DIET, PRODUCTION AND REPRODUCTION IN DAIRY-COWS

Reproductive efficiency has an important influence on gross margin per cow per year. Gross margin per cow is optimal when the combination of heat detection rate times the conception rate equals 0.35, which is t he pregnancy rate. Milk production and time post calving should have l ittle influence on fertility in a herd of dairy cows. If conception ra te is reduced in the higher producing half of the herd, or if concepti on rate changes dramatically with time post calving, then nutritional stress may be reducing fertility. Energy management from the late gest ation period through the post-calving period may have significant effe cts on reproductive function. Mismanagement of energy within a herd ma y be apparent in excessive body condition loss. Protein effects on fer tility may be apparent as increased repeat breeding and associated wit h elevated plasma urea nitrogen. Deficiencies in trace elements and vi tamins, particularly selenium and vitamin E, may be associated with in creased reproductive disease. Reduction in reproductive performance in a herd should be examined in a systematic fashion to isolate the caus e, which may be management, cow, bull, or environmentally related. Nut ritional causes are more likely first due to energy management, second ly excessive protein feeding, and lastly trace element and vitamin def iciencies. Appropriate clinical tests may help confirm a diagnosis.