Oestrous behaviour, cumulus cell-oocyte complex (COC) quality, and steroid concentrations were characterised in dairy heifers of high and low values for fertility breeding value (FBV). The hypothesis was that the greater FBV is partly mediated through improved oocyte quality. Ovum pick-up (OPU) was used to collect COCs from the preovulatory follicle of 40 heifers observed in oestrus. Multiplex Taqman qPCR was used to investigate gene expression in cumulus cells (eight genes) and oocytes (three genes) of the recovered healthy COCs (n=9 per group). Plasma and follicular fluid steroid concentrations were measured using high-performance liquid chromatography. Low-FBV heifers were more active in the first eight hours of oestrus (P<0.05), leading to earlier detection and OPU (P<0.05). Consequently, COCs recovered from low-FBV heifers were morphologically less mature (P<0.05) and tended to have lower expression of genes regulating maturation compared with high-FBV heifers. Our findings suggest COC development is retarded in low-FBV heifers relative to the timing of visually observed oestrus, which may result in a poorly developed oocyte at ovulation.
Proceedings of the New Zealand Society of Animal Production, Volume 77, Rotorua, 29-33, 2017
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