Ten-day periods of water restriction followed by 2 h ad lib. water caused radical changes in camel milk. The changes were different from those reported in other mammals. At the end of each dehydration period there were increased water percentages in the milk when compared with milk of hydrated camels. The content of fat, lactose and protein declined. Concentrations of Na, K, phosphate and chloride in milk increased while Ca and Mg concentration declined. The urea concentration of the milk was unchanged. The young suckling calves showed no signs of stress during the dehydration periods. It was concluded that the milk of dehydrated camels is an excellent human food in arid areas, as the water and salt content are high while the nutritive value remains good.

Deflector shields were inserted in the teatcup to prevent ‘impacts’ against the teat end, and their effect on the rate of new udder infections was studied on 15 commercial dairy farms in Britain and 16 in Australia. Small metal shields were fitted between the liner barrel and short milk tube of 2 teatcups in each cluster in a milking installation so that all cows in a herd always had the same 2 quarters shielded. Half-udder comparisons were made using 1039 cows in the British herds and 1268 in the Australian herds. Herds were quarter-sampled for cytological and bacteriological examination when shields were fitted at the start of the experiment and again after 6 months. The shield effects were similar in the 2 experiments. The combined results from the 31 farms showed that 10·5% fewer quarters became infected when protected by shields (P < 0·05). In the 1287 cows that had no infected quarters at the start of the trial, 15% fewer quarters became infected when protected by shields (P < 0·01). The shield effect was mainly confined to hind quarters in which 23% fewer shielded quarters became infected (P < 0·001). The small reduction of 2% in forequarters was not significant. In the 16 herds in which post-milking disinfection of teats was practised, shielded quarters had 23·5% fewer new infections than unshielded quarters (P < 0·01). In 6 British herds milked in installations classed as non-standard, shielded quarters had almost 50% fewer new infections than the unshielded quarters (0·05 < P < 0·10). The results provide evidence of a milking machine effect, at varying levels of intensity, to increase new infection rates on all or most farms. Control of this machine effect could lead to substantial reduction in new infections in some herds and a modest reduction in most.

A pre-milking wash disinfectant procedure employing a 2% (w/v) chlorhexidine solution in a detergent base did not reduce the rate of new intramammary infection in a lactating herd challenged with Staphylococcus aureus. Teat-end swabs showed no significant difference in the number of Staph aureus isolated from the teat-ends pre-washed with either water, or water and chlorhexidine. In contrast, disinfecting teats after milking with a solution containing 5000 mg available iodine/1 significantly reduced the staphylococcal population of the teat-ends and the rate of new intramammary infection, compared with teats not disinfected.

Rhythmic motility of teats in lactating cows in vivo was studied by an improved plethysmographic technique. Oxytocin was infused intravenously and drugs were injected into the artery of the filled udder. The β-adrenergic agent, isoprenaline, induced relaxation of the teats whereas the α-adrenergic agents phenylephrine and noradrenaline, elicited contraction. In one animal however, noradrenaline always exerted a biphasic effect. Pre-treatment with propranolol, a β-adrenergic blocking agent, changed the biphasic effect into a purely activating response. Adrenaline, which exhibits both a and β effects, induced relaxation, but after propranolol treatment relaxation was abolished and even converted into contraction of the teat. It seems clear that both α and β adrenoceptors are present in longitudinal smooth muscles of the teats.

Milk losses as intermittent spurts were observed in several cows. Spurts occurred synchronously with rhythmical teat motility in the filled udder during oxytocin infusion. The intensity of milk leakage was increased by isoprenaline and inhibited by noradrenaline, indicating the presence of α and β receptors in teat sphincter muscles. Starting and stopping of milk spurts in correlation with rhythmical teat contractions were studied by audiovisual synchronization of video recording tape. The most common type of spurt began near the middle of the teat's relaxation phase and ended either just before or exactly at the beginning of the contraction phase. Interruption of the spurt is primarily due to closure of the streak canal.

Electronic somatic cell counts (ESCC) and relative cell volume distributions (RCVD) in milk samples were obtained simultaneously on a Coulter Counter Model TA and their potential assessed, either singly or in combination, for identifying mastitic quarters and cows in 2 herds. Using log (ESCC) alone the probability Pm of misclassifying quarters infected with major pathogens was 6–7 % for herd 1 and 18–1% for herd 2. The inclusion of RCVD variables with log (ESCC) did not substantially improve the chance of detecting quarters infected with major pathogens. However, the RCVD variables did improve the chance of identifying quarters infected by major and minor pathogens compared to the use of log (ESCC) alone, the Pm figures being reduced by about one third.

When testing composite quarter samples, where milk from infected quarters was diluted with that from uninfected quarters, the inclusion of RCVD variables decreased the Pm compared to the use of log (ESCC) alone. In herd 1 the improvement was from 26–1 to 3·0 %, while in herd 2 the effect was less marked, the Pm being reduced from 28–6 to 21–6%. However, as the RCVD assessment is provided simultaneously with ESCC, the additional information is obtained at minimal cost.

The teats of 18 cows were externally exposed to infection with mastitis organisms by dipping them daily for 1 or 2 weeks in a mixed suspension of Streptococcus dysgalactiae and Str. uberis at the start, the middle or the end of the dry period. The teat sinuses of quarters which remained uninfected after external exposure at the beginning or the middle of the dry period were then infused with the same strains of streptococci. Of the 9 quarters infected following external exposure 8 occurred in animals exposed at the start and one in the middle of the dry period. Thirty-six new infections occurred after infusion of bacteria into the teat sinuses of 38 quarters. In a further trial with 10 cows, Staphylococcus aureus and Str. zooepidemicus were inoculated into the distal 3 mm of the streak canals of 5 cows immediately after drying-off and into those of 5 cows which had been dry for 28 weeks. Animals were slaughtered 48 h later and infection determined by teat puncture. Five infections occurred in cows which were at the start of the dry period and only one in the cows dry for 28 weeks. It is suggested that these differences in the rates of new infection between the early dry period and a very extended dry period are due to differences in the ease with which bacteria can penetrate the teat canal. At the later stage bacterial growth through the teat canal appeared to be inhibited.

An iodine teat skin disinfectant tested in lactating cows over a range of concentrations, 100 to 10 000 mg available iodine/1 (mg avI/l) was found bactericidally effective against Staphylococcus aureus when containing 1000 mg avI/l or greater. Against Streptococcus dysgalactiae 5000 mg avI/l or greater was bactericidally effective.

The addition of glycerine to a disinfectant containing 5000 or 1000 mg avI/l at levels of 225 ml/1 and 105 ml/1, respectively, resulted in a reduction in bactericidal efficacy of the disinfectant. Emulsified paraffin added at concentrations of between 50 and 500 ml/1 had no effect on the efficacy of the 5000 mg avI/l disinfectant, but the addition of 200 ml/1 emulsified paraffin to a 1000 mg avI/l disinfectant significantly reduced its efficiency. Iodine disinfectants containing emulsified paraffin phase separated rapidly during storage, and the bactericidal efficacy of the phases differed significantly and diminished with time.

135 Cows which were expected to produce a second or subsequent calf within 4–11 d received an intramuscular injection of 500 μg lα-hydroxycholecalciferol (lα-OHD3). In those animals in which the interval between injection and calving was at least 7 d there was, at 7 d after injection of lα-OHD3, a significant increase (P < 0.001) in the blood plasma concentrations of Ca and Pi and a significant reduction (P < 0.05) in that of Mg, compared with those in control animals. Within 24 h of calving there was a significant increase (P < 0.001) in the concentration of Pi but no change in Ca or Mg compared with pre-injection levels, whilst the control animals showed a significant fall (P < 0.001) in the concentration of Ca and a rise in those of Pi (P < 0.001) and Mg (P < 0.05). There was a significant reduction (P < 0.001) in the number of animals with hypocalcaemia (defined as a plasma Ca concentration <1.9 mmol/1) in all animals injected with lα-OHD3; this reduction was particularly marked when the interval between injection and calving was between 1 and 8 d. The previously reported reduction in the incidence of clinical milk fever is considered to be a consequence of the effect of lα-OHD3 on the concentration of Ca in plasma.

The effects of supplementing a basal diet of grass silage with various oil-enriched mixtures on milk yield and composition, fatty acid composition and the melting characteristics of the milk fats are reported. In the first experiment, various dietary fats (soya oil, tallow and a palm oil/palmitic acid mixture) were fed at a fixed level (10% by weight of the concentrate ration). Soya oil had no effect on the proportion or yield of milk fat, and increased the proportion of low melting material in the milk fat; tallow increased the proportion of milk fat, and had little effect on the melting characteristics of the milk fat; the palm oil/palmitic acid mixture increased both the content and the yield of milk fat, and increased the proportion of high-melting material in the milk fat. In the second experiment, soya oil was fed at 3 levels (10, 15 and 20% by weight of the concentrate ration). No statistically significant effect on the yield of milk or of its constituents was observed; the proportion of low-melting material in the milk fat increased progressively with increasing intake of soya oil.

Use of an iodine teat dip containing 5000 mg available iodine/l (mg avI/l) resulted in a significant reduction in the number of new Staphylococcus aureus infections in a lactating herd, while no significant reduction was found with a disinfectant containing only 1000 mg avI/l. When Streptococcus dysgalactiae was used as the challenge organism, the rate of new infection was extremely low, and no reduction in levels of new infection were found with either disinfectant. The pathogenicity of the Str. dysgalactiae strain was high, as 60 % of the quarters becoming infected produced clinical symptoms.

Feeding lactating cows at a reduced level for a 6-d-period caused blood serum and milk free fatty acids (FFA) to rise. Milk lipolysis developed more slowly and lasted longer than elevation of the level of FFA in blood. In a second experiment protected rape seed oil was given to underfed animals and inhibited the development of rancidity in the milk. Since unsaturated fat reduced lipoprotein lipase activity in the underfed cow, this supplement appears to reduce the effect of underfeeding if it is accepted that a normal response to underfeeding is to improve the efficiency of fat metabolism through increased lipoprotein lipase activity.

The localization of glycosylated k-casein in isolated bovine casein micelles was investigated at the ultrastructural level with gold granules labelled with the Ricinus communis lectin specific for galactose. No evidence was obtained for the presence of glycosylated k-casein on the surface of glutaraldehyde-fixed micelles whether or not they had been treated with neuraminidase. Glycosylated k-casein was mainly located in the bridging network interconnecting the micelles and appeared to be loosely associated with the micelles. When thin sections of micelles were marked, no clear-cut evidence was observed for the presence of intramicellar glycosylated k-casein.

The formation of lysinoalanine, N-є-(2-amino-2-carboxyethyl)-L-lysine, by treatment of αs0-, αsl- and β-casein with alkali, has been studied. In all 3 proteins lysinoalanine was formed by reaction of lysyl residues with dehydroalanyl residues produced by alkaline degradation of those phosphoseryl residues which occupy isolated positions in the proteins' structures. The contribution to lysinoalanine production made by phosphoseryl residues which were arranged in clusters, as occurs in the sequence -Ser(P)-Ser(P)-Ser(P)-, was not significant.

The triglyceride compositions of 76 Australian milk fats obtained from 3 factories during a whole year were determined by gas-liquid chromatography. It was shown that all the data fitted the equation

with a S.D. of of 0·7088 where C40, C42 and C44 are the weight percentages of triglycerides with carbon numbers 40, 42 and 44. The triglyceride compositions of 10 samples of milk fat from countries other than Australia were also shown to fit the equation. If the equation is assumed to define pure milk fat, it is shown that as little as 5% of any non-milk fats can be detected with > 99% confidence. The amount of non-milk fat in mixtures of milk and non-milk fats can be quantified to better than ±2% with > 95% confidence. Also, the identity of the non-milk fat can usually be deduced by calculation of its triglyceride composition. Analyses of known mixtures and of chocolate and a table spread comprising butter and vegetable oil showed an agreement between observed and expected results well within the predicted confidence limits.

Teat dipping of lactating cows with either 1000 or 5000 mg available iodine/; (mg avI/;) solution and thoroughly washing and drying of the teats before sampling resulted in levels of 70 and 99 µg avI per quarter per milking respectively. Without any pre-milking udder preparation prior to sampling the levels of iodine recorded were 143 and 291 µg avI per quarter per milking respectively. Some systemic transfer of iodine from the teat skin to the milk was observed, but the bulk of iodine residue in milk was of direct teat skin origin.

Differential counts of electron microscope sections of cell pellets isolated from bovine udder secretions showed that no secretory epithelial cells and very few ductal epithelial cells were present at any stage. The predominant cell type was the macrophage in dry and lactating cows or the polymorphonuclear leucocyte (PMNL) in colostrum. Lymphocytes were also present but no plasma cells were found. The macrophages took up polystyrene latex particles (as did the PMNL) and adhered toglass in culture. Neither macrophage-nor PMNL-rich cell suspensions produced any increase in free fatty acid levels when incubated with fresh milk.

From bovine mammary secretion during the dry period, the total number of cells was between 1·2 and 5·9 Ǻ 106/ml. A mean of 35% of these cells were classified as lymphocytes and ∼ 85% of them could be isolated by the Ficoll-isopac method. Centrifugation separated 6% of the cells into the fat; 5% of them were lymphocytes. About 47% of the lymphocytes bound Helix pomatia agglutinin, a T-cells marker, while the proportion of Ig-bearing cells was ∼ 28%. The mammary lymphocytes were stimulated by the lectins phytohaemagglutinin, pokeweed mitogen, concanavalin A and by lipopolysaccharide from Salmonella typhimurium. The stimulation indices of mammary lymphocytes were generally lower than those for peripheral blood lymphocytes from the same animals. The background values, i.e. counts/min of lymphocytes incubated without mitogen, were often higher for lymphocytes isolated from mammary secretion than from blood.

The heat stability of a standard reconstituted skim-milk preparation has been investigated as a function of pH, temperature of coagulation, and forewarming treatment. Apparent activation energies have been calculated from the temperature dependence of coagulation time, and a constant value of 144 kJ/mole has been found for milks between pH 6·6 and 6·9. The effect of forewarming resulted in a decrease in stability at the most acid pH values, a slight increase at higher pH but below the pH maximum, and a decrease in the region of the pH minimum. A working hypothesis is proposed for the mechanisms leading to the coagulation of milk at elevated temperatures, based upon Ca induced precipitation of casein, protein polymerization, β-lactoglobulin: κ-casein interaction, and precipitation of insoluble Ca phosphates.

In 2 experiments, chloroform was introduced into the rumen of lactating goats given a mixture of 40% chopped hay and 60% barley-based concentrates. The effects on food intake, apparent digestibility, rumen fermentation and the yield and composition of milk were measured. In expts 1 and 2 food intake was reduced by 7% and less than 1% respectively. There were no significant effects on apparent digestibility in expt 1, but there were significant increases in the apparent digestibility of the dry matter and organic matter in expt 2. The results of in vitro determinations suggested that the loss of energy in combustible gas was reduced by 52 and by 25% in expts 1 and 2 respectively. As a result of these changes, the metabolizability of the dietary energy was increased by 2·1 and 4·8% respectively. In both experiments, the total volatile fatty acid concentration in the rumen was reduced when chloroform was added and there were changes in the molar proportions of the individual fatty acids, principally a reduction in acetic acid and an increase in propionic acid. Milk yield was not affected, but the fat content of the milk was reduced and, in expt 1, the protein content was increased.

The effect of 15 amides and related compounds on the heat stability of milk was investigated; of these urea, biuret, triuret, methyl urea and ethyl urea had a similar stabilizing effect. These 5 compounds reacted with lysine to form a ninhydrin-positive compound, possibly homocitrulline, and with lactose produced Maillard-type browning, but some of the other compounds studied were also capable of participating in one or both of these reactions. The only effect which the 5 stabilizing amides had in common and which the other compounds did not share was a significant pH-buffering capacity in synthetic systems and in milk. It is suggested that urea exercises its stabilizing influence in milk principally through its ability to buffer the pH of the system during heating.