Summary

(1) A tentative scheme is proposed for the quantitative estimation of the effects of various factors on one major milk constituent, lactose, from analyses of the milk of individual cows within herds. The potential lactose content in the milk of individual cows is predicted from the observed potassium-to-lactose ratio in the milk, and the difference between the predicted potential and the actual lactose content is partitioned into fractions that are attributed to ...

1. The effects in the cow of intraruminal infusions of acetic acid, propionic acid or butyric acid on the secretion of the component fatty acids of the milk fat, and of these acids and of lactic acid on the composition of the blood plasma of the jugular vein, have been studied. 2. The infusion of acetic acid or butyric acid increased the yield of the C(4)-C(16) acids of milk fat but decreased the yield of C(18) acids. The infusion of propionic acid decreased the yields of all major ...

1. Two experiments are described in which the effects of dietary fat on the synthesis of milk fat in the dairy cow have been investigated. In the first experiment a change-over design was used with two cows to study the effect of removing a mixed-oil supplement to a basal diet low in fat on the concentration and composition of plasma lipids and on the yield and composition of milk fat. 2. Reducing the dietary fat intake from about 430 to 170 g/day caused falls in the concentrations in ...

1. In five experiments, groups of milking cows were changed abruptly from winter-stall feeding to graze a number of different swards, and changes in the concentration of blood-serum magnesium and of other blood constituents have been studied. 2. Wide variations in the severity of hypomagnesaemia in individual cattle were found in all experimental groups, due possibly to such factors as individual variations in the intake of herbage, the requirement and body reserves of magnesium and the ...

1. The plasma levels of individual amino acids were studied in dairy cows under different conditions of production and energy nutrition. 2. A preliminary experiment was conducted which established that there was no regular change in amino acid levels with time of sampling in animals offered food twice daily at milking. 3. For animals in the 8th month of pregnancy plasma concentrations of lysine, valine, serine and isoleucine were higher, and of threonine lower, in Jersey than in Friesian ...

1. A study was made of the effects of feeding regimen and the composition of the diet on the ruminal production of V.f.a. 'S in cattle. 2. The day-to-day variations in the pattern of rumen fermentation in cows given a diet of hay and concentrates indicated that within-cow differences in the molar proportions of the acids from diet to diet are of significance if they exceed about 3% (of the mean value) for acetic acid, about 10% for propionic and butyric acids, and about 25% for valeric ...

Summary

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 ...

1. The effects in the cow of intravenous infusions of sodium acetate, butyrate, propionate, beta-hydroxybutyrate, malonate, citrate or succinate, of glucose or of an emulsion of cottonseed oil on the secretion of the component fatty acids of milk fat and on the composition of the blood plasma of the jugular vein have been studied. 2. Glucose and cottonseed oil were the only metabolities consistently to affect the yield of milk fat. Glucose decreased the yield of milk fat through a ...

1. The effect of reducing the hay and of increasing the proportions of concentrate and flaked maize in the diet of cows on the secretion of milk fat and its component fatty acids and on the proportions of volatile fatty acids in the rumen liquor has been studied. 2. The low-hay diet caused a fall in the milk fat content to about half of the values in the initial control period and the secretion of all the major fatty acids in the milk was reduced. The general pattern of change in the ...

Summary

The effects of stage of lactation and of age on milk and composition yield of cows kept under controlled conditions of feeding and management were investigated. Two groups each of 3 Friesian heifers were used: one group (

A

) was given a daily diet of 18 lb hay and concentrates at the rate of 3·8 lb/10 lb of milk and kept on experiment throughout the first 3 lactations; a second group (

...

1. The effects of the introduction into the diet of natural fats rich in individual fatty acids or of simple triglycerides on the composition of blood lipids and of milk fat in the sow were investigated. 2. Replacement in the diet of a mixture of animal, vegetable and marine oils by a single natural fat had varying effects on the concentrations of plasma lipid fractions, whereas replacement of tallow by simple triglycerides, with few exceptions, increased the concentrations of all ...

1. Measurements were made of arterial and coccygeal concentrations of plasma constituents and of arteriovenous differences across the mammary gland in two anaesthetized lactating sows, and of coccygeal-mammary-venous differences in three conscious sows when lactating and again later when ;dry'. 2. With the possible exception of acetate concentration, the compositions of arterial and coccygeal plasma were similar, and arteriovenous differences in the anaesthetized lactating sow ...

Continuous metabolic studies were made with calves given rations containing different amounts of magnesium.Studies of the cumulative retention of magnesium showed that in calves given normal amounts of magnesium, retention could be predicted from simultaneous data on calcium and nitrogen retention.Magnesium deficiency had no effect on calcium metabolism or nitrogen metabolism.It was shown that it was necessary to deplete the calf of 30 per cent of its total body magnesium to cause ...

Summary

The effect of bacterial infections, produced by infusions of

Streptococcus dysgalactiae

and of

Staphylococcus pyogenes

into one quarter of the udder, on milk yield and composition in heifers has been investigated. After a quarter became infected there was invariably a decrease in the yield of milk and in the concentrations of lactose and potassium, while there ...

Summary

The effects, on the yield and composition of the milk of the cow, of additions to the diet of the calcium salts of acetic, propionic, butyric or lactic acids were determined in 3 change-over experiments. In all cases yield of milk was increased slightly and milk fat content was reduced; solids-not-fat (SNF) percentage was depressed by acetate and butyrate. The effects of these treatments differed markedly from those observed previously when dilute solutions of ...