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 the pregnancy rate. Milk production and time post calving should have little influence on fertility in a herd of dairy cows. If conception rate is reduced in the higher producing half of the herd, or if conception rate changes dramatically with time post calving, then nutritional stress may be reducing fertility. Energy management from the late gestation period through the post-calving period may have significant effects on reproductive function. Mismanagement of energy within a herd may be apparent in excessive body condition loss. Protein effects on fertility may be apparent as increased repeat breeding and associated with elevated plasma urea nitrogen. Deficiencies in trace elements and vitamins, particularly selenium and vitamin E, may be associated with increased reproductive disease. Reduction in reproductive performance in a herd should be examined in a systematic fashion to isolate the cause, which may be management, cow, bull, or environmentally related. Nutritional causes are more likely first due to energy management, secondly excessive protein feeding, and lastly trace element and vitamin deficiencies. Appropriate clinical tests may help confirm a diagnosis.