Reaction of the pituitary gland to a single GnRH administration in the dependence of energy balance in cattle in the puerperium]

After reviewing the relevant literature about the relationship of negative energy balance post partum and the onset of cyclicity the aim of this study will be described. The objective of this trial was to evaluate the influence of negative energy balance on the sensitivity of the pituitary for GnRH. Two groups of Holstein Friesian cows were randomly treated either with GnRH (Fertagyl) or a placebo. Considering the weekly calculated negative energy balance, the reaction of the pituitary was determined by analyzing LH in 16 blood samples, collected every 20 minutes starting one hour before and ending four hours after treatment. All cows treated with GnRH showed an intensive LH-surge, significantly different from the controls. These data suggest, that the sensitivity of the pituitary gland is not directly influenced by negative energy balance. The hypothalamus has the inhibiting priority over the pituitary delaying post partum cyclicity.