INFLUENCE OF SUPPLEMENTAL PROTEIN-SOURCE AND FEEDING FREQUENCY ON RUMEN FERMENTATION AND PERFORMANCE IN DAIRY-COWS

Multiparous Holstein cows in early lactation were fed a basal mixed ra tion of 4% (DM) alfalfa and timothy silage and 53% barley and com conc entrate twice daily for ad libitum intake at 1630 and 0600 h. Two supp lemental protein sources that differed in their resistance to rumen pr oteolysis were fed at 9% of total DMI in either two meals per day at 1 730 and 0700 h or five meals per day at 1730, 2130, 0200, 0700, and 12 00 h. 'rhe study was a 4 x 4 Latin square design with six blocks of 4 cows in which one block of cows was fitted with rumen cannulas. Intake s of DM, OM, NDF, and CP were not influenced by treatments. However, c ows supplemented with five meals a day tended to consume the mixed rat ion more rapidly after both the p.m. and a.m. feedings. Milk yield and its content of protein, fat, and lactose also were not influenced by treatments. Average rumen pH was higher, and propionate concentrations were lower, for cows supplemented with five meals, but diurnal patter ns were not influenced. Propionate and rumen ammonia N concentrations were lower for cows supplemented with the more resistent protein sourc e; however, rumen VFA, as well as soluble and peptide N concentrations , were not influenced by the type of supplemental protein. Results do not support benefits of synchronized rumen release of energy and N to overall cow production, but rather support previous research that solu ble protein or peptide N, or both, may act as a pool to provide N for microbial growth at times of the day when ammonia N concentrations are very low.