INDICATIONS AND IMPLICATIONS FOR TESTING OF MILK UREA IN DAIRY-CATTLE- A QUANTITATIVE REVIEW - PART 2 - EFFECT OF DIETARY-PROTEIN ON REPRODUCTIVE-PERFORMANCE

Dietary protein and dairy cow fertility. Feeding more dietary protein has been negatively associated with dairy cow fertility in some but no t all studies. We used meta-analysis to examine the relationship betwe en dietary crude protein and conception rate. While a higher intake of dietary crude protein significantly lowered conception rate, the pote ntial for feeding less degradable dietary protein to modify this relat ionship was not demonstrated. Milk urea concentrations and dairy cow f ertility. The use of milk urea as an indicator of dietary energy and p rotein intake and as an indictor of reproductive performance has been questioned. We found that changes in urea concentration in body fluids explained only 25% (p = 0.08) of the variance in conception rate afte r conducting a meta-analysis of available studies. Interpretation of m ilk urea concentrations. High intakes of dietary protein may induce ad aptations in urea metabolism, and the negative relationship identified between high intakes of dietary protein and fertility for Northern He misphere dairy herds may not necessarily apply in Australasian dairy h erds. Because of the potential for cows to adapt to high protein diets , the use of a single milk urea determination on a herd will have limi ted value as an indicator of nutritional status and little value as a predictor of fertility.