Relationships between nutrition and fertility in dairy cattle

The reduced fertility that is becoming more evident in high yielding dairy cows may be related to many factors including changes in milk production, food intake and fluctuations in body condition. Metabolic and production markers have been studied as a way of predicting success to a particular artificial insemination. Successful conception to a particular service was not associated with milk production, body condition or plasma concentrations of several indicators of metabolic state around the time if insemination. This highlights the importance of time of information collection in fertility management programmes. Increased food intake may reduce systemic progesterone concentrations. This is more evident in sheep than cattle, but a positive relationship between systemic progesterone early post mating and establishment of pregnancy in cattle has been reported. However, progesterone concentrations in the ovarian vein and endometrium are not strongly correlated with systemic progesterone. Thus, the significance of modest changes in systemic progesterone in affecting oocyte and embryo development must be questioned. Blood urea concentrations can be altered by diet, and reduced pregnancy rates have been reported in cows with high urea concentrations. However, in other recent studies, no difference was reported in serum urea in cows that conceived and those that failed to conceive. Pregnancy rate was equally high in heifers when in-vitro produced embryos were transferred to heifers on high and low urea diets. When embryos were produced in sheep on high and low dietary urea, the effects on embryo development appear to occur early in the developmental process, suggesting a substantial effect on the development of the oocyte. The developmental capacity of oocytes and quality of embryos is reduced in cattle maintained on extremely high dietary intakes. Oocyte developmental capacity is reduced in cows of higher genetic merit and embryo quality can be substantially reduced in the early postpartum period. Collectively, these results suggest that high dietary intake or high metabolic load is deleterious to normal oocyte development and establishment of pregnancy. This highlights the importance of further studies on the effect of dietary intake on metabolic state and follicle, oocyte and embryo development. In a practical context, these results highlight the importance of nutritional management and avoiding changes in the amount or type of diet around the time of mating in high-production dairy cows.