The modified technique for transplanting one mammary gland of a lactating goat to the neck, with the mammary (pudic) artery and vein anastomosed to the carotid artery and jugular vein respectively, is described. This technique was successful in 6 operations and there were no significant differences between the milk yield of the transplanted and control (in situ) glands at any stage after operation. These results are compared with those from an earlier series in which no special provision was made for lymphatic drainage and in which anticoagulant therapy and treatment of the gland prior to attachment were not standardized.

Mammary lipoprotein lipase of lactating goats was extracted by 3 methods: homogenization of tissue acetone-ether powders; aqueous homogenization of crude tissue using an Ultra-Turrax apparatus; aqueous homogenization of crude tissue using a Sorvall Omni-mixer microhomogenizer. Although there were differences between absolute values obtained by the 3 methods, each type of homogenate had a lipolytic activity with lipoprotein lipase characteristics (i.e. more than 90% inhibition by serum omission or NaCl addition). Furthermore, the 3 methods were highly correlated and presented similar variations with the stage of lactation, in parallel with long-chain fatty acid secretion into milk. Repeatability of the measure of homogenate lipolytic activities was about 8%, whereas day-to-day repeatability of enzyme extraction and assay was about 20% for each method.

Twelve of twenty-one udder quarters with colonized teat ducts became infected within 13 d when milked with a machine producing large cyclic and irregular vacuum fluctuations in the teatcup; of 23 quarters milked under the same conditions, but with metal shields fitted inside the liners to protect the teat apex (Thiel, 1974), only 2 quarters became infected in the same period. The introduction of a post-milking teat disinfectant teat dip resulted in the elimination of orifice colonization from 15 teats dipped in Na hypochlorite solution (40 g/l available chlorine) and from all but 2 of 15 teats dipped in an iodophor solution (5 g/l available iodine).

Examination of data pertaining to milk yield and litter growth rate of guinea-pigs at peak lactation showed that milk yield increased with increasing number of pups carried by the dam during pregnancy and also with increasing maternal weight. There was a significant linear correlation (P < 0.05) of mammary gland weight (expressed per unit of maternal body weight) with litter size. Increasing litter size, within 18 h of parturition, from 1 pup to 5 pups did not elicit a response in milk yield. Decreasing litter size from 5 pups to 1 pup reduced milk yield to the level expected of a monotocous dam. Data are presented showing the ability of the guinea-pig pup to survive from birth without access to milk and the inadequacy of milk supply to meet litter requirements when the litter size is more than 2 pups. The mechanisms controlling lactation in the guinea-pig are discussed in relation to data obtained in other species.

The effect of lactation and diet on milk lipoprotein lipase activity (LPL), cell count, serum albumin concentration and free fatty acid levels, expressed in terms of acid degree value (ADV), was examined in 2 experiments. In addition, the ability of blood plasma from cows on different diets to activate LPL was also investigated.

Changes in ADV were not consistently associated with changes in LPL, cell count or serum albumin throughout lactation, although results indicated that ADV appeared to be influenced by cell count in early lactation, and by the amount of blood plasma proteins reaching the milk during the remainder of lactation. LPL activity was low in colostrum, but increased rapidly between d 2 and 12 post-partum, reaching a peak at 5 months. Activity was unaffected by diet.

There was no effect on ADV of feeding concentrate: hay ratios of 75:25 and 60:40, but ADV was higher in cows fed a low protein diet (crude protein 9%) between 10 and 60 d post-partum, than in cows fed a high protein diet (crude protein 18 %) during the same period. In addition, the blood plasma for cows on the low protein diet had a greater ability to activate LPL although, on the basis of the millk: blood serum albumin ratio, a smaller proportion of blood constituents had reached the milk. The ability of blood plasma to activate LPL was also found to increase with increasing levels of lipoprotein lipid in the blood.

No relationship was found between the trisaturated glyceride content and the softening point (SP) of milk fat. Inter-esterification of milk fat increased its SP, but did not change the trisaturated glyceride content or the fatty acid composition of the trisaturated glyceride fraction. Inter-esterification increased the amount of both low and high and decreased the amount of medium molecular weight triglyceride species in the trisaturated glyceride fraction. The increase in the amount of high molecular weight triglyceride species was up to 3 times greater than the increase in the amount of low molecular weight triglycerides.

The triglyceride species composition of the trisaturated glyceride fraction of milk fat was found to vary seasonally. Excellent correlation was found between SP and groups of low molecular weight triglycerides, groups of high molecular weight triglycerides and some individual triglyceride species. Correlation coefficients were higher than those previously reported between groups of fatty acids and SP.

In dilute buffers ⋟ pH 5·8, chymosin hydrolysed bovine αs1-casein to αs1-I, αs1-II and αs1-III/αs1-IV in a sequential manner while at pH 4·6 αs1-casein was hydrolysed to αs1-I which was then hydrolysed to αs1-V. In the presence of 5 % (w/v) NaCl at pH 5·2, αs1-casein was hydrolysed to αs1-I which was then hydrolysed to αs1-VII and αs1-VIII. αs1-I, αs1-II and αs1-III/αs1-IV were isolated by chromatography on cellulose phosphate followed by preparative slab-gel electrophoresis; αs1-V was isolated by repeated preparative slab-gel electrophoresis and αs1-VII by gel filtration on Sephadex G-150 followed by preparative slab-gel electrophoresis. The mol. wts of the peptides, estimated by gel filtration on Sephadex G-100, were 21000, 17600, 15600, 19900 and 14600 for αs1-I, αs1-II, αs1-III/αs1-IV and αs1-V and αs1-VII respectively. Characterization of the peptides by amino acid, phosphorus and terminal residue analysis showed that they probably consisted of segments of the αs1-casein chain as follows: αs1-I: residues 24/25–199; αs1-II: residues 24/25–169; αs1-III/αs1-IV: residues 24/25–149–150; αs1-V: residues 29/33–199; αs1-VII: residues 56–179. Peptide bonds close to phosphate residues on the αs1-casein chain were not hydrolysed by chymosin at high pH values (⋟ 5·8) when the phosphate groups were charged, but became available for hydrolysis when the reaction pH was reduced. Proteolytic specificity was also modified by NaCl.

The relationship between extent of κ-casein proteolysis and aggregatability of milk casein micelles has been studied using chymosin either bound to porous glass supports or free in solution. Both enzyme preparations demonstrated that, overall, 86–90 % of the κ-casein had to be destroyed before any aggregation could occur. Based on these results, a mathematical model of chymosin action on casein is described involving (i) the attack on κ-casein by chymosin, via a Michaelis–Menten mechanism (ii) the probability that sufficient κ-casein on any micelle is destroyed to allow aggregation, and (iii) the aggregation of para-casein micelles by a von Smoluchowski mechanism.

Powders were prepared from whole and skim-milk using reverse osmosis (RO) as a first stage followed by either evaporation and spray drying or spray drying alone. They were compared with powders made by the conventional method of evaporation and spray drying. Measurements were made of powder solubility, free fat content, whey protein denaturation, vitamin content, powder morphology and bacterial count. The free fat contents of powders prepared from whole milk concentrated by RO were high; otherwise, there were no significant differences in the properties of powders made from milks concentrated initially by RO and those prepared by conventional evaporation. The results indicate that it is feasible to use RO for the manufacture of skim-milk powder and for dried whole milk production where higher free fat levels are not detrimental.

An insoluble benzoquinone derivative, obtained by reacting benzoquinone with Sepharose 4B and subsequent deactivation with ethanolamine, selectively absorbed chymosin from a mixture of milk-clotting enzymes and other proteins such as in rennets. This selective absorption has been used for developing a purification method and for quantitatively estimating the chymosin content of commercial rennets. Thus, from a powdered calf rennet, it was possible to obtain in one step an 8-fold purified chymosin free of bovine pepsins. The proposed analytical test involves 2 milk-clotting activity measurements and a chromatographic elution of the sample on a quinonated Sepharose column. It can be applied directly to commercial rennets, because it does not require pre-dialysis of the sample against the elution buffer. Furthermore, a combination of quinonated Sepharose and DEAE-cellulose chromatography gave a method for isolation of bovine pepsin I from rennets.