43. Effects of Chromium Propionate Supplementation on Performance, Ovarian Follicle Diameter, and Puberty Attainment in Replacement Angus Heifers.

Abstract This study evaluated the effects of chromium propionate (CrP) supplementation on growth performance, ovarian follicle diameter, and puberty attainment in replacement Angus heifers over a 138-d period. Thirty-four heifers were stratified by age and body weight (BW) and randomly assigned to one of two treatments: 1) supplementation with dried distillers’ grains plus a commercial mineral mix at 0.91 kg·hd⁻¹·d⁻¹ (CON; n = 17); or 2) the same supplementation including 10 g of CrP (CrP; n = 17; KemTRACE® Chromium 0.04%, Kemin Industries, Inc., Des Moines, IA). Heifers were maintained on a single pasture equipped with SmartFeed® bunks (C-Lock Inc., Rapid City, SD) to monitor individual supplement intake. Body weight was recorded on days 0 and 138 following a 16-h feed and water withdrawal, and average daily gain (ADG) was calculated as the difference between final and initial BW divided by the number of days. Blood samples were collected every 7 d to determine plasma progesterone concentrations, and puberty attainment was defined as progesterone ≥ 1 ng/mL in two consecutive samples. Heifers were subjected to an estrus synchronization protocol consisting of gonadotropin-releasing hormone (GnRH) administration and controlled internal drug-releasing (CIDR) insertion (day −18 of the synchronization protocol). On day −9, prostaglandin F₂α (PGF) was administered and the CIDR was removed. Forty-eight hours later, a second GnRH injection was administered with CIDR reinsertion. On day −2, PGF was administered and the CIDR was removed. Ovarian ultrasonography was performed on days −2 and 0 to measure the diameter of the largest follicle. Data were analyzed using the GLIMMIX and MIXED procedures of SAS, with heifer as the experimental unit and treatment as a fixed effect. As designed, age and initial BW did not differ (P > 0.90) between treatments (9 ± 0.11 mo; 227 ± 6.26 kg). Supplement intake was also similar (P = 0.13) between treatments (0.67 and 0.73 kg·hd⁻¹·d⁻¹ for CON and CrP, respectively). Heifers supplemented with CrP tended to have greater final BW (P = 0.07; 326 vs. 311 ± 5.62 kg) and ADG (P = 0.07; 728 vs. 621 ± 40.5 g) compared with CON heifers. Additionally, CrP heifers had a greater (P = 0.05) diameter of the largest follicle (12.1 vs. 11.0 ± 0.36 mm). However, no treatment effects were observed (P = 0.34) for puberty attainment. In summary, CrP supplementation tended to improve growth performance and increased ovarian follicle diameter but did not affect puberty attainment.