Low numbers of ovarian follicles ≥3 mm in diameter are associated with low fertility in dairy cows

Abstract

The total number of ovarian follicles ≥ 3mm in diameter (antral follicle count, AFC) during follicular waves varies among cattle of similar age, but AFC is highly repeatable within individuals. We hypothesized that lower AFC could be associated with reduced fertility in cattle. The AFC was assessed by ultrasonography for 2 d consecutively during the first wave of follicular growth of the estrous cycle, 4.6±1.43 d (mean ± SD) after estrus, in 306 Holstein-Friesian dairy cows approximately 70 d postpartum. Cows were classified into 3 groups based on AFC: low (AFC ≤15), intermediate (AFC=16 to 24), and high (AFC ≥25). During the cycle in which AFC was assessed and in subsequent cycles, cows were artificially inseminated (AI) following detection of estrus, and pregnancy status was assessed using ultrasonography. Cows with high AFC had 3.34 times greater odds of being pregnant at the end of the breeding season compared with cows with low AFC; the odds of a successful pregnancy at first service were 1.75 times greater in the intermediate compared with the low group. The predicted probability of a successful pregnancy by the end of the breeding period (length of breeding season was 86±16.3 d) was 94, 88, and 84% for the high, intermediate, and low AFC groups, respectively. No difference was evident among groups in 21-d submission rate (proportion of all cows detected in estrus and submitted for AI in the first 21 d of the breeding season), but the interval from calving to conception was shorter in the high (109.5±5.1 d) versus low (117.1±4 d) group, and animals with intermediate AFC received fewer services during the breeding season (2.3±0.1) compared with animals with low AFC (2.7±0.1). Lactating cows with ≤15 ovarian follicles have lower reproductive performance compared with cows with higher numbers of follicles, but the existence of a positive association between high numbers of ovarian follicles and fertility is yet to be established.

A putative role for anti-Müllerian hormone (AMH) in optimising ovarian reserve expenditure

“…In mice, artificially reducing the ovarian reserve by unilateral ovariectomy causes reduced embryo viability in late reproductive life when compared to age-matched females (Biggers et al 1962, Brook et al 1984. Similarly, a low antral follicle count is associated with reduced pregnancy rates in cows (Mossa et al 2012, Martinez et al 2016). In humans, multiple studies suggest that increased rates of aneuploidy (Kline et al 2000, Haadsma et al 2010, KatzJaffe et al 2013, Grande et al 2015 or an inability to achieve pregnancy (Scott et al 1995, El-Toukhy et al 2002) is associated with low ovarian reserve.…”

Contagem de folículos antrais em fêmeas Nelore submetidas a inseminação artificial em tempo fixo

“…Adicionalmente, observou-se uma média correlação positiva (r=0,34) e significativa (P=0,0001) entre o DOV e a CFA. Estes resultados foram suportados por diversos pesquisadores, que também verificaram inter-relação entre estes parâmetros (CUSHMAN et al, 2009;IRELAND et al, 2008;MOSSA et al, 2012). A literatura demonstrou ainda que fêmeas apresentando um maior DOV tiveram maior número de folículos e oócitos saudáveis (IRELAND et al, 2008;SILVA-SANTOS et al, 2014).…”

Fertilidade de fêmeas Nelore após inseminação artificial em tempo fixo conforme a contagem de folículos antrais

“…Uma das possibilidades de se superar estes índices é a associação dos resultados alcançados na IATF com a população folicular antral em bovinos (Baruselli et al, 2012;Evans et al, 2012). Segundo Burns et al (2005), essa característica tem alta variabilidade e repetibilidade individual, mas alguns trabalhos sugerem que ela pode impactar direta ou indiretamente a fertilidade de bovinos (Ireland et al, 2008;Jimenez-Krassel et al, 2009).…”

“…Estas evidências fisiológicas de comprometimento da fertilidade foram recentemente confirmadas por Mossa et al (2012), em programas de inseminação artificial convencional em vacas Holandesas. Assim, a população folicular antral, avaliada por meio da contagem de folículos antrais (CFA), pode influenciar as taxas de concepção em programas de IATF (Baruselli et al, 2012;Evans et al, 2012).…”

“…Entretanto, a literatura aponta a escassez de estudos quanto ao efeito do número de foliculos antrais sobre IATF em fêmeas Nelore, medido através da CFA (Evans et al, 2012).…”