Effects of Zinc Source and Level on Performance, Carcass Characteristics, and Metabolic Hormone Concentrations of Growing and Finishing Lambs

Twenty-eight days after weaning, 16 Debouillet wethers (average BW = 27 kg) were assigned to one of four treatments (four lambs per treatment) to examine effects of supplemental Zn on growth, carcass characteristics, and metabolic hormones. Experimental diets were: Basal (60% concentrate, 14.1% Cp, 30 mg/kg of supplemental Zn [B]); Basal + 35 mg/kg of Zn from ZnSO₄ (LZn); Basal + 70 mg/kg of Zn from ZnSO₄ (HZn); and Basal + 35 mg/kg of Zn from Zn Met. Lambs were maintained in individual pens in an indoor facility (14 h light: 10 h dark) with ad libitum access to feed and water. Serum samples were collected via jugular venipuncture on d 7,28, and 56. On d 62, lambs were slaughtered and carcass data and cut-out information were recorded. A 5- cm section of lean was collected from the 12th rib. Lamb BW, gain, feed intake, and feed efficiency did not differ (P>.10) among treatments on d 0,27, and 55. No differences were detected (P>.10) among treatments for serum insulin, insulin-like growth factor-I, and thyroxine. Serum growth hormone was greater (P<.10) 1 h after feeding for lambs fed the Zn Met diet than for those fed the B, LZn, and HZn diets. Serum prolactin concentrations were greater (P<.10) in lambs fed Zn Met at 1 and 5 h after feeding than in lambs fed B, and values were greater (P<.10) with Zn Met than with the other three treatments at 6 h after feeding. Similar (P<.05) results to those with prolactin were detected at 6 h after feeding with serum triiodothyronine. Alkaline phosphatase activity was increased (P< .10) on d 28 in lambs fed Zn Met compared with lambs fed the B and LZn treatments. On d 56, lambs fed the LZn, HZn, and Zn Met diets had greater (P<.05) alkaline phosphatase activity than those fed B. Carcass measurements and lean tissue composition were not altered (P> .10) by supplemental Zn. These data suggest that Zn Met at the concentration fed increased serum growth hormone, prolactin, and triiodothyronine after feeding. Zinc status of the lambs seemed to be improved by Zn supplementation in excess of requirements, as indicated by increased alkaline phosphatase activity.