Evaluation of antral follicle count and ovarian morphology in crossbred beef cows: Investigation of influence of stage of the estrous cycle, age, and birth weight1,2

Abstract

Depletion of the ovarian reserve is associated with reproductive senescence in mammalian females, and there is a positive relationship between the size of the ovarian reserve and the number of antral follicles on the surface of the ovary. Therefore, we conducted a series of experiments to investigate the influence of stage of the estrous cycle, age, and birth weight on antral follicle counts (AFC) in beef cows and heifers. Pairs of ovaries were collected from crossbred beef cows at slaughter (n = 72) or at necropsy (n = 333; 0 to 11 yr of age); all visible antral follicles were counted, the ovaries were weighed, and stage of the estrous cycle was estimated based on ovarian morphology. There was no influence of estimated stage of the estrous cycle on AFC (P = 0.36). There was a small but positive effect of birth weight on AFC [AFC = -1.7 + 0.31(birth weight); P = 0.007, r(2) = 0.05]. When antral follicle counts were regressed on age, there was a quadratic effect of age such that AFC increased until 5 yr of age and decreased thereafter [AFC = 12.9 + 9.0(yr) - 0.86(yr(2)); P < 0.001, r(2) = 0.22]. In a third experiment, crossbred beef heifers (n = 406; 353 to 463 d of age) at 3 locations were subjected to ovarian ultrasonography on unknown day of the estrous cycle. Heifers were classified as low AFC (<15 follicle, n = 84) or high AFC (>24 follicles, n = 178). Whereas estimated stage of the estrous cycle did not influence AFC (P = 0.62), heifers classified as low AFC had smaller ovaries (P = 0.001), decreased birth weight (P = 0.003), and a decreased heifer pregnancy rate (P = 0.05) compared with heifers in the high AFC group. From these results, we conclude that AFC in beef cows and heifers is influenced by birth weight and age but not by stage of the estrous cycle. In beef cows, the number of antral follicles increases to 5 yr of age and then begins to decline. This may indicate that a decrease in fertility due to decline of the ovarian reserve may begin earlier than previously thought in beef cows.

Epigenetics and developmental programming of welfare and production traits in farm animals

“…Similar to sheep, prenatal maternal nutrition did not affect the onset of puberty in beef cattle (Martin et al 2007;Sullivan et al 2009;Mossa et al 2013), but higher offspring pregnancy rates were observed following protein supplementation in late pregnancy (Martin et al 2007) and when the AFC before breeding was high (Cushman et al 2009). In contrast, manipulation of the post-weaning diet in beef heifers did not affect AFC or overall pregnancy rate (Eborn et al 2013).…”

“…Nevertheless, it is well established that the number of antral follicles present at all stages after birth is a direct reflection of the ovarian follicle reserve established prenatally . Thus, birthweight (as a proxy for fetal nutrient supply) was positively associated with the antral follicle count (AFC) in a large population of neonatal beef calves that died due to dystocia, and in adult heifers examined by ultrasound (Cushman et al 2009). Reduced ovarian weight and large follicle diameter at 30 months is reported following slow prenatal growth rates (Wilkins et al 2006), whereas a general reduction in all follicle types was evident following exposure to a low-then highprotein diet during the first two-thirds of gestation (Sullivan et al 2009).…”

Antral follicles population in heifers and cows of Nelore and Girolando breeds

“…Subsequent counts were performed twice at 35-day intervals without synchronization and in accordance with other studies (CUSHMAN et al, 2009;SILVA-SANTOS et al, 2014a), no influence of stage of estrous cycle on OAFPs was observed. However, based on consideration of ovary characteristics as well as the historical age at puberty for Girolando and Nelore breeds in the study region, heifers were considered to be prepubertal at the time of the study and were therefore not subjected to the estrus synchronization treatment administered to cows.…”

“…Marked growth of the reproductive tract observed in cattle within the first few months of age and prior to first ovulation reflects phases of increased ovarian follicle numbers and size (HONARAMOOZ et al, 2004). For beef heifers and cows, OAFPs have been correlated to birth weight and to age with an increased number of antral follicles observed until 5 years of age, following which decreasing OAFPs are seen (CUSHMAN et al, 2009). These reports are in accordance with our observation of differences in OAFPs between Nelore heifers (16.2 follicles) and cows (30.9 follicles), and between Girolando heifers (18.1 follicles) and cows (26.7 follicles), confirming an increase in OAFPs in cattle of these breeds between the ages of 12 and 60 months (Table 2).…”

Parâmetros da produção in vitro de embriões da raça Sindi

“…Houve efeito da doadora sobre a PIV de embriões mas não sobre a taxa de clivagem (Tabela 2), o que pode estar relacionado ao fator individual quanto à competência dos oócitos para o desenvolvimento, apesar das variações pertinentes à raça, idade e escore de condição corporal (Cushman et al, 2009). De fato, observou-se uma grande variabilidade entre as doadoras relacionada ao padrão individual de recrutamento folicular.…”