Postweaning nutritional programming of ovarian development in beef heifers1,2

Abstract

Peripubertal caloric restriction increases primordial follicle numbers at breeding, which may improve reproductive potential. Our hypothesis was that feed restriction was changing primordial follicle number through stimulation of follicle formation via leptin, roundabout axon guidance receptor, homolog 4 (), or or through inhibition of follicle activation via anti-Müllerian hormone (). Heifers ( = 30) were fed a ration consisting of 30% alfalfa hay, 69.8% corn silage, and 0.2% salt as DM. Heifers received the control diet for 42 d before an initial 6 heifers were ovariectomized at 8 mo of age. The remaining 24 heifers were divided into 2 treatment groups. Controls were offered 97.9 g DM/kg BW over the entire feeding period. Stair-step heifers received 67.4 g DM/kg BW for 84 d. Following the 84-d restriction, heifers were stepped up to receive 118.9 g DM/kg BW over a 15-d period and were held at this feeding level 68 d. At the end of the feed restriction (11 mo of age), ovaries were collected from 6 heifers per treatment, and at the end of the refeeding period (13 mo of age), ovaries were collected from 6 heifers per treatment. Plasma leptin concentrations were greater in control heifers than in stair-step heifers at 11 mo of age ( < 0.0001). In histological sections, stair-step heifers had more primordial follicles ( = 0.03) than control heifers at 13 mo of age. There was no difference in secondary or antral follicle numbers between dietary treatment groups or ages. Relative abundance of mRNA in ovarian cortex of control heifers was greater at 13 mo than at 11 mo or before feed restriction (8 mo; = 0.01). Relative abundance of mRNA in stair-step heifers at 13 mo was greater than before feed restriction ( = 0.02) and at 11 mo did not differ from 8 or 13 mo ( = 0.70). Relative abundance of mRNA in the ovarian cortex followed a similar pattern, being greater in stair-step heifers at 11 mo compared with control heifers ( = 0.001). At 13 mo, mRNA did not differ between treatments ( = 0.30). Abundance of mRNA in the ovarian cortex did not change due to dietary treatment or age ( > 0.10). In conclusion, developing heifers on a stair-step compensatory growth scheme resulted in larger ovarian reserve before the onset of breeding, which may have beneficial effects on increasing reproductive lifespan.

Maternal age influences the number of primordial follicles in the ovaries of yearling Angus heifers

“…The investigator performing the ovarian morphological measurements was uninformed as to the age of the dam of the heifer from which the ovaries originated. A representative cross-sectional piece of tissue (∼5 mm thickness) was cut from the center, perpendicular to the length of the ovary contra-lateral to the CL and fixed overnight in 10% Neutral Buffered Formalin for histological evaluation (Cushman et al, 2001;Amundson et al, 2015). The ovarian tissues were rinsed in phosphate buffered saline for 1 h at room temperature, followed by 20% ethanol, 35% ethanol, 50% ethanol, and 70% ethanol, each for 1 h at room temperature to dehydrate the tissues.…”

“…Pre-antral follicles were classified as primordial, primary, or secondary as described previously (Cushman et al, 2001(Cushman et al, , 2002Amundson et al, 2015). Briefly, a primordial follicle was defined as an oocyte surrounded by a single layer of squamous pregranulosa cells.…”

“…More recently, it was reported that heifer born to mature beef cows had greater circulating concentrations of anti-Müllerian hormone (AMH), a blood marker of size of the ovarian reserve, and greater fertility than heifers with primiparous dams (Akbarinejad et al, 2018). While both number of antral follicles (Cushman et al, 1999) and circulating concentrations of AMH (Ireland et al, 2008) are generally correlated to the size of the ovarian reserve, there are studies where differences in numbers of primordial follicle do not result in differences in numbers of antral follicles (Freetly et al, 2014;Amundson et al, 2015). It, therefore, is important to perform the histological evaluation to clearly identify whether there are differences in the size of the ovarian follicle reserve between heifers with primiparous dams as compared with those from multiparous dams as a first step in understanding the mechanisms behind these differences.…”

Recuento de folículos antrales y concentraciones de hormona anti-Mülleriana: dos potenciales herramientas de selección de reemplazos

“…Sin embargo, la información sobre repetibilidad individual realizando mediciones más separadas en el tiempo, por ejemplo 6 meses, en animales pre-púberes Bos Taurus o Indicus (para carne y leche) es escasa. Además, los cambios nutricionales pre y posnatales pueden afectar la reserva folicular (Amundson et al, 2015;Evans et al, 2012;Mossa et al, 2013), y reducir la repetibilidad si las mediciones se realizan antes y después de aplicar planos nutricionales diferenciales. Se ha sugerido que el número de folículos antrales aumenta hasta los 5 años de edad, y luego disminuye (Cushman et al, 2009), lo que podría estar asociado a la longevidad promedio de los animales de alta y baja cuenta folicular en el rodeo.…”

“…Los resultados sugieren que vaquillonas con menor RMFA fueron más livianas, tuvieron menor AOB y fueron más bajas, que las de medio y alto RMFA. Estos resultados concuerdan con datos publicados anteriormente (Eborn et al, 2013), y sugieren que la nutrición pre y pos-natal podrían afectar la reserva ovárica (Amundson et al, 2015;Evans et al, 2012;Mossa et al, 2013). La asociación de los parámetros de crecimiento y desarrollo con la edad a la pubertad (Patterson et al, 1992) sugiere que vaquillonas con un mayor potencial de crecimiento alcanzan el porcentaje de peso adulto crítico para comenzar a ciclar a una edad más temprana.…”