Effects of zinc source and dietary concentration on serum zinc concentrations, growth performance, wool traits, and reproductive characteristics in developing rams

Authors: PAGE, CHAD - University Of Wyoming; VAN EMON, MEGAN - Montana State University; MURPHY, THOMAS - Montana State University; LARSON, CONNIE - Zinpro Corporation; BERARDINELLI, JAMES - Montana State University; MCGREGOR, IAN - Montana State University; Taylor, Joshua - Bret; STEWART, WHIT - University Of Wyoming

Submitted to: Animal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2019
Publication Date: 10/27/2019
Citation: Page, C.M., Van Emon, M.L., Murphy, T.W., Larson, C.K., Berardinelli, J.G., McGregor, I.R., Taylor, J.B., Stewart, W.C. 2019. Effects of zinc source and dietary concentration on serum zinc concentrations, growth performance, wool traits, and reproductive characteristics in developing rams. Animal. 14(3):520-528. https://doi.org/10.1017/S1751731119002180.
DOI: https://doi.org/10.1017/S1751731119002180

Interpretive Summary: Dietary zinc requirements for developing rams have been estimated to be 24 to 51 mg per kilogram of body weight per day. However, these estimated requirements were suggested nearly 30 years ago and have not been adjusted to account for greater growth performance and body size of current day rams found in the U.S. West. Therefore, we conducted an experiment to determine if the dietary form and “above-requirement” amounts of Zn fed to Targhee rams affects the rams’ Zn concentrations in the serum and seminal plasma, growth performance, wool traits, and reproductive performance. We found that above-requirement amounts of Zn improved ram daily growth, serum Zn concentration, wool staple length growth, and feed efficiency. Because beneficial effects of above-requirement dietary Zn were observed, we suggest that reevaluation of the estimated Zn requirements for growing rams is warranted. Furthermore, we suggest that producers that are raising yearling rams will benefit from increasing dietary zinc for their rams, especially in areas where locally produced forages and feedstuffs are low in dietary Zn.

Technical Abstract: The objectives of this study were to evaluate the effects of dietary zinc (Zn) source and concentration on serum Zn concentrations, growth performance, wool traits, and reproductive performance in rams. Forty-four Targhee rams (14 months [mo]; 68 +/- 18 kg body weight [BW]) were used in an 84-day (d) completely randomized design, and were fed one of three pelleted dietary treatments: 1) a control without fortified Zn (CON; n = 15); 2) a diet fortified with a Zn amino acid complex (ZnAA, Zinpro Corp; n = 14); and 3) a diet fortified with ZnSO4 (ZnSO4; n = 15). Growth and wool traits measured throughout the course of the study were average daily gain (ADG), dry matter intake (DMI), gain:feed efficiency (G:F), BW, loin muscle depth (LMD), back fat (BF), wool staple length (SL), and average fiber diameter (AFD). Blood was collected from each ram at four time periods to quantify serum Zn and testosterone concentrations. Semen was collected 1-2 d after the trial was completed. There were no differences in DMI (P = 0.18), BW (P = 0.45), LMD (P = 0.48), BF (P = 0.47), and AFD (P = 0.9) among treatment groups. ZnSO4 had greater (P = 0.03) serum Zn concentrations compared to ZnAA and CON treatments. Rams consuming ZnAA had greater (P = 0.03) ADG than ZnSO4 and CON. There tended to be differences among groups for G:F (P = 0.06), with ZnAA being numerically greater than ZnSO4 and CON. Wool staple length regrowth was greater (P < 0.001) in ZnSO4 and tended to be longer (P = 0.06) in ZnAA treatment group compared to CON. No differences were observed among treatments in scrotal circumference (P = 0.59), testosterone (P = 0.59), semen concentration (P = 0.24), % motility (P = 0.37), % live sperm (P = 0.90), and % sperm abnormalities (P = 0.23). These results indicate that the source and concentration of a Zn supplement appeared to improve ram development, specifically ADG, serum Zn concentrations, wool staple length regrowth, and there was a tendency to improve G:F. These results may be used to make sound management decisions when accounting for minerals with developing rams in Montana and other northern range lands.