Some new aspects of nutrition, health conditions and fertility of intensively reared dairy cows

Speaking in terms of the general relationship between nutrition and reproduction, many different aspects are more or less involved depending on geographical areas, species, production systems, technological levels etc. There are deficiency conditions: energy, proteins, vitamins and minerals; but also some excesses (namely protein and few minerals) or toxic substances such as micotoxins or plant compounds (i.e. phyto-oestrogens). Their relevance is different in the intensive systems for better feeds and relative easiness to create appropriate diets. Nevertheless, intensification does not reduce the nutritional risks for livestock reproduction for several reasons: namely, a suspected higher susceptibility of high genetic merit cows to the usual stresses. There is also a new risk: metabolic stress (e.g. negative energy balance). The latter is particularly relevant when early lactation and new pregnancy are close (as in dairy cows), however, of great importance are also oxidative stress and disease stress (pro-inflammatory cytokines). In dairy cows, inflammatory phenomena around calving - when an immune response occurs in spite of clinical symptoms are missing - are significantly related to a lower pregnancy rate. A possible explanation can be seen in the pro-inflammatory cytokines, which modify liver synthesis and seem to impair energy balance thereby reducing feed intake and increasing energy expenditure. This suggests that in order to improve fertility not only better feeding mecahnisms, but any husbandry tool that can reduce diseases and health disorders are needed.