A study relating the composition of follicular fluid and blood plasma from individual Holstein dairy cows to the in vitro developmental competence of pooled abattoir-derived oocytes

Abstract

The fertility of high-performance (high milk yield) dairy breeds such as the Holstein within the Australian dairy herd has been on the decline for the past two decades. The 12-month calving interval for pasture-based farming practices results in oocyte maturation coinciding with peak lactation, periods of negative energy balance, and energy partitioning for lactation, causing energy deficiency in some organ systems, including the reproductive system. Oocyte developmental competence (the ability to undergo successful fertilization, embryo development, and establishment of pregnancy) is intrinsically linked with the composition of follicular fluid (FF). The aim of this study was to determine if there was a relationship between the fat and carbohydrate levels in plasma and FF and the ability to support in vitro oocyte maturation (IVM). Plasma and FF were collected in vivo from eight Holstein cows between 52 and 151 days post-partum. Plasma glucose trended (P = 0.072) higher and triglyceride levels were significantly higher than in FF (P < 0.05), but there were no relationships between FF and plasma composition. Glucose FF concentration was negatively related to follicular lactate and nonesterified fatty acid (NEFA) levels and days post-partum. Conversely, FF triglyceride concentrations were positively related to FF NEFA levels and negatively related to milk fat and protein composition. Abattoir-derived cumulus-oocyte complexes were cultured in either 50% FF (FF-IVM) or 50% plasma (plasma-IVM), with on-time embryo development then assessed. Although there were no differences between animals, the blastocyst rates after FF-IVM were negatively related to plasma glucose and days post-partum and positively related to body condition score and plasma NEFA levels. In comparison to the previous studies, total NEFA levels in FF were not related to animal parameters and did not influence oocyte developmental competence in vitro. Results from this study suggest that days post-partum and body condition score influence carbohydrate metabolism within the follicular environment, and this may be attributed to the pasture-based feed system applied in the Australian dairy industry.

Keywords: Cumulus–oocyte complex; Dairy cattle; Developmental competence; Follicular fluid; Plasma.