The effect of concentrates of high or low starch equivalent, both fed at two levels, on the milk production of dairy cows

Abstract

1. In a winter feeding trial, using eight Ayrshire cows, two concentrates with digestible crude protein contents of 15% and starch equivalents of 63 and 79 were each fed at 2·6 and 4·6 lb./gal. of milk.2. The basal ration was hay, silage, dried grass and fodder-beet.3. Milk yield was significantly increased from 30·9 to 34·7 lb./day when the amount of concentrate fed increased from 2·6 to 4·6 lb./gal., but the average milk yields when the concentrates low in starch equivalent were fed did not differ significantly from those obtained when the concentrates high in starch equivalent were fed at the same levels.4. The fat content of the milk was similar on all four rations with an average value of 3·84%, whereas the solids-not-fat varied from 8·53% on the low starch concentrate fed at the lower rate to 8·77% on the high starch concentrate fed at the higher rate.5. The cows which were fed at the rate of 4·6 lb./gal. were significantly heavier by an average of 33 lb./cow than the ones fed at the rate of 2·6 lb./gal. The two different qualities of concentrate did not cause differences in live weight.6. The weight of dry matter in the basal ration consumed per day was similar on all four treatments.7. A comparison of feeding costs and the value of the milk showed that the largest margin was obtained with the low starch equivalent concentrate fed at the rate of 2·6 lb./gal.8. It was concluded that because of the loss in live weight on the lowest level of feeding, and because the quality of the concentrate gave no improvement in milk yield or liveweight and little improvement in milk composition, the optimal level of feeding in this experiment was 4·6 lb./gal. of the low starch equivalent concentrate.