Effects of L-carnitine on nitrogen retention and blood metabolites of growing steers and performance of finishing steers

Two experiments were conducted to evaluate L-carnitine supplementation to c attle fed grain-based diets. In Exp. 1, seven Angus-cross steers (216 kg) w ere used in a 7 x 4 incomplete Latin square experiment to evaluate the effe cts of supplemental L-carnitine on N balance and blood metabolites. Steers were fed a corn-based diet (17.5% CP) at 2.5% of BW. Treatments were 0, 0.2 5, 0.5, 1.0, 1.5, 2.0, and 3.0 gld of supplemental carnitine. The 18-d peri ods included 13 d for adaptation and 5 d for collection of feces and urine. Blood was collected before feeding and 3 and 6 h after feeding on d 18 of each period. Dry matter intakes tended to be highest when 1.5 g/d of carnit ine was supplied, but N retention was not affected by carnitine and average d 29.3 g/d. Plasma carnitine concentrations and urinary excretion increased with increasing carnitine supply, indicating that at least some of the car nitine escaped ruminal degradation and was absorbed by the steers. Plasma c oncentrations of NEFA demonstrated a treatment x time interaction; they dec reased linearly in response to carnitine before feeding but increased linea rly in response to carnitine at 6 h after feeding. Serum insulin and plasma glucagon, IGF-I, cholesterol, triglyceride, and amino acids were not affec ted by carnitine. Plasma concentrations of glucose, glycerol, urea, and bet a -hydroxybutyrate all were increased by some of the levels of carnitine su pplementation, but results for these measurements did not follow easily des cribed patterns and seemed to be related to differences in DMI. In Exp. 2, 95 crossbred steers (357 kg initial BW) were fed finishing diets (14.5% CP) for 129 d. Diets were based on steam-flaked corn and contained 6% alfalfa and 4% tallow. Feed intakes, gains, and feed efficiencies were not affected by supplementation with 2 g/d L-carnitine. However, steers receiving L-car nitine tended to have fatter carcasses, as indicated by tendencies (P < 0.2 ) for thicker backfat, higher marbling scores, and higher yield grades. In conclusion, carnitine supplementation did not alter lean deposition in grow ing steers but it did alter plasma NEFA concentrations of growing steers fe d a corn-based diet and also seemed to increase fat deposition in finishing cattle.