Reproduction in Domestic Animals

100 JLMR Leroy, T Vanholder, ATM Van Knegsel, I Garcia-Ispierto and PEJ BolsIt is speculated that changes in management are morelikely to have a positive effect on EB. Shortening or evenskipping the dry period improves dry matter intakeperipartum, reduces milk production in early lactation,improves energy balance and reduces the number ofdays postpartum till resumption of ovarian activity(Gumen et al. 2005; Rastani et al. 2005).Besides this, growing attention is being paid to dietaryfatty acid content and composition provided by supplementedby-pass fats during the early postpartum period.Not the effect on energy balance as such but improvedsteroid secretion and alteration of the fatty acid profile(more x-3 poly-unsaturated fatty acids), resulting inmodified prostaglandin metabolism (Thatcher et al.2006). Suppression of milk fat synthesis by supplementationof rumen-protected conjugated linoleic acids(trans-10, cis-12) has been suggested to restrict energyloss through milk (Castaneda-Gutierrez et al. 2005).Yet, in spite of several recent interesting papers, theoutcome on energy balance and fertility are equivocal.An extensive description and clear overview of nutritionalstrategies supporting the metabolic demandsduring the transition period are given by Overton andWaldron (2004) and are beyond the scope of the presentpaper.Finally, genetic selection programmes in the dairyindustry have emphasized milk production traits byunintended mobilization of cow body reserves. This lossin BCS is not only dependent on the available mass ofadipose tissue but also on a genetically determined setpointfor BCS. This set-point is correlated with reproductiveoutcome (Lucy 2007). Therefore, not onlyfertility traits as such (Royal et al. 2000), but alsovariables comprising changes in BCS early postpartumshould be included in genetic selection criteria.ConclusionsIntense selection for milk production has resulted in animmense priority for the high-producing dairy cow topartition energy to milk, at the cost of body reserves.This has resulted in excessive NEB and poor reproductiveperformance. Thus, milk production and reproductiveperformance have conflicting interests inhigh-producing dairy cows. Metabolites and metabolichormones associated with energy prioritizing for milkproduction (NEFA, insulin, glucose, IGF-1, b-OH)influence fertility, indirectly by modulating the somatotropic⁄ gonadotropic axis, as well as directly at theovary, follicle or uterine environment. Strict follow-upperipartum to monitor health and BCS loss and directtreatment of (infectious or metabolic) disorders in earlylactation will limit fertility disorders postpartum. Furthermore,a series of promising management, geneticselection and nutritional strategies have been proposed,which have the potential to shift the somatotropic axisprioritizing energy partitioning of milk to a somatotropicaxis with an increased priority for body reserves toimprove fertility. Yet, research in this area is limited.Exploring such strategies, comparing their benefit oreven combining two or more strategies is an extremelyinteresting area of research, and essential to improvehealth and welfare of the modern dairy cow.ReferencesAmstalden M, Harms PG, Welsh TH Jr, Randel RD, WilliamsGL, 2005: Effects of leptin on gonadotropin-releasinghormone release from hypothalamic-infundibular explantsand gonadotropin release from adenohypophyseal primarycell cultures: further evidence that fully nourished cattle areresistant to leptin. 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