrogen, albumin and globulin. Macro-mineral status uses calcium, inorganic phosphorus and magnesium; trace-element status uses liver or blood copper, whole-blood glutathione peroxidase (for selenium), vitamin B12 or methylmalonic acid (for cobalt) and plasma inorganic iodine or thyroxine. Modern transition-cow profiles are narrower and sharper: NEFA in cows 2 to 14 days before calving, BHB and NEFA in cows 3 to 14 days after calving, and calcium in the first 48 hours after calving. Results are interpreted for the group: usually about 12 cows are sampled, and the key statistic is the proportion above a threshold, because a mean hides the sick minority.
Commonly cited cow-level thresholds, from field studies in North America, are a prepartum NEFA of about 0.3 mEq/L or more, a postpartum NEFA of about 0.6 to 0.7 mEq/L or more, and a postpartum blood BHB of 1.2 mmol/L or more (some studies use 1.0 or 1.4). Cows above these values have more displaced abomasum, clinical ketosis, metritis and culling, and lower milk yield. Herd alarm levels are often set at 10 to 15 percent of sampled cows above threshold. Clinical ketosis is usually associated with BHB of about 3.0 mmol/L or more. For calcium, subclinical hypocalcaemia is commonly defined as total serum calcium below about 2.0 mmol/L (8 mg/dL), with cut-offs between 1.8 and 2.2 mmol/L in different studies. Sampling technique changes results. NEFA rises with handling stress and falls after feeding, so samples are taken before feeding and with minimal restraint; haemolysed or delayed samples are unreliable. BHB rises for several hours after silage feeding, especially with silage high in butyric acid. The coccygeal (tail) vein is the usual site. Convert units carefully: to change calcium from mg/dL to mmol/L multiply by 0.2495 (divide by about 4), for magnesium multiply by 0.411, for inorganic phosphorus multiply by 0.323, and for BHB divide mg/dL by 10.41.
Subacute ruminal acidosis (SARA) is repeated periods of low rumen pH, commonly taken as pH 5.5 or below when measured in fluid collected by rumenocentesis, caused by rations high in rapidly fermentable starch and low in physically effective fibre, by feed sorting or by large, infrequent concentrate meals. It rarely produces a sick cow on the day; instead the herd shows variable intake, milk fat depression, loose faeces with fibre particles, claw horn lesions and laminitis, and later rumenitis with liver abscesses (Fusobacterium necrophorum) and caudal vena cava thrombosis. Herd diagnosis is by rumenocentesis of about 12 cows at the expected low point after feeding; if 25 percent or more are at or below 5.5, SARA is a herd problem. Stomach-tube samples read higher because of saliva. Displaced abomasum (DA) is displacement of the gas-filled abomasum, most often to the left, usually in the first month after calving. Risk factors are hypocalcaemia, ketosis, metritis, retained placenta, low intake and low-fibre diets, all of which reduce abomasal motility. A left DA gives a high-pitched ping on simultaneous percussion and auscultation between about the 9th and 13th ribs on the left. It is corrected surgically (right-flank omentopexy, left-flank abomasopexy, right paramedian abomasopexy) or by closed methods. Right displacement with volvulus is an emergency and produces hypochloraemic, hypokalaemic metabolic alkalosis.
Milk fever, also called parturient paresis or clinical hypocalcaemia, is an afebrile flaccid paresis caused by an acute fall in blood calcium at the onset of lactation. Despite its name there is no fever; body temperature is usually normal or low. Most cases occur within 72 hours of calving, the majority in the first 24 hours. Risk rises with age and parity (it is rare in first-calf heifers), with high milk yield, and in Jersey and other Channel Island breeds. The size of the challenge is easy to show. An adult cow has only about 3 g of calcium in her plasma and roughly 8 to 9 g in all extracellular fluid, while colostrum contains about 1.7 to 2.3 g of calcium per litre, so 10 litres of colostrum removes several times the plasma pool in a day. Unless intestinal absorption and bone resorption increase within hours, blood calcium falls. Most cows have subclinical hypocalcaemia around calving; only some become recumbent. In ewes, hypocalcaemia more often appears in late pregnancy, precipitated by stress, transport or fasting.
Blood calcium is controlled by parathyroid hormone (PTH), which increases bone resorption and renal calcium reabsorption and stimulates the kidney to make 1,25-dihydroxyvitamin D (calcitriol), which increases intestinal calcium absorption. Milk fever is a failure of this system to respond fast enough, not a lack of body calcium. Two factors dominate. The first is metabolic alkalosis. Diets high in potassium and sodium, typical of grass and legume forages, make the blood alkaline; alkalosis changes the PTH receptor so bone and kidney respond poorly to PTH. This is the basis of feeding a negative dietary cation-anion difference before calving. The second is magnesium: hypomagnesaemia reduces both PTH secretion and tissue responsiveness, so a cow with low magnesium will not mount a normal calcium response. A high calcium intake in the dry period also suppresses the system, because the cow has no stimulus to switch it on before calving. Low calcium impairs acetylcholine release at the neuromuscular junction and weakens skeletal and smooth muscle contraction. That explains flaccid paralysis, ruminal stasis, bloat, constipation, poor teat sphincter tone (and hence mastitis), uterine inertia and uterine prolapse. Blood phosphorus usually falls at the same time.
Stage 1: the cow is still standing but is excitable and hypersensitive, with fine muscle tremors of the head and limbs, ear twitching, shuffling of the hind feet and reluctance to eat. It is often missed. Stage 2: sternal recumbency. The cow is dull, often lies with her head turned into her flank (an S-shaped neck in some cows), and has cold extremities, a dry muzzle, dilated pupils with a sluggish light reflex, subnormal temperature, a weak rapid pulse with quiet heart sounds, ruminal stasis, mild bloat, a relaxed anus and loss of the anal reflex. Stage 3: lateral recumbency with flaccid paralysis, severe bloat, a very weak or impalpable pulse and progressive loss of consciousness. Without treatment, death follows within hours from bloat, aspiration of rumen contents or circulatory failure. Diagnosis is clinical, backed by response to treatment. Total serum calcium is usually below about 1.4 mmol/L (5.5 mg/dL) in recumbent cows; take a sample before treatment for confirmation. Differentials include toxic mastitis or metritis, hypomagnesaemia, calving injuries (obturator or sciatic nerve damage, hip dislocation, pelvic fracture), hypophosphataemia, hypokalaemia and fatty liver.
The treatment of choice for a recumbent cow is calcium given slowly intravenously, usually as calcium borogluconate. A commonly cited adult dairy cow dose is about 8 to 11 g of calcium, roughly 2 g of calcium per 100 kg body weight, given intravenously over 10 to 20 minutes — confirm against the product label and your national formulary. The label must be read for its calcium content, not only its percentage of calcium borogluconate, because formulations differ; a 20 percent calcium borogluconate solution contains only about 1.5 g of calcium per 100 mL. Auscultate the heart throughout. Calcium is cardiotoxic when given too fast: bradycardia, arrhythmia and cardiac arrest can follow. Slow or stop the infusion if the rhythm becomes irregular or the rate falls sharply. A good response includes muscle tremors, eructation, defecation, a stronger slower pulse and, often, standing within an hour or two. Keep the cow sternal, not lateral, to reduce bloat and aspiration. Subcutaneous calcium alone is absorbed poorly in a cold, poorly perfused cow and should not be the sole treatment of a recumbent cow. Oral calcium (calcium chloride, calcium propionate or calcium sulfate formulations) is useful for standing cows and after intravenous treatment to reduce relapse, but must never be drenched into a cow that cannot swallow properly, because of the risk of aspiration. Calcium chloride is also caustic.
The dietary cation-anion difference (DCAD) is usually calculated in milliequivalents per kg of dry matter as (Na + K) minus (Cl + S). Each element's percentage is converted to mEq/kg by multiplying by 10 to give g/kg and dividing by the equivalent weight in grams per mEq: 0.023 for sodium, 0.039 for potassium, 0.0355 for chloride and 0.016 for sulfur (sulfate carries two charges). Feeding a negative DCAD in the last two to three weeks before calving, by adding anionic salts or commercial acidogenic feeds (chloride and sulfate sources) and choosing low-potassium forages, produces a mild compensated metabolic acidosis that restores tissue sensitivity to PTH. Targets vary. Many advisers aim for about -50 to -150 mEq/kg DM. Success is monitored by urine pH in cows fed the diet for at least a few days: commonly about 6.0 to 7.0 in Holsteins for partial acidification and lower, around 5.5 to 6.0, for full acidification. A urine pH below about 5.5 suggests excessive acid load, which lowers intake. Other methods are a low-calcium dry-cow diet (the aim is to stimulate PTH before calving), calcium-binding agents that reduce calcium absorption before calving, oral calcium boluses at and shortly after calving for high-risk cows, adequate dietary magnesium in the close-up diet, and avoiding over-conditioned cows.
A downer cow is a cow that is recumbent and cannot rise. The term is used in two ways. Broadly, it is any cow that cannot rise. More narrowly, downer cow syndrome means a cow that is still recumbent more than about 24 hours after treatment for milk fever, while remaining bright and alert, often called the alert downer. Most downer cows begin as milk fever cases, and the longer the delay to treatment the higher the risk. Other primary causes are calving injuries (damage to the obturator nerve as the calf passes through the pelvis, sciatic or peroneal nerve damage, sacroiliac luxation, pelvic or femoral fracture, hip dislocation), toxic mastitis or metritis, hypophosphataemia, hypomagnesaemia, hypokalaemia and severe fatty liver. Whatever the first cause, recumbency itself creates the most important secondary lesion. A heavy cow lying on a hind limb compresses the muscles, especially the semitendinosus and adductor group, and the sciatic nerve. Within about 6 hours or more of recumbency on a hard surface, ischaemia damages the muscle; swelling within the fascial sheath raises pressure further, producing a compartment syndrome and ischaemic necrosis. The damaged muscle cannot support the cow, so she stays down, and the injury worsens.
The alert downer eats and drinks, often attempts to rise, and may creep along the ground with hind legs extended backwards (the so-called creeper cow). Examination must cover the whole cow: rectal examination for pelvic fractures, limb manipulation for dislocations or fractures, the udder and uterus for toxic disease, and neurological assessment of the hind limbs. Hypokalaemic cows are profoundly weak, often lie with the head turned back into the flank and cannot hold the head up; this is classically seen after repeated doses of the corticosteroid isoflupredone acetate, which has mineralocorticoid activity, combined with anorexia. Serum potassium below about 2.5 mmol/L supports the diagnosis. Muscle enzymes help judge muscle damage. Creatine kinase (CK) rises within hours of muscle injury and falls quickly once damage stops; aspartate aminotransferase (AST) rises more slowly and stays high longer. A very high and still rising CK suggests continuing muscle necrosis and a worse prognosis. Myoglobinuria and proteinuria reflect muscle damage and can injure the kidney. Blood calcium, phosphorus, magnesium, potassium, glucose and BHB should all be checked in a cow that has not responded to calcium.
Nursing is the treatment. Move the cow onto deep bedding, sand or pasture, prop her in sternal recumbency and roll her from side to side every few hours. Give free access to water and palatable feed and protect her from weather. Correct any identifiable deficiency: calcium, phosphorus, magnesium or potassium (oral potassium chloride is the usual route for hypokalaemia). Give analgesia by drug class, usually a non-steroidal anti-inflammatory drug, once the cow is hydrated. Assisted lifting helps selected cows. Flotation tanks, in which the cow is supported in warm water, have the best reported outcomes. Hip lifters (hip clamps) can bruise the tuber coxae and should only be used briefly, with padding, to test whether the cow can bear weight. Slings and inflatable bags are alternatives. Prognosis depends on the cause and duration. Cows that remain bright, eat, keep trying to rise and can bear weight when lifted recover more often; cows with fractures, dislocations, severe muscle necrosis, persistently rising CK, or systemic disease rarely do. Welfare is central. A recumbent cow that cannot be moved humanely must not be transported, and many countries regulate this in law. Set a time point for re-evaluation and discuss euthanasia openly when recovery is unlikely.
Ketosis (acetonaemia) is a disorder of energy metabolism in which ketone bodies accumulate in blood, urine and milk. The ketone bodies are acetoacetate, beta-hydroxybutyrate (BHB) and acetone. Ruminants absorb little glucose from the gut, because rumen microbes ferment carbohydrate to volatile fatty acids. Glucose is made in the liver by gluconeogenesis, mainly from propionate, with contributions from amino acids, lactate and glycerol. A high-yielding cow needs large amounts of glucose to make lactose, the main osmotic determinant of milk volume, and each kilogram of lactose requires slightly more than a kilogram of glucose. When energy intake falls short, low insulin and high glucagon and catecholamines release NEFA from adipose tissue. The liver takes up NEFA in proportion to their blood concentration. It can oxidise them completely in the tricarboxylic acid (TCA) cycle, convert them to ketone bodies, or re-esterify them to triglyceride. When oxaloacetate is diverted to gluconeogenesis, acetyl-CoA from fat cannot all enter the TCA cycle and is converted to acetoacetate and BHB.
Type I (spontaneous or underfeeding) ketosis occurs at about 3 to 6 weeks after calving, near peak milk yield, when demand is highest and the cow is not fed enough energy. Blood glucose and insulin are low and the liver is not heavily fatty. Type II ketosis occurs in the first 1 to 2 weeks after calving, typically in cows that were over-conditioned at calving. Insulin resistance and heavy fat mobilisation lead to fatty liver, and response to treatment is poorer. Secondary ketosis follows any disease that reduces feed intake, especially displaced abomasum, metritis, mastitis and lameness; always look for the primary disease. Alimentary (butyric) ketosis follows feeding silage with high butyric acid content. In the wasting form, the most common, the cow eats less, often refusing concentrates before forage, milk yield falls, she loses weight rapidly and becomes dull, the faeces are firm and dry, and a sweet acetone smell may be noticed on breath or milk (not everyone can smell it). In the nervous form, a minority of cases, signs include licking at objects or herself, chewing movements, salivation, apparent blindness, circling, head pressing, hyperaesthesia, bellowing and aggression. These signs are attributed partly to isopropanol, a breakdown product of acetoacetate in the rumen. Subclinical ketosis, a raised BHB without signs, is far more common than clinical ketosis.
Diagnosis rests on history, signs and ketone measurement. Nitroprusside tests (Rothera's test and its tablets or strips) detect acetoacetate and, less strongly, acetone, but not BHB. They are useful in urine and milk; urine tests are very sensitive but can be positive in healthy cows. Hand-held meters measure blood BHB directly and are now the usual cow-side test. Blood BHB of about 1.2 mmol/L or more indicates subclinical ketosis, and clinical ketosis is usually associated with about 3.0 mmol/L or more. Milk BHB strips and a milk fat-to-protein ratio above about 1.4 to 1.5 on test-day records are herd screening tools. Treatment aims to restore glucose supply and reduce fat mobilisation. Intravenous 50 percent dextrose (commonly 500 mL for an adult cow — confirm against the product label and your national formulary) gives a rapid but short-lived rise in blood glucose, and much of it may be lost in urine. Oral propylene glycol, a glucose precursor, is the mainstay: commonly 300 mL by mouth once or twice daily for 3 to 5 days in adult cattle — confirm against the product label and your national formulary. Glucocorticoids by class (for example dexamethasone) raise blood glucose by redistributing glucose and reducing milk yield; they are avoided in late-pregnant cows because they can induce parturition. Long-acting insulin with glucose is used in type II cases. Prevention focuses on avoiding over-conditioning at dry-off (commonly aiming for BCS about 3.0 to 3.5 on a 5-point scale), maintaining intake around calving, careful ration change, routine BHB monitoring in fresh cows, and, where licensed, ionophores such as monensin, which increase ruminal propionate.
Pregnancy toxaemia (twin-lamb disease, twin-kid disease) is a ketosis of late pregnancy in small ruminants. It occurs in the last 4 to 6 weeks of gestation, when fetal glucose demand is highest, and mainly in ewes and does carrying twins or triplets. Fat and thin animals are both at risk; triggers include inadequate feed in late pregnancy, sudden fasting from snow, transport or handling, and concurrent disease. Signs begin with separation from the flock, dullness and anorexia, then neurological signs: apparent blindness, star-gazing, head pressing, fine tremors of the head, teeth grinding, and later recumbency, coma and death. Fetal death may occur, followed by toxaemia. Blood BHB is raised, commonly above about 3.0 mmol/L in clinical cases (thresholds vary), and urine ketones are strongly positive. Blood glucose is low early but may be normal or high later, after fetal death or with stress. Concurrent hypocalcaemia is common, so calcium is often given as well. Treatment in early cases is oral glucose precursors, such as propylene glycol or glycerol, with fluids and calcium. In more advanced cases the key step is removing the energy drain: induce parturition with a corticosteroid when the ewe is close to term, or perform caesarean section. Recumbent ewes have a poor prognosis. Prevention depends on scanning for fetal numbers, feeding multiple-bearing groups more energy in late pregnancy, and monitoring BCS and BHB.
Fatty liver (hepatic lipidosis, fat cow syndrome) is accumulation of triglyceride in hepatocytes, usually developing in the week before and the first weeks after calving. The liver takes up NEFA in proportion to their blood concentration. It can oxidise them or export them as triglyceride inside very-low-density lipoproteins (VLDL). The ruminant liver exports VLDL slowly, so when NEFA supply is high the excess is stored as triglyceride. The main risk factor is over-conditioning at calving: fat cows lose appetite earlier before calving, mobilise more fat and are more insulin resistant. Any disease that reduces intake in the transition period, such as milk fever, metritis, displaced abomasum or retained placenta, adds to the load. Fatty infiltration impairs hepatocyte function. Gluconeogenesis and ureagenesis fall, ketogenesis rises, and immune function and fertility are worse. Mild fatty liver is very common and often subclinical; severe fatty liver can cause anorexia, weakness, recumbency, hepatic encephalopathy and death, and responds poorly to treatment. Type II ketosis and fatty liver are closely linked.
The definitive diagnosis is liver biopsy, taken percutaneously through the right 10th or 11th intercostal space, and measurement of triglyceride content or histological fat fraction. A flotation test of the biopsy in solutions of known specific gravity gives a rough estimate. Blood findings (raised NEFA, BHB and AST, low glucose and cholesterol) are supportive but not specific. Liver ultrasound can also estimate fat content, and serial BHB and NEFA help follow the response to treatment. Treatment aims to raise glucose supply, reduce fat mobilisation and restore feed intake: intravenous glucose, oral propylene glycol, insulin in combination with glucose, treatment of concurrent disease, and forced feeding or transfer of rumen fluid from a healthy cow to support intake. Prevention is the same as for ketosis: control body condition in late lactation and the dry period, avoid sudden changes, keep dry and fresh cows eating with adequate space and comfort, and minimise transition diseases. Rumen-protected choline, which supports VLDL export, is used in some transition diets.
In ponies, donkeys and miniature horses, hyperlipaemia follows negative energy balance, often triggered by illness, pregnancy or lactation, transport or sudden reduction of feed, especially in obese or insulin-resistant animals. Plasma triglyceride rises; hyperlipaemia is commonly defined as serum triglyceride above about 5.6 mmol/L (500 mg/dL) with visibly lipaemic (cloudy) plasma, and the milder hyperlipidaemia as a lower rise without gross lipaemia. Fat infiltrates the liver and kidneys, and liver failure may follow. Treatment is to correct the primary disease and restore energy intake by enteral feeding or intravenous glucose, with fluids; insulin is used in some cases. Mortality is high, especially in donkeys, whose signs are subtle. In cats, idiopathic hepatic lipidosis develops after a period of anorexia, most often in obese cats. Jaundice, vomiting, weight loss and hepatic encephalopathy may follow. The key treatment is nutrition, usually through an oesophagostomy or nasogastric feeding tube, often for weeks, with correction of fluid and electrolyte deficits (especially hypokalaemia and hypophosphataemia, which can worsen during refeeding). In broilers, fatty liver and kidney syndrome is associated with biotin deficiency.
Hypomagnesaemia is a low blood magnesium concentration. When severe it causes tetany. Magnesium has no hormonal control that can release it quickly from bone, so blood magnesium depends on daily intake. In adult ruminants magnesium is absorbed mainly from the rumen by a sodium-linked active transport. High potassium intake (lush spring grass fertilised with potash) depolarises the rumen wall and reduces absorption; low sodium, high nitrogen with ammonia production, and low magnesium content of fast-growing grass make it worse. Lactation tetany (grass tetany, grass staggers) affects lactating cows, especially older beef and dairy cows, grazing lush, heavily fertilised spring or autumn pasture, often in cold wet weather. Winter tetany affects beef cattle on poor-quality diets. Transport tetany follows transport and fasting. Hypomagnesaemic tetany of calves occurs in calves of about 2 to 4 months fed mainly milk or milk replacer without supplementation, because milk is low in magnesium and absorption falls as the calf ages. Sheep are affected, especially lactating ewes on spring grass. Fasting for even a day or two sharply lowers blood magnesium in at-risk cattle, which is why bad weather and handling often precede outbreaks.
In the acute form the animal is alert and hyperaesthetic, with ears pricked, head held high, muscle twitching, a stiff staggering gait and sometimes aggression. Sudden noise or handling can trigger a convulsion: lateral recumbency with paddling, champing of the jaws, frothing at the mouth, opisthotonus and nystagmus. The heart rate is fast and the heart sounds loud enough to be heard some distance from the chest wall. Death may occur within an hour, so many animals are simply found dead with signs of paddling in the soil around them. A subacute form has milder incoordination and ataxia over days, and chronic subclinical hypomagnesaemia reduces yield. Serum magnesium below about 0.5 mmol/L (1.2 mg/dL) is typical of clinical tetany; normal values are commonly around 0.8 to 1.2 mmol/L, varying by laboratory. Calcium is often also low. Urinary magnesium is a useful herd indicator of intake: very low urine magnesium in several cows suggests inadequate supply. After death, blood magnesium is unreliable because it leaks from cells. Low magnesium in vitreous humour (aqueous humour less reliably) taken within about 48 hours of death supports the diagnosis. Differentials include lead poisoning, rabies, nervous ketosis, polioencephalomalacia and, in sudden death, anthrax, which must be excluded before opening a carcass in endemic areas.
Treat as soon as possible and with minimum stress, because excitement can precipitate a fatal convulsion. A convulsing animal may need sedation first. Give a combined calcium and magnesium solution slowly intravenously, monitoring the heart; magnesium given rapidly intravenously can cause cardiac arrest and respiratory depression. Follow this with magnesium sulfate subcutaneously, which gives a sustained rise; a commonly cited adult cattle dose is 200 mL of 50 percent magnesium sulfate solution subcutaneously, divided between sites — confirm against the product label and your national formulary. Relapse is common unless intake is corrected, so give oral magnesium once the animal can swallow and supplement the group immediately. Prevention during risk periods relies on a daily supply of magnesium, because the body stores very little. Options include magnesium oxide in concentrates or mineral mixes (a commonly quoted allowance is about 50 to 60 g per cow per day, but advice varies), dusting pasture with magnesium oxide, magnesium salts in drinking water, slow-release intraruminal boluses, and feeding hay or straw with lush grass. Avoid potash fertiliser on grazing pastures in spring, provide salt, and keep high-risk cows on the safest pastures. For calves, supplement magnesium and introduce forage and concentrate early.
Post-parturient haemoglobinuria (PPH) is an acute intravascular haemolytic anaemia of high-yielding cows and buffaloes, usually in the first few weeks after calving (commonly 2 to 6 weeks), most often in the third to sixth lactation. It is closely associated with hypophosphataemia: affected animals often come from farms with phosphorus-deficient soils or rations, and serum inorganic phosphorus is usually very low. In India and neighbouring countries it is an important disease of buffaloes, especially in winter. Cruciferous plants such as rape, kale, turnips and cabbage are a second recognised factor. They contain S-methylcysteine sulfoxide, which the rumen converts to dimethyl disulfide, an oxidant that causes Heinz body haemolytic anaemia. In New Zealand, copper deficiency has also been linked to the disease. The favoured explanation for the phosphorus link is that red cells need inorganic phosphate for glycolysis; when phosphate is severely low, red cell ATP falls, the membrane becomes fragile, and cells rupture inside blood vessels. This mechanism is supported but not fully proven, and the disease is best viewed as multifactorial. Haemoglobin released into plasma exceeds the binding capacity of haptoglobin and passes into the urine, which becomes red-brown to dark coffee-coloured.
The cow becomes weak, with pale then jaundiced mucous membranes, a fast heart rate, a jugular pulse and laboured breathing. Temperature is normal. Severe cases collapse and die within days from anaemic hypoxia; recovered cows may take weeks to regain condition. Diagnosis rests on haemoglobinuria with anaemia in a recently calved, high-yielding cow without fever, together with low serum inorganic phosphorus. Heinz bodies on a blood smear point to brassica feeding. To separate the causes of red urine, centrifuge urine and blood. Red cells that settle out of urine indicate haematuria. Red urine that stays red after centrifugation contains haemoglobin or myoglobin; pink plasma indicates haemoglobin, and clear plasma with red urine suggests myoglobin. The main differentials of haemoglobinuria in cattle are babesiosis and anaplasmosis (anaplasmosis gives anaemia and jaundice but not usually haemoglobinuria), leptospirosis in calves, bacillary haemoglobinuria caused by Clostridium haemolyticum, chronic copper poisoning (mainly sheep), water intoxication in calves, and brassica or onion poisoning. Fever, blood smears and history separate most of them.
Severely anaemic cows need a whole-blood transfusion from a healthy donor, which buys time while the marrow responds. Phosphorus is replaced intravenously with a sodium phosphate solution (monosodium or disodium phosphate) and then orally with a bioavailable phosphorus source such as monosodium phosphate or dicalcium phosphate. Sodium hypophosphite, found in some older injectable products, does not supply usable phosphate and should not be relied on; dicalcium phosphate must never be given intravenously. Supportive care includes fluids, keeping the cow quiet, avoiding unnecessary handling of a severely anaemic cow (which can precipitate collapse), and removing brassicas from the diet. Recovered cows need good feeding to rebuild red cell mass and body condition, and herd-mates on the same ration should be checked for low phosphorus. Prevention is to feed phosphorus at the recommended level for yield, test soils and forages in endemic areas, limit brassicas in the diet of high-yielding cows, and include phosphorus-rich concentrates for buffaloes in late pregnancy and early lactation in deficient areas.
Azoturia is the old name for exertional rhabdomyolysis of horses, a syndrome of muscle cramping and damage associated with exercise. It is also called tying-up, Monday morning disease and set-fast. The classic history is a working horse kept on full grain over a rest day that develops stiffness soon after returning to work. The dark urine contains myoglobin. Modern classification separates sporadic from chronic or recurrent forms. Sporadic exertional rhabdomyolysis follows exercise beyond the horse's fitness, electrolyte imbalance, heat and exhaustion, or high grain feeding with irregular exercise. Recurrent exertional rhabdomyolysis is recognised in Thoroughbreds and Standardbreds, particularly nervous young fillies in training, and is associated with abnormal regulation of intracellular calcium in muscle. Polysaccharide storage myopathy type 1 (PSSM1) is caused by a dominant mutation of the glycogen synthase 1 (GYS1) gene and occurs in Quarter Horses, related breeds and draught breeds; affected muscle stores abnormal polysaccharide. A second form without the GYS1 mutation is also described.
Signs range from stiffness and a short stride to refusal to move, sweating, raised heart and breathing rates, and firm, painful gluteal and lumbar muscles; severe cases may go down and look like colic. Urine may be red-brown to dark coffee-coloured because of myoglobinuria. A urine dipstick reads positive for blood, but no red cells are seen on microscopy. Myoglobin can damage renal tubules, particularly when the horse is dehydrated, causing acute kidney injury. Creatine kinase (CK) rises within hours and peaks early; aspartate aminotransferase (AST) peaks later, about a day after the episode, and can stay high for one to several weeks. Comparing the two helps date the injury and judge whether damage is continuing. For recurrent cases, a controlled exercise test (CK measured before and a few hours after light exercise), muscle biopsy and, for PSSM1, a genetic test for the GYS1 mutation are used. Differentials include colic, laminitis, aortic-iliac thrombosis and other myopathies, such as selenium and vitamin E deficiency and atypical myopathy from sycamore or box elder seeds.
Stop exercise at once and do not force the horse to walk home; move it by trailer if needed. Assess hydration and renal function. Horses with myoglobinuria or dehydration need intravenous or oral fluids to protect the kidneys. Non-steroidal anti-inflammatory drugs are used for pain once the horse is well hydrated, because they reduce renal perfusion in dehydrated horses. Acepromazine is sometimes used for its sedative and vasodilatory effect in hydrated horses but is avoided in dehydrated ones because it lowers blood pressure. Muscle relaxants and other drugs are chosen by class according to the case. Early small-paddock turnout and gradual return to work usually beat long box rest. Prevention rests on daily exercise or turnout, feeding to workload, reducing starch and sugar (non-structural carbohydrate) and replacing calories with fat and fibre, particularly for PSSM and recurrent forms, balanced electrolytes and adequate selenium and vitamin E. In recurrent exertional rhabdomyolysis, reducing excitement and stress helps; the muscle relaxant dantrolene is sometimes given before exercise, subject to competition rules.
Bone is a collagen matrix mineralised with calcium phosphate (hydroxyapatite). Its mineralisation needs adequate calcium, phosphorus and vitamin D, and it is continuously remodelled under the control of PTH, calcitriol and calcitonin. Rickets is defective mineralisation of cartilage and newly formed bone matrix (osteoid) in young, growing animals, so the growth plates and metaphyses are most affected. Osteomalacia is the same failure of mineralisation in adults, whose growth plates have closed; it affects remodelling bone, so osteoid accumulates. Osteodystrophia fibrosa is excessive osteoclastic resorption of bone with replacement by fibrous tissue, caused by persistently raised PTH (hyperparathyroidism). Osteoporosis is different again: reduced bone mass with bone that is normally mineralised, caused for example by starvation, copper deficiency or disuse. Metabolic bone disease is a collective name used especially for reptiles and birds. The causes of rickets and osteomalacia are deficiency of phosphorus (the most common cause in grazing ruminants), vitamin D (housed animals, sheep at high latitudes in winter, animals kept without sunlight) or, less often, calcium, and a badly unbalanced calcium-to-phosphorus ratio.
Rickets in calves, lambs, piglets and pups causes lameness, reluctance to move, enlarged joints and swollen ends of long bones, bowing of the limbs, enlarged costochondral junctions (the rachitic rosary), and in severe cases pathological fractures and poor growth. Osteomalacia in adult cattle on phosphorus-deficient pastures causes stiffness, a creaking gait, lameness, fractures, and depraved appetite (pica, including osteophagia, the chewing of bones). Osteophagia links phosphorus deficiency with botulism when carcasses containing Clostridium botulinum toxin are chewed, as described in southern Africa. Phosphorus deficiency also reduces fertility and growth before bone signs are obvious. Diagnosis uses the diet, radiographs (widened, irregular, cupped growth plates in rickets; reduced bone density), serum phosphorus (low in phosphorus deficiency, although it varies with recent intake and age), serum alkaline phosphatase (often raised), and 25-hydroxyvitamin D concentration. At post-mortem, a low ash content of dry, fat-free bone, soft bones that cut easily, and wide growth plates confirm the diagnosis.
Nutritional secondary hyperparathyroidism develops when the diet is low in calcium, high in phosphorus, or both. The body responds with sustained PTH secretion, bone is resorbed and replaced by fibrous tissue, and the lesions are most visible in the facial bones. In horses it is called bran disease or big head: feeding large amounts of wheat bran, which is rich in phosphorus and poor in calcium, or grazing tropical grasses that contain soluble oxalate, which binds calcium, leads to symmetrical enlargement of the facial bones, shifting lameness, and loose teeth. In dogs and cats fed all-meat diets, which have a calcium-to-phosphorus ratio of about 1:15 to 1:20, young animals develop lameness, pain, thin cortices and folding fractures. Reptiles kept without dietary calcium or ultraviolet B light develop soft jaws and fractures. Renal secondary hyperparathyroidism occurs in chronic kidney disease, when phosphate retention and reduced calcitriol production drive PTH secretion; in dogs the jaw can become soft and pliable (rubber jaw). Treatment is to correct the diet: restore calcium, reduce phosphorus, provide a calcium-to-phosphorus ratio of about 1:1 to 2:1 in most species, and provide vitamin D or sunlight where it is lacking. Bone lesions improve over months, but deformities may remain. Rest is needed while bones are fragile.
Trace minerals are needed in small amounts, mostly as parts of enzymes and hormones. Deficiency is primary when the diet is low, usually because soil and forage are low, and secondary (conditioned) when intake is adequate but another dietary factor blocks absorption or use. Deficiencies are regional, because they follow geology, soil pH, rainfall and fertiliser use; national soil and forage surveys are the best guide. Several may coexist. Diagnosis at herd level combines clinical signs, diet or forage analysis, tissue concentrations (liver is often best for copper, cobalt as vitamin B12, and selenium), functional markers such as enzyme activity, and, most convincingly, a response to supplementation in treated versus untreated animals. The margin between requirement and toxicity is narrow for copper, especially in sheep, and for selenium, so supplementation must be measured and legal limits observed. Before buying supplements for a whole herd, confirm the deficiency: many wasting and infertility problems blamed on minerals turn out to be energy, protein or parasite problems.
Copper is part of cytochrome oxidase, lysyl oxidase (collagen and elastin cross-linking), tyrosinase (melanin), caeruloplasmin (iron transport) and superoxide dismutase. Primary deficiency occurs on copper-poor soils. Secondary deficiency is more common: high molybdenum and sulfur form thiomolybdates in the rumen that bind copper, and high iron also reduces absorption. Teart pastures in England, rich in molybdenum, cause severe scouring. Signs include loss of coat colour (achromatopilia), producing spectacle-like rings around the eyes in cattle; diarrhoea; poor growth; anaemia; fragile bones and fractures; and loss of crimp in wool, giving steely or stringy wool. In lambs, enzootic ataxia (swayback) results from defective myelination when ewes are deficient in pregnancy: congenital swayback lambs are ataxic at birth, and delayed swayback appears in the first months. In Australia, falling disease of cattle is sudden death from myocardial fibrosis. Liver copper is the best measure of status; serum or plasma copper falls only when liver stores are depleted. Supplementation is by copper oxide wire particles orally, injectable copper, copper in mineral mixes or pasture fertiliser. Sheep are very sensitive to copper toxicity, and some breeds more so, so supplements for cattle must not be fed to sheep.
Cobalt is needed by rumen microbes to make vitamin B12 (cobalamin). B12 is the coenzyme of methylmalonyl-CoA mutase, which allows propionate to enter gluconeogenesis, so deficiency is effectively an energy deficiency. It causes wasting, anorexia, rough coat, anaemia and weeping eyes, known as pine or pining in Britain, bush sickness in New Zealand and enzootic marasmus in Australia; in lambs, ovine white liver disease is associated with it. Sheep are more susceptible than cattle. Diagnosis is by serum or liver vitamin B12 or raised methylmalonic acid; treat with vitamin B12 injections or oral cobalt, and prevent with cobalt in fertiliser, mineral mixes or intraruminal boluses. Selenium is part of glutathione peroxidase, which with vitamin E protects cell membranes from oxidative damage. Deficiency of selenium, vitamin E or both causes nutritional muscular dystrophy (white muscle disease, stiff lamb disease) in calves, lambs and foals, affecting skeletal and cardiac muscle; mulberry heart disease and hepatosis dietetica in pigs; and exudative diathesis in chicks. Retained placenta and poor fertility are also linked. Whole-blood glutathione peroxidase activity and blood or liver selenium measure status. Selenium supplements are regulated because toxicity is easy. Iodine is needed for thyroid hormones. Deficiency causes goitre and, most obviously, stillbirth or weak newborn animals, some hairless (for example hairless piglets), with enlarged thyroids. Primary deficiency occurs in inland and mountain regions; goitrogens in brassicas and some legumes cause secondary deficiency. Iodised salt prevents it.
Zinc is part of many enzymes and is needed for skin and hoof keratinisation and immune function. In pigs, parakeratosis (thick, crusted skin) occurs on diets with marginal zinc and high calcium or phytate, which reduce zinc absorption. In dogs, zinc-responsive dermatosis occurs as a syndrome in Siberian Huskies and Alaskan Malamutes, which absorb zinc poorly, and as a syndrome in fast-growing puppies on diets high in calcium or phytate. Manganese is required for cartilage matrix synthesis. Deficiency causes perosis (slipped tendon) in poultry, in which the gastrocnemius tendon slips from its groove, together with chondrodystrophy; choline and biotin deficiency can produce similar lesions. In ruminants it is linked to poor fertility and congenital limb deformities. Iron deficiency anaemia of piglets is the classic iron deficiency. Piglets are born with small iron stores, sow milk is low in iron, and rapid growth expands blood volume, so housed piglets without soil access become anaemic at about 2 to 3 weeks of age, with pallor, poor growth, thumping (laboured breathing) and sudden deaths. It is prevented by injecting iron dextran or another iron preparation in the first days of life; a commonly used amount is 100 to 200 mg of iron per piglet by intramuscular injection — confirm against the product label and your national formulary. Iron overdose can be toxic, especially in piglets deficient in vitamin E or selenium.
Vitamin A (retinol) is needed for vision (rhodopsin in the rods), for the integrity of epithelia, and for bone growth. Herbivores make it from beta-carotene in green forage; cats cannot convert beta-carotene efficiently and need preformed vitamin A. Deficiency occurs on dry, weathered pasture in droughts, long-stored hay, and cereal diets without green forage. The first sign is night blindness (nyctalopia). Others are xerophthalmia, squamous metaplasia of epithelia, poor fertility, weak or blind newborn animals, and in growing calves raised cerebrospinal fluid pressure with papilloedema, blindness and convulsions. Cats fed large amounts of liver develop hypervitaminosis A with deforming cervical spondylosis. Vitamin D deficiency causes rickets and osteomalacia (chapter 9). Vitamin E is the main fat-soluble antioxidant and works with selenium (chapter 10). Low vitamin E in horses is linked to equine degenerative myeloencephalopathy and equine motor neuron disease; in chicks, vitamin E deficiency causes encephalomalacia (crazy chick disease) as well as exudative diathesis. Vitamin K is needed for activation of clotting factors II, VII, IX and X. Primary deficiency is uncommon because gut bacteria make it; vitamin K antagonism by dicoumarol in mouldy sweet clover, by anticoagulant rodenticides, and by some sulfonamides in poultry causes bleeding and is treated with vitamin K1.
Thiamine (vitamin B1) is a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase, so the brain, which depends on glucose, is most affected by deficiency. In ruminants, rumen microbes normally make enough thiamine. Polioencephalomalacia (PEM, cerebrocortical necrosis) is necrosis of the cerebral cortex associated with thiamine inadequacy (thiaminase activity in the rumen on high-grain diets, or thiaminase-containing plants) and with high dietary sulfur, from water, feed or sulfate-containing supplements. Signs are sudden apparent (cortical) blindness with preserved pupillary light reflexes, head pressing, opisthotonus, dorsomedial strabismus, nystagmus, and recumbency with convulsions. Under ultraviolet light the affected cortex may fluoresce. Early treatment with high doses of thiamine given parenterally and repeated often leads to recovery; delay leads to permanent damage. Dexamethasone is sometimes added for cerebral oedema. In horses, bracken fern (Pteridium aquilinum) and horsetail (Equisetum) contain thiaminase and cause incoordination and weakness (bracken staggers), responsive to thiamine. In cats and dogs, diets based on raw fish containing thiaminase, or overcooked or sulfite-preserved foods, cause ventroflexion of the neck, ataxia, seizures and death; in farmed foxes this is Chastek paralysis. In chicks, thiamine deficiency causes star-gazing (opisthotonus).
Riboflavin (vitamin B2) deficiency in chicks causes curled toe paralysis, from peripheral nerve damage. Niacin deficiency causes black tongue in dogs, the canine equivalent of human pellagra, and poor feathering and hock enlargement in poultry. Biotin deficiency causes foot lesions and cracked hooves in pigs, dermatitis in poultry, and is linked to fatty liver and kidney syndrome in broilers. Choline deficiency, like manganese deficiency, can cause perosis in poultry. Vitamin B12 deficiency in ruminants is effectively cobalt deficiency (chapter 10); in dogs, inherited cobalamin malabsorption is recognised in some breeds. Vitamin C (ascorbic acid) is made from glucose by most mammals. Guinea pigs, primates and some fruit bats lack the enzyme L-gulonolactone oxidase and must receive vitamin C in food; deficient guinea pigs develop scurvy with swollen painful joints, bleeding gums, poor wound healing and reluctance to move. Taurine, an amino acid, is essential for cats: deficiency causes central retinal degeneration and dilated cardiomyopathy.
Diabetes mellitus is persistent hyperglycaemia from absolute or relative insulin deficiency. In dogs it resembles human type 1 diabetes: beta-cell loss, often immune-mediated or following pancreatitis, so dogs need insulin for life. In cats it resembles type 2 diabetes: insulin resistance (obesity, glucocorticoids, progestogens, acromegaly) with amyloid deposition in islets and glucose toxicity; with prompt insulin treatment and a low-carbohydrate diet, some cats go into remission. Signs are polyuria, polydipsia, polyphagia and weight loss; cats may develop a plantigrade stance from diabetic neuropathy, and dogs cataracts. Diagnosis needs persistent fasting hyperglycaemia with glucosuria. In cats, stress raises blood glucose markedly, so serum fructosamine, which reflects glucose over the previous one to three weeks, helps separate diabetes from stress hyperglycaemia. Diabetic ketoacidosis (DKA) is the emergency form: insulin deficiency with high glucagon drives lipolysis and hepatic ketone production, causing metabolic acidosis, dehydration, vomiting and depression. Treatment is intravenous fluids first, then regular (short-acting) insulin at a low, carefully adjusted rate, with close monitoring of potassium and phosphate, which fall once insulin is given. Stable patients receive intermediate- or long-acting insulin.
Hypoadrenocorticism (Addison's disease) in dogs is usually primary adrenal failure from immune-mediated destruction, so both glucocorticoid and mineralocorticoid (aldosterone) are lacking. It is uncommon in cats. Signs wax and wane: vomiting, diarrhoea, lethargy, weight loss and weakness, sometimes with collapse in an Addisonian crisis with bradycardia caused by hyperkalaemia and hypovolaemic shock. Typical laboratory findings are hyponatraemia, hyperkalaemia, a sodium-to-potassium ratio below about 27:1, pre-renal azotaemia, and, in a stressed sick dog, the absence of a stress leukogram. The ACTH stimulation test confirms the diagnosis: cortisol stays low before and after ACTH. Emergency treatment is intravenous 0.9 percent sodium chloride, treatment of hyperkalaemia, and a glucocorticoid; long-term treatment replaces mineralocorticoid and glucocorticoid. Hyperadrenocorticism (Cushing's syndrome) in dogs is most often pituitary-dependent (about 80 to 85 percent of cases), from an ACTH-secreting pituitary tumour, with the remainder adrenal tumours; iatrogenic disease follows glucocorticoid treatment. Signs are polyuria, polydipsia, polyphagia, a pot-bellied appearance, bilateral symmetrical alopecia, thin skin, calcinosis cutis and panting. Dogs have a markedly raised alkaline phosphatase because glucocorticoids induce a specific isoenzyme. Screening and diagnosis use the low-dose dexamethasone suppression test, the ACTH stimulation test and the urine cortisol-to-creatinine ratio (which is good for ruling out the disease), with imaging to separate pituitary from adrenal disease. Treatment is medical (drugs that block cortisol synthesis, such as trilostane) or surgical for adrenal tumours.
Hypothyroidism in dogs is usually primary, caused by lymphocytic thyroiditis or idiopathic atrophy, and mainly affects middle-aged medium and large breeds. Signs are lethargy, weight gain, heat seeking, bilateral truncal alopecia and a thin tail (rat tail), recurrent skin infections, bradycardia and hypercholesterolaemia. Diagnosis combines low total or free thyroxine (T4) with high thyroid-stimulating hormone (TSH). Non-thyroidal illness and some drugs lower T4 in euthyroid dogs (euthyroid sick syndrome), so a low T4 alone is not enough. Treatment is oral levothyroxine with monitoring of post-pill T4. Hyperthyroidism in cats is the most common feline endocrine disease of older cats, usually caused by benign adenomatous hyperplasia or adenoma of one or both thyroid lobes. Signs are weight loss despite a good appetite, hyperactivity, vomiting, polyuria and polydipsia, tachycardia, and a palpable thyroid nodule. Raised total T4 confirms most cases. Treatment options are anti-thyroid drugs (methimazole or carbimazole), radioactive iodine (iodine-131), thyroidectomy (risking hypoparathyroidism) and an iodine-restricted diet. Treatment lowers glomerular filtration rate and may unmask chronic kidney disease. Puerperal tetany (eclampsia) is acute hypocalcaemia in lactating bitches, usually small breeds, commonly 1 to 4 weeks after whelping when milk demand is high. Unlike milk fever in cows it causes tetany: restlessness, panting, stiff gait, tremors, seizures and hyperthermia. Treat with slow intravenous 10 percent calcium gluconate while monitoring the heart rate and rhythm, then oral calcium, and wean or partly remove the puppies. Calcium supplementation during pregnancy can predispose to it, by the same mechanism as a high-calcium dry-cow diet.
Learn each disease as a chain: what the animal is short of, why the body cannot correct it, what that does to muscle, nerve, liver or bone, and therefore what the signs, tests and treatment must be. Practise the numbers until they are automatic: converting mg/dL to mmol/L for calcium, magnesium and BHB, calculating DCAD from a feed analysis, and working out the volume of a calcium solution from its label. On clinical rotation, examine every fresh cow systematically, check the heart while calcium runs, and learn to tell a flaccid hypocalcaemic cow from a hyperaesthetic hypomagnesaemic one at the gate.
Most of your work is the fresh cow and the herd behind her. Treat milk fever calmly with slow intravenous calcium and a stethoscope on the chest; examine every downer fully before deciding on nursing or euthanasia; check blood BHB in any off-feed fresh cow and look for the displaced abomasum or metritis behind it. When cases cluster, move from cow to herd: sample 12 fresh cows for BHB, 12 close-up cows for NEFA and urine pH, score body condition, and walk the dry-cow and fresh-cow pens with the nutritionist. For sheep clients, scan ewes and plan late-pregnancy feeding to stop pregnancy toxaemia.
At this stage the decisions are about systems and people. You set herd health plans with transition monitoring targets, audit dry-cow DCAD and urine pH, and use records to track milk fever, ketosis, displaced abomasum and culling rates over years. You judge when a mineral problem is real, by designing supplementation trials with untreated controls instead of dosing everything, and you know the local soil maps for copper, selenium, cobalt and phosphorus. You also carry welfare and legal responsibility for downer cows and fitness for transport, and you mentor younger vets on when to stop treating.
Research questions here are about mechanism and prediction. Examples include how metabolic alkalosis alters PTH receptor signalling, why some cows mobilise fat excessively, how inflammation around calving interacts with insulin resistance and ketosis, and whether sensor data such as rumination time, activity and milk components can predict disease before blood values change. Trace mineral research deals with bioavailability, antagonisms and the thin line between deficiency and toxicity. A senior researcher must design adequately powered trials, choose thresholds from outcome-based studies rather than reference ranges, and translate findings into practical, affordable prevention for smallholder and pasture-based systems as well as large confinement dairies.
The curriculum has no separate unit for subacute ruminal acidosis or displaced abomasum, so they are covered in chapter 1 but have only a few questions, placed under metabolic profile testing, milk fever and ketosis. Drug doses are given only for a few standard uses (calcium for milk fever, dextrose and propylene glycol for ketosis, magnesium sulfate for hypomagnesaemia, iron for piglets); other treatments are described by drug class, and withdrawal periods are not given because they depend on product and country. Reference ranges and herd alarm thresholds are the commonly cited North American and European values and differ by laboratory, analyser and country. Buffalo-specific thresholds, camelid and poultry metabolic disease, equine endocrine disease (PPID, equine metabolic syndrome), insulinoma, hyperparathyroidism and hypoparathyroidism in companion animals, and region-specific soil deficiency maps are not covered in depth.
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