An experiment has been performed with 2 Jersey cows to determine the effect of a reduction in udder temperature on milk production. One half of the udder was covered while the other half was cooled by an increase in air movement at an air temperature of 6−10°C; for closely clipped udders it was estimated that the cooling conditions might be equivalent to an air temperature of −10°C with low air movement. Yields of milk, fat, protein and lactose were reduced significantly at the morning milking after 22 h cooling; the decreases which occurred at the afternoon milking after 9 h cooling, in all components except fat, were not significant. Wisconsin Mastitis Tests on the milk indicated that changes in udder health did not contribute to these effects.

The specificity of the interaction between κ-casein, αs-casein and β-casein which forms the basis of micelle stabilization was studied by investigating the extent to which κ-casein could be replaced by other proteins. Of those tested, only gelatin replaced κ-casein and even it was only 2·5% (w/v) as effective and required a long pre-incubation period. The micelles formed by each of κ-casein and gelatin with αs-casein and Ca2+ were of a similar size to the casein—Ca complexes which compose natural micelles. Gelatin also formed complexes with αs- and with β-casein at 30°C in the absence of CaCl2. Evidence was obtained that the interactions between gelatin and the caseins had a much stronger ionic component than had those between κ-casein and the other caseins. It was concluded that the interactions between κ-casein and αs- and β-caseins which lead to micelle formation are highly specific and probably involve definite sites in each molecule.

The cationic detergent cetyltrimethylammonium bromide (CTAB), the anionic detergents sodium lauryl sulphate and sodium deoxycholate, and the nonionic detergents Tween 20, Tween 80 and Brij 35, and lecithin, starch, glycogen, chondroitin sulphate and polyethylene glycol, were tested for their ability to replace κ-casein in stabilizing αs- and β-caseins against precipitation by Ca2+. Of the materials tested, CTAB and Tween 20 stabilized both caseins and Brij 35 stabilized only αs-casein. Analytical ultracentrifugation of mixtures of CTAB with each casein and of Brij 35 with αs-casein indicated that both detergents acted by disrupting the casein aggregates and complexing with the monomers. Addition of CaCl2 did not aggregate the Brij 35–αs-casein complex. It is concluded that the basis of the stabilization phenomenon involves specific interactions between κ-casein and αs-casein or β-casein at mainly hydrophobic sites.

(1) Two wether sheep fitted with ruminal and duodenal re-entrant cannulas were used to study the influence of the physical form of a barley grain and barley straw diet and intraruminal addition of ammonium salts (mainly acetate) on digestibility of dietary constituents, the flow of digesta to the duodenum and the composition of digesta from the rumen and duodenum.

(2). Grinding and pelleting of the diet depressed the digestibility of crude fibre and increased that of the nitrogen-free extract and addition of ammonium salts increased the digestibility of crude fibre. The effects of the physical form of the diet on the composition of the short-chain fatty acids of rumen liquor were not consistent and the addition of ammonium salts produced changes over and above those attributable to the small amounts of acids in the mixture. The extreme values observed for the molar proportion of propionic acid were 12·3 and 38·1% and the corresponding values for η-butyric acid were 28·1 and 9·0%.

(3). Variations in the flow of nitrogenous materials to the duodenum were related more to the pattern of fermentation established in the rumen than to the experimental treatments. There was a highly significant relationship between the molar proportion of propionic acid and the abomasal output of nitrogen and also the abomasal output of α-ε-diaminopimelic acid and α-linked glucose polymers. The amino acid composition of duodenal digesta differed from that of the diet—in particular the proportion of glutamic acid was decreased and the proportions of aspartic acid, alanine, lysine and histidine were increased—but differences in composition between treatments and between animals were small.

(4). The faecal output of nitrogen differed little between animals and between treatments, but nitrogen retention was significantly increased during the intraruminal infusion of ammonium salts.

In a feeding experiment with 6 cows in mid-lactation a portion of the starch in the concentrate part of the diet was isocalorically replaced by 8% soybean oil, and the effects on the yield and composition of the milk were studied. The oil was incorporated into the diet either as coarsely ground soybeans or by direct addition of the oil itself. The concentrate mixtures were given with a high-roughage diet that supplied 5·5 kg hay and 2·7kg sugar-beet pulp/day.

When the soybean oil was included in the diet either in the form of soybeans or as the oil itself there was an increase in the yields of milk, solids-not-fat (SNF) and lactose, and an increase also in the percentage of lactose in the milk. The percentage of protein, however, was decreased.

When the oil was included in the form of soybeans there was an increase in the yield of fat but a decrease in the percentage of SNF in the milk.

When soybean oil was included in the diet, the yield of protein was increased but the yield of fat and the percentage of fat in the milk were both decreased.

With both methods of incorporating the oil there was an increase in the relative proportion of propionic acid and a decrease in that of butyric acid in the total volatile fatty acids of the rumen liquor. When the oil was added directly, but not when it was added as soybeans, there was a decrease in the proportion of acetic acid in the total volatile fatty acids. The implications of these findings are discussed.

The effects of the isocaloric replacement of starch in a low-fat concentrate mixture by 8% soybean oil on the yield and composition of milk fat were investigated in a feeding experiment with 6 cows in mid lactation. Two high-fat concentrate mixtures were given to the cows. In one the requisite amount of soybean oil was given by including 50% coarsely ground soybeans in the concentrate mixture. In the other an equal amount of soybean oil was added directly to the concentrate mixture. The concentrate mixtures were given with a high-roughage diet that supplied 5·5kg hay and 2·7kg of sugar-beet pulp/day.

When the 2 high-fat rations were given to the cows there were reductions in the percentages and yields of 10:0, 12:0, 14:0, 14:1, 16:0 and 16:1 fatty acids and increases in the concentrations and yields of 18:0, 18:1 and 18:2 fatty acids in the milk fat. The direct addition of the soybean oil to the diet also reduced the percentage and yield of 6:0 and 8:0 whilst the inclusion of the soybeans increased the percentage of 4:0 and the yields of 4: 0 and 6:0 in the milk fat.

When both high-fat rations were given to the cows there were increases in the yields and concentrations of as-9–18:1 in the milk fat, whilst inclusion of the soybean oil in the diet increased also the concentration and yield of trans-11–18:1.

The implications of these findings are discussed.

The effects on the composition of the plasma lipids of the isocaloric replacement of starch in a low-fat concentrate mixture by 8 % soybean oil were investigated in a feeding experiment with 6 cows in mid-lactation. Two high-fat concentrate mixtures were given: in one, the soybean oil was incorporated into the diet by the inclusion of the appropriate amount of coarsely ground soybeans; in the other, the soybean oil was incorporated directly in the concentrate mixture. The concentrate mixtures were given with a high-roughage diet that supplied daily 5·5kg hay and 2·7kg of sugar-beet pulp.

When the cows were given the 2 high-fat diets there were increases in the concentrations of total plasma fatty acids and in the concentrations of fatty acids circulating in the plasma as phospholipids and cholesteryl esters. There were increases in the concentrations of plasma unesterified fatty acids and triglyceride fatty acids when the cows were given the diet containing soybeans but there were decreases in the concentrations of these 2 fractions when the cows were given the diet containing soybean oil.

The inclusion of soybeans in the diet increased the concentration of 18:0 in the plasma triglycerides and unesterified fatty acids whilst the inclusion of soybean oil in the diet increased the concentrations of 18:0 and 18:1 but decreased the concentration of 18:2 in the plasma unesterified fatty acids.

When the cows were given the 2 high-fat diets there were decreases in the concentrations of 16:0 and 16:1 and increases in the concentration of 18:2 in the plasma cholesteryl esters. The inclusion of soybeans in the diet also reduced the concentrations of 18:1 and 20:3 in the plasma cholesteryl esters but increased the concentrations of 18:0 and 18:2 in the plasma phospholipids.

The major fatty acid circulating in the plasma of the cows was 18:2 (46·4–55·3%) on all diets but only about 1% (0·40–1·04%) of the total plasma 18:2 occurred in the plasma triglycerides.

The results are discussed in relation to the changes in the composition of the milk fatty acids produced by the cows when they were given the experimental diets.

Fat analyses were carried out on fore-milk and residual milk samples to elucidate the significance of the changes in fatty-acid composition of milk fat during milking previously reported by other workers. The levels of phospholipid in fore-milk samples per unit weight of fat were considerably higher than those of residual milk samples. The fatty acid composition of the triglyceride in fore-milk and residual milk samples was similar. These results suggest that the differences in fatty acid composition of milk fat collected during milking can be attributed to decreases in the relative amount of phospholipid-rich globule membrane associated with increasing globule diameter.

A method based on salt fractionation, iso-electric precipitation and gel filtration chromatography is described for the purification of the enzyme rennin (E.C. 3.4.4.3).

(1). A study is reported on the effects of 4 levels of coconut oil, added to a basal diet low in fat, on the secretion in cow's milk of fat and its component fatty acids. (2) A significant reduction in the yield of milk fat occurred at the highest level of supplementation. In terms of individual fatty acids the yields of lauric and myristic acids increased progressively with increased intake, maximum yields being obtained with the 7% level of coconut oil. Conversely the yields of caproic, caprylic, capric and palmitic acids progressively decreased with increased coconut oil intake. The yields of C18 acids were unchanged.