Herbage allowances of native grasslands and cow genotype affect follicular and uterine parameters in beef cows

Reproduction is crucial in the efficiency of grazing-based beef production systems. There are different ways to improve reproductive indices in cattle, such as through herd management, nutrition and/or genetics. It was shown that different levels of herbage allowance and the use of crossbred cows could improve the follicular and uterine characteristics that translate into higher cow fertility. Our study aimed to evaluate the follicle size, oocyte quality, and changes in follicular fluid composition and uterine gene expression in crossbred and purebred cycling beef cows grazing native pastures at two different levels of herbage allowance for three years. The experimental design was a complete randomized block with two replications. We allocated a total of 32 multiparous cows, with eight cows per block in a two-by-two factorial arrangement of herbage allowance (HA: High (HI) and Low (LO)) and cow genotype (CG: Purebred (PU) and Crossbred (CR)). Cows with at least two previous ovulations were slaughtered at 190 ± 15 days postpartum and uterine tissue and ovaries of the cycling cows were collected. We obtained that the preovulatory follicle size, progesterone, and insulin-like growth factor 1 (IGF1) were greater in cows with HI than with LO long-term herbage allowance. Furthermore, the non-esterified fatty acids (NEFA) concentration was lower in crossbred cows. It suggests a lower mobilization of energy reserves in crossbred than in purebred cows. For the gene expression in uterine tissues, we only observed a greater expression of IGFBP2 and IGFBP4 mRNA in cows under LO HA. These findings reveal an effect of the herbage allowance and cow genotype in follicular and uterine parameters that can be translated into better cow fertility.