Growth and metabolic responses of Holstein calves fed broiler litter-based diets supplemented with L-carnitine

Thirty-nine growing Holstein calves (150.1 +/- 5.5 kg) were used to determine the effects of adding 3-hydroxy-4-N-trimethylaminobutyric acid (L-carnitine) to diets containing excess crude protein, derived primarily from poultry litter, on growth performance and blood and rumen metabolites. Calves were blocked by body weight (BW) and fed one of the three experimental diets: (1) protein control diet (PC; 17.3% crude protein (CP)), 46.5% corn-soybean meal, 53.5% cottonseed hulls-hay, (2) broiler litter (BL; 22.7% CP), 55% broiler litter, 23% corn and soybean meal, 22% cottonseed hulls-hay, and (3) diet 2 + 250 PPM L-carnitine (BL + Q. Calves were catheterized and intravenous (i.v.) glucose tolerance tests (IVGTTs) were conducted on the final day of the experiment. Mean dry matter intake, average daily gain (ADG), and gain: feed ratio through 42 days were higher (P < 0.05) in calves fed PC compared with those fed BL and BL + C. Calves fed supplemental L-carnitine had an 8% higher (P = 0.003) efficiency of feed conversion. Total rumen volatile fatty acid (VFA) concentrations were higher (P = 0.02) in calves fed the PC compared with those fed the two BL diets (58.2 versus 49.7 mM); however, supplemental L-carnitine did not alter VIA concentrations in calves fed BL. Plasma ammonia N did not differ among treatments. Plasma urea N concentrations were lower (P < 0.01) in calves fed the PC, compared with those fed the BL diets, on both days 21 and 42 of the study. Although similar at day 2 1, plasma urea N concentrations in samples collected at day 42 were lower (P = 0.01) in calves fed BL + C compared with those fed BL (15.22 versus 19.15 mM). Both plasma glucose concentrations and glucose clearance rate were higher (P < 0.05) in calves fed the PC compared with those fed the broiler litter diets. Supplemental L-carnitine did not affect blood glucose concentrations or glucose clearance rate in calves fed diets containing broiler litter. Results suggest that supplemental L-carnitine may improve performance of calves fed excess levels of soluble protein. (C) 2002 Elsevier Science B.V. All rights reserved.