Extensive use of steroidal implants (NAHMS, 2013; Samuelson et al., 2016) has resulted in increased efficiency of growth and profitability in the beef feedlot industry (Duckett and Pratt, 2014). Steroidal implants increase Zn absorption and retention in lambs (Hufstedler and Greene, 1995) and lessen plasma Zn concentrations compared to non-implanted beef steers (Messersmith, 2018). These data indicate steroidal implants affect Zn metabolism in ruminants, potentially to support the rapid growth occurring in implanted animals. Therefore, strategic supplementation of Zn may optimize growth performance of cattle administered steroidal implants. The research studies discussed in this dissertation were designed to 1) determine the effects of increasing dietary Zn supplementation on the growth performance, carcass characteristics, and expression of genes related to steroidal implant function and Zn metabolism of non-implanted and implanted beef steers, 2) examine how increasing supplemental Zn concentrations influence performance, carcass characteristics, and markers of energy and protein metabolism in beef steers, 3) assess the effects of supplemental Zn on performance, carcass characteristics, and liver trace mineral concentrations of beef heifers administered an extended-release implant or a two-implant strategy, and 4) evaluate the effects of Zn source on the performance, carcass characteristics, and plasma and tissue trace mineral concentrations within non-implanted and implanted beef steers. Through our first research objective, increasing supplemental Zn, as ZnSO4, up to 5 times the NASEM (2016) recommendation linearly increased steer performance and gene expression of steroidal implant signaling proteins in the muscle during peak hormonal payout of a high potency implant but did not influence these parameters in non-implanted steers. During this period implanted steers had 6% lesser plasma Zn concentrations than non-implanted steers, suggesting steroidal implant-induced growth influences Zn metabolism to accommodate high growth rates. Within our second research objective, increasing Zn supplementation, as ZnSO4, up to 6 times the NASEM (2016) recommendation linearly increased growth during peak hormonal payout of the steroidal implant, but had minimal effects on beta agonist period ADG. Similarly, liver Mn concentrations were correlated with liver arginase activity and ADG directly following implant administration, but not during beta agonist supplementation. These data indicate Zn's effects on growth, in combination with steroidal implants, influence protein degradation. Through our third research objective, beef heifers supplemented consultant-recommended concentrations of Zn (100 mg Zn/kg dry matter from ZnSO4; Samuelson et al., 2016) were 7 kg heavier than heifers supplemented NASEM (2016; 30 mg Zn/kg dry matter from ZnSO4) recommendations of Zn during peak hormonal payout of the extended-release implant and two-implant strategies. Although no differences in final performance were noted between implant strategies, interim period ADG of heifers corresponded to peak hormonal payout of each implant. These data suggest greater supplementation of Zn is beneficial to the growth of heifers administered either an extended-release implant or two-implant strategy and that these implant strategies are equally effective. Finally, our fourth research objective revealed implanted steers were 45 kg heavier than non-implanted steers at the end of the trial. However, an interaction between implant and Zn source (100% ZnSO4 or 70% ZnSO4 + 30% basic ZnCl or Zn glycinate) was observed in final body weight (BW) where steers supplemented 100% ZnSO4 tended to be heavier than those supplemented a basic ZnCl blend, but not heavier than steers receiving the Zn glycinate blend. No differences in final BW due to Zn source were observed within non-implanted steers. These data suggest steroidal implants influence Zn metabolism resulting in BW differe
展开▼
