L D Bunting

Growth and metabolic characteristics of Suffolk and Gulf Coast Native yearling ewes supplemented with chromium tripicolinate

Abstract An experiment was conducted to investigate differences in production and physiological criteria in yearling ewe lambs from two distinct breeds fed a concentrate–base diet (13.5% CP) supplemented with 0 (BAS) or 370 ppb (CRP) chromium tripicolinate. The breeds used were Suffolk (SFK, n=8, BW 58.9±1 kg), representing a breed selected for meat production, and Gulf Coast Native sheep (GCN, n=8, BW 44.9±1 kg), representing a breed selected for adaptability and wool production. Lambs were fed the BAS diet for 10 days. On day 0 of the experimental period, the lambs were stratified by BW within breed and randomly assigned to the experimental diets. On days 0, 11 and 22, after 18 h of feed deprivation, lambs were bled via jugular venipuncture and weighed. Moreover, on day 22, lambs were catheterized and an i.v. glucose tolerance test (IVGTT; 500 mg glucose kg−1 BW) was conducted. Statistical analyses of plasma metabolite and hormone measurements were conducted on their concentrations, as well as the relative changes (percent change) of these measurements for days 11 and 22 compared with day 0. Growth rate, feed intake and glucose and insulin kinetics in response to an IVGTT were not affected (P>0.10) by CRP. Relative to BAS, CRP decreased plasma NEFA concentration (P 0.10) plasma glucose, albumin, triacylglycerol or cortisol concentrations. CRP reduced plasma NEFA, but did not affect glucose kinetics. There were major differences in physiological measurements between the two distinct breeds of sheep that could explain the differences observed in performance.

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 conducted as a randomized block design with a 2x2 factorial arrangement of treatments. Lambs (77.4kg BW, n=24) were fed a total mixed ration (12.1-13.6% CP) with two levels of L-carnitine (0 or 250ppm) 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 3h post-feeding, and ruminal fluid samples were collected at 1h post-feeding, during days 1, 8, 29, and 50 of the experiment. Average daily gain (121 versus 214g) 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 2.8mmol/l), and plasma ammonia N (177.1 versus 49.5µmol/l) than lambs not fed NPN. Additionally, lambs fed the NPN diets had lower plasma urea N (14.5 versus 17.5mmol/l; P<0.003) and thyroxine (T(4)) concentrations (65.8 versus 78.4ng/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 3.70mmol/l). Two oral urea load tests (OULT 1 and OULT 2) were conducted during the 50-day trial. Urea solutions (0.835g/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.