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

Abstract

The influence of supplemental l-carnitine was investigated in growing sheep fed rations containing non-protein nitrogen (NPN). The experiment was conducted as a randomized block design with a 2×2 factorial arrangement of treatments. Lambs (77.4 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. Jugular blood samples were collected at 0, 1, and 3 h post-feeding, and ruminal fluid samples were collected at 1 h post-feeding, during days 1, 8, 29, and 50 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 μmol/l) than lambs not fed NPN. Additionally, lambs fed the NPN diets had lower plasma urea N (14.5 versus 17.5 mmol/l; P<0.003) and thyroxine (T 4) concentrations (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 higher ( P<0.05) in lambs fed l-carnitine (3.83 versus 3.70 mmol/l). Two oral urea load tests (OULT 1 and OULT 2) were conducted during the 50-day trial. 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 were 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-carnitine 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 NPN and l-carnitine groups, but did not differ ( P>0.10) from the control group. 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.