Influence of dietary protein and supplemental niacin levels on lactational performance in cows fed normal and low fibre diets

Zimmerman, C.A.; Rakes, A.H.; Daniel, T.E.; Hopkins, B.A.

Journal of Dairy Science 74(Suppl 1): 218


ISSN/ISBN: 0022-0302
Accession: 002136924

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23 multiparous (MP) and 24 primiparous (PP) cows were randomly assigned to 1 of 4 normal fibre (NF) 20.5% ADF diets for wk 2-5 post partum. Dietary treatments were arranged in 2 x 2 factorial design with 2 levels of dietary protein (13.8 vs. 18.8% CP) and 2 levels of supplementary niacin (0 vs. 12 g/day). During wk 6-13 post partum, cows were given low-fibre (LF) 11.8% ADF diets while maintaining CP and niacin treatments. Low-protein diets contained soyabean meal while a rumen bypass-enhanced soyabean meal (ProtekReg.) was substituted in the high-protein diets. Chopped lucerne hay served as the forage source. During the NF period in PP cows, production (kg) of milk, 4%-FCM, protein, fat and SNF, as well as DM intake, were enhanced by high protein (P<0.01). Milk protein percentage in MP cows was higher (P<0.07) for cows on the high-protein diets during the NF period. There were no production effects attributable to niacin supplementation during the NF period in either parity group. When switched to LF diets, 4%-FCM yield increased on low-protein diets while decreasing on high protein (P<0.05) in PP cows. This same trend (P<0.08) occurred in PP cows given 0 g of niacin. In addition, milk fat production decreased more (P<0.06) on the high-protein diets. DM intake increased more on the low-protein diets than the high-protein diets (P<0.01) in PP cows during the LF period. There were no significant production differences due to treatments when MP cows were switched to the LF diets. High-protein diets improved lactational performance in PP cows.