Effects of repeated cycles of feed intake shifts on growth, feed efficiency and endocrine profiles of wether lambs

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 m.o. old, 45 +/- 1.5 kg) received a control diet (50% concentrate, 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 (T4) decreased (P < 0.01) in locoweed-fed rams. Effects on serum AP and T4 remained constant in rams during the 21 d of locoweed feeding. Treatment with MUSE did not influence (P > 0.10) AP or T4. Locoweed-fed rams had reduced (P < 0.05) intake and body weight for the 2-wk period after locoweed feeding ended. The 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 administration 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 lower (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, serum 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 locoweed 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.

Semen traits and metabolic and gonadotropic hormone profiles in ram lambs treated with glucose

Two experiments were conducted to examine reproductive and endocrine responses of ram lambs to exogenous glucose. In Experiment 1, three ram lambs (6 mo of age) received 100 ml ip of saline (0.9%) daily and three animals received 50 g glucose (100 ml 50% dextrose) daily for 18 d. In Experiment 2, ten lambs (5 per group) were treated similarly for 10 d. Serum samples were collected intensively before and after GnRH treatment on the last day of both experiments. After 15 d of glucose treatment in Experiment 1, treated rams weighed 58 kg compared with 68 kg for the controls (P = 0.08). A similar numerical trend was observed in Experiment 2, suggesting that intraperitoneal glucose decreases feed intake. In both experiments, 50 g of glucose induced a rapid elevation in serum glucose to greater than 120 mg/dl compared with 70 to 80 mg/dl for the controls (P < 0.05). Serum insulin rose to over 6 ng/ml in both trials in lambs receiving glucose compared with values of about 2 ng/ml for the controls (P < 0.01). Serum growth hormone was not altered (P > 0.10) by glucose in either experiment and IGF-1 was similar (P > 0.20) between groups in Experiment 2. Although serum concentrations of prolactin tended (P = 0.14) to be reduced by glucose treatment (64 +/- 21 ng/ml) compared with that of the controls (120 +/- 21 ng/ml) in Experiment 1, the opposite trend (P = 0.20) was observed in Experiment 2. Serum thyroxine was elevated (P = 0.08) in glucose-treated rams compared with that in controls in Experiment 2 but triiodothyronine concentrations were similar (P > 0.80) between groups. In Experiment 1, area under the curve (AUC) for LH after a GnRH challenge tended (P = 0.14) to be greater in glucose-treated (1,351 units) than in control (999 +/- 139 units) animals. The AUC for FSH (Experiment 1) did not differ (P = 0.30) between groups. The LH AUC in Experiment 2 was about 2,500 units for both groups (P = 0.80). The AUC for testosterone in Experiment 1, was 5,452 and 2,597 (+/- 1051) units for rams treated with 0 and 50 g glucose/d (P = 0.13), but testosterone AUC in Experiment 2 was similar between groups (P > 0.70). No effect of exogenous glucose was evident in either experiment for semen traits. Results suggest that 50 g ip glucose daily for 10 or 18 d induced large increases in serum insulin but other metabolic and reproductive hormones were not greatly influenced.