18 Impacts of supplementing sulfate vs. hydroxychloride sources of Cu, Mn, and Zn on heifer growth performance and physiology during feed restriction and high-starch challenge periods

Abstract This study evaluated the effects of supplementing different sources (sulfate vs. hydroxychloride) of Cu, Mn, and Zn during feed restriction and high-starch challenge periods on heifer growth performance and physiology. On d 0, Nelore heifers (n = 40) were stratified by body weight (BW = 238 ± 38 kg) and age (21 ± 1 mo), and individually allocated into 1 of 40 drylot pens. The study was divided: washout (d 0 to 27), nutrient surplus (d 28 to 55), nutrient restriction (d 56 to 83), and high-starch challenge (d 84 to 112). The washout period consisted of limit-feeding Tifton hay (2.5% of BW; DM basis) and providing free choice access to white salt only. On d 28, heifers were randomly assigned to receive protein DM supplementation (0.10 to 0.20% of BW) added with sulfate (SUL) or hydroxychloride (HYD) sources of Cu, Mn, and Zn (≥ 260, 200, and 960 mg of Cu, Mn, and Zn per kg of supplement DM) from d 28 to 112 (n = 20 heifers/treatment). From d 28 to 55, heifers were offered ad libitum Tifton hay. From d 56 to 83, heifers were limit-fed 50% of average hay DM intake consumed in the last 6 d of the previous phase (d 50 to 55). From d 84 to 112, each respective protein supplement was mixed with a starch-based total mixed ration (TMR). Heifers were gradually adapted to the starch-based TMR by increasing the concentrate DM amount while simultaneously decreasing the hay DM amount by 20% every 7 d (starting with 35% concentrate and 65% hay on d 84 and ending with 80% concentrate and 20% hay from day 106 to 112). Individual heifer shrunk BW were collected on d 0, 28, 56, 84, and 112, following 12 h of feed and water withdrawal. Effects of treatment × day and treatment were not detected (P ≥ 0.37) for heifer BW, average daily gain (ADG), and dry matter (DM) intake, except for ADG from d 28 to 56, which was less (P = 0.05) for SUL vs. HYD heifers (-0.21 ± 0.05 vs. -0.10 ± 0.05 kg/day, respectively). Effects of day, but not treatment × day and treatment (P ≥ 0.43), were detected for fecal pH, which remained relatively constant from d 0 to 84, and then decreased (P < 0.01) from 7.2 on d 84 to 5.8-6.0 on d 110. Overall, protein supplementation added with hydroxychloride sources of Cu, Mn, and Zn had minor positive effects on heifer growth performance immediately following a washout period, but did not improve heifer growth performance and fecal pH during nutrient restriction and high-starch challenge periods, compared with protein supplementation added with sulfate sources of same metals.