Dairy Science & Technology · Foundations · also Livestock Production Management, Dairy Husbandry, Dairy Cattle Management
Dairy breeds, lactation physiology, feeding, health and herd records as they affect milk quantity and quality. The veterinary track (livestock-production-management-ruminants, applied-nutrition-ruminants) goes deeper.
In the exams: ICAR AIEEA-PG and AICE Part A animal husbandry questions; ICAR AICE subject 19 (LPM) for dairy farm management
Every property of milk that a dairy technologist measures, processes or sells begins in the animal. The species and breed set the composition; the mammary gland synthesises the fat, protein and lactose; feeding shifts fat and protein content; udder health decides the somatic cell count, enzyme activity and cheese yield; milking hygiene and cooling decide the bacterial load; and veterinary treatment decides whether residues reach the milk. A technologist who understands the animal can trace a processing problem back to its cause on the farm and speak credibly with farmers and veterinarians.
This manual gives the dairy technologist the animal science needed for that work, without going into the full depth of veterinary or animal husbandry degrees. It covers dairy breeds of cattle and buffalo worldwide; dairy goats, sheep and camels; the anatomy of the mammary gland; lactation physiology and the synthesis of milk constituents; milk let-down and hand and machine milking; feeding for milk yield and composition; mastitis and somatic cell count; herd records, lactation curves and economic traits; housing, welfare and heat stress; and the use of veterinary drugs and withdrawal periods.
Entrance examinations for dairy technology degrees and public-service recruitment ask direct questions on breeds, udder anatomy, let-down, mastitis and feeding. Postgraduate examinations ask about milk synthesis pathways, the effect of feed on milk fat and protein, mastitis and its effect on milk quality, and residues. The manual covers these, with examples from dairy regions on every continent and short calculations of the kind examinations use.
Dairy cattle belong to two main types. Taurine cattle (Bos taurus), developed in Europe and the Middle East, dominate temperate dairying. Indicine or zebu cattle (Bos indicus), with a hump, dewlap and loose skin, developed in South Asia and Africa and tolerate heat, ticks and poor feed better but usually yield less milk.
The Holstein-Friesian, from the Netherlands and northern Germany and developed further in North America, is the most numerous dairy breed in the world. It gives the highest volume, often well over 8,000 to 10,000 kg per lactation in intensive systems, with relatively low fat and protein percentages, typically around 3.5 to 4% fat. The Jersey, from the Channel Islands, is small, efficient and gives milk rich in fat (often around 5%) and protein, with larger fat globules and more carotene, valued for butter and cheese; it tolerates heat better than the Holstein. Other important taurine dairy breeds include the Guernsey, the Ayrshire from Scotland, the Brown Swiss, whose milk is valued for cheese, the Scandinavian red breeds, the Montbéliarde of eastern France, used for many protected cheeses, and dual-purpose breeds such as the Simmental or Fleckvieh.
Zebu dairy breeds of South Asia include the Sahiwal, Gir, Red Sindhi and Tharparkar; in Africa, the Kenana and Butana of Sudan are dairy zebus. Crossbreeding taurine with zebu cattle combines yield with adaptation, and has produced synthetic breeds in many tropical regions, such as the Girolando of Brazil (Gir × Holstein), the Australian Milking Zebu, the Jamaica Hope and several South Asian and East African crossbred populations. In smallholder tropical systems the appropriate level of taurine inheritance depends on feed, health care and climate; high-grade Holsteins often perform poorly where these are limited.
The water buffalo (Bubalus bubalis) is the second most important dairy species. Two types exist. River buffalo, with 50 chromosomes, are kept mainly for milk in South Asia, the Middle East, Egypt, the Mediterranean and parts of South America. Swamp buffalo, with 48 chromosomes, are kept mainly for draught and meat in South-East Asia and southern China and give little milk; crosses with river buffalo are used to raise milk yield.
The Murrah, a jet-black river breed with short, tightly curled horns, is the best-known dairy buffalo and has been exported widely to improve buffalo populations. The Nili-Ravi, characterised by white markings and 'wall eyes', is important in the Punjab region on both sides of the border. Other South Asian breeds include the Jaffarabadi, a heavy breed with drooping horns, the Mehsana and the Surti. The Mediterranean buffalo of southern Italy, whose milk makes mozzarella di bufala, and the Egyptian buffalo are other dairy populations.
Buffalo milk is richer than cow milk, commonly 6 to 8% fat and over 4% protein, with more calcium and casein and larger fat globules; it is white because buffalo convert carotene to vitamin A. Buffaloes are well adapted to wet, hot climates but have few sweat glands and dark skin, so they rely on wallowing or water sprinkling to keep cool. Their reproduction is slower and more seasonal than that of cattle, with later age at first calving and longer calving intervals, and silent heat makes oestrus detection difficult; these traits affect the year-round supply of buffalo milk.
Goats are milked across Asia, Africa, the Mediterranean, Latin America and increasingly in specialised commercial herds in Europe, North America and Oceania. They are browsers, efficient on poor feed, and suit smallholders and dry regions. The Saanen, a white Swiss breed, gives the highest yields; the Alpine and Toggenburg are other Swiss-origin breeds; the Anglo-Nubian, with long lop ears and a Roman nose, gives less milk but higher fat and protein; the Damascus or Shami goat is important in the Middle East; and the Jamunapari and Beetal are dairy breeds of South Asia. Goat milk has smaller average fat globules, more short- and medium-chain fatty acids (caproic, caprylic and capric acids, named from the Latin for goat), and lacks the agglutinin that clusters cow fat globules, so it creams slowly. Some goats carry αs1-casein variants that give very low αs1-casein content, which affects cheese yield.
Dairy sheep are concentrated around the Mediterranean and in the Middle East, with growing industries elsewhere. Specialised breeds include the East Friesian, the highest-yielding; the Lacaune of southern France, whose milk makes Roquefort; the Awassi of the Middle East and its improved Israeli strains; the Assaf (Awassi × East Friesian); and the Sarda, Manchega and Chios breeds of Italy, Spain and Greece. Sheep milk is very rich, often about 6 to 7% fat and 5 to 6% protein, so it gives high cheese yields and is used mainly for cheese and yoghurt. Sheep and goats have udders with two halves and two teats, and their lactations are shorter and more seasonal than those of cows.
Camels are the dairy animals of arid lands. The one-humped dromedary is milked in the Horn of Africa, the Sahel, North Africa, the Arabian Peninsula and parts of South Asia; the two-humped Bactrian camel is found in Central Asia and Mongolia. Camels tolerate heat, dehydration and poor grazing and continue to produce milk in droughts when cattle fail, which makes them central to the food security of pastoral peoples. Lactations are long, often a year or more, and yields of several litres a day are common under pastoral conditions, with higher yields in intensive systems that have developed in the Gulf states.
Camel milk is lower in fat than buffalo or sheep milk, typically around 3 to 4%, has smaller fat globules, more vitamin C than cow milk, and lacks β-lactoglobulin. Its casein micelles are larger and its κ-casein content lower, so it forms weak curds with calf rennet; camel chymosin produced by fermentation is used to make camel cheese. Let-down in camels often requires the presence of the calf, which complicates machine milking.
Other species provide milk locally: yaks on the Tibetan plateau and in the Himalaya and Mongolia, mares in Central Asia, where their milk is fermented into koumiss, donkeys in parts of Europe for specialised products, and reindeer in the far north. Each species brings its own composition, seasonality and processing challenges, and labelling rules usually require the species to be named when milk is not from cows.
The mammary glands are modified skin glands. In the cow and buffalo the udder consists of four quarters, each a separate gland with its own teat and duct system, so that milk from one quarter does not pass into another and one quarter can be infected while the others are healthy. The rear quarters usually produce somewhat more milk than the front quarters. Goats and sheep have two halves, each with one teat. The udder of a high-yielding cow may weigh tens of kilograms when full.
The udder is held against the body wall by a suspensory apparatus. The median suspensory ligament, made of elastic tissue, runs between the right and left halves and allows the udder to stretch as it fills; the lateral suspensory ligaments, made of less elastic fibrous tissue, support the sides. Weakening of these ligaments with age leads to a pendulous udder that is more easily injured and contaminated.
Blood reaches the udder mainly through the external pudendal arteries and leaves through the external pudendal veins and the subcutaneous abdominal veins, the prominent 'milk veins' on the belly. Blood flow is very high: several hundred litres of blood, often quoted as roughly 400 to 500 L, pass through the udder for every litre of milk produced, because the gland extracts its precursors from the blood. Lymph drains through the supramammary lymph nodes, which enlarge in mastitis. Nerves supply the skin and teats and carry the sensory signals that trigger milk let-down.
Inside each quarter, milk is made in millions of tiny sacs called alveoli. Each alveolus is lined with a single layer of secretory epithelial cells, the lactocytes, which take up precursors from the blood and synthesise and secrete milk into the central lumen. Around each alveolus lies a basket of myoepithelial cells, which contract in response to oxytocin and squeeze milk out. A dense network of capillaries surrounds the alveoli. Groups of alveoli form lobules, lobules form lobes, and small ducts join into larger ducts that drain into the gland cistern, a cavity above the teat.
The gland cistern opens into the teat cistern within the teat, separated by an annular fold. At the tip of the teat, the streak canal, also called the teat canal, leads to the outside. It is closed between milkings by a sphincter muscle and lined with keratin, which traps and kills bacteria and forms a plug; at its inner end the folds of Fürstenberg's rosette help seal it. The streak canal is the main barrier against infection. During and for some time after milking it stays partly open, which is why cows should stand for a while after milking, for example by being offered feed, and why post-milking teat disinfection is important.
Most milk at any time is held in the alveoli and small ducts rather than in the cisterns; only the cisternal fraction, a minority in cows, can be removed without let-down. This is why stimulation and oxytocin release are needed for complete milking. Species differ: dairy goats and sheep have larger cisterns, which store a higher proportion of their milk and allow longer milking intervals.
The mammary gland develops in stages. Mammogenesis, the growth of ducts and alveoli, occurs mainly during puberty and pregnancy, driven by oestrogen for duct growth, progesterone for alveolar development, and prolactin, growth hormone, glucocorticoids and placental hormones. Lactogenesis, the onset of copious milk secretion, begins around parturition, when progesterone falls sharply while prolactin and glucocorticoids rise; colostrum is formed in the days before calving. Galactopoiesis, the maintenance of lactation, depends in ruminants mainly on growth hormone (somatotropin), with prolactin, thyroid hormones and insulin also involved, and above all on regular, complete removal of milk.
Milk removal matters because the gland regulates itself locally. If milk is left in the gland, a feedback inhibitor in milk and the pressure of accumulated milk reduce secretion, and over days the alveoli regress. This explains why milking three times a day raises yield compared with twice, why incomplete milking lowers yield, and why stopping milking at drying off leads to involution of the gland.
The lactation follows a characteristic curve: yield rises after calving to a peak, usually at about four to eight weeks, and then declines gradually. The standard lactation for recording in cattle is 305 days, followed by a dry period of about 40 to 60 days before the next calving, which lets the gland regenerate. Colostrum, secreted at the start, is rich in immunoglobulins, protein, fat, vitamins and minerals and low in lactose; ruminant calves are born without circulating antibodies and depend on absorbing colostral IgG in the first day of life.
Lactose is synthesised in the Golgi apparatus of the lactocyte from glucose and UDP-galactose by lactose synthase, a complex of galactosyltransferase with α-lactalbumin, which changes the enzyme's specificity so that it uses glucose. Because lactose cannot leave the Golgi vesicles, it draws water in osmotically, so lactose synthesis largely determines milk volume, and lactose concentration is fairly constant within a species. Ruminants absorb little glucose from the gut; their liver makes it from propionate and other precursors by gluconeogenesis, so glucose supply is a key limit on yield.
Milk fat comes from two sources. Short- and medium-chain fatty acids, from C4 to C14 and about half of C16, are synthesised in the lactocyte from acetate and β-hydroxybutyrate, which are products of rumen fermentation. Long-chain fatty acids, C18 and the other half of C16, are taken up from blood lipoproteins with the help of lipoprotein lipase, and come from the diet or from body fat reserves. Triglycerides assemble in the endoplasmic reticulum into lipid droplets that move to the cell apex and are released wrapped in the cell membrane, which becomes the milk fat globule membrane.
Caseins, β-lactoglobulin and α-lactalbumin are synthesised in the lactocyte from blood amino acids on ribosomes of the rough endoplasmic reticulum, then modified in the Golgi, where caseins are phosphorylated and assembled with calcium phosphate into micelles before secretion by exocytosis. Immunoglobulins and serum albumin are transferred from blood; in ruminants, IgG1 is actively transported into colostrum. Between the cells, tight junctions normally prevent leakage; they open in colostrum formation and in mastitis, letting blood components such as sodium, chloride and serum proteins into milk.
Milk let-down, or milk ejection, is a neuroendocrine reflex. Stimulation of the teats by a calf, by hand or by the pre-milking routine sends nerve impulses to the hypothalamus, which causes the posterior pituitary gland to release oxytocin into the blood. Oxytocin reaches the udder within about a minute and makes the myoepithelial cells around the alveoli contract, forcing milk into the ducts and cisterns, where it can be removed. Internal udder pressure rises noticeably. The effect lasts only several minutes, because oxytocin is quickly cleared from the blood, so milking should start soon after stimulation, within about one to two minutes, and be completed promptly.
The reflex can also be conditioned: cows used to a routine may release oxytocin in response to the sounds and sights of milking time. It can be blocked by fear, pain or stress, which release adrenaline; adrenaline constricts blood vessels so less oxytocin reaches the udder and directly inhibits myoepithelial contraction. Rough handling, unfamiliar surroundings and painful udders therefore reduce yield and leave residual milk, which in turn lowers future production and increases mastitis risk. Calm, consistent routines improve both yield and milk quality.
Species differ. Buffaloes typically need longer stimulation before let-down; zebu cattle and camels often need the calf present at the start of milking; sheep and goats, with large cisterns, can be milked partly without full let-down. Some dairies use calf presence or careful manual stimulation to adapt milking to these animals.
Hand milking is still used on most of the world's dairy farms, which are small. The recommended method is full-hand milking: the base of the teat is closed with thumb and forefinger to trap milk in the teat, and the remaining fingers squeeze in turn to push it out. Stripping, in which milk is pulled out by sliding finger and thumb down the teat, and knuckling, in which the teat is pressed with bent thumb, stretch and injure teat tissue and are discouraged except for stripping the last milk. Hands must be clean and dry, and milk should not be used to wet the teats.
A milking machine removes milk by vacuum and protects the teat by pulsation. Each teat cup has a rigid shell and a flexible liner. A steady vacuum, typically around 40 to 50 kPa at system level, is applied inside the liner to draw milk from the teat. A pulsator alternately admits air and vacuum to the space between liner and shell: when this space is under vacuum the liner opens and milk flows (milking phase); when air is admitted the liner collapses around the teat, massaging it and relieving congestion (rest phase). Typical pulsation rates are about 50 to 60 cycles per minute with ratios such as 60:40 or 65:35 of milking to rest. Milk flows through the claw and milk line to a receiver and bulk tank.
Machine faults cause teat damage and mastitis: vacuum too high or unstable, worn liners, faulty pulsation, and overmilking, where the machine stays on after milk flow ends. Automatic cluster removers detach the unit when flow falls below a threshold. Machines should be tested regularly against international standards for design and performance, and milked cows should be prepared hygienically before the cups are attached.
Dairy cattle, buffaloes, goats, sheep and camels are ruminants or pseudo-ruminants: microbes in the forestomach ferment feed before the animal digests it. Rumen fermentation produces volatile fatty acids, chiefly acetate, propionate and butyrate, which supply most of the animal's energy, and microbial protein, which supplies most of its amino acids. The proportions matter for milk. Fibrous forages favour acetate, the main precursor of de novo milk fat synthesis. Starch-rich concentrates favour propionate, which the liver turns into glucose for lactose and so supports milk volume, and which raises milk protein through better energy supply but can depress milk fat.
Milk fat percentage is the component most responsive to diet. Diets low in effective fibre, high in rapidly fermentable starch, or rich in unsaturated oils cause milk fat depression. The current explanation is that under these conditions rumen biohydrogenation of unsaturated fatty acids follows altered pathways, producing intermediates such as trans-10, cis-12 conjugated linoleic acid that strongly inhibit fat synthesis in the mammary gland. A low ratio of milk fat to protein, below about 1.0 in cows, can signal subacute rumen acidosis or milk fat depression; a high ratio, above about 1.4 to 1.5, especially early in lactation, can signal excessive body fat mobilisation and ketosis risk.
Milk protein percentage responds less, mainly to energy intake and to the supply of limiting amino acids such as methionine and lysine reaching the intestine. Lactose concentration hardly changes with diet. Fatty acid composition reflects diet strongly: pasture and oilseeds increase unsaturated fatty acids and conjugated linoleic acid and give softer butter; palm-based supplements raise palmitic acid and firmness.
High-yielding dairy animals have very high nutrient needs, and in early lactation their intake cannot keep up with output, so they mobilise body fat and lose condition: negative energy balance. This raises the risk of ketosis and fatty liver, raises milk fat percentage temporarily and lowers protein. Around calving, the sudden demand for calcium for colostrum can cause milk fever (hypocalcaemia), managed by controlling the dietary cation-anion difference before calving. Dry matter intake of lactating cows is commonly around 3 to 4% of body weight. Rations are formulated to balance energy, protein, effective fibre, minerals and vitamins.
To compare cows producing milk of different composition, yields are corrected to a standard energy content. A common formula for 4% fat-corrected milk is FCM = 0.4 × milk (kg) + 15 × fat (kg); a cow giving 20 kg of milk with 3.5% fat (0.7 kg fat) produces 0.4 × 20 + 15 × 0.7 = 18.5 kg of 4% FCM. Energy-corrected milk formulas include protein as well.
Feed also affects milk safety and processing quality. Aflatoxin B1 in mouldy feed is converted in the liver to aflatoxin M1, which passes into milk; carry-over is usually a few per cent of intake, often about 1 to 3%. A cow eating 20 kg of feed with 20 µg/kg aflatoxin B1 ingests 400 µg a day; at 2% carry-over and 25 kg of milk, the milk contains 8/25 = 0.32 µg/kg aflatoxin M1, well above the European Union limit of 0.05 µg/kg though below the Codex maximum of 0.5 µg/kg. Silage of poor quality can introduce Clostridium tyrobutyricum spores that cause late blowing in hard cheeses. Strong-flavoured feeds such as some brassicas, onions and certain weeds cause feed flavours in milk if fed shortly before milking. Iodine supplements and teat dips affect milk iodine; selenium and vitamin E supplementation improve oxidative stability.
Mastitis is inflammation of the mammary gland, almost always caused by bacterial infection entering through the teat canal. It is the most costly disease of dairy herds worldwide. Clinical mastitis shows visible changes: clots, flakes, watery or bloody milk, a swollen, hot or painful quarter and, in severe cases, fever and systemic illness. Subclinical mastitis shows no visible signs but raises the somatic cell count and reduces yield; it is far more common than clinical mastitis and causes most of the economic loss.
Pathogens are grouped by their main reservoir. Contagious pathogens live in infected udders and spread from cow to cow during milking, through milkers' hands, cloths and liners: Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma species and Corynebacterium bovis. Environmental pathogens live in bedding, manure, soil and water and infect teats between milkings: Escherichia coli, Klebsiella species, Streptococcus uberis and others. Control differs accordingly: contagious mastitis is controlled mainly by milking hygiene, teat disinfection and culling of chronic cases; environmental mastitis by clean, dry bedding and housing.
Somatic cells in milk are mostly white blood cells, with some epithelial cells. A healthy quarter usually has fewer than about 100,000 cells/mL; counts above about 200,000 cells/mL suggest infection. Counts are measured in laboratories by fluorescence flow cytometry and on farms by the California Mastitis Test, in which a detergent reagent lyses the cells and their DNA forms a gel whose thickness reflects the count. Electrical conductivity rises in mastitic milk because of increased sodium and chloride, and is monitored in many milking systems. Bacterial culture identifies the pathogen.
Mastitis changes milk composition in ways that matter to processors. Damage to secretory cells and leaky tight junctions lower lactose, casein and often fat, and raise sodium, chloride, serum albumin, immunoglobulins and pH, while potassium falls. Proteolytic and lipolytic activity rises: plasmin and enzymes from somatic cells break down casein, and lipases release free fatty acids. The results are lower cheese yield and quality, slower coagulation, weaker curd, more fat and protein lost in whey, bitterness and rancidity, and shorter shelf life of pasteurised and UHT milk. Bulk milk somatic cell count is therefore used in payment systems and regulations; for example, European Union rules require a rolling geometric mean below 400,000 cells/mL for raw cow milk, and other countries set their own limits.
Bulk tank count is the volume-weighted average of the cows contributing. In a herd where cows give 10 kg at 100,000 cells/mL, 20 kg at 400,000 and 10 kg at 1,000,000, the bulk count is (10 × 100 + 20 × 400 + 10 × 1,000)/40 thousand = 475,000 cells/mL: one high-count cow can push the bulk milk over a limit.
Control follows a long-established set of measures, often called the five-point plan: post-milking teat disinfection, treatment of all quarters at drying off (now often selective dry cow therapy combined with internal teat sealants to reduce antibiotic use), prompt treatment of clinical cases, culling of chronically infected cows, and regular maintenance of the milking machine. Modern programmes add clean housing and bedding, pre-milking teat preparation, record keeping and monitoring of individual cow counts, and attention to nutrition and immunity. Treatment with antimicrobials must respect withdrawal periods, discussed later.
Milk recording measures each cow's yield and usually its fat, protein, lactose and somatic cell count at regular test days, typically about monthly, and combines these into lactation records. Records are used for management, feeding, culling and breeding decisions and for genetic evaluation. International standards for animal recording, set by the International Committee for Animal Recording, harmonise methods so that records from different countries can be compared.
Lactation yield is commonly standardised to 305 days. The shape of the lactation curve is described by models such as Wood's incomplete gamma function, y = a t^b e^(−ct), where y is daily yield at time t, a reflects initial yield, b the rate of increase to peak and c the rate of decline; the time of peak is t = b/c. With b = 0.2 and c = 0.004 per day, peak yield occurs at 50 days. Persistency describes how well yield is maintained after the peak; flatter curves are easier to feed and less stressful for the cow.
Reproductive records are as important as milk records. Key measures include age at first calving (often around 24 to 30 months in well-managed cattle herds, later in buffaloes and many tropical systems), calving interval (an often-quoted target for cattle is about 12 to 13 months), days open from calving to conception, and services per conception. A calving interval of 400 days with a 305-day lactation means a dry period of 95 days, longer than needed, which lowers lifetime yield per day.
The economic traits of dairy animals include milk yield, fat and protein yield and percentage, somatic cell count, fertility, longevity, calving ease, udder and leg conformation, temperament, milking speed and, increasingly, feed efficiency, health traits and methane emissions. In many markets payment for components makes protein and fat yield more valuable than volume. Milk protein genetic variants also matter: κ-casein B and β-lactoglobulin B are associated with better cheese properties, and the A1 and A2 variants of β-casein are used to market 'A2 milk' in some countries.
Heritability, the proportion of variation in a trait due to additive genetic effects, determines how quickly selection can change it. Milk yield has moderate heritability, typically about 0.25 to 0.35; fat and protein percentages are more heritable, about 0.5; fertility and health traits have low heritability, often below 0.1, so they improve slowly by selection and depend more on management.
Genetic improvement in dairy cattle relies on artificial insemination, which allows a few bulls to sire many daughters. Bulls were traditionally evaluated by progeny testing, comparing the records of their daughters, which took several years. Genomic selection, using thousands of DNA markers to predict breeding values from a young animal's genotype, has greatly shortened the generation interval since about 2009. Selection indexes combine traits weighted by their economic value. Crossbreeding, sexed semen, embryo transfer and in-vitro fertilisation are other tools. In smallholder systems, improvement programmes must match genotypes to available feed and health care.
Housing systems range from tethering in simple sheds, common on smallholdings, through tie stalls, to loose housing in free-stall barns with individual lying cubicles, open yards and compost-bedded packs, and to pasture with minimal shelter. A good system gives cows a dry, comfortable place to lie, enough space at the feed face and water, good footing, ventilation and protection from extremes of weather. Dairy cows spend about 10 to 14 hours a day lying down; reduced lying time is linked to lameness, lower yield and poorer welfare.
Animal welfare is commonly assessed against frameworks such as the Five Freedoms (freedom from hunger and thirst, discomfort, pain, injury and disease, fear and distress, and freedom to express normal behaviour) and the more recent Five Domains model, which adds attention to positive experiences. The World Organisation for Animal Health has standards for dairy cattle welfare in its Terrestrial Animal Health Code, and many retailers, processors and countries have welfare requirements or assurance schemes. Key welfare indicators for dairy herds include lameness, body condition, injuries, mastitis, cleanliness, lying behaviour, longevity and calf management, such as colostrum feeding and the timing of separation from the dam.
Welfare is linked to milk quality and safety: lame, stressed or sick cows produce less, have more mastitis and are treated more often with drugs. Clean housing and bedding reduce environmental mastitis and the bacterial count and spore load of milk. Processors increasingly include welfare requirements in supplier contracts.
Heat stress is a major limit on dairy production in the tropics, subtropics and, increasingly, temperate regions during summer heatwaves. High-yielding cows produce a great deal of metabolic heat and have a narrow comfort zone. Heat stress is assessed with the temperature-humidity index (THI). One widely used formula is THI = (1.8T + 32) − (0.55 − 0.0055RH)(1.8T − 26), where T is air temperature in °C and RH relative humidity in per cent; at 30 °C and 60% RH, THI ≈ 80. High-yielding cows begin to show heat stress at THI values around 68 to 72, with severity rising above about 78 to 80.
Heat-stressed cows eat less, pant, seek shade and water and lie down less. Milk yield falls, and fat and protein percentages often fall too, which lowers cheese yield; somatic cell counts may rise; fertility drops sharply, with poor oestrus expression and conception; and the effects can extend to calves born to cows stressed in late pregnancy. Bacterial growth in milk is faster in hot weather, so cooling becomes even more important.
Mitigation combines shade, which reduces radiant heat load; ventilation with fans; evaporative cooling by sprinklers or soakers combined with fans; adequate clean water; feeding at cooler times of day and adjusting rations to reduce heat increment; and choosing or breeding animals adapted to heat, such as zebu crossbreeds and animals with slick hair coats. Buffaloes, with few sweat glands and dark skin, depend on wallowing or showers. Planning for heat stress is part of climate adaptation in dairying.
Dairy animals are treated with antimicrobials for mastitis and other infections, with anti-inflammatory drugs, antiparasitic drugs and hormones. Drugs and their metabolites can pass into milk. To protect consumers and processing, each product authorised for lactating animals carries a withdrawal period for milk: the minimum time after the last dose during which milk must be discarded. Withdrawal periods are set by regulators from residue depletion studies so that, after the period, residues fall below the maximum residue limit (MRL). Codex sets MRLs for many veterinary drugs in milk on the advice of the Joint FAO/WHO Expert Committee on Food Additives; for benzylpenicillin, for example, the Codex MRL in milk is 4 µg/kg. National authorities set their own MRLs and withdrawal periods, which may differ.
Withdrawal periods are counted from the last treatment and often expressed in hours or milkings. A cow given its last intramammary treatment at 18:00 on Monday with a 72-hour withdrawal may have its milk used from 18:00 on Thursday. Using a drug in a way not on the label, called off-label or extra-label use, is allowed only under veterinary direction in many jurisdictions and requires a longer, often statutory minimum withdrawal. Dry cow products have special rules for milk after calving.
Residues matter for three reasons. They can harm consumers, for example by causing allergic reactions to penicillin in sensitised people. They inhibit starter cultures, so yoghurt and cheese fail to acidify, causing large losses. And they contribute to the selection of antimicrobial-resistant bacteria. Some hormones raise other issues: bovine somatotropin to boost yield is permitted in some countries and prohibited in others, including the European Union and Canada.
Residues in milk almost always result from human error: treated cows milked into the bulk tank, withdrawal periods not observed, records not kept, drugs used at higher doses or by unlabelled routes, or milk from cows bought already treated. Prevention therefore relies on farm procedures. Treated cows are clearly marked, for example with leg bands or tail tape, recorded in a treatment log with the drug, dose, date and end of withdrawal, and milked last or with separate equipment so their milk does not enter the bulk tank; equipment used for treated cows is cleaned before reuse. Farmers use drugs according to veterinary advice and the label, and store them safely.
Testing provides a second line of defence. Microbial inhibitor tests incubate milk with spores of a sensitive organism, commonly Geobacillus stearothermophilus, and a pH or redox indicator; if antimicrobials are present, the organism does not grow and the colour does not change. These tests detect a broad range of drugs. Rapid receptor and immunoassay tests detect specific groups, such as β-lactams and tetracyclines, within minutes and are used on tankers before unloading. Positive results lead to rejection of the load, tracing to the farm and financial penalties. Confirmatory analysis uses liquid chromatography-tandem mass spectrometry.
National residue monitoring programmes test milk for veterinary drugs, pesticides and contaminants and report results. Reducing the need for treatment through good udder health, vaccination, biosecurity and selective dry cow therapy is the most sustainable way to cut both residues and antimicrobial resistance, in line with One Health action plans.
A student uses this subject to connect milk on the laboratory bench with the animal that produced it. When a sample shows high sodium and low lactose, they recognise mastitis; when fat is low in summer, they think of diet and heat stress. In examinations they answer questions on breeds, udder structure, let-down, milk synthesis and mastitis, and calculate fat-corrected milk, bulk somatic cell counts and withdrawal times. Farm visits during training make these ideas concrete. They also learn the vocabulary needed to talk with farmers and veterinarians, which makes later work in procurement and quality far easier.
A milk procurement or quality officer with five years' experience uses this knowledge to improve the milk supply. They interpret somatic cell and bacterial counts by farm, advise farmers on milking routines, teat dipping and machine checks, investigate residue positives and design residue prevention training, recognise feed-related flavour and composition problems, and explain heat stress effects on supply and composition. They also judge whether a farm's welfare and drug-use practices meet customer requirements. They work with veterinarians and extension staff to run farmer meetings and follow up problem farms until their milk improves.
A senior manager uses the subject at the level of the milk shed and the company. They set payment schemes that reward low cell counts and good composition, decide on investments in farmer services such as veterinary and breeding support, respond to welfare and antimicrobial-use requirements from retailers and regulators, and plan for the effects of climate change and heat stress on milk supply. They speak with authority to farmer bodies, veterinarians and government on milk quality from the cow onwards.
A senior researcher works at the interface of animal science and dairy technology: studying how genetics, nutrition and udder health shape milk composition and processability, using omics to understand milk synthesis, developing sensors and data systems for herd health, and evaluating strategies that reduce antimicrobial use and heat stress. They advise breeding and extension programmes and translate animal science findings into practical milk quality standards. They also train veterinarians and technologists together, so that both professions share an understanding of how animal health reaches the product and the consumer.
This manual covers animal science only to the depth a dairy technologist needs; detailed breeding, nutrition, reproduction and disease management belong to animal science and veterinary courses. Yields, composition figures and thresholds are representative and vary with breed, system and country. Drug withdrawal periods and maximum residue limits must always be taken from the product label and national rules; no doses are given here. Somatic cell limits and welfare requirements differ between jurisdictions.
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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