Records of 81 heifers, daughters of 6 bulls, were examined to determine the regressions of milk yield, corrected for lactation length, on initial liveweight and age at calving.

Age was found to have no significant effect and was discarded in the final analysis.

The regression equations were similar for the different groups of half-sibs, except for one group whose members had not been fed according to milk yield. After removal of this group, a highly significant positive relationship between lactation yield and liveweight at calving was found ‘within bull groups’. The mean values of groups of halfsibs did not show this relationship, and significant differences in milk yield still persisted between groups after adjustment for liveweight differences.

It was concluded that herd improvement by choosing heifers solely on the basis of liveweight shortly after calving appears unlikely to be effective unless the sire's potential is known and the feeding during lactation takes into account the greater maintenance requirements of heavier animals.

The volatile fatty acids produced during fermentation in the rumen have been shown to vary in their nutritive properties. Armstrong & Blaxter (1957) found that for lipogenesis in the adult sheep the value of the acids increases with increasing chain length. Rook & Balch (1961) showed that the individual acids have characteristically different effects on the synthesis of the various constituents of milk. In consequence the nature of the end products of fermentation must be one factor affecting the utilization of foods for productive purposes.

In cross-over experiments it has been established that milk yield increased and the fat solids-not-fat (SNF) contents of the milk decreased when cows were given approximately 15 lb dry matter/day of early-cut silage compared with the values obtained by giving the same amount of silage made from herbage cut at a later stage of maturity.

Increasing the proportion of concentrates to silage in the cow's diet so that the milk yield remained unchanged increased the SNF content of the milk but had no effect on the fat content.

Supplementing early-cut silage with 5 lb hay/day increased the fat content of the milk, but had no effect on either milk yield or the SNF content of the milk.

Compared with a silage to which molasses had been added, untreated silage decreased milk yield, and increased the fat content without affecting the SNF content of the milk.

Results are given for the effect of different ultra-high-temperature milk sterilizing processes on the thiamine, vitamin B6 and vitamin B12 contents of milk. For all the processes examined, the loss of thiamine is negligible, and the losses of vitamins B6 and B12 lie between zero and 35%. Indirect-heating processes appear to cause more loss of vitamin B12 than of vitamin B6, but the reverse is true of directheating processes.

Spray-dried whole milk powders were prepared containing 0·01% of γ-tocopherol and of a mixture of α-γ- and δ-tocopherols. Control powders and powders containing 0·01% of dodecyl gallate, an antioxidant of known effectiveness, were also made. The powders were stored at 37°C and examined at intervals for taste, peroxide value and absorbed oxygen. The protection against oxidation afforded by both the tocopherol additions was small, although γ-tocopherol was more effective than the mixture of tocopherols. Dodecyl gallate was again found to be a good antioxidant for whole milk powder.

Solutions of labelled benzyl mercaptan-(35S) in water and cream were subjected to steam distillation in a continuous vaporization equilibrium still, and the concentrations of mercaptan in distillates and residues were obtained by measurement of the radioactivity in toluene extracts.

In the steam distillation from aqueous solution the vapour/liquid equilibrium relationship was not linear. The vapour/liquid equilibrium coefficient increased from 73 to 108 over the range of concentrations 0·01–0·05 ppm. in the liquid fraction at the time of partition.

In the steam distillation from cream containing 30% fat the relationship was linear, with an equilibrium coefficient of 1·35 over the range 0·1–0·6 ppm. in the cream at the time of partition.

The values of the vapour /liquid equilibrium coefficients are of the same order as those reported previously, 105 and 1·30, respectively, for which estimations were made by an absorption method.

The butterfat/water partition coefficient for benzyl mercaptan was found to be 160, which is consistent with the large difference found between the steam volatilities of the substance from water and from cream.

The vapour/liquid equilibrium coefficient for benzyl mercaptan, which is the substance causing ‘landcress’ taint in butter from the milk of cows grazing pastures infested with the cruciferous weed Coronopus didymus, was found by use of a continuous vaporization equilibrium still to be 105 from solution in water and 1·30 from solution in cream of 30% fat content. It was concluded that complete removal of heatdeveloped landcress taint from cream would not be commercially practicable.

The role of the essential fatty acids, linoleic and arachidonic acids, in human nutrition has been widely studied, particularly with respect to their possible action in preventing arterial disease in adults, e.g. Kinsell (1963). In addition, Hansen, Haggard, Boelsche, Adam & Wiese (1958) have emphasized the importance of linoleic acid in the nutrition of infants. Although milk fat contains only relatively small amounts of linoleic and arachidonic acids, the part played by milk and milk products in contributing essential fatty acids to the human diet has received considerable attention (Combes, Pratt & Wiese, 1962; Kon, 1962; Hansen et al. 1963; Garton, 1964). However, despite the initial dependence of many infants on dried milk as an exogenous source of essential fatty acids the effects of commercial drying processes on the constituents of milk fat have not been much investigated. A comparative study of the fatty acid compositions of raw and dried milk was therefore undertaken.

The effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk has been investigated. At the 1st milking after either treatment, the yield of milk was augmented by a carry-over of milk but at the 2nd milking the yield was invariably depressed and then increased until the original yield, or slightly less, was recovered within 5 days. The concentration of lactose and potassium decreased and of sodium, chloride, whey proteins and casein increased during the period of the treatment, and on the resumption of normal milking the original composition was rapidly recovered. The changes in the composition of fat were less clearly defined because of residual milk effects but over the period of the treatment and the succeeding 6 milkings the effect was invariably to increase fat percentage. The differing effects on composition resulted in a more marked effect on the yields of lactose, potassium and casein than on those of sodium, chloride or the whey proteins throughout the treatment and recovery periods. When milk was removed in portions after an extended milking interval there were decreases in the concentrations of lactose and potassium and increases in those of sodium and chloride throughout normal milking. When the residual milk was obtained after an injection of oxytocin the composition of the portions of milk resembled that of the first portions of milk removed from the udder. The possible effects of the treatments on the secretory cells and the permeability of the udder tissue are discussed.

A C20 multibranched fatty acid earlier isolated from butterfat in trace amounts has been conclusively identified by means of mass and infra-red spectrometry and gas-liquid chromatography as 3,7,11,15-tetramethylhexadecanoic acid.

Sixteen single-strain cultures, 10 of Streptococcus cremoris, 3 of Str. lactis and 3 of Str. diacetilactis were examined for their ability to withstand freezing and storage at –17·8 and –23·3°C. The numbers of surviving bacteria decreased as storage time increased. For the majority of strains, the survival rate was greater at the lower temperature. At both storage temperatures there were differences between the percentages of surviving bacteria for different strains.

The results suggest that the relative proportion of strains in mixed cultures would not remain constant under frozen storage.

The changes in yield and composition of milk when 4 cows were milked throughout the whole of pregnancy have been studied. The yield decreased to a minimum 1–20 days before parturition and then gradually increased. The changes in composition before parturition were similar to those observed in late lactation but more pronounced. The content of proteose-peptone plus globulin increased in late pregnancy with a sharp peak, of about 5 times the value observed in mid-lactation, within the last 10 days before parturition, and then decreased rapidly. After parturition milk yield increased rapidly and the changes in composition were less marked than in animals with the usual ‘dry period’. The results are discussed in relation to current knowledge of colostrum formation.

Small volumes of milk each containing an average of less than 10 colonyforming units of Staphylococcus aureus were injected into the teat cisterns of 39 quarters of 10 cows.

Typical staphylococci were recovered from only 14 quarters following overnight incubation of milk stripped manually from each quarter 10 min after injection. There was an inverse relationship between the total leucocyte count of the milk taken from the quarter before infusion and recovery of staphylococci.

From 4 of 8 quarters from which Staph. aureus could not be recovered by enrichment it was possible to recover the organism by centrifuging the milk and culturing the deposit of leucocytes and bacteria.

It is suggested that release of ingested staphylococci from defunct phagocytes may be important in initiation of infection, failure of antibiotic therapy and recurrence of infection.

After an injection of oxytocin and the removal of residual milk, the milk obtained at the next milking had an increased content of sodium, chloride and whey proteins and a decreased content of lactose. The effect persisted for several milkings. It is suggested that this was due to a direct effect of oxytocin on the permeability of the mammary epithelium and that oxytocin should be used with caution in certain types of milk secretion experiment.

A strain of Streptomyces albus, presumed to have originated in raw milk, was found in large numbers in a pair of experimental cheeses. The numbers of streptomyces in both cheeses remained constant over the 4-month period of sampling and a comparison of the numbers obtained from cheese dissolved in citrate with and without mechanical aid revealed no differences, suggesting that the streptomyces was present in the conidial state. The heat resistance of mycelium and of conidia was determined at 62·7 °C (145 °F) and 71·7 °C (161 °F). The mycelial cells showed no resistance to either temperature, there being 100% kill after 15 min at 62·7 °C and 17 sec at 71·7 °C. The conidia, however, were very much less affected after 2 h at 62·7 °C, and 3% remained viable even after 30 min at 71·7 °C. Although the strain was found to be proteolytic, lipolytic and saccharolytic, it appeared to be inactive in the cheese, being present in the conidial state.

Small numbers of bovine staphylococci, usually less than 30, were infused into the teat cistern of 17 cows secreting less than 100 000 leucocytes/ml milk. Infection was assumed to have occurred if the organisms multiplied sufficiently to be recovered in the foremilk and inflammation was regarded as demonstrated if there was an increase in leucocytes. If the staphylococci were recovered at the 1st post-infusion milking they were consistently recovered thereafter and inflammation always followed but was never evident at the 1st post-infusion milking. Inflammation was usually evident by the 3rd but in one instance was delayed to the 11th post-infusion milking. There was never inflammation in the absence of infection. When there was a high probability that the infusion contained one organism or more, infection occurred in 2 of 10 quarters infused with coagulase-negative staphylococci and 23 of 25 quarters infused with coagulase-positive staphylococci.

A significant positive relationship was found between the number of staphylococci found at the 1st post-infusion milking and the number of leucocytes at the 3rd postinfusion milking.

Microscopical and chemical studies of seaminess in Cheddar cheese revealed that the white lines or seams characteristic of the defect are sections through layers of crystals lying between the milled curd particles. The crystals were identified from their X-ray diffraction pattern and by their refractive index as calcium orthophosphate dihydrate, CaHPO4. 2H2O. On each side of the adjoining curd surfaces in affected cheese there is a zone about 20 μm thick of strongly contracted protein which is almost devoid of crystals.

Adding sodium chloride to cheddared curd increased the quantities of calcium, phosphorus and water released. The increases were proportional to the amount of salt applied within the range 0–2·5 g NaCl per 100 g curd.

The solubility of calcium orthophosphate was found to rise from about 0·0025 M in water to a maximum of 0·008M in 2 M sodium chloride solution.

It is postulated that calcium and phosphate ions released from the curd into the seam crystallize in the form of CaHPO4. 2H2O as the solubility of the compound is lowered by diffusion of salt from the surfaces into the curd particles.

Samples of butter were reworked at various times after removal from the churn, either in a laboratory mixer or by pressing between a microscope slide and cover glass. Moisture distribution was studied by microscopic examination and by indicator papers.

Reworking within 30 min of completion of the original working caused no change in moisture distribution but delayed reworking caused aggregation of water droplets. The further the setting of the butter had proceeded before reworking, the greater was the extent of aggregation.

Cream-cooling treatments which resulted in a softer butter delayed or decreased the aggregation of droplets caused by reworking.

A theory is suggested relating changes on reworking with the formation of a crystal structure on setting.

Fifty-seven inoculations of a strain of Staphylococcus aureus were made into the outer 4 mm of the teat ducts of 8 cows. The inocula ranged from 10 to 600 colony-forming units (CFU) and were made with a stainless steel instrument designed to overcome the disadvantages of glass rods and cotton swabs hitherto used.

A single inoculation resulted in either no colonization of the duct, in temporary colonization for up to 7 days, or in colonization followed by intramammary infection.

The recovery of the organisms depended on the size of the inoculum. When 70–100 CFU were placed in the teat duct no organisms were recovered from 12 of 24 quarters after the 1st post-inoculation milking. When 500–600 CFU were used, organisms were recovered from all of 31 quarters for at least 3 milkings, and from 61% for 6 milkings or more, in spite of dipping the teats in a strong disinfectant twice daily.

Intramammary infection developed in 1 of 12 quarters (8%) inoculated in the teat duct with about 600 CFU when the animals were milked twice daily, and in 5 of 19 (23%) quarters if the 1st post-inoculation milking was omitted.

There was no evidence of sensitization resulting from previous infection.

Cream-cooling rates, cream-pre-cooling treatments (Alnarp) and seasonal changes in the chemical composition of butterfat were found to influence the setting rate of butter. Vacreator pasteurization, however, especially at high steam intensity, had the greatest effect. Comparative hardness values of butter made from platepasteurized and Vacreator-pasteurized cream were 1·5 and 2·9 kg and 4·4 and 8·3 kg at the end of ½ and 5 h, respectively, after the completion of working. The highest setting rate, which resulted in a hardness of 6 kg at the end of 30 min, was recorded for butter made from Vacreator-pasteurized cream which was rapidly cooled to 5 deg F below normal churning temperature and churned after holding for 30 min. Abrupt breaks noted in the setting curves of this rapidly setting butter lead to speculation that changes in the butterfat crystal form may be involved

In general, the final hardness values of butter stored at 45 °F for 30–50 days were not greatly influenced by the setting rates observed at 55 °F during the 5-h period immediately after the completion of working. Exceptions to this observation were obtained when the cream was rapidly cooled to or slightly below churning temperature and also when the cooling of plate-pasteurized cream was delayed at 65 °F for 3–4 h before final cooling to the churning temperature.

The causes of the differences observed in the setting and final hardness values of butters made from plate- and Vacreator-pasteurized cream were not determined and warrant further investigation.