Over 3 years, 4 groups of heifers and 6 groups of cows calving in the autumn were used in a study of electronically controlled compound feed dispensers. For each group the treatments consisted of access or no access to the dispensers (selector feeders) arranged factorially with 2 levels of compound feed in the milking parlour. These were applied in weeks 3–15 of lactation. A basal diet including high quality silage was fed ad lib. communally to each group. The mean intake of compound from the dispensers was 5·6 kg/d, but there was considerable variation from animal to animal. The dispensers were visited at all times of the day and notably during the night. There was no bullying around the feeders. Milk yield was greater with the higher level of parlour feeding, and with access to the feed dispenser at the lower, but not the higher level of parlour feeding. Liveweight change benefited from additional compound feed supplied by either method.

Salivary and pancreatic lipases of the pre-ruminant calf have been studied using ion-exchange chromatography and gel filtration. In addition, pancreatic lipase has been fractionated using concanavalin A-affinity chromatography. The effects of 5,5′-dithiobis(2-nitrobenzoic acid), organic solvents and trypsin on pancreatic lipase have also been investigated. The effect of taurodeoxycholate on the lipolytic activity of the 2 lipases has been compared. Salivary lipase behaved as a single enzyme on ion-exchange chromatography, and gel filtration gave a mol. wt value of 52000 for the enzyme. Although pancreatic lipase appeared to be a single enzyme on gel filtration, with a mol. wt of almost 80000, the lipase was shown by ion-exchange and affinity chromatography to consist of at least 2 enzymes of mol. wts 72000 and 60000, and did not require colipase for maximum activity in the presence of high concentrations of bile salts. Colipase-dependent lipase, mol. wt about 45000, and probably amounting to not more than 10% of the total activity, was also present. This was the predominant form only after large losses in total lipolytic activity had occurred, as after treatment with a mixture of ether, ethanol and deoxycholate, or prolonged action of trypsin. When the concentration of taurodeoxycholate was increased from zero to 1 mM in a tributyrin substrate, the lipolytic activites of calf salivary and pancreatic lipases, and pig pancreatic lipase, increased. At a concentration of 4 mM-taurodeoxycholate, calf salivary lipase activity was higher, that of calf pancreatic lipase slightly lower and pig pancreatic lipase activity markedly lower.

Bulk milk with an apparently high electronic cell count (ECC) was found to have a normal cell count when the latter was determined directly with a microscope or when cell nuclei were counted with a Fossomatic apparatus. Particles in the form of collapsed spheres formed by aggregated casein micelles were found in bulk milk which accounted for the falsely high ECC values. The ECC value agreed with the values obtained by the other methods if the milk was heated to 55 °C for 15 min before fixation. The shape of the particles and the fact that they were only present after the milk had passed through the milking machine suggested that they may be produced as vacuum vacuoles arising from cavitation in the pump.

Freeze fractures of the tight junctions at the apices of sheep mammary secretory cells showed that the junction at 72 d of pregnancy was significantly wider than at any later stage. The number of ridges in the junction only increased significantly between 122 and 142 d of pregnancy. The initially even distribution of intramembrane particles across the tight junction changed gradually until in the fully lactating animal there were far more particles on the lateral surface of the plasmalemma. Possible correlations between these changes, the alterations in permeability of the mammary epithelium, and the differences in hormone levels are briefly discussed.

The relationship between nutrition, fertility and blood composition was studied in 400 cows from commercial farms. Fertility evaluated by overall conception rate (OCR) was shown to be significantly related to the relative proportion of concentrate and roughage feeds in the diet, and to its content of dry matter, digestible protein, Ca and P. The ratio of serum total lipids to glucose and a newly introduced parameter, ΔPi (a calculated value, obtained by subtracting whole blood levels of Pi from those of the blood serum), showed a highly significant relationship to OCR. No significant relationship was found between OCR and serum, total lipids, cholesterol, urea, Ca, Mg, organic and inorganic phosphate. The values and significance of the 2 blood parameters which showed a relationship to fertility are discussed.

A series of short duration experiments show that the way in which the milking machine cluster is removed from the udder influences the rate at which new udder infections occur when bacterial exposure is high at the end of milking. Shields fitted in the base of the liners controlled most of the infections caused by abrupt removal of the cluster.

Bulk milk cell counts obtained by a Coulter Milk Cell Counter were shown to be falsely elevated because of the formation of non-cellular particles (NCP). The NCP, which were detected by the use of a particle size analyser, were removed if the milk samples were heated to 55 °C for 15 min before the addition of formalin. A survey of bulk milk supplies in New South Wales showed that NCP occurred in milk from 2 % of farms, the counts being falsely elevated by about 200000 cells/ml. Surveys of milking equipment of farms where the bulk milk had shown this phenomenon demonstrated a relationship between the use of centrifugal milk pumps and the presence of NCP with a much lower prevalence in herds where spit chamber releasers were used. These particles were not air bubbles since air was removed from the milk by heating to 60 °C for 5 min, vacuum at 65 mmHg for 15 minor 0·5% v/voctan-2-ol; only the heat treatment removed the NCP.

The concentrations of diffusible Ca and Mg in milk diffusates from 3 goats were determined before, during and after a 2-d period of starvation. Free Ca-concentrations were determined by a murexide method and compared with values calculated from a detailed model of the ion equilibria. It was shown that diffusible Ca increased as citrate increased during fasting and both decreased after refeeding, but there was a difference of about half a day in the response curves, with citrate following Ca. The difference was accounted for mainly by a change in free Ca2+ concentration which in turn was related mainly to changes in milk pH. Diffusible Mg underwent changes similar to those of diffusible Ca.

During an outbreak of mastitis due to Streptococcus uberis the organism was frequently isolated from samples of straw bedding used by the cattle. More than one million Str. uberis/g straw were isolated from 36% of samples. The organism was also recovered from 34% of samples of bovine faeces, but usually in low numbers. An examination of straw samples collected from cattle yards on 32 other dairy farms demonstrated that this was not an isolated occurrence since Str. uberis was found in 24% of samples from 56% of the herds. No correlation was found between counts of Str. uberis and coliforms. The significance of these observations is discussed.

Mice were fasted during pregnancy or early lactation and the effects on mammary development and milk yield studied on d 13 and d 18 of pregnancy and on d 7 of lactation. Fasting during pregnancy reduced body weight and mammary weight on d 13 of pregnancy but not on d 18. Mammary concentrations and total contents of DNA and RNA ([DNA], [RNA], DNAt, RNAt) were increased or unchanged on d 13 but significantly decreased on d 18. Fasting had no effect on fetal number or weight at either stage of pregnancy. Fasting on d 1 of lactation reduced mammary weight, DNAt and RNAt (but not [DNA] or [RNA]) and the incorporation of tritiated thymidine into DNA on d 2 of lactation. Mammary gland weight and composition on d 7 of lactation were not significantly affected by fasting for 24 h on d 1 of lactation or for 40 h on d 11–13 of pregnancy, except that DNAt was decreased slightly by the latter treatment.

Milk yield (litter weight gain) was depressed markedly during fasting on d 1 of lactation, but thereafter recovered so that it was the same as controls between d 3 and 13 of lactation; after d 13 it fell once more. A 40 h fast on d 11–13 of pregnancy had no effect on milk yield. Thus, although normal mammary development was inhibited by starvation, the gland was subsequently able to compensate so that milk yield was not reduced.

The manufacture of skim-milk powder with heat stable characteristics was investigated commercially during the course of 8 trials carried out over a 12-month period. Skim-milk was preheated to temperatures ranging from 110 to 130 °C with a 2-min holding time prior to evaporation and drying. The effect of added urea was also examined during each trial run. Heat coagulation times at 120 °C were determined upon reconstitution of the powders to 20% total solids. From February to April the heat stability of the skim-milk powders increased, with the more heat stable samples being obtained at the higher preheating temperatures. Addition of urea increased the heat stability, particularly so in those milks which had been preheated to 130 °C. The presence of added urea during preheating was not found to be necessary as an equal effect on heat stability was observed when urea was introduced at the concentrate stage before drying. Later in the season optimum heat coagulation times were obtained by maintaining preheating temperatures at 118–120 °C.

Eight cows in mid lactation and receiving a diet of perennial ryegrass silage and barley (70:30 on a DM basis) were given intravenous supplements of l-methionine (8 g/d). The methionine treatment had no significant effect on milk yield, protein content or lactose content, but increased milk fat content and yield by approximately 10% (P < 0·05).

Proteolysis was measured quantitatively in normal bulk milk, either raw, pasteurized or heated (95 °C, 15 min). During incubation at 37 °C for 24 h, about 0·7 mM of peptide bonds were split in raw milk, and 1·8 mM after activation of the zymogen with urokinase. The same values were observed in pasteurized milk, and no significant activity was present in heated milk. When compared with a commercial plasmin preparation, these levels correspond to about 1·4 and 3·6μg/ml of plasmin respectively. Most of this activity was separated in the micellar fraction, and it was suppressed by addition of soyabean trypsin inhibitor (SBTI). The remaining activity in the serum phase was not inhibited by SBTI and gave a rather non-specific breakdown with few well-defined casein fragments being produced. Upon further incubation, after the first 24 h, the activity increased, indicating that activation of the zymogen (plasminogen) occurred spontaneously. The rate of this activation was independent of the addition of more plasminogen and was higher in pasteurized than in raw milk. In pasteurized milk, all the native milk proteinase was in the form of the zymogen at the time of secretion. β-Casein was the preferred substrate for the milk proteinase (plasmin) and produced γ-caseins and proteose-peptone components 5 and 8-fast; other fragments were clearly visible on polyacrylamide gel electrophoresis, and included degradation products of αs1-casein. The formation of all these fragments was enhanced by addition of urokinase alone, or of plasminogen and urokinase, or by increasing the incubation time. They were also produced by incubating the micellar fraction alone, but not the serum fraction. Additional fragments were produced when porcine plasmin was added presumably due to differences in specificity between the porcine and bovine enzymes or to contaminating enzymes. Proteolysis induced by additions of plasminogen alone, or of plasminogen plus urokinase, was closer to that observed for the native milk proteinase, and must be recommended for future work in which it is desired to enhance the level of proteinase without altering breakdown patterns, unless a very pure bovine plasmin is available.

Swabs taken from the rectum and vulva of 14 dairy cows on 7 occasions at approximately weekly intervals revealed a pattern of isolations of Streptococcus uberis which were not random. Two of the 14 cows were responsible for 80 and 40% respectively of the swabs of the rectum and vulva which were found to be positive. It is suggested that these patterns are consistent with these 2 cows being intestinally colonized with Str. uberis. The implications of this work are discussed with reference to the sources of Str. uberis in the dairy herd.

Urea stabilizes milk to heat only in the presence of a carbonyl compound, such as a reducing sugar. Low molecular weight carbonyl compounds can increase stability in the absence of urea whereas larger molecules, e.g. hexoses and reducing disaccharides, cannot. However, the efficacy of all carbonyl compounds is increased considerably in the presence of urea. Aldehydes and ketones of similar molecular weights appear to be equally effective stabilizers. The optimum concentration of lactose in milk for stability was approximately 1% irrespective of urea concentration within the range 5–20 mM. However, modifying the lactose content of concentrated milks (approximately 8.5% protein) had little effect on heat stability.

Experiments involving the depletion of milk calcium phosphate (MCP) with EDTA have shown that it has a Ca to phosphate ratio of 1·61±0·04, close to that of dental enamel. The calcium phosphate also contains small amounts of citrate (citrate/Pi = 0·097±0·011) and Mg (Mg/Pi = 0·044 ± 0·011). These experiments and model calculations indicate that the Ca binding capacity of casein is not reduced by mineralization with calcium phosphate and hence that ion binding sites and nucleation sites are distinct, or nearly so. Calculations of the ionic equilibria in the aqueous phase of milk show that there is an invariant ion activity product for a molecular formula close to that of dicalcium phosphate. It is suggested that MCP is a mixture of salts, with dicalcium phosphate a precursor of more basic salts such as octacalcium phosphate and hydroxyapatite.

Implantation of 1 μg Escherichia coli endotoxin into one papillary duct of a bovine udder frequently resulted in a mild inflammatory process in the treated quarter which was measured by use of the Wisconsin mastitis test (WMT) on quarter fore milk samples. Inflammation of a fore quarter was usually (18/24) accompanied by a transient elevation in WMT score from the homolateral hind quarter, but rarely (1/25) from the contralateral quarter. Inflammation in a hind quarter rarely (2/26) affected the homolateral fore quarter and never (0/25) the contralateral quarter. The pattern of responses suggests that absorption and initial removal of endotoxin from the mammary gland occurs via the lymphatic rather than the blood system.

The effects of feeding lipids protected against microbial degradation in the rumen, on the metabolism of β-carotene and cholesterol in the blood and milk of cows were studied. The diets fed to the cows consisted of a basal mixture of crushed oats and lucerne hay with a protected vitamin supplement containing α-tocopheryl acetate and β-carotene fed in conjunction with either (i) protected sunflower oil-seed rich in linoleic acid (PO), (ii) protected tallow (PT), or (iii) formaldehyde-treated casein (C) as a control. Diets PO and PT raised the concentrations of β-carotene and cholesterol in the blood plasma over that observed for diet C. Milk cholesterol concentrations were not affected by dietary supplements, but the level of β-carotene in milk of cows on diet PO showed a tendency to fall compared with milk from cows fed PT or C. The properties of the high density lipoprotein (HDLP) of the blood plasma which contained the β-carotene were affected by the PO diet. As a result of feeding this diet, the fatty-acid composition of the HDLP was altered and it emerged from a gel-filtration chromatographic column earlier than the control. This change in chromatographic behaviour was used as a measure of the effect of the diet, which, for some cows, was apparent long after the diet was changed. It is suggested that the altered lipid composition resulting from the PO diet affected the distribution of particle sizes of the HDLP and might interfere with the transfer of β-carotene from plasma to milk.

Optimum conditions have been determined for the use of Hide Powder Azure (HPA) to estimate extracellular proteinases produced by psychrotrophic Gram-negative bacteria. This assay is quicker, more precise and 3·2 times more sensitive than assays of soluble N released from casein. It provides a simple alternative method for monitoring proteinase purification schemes. With the modification described it is now possible to determine proteinase activities directly in milk. In its simplest form the HPA assay is sufficiently sensitive to detect proteinases produced by as few as 1·5 x 106 c.f.u. ml-1 psychrobtrophs without the necessity for any sample processing.

Proteolytic activity in mastitic skim-milk was often 5–10 fold higher than in normal milk, its level being related to somatic cell count but not precisely correlated with it. In milks with the highest levels of activity plasmin accounted for about one third of the total proteinase. A further third was sedimented with the micellar fraction together with the plasmin, but unlike plasmin, was not inhibited by addition of soyabean trypsin inhibitor (SBTI). The final third remained in the serum phase.

Polyacrylamide gel electrophoresis (PAGE) showed that αsl- and β-caseins were degraded at about the same overall rate. The plasmin produced the usual readily identified fragments from β-casein, but incubation of mastitic milk also produced changes in patterns in the γ-casein region differing from plasmin-induced changes which were also apparent when the micellar fraction was incubated. As they were inhibited by SBTI, a second trypsin-like enzyme in addition to plasmin may also have been present. Other proteinase(s) not inhibited by SBTI was also associated with casein micelles and produced at least 3 characteristic protein fragments seen on PAGE. The serum phase proteinase(s) was likewise not inhibited by SBTI, and did not produce any well-defined electrophoretic bands, suggesting a rather non-specific breakdown of caseins. After separation of mastitic whole milk, a considerable proportion of the proteolytic activity was found in the cream phase. The proportion was enhanced by freezing and thawing, and the enzyme appeared to be identical to the SBTI-resistant micellar proteinase.

Because of the considerable proteolysis likely to occur under the time and temperature conditions involved, our results may provide some explanation for the problems encountered in cheesemaking with mastitic milks (e.g. yield losses, poor curd strength and off-flavour development).