Circulating AMH, antral follicle count and ovulation rate after unilateral ovariectomy in cattle: influence of the bovine fecundity allele Trio
Trio, a novel high ovulation allele in cattle, reduces ovarian follicular growth rate and results in multiple smaller sized ovulatory follicles in contrast to the single ovulatory follicle in wild-type cattle. The objective was to evaluate the effect of unilateral ovariectomy (ULO, surgical removal of one ovary) on antral follicle count (AFC; > 1 mm) and anti-Mullerian Hormone (AMH) in carriers and non-carriers of the Trio allele (n = 9/group). On D0, the ovary containing the largest follicle was surgically removed by flank laparotomy. Serum AMH, AFC and ovulation rate were determined before ULO and at multiple times after ULO until D230. Data were analyzed using linear mixed models and generalized estimating equations. Prior to ULO, AMH and AFC were not different (P > 0.7) for Trio carriers (349.7 ± 51 pg/ml; 21.2 ± 1.9 follicles) and non-carriers (334.8 ± 49 pg/ml; 22.1 ± 1.4 follicles). Ovulation rate was greater (P < 0.01) in Trio carriers (3.2 ± 0.1) than non-carriers (1.2 ± 0.1) both prior and after ULO, indicating that ULO did not affect ovulation rate. On D1, AFC decreased to 49.7% (carriers) and 50.6% (non-carriers) of pre-ULO values. AFC returned to control values (100%) in 77.8% of heifers but timing of return was earlier in Trio carriers (65.8 ± 14.3d) than non-carriers (131.0 ± 29d). By D230, AFC was similar to pre-ULO in Trio carriers (119%) and non-carriers (91%). For AMH, there was an effect (P < 0.01) of genotype, day, and genotype by day interaction on percentage change in circulating AMH. By D3, circulating AMH decreased in both Trio carriers (57.4%) and non-carriers (48.8%). By D230, AMH returned to pre-ULO values in Trio carriers (94.6%) but not in non-carriers (48.1%). Unique observations were: 1) ULO decreased AFC and AMH to ~50%, 2) AFC eventually returned to pre-ULO values by 2 (Trio carriers) to 4 (non-carriers) months, and 3) ovarian compensation, based on AMH, occurred in Trio carriers (~8 months) but not in non-carriers by conclusion of the study (D230). Results obtained from this study further the understanding of the process of folliculogenesis and the control of ovulation rate in monovular species and can aid in the development of improved strategies to prevent twinning, an undesirable trait in cattle.