Plasma insulin-like growth factor-I (IGF-I) levels in pasture fed lactating Holstein Friesian cows during the post-partum period

Abstract

Insulin-like growth factors (IGF-I and IGF-II) regulate cell growth, differentiation and differentiated cell function by interacting with three cell surface receptors (IGF-IR, IGF-IIR, and insulin-R), which is inturn, modulated by six binding proteins (IGFBP-1-6). IGFs are synthesized and secreted by many tissues and act as autocrine, paracrine and/or endocrine factors. IGFs and IGFBPs may be involved in mediating the effects of nutrition on the reproductive system. Research in Europe and North America using intensive feed-lot cattle systems has established a relationship between circulating IGF-I concentration and changes in energy balance in high genetic merit dairy cows fed total mixed rations. This study aims to evaluate the effect of dry matter and/or energy intake on plasma IGF-I concentrations in Australian pasture-fed lactating dairy cows in early lactation.