S. Bartlett

Apparatus for the separate collection of faeces and urine from cows.

The cost of conducting digestibility trials with cows is high, due to the need for either elaborate equipment for separating faeces and urine or a considerable number of assistants to remain constantly behind the cows catching the excreta as they are voided. Manual collection of excreta was used extensively by earlier workers, and, in a recent report of the most suitable arrangements for experiments using this method, Eheart, Holdaway & Pratt (1945) found that one attendant was necessary for every cow on test with a trained chemist also present in the shed at all times.

557. Studies of the secretion of milk of low fat content by cows on diets low in hay and high in concentrates: IV. The effect of variations in the intake of digestible nutrients

1. Digestibility trials were conducted, and the rate of passage of hay was measured, with five Shorthorn cows during a period of normal diet and during two experimental periods in which diets low in hay and high in concentrates were given. In the first experimental period the concentrates were cubes of the wartime type sold as National Cattle Food No. 1, and containing a variety of constituents; in the second they were a mixture offlakedmaize (50%), weatings (35%) and decorticated ground-nut cake (15%). For convenience these are referred to as concentrate ‘cubes’ and ‘mixture’ respectively. 2. During the initial and final control periods the cows consumed daily 17–21 lb. hay, and about 4·5 lb. concentrates per 10 lb. of milk produced. In the initial control period the concentrates were the concentrate cubes, and in the final they were the concentrate mixture. The hay was reduced to 4 lb. daily during the two experimental periods and the remainder of the standard requirements of the animals were met by concentrates. The concentrates were the cubes in the first experimental period and the mixture in the second experimental period. 3. Seducing the hay to 4 lb. did not affect the fat content of the milk when the other food in the diet was the concentrate cubes, but there was a striking mean fall of 1·04% fat when the cubes were replaced by the concentrate mixture. This represented a loss of over 30% in the yield of fat. 4. Digestibility trials, conducted in the initial control and first and second experimental periods, indicated that the fall in milk fat content was not the result of changes in the amounts of dry matter, crude protein, ether extract, crude fibre, cellulose, cellulosans or pentosans not in cellulose digested. The essential difference between the diet of low hay with the concentrate mixture and the other diets given in this experiment was that it provided a high intake of starch yet had little of the physical property of roughage. It is concluded that depression of milk fat content results from a combination of these two factors and probably originates from changes in the physical and biochemical processes of the reticulo-rumen. 5. The intake of starch equivalent, as calculated from the intake of digestible nutrients, was close to standard requirements in all periods of the experiments, but there was a surplus of digestible crude protein. 6. The mean solids-not-fat content of the milk rose 0·48% at the time of the fall in milk fat, and this was entirely due to an increase in milk protein. After the return to normal diets the recovery of solids-not-fat was slower, but no less complete, than the recovery in milk fat.

Field investigations into hypomagnesaemia in dairy cattle, with particular reference to changes in the concentration of blood constituents during the early grazing period.

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 capacity to absorb magnesium from the gut. 3. The degree of hypomagnesaemia observed was independent of the level of milk production, but was generally less severe in Friesian than in Shorthorn and Guernsey cattle. The onset of hypomagnesaemia was delayed for a few days in cattle with a high serum-magnesium concentration at the commencement of grazing. 4. In two out of three experiments in which the effect of fertilizer treatment was studied, the incidence and severity of hypomagnesaemia was increased by the application to the sward of heavy dressings of nitrogenous fertilizer. In the third experiment, severe hypomagnesaemia occurred on a plot which had received no nitrogen fertilizer, due, it is thought, to a restricted intake of herbage magnesium, since the sward was extremely sparse. The feeding of supplements of flaked maize, crushed barley, crushed dredge corn, molassed sugar-beet pulp or a concentrate mixture balanced for milk production, to grazing cattle did not reduce the incidence of hypomagnesaemia. 5. The cutting of grass and feeding it in the stall did not prevent the development of hypomagnesaemia. 6. Blood pH and the concentrations of bloodserum calcium, sodium, potassium and blood glucose in cattle were unaffected by a change from winter feed to spring grazing, but a marked change in blood-serum non-protein and urea nitrogen and blood ammonia nitrogen, but not in any other nitrogenous constituents of the serum, was observed. The concentrations of serum non-protein and urea nitrogen and blood ammonia nitrogen were highest in groups of cattle grazing swards which had received a heavy dressing of nitrogen fertilizer and had a high nitrogen content. 7. In the two experiments in which the severity of hypomagnesaemia was increased by the application of nitrogenous fertilizer, there was a close group association between high concentrations of blood serum non-protein and urea nitrogen and blood ammonia and low concentrations of blood-serum magnesium. High levels of serum urea and blood ammonia during grazing are thought to reflect a high ammonia production in the gut, which may be responsible for the disturbance in magnesium metabolism which produces hypomagnesaemia.

76. Variations in the Solids-not-Fat Content of Milk. I and II

1. The solids content of fat-free milk shows little variation throughout the milking process, i.e. first and last drawn milk are of similar concentration. 2. Curves are presented showing the normal variation in the solids content of fat-free milk throughout a lactation period. These curves are influenced by the age of the cow and by pregnancy.

196. The influence of various fodder supplements on the production and the nutritive value of winter milk

1. An experiment is described in which comparisons were made between the effect of (a) mangels (control feeding), (b) artificially dried grass, (c) sprouted maize, and (d) kale used as dietary supplements on the production and nutritive properties of the milk of dairy cows. 2. No significant differences were found between any of the foods in their effect on yield of milk, or its content of fat or solids-not-fat. 3. The feeding of kale and of artificially dried grass markedly increased the colour and vitamin A content of the milk, but sprouted maize had no more effect in this respect than mangels. 4. As compared with the feeding of mangels, sprouted maize and artificially dried grass had no measurable effect on the vitamin B complex level of the milk. 5. The vitamin B2 (complex) level was more variable and was lowest in the milk from the sprouted maize cows. It is not known, however, whether the difference was due to the feeding or to differences in the cows themselves. 6.The same statement applies to figures for the vitamin C level which was highest in the sprouted maize milk. 7. The growth-promoting properties of the milks produced on mangels, artificially dried grass and sprouted maize were compared. The milks were fed, supplemented either with minerals alone, or with minerals plus sugar as a source of energy. In one series of experiments the milks were given adlibitum , in another the intake was “equalized.” No differences were found and it is concluded that under English conditions, this technique does not disclose the presence in milk of a new essential factor.

43. Normal Growth of Dairy Cattle

1. Normal curves of growth for dairy Shorthorn cattle from birth to 5 years of age are presented. These include height at withers, length of body, depth of chest and live weight. 2. The expression of growth by the “Relative growth rate” method is discussed and illustrated. The method is particularly suitable for expressing the growth of calves under 6 months of age.

556. The use of seaweed meals in concentrate mixtures for dairy cows

The relative effects upon milk yield and composition of three concentrate mixtures containing 10% of two types of seaweed meal ( Ascophyllum nodosum and Laminaria cloustoni ) and an oatfeed-salt mixture, have been observed. Each cow received daily a basal ration of 30 lb. marrowstem kale and 18 lb. hay for maintenance and the first 1½ gal. of milk and 31½ lb. concentrates for each gallon thereafter. No significant effects of treatment upon milk yield or fat percentage were observed. The milk produced on the oatfeed-salt mixture had a slightly but significantly higher solids-not-fat content than that on the mixtures containing seaweed meals. The results showed that seaweed meals have a nutritive value no greater than that of a mixture of 7 parts oatfeed and 1 part salt, which had an estimated starch equivalent of only 39. In view of the relatively high cost, low palatability and low nutritive value of seaweed meals, their possible use in the feeding of dairy cows appears very limited.

81. Variations in the Solids-not-fat Content of Milk. III. The Lactation Yield and Factors Affecting it

1. The influence of the age of cows on the milk yield and on the milk solids is traced. The milk yield reaches a maximum at about the sixth lactation and then declines. The concentration of fat and solids-not-fat shows a gradual decline from the first lactation onwards. 2. During lactations in which the yield is below the normal productivity of a cow, the quality of the milk also tends to be subnormal.

Normal day to day variability of yield of milk and fat of individual cows

1. The day to day variability in the yield of milk and fat of cows is affected by many factors, two of which are stage of lactation and season of the year. Variability is high during the first month of lactation (particularly during the first few days after the calf is weaned), but after this a fairly constant variability may be expected. Under the conditions of management in the herd under discussion and probably in most herds in Southern England variability is highest during the month of May and also tends to be higher during the summer than the winter months. 2. A method is presented of calculating the variability in the yield of mixed milk from a herd of cows and the error to be expected when milk records and fat percentages of individual cows are calculated from a few samples. 3. When cows are milked twice daily at unequal intervals the yield of milk obtained in 24 hours is slightly less variable if a morning milk yield is added to the subsequent evening yield, than if an evening yield is added to the subsequent morning yield.

139. A Comparison between Blood Meal and Wheat Gluten as a Supplement to a Low-Protein Diet for Dairy Cows

1. A ration for dairy cows which supplied less protein than the recognized protein standards for milk production and contained less lysine than most rations normally used in English farming practice was selected. A comparison was then made between cows receiving this ration supplemented with ( a ) wheat gluten, a lysine-poor protein, and ( b ) blood meal, a lysine-rich protein. The addition of blood meal produced no measurable effect on the milk yields, but there was a small and almost significant advantage in the live weights of the cows. 2. In a subsidiary experiment a large increase in the dietary protein produced a very small and non-significant increase in milk yield.