Effects of Synovex® C and H growth implants administered to beef heifers post-weaning on subsequent ovarian activity and fertility during their vrgin breeding season

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2019-08

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Abstract

The objective of this study were to examine the influence of growth promoting implants on replacement heifer fertility when administered post-weaning. Three treatments were applied: 1) Non-implanted control (NIC; n=4), 2) Synovex-C [10 mg of estradiol benzoate and 100 mg of progesterone, Zoetis, Florham Park, NJ] (SYNC; n = 6), and 3) Synovex H [200 mg testosterone propionate and 20 mg estradiol benzoate, Zoetis, Florham Park, NJ] (SYNH; n = 5). Heifers were implanted post-weaning (mean age = 234 d) and managed in the same pen continuously through the entire duration of the study. Heifers were provided ad libitum native grass hay and limit fed a grower ration targeted to achieve 0.85 kg per day of body weight (BW) gain in order to allow heifers an opportunity to reach puberty prior to the start of their virgin breeding season. Individual BW were collected on d 0, 28, 56, 84, 112, 140, and 197. Prior to ovarian scanning, heifers were synchronized via a 5-d CO-synch + CIDR protocol. Ten days following synchronization, heifers were administered an additional injection of GnRH to restart ovarian follicular growth. Subsequently, transrectal ultrasonography was performed daily to quantify ovarian activity dynamics through spontaneous ovulation and then again 7-d later to document the resulting corpus luteum (CL) size. Plus, daily coccygeal blood samples were acquired for progesterone analysis from spontaneous ovulation through the 7-d CL scan. Data was analyzed as a generalized randomized block design with implant treatment as a fixed effect and age at implantation as a covariate. Heifers were assigned blocks based on light and heavy BW groups. Overall, the implanted heifers had an increased rate of BW gain for the entire trial (P ≤ 0.03) and a substantial increase in pelvic area (P < 0.01). There were no differences observed between treatments in hip height (P = 0.19), frame score (P ≥ 0.19), body condition score (P ≥ 0.23), or reproductive tract score (P ≥ 0.25). Average overall antral follicle counts were not different across treatments (P = 0.14), however, the SYNH group had higher AFC on d 2 and 3 than the NIC and SYNC groups (P ≥ 0.10). Dominant follicle size at ovulation was similar between treatments (P = 0.14). Follicular wavelength was shorter for SYNH compared to NIC and SYNC (P = 0.02). Corpus luteum volume 7-d post-estrus was similar across treatments (P = 0.63), and circulating progesterone concentrations 7-d post-estrus was not different (P = 0.94). Results from this study demonstrate that implanting replacement heifers post-weaning does not influence pubertal attainment while increasing pelvic area. Overall it doesn’t appear that implants had a deleterious impact on ovarian activity, and in fact, implants containing testosterone may have beneficial effects. Further investigations into their impact on conception rates and subsequent calving ease is warranted with larger sample sizes.

Keywords: heifer, growth implant, fertility, ovarian activity

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Keywords

Heifer, Growth implant, Fertility, Ovarian activity

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