Effects of Dietary Crude Protein Level on Growth Performance and Blood Parameters of Holstein Heifers and Steers Fed Ad Libitum

摘要

Two levels of dietary CP on growth performance, feed efficiency and blood parameters of Holstein heifers and steers were examined. Experimental diets consisted of 12 and 16% CP along with 2.5 Mcal kg 1 of ME (DM basis). Ratios of CP: ME were 49 and 64 g/Mcal for 12 and 16% CP containing diets, respectively. Eight animals were assigned to each experimental diet in a 2X2 factorial arrangement of completely randomized design for 8 wk period. Diets containing 48% corn silage and 52% concentrate (DM basis) were fed twice daily in a total mixed ration. Intake of DM was higher for 12% CP (11.0 kg d 1) compared to 16% CP containing diet (7.7 kg d 1) across the groups. There was a higher BW gain for steers (1.27 kg d 1) compared to heifers (0.99 kg d 1) but no significant dietary CP level difference was observed for BW. Feed efficiency was higher for 16% CP (0.17) compared to 12% CP containing diet (0.11). There was no significant difference detected for serum urea N (8.6 mg dL 1) and creatinine (1.1 mg dL 1) concentrations between treatment groups. Data indicates that heifers during the growth period responded to 12% dietary CP better than 16% CP based on higher BW gain (1.16 kg d 1) and lower serum urea N concentration (8.3 mg dL 1). In steers, no difference in BW gain but higher feed efficiency (0.17 vs. 0.11) made 16% CP containing diet more preferable than 12% CP during the growth period.