Effect of a Highly Fortified Vitamin-Mineral Supplement in High- and Low-Concentrate Rations for Dairy Cows

Sixteen high-producing Holstein cows were used in a ll2-day continuous feeding trial to study the effect of feeding a highly fortified vitamin-mineral supplement with 15:85 and 60:40 hay-concentrate ratios on milk yield and composition, conversion of total digestible nutrients (TDN) to fat-corrected milk (FCM), and digestibility of the rations. The cows fed the supplemented lowconcentrate ration maintained their level of FCM production significantly (P < .05) better than those receiving the nonsupplemented low-concentrate ration; however, supplementation showed no advantage with the high-concentrate ration. The change in FC}[ production over the experimental period was not significantly different between the high-and low-concentrate rations. The conversion of TDN to FCM was significantly (P < .01) greater for the highconcentrate rations than for the low-concentrate rations; however, the average TDN intake from the high-concentrate rations was 16.7% less than that from the low-concentrate rations. Supplementation had no effect upon conversion o~ TDN to FCM. The milk fat percentage decreased markedly during the first 4 wk for the high-concentrate rations but increased during the remainder of the trial to a level comparable with that of the low-concentrate rations. There were no significant differences between TDN coefficients of the rations due to supplementation or hay-concentrate ratio.