Relationship between resumption of ovarian activity, days open, energy balance and metabolic status in dairy cows with different dry period lengths in early lactation

Negative energy balance (NEB) in dairy cows results from a fast increase in milk production post calving while feed intake is limited in this period. NEB is accompanied with an altered metabolic status, which triggers metabolic disorders. Metabolic status in early lactation is related with reproductive performance, e.g. reduced concentrations of insulin and IGF-I, which contributes to reduced follicular responsiveness to gonadotrophic stimulation, and thus prevents the dominant follicle to ovulate, resulting in a delay in the resumption of cyclicity. Omitting or shortening the dry period (DP), adjusting dietary energy level or feeding different dietary energy sources is of interest because that could minimize the risk of NEB, postpartum metabolic diseases and suboptimal fertility like delayed resumption of postpartum ovarian cyclicity. The aim of this study is to investigate the effect of DP length, dietary energy level, dietary energy source and interactions among these factors on fertility (resumption of ovarian cyclicity and days open) of dairy cows postpartum. Additionally, the relation between energy balance and metabolic status of dairy cows during early lactation and resumption of ovarian cyclicity and days open will be evaluated.