Influence of dietary carnitine in growing sheep fed diets containing non-protein nitrogen

The influence of supplemental L-carnitine was investigated in growing sheep fed rations containing non-protein nitrogen (NPN). The experiment was cond ucted as a randomized block design with a 2 x 2 factorial arrangement of tr eatments. Lambs (77.3 kg BW, n = 24) were fed a total mixed ration (12.1-13 .6% CP) with two levels of L-carnitine (0 or 250 ppm) and two levels of NPN (urea contributing 0 or 50% of total dietary N) for a 50-day period. Jugul ar blood samples were collected at 0, 1, and 3h post-feeding, and ruminal f luid samples were collected at Ih post-feeding, during days 1, 8, 29, and 5 0 of the experiment. Average daily gain (121 versus 214 g) was lower (P <0. 0001) in lambs fed the NPN diets. Lambs consuming diets containing NPN had higher (P < 0.0001) ruminal fluid pH (6.6 versus 5.9), ruminal ammonia N (4 .8 versus 2.8 mmol/l), and plasma ammonia N (177.1 versus 49.5 mu mol/l) th an lambs not fed NPN. Additionally, lambs fed the NPN diets had lower plasm a urea N (14.5 versus 17.5 mmol/l; P < 0.003) and thyroxine (T-4) concentra tions (65.8 versus 78.4 ng/ml; P <0.02), and lower T-4:triiodothyronine (T- 3) ratio (37.9 versus 43.9; P <0.02). Plasma glucose concentrations were hi gher (P < 0.05) in lambs fed L-carnitine (3.83 versus 3.70 mmol/l). Two ora l urea load tests (OULT 1 and OULT 2) were conducted during the 50-day tria l. Urea solutions (0.835 g/kg(0.75) BW) were administered as oral drenches. During the OULT 1 (day 10), plasma ammonia N and glucose concentrations we re highest (P <0.0001) in the lambs fed NPN with L-carnitine compared with lambs fed control, L-carnitine, and NPN diets. During the OULT 2 (day 50), plasma ammonia N was highest (P < 0.0001) in the NPN and NPN with L-carniti ne groups compared with the control and L-carnitine groups. Plasma glucose was lowest (P < 0.04) in the NPN with L-carnitine group compared with the N PN and L-carnitine groups, but did not differ (P > 0.10) from the control g roup. Plasma urea N levels in both OULT 1 and OULT 2 were lower(P <0.0001) in the NPN and NPN with L-carnitine groups compared with the control and L- carnitine groups. In the present experiment, production and plasma criteria were affected by NPN incorporation in the diets. Production criteria were not affected by inclusion of L-carnitine in the diet, however, L-carnitine reduced experimentally induced hyperammonemia by day 50 of the trial. (C) 2 001 Elsevier Science B.V, All rights reserved.