Location: Reproduction ResearchTitle: Antral follicular count has limited impact in the selection of more fertile beef heifers
|CUNHA, FERNANDO - University Of Montevideo|
|Cushman, Robert - Bob|
|SANTA CRUZ, RODGRIGO - University Of Montevideo|
|DE NAVA, GUILLERMO - University Of Montevideo|
|VINOLES, CAROLINA - University Of Montevideo|
Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2020
Publication Date: 8/26/2020
Citation: Cunha, F., Cushman, R.A., Santa Cruz, R., de Nava, G., Vinoles, C. 2020. Antral follicular count has limited impact in the selection of more fertile beef heifers. Livestock Science. 241:104230. https://doi.org/10.1016/j.livsci.2020.104230.
Interpretive Summary: Beef heifers that give birth early in their first calving season have greater lifetime productivity. The objective of the current study was to examine the relationship between age at puberty and antral follicle count in beef heifers in Uruguay. Heifers that attained puberty earlier conceived earlier but were larger and had greater fat deposition than heifers that attained puberty later in the breeding season. Heifers with increased numbers of antral follicles conceived earlier but did not differ from heifers with diminished numbers of follicles in body size or fat deposition. There was no interaction between age at puberty and antral follicle count for any of the parameters examined. Selecting replacement heifers based on antral follicle counts will allow us to increase fertility and reproductive longevity without increasing cow size.
Technical Abstract: The selection of replacements using applications such as reproductive tract scores and antral follicle count may be useful to eliminate less fertile animals before breeding. Previously, we reported that heifers with increased numbers of follicles achieved puberty earlier than heifers with diminished numbers of follicles. We, therefore, hypothesized that heifers that achieved a reproductive tract score =4 earlier in the breeding season would have greater numbers of follicles than heifers that achieved a reproductive tract score =4 later in the breeding season. The uterus and ovaries of three hundred and fifty beef heifers from a commercial farm were evaluated by transrectal ultrasonography 20 days before breeding and parameters of growth and development were recorded. The antral follicle count (AFC) of both ovaries was recorded and the heifers assigned a reproductive tract score (1 to 5). Only heifers with a reproductive tract score =4 entered to two fixed timed artificial insemination (FTAI) programs. The first group (FTAI1, n = 269) started the day of the beginning of the breeding period and the second group (FTAI2, n = 61) one month later. The rest were naturally mated (no FTAI, n = 20). Serial pregnancy scanning was performed throughout the breeding season and 45 days after bull removal to estimate the day of conception. Data indicative of growth and development were analysed using the REG and GLM procedures of SAS with FTAI (0, 1 and 2), AFC (low, medium and high), and the interaction as the independent variables. Reproductive tract development was negatively associated to AFC (P > 0.0001). There was no interaction between FTAI and AFC (P > 0.11). Heifers inseminated at FTAI1 were heavier and taller, had greater deposition of fat and muscle, and conceived earlier than those inseminated at FTAI2 (P < 0.05); however, there was no difference in AFC between heifers inseminated in FTAI1 and FTAI2 (15.6 ± 0.4 vs. 16.7 ± 0.9 follicles, respectively; P = 0.3). Furthermore, conception rates did not differ statistically between heifers in FTAI1 and FTAI2 (P = 0.12). Antral follicle count influenced growth and carcass traits (P > 0.05) and heifers in the High AFC class conceived approximately 1 week earlier than heifers in the Low and Medium AFC class (P < 0.05). We conclude that pubertal heifers have less AFC, thus similar numbers were observed for heifers in both FTAI programs and no differences in pregnancy rate. Antral follicle count may allow for the selection of heifers that conceive earlier, but may result in a lower pregnancy rate.