Development of ovarian follicles, quality of oocytes and fertility of cows in view of a negative energy balance in the transition period

Energy metabolism in cows during the first three weeks after calving has a decisive effect on the incidence of the first estrus postpartum, the length of the voluntary waiting period and interpregnancy period. Additionally, the negative energy balance (NEB) is usually promoted by the relatively one-sided selection of cows towards high production accepting the occurrence of NEB after calving as well as excessive body condition of cows before calving. In case of a rapid body condition loss in cows after calving, connected with fat mobilization, characteristic of cows in excessive body condition during drying off, ovarian follicles are not properly formed. Disorders of the ovulation process as well as a lower secretion of progesterone are more frequently recorded in those cows. As a result of an energy deficit at the beginning of lactation, the frequency of GnRH pulses from the hypothalamus is lower in high-producing cows. A lack of pulsation secretion of LH as an effect of the prolonged lack of adaptation of a sufficient amount of energy to the needs of the female was found both in beef and dairy cows. The recurrence of LH pulses, stimulating the onset of ovarian activity and the pre-ovulatory development of ovarian follicles, is crucail to the return of cyclical activity in the postpartum period in cows suffering from NEB. An energy deficit causes the incidence of a dysfunction of the reproductive system in the form of persistent ovarian failure, a delayed onset of normal ovarian activity, and the appearance of the first corpus luteum postpartum. The number of estrus cycles occurring before effective insemination is also reduced and both the voluntary waiting period and interpregnancy period are longer. An energy deficit in the postpartum period results in disorders in the functioning of the endometrium. Disturbed energy-consuming processes of endometrium remodeling lead to delays in uterine involution. Reduced uterine contractility and changes in its environment constitute causes for the retention of the placenta and postpartum metritis; in cows with NEB it was a reduced mitogen response of lymphocytes to cytohaema gglutinin. Moreover, a reduced phagocytic activity of macrophages was found in the milk of cows, in which high contents of ketone compounds were found in their plasma. Similarly, the activity of lymphocytes and neutrophiles was reduced in the environment with an addition of beta-hydroxybutyric and acetoacetic acids, as well as elevated PUFA levels and a reduced blood leptin concentration.