Carotene and immunoglobulin concentrations in the colostrum and milk of pasture-fed cows
Summary The carotene and immunoglobulin concentrations in colostra and milks of 6 Jersey, 4 Friesian and 6 Jersey × Friesian cows were determined during the first 21 d of lactation. Carotene concentrations of between 50 and 300 μg/g milk fat were found at first milking and these declined to normal concentrations, in the range 9–21 μg/g milk fat, by the eighth to tenth day of lactation. Immunoglobulin concentrations at first milking were in the range 4–40 g/l milk and decreased to normal concentrations, in the range 0·3–0·5 g/l, by the fifth to seventh day of lactation. For both substances the data from each cow's milk fitted an exponential decay model. The fractional rates of decrease in concentration of carotene were 0·19–0·57/d and of immunoglobulin were 0·40–0·73/d. Breed-group differences were observed in both carotene and immunoglobulin concentrations in milks after the fourteenth day of lactation. In Jersey milks, the average carotene and immunoglobulin concentrations were respectively 18·5 μg/g milk fat and 0·32 g/l of milk, while in Friesian milks the concentrations were respectively 11·4 μg/g milk fat and 0·46 g/l milk. There was also a difference between breed groups in the daily rates of decrease of the immunoglobulin concentrations. The average rate of decrease for the Friesians was about 1·5 times the rate for the Jerseys.
352. Variations in the carotene and vitamin A contents of certain New Zealand butterfats
1. Chemical estimations of carotene and vitamin A in New Zealand butters from two of the principal butter-making districts of the North Island during the seasons 1935–6 show that the total vitamin A potency was fairly high. 2. There were seasonal variations apparently due to nutritional rather than physiological causes. The minimum values (33–37 i.u./g. butterfat) for total vitamin A were found in late summer (February) at the time when the pasture normally tends to dry up, while the peak values (42–53 i.u./g. butterfat) occurred in late winter and spring (July-October). The variations in vitamin A potency with season were in the opposite direction to the variations recorded in the literature for Europe and America. The difference is no doubt due to the practice of stall-feeding in these countries in contrast with the all-the-year-round grazing commonly practised on dairy farms in New Zealand. The spring flush of grass is also later in the season in Europe than in New Zealand. 3. The more deeply-coloured Jersey butterfat was only slightly richer in total vitamin A potency than Friesian butterfat. 4. Contents of carotene and vitamin A in the fat of colostrum were very high, but reached normal values within 4 or 5 days after parturition.
The Preparation and Nutritive Value of A.I.V. Silage for Dairy Cows
Summary The preparation by the A.I.V. method of two lots of alfalfa and one of soy bean silage, consisting respectively of 10, 17, and 11 tons, is described. The data show that the loss of nitrogen and of dry matter in the drainage juice amounted to 0.9 and 1.8 per cent respectively. There were marked changes in the distribution of nitrogen in the silage. Based on the total nitrogen, the water soluble nitrogen increased in the two lots of alfalfa silage from 31 to 45 per cent and from 15 to 40 per cent respectively, and from 20 to 35 per cent in the soy bean silage. Increases in amino nitrogen paralleled those of the water soluble nitrogen. Ammonia nitrogen also increased, but the absolute quantity was small. There was apparently no loss of carotene. Counts of the number of bacteria and determination of volatile acids and lactic acid showed that some fermentation took place in spite of the low pH of the silage. A double reversal feeding trial was conducted consisting of a six week fore-period, a seven week A.I.V. silage period, and a seven week after-period with ten dairy cows of various breeds in two groups of five each. No unusual changes were noted in milk production due to the feeding of A.I.V. silage. Spectroscopic analyses of the butterfat for carotene and vitamin A indicated a definite increase in these components with silage feeding. During the control period an average value of 4.2 micrograms of carotene per gram of butterfat was obtained and in the A.I.V. period the figure rose to 6.8. Vitamin A analyses showed an average value of 4.0 micrograms per gram of butterfat for the control period and a marked rise to 9.0 in the A.I.V. period. However, the values for carotene and vitamin A during the A.I.V. feeding were not as high as those previously found for pasture feeding. Increases in the carotene content of the blood plasma paralleled those in the butterfat. Balance studies on the carotene intake in the feed and output in the milk showed a corresponding increase in both of these factors with the inclusion of A.I.V. silage in the ration. Blood and urine analyses indicated that the high acid intake of the cows was neutralized by means which prevented any noticeable deleterious effects on the animals.