The present study sought to assess the combined effects of body composition and diet (level of feeding) on the postfertilization developmental potential of oocytes recovered from heifers using ultrasound-guided transvaginal follicular aspiration and to relate oocyte quality to the metabolic status of these animals. By collecting oocytes on repeated occasions spanning several weeks, it was possible to assess the cumulative effects of changes in nutritional status on oocyte quality over this period. Twenty-four heifers of low and moderate body condition were placed on one of two levels of feeding (equivalent to once or twice the maintenance requirements of these animals). Oocytes were recovered at two defined time points within each of three successive estrous cycles and were matured, fertilized, and cultured to the blastocyst stage in vitro. The results show that the effect of feeding level on oocyte quality is dependent on the body condition of the animal, with the high level of feeding being beneficial to oocytes from animals of low body condition but detrimental to oocytes from animals of moderately high body condition. Furthermore, the effects of high levels of feeding on oocyte quality were cumulative, with blastocyst yields for relatively fat heifers on twice the maintenance requirement deteriorating with time relative to yields for relatively thin heifers on the same level of feeding. Finally, a significant proportion of the moderately fat animals on the high level of feeding were hyperinsulinemic, and we show, to our knowledge for the first time in ruminants, that this condition is associated with impaired oocyte quality.
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