Veterinary · Pre-clinical and foundation · also MSVE ANN-121
The rumen and how to feed cattle, buffalo, sheep and goats through each stage of life, including ration formulation by the Pearson square and least-cost methods.
In the exams: ICAR AICE-JRF core group 05; ICAR AIEEA-PG 14 (Animal Nutrition)
Applied ruminant nutrition is the art and arithmetic of feeding cattle, buffalo, sheep and goats so that the rumen works well, the animal meets its production target and the farmer makes money. It begins where the principles of nutrition stop: once you know what crude protein, NDF and metabolisable energy mean, this subject asks how much of each a 450 kg cow in her third month of lactation needs, which feeds on this farm can supply it, what the cheapest combination is, and what disease will follow if the ration is wrong.
The physiology of the rumen is the same everywhere. What differs is the feed base (irrigated maize silage in one place, wheat straw and green berseem in another, dry-season grass and tree leaves in a third), the feeding standard used, and the legal status of certain additives. This manual names those differences rather than choosing one country's practice as the rule.
In Indian postgraduate and PhD entrance papers the subject appears under Animal Nutrition (ICAR AIEEA-PG Code 14 and AICE-JRF core group 05), with frequent short calculations (Pearson square, dry matter conversion, thumb rules), rumen fermentation facts and silage quality. Licensing examinations such as NAVLE, the RCVS Statutory Membership Examination and the Australasian Veterinary Examination test the same knowledge through cases: a herd with low milk fat, a ewe with pregnancy toxaemia, a cow down after calving. State public-service papers ask direct recall. A practitioner uses all of it daily, because most production-animal disease is first a feeding problem.
Values given here are textbook values used for teaching. Requirements differ with breed, climate, feed and the feeding standard chosen, and additive rules differ by country; always check the standard in use locally and, for any product, its label and the national regulations.
The ruminant stomach has four compartments: rumen, reticulum, omasum and abomasum. The rumen and reticulum (together the reticulo-rumen) form a fermentation vat that in an adult cow holds roughly 100 to 150 litres and in a sheep or goat roughly 10 to 20 litres, the exact volume depending on size and diet. The omasum absorbs water and volatile fatty acids and regulates passage; the abomasum is the true glandular stomach that secretes acid and pepsin like the monogastric stomach.
The rumen is kept at about 39 to 40 °C, is anaerobic, and has a pH that normally lies between about 6.0 and 7.0. Saliva, produced in large volume (well over 100 litres a day in a grazing or long-forage-fed cow), carries sodium bicarbonate and phosphate that buffer the acids of fermentation. Chewing and rumination drive saliva flow, which is why the physical length of forage matters for rumen pH.
Three groups of microbes live there. Bacteria are the most numerous, commonly quoted at 10^10 to 10^11 cells per millilitre, and do most of the fermentation; they include cellulolytic species (for example Fibrobacter succinogenes and Ruminococcus species), amylolytic species (Streptococcus bovis, Ruminobacter amylophilus), lactate utilisers (Megasphaera elsdenii, Selenomonas ruminantium) and many proteolytic types. Protozoa, mainly ciliates, are fewer (about 10^4 to 10^6 per millilitre) but large, so they can form a substantial share of microbial mass; they engulf starch granules and bacteria, which slows starch fermentation but also recycles bacterial protein within the rumen. Anaerobic fungi attach to and penetrate fibrous plant tissue. Methanogenic archaea use hydrogen and carbon dioxide to make methane, which keeps hydrogen pressure low and allows fermentation to continue.
Microbes ferment cellulose, hemicellulose, starch and sugars to pyruvate and then to the three main volatile fatty acids (VFAs): acetic, propionic and butyric acid, together with carbon dioxide and methane. The VFAs are absorbed through the rumen wall and supply most of the energy the animal uses; figures of 60 to 80 percent of metabolisable energy are standard. On a high-forage diet the molar proportions are typically about 65 to 70 percent acetate, 15 to 20 percent propionate and about 10 percent butyrate. Feeding more starch shifts the pattern towards propionate.
Each VFA has a separate fate. Acetate is the main precursor of milk fat synthesised in the udder and of body fat. Propionate is the main substrate for gluconeogenesis in the liver, which matters because the ruminant absorbs little glucose from the gut and the udder needs glucose to make lactose. Butyrate is largely converted to beta-hydroxybutyrate (BHB) in the rumen wall and is a stimulus for the growth of rumen papillae in the young calf. The acetate to propionate ratio is therefore a useful shorthand: high ratios support milk fat, low ratios favour gluconeogenesis and fattening and, when extreme, go with milk fat depression.
Fermentation is not free. Methane carries away energy; losses of roughly 2 to 12 percent of gross energy intake are the commonly quoted range, with the higher values on poor forage at maintenance intake.
Dietary protein is divided into rumen-degradable protein (RDP) and rumen-undegradable protein (RUP, also called bypass or escape protein). Microbes break RDP down to peptides, amino acids and ammonia, and many rumen bacteria, especially fibre digesters, use ammonia as their main nitrogen source. Non-protein nitrogen such as urea is hydrolysed rapidly to ammonia by bacterial urease. The microbes combine ammonia with carbon skeletons and energy from fermentation to build microbial protein, which flows to the abomasum and small intestine and is digested like any other protein. Microbial protein has a good amino-acid profile and supplies the larger part of the metabolisable protein in most diets.
Microbial growth needs energy and nitrogen at the same time. If ammonia is released faster than energy is available, the excess ammonia is absorbed, converted to urea in the liver and largely lost in urine, with some recycled to the rumen through saliva and across the rumen wall. A rumen ammonia concentration of about 5 mg ammonia-nitrogen per 100 ml is the classical figure for maximal microbial growth in vitro; higher concentrations may be needed for maximal fibre digestion on poor forage. This synchrony principle underlies urea feeding, the use of molasses with urea, and the design of RDP and RUP in feeding standards.
Rumen microbes also hydrogenate unsaturated fatty acids (biohydrogenation), which is why ruminant fat is more saturated than the fat eaten, and they synthesise B vitamins and vitamin K, so healthy adult ruminants rarely need dietary B vitamins. The main exception is cobalt: microbes need it to make vitamin B12, so cobalt deficiency presents as B12 deficiency.
Rumen manipulation means deliberately changing the fermentation to improve efficiency, product yield or health. The usual aims are: to increase propionate and reduce methane, so that less feed energy is wasted; to protect good-quality protein and fat from rumen degradation so they reach the intestine; to stabilise rumen pH on high-concentrate diets; to increase fibre digestion on poor roughage; and to detoxify plant toxins.
The tools fall into a few groups. Diet itself is the most powerful: forage to concentrate ratio, type of starch (barley and wheat ferment faster than maize or sorghum), grain processing (steam-flaking and fine grinding increase rumen starch digestion), particle length and feeding frequency. Buffers and alkalisers such as sodium bicarbonate and magnesium oxide are added to high-grain diets to support pH, typically in the order of 0.5 to 1 percent of dry matter intake; the exact rate should follow local advice and the product label. Ionophores, a class of antimicrobials that act on gram-positive bacteria, shift fermentation towards propionate, reduce methane and lactate production and improve feed efficiency in growing cattle; their use as growth promoters is banned in the European Union since 2006 and they are permitted in many other countries under veterinary or feed-additive rules, so the legal position must be checked locally. Direct-fed microbials and yeast cultures, enzymes, plant secondary compounds (tannins, saponins, essential oils) and synthetic methane inhibitors are further options with varying strength of evidence.
A high-yielding cow needs more amino acids at the intestine than microbial protein alone can supply, so part of the dietary protein is offered as RUP. Some feeds are naturally less degradable (heat-processed oilseed meals, fish meal where permitted, maize gluten meal), and degradability can be lowered by heat treatment or by chemical treatment such as low-level formaldehyde treatment of oilseed cakes, which has been used in India and elsewhere; its legal status varies. Rumen-protected amino acids, usually methionine and lysine coated or chemically modified so that they escape the rumen, are used to balance the first-limiting amino acids for milk protein.
Fat is added to raise energy density without adding starch. Unsaturated oils are toxic to fibre-digesting bacteria and can depress fibre digestion and milk fat, so total fat is usually kept below about 6 to 7 percent of diet dry matter. Rumen-inert fats such as calcium salts of long-chain fatty acids or hydrogenated fats are used to add energy with less effect on the rumen. Some trans fatty acid intermediates of incomplete biohydrogenation, notably trans-10, cis-12 conjugated linoleic acid, directly inhibit fat synthesis in the udder and are the accepted explanation of diet-induced milk fat depression.
Removing protozoa (defaunation) experimentally increases the flow of bacterial protein and reduces methane in some studies, but it is not a practical field tool and its effects are inconsistent. Microbial detoxification is a clearer success: the toxic amino acid mimosine in the tree legume Leucaena leucocephala is broken down to 3,4- and 2,3-DHP, and the DHP is degraded by rumen bacteria (Synergistes jonesii) that are present in ruminants in some regions and can be transferred by rumen-fluid inoculation to animals elsewhere. Rumen adaptation also explains why a gradual change of diet protects against toxic plants such as those containing oxalates.
Enteric methane is now a policy target because ruminants are a major source of agricultural greenhouse gas. Measures with consistent effect include improving feed digestibility and productivity (less methane per litre of milk), adding fat, feeding more starch, and specific inhibitors of methanogenesis; one synthetic inhibitor, 3-nitrooxypropanol, is approved as a feed additive in a number of jurisdictions. For many other additives the evidence is weaker; ask for replicated trials.
A feeding standard is a published set of nutrient requirements for defined classes of animals, together with the feed evaluation system needed to meet them. It states requirements for maintenance, growth, pregnancy, lactation and work, usually as dry matter intake, energy, protein, minerals and vitamins, and it comes with tables of feed composition and equations for predicting intake and supply.
Several standards are in use worldwide. In India the Indian Council of Agricultural Research published Nutrient Requirements of Animals for cattle and buffalo and for sheep, goat and rabbit in 2013, expressing energy as TDN and metabolisable energy and protein as crude protein and metabolisable protein, with values derived largely from Indian feeding trials; older Indian texts use the Kearl (1982) tables. In North America the National Research Council (NRC) issued the Nutrient Requirements of Dairy Cattle (seventh revised edition, 2001) and its successor from the National Academies of Sciences, Engineering, and Medicine (NASEM, eighth revised edition, 2021), Nutrient Requirements of Beef Cattle (NASEM eighth revised edition, 2016) and Nutrient Requirements of Small Ruminants (NRC 2007). France uses the INRA system (the UFL and UFV net energy units and PDI for protein, revised in 2018), the United Kingdom has used the AFRC metabolisable energy and metabolisable protein systems, Australia the CSIRO Nutrient Requirements of Domesticated Ruminants (2007), and the Cornell Net Carbohydrate and Protein System is a mechanistic model used in many ration programs.
Energy in modern standards is expressed as net energy (NE) or metabolisable energy (ME). NRC dairy uses net energy for lactation (NEL), which treats maintenance, lactation and late pregnancy on one scale; beef systems use separate NE for maintenance (NEm) and gain (NEg). Maintenance requirements are scaled to metabolic body weight, the live weight raised to the power 0.75. In NRC 2001 the maintenance NEL of a mature, non-pregnant dairy cow is 0.080 Mcal per kg of metabolic weight; for a 600 kg cow that is 0.080 × 600^0.75 = 0.080 × 121.2 = 9.7 Mcal NEL per day. The energy content of milk depends on its composition; NRC gives NEL (Mcal/kg) = 0.0929 × fat% + 0.0547 × protein% + 0.0395 × lactose%, which for milk of 3.5 percent fat, 3.0 percent protein and 4.8 percent lactose is 0.68 Mcal/kg. A 600 kg cow giving 25 kg of such milk therefore needs about 9.7 + 25 × 0.68 = 26.7 Mcal NEL per day, before allowances for pregnancy, growth or activity.
Older systems used total digestible nutrients (TDN) and digestible crude protein (DCP), which remain common in South Asian teaching; 1 kg TDN is taken as about 4.4 Mcal digestible energy, and ME is roughly 0.82 of DE. Modern protein systems use metabolisable protein (MP), the true protein digested and absorbed in the intestine, made up of microbial protein and digestible RUP, and require that RDP be adequate for the microbes.
Dry matter intake (DMI) sets the ceiling. Adult cattle eat roughly 2 to 3 percent of body weight as dry matter, high-yielding dairy cows more (often 3.5 to 4 percent at peak), and goats relatively more than cattle. Intake falls with high NDF, heat stress and around calving. Feeding standards also set fibre limits: NRC 2001 recommends a minimum of 25 percent NDF in diet DM with at least 19 percent coming from forage, and a maximum of about 44 percent non-fibre carbohydrate, with adjustment for forage particle size.
Because fat is the most energy-dense component, milk yields are often converted to a common basis. The classical 4 percent fat-corrected milk (FCM) formula is FCM (kg) = 0.4 × milk (kg) + 15 × fat (kg). A cow giving 20 kg of milk at 5 percent fat yields 1 kg fat, so her FCM is 0.4 × 20 + 15 × 1 = 23 kg. Energy-corrected milk equations that include protein are also used; they differ between countries.
In South Asian smallholder practice, simple thumb rules derived from the standards are widely taught: roughage to about two-thirds and concentrate to about one-third of the dry matter for moderate yielders; for production, about 1 kg of concentrate mixture for every 2.5 kg of milk in cows and for every 2 kg of milk in buffalo (higher-fat milk); an extra allowance of concentrate in the last two to three months of pregnancy. These rules assume an average concentrate mixture and ordinary roughage and are only a starting point. They fail with very good green fodder or straw-only roughage, and they do not balance minerals.
Whatever standard is used, the practical sequence is the same: define the animal (weight, stage, yield, milk composition, target gain), estimate intake, list requirements, list the feeds with their analysed or tabulated composition on a dry matter basis, formulate, then check the result against the animals' response (milk, body condition, dung, rumination, blood or milk metabolites) and adjust.
The Pearson square is a quick way to find the proportions of two feeds (or two premixed groups of feeds) that give a mixture with a desired concentration of one nutrient. Draw a square; write the target value in the centre, the nutrient content of feed A at the upper left corner and of feed B at the lower left corner. Subtract diagonally, ignoring signs: the difference between B and the target, written at the upper right, is the parts of A; the difference between A and the target, at the lower right, is the parts of B. Divide each by the sum of parts to get percentages.
Two rules must hold. The target must lie between the two feed values; if both feeds are richer or both poorer than the target, no mixture of them can hit it. And all values must be on the same basis, either all as-fed or all dry matter; mixing bases is the commonest error students make.
Worked example. A dairy farmer wants a concentrate mixture of 18 percent crude protein from maize grain (9 percent CP) and an oilseed cake (42 percent CP). Parts of maize = 42 − 18 = 24; parts of cake = 18 − 9 = 9; total = 33. Maize = 24/33 × 100 = 72.7 percent and cake = 9/33 × 100 = 27.3 percent. Check: 0.727 × 9 + 0.273 × 42 is about 18. The method solves one nutrient only; energy, minerals and cost must then be checked separately.
Real mixtures contain fixed items such as mineral mixture and salt, which carry no protein. If 2 percent mineral mixture and 1 percent salt are fixed, the remaining 97 percent must supply all the protein, so the target for the variable part is raised: 18 ÷ 0.97 = 18.56 percent CP. Solving the square with 18.56 gives maize 23.44 parts and cake 9.56 parts, which scale to 68.9 percent maize and 28.1 percent cake in the final mixture, plus 2 percent mineral mixture and 1 percent salt.
With more than two feeds, group them. For example, a grain mix of maize and wheat bran in a fixed ratio is treated as one feed whose protein is the weighted average; the protein supplements are grouped as a second feed. The square is then solved between the two groups. A 'double Pearson square' solves one square for a nutrient and a second to adjust another, but for more than one constraint at once linear programming is the proper tool.
The square is also used to balance a whole ration on a dry matter basis, for example to find how much concentrate of known CP must be mixed with a roughage of known CP to reach a required CP in total ration dry matter. Converting to as-fed amounts then needs each feed's dry matter content: kilograms as fed = kilograms of DM ÷ DM fraction.
Least-cost formulation finds the combination of available feeds that meets every nutrient requirement at the lowest cost. It is solved by linear programming (LP): the objective function is the total cost (the sum of each feed's quantity times its price), and the constraints are the nutrient minimums and maximums (energy, CP, RDP, NDF, calcium, phosphorus and so on), the limits on individual feeds (for example no more than a set proportion of a feed with an anti-nutritional factor, or of urea), and the requirement that the proportions sum to 100 percent. The simplex method or its modern equivalents solve such problems quickly; spreadsheet solvers and dedicated ration software do the same.
The output gives more than the ration. Shadow prices (dual values) show how much the ration cost would fall if a constraint were relaxed by one unit, which tells the nutritionist which requirement is expensive to meet. Ranging or sensitivity analysis shows the price range over which each feed stays in the solution; a feed that is just out of the ration will enter if its price falls below a calculable level.
A simple way to compare protein sources before running a full program is cost per unit of nutrient. If cake X has 42 percent CP and costs 40 currency units per kg, a kg of CP from it costs 40 ÷ 0.42 = 95.2; a cake Y with 30 percent CP at 24 per kg gives CP at 24 ÷ 0.30 = 80.0. Y is the cheaper protein even though X is richer. Such comparisons must be made on the nutrient that is actually limiting and on a dry matter basis, and they ignore the other nutrients each feed brings, which is why LP is preferred.
An LP solution is only as good as its inputs. Tabulated feed values may differ widely from the feeds on a given farm, especially for forages; laboratory analysis of the main forages is the single most useful improvement. Least-cost solutions tend to push up to the constraint limits, so a ration can be technically balanced yet unpalatable, dusty or unstable in the rumen. Constraints on physically effective fibre, starch, fat and inclusion rates of by-products are needed to keep the ration safe. LP also minimises cost per day, not cost per litre of milk or per kg of gain; a slightly dearer ration that raises yield may be more profitable, which is why some programs maximise margin over feed cost instead.
A total mixed ration (TMR) is a single mixture of forages, concentrates, minerals and additives, chopped and blended so that every mouthful has the same composition. It is fed ad libitum or to a small refusal (commonly around 3 to 5 percent of offered feed). Its advantages are stable rumen fermentation, because starch and fibre arrive together, higher intake, easy inclusion of by-products and unpalatable ingredients, and precise control of the ration.
Common faults are overmixing (which grinds the fibre), undermixing, wrong loading order, sorting by cows that pick out concentrate and leave long fibre, and variation in forage dry matter that silently changes the ration. Forage dry matter should be checked regularly, weekly or more often for silage, and the as-fed quantities adjusted. Particle size is checked with a sieve-based particle separator; the fraction of long particles and the physically effective NDF (peNDF, NDF multiplied by the proportion of particles large enough to stimulate chewing) indicate whether the ration will support rumination and rumen pH. Partial mixed rations, with extra concentrate fed separately in the parlour or by feeder, are common in pasture-based and smallholder systems.
The ruminant placenta does not pass immunoglobulins, so the newborn is born almost without circulating antibody and depends on colostrum. The gut absorbs intact immunoglobulins for only a short time after birth; absorption efficiency falls from birth and is minimal by about 24 hours (gut closure). The standard advice for dairy calves is to feed high-quality colostrum as soon as possible, ideally within the first 1 to 2 hours, in a volume of about 10 percent of birth weight for the first feed (about 4 litres for a 40 kg Holstein calf), and more in the following hours. Good colostrum is commonly defined as more than 50 g IgG per litre; on a Brix refractometer a reading of 22 percent or above is the usual cut-off for good quality. Colostrum should be clean, because bacteria reduce IgG absorption.
Failure of passive transfer is traditionally defined as a serum IgG below 10 g/L at 24 to 48 hours; serum total protein measured by refractometer is used as a herd-level proxy, and newer targets grade transfer as excellent, good, fair or poor. The expected serum IgG can be estimated: IgG fed × apparent efficiency of absorption ÷ plasma volume (about 9 percent of body weight). A 40 kg calf fed 200 g IgG with an absorption efficiency of 35 percent reaches about 200 × 0.35 ÷ (40 × 0.09) = 19.4 g/L. Lambs and kids follow the same principles, usually with about 50 ml per kg body weight in the first feed and a total of around 200 ml per kg over the first day, with local variation.
In the pre-ruminant calf, milk bypasses the rumen through the oesophageal (reticular) groove, which closes reflexly when the calf sucks or drinks milk, and is digested in the abomasum where casein clots. Whole milk or milk replacer was traditionally fed at about 10 percent of body weight per day; many herds now feed more (often 15 to 20 percent of body weight, or about 6 to 8 litres a day for a Holstein) because it improves early growth and welfare, with a gradual step-down before weaning. Milk replacers should be based on milk proteins for the youngest calves; unprocessed plant proteins and starch are poorly digested in the first weeks because the calf lacks enough sucrase, amylase and maltase.
Rumen development needs solid feed. A palatable, textured calf starter of about 18 to 20 percent CP should be offered from the first week, with fresh clean water always available, because the butyrate and propionate produced from fermentation of starter stimulate papillae growth. Weaning is based on starter intake rather than age alone: a common guide for large-breed dairy calves is weaning once a calf eats about 1 kg of starter a day for several consecutive days, often at 6 to 8 weeks. In many smallholder systems calves, especially buffalo calves, are starved of milk so that more can be sold, a major cause of calf loss.
Lambs and kids are reared on the dam or artificially on ewe or goat milk replacer; creep feeding, where young stock can reach a concentrate that the dams cannot, improves growth, especially of twins and triplets.
Nutritional (dietary) diarrhoea follows overfeeding, abrupt changes, poorly mixed or low-quality replacer and inconsistent temperature. Ruminal drinking, when milk enters the rumen because the groove fails to close (often in weak calves or with forced tube feeding of large volumes at later feeds), causes milk to ferment in the rumen, with bloat, poor growth and acidosis. White muscle disease (nutritional myopathy) is caused by deficiency of selenium and/or vitamin E and is common in lambs, kids and calves born in selenium-deficient areas. Hypoglycaemia and hypothermia kill newborn lambs that fail to suck in cold weather. Copper deficiency in the dam gives enzootic ataxia (swayback) in lambs and kids.
The replacement heifer is an investment that returns nothing until she calves, so the goal is to reach the target size at first calving at the right age at the least cost, without making her fat. For large-breed dairy heifers a first calving at about 22 to 24 months is the usual target in intensive systems; smaller breeds, indigenous zebu cattle and buffalo calve later, often 30 to 40 months or more under smallholder conditions, largely because of slow growth on poor feed rather than genetics alone.
Growth targets are set as fractions of mature body weight: breeding at about 55 percent of mature weight and calving at about 80 to 85 percent. For a herd with a mature cow weight of 650 kg, the breeding target is about 0.55 × 650 = 357.5 kg. If the heifer is born at 40 kg and is to be bred at 15 months (about 456 days), she must gain (357.5 − 40) ÷ 456 = about 0.7 kg per day.
Very rapid gain before puberty, from high-energy diets, has been associated with fat deposition in the mammary fat pad and reduced milk yield in several studies, so energy should be matched with enough protein to promote frame and lean growth rather than fat. Underfeeding delays puberty and first calving and increases lifetime rearing cost. Heifers should be weighed or measured by heart girth tape regularly and grouped by size.
Beef systems range from cow-calf herds on range or pasture, through backgrounding (growing weaned calves on forage), to finishing on pasture or in a feedlot on high-grain diets. Gain is predicted in net energy systems from the NEg of the diet after maintenance is met; protein needs are highest for young, lean-growing animals. Compensatory growth, the faster than normal gain of animals refed after a period of restriction, is used in systems that grow cattle cheaply on forage before finishing.
Feedlot cattle are moved from forage to high-grain diets by a series of step-up diets over about two to four weeks, allowing the rumen microbes and papillae to adapt. Grain is processed (rolled, ground, steam-flaked) to raise starch digestibility; the more processed the grain, the greater the risk of acidosis. Liver abscesses, from bacteria entering portal blood through a damaged rumen wall, and bloat are the main nutritional diseases of feedlots; in wethers and steers, urinary calculi occur when high-grain diets bring too much phosphorus relative to calcium.
Weaned lambs and kids are grown on pasture, crop residues and browse, or finished intensively on concentrate. Goats browse and select leaves and are more tolerant of tannin-rich browse than sheep. For intensive finishing, the same principles as feedlot cattle apply: gradual introduction to grain, adequate fibre, a calcium to phosphorus ratio of about 2:1, and often a urinary acidifier such as ammonium chloride to prevent urolithiasis in males. Coccidiosis and internal parasites often limit growth more than the ration, and a nutritionist should check both.
The dry period lets the udder involute and regenerate secretory tissue before the next lactation, and it is the time to prepare the cow for calving. A dry period of about 45 to 60 days is standard in dairy cows; shorter periods reduce the following lactation somewhat and are used deliberately in some herds. The dry period is commonly split into the far-off phase (from drying off to about three weeks before calving) and the close-up phase (the last three weeks).
Far-off cows need a ration that meets maintenance and pregnancy without making them fat. Body condition score at calving of about 3.0 to 3.5 on the 5-point scale is the usual target; fat cows eat less after calving, mobilise more fat and are prone to fatty liver, ketosis, displaced abomasum and retained placenta. Condition should be corrected in late lactation, when the cow uses energy efficiently, rather than in the dry period. Controlled-energy diets based on straw or other low-energy forages, which let the cow eat to appetite without exceeding her energy need, are a widely used approach.
Pregnant animals of all species need extra nutrients mainly in the last third of gestation, when most foetal growth occurs. Indian practice calls the extra concentrate given in late pregnancy 'steaming up'; it provides for the foetus and accustoms the rumen to concentrate before lactation.
At calving, the calcium demand for colostrum and milk rises suddenly, and a cow that cannot mobilise bone calcium and increase gut absorption fast enough becomes hypocalcaemic. The close-up diet is designed to prime these mechanisms. The main strategies are feeding a diet with a negative dietary cation-anion difference (DCAD), restricting calcium intake before calving, or binding dietary calcium, with adequate magnesium in all cases (commonly about 0.35 to 0.45 percent of DM in close-up rations).
DCAD is usually calculated as (Na + K) − (Cl + S), in milliequivalents per kg of diet dry matter. To convert a percentage to mEq per kg, multiply by 10,000, divide by the atomic weight and multiply by the valence. For a close-up ration with 0.12 percent Na, 1.20 percent K, 0.65 percent Cl and 0.40 percent S: Na = 52, K = 307, Cl = 183, S = 249 mEq/kg, so DCAD = 52 + 307 − 183 − 249 = about -73 mEq/kg DM. Negative DCAD produces a mild compensated metabolic acidosis that increases bone resorption and gut calcium absorption. Anionic salts or acidified feeds are used to achieve it, and success is monitored by urine pH, whose target range depends on whether full or partial acidification is intended and on the breed (targets of about 5.5 to 6.5 are widely cited for Holstein cows). High-potassium forages (lush grass, heavily manured forage) make a negative DCAD hard to reach and are the commonest reason for failure.
Ewes and does carrying twins or triplets have a high glucose demand in late pregnancy while rumen space is squeezed by the uterus. If energy intake falls (poor feed, sudden weather change, shearing, transport), they develop pregnancy toxaemia, a ketosis with hypoglycaemia that is often fatal. Prevention is to score condition, scan to identify multiple-bearing ewes, feed them more energy-dense concentrate in the last six weeks, and avoid stress. Flushing, a rise in energy intake for about two to three weeks before and during mating, increases ovulation rate in ewes that are in moderate condition. Buffalo, whose dry periods are often long under smallholder conditions, lose productive life when underfed while dry; a balanced late-pregnancy ration shortens the calving to conception interval.
Milk yield in a dairy cow rises to a peak at roughly 6 to 8 weeks after calving and then declines, while dry matter intake rises more slowly and peaks later. For the first weeks the cow is in negative energy balance, supplying the gap by mobilising body fat. Too much mobilisation raises blood non-esterified fatty acids (NEFA), overloads the liver and leads to fatty liver and ketosis, and a large loss of condition delays return to cyclicity and reduces fertility. The feeding goals in early lactation are to maximise intake quickly, keep the rumen healthy, and supply glucogenic energy and metabolisable protein; in mid lactation to sustain yield and restore condition; and in late lactation to rebuild condition to the drying-off target.
Practical signs of an adequate early-lactation diet include steady intake, rumination with most resting cows chewing cud, dung of porridge-like consistency, stable milk fat and protein, and loss of no more than about one condition score. Milk fat to protein ratio is a simple herd screen: a ratio above about 1.4 to 1.5 in early lactation suggests excessive fat mobilisation and ketosis risk, while a herd in which milk fat falls below milk protein suggests subacute ruminal acidosis or milk fat depression; thresholds vary with breed.
A dairy ration is built from a forage base plus concentrate. Forage supplies fibre for rumination and rumen pH and much of the energy on good forage; concentrate supplies energy and protein density. High-yielding cows are commonly fed rations of roughly 16 to 18 percent CP in DM, with attention to RDP and RUP, while low and moderate yielders on good legume fodder may need little supplementary protein. Leguminous fodders (berseem, lucerne, cowpea) are rich in protein and calcium; cereal fodders (maize, sorghum, oats) supply energy; straws of wheat and paddy are low in protein and digestibility, and rice straw is high in silica and oxalate.
Buffalo digest fibre efficiently, produce milk with about 6 to 8 percent fat, and so need more energy per kg of milk than cows; the Indian thumb rule of 1 kg concentrate per 2 kg milk reflects this. Buffalo are also more sensitive to heat because of dark skin and few sweat glands; wallowing or sprinklers support intake in summer.
Heat stress in all dairy animals reduces intake. Feeding in the cooler part of the day, increasing energy density with fat rather than extra starch, keeping fibre digestible, and raising dietary potassium and sodium to replace sweat losses are standard measures. A lactating cow drinks roughly 3 to 5 litres of water per kg of DM eaten, plus several litres per kg of milk, depending on temperature.
Lactating ewes and does have their highest needs in the first weeks after lambing or kidding, especially with twins. Dairy goats can eat a higher proportion of their body weight as DM than cattle and select strongly, so they waste more feed if offered coarse forage. Milk yield in pasture-based systems (for example in New Zealand, Ireland and parts of Australia) is determined largely by pasture allowance and quality; the nutritionist manages grazing rotation, pasture cover and supplements rather than a mixed ration. Lush spring pasture is high in protein and potassium and low in fibre and magnesium, which predisposes to grass tetany and milk fat depression; supplementing magnesium and offering some fibre are standard precautions.
Much of the world's ruminant population lives on crop residues and seasonal grazing, with a lean season every year and periodic drought. The principles are to prioritise (breeding females, young stock and working animals first; sell or slaughter unproductive stock early, before prices fall), to feed for survival and maintenance rather than production, and to make the most of low-quality roughage. Straws can be improved by urea treatment, which raises nitrogen content and digestibility: a common recipe is 4 kg urea dissolved in about 40 to 60 litres of water per 100 kg straw, sprayed, packed and sealed for about three weeks in warm weather, longer in cold. Urea-molasses mineral blocks supply fermentable nitrogen, energy and minerals as a lick. Tree leaves and shrubs, spineless cactus, sugarcane tops and agro-industrial by-products are used where available, with attention to tannins, oxalates, nitrate and mycotoxins.
Water is often the first limiting nutrient in drought. Starved animals must be refed gradually, with roughage before concentrate, to avoid acidosis and death; grain should be introduced in small steps over one to two weeks. Fodder banks, silage made in the flush season, hay and feed reserves, and community fodder development are the long-term answers, and they are central to drought-relief planning by agencies such as FAO.
Silage is forage preserved by anaerobic fermentation in which lactic acid bacteria convert water-soluble carbohydrates (WSC) to lactic acid, lowering the pH until microbial activity stops. Good ensiling needs a crop with enough WSC relative to its buffering capacity, a suitable dry matter content, fine chopping, rapid filling, heavy consolidation to expel air, and an airtight seal. Maize and sorghum, with high sugar and low buffering capacity, ensile easily; legumes such as lucerne and berseem have low sugar and high buffering capacity and are harder to ensile and are usually wilted and often treated with additives or mixed with a cereal fodder.
Maize for silage is usually harvested at about 30 to 35 percent DM, around the half to two-thirds milk-line stage of the kernel. Crops that are too wet (below about 25 percent DM) favour clostridial fermentation and effluent loss; crops that are too dry pack poorly and heat. At feed-out, air re-enters and yeasts and moulds can cause aerobic spoilage and heating. Silage additives include homofermentative and heterofermentative bacterial inoculants, sugar sources such as molasses, acids and enzymes.
Silage is judged by sight, smell and laboratory analysis. Good silage is light green to yellowish-brown, has a pleasant sharp acidic smell, and firm texture without slime or mould. Butyric-smelling (rancid) silage indicates clostridial fermentation; a strong vinegar smell, excess acetic acid; a tobacco-like or caramelised smell with dark brown colour, overheating (Maillard reaction) that reduces protein availability; white or blue mould, air penetration.
Laboratory indices include pH, DM, organic acids and ammonia-nitrogen. Well-fermented maize or grass silage of ordinary DM usually has a pH of about 3.7 to 4.2, lactic acid as the main acid, little or no butyric acid, and ammonia-N below about 10 percent of total nitrogen. Ammonia-N above about 15 percent of total N indicates substantial protein breakdown. Acceptable pH rises with DM, so a wilted, drier silage may be stable at a higher pH. The Flieg (Flieg-Zimmer) point system scores silage from the proportions of lactic, acetic and butyric acid and is still taught in several countries. Heat-damaged protein is measured as acid detergent insoluble nitrogen (ADIN).
Hay is forage dried to a moisture content low enough for safe storage, usually below about 15 to 20 percent moisture depending on bale type. Losses occur through continued plant respiration, leaf shatter (especially in legumes, whose leaves hold most of the protein), rain leaching, and moulding and heating if baled too wet; hay baled wet can heat enough to ignite. Stage of maturity at cutting is the main determinant of quality: as the plant matures, stem proportion, NDF, ADF and lignin increase and protein and digestibility fall.
Relative feed value (RFV) is an index for legume and mixed hay used in North America. Digestible dry matter (DDM, %) = 88.9 − 0.779 × ADF%; dry matter intake (as % of body weight) = 120 ÷ NDF%; RFV = DDM × DMI ÷ 1.29. Full-bloom lucerne (ADF 41, NDF 53) has an RFV of about 100 by definition. A hay with 35 percent ADF and 50 percent NDF has DDM = 88.9 − 0.779 × 35 = 61.6 percent, DMI = 120 ÷ 50 = 2.4 percent of body weight, and RFV = 61.6 × 2.4 ÷ 1.29 = about 115. Relative forage quality (RFQ), which uses digestible NDF, is the newer index and is better for grasses. Where these indices are not used, CP, NDF, ADF and in vitro digestibility are reported directly. Visual assessment (leafiness, colour, smell, no mould) remains a useful first check.
The mineral content of forage reflects the soil it grows on, the plant species, fertiliser and irrigation, and season. Deficiencies and excesses of minerals are therefore geographically patterned. Worldwide, common deficiencies in grazing and crop-residue-fed ruminants include phosphorus, copper, cobalt, selenium, iodine, zinc and sodium, while excesses include selenium (seleniferous soils), molybdenum and sulphur (which lock up copper), fluorine (from water and rock phosphate) and iron. A single generic mineral mixture can therefore oversupply one element and miss another.
An area-specific mineral mixture (ASMM) is formulated from a survey of the soil, feeds and fodders, and animal blood or tissue of a defined area, so that it supplies only the elements that are deficient there, in the right amounts. The approach has been developed extensively in India by ICAR institutes and state universities, which mapped deficiencies district by district; phosphorus, copper and zinc deficiencies are widely reported, and several states produce their own formulations. Seleniferous pockets in Punjab (for example parts of Hoshiarpur and Nawanshahr districts) and fluoride-endemic areas are classical examples where a standard mixture would be wrong.
A mineral mixture supplies the major minerals (calcium, phosphorus, magnesium, and sometimes sodium chloride) and trace minerals (copper, zinc, manganese, iodine, cobalt, iron, selenium), with or without vitamins. In Indian compounded cattle feed, mineral mixture is usually included at about 1 to 2 percent and common salt at about 1 percent of the concentrate; a free-choice or top-dress allowance for adult cattle is typically in tens of grams a day, as the product label and local advice state. National standards define minimum contents; they differ by country.
Interactions matter as much as amounts. Molybdenum and sulphur form thiomolybdates in the rumen that bind copper, so a pasture with ordinary copper can produce copper deficiency if molybdenum is high. Sheep are unusually susceptible to copper toxicity, because they store copper in the liver readily and excrete it poorly; mixtures made for cattle, and some concentrates, can poison sheep. A calcium to phosphorus ratio of about 1:1 to 2:1 is generally recommended; very wide ratios in either direction cause problems. Rock phosphate that is not defluorinated can cause fluorosis. Organic (chelated) trace minerals have higher availability in some studies and are used at lower rates.
Phosphorus deficiency gives pica (osteophagia), poor fertility, anoestrus, low intake and, in severe cases, rickets or osteomalacia; it predisposes to botulism when cattle chew bones. Copper deficiency gives achromotrichia (loss of hair colour, 'spectacles' around the eyes), diarrhoea (especially with molybdenum excess), poor growth, infertility and swayback in lambs. Cobalt deficiency gives wasting (pine) with anaemia because vitamin B12 is not made. Iodine deficiency gives goitre and weak or stillborn young. Selenium deficiency gives white muscle disease and retained placenta. Zinc deficiency gives parakeratosis and poor hoof and skin. Magnesium deficiency presents acutely as grass tetany. Sodium deficiency gives salt craving, licking of soil, urine and sweat. Diagnosis rests on history, response to supplementation and the right samples (liver for copper, blood selenium or glutathione peroxidase, serum magnesium, B12 or methylmalonic acid for cobalt), not feed analysis alone.
Acute rumen acidosis (grain overload) follows sudden access to large amounts of fermentable carbohydrate. Lactic acid accumulates, rumen pH falls below about 5.0, the rumen becomes static, fluid is drawn into the rumen by osmosis and the animal becomes dehydrated, acidotic, depressed and often dies; survivors can develop rumenitis, liver abscesses, laminitis and fungal rumenitis. Subacute ruminal acidosis (SARA) is a herd problem in which rumen pH stays below about 5.5 to 5.8 for several hours a day; it shows as variable intake, low milk fat, loose dung with undigested fibre and grain, laminitis and culling. Prevention is gradual adaptation, adequate peNDF, controlled starch and its rate of fermentation, frequent feeding or TMR, and buffers where appropriate.
Bloat is excessive distension of the rumen with gas. Frothy bloat occurs when gas is trapped in a stable foam, typically on lush legume pasture (soluble leaf proteins) or on finely ground high-grain diets; free-gas bloat results from failure of eructation, such as oesophageal obstruction or vagal damage. Frothy bloat is prevented by grazing management, feeding fibre before turnout, mixing grass with legumes, and anti-foaming agents such as vegetable oils or approved surfactants — confirm against the product label and your national formulary; emergency relief of severe bloat is by stomach tube or trocarisation.
Milk fever (parturient paresis) is acute hypocalcaemia around calving, most common in older, high-yielding cows and Jersey and other high-fat breeds. Subclinical hypocalcaemia, with serum calcium below about 2.0 mmol/L (about 8 mg/dl) and no recumbency, is much more common and increases the risk of other diseases. Prevention is by the close-up strategies described earlier. Ketosis results from excessive fat mobilisation in early lactation; blood BHB of about 1.2 mmol/L or more is widely used to define subclinical ketosis and about 3.0 mmol/L for clinical ketosis, with thresholds varying slightly between sources. Fatty liver develops when fat accumulates faster than the liver can oxidise or export it. Displaced abomasum, retained placenta and metritis are linked to the same transition-cow problems. Oral glucogenic precursors such as propylene glycol are used for treatment and prevention of ketosis — confirm against the product label and your national formulary.
Hypomagnesaemic tetany (grass tetany) occurs in cattle and sheep on lush, fertilised, fast-growing pasture high in potassium and low in magnesium, or in underfed animals in cold weather. Magnesium is not stored in a readily mobilised form, so a daily supply is needed; supplementation by magnesium oxide in feed, dusting pasture, or water treatment is standard. A high K/(Ca + Mg) ratio in forage (above about 2.2 in milliequivalents) is a classical warning sign.
Urea (non-protein nitrogen) toxicity occurs when urea is overfed, poorly mixed, fed to unadapted animals or on low-energy diets: rumen ammonia rises, blood ammonia exceeds the liver's capacity, and animals show tremors, incoordination, bloat and death within hours. Safe practice limits urea to about 1 percent of total ration DM (or about one-third of total dietary nitrogen), mixes it thoroughly, introduces it gradually, provides fermentable energy and avoids it in young calves whose rumen is not functional. Oral cold water and dilute acetic acid (vinegar) are the classical first aid, reducing ammonia absorption.
Polioencephalomalacia (cerebrocortical necrosis) is associated with thiamine deficiency or high dietary sulphur (above about 0.3 to 0.4 percent of diet DM, including water sulphate), and responds to early thiamine treatment. Nitrate poisoning follows drought-stressed or heavily fertilised cereal fodders and weeds; nitrite converts haemoglobin to methaemoglobin (chocolate-brown blood); methylene blue is the specific antidote. Oxalate poisoning occurs with some tropical grasses and weeds; hydrocyanic acid poisoning with young or wilted sorghum; mycotoxin problems (aflatoxin in oilseed cakes, zearalenone, deoxynivalenol) with poorly stored feeds; and aflatoxin M1 is a residue concern in milk. Urolithiasis in castrated male sheep and goats reflects high-grain, high-phosphorus rations. Copper poisoning in sheep, vitamin A deficiency on long-stored dry roughage, and vitamin E and selenium deficiency complete the list most examined.
Clinical nutrition is herd medicine. When one animal shows a nutritional disease, the veterinarian examines the ration offered, the ration eaten, the feeding routine and a representative group of animals (body condition, rumen fill, dung, locomotion), and uses targeted blood and milk tests to confirm before changing the diet.
Learn the rumen as a fermentation system first: which microbes do what, what each VFA becomes, and why RDP and energy must arrive together. Then practise the calculations until they are automatic: dry matter conversion, Pearson square with fixed ingredients, FCM, metabolic weight, DCAD and RFV. In the clinic, when you see a down cow, a bloated heifer or a ewe with pregnancy toxaemia, ask what the animal was fed in the last two weeks before you reach for a bottle. Visit a farm and weigh what is actually fed; it is rarely what the owner says.
Most of your production-animal calls are feeding problems in disguise. Build a routine herd nutrition check: ration offered versus eaten, forage DM and analysis, body condition by group, rumen fill, dung, rumination, lameness, milk fat and protein trends, and targeted BHB and calcium tests in fresh cows. Use it to set up a close-up diet with a urine pH check, a colostrum protocol with serum protein monitoring in calves, and a heifer growth programme with regular weighing. Advise smallholders with simple, costed rations using local feeds and the right mineral mixture for the area.
At this stage you shape systems rather than rations: feed budgets across a season, silage and forage programmes, drought contingency plans, group housing and feeding space, and decisions about additives that must be justified by evidence and permitted by law. You interpret the economics, weighing margin over feed cost rather than feed cost alone. You train farm staff and junior colleagues to read cows, and you work with feed mills and cooperatives on area-specific mineral mixtures and ration-balancing programmes that reach thousands of smallholders.
Research questions that remain open include the prediction of intake and nutrient supply in tropical feeds, which are underrepresented in the databases behind NASEM and INRA models; metabolisable protein and amino-acid requirements of buffalo and indigenous cattle; methane mitigation that is safe, legal and affordable at smallholder scale; the rumen microbiome's role in efficiency and its heritability; and validated mineral maps. A senior researcher also judges the quality of evidence behind feed-additive claims, designs trials with adequate replication, and translates models into advisory tools that work with the feeds farmers actually have.
This manual does not reproduce the ICAR 2013, NASEM or INRA requirement tables, which are copyrighted and must be consulted for real rations; worked examples use formula-level values only. It gives no additive or drug doses beyond general inclusion ranges; any product must be checked against its label and national regulations. District-level mineral deficiency maps, the national mineral mixture standards by number, camelid and yak feeding, and detailed amino-acid balancing models (CNCPS and NASEM MP equations) are not covered. Buffalo and indigenous cattle requirements are less well established than those of Holstein cows, and the manual says so rather than extrapolating.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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