| Abstrakt: |
The objective of this study was to investigate the effects of feeding endophyte-infected tall fescue seeds on ADG (kg/d) and activities of hepatic cytochrome P450 1A, 2C, 3A, aldo-keto reductase 1C, and Uridine 5'-diphospho-glucuronosyltransferase (UGT). Twelve Angus steers of 181 d of age and an average pre-weaning weight of 194.6 kg were blocked by initial BW at weaning. A control (KY32 or E–) and a treatment (KY31 or E+, 20 µg of ergovaline per kg of BW) were randomly assigned to animals within blocks (n= 6) by using Calan gates in two trials of 70 (summer 2015) and 56 d (winter 2016). Body weight was recorded on d 0 and every 14 d. Liver biopsies were collected before each trial and on d 3. Proteins in the S9 fractions were extracted into phosphate buffer and diluted to a concentration of 4000 μg/mL. Enzyme activity (RLU/min/mg of protein) was determined by a Promega Multi-Plus plate reader (Madison, WI) after incubation with specific substrates and detection reagents. Statistical analysis was performed by the GLIMMIX and FACTOR procedures of SAS 9.4 (SAS Institute Inc., Cary, NC) with statistical significance being determined at P≤ 0.05. In trial 1, E+ steers gained 0.323 kg/d less than E- steers (P= 0.013) between d 28 and d 70. Cytochrome 2C activity differed initially (P= 0.042) but did not on d 3 (P= 0.675). Cytochrome 1A and 3A activities were correlated (r= 0.621, P= 0.042). In trial 2, no treatment effect on ADG was found (P= 0.435). From d 28 to d 56, ADG increased consistently from 0.567 to 1.393 kg/d, whereas ADG remained similar (P> 0.392; 0.539 to 0.574 kg/d) in trial 1. Only initial UGT activity was 42% greater in E+ steers in trial 2. Cytochrome 1A and 2C activities were correlated (r= 0.912, P =0.002). Other enzyme activities were similar in both trials (P> 0.180), and no treatment × d interaction on ADG was found (P> 0.142). Principal component analysis indicated that the activities of 1A, 2C, 3A, and 1C explained 65.88 to 66.41% of enzyme activity variances, whereas UGT activities explained the rest of the variances on d 3. Correlation coefficients of these two groups of enzymes with each principal component confirmed that they acted in separate pathways. |
