Return to estrus following the postpartum interval to achieve pregnancy success on time is a considerable obstacle for beef females. Chromium supplementation increases available glucose and insulin sensitivity within cells. Two experiments were conducted to investigate the effects of supplementing Chromium propionate (CrP) during the peripartum until weaning on productive and reproductive performance in Bos taurus beef cows. In Exp. 1, 62 Angus-based beef cows were stratified by predicted calving date, body weight (BW) and randomly assigned to one of two treatments: 1) CON, (n=30) supplementation of corn gluten, soy hull pellet feed (50:50) with a mineral pack at 1 kg -1hd-1d; or 2) TRT, (n=32) supplementation at 1 kg -1hd-1d of corn gluten, soy hull pellet feed (50:50) with a mineral pack containing 1.4 g of Chromium Propionate (KemTRACE® Chromium 0.4%, Kemin Industries, Inc., Des Moines, IA). Cows remained on a single pasture equipped with SmartFeed trailers for individual supplement intake (SmartFeed®, C-lock Inc., Rapid City, SD). The experiment lasted 98 days, starting 63 days pre-breeding to 35 post-fixed-time artificial insemination (TAI). Ovarian ultrasonography was performed on days -10, -3, 0 (TAI Day), and 7 to determine the diameter of the largest follicle and corpus luteum (CL) volume. Age, days postpartum (DPP), initial and final BW, and supplement intake were similar (P>0.05) between treatments. However, TRT cows had a larger follicle (P=0.028) on d 0, increased CL volume (P=0.038), and increased (P=0.0213) circulating progesterone (P4) on day 7. In Exp. 2, 953 beef cows across nine locations were assigned to one of two treatments: 1) CON, supplementation of a mineral product at 113 g -1hd -1d (n=464 cows; 16 experimental units); or 2) TRT, supplementation of mineral product at 113 g -1hd -1d containing 1.4 g of CrP n=489 cows; 16 experimental units). Supplementation started approximately 37 days pre-calving and continued until weaning for 345 days. Age, DPP, d-10 body condition score (BCS), initial and final BW, BCS, calf birth and weaning weight, and mineral disappearance were similar (P>0.05) between treatments. However, CrP cows tended (P=0.081) to have greater estrus expression (68.3 and 60.2 ± 3.1 %, for CrP and CON, respectively) and greater (P=0.045) TAI pregnancy rates (55.2% vs. 49.9% ± 2, for CrP and CON, respectively). We conclude that supplementation of CrP to beef cows during the peripartum through weaning did not affect BW or BCS, but increased ovulatory follicle diameter, estrus expression, CL volume, and P4 concentration, and one or more of these positive effects of CrP likely contributed to the improvement in TAI pregnancy rate. / Master of Science / Reproductive efficiency in beef cow-calf operations relies heavily on pregnancy success as early in the breeding season as possible. Several factors influence the return to cyclicity after calving, including days post-calving, body condition, and nutritional status of the dam. Chromium is an essential trace mineral that can be added to cattle diets to promote glucose uptake by cells and mitigate the negative impacts of the stressful postpartum period. Two studies were designed to evaluate the effect of chromium propionate supplementation to beef cattle during the pre-calving through weaning period on reproductive parameters and overall cow performance. In experiment one, 62 cows were assigned to two treatment groups: control (feed containing a standard mineral pack) and treatment (feed containing 1.4g of chromium propionate supplementation). The second experiment included 953 cows assigned to one of two treatment groups: control (supplementation of free choice mineral product) and treatment (supplementation of free choice mineral containing 1.4 grams of chromium propionate). Both groups in experiment two had the same target feed intake. In both experiments, beef females were exposed to estrous synchronization and timed artificial insemination and were exposed to a bull for natural service in the next estrous cycle. Cows receiving the chromium supplementation did not experience any changes in body condition score, weight change, or average daily gain in either experiment. However, reproductive performance was affected by chromium-supplemented cows had an increased dominant follicle size on the day of timed-artificial insemination (TAI), larger corpus luteum volume 7 days post artificial insemination, increased progesterone concentrations, and increased progesterone to corpus luteum ratio in experiment 1. Supplementation of Cr in experiment 2 tended to increase estrus expression and showed an increase in the pregnancy rate of TAI. Calf performance was not impacted by chromium propionate supplementation. These results indicate that chromium propionate supplementation could benefit the reproductive performance of beef cows.

Doctor of Philosophy / Department of Animal Sciences and Industry / James S. Drouillard / Four studies evaluated effects of mineral supplementation on feedlot performance, carcass characteristics and ruminal fermentation of finishing cattle. Study 1 supplemented 0 or 3.3 g/d yeast combined with Cr propionate to steers separated into light and heavy groups. No treatment x weight group interactions were observed for ADG, DMI, final BW, carcass traits, or plasma glucose of lactate concentrations (P ≥ 0.06). A treatment x weight group interaction was observed for G:F (P = 0.03). In study 2, steers were supplemented 60 or 300 mg Zn/kg DM with or without zilpaterol hydrochloride (ZH). No interactions or effects of Zn or ZH were observed for IGF-1, plasma glucose, or lactate concentrations (P > 0.05). Plasma urea nitrogen (PUN) concentration decreased with ZH (P < 0.01). No interactions or effects of Zn or ZH were detected for ADG, DMI, final BW, G:F, and carcass traits were minimally affected (P ≥ 0.05). Study 3 evaluated effects of supplementing 30 or 100 mg Zn/kg DM (30 or 100Zn) with and without ractopamine hydrochloride (RH; 200 mg/d). No interactions or effects of Zn were observed for feedlot performance or PUN (P ≥ 0.07). Final BW, ADG, and HCW increased when heifers were fed RH (P ≤ 0.02). Zinc x RH interactions were observed for LM area and yield grade (P ≤ 0.01), but other carcass traits were not affected (P ≥ 0.08). In study 4, heifers were supplemented 0, 30, 60, or 90 mg Zn/kg DM. Zinc supplementation did not affect final BW, ADG, or DMI (P ≥ 0.07), but G:F increased linearly (P = 0.02). Carcass traits were not affected by Zn supplementation (P ≥ 0.07). Effects of in vitro Zn titration (0, 30, 60, 60, 90, 120, or 150 mg/kg Zn) were evaluated using ground corn and soybean meal as substrate. In vitro fermentation was not affected by added Zn (P ≥ 0.05). These studies suggest Cr and Zn supplementation minimally affected carcass traits, but Zn supplementation up to 60 mg/kg improved feed efficiency with minimal impact on ruminal fermentation. Supplementing increased Zn concentrations may alter fat and muscle deposition when fed with RH.