231 Ovarian follicle diameter and corpus luteum volume of beef cows enrolled in fixed-time artificial insemination while receiving chromium propionate supplementation

Abstract We investigated the effects of chromium propionate (CrP) supplementation on reproductive performance of beef cows during the pre-partum and breeding periods. Angus-based commercial suckled beef cows were stratified by predicted calving date, body weight (BW) and randomly assigned to one of two treatments: 1) Control, (n = 30) supplementation of a corn gluten, soy hull pellet feed (50:50) with a mineral pack at 1 kg ּ cows-1 d-1; or 2) CrP, (n = 32) supplementation at 1 kgּ cow-1ּּ d-1 of a corn gluten, soy hull pellet feed (50:50) with a mineral pack containing 1.4 g of CrP (KemTRACE chromium 0.4%, Kemin Industries, Inc., Des Moines, IA). Cows remained on a single pasture equipped with feed bunks capable of monitoring individual supplement intake (SmartFeed, C-lock Inc., Rapid City, SD). Treatments were initiated at 92 d prepartum and ended on d 35 post fixed-time artificial insemination (TAI), for a total of 127 d. Cows were enrolled in the 7-d CO-Synch+CIDR TAI protocol. Ovarian ultrasonography was performed to determine diameter of the largest follicle, and the volume of a corpus luteum (CL) on d -10, -3, 0 (TAI day), and 7. Pregnancy diagnosis was performed by ultrasonography on d 35. Cow BW was recorded on d -92, 0, and 35. Data were analyzed using the GLIMMIX and MIXED procedures of SAS with cow as the experimental and fixed effect of treatment. Age, days postpartum, and initial BW were similar (P > 0.05) between treatments (7.4 and 7.2 ± 0.61 yr, 81.3 and 80.8 ± 4.61 d, 526.2 and 528.6 ± 16.21 kg for Control and CrP, respectively). Supplement intake was similar (P = 0.534) between treatments (1.22 and 1.03 gּ cow-1ּּ d-1, for Control and CrP, respectively). Cow BW was similar (P > 0.05) between treatments on d 0 and 35 (548.5 and 551.4 ± 13.50 kg, 562.8 and 574.6 ± 11.41 kg, for Control and CrP, respectively). Furthermore, estrus expression and TAI pregnancy rate was similar (P > 0.05) between treatments (62.1 and 61.1 ± 1.2% estrus, 55.1 and 81.2 ± 20.1% TAI pregnancy rate, for Control and CrP, respectively). However, CrP cows had a larger follicle (P = 0.028) on d 0 (13.79 and 15.56 ± 0.58 mm, for Control and CrP, respectively). Additionally, on d 7, CrP cows had an increased (P = 0.038) CL volume (15.24 and 17.55 ± 0.68 mm3, for Control and CrP, respectively). Supplementation of CrP to beef cows from the pre-partum until breeding did not change cow BW, but increased follicle diameter at TAI and subsequent CL volume.