Studies of the secretion of milk of low fat content by cows on diets low in hay and high in concentrates. IV. The effect on the physical and biochemical processes of the reticula-rumen
Balch, C.C.; Balch, D.A.; Bartlett, S.; Bartrum, M.P.; Johnson, V.W.; Rowland, S.J.; Turner, J.
Jour Dairy Res 22(3): 270-289
Two Shorthorn cows with rumen fistulas were used to investigate the effect of diets high in concentrates and low in hay on the physical and bio- chemical processes of the reticula-rumen. The experimental period was 27 weeks divided as follows: weeks 1-7 cows fed 16 lbs. hay and 20 lbs. concentrates daily, weeks 8-13 the hay was reduced to 2 lbs. and the concentrates increased to 24 lbs. daily, weeks 14-19 cows fed as in 8-13 with the addition of 5 lbs. of straw pulp and concentrates reduced to 20 lbs. daily in week 15, weeks 20-21 the straw pulp was removed with the diet being 2 lbs. hay and 20 lbs. concentrates, weeks 22-27 diet changed to 18 lbs. hay and 10 lbs. concentrates. Milk fat content was reduced very markedly during the low hay period. Digestibility of the fibrous feed fractions was lower during the low hay period. Rate of passage of undigested residues of hay was abnormally slow during the low hay period. Rate of reticular movements was slower, except during eating, in the low-hay period and there was a reduction in the time spent ruminating. The pH and concentration of organic acids fluctuated more widely (less buffering) when fed the low hay ration. The proportion of total volatile acids represented by acetic acid fell from 50% in the control period to 33% in the low-hay period. Inasmuch as acetate is a precursor of milk fat and a source of energy to the mammary gland it seems probable that low milk fat secretion may be due to acetate deficiency.