Serum luteinizing hormone, testosterone, and thyroxine and growth responses of ram lambs fed locoweed (Oxytropis sericea) and treated with vitamin E/selenium

Sixteen ram lambs (5 mo old, 45 +/- 1.5 kg) received a control diet (50% co ncentrate, no locoweed, n=4), locoweed (20% locoweed for 21 d, n=4), MUSE ( 2 mL i.m. of MUSE containing 5 mg selenium and 50 mg vitamin E/mL, n=4) on Days 21 and 35([Day 0 = first day of trial]), or locoweed + MUSE (n=4). The rams were maintained in individual pens (3 x 9 m) with free access to feed , water, salt and shade. On Day 7 after initiating locoweed, serum alkaline phosphatase (AP) increased (P < 0.01), and serum thyroxine (T-4) decreased (P < 0.01) in locoweed-fed rams. Effects on serum AP and T-4 remained cons tant in rams during the 21 d of locoweed feeding. Treatment with MUSE did n ot influence (P > 0.10) AP or T-4. Locoweed-fed rams had reduced (P < 0.05) intake and body weight for the 2-wk period after locoweed feeding ended. T he MUSE regimen or diet had no effect on intake or body weight (P > 0.50). Neither locoweed nor MUSE affected serum LH before or after GnRH administra tion on Day 22 (P > 0.10). On Day 50, however, area under the LH curve (AUC ) was 966 units in locoweed-fed rams and 1,373 units (+/- 154) in controls (P = 0.09). Serum testosterone (T) was reduced in locoweed-fed rams before and after (P < 0.05) GnRH on Day 22. On Day 50, the T AUC was numerically l ower (P = 0.14) in locoweed-fed rams (1,252 units) than in controls (1,539 +/- 130 units). Conversely, MUSE treatment resulted in increased (P = 0.02) T AUC on Day 50 (1,148 and 1,643 +/- 130 units in control and MUSE-treated ram lambs, respectively). During the 6-wk period after locoweed feeding, s erum immunoglobulin G averaged 14.0 and 18.6 (+/- 1.1) mg/mL in control and locoweed- fed rams (P < 0.01), respectively. Twenty percent dietary locowe ed for 21 d exerts adverse effects on feed intake, growth, and reproduction in young ram lambs and MUSE was not effective in reversing these effects. (C) 1999 by Elsevier Science Inc.