Non-secretory mammary expiants from virgin goats showed higher RNA and protein synthesis in a low O2 gas phase (air) than in high O2 (95% O2). Lipid and casein synthesis was not affected significantly by the concentration of O2 in the atmosphere during culture. on the other hand, the more developed mammary tissue from primigravid goats showed higher lipid, casein and protein synthesis in 95% O2. The relative response of mammary tissue to hormones was not substantially different when cultured in the presence of a low or high O2 gas phase. As Hepes-buffered medium was found not to need a supply of CO2 to maintain the correct pH and as Hepes did not interfere with biochemical activities of cells, it is recommended to use it for cultures in a low O2 gas phase.

Ca soaps of fatty acids (CSFA, 0·5 kg/d) were added to the diet of lactating cows for 170 d, and production, body condition score and blood lipids were examined.

Production of fat-corrected milk was increased by 1·5 kg/d owing to increase in both milk and fat production. Over 250 d lactation, production of fat-corrected milk was enhanced by 1·3 kg/d. Body condition scores were lower in cows fed CSFA in early lactation, but tended to exceed those of control cows after 80 d lactation. Reproductive performance was improved in cows fed CSFA.

Serum total lipids, phospholipids and cholesterol were increased in CSFA cows at 15 and 29 d but not at 59 d post partum. The cholesterol increase was mainly in the high density lipoprotein fraction.

Eighty-nine autumn-calving first calf and adult Friesian cows participated in an experiment on the effect of feeding over three lactations on milk production and live weight change. Fixed daily allowances of digestible energy (DE) formed two of the treatments (high, H; moderate, M). Diets of similar composition were used for both treatments and rations were weighed daily for each cow. The cows within these treatments were re-randomized to H or M at second and again at third parturition on experiment. A further treatment (ALF), applied continuously over three lactations, consisted of the M allowance of compound feed, weighed daily for each cow, plus ad lib. weighed, group-fed forages. The ALF animals were randomized for each lactation into two groups both of which received the same total compound feed allowance over the first 26 weeks of lactation. For one group (Flat) equal amounts were given daily whilst for the other group (Step) the daily amount was decreased monthly. After week 26 equal rations were fed. Hay, maize silage and grass silage formed the forages in winter. Grass, cut for the H and M groups but grazed for the ALF group, provided the summer forage. Energy intakes covered some 80–110% of requirements (Alderman et al. 1975)

Yields of milk and of milk solids responded similarly for both parities. In the first experimental lactation, treatment H led to greater yields compared with M. H also led to smaller losses of live weight in early lactation, equal gains in mid lactation, and smaller gains in late lactation and the dry period, compared with M. Extension of H into a second lactation increased the advantage in milk and solids yields observed in the first lactation on experiment. Recovery of body reserves on treatment M continued. Treatment H in a second lactation on experiment after M in the first lactation led to even greater compensatory gains in live weight at the expense of milk production. There was no effect in the third lactation on experiment of treatments applied in the first lactation. Treatments H and M applied factorially over lactations 2 and 3 gave the same pattern of treatment effects as in lactations 1 and 2. Treatment ALF broadly supported the same milk yield and live weight change as treatment H but improved fat, protein and lactose yields. Within treatment ALF, Flat and Step distribution of compound led to equal performance. Multiple lactation effects of ALF equalled those of H. The effects on milk composition of H compared with M treatment were variable. In general an advantage accrued to ALF over M but without long term effects.

The effect of variation in intake on performance of the dairy cow has been extensively documented for short periods within lactations (Broster, 1972), and more so for milk production than live weight change. However, the evidence on the size and development of effects of variation in feeding over protracted periods within the adult life span of the dairy cow, e.g. some four lactations in the UK, is extremely limited (Broster & Broster, 1984; Broster et al. 1984), both for plane of nutrition and for diet composition. The problem has added point with the introduction of simplified feeding systems which lead to the provision of less attention to the individual cow than hitherto (Johnson, 1982; Leaver, 1986). This dearth of information on the long term feeding of the adult contrasts with the widely gathered evidence on the effect of feeding during rearing on the performance of the mature cow, which is also an important long term relationship. More multi-lactation research is needed and in the present trial, with both young and adult lactating cows, the effects of amount and composition of feed allowance over three lactations were studied.

In five cows that were regularly milked before parturition, cholesteryl esters were continuously released into the mammary fluid; their concentration in the fluid was initially high, but decreased a few days before parturition when mammary secretion of fluid and triglyceride was increasing. The composition of fatty acids in the cholesteryl esters of mammary fluid and in blood plasma was different, suggesting mammary synthesis of cholesteryl esters.

The degradation of bovine β-casein by plasmin was used as a model system to investigate the applicability of an enzyme recycle reactor for the continuous production and isolation of peptide fractions. A simple, ultrafiltration-type membrane reactor was used incorporating a commercially available hollow-fiber module normally employed for dialysis purposes (artificial kidney). The results were compared with those obtained in a batch reactor process, using HPLC to monitor the course of proteolysis.

Peptide fragments were isolated and were characterized using amino-acid analysis and N-terminal end-group determination. Sixteen peptide fragments were identified, which together accounted for virtually all the potential cleavage sites in β-casein. In the system studied the N-terminal half of β-casein appeared to be more sensitive to plasmic hydrolysis than the rest of the molecule.

Lactating goats were milked incompletely in one gland and normally in the other gland twice daily for 24 weeks. Yields of the incompletely milked glands were adjusted so that a calculated 100 ml milk remained in the gland at the end of milking. On average this residual volume was greater by 7·6% of the total milk volume than that left after normal milking and was 25·9% greater than the capacity of the alveoli. After 24 weeks, the weekly milk yield of the incompletely milked gland was 23·8% lower than that of the other gland (P < 0·001) when expressed in relation to cell number. The metabolic capacity of secretory cells in the two glands was measured in serial tissue biopsies. Two weeks of incomplete milking had no effect on enzyme activities or metabolic fluxes in the incompletely milked gland, but after 24 weeks the activities of several key enzymes were significantly lower in this gland. This was associated with a reduced rate of synthesis of total protein and casein in expiants freshly prepared from the tissue. The rate of lactose synthesis also tended to be lower in expiants from the incompletely milked gland. Secretory cell number in the two glands was similar at the end of incomplete milking. The data indicate that incomplete milking over a long period caused partial secretory cellular involution via a local chemical feedback mechanism in the gland.

An automatic device, which infuses disinfectant into the mouthpiece of the liner of the milking machine cluster as teatcups are removed, is described. Application at this time avoids any delay in disinfection, reduces the workload in the parlour and increases reliability of application. The teats of 20 cows were contaminated before each milking by immersion in a suspension of Staphylococcus aureus and Streptococcus agalactiae and then disinfected manually or automatically with iodophor after milking. Str. agalactiae was recovered from < 5% of swabs and there was no difference between the results from the two methods. Neither method of disinfection was as effective against Staph. aureus and the recovery rate was significantly greater for the automatic method for both swabs from teat barrel (P < 0·05) and teat apex (P < 0·001). Rates of intramammary infection for quarters automatically or manually disinfected were similar and low (3/40 v. 6/40 respectively). The automatic method facilitates cluster removal by relieving vacuum and decreasing frictional contact at the mouthpiece lip, and utilizes approximately half the quantity of disinfectant used by manual dipping (0·9 v. 1·9 ml/teat). However, iodine contamination in the milk from the iodophor teat disinfectant was significantly increased from 14·4 to 102·2 μg I2/100 ml milk when no backflushing was practised.

With two groups of 12 cows, a procedure involving foremilking, teat washing and drying before milking was compared with no premilking preparation for its effects on mastitis and teat contamination. Half the cows in each group were deliberately infected in a single udder quarter with Staphylococcus aureus and milked alternately with uninfected cows for 9 weeks. To minimize transfer during milking all cows were milked with the use of a multi-valved claw.

Five new staphylococcal infections developed in the 12 animals in the teat preparation group compared to one in the control group. A significantly higher incidence of teat orifice colonization developed in the prepared cows compared to the control cows (17 v. 7). Foremilking and teat preparation led to transfer of staphylococci between quarters (within cow) but this was effectively prevented by the multi-valve claw in the absence of teat preparation.

Six lactating, non-pregnant Jersey cows were given subcutaneous injections of recombinantly derived bovine growth hormone for 7 d. Milk yield was increased by 4·5 kg/d on d 7, compared with the average yield of 10·7 ± 0·4 kg/d (mean ± s. e. m.) for the 7d preceding treatment. Concentrations of insulin-like growth factor I (IGF-I) in the milk increased from 0·44 ± 0·04 nmol/1 (mean ± s. e. m.) during the 7 d preceding treatment to 1·6 ± 0·2 nmol/1 on d 7 of treatment. Taking the increase in milk yield into account the total increase in the secretion of IGF-I into milk of one udder half was 6-fold. Plasma concentrations of total IGF-I rose from 15·5 + 1·3 nmol/1 (mean ± s. e. m.) on the day preceding treatment to 56·9 ± 3·6 nmol/1 (mean ± s. e. m.) on d 7 of treatment. Mammary plasma flow increased from 1·6 ± 0·09 to 2·2 ± 0·06 1/min udder half over the same time. Estimates of the amount of IGF-I that reached the mammary gland gave values of 24 and 116 nmol/min udder half before and during treatment respectively. IGF-I in milk of treated cows was associated predominantly with proteins ranging from 40000 to 150000 mol. wt, but a significant proportion (19%) of the total IGF-I was present in the free unbound form. IGF-I crosslinking studies revealed the presence in milk of one specifically labelled band at 31000 mol. wt.

Experiments were designed to study the effects of catecholamines on oxytocin responses and milk removal in dairy cows. Adrenalin, noradrenalin, dopamine, isoproterenol (a β-adrenoceptor agonist), phentolamine (an α-adrenergic blocker) and propranolol (a β-adrenergic blocker) were infused intravenously. In addition, adrenalin was infused together with phentolamine and/or propranolol. Infusions started 8 min before milking and lasted until the end of milking. In some cases electroshocks (for 5 s) were applied immediately before milking in the absence and presence of phentolamine and propranolol. Adrenalin, noradrenalin and dopamine reduced milk removal, but only if administered in supraphysiological amounts. The effect of adrenalin and electroshocks on milk removal could be inhibited by α-, but not by β-adrenergic blockade. The effect of dopamine could be inhibited only partly by phentolamine. Inhibition of milk removal was not mediated by reduced oxytocin responses. Enhanced local release of catecholamines from sympathetic nerves was presumably responsible for lowered milk removal in response to electroshocks. Milk removal was facilitated during α-adrenergic blockade and during β-adrenoceptor stimulation.

A cows' milk identification test (COMIT) has been successfully developed for the detection of defined amounts of cows' milk (3–100%) in ewes' milk. The assay uses polyclonal antibodies raised in goats against bovine whey proteins. The test, an agar-gel immunodiffusion technique, uses agar plates with a printed template for correct placement of the test components (antisera discs, positive and negative milk reference discs and sample discs). The presence of cows' milk in the sample was recorded as positive when the precipitin lines appearing between the sample disc and the antisera disc fuse completely with those from the positive cows' milk reference disc. This test is reliable, practical and easy to perform in the field and in dairy factories. Furthermore, the nature and stability of the components of the test make it suitable for commercial development into kits which should be highly practical in any kind of inspection programme concerned with milk species identification.

When six cows were milked every 4 h over 48 h the average milk yield per cow increased by 1O·7% for the last 24 h period compared with the previous 5 d. Milk composition was similar to pre-experimental values although fat content was 0·5% lower in the last 24 h. The somatic cell count rose to twice the pre-experimental value over the first 24 h but was not significantly different by the second 24 h. It appears that cows responded quickly to an increased frequency of milking and milk of an acceptable composition was produced. This has implications for management of milk production where quotas are in operation and for robotic milking systems.

Casein phosphopeptides (GPP) were produced by tryptic hydrolysis of sodium caseinate and further purified by precipitation and chromatography on QAE-Sephadex A-25. Their physico-chemical properties were compared with the properties of an enzymically dephosphorylated equivalent preparation (DPP). Binding of Ca2+ to the peptides was measured using a Ca selective electrode and was found to increase with pH and to show 1/1 stoicheiometry Ca/Porg in CPP at pH 6·5 a.nd 7·6. Klotz plots indicated equivalent binding sites at these two pH values, but some heterogeneity was seen at pH 3·5. In contrast, DPP did not bind significant amounts of Ca2+.

CPP effectively inhibited the formation of insoluble calcium phosphates at different Ca/P ratios. The effective CPP concentration was 10 mg/1 and complete stability of calcium phosphate solutions was obtained at about 100 mg/1. This stabilizing effect was dependent on the presence of organic P.

Effects of agitation, temperature change, blood serum and heparin on lipolysis and on distribution of lipoprotein lipase (LPL) in cold-stored cows' milk were measured. All individual milks (n = 135) were susceptible to activation treatments. With ‘gentle’ treatments, induced lipolysis was strongly correlated to spontaneous lipolysis (r ≥ 0·74). In contrast, induced lipolysis in response to ‘vigorous’ treatments was more variable (0·7 > r > 0·34) and levelled off in milks with high spontaneous lipolysis. Induced lipolysis always resulted from an increase in LPL associated with cream. Strong correlations (0·79 ≤ r ≤ 0middot;94) were found between free fatty acid levels and cream LPL. All treatments (except heparin addition) also promoted lipolysis/unit cream LPL.

Cows were fed on diets supplemented with soyabean oil or soyabean fatty acids which in some cases were protected from rumen hydrogenation. The fat-containing diets reduced the output of short- and medium-chain fatty acids in milk. Associated with this fall in short- and medium-chain fatty acids was a decrease in the concentration of 2-oxoglutarate and an increase in that of isocitrate and citrate. Protection of polyunsaturated fat from rumen hydrogenation had no significant effect. Milk yields were unaffected by diet, but the variation in milk yield among cows correlated positively with the concentration of glucose in milk.

The in vivo formation of biologically active caseinopeptides was studied. It was proved that bioactive peptides were released in the small intestine of minipigs in the course of luminal digestion of diets containing bovine casein. An opioid peptide and a phosphopeptide were isolated from jejunal chyme and were chemically characterized. The opioid peptide has been identified as a fragment of β-casein (60–70). This peptide, named β-casomorphin-ll, displayed substantial opioid activity in an opiate receptor-binding assay. The caseinophosphopeptide has been shown to be a fragment of αs1-casein (66–74). Casein-derived phosphopeptides exhibit a potent ability to form soluble complexes with Ca and trace elements. Evidence exists that casomorphins and caseinophosphopeptides participate in the regulation of nutrient entry.

Heat stability of secreted bacterial proteinase is normally assessed using an oil bath test in which the sample is heated at a temperature and time representing the commercial UHT treatment of milk. The temperature/time (T/t) profiles of the oil bath and the commercial UHT process being represented are not taken into account. Two laboratory procedures were used to simulate a commercial UHT process in which milk was heated to 140°C and held for 3 s in a Spiroflo heat exchanger. They consisted of a conventional oil bath test and the use of a programmable, electronically temperature-controlled oven. T/t profiles were established for each heat treatment. The T/t profile of the oil bath test was predicted accurately using the governing heat transfer equation. B* and C* values, which measure the severity of a heat process, were calculated from the T/t profiles and used to compare the three different heat treatments. B* and C* values of 4·95 and 1·92 respectively were calculated for the Spiroflo heat exchanger. An oil bath test, in which the sample was immersed in a bath at 136°C for 73 s, gave approximately the same B* and C* values as calculated for the Spiroflo heat exchanger. B* and C* values of 5·01 and 1·73 respectively were calculated for the oven procedure. The oven test gave the better laboratory simulation of the Spiroflo UHT treatment. Despite the slight difference in each of the B* and C* values between the oven and the Spiroflo, the T/t profile of the oven test closely resembled that of the Spiroflo. The T/t profile of the oil bath was completely dissimilar. Although it was possible to use an oil bath test to replicate simultaneously both the B* and C* values of this particular UHT treatment, this would not be the case for other commercial processes.

Pituitary-derived bovine growth hormone (bGH) was administered to Jersey cows during late lactation for 7 d. Milk yield increased significantly during treatment and by a maximum of 49·6% on d 7. The magnitude of the increase was similar to that of mammary plasma flow (47·8±18·3%) over the same period. By 15–21 d after treatment, both variables had returned to pretreatment values. With respect to milk composition, bGH had negligible effect on lactose and fat concentrations but there were significant decreases in protein, sodium and chloride. Arterial plasma concentrations of bGH increased substantially during treatment, but the associated rise in insulin was not statistically significant. Haematocrit decreased significantly, the lowest value being recorded 3 d after bGH treatment ceased. Mammary respiratory quotient fell progressively after the start of bGH treatment and reached the lowest recorded value 3 d after treatment ceased (62·2 ± 7·3% of pretreatment value). Glucose and acetate uptake by the mammary gland increased significantly during treatment, increase in glucose uptake being due both to a greater arterio-venous difference and to mammary plasma flow. There was strong evidence that the acute response in increased milk yield was associated with multiple effects in terms of mammary plasma flow and metabolism, as well as haematocrit changes indicative of increased plasma volume.