EFFECT OF DIETARY ENERGY RESTRICTION ON THE EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR-I IN LIVER AND CORPUS-LUTEUM OF HEIFERS

The effects of energy balance on the corpus luteum may be mediated by IGF-I. Our objective was to determine whether negative energy balance decreases expression of IGF-I mRNA in the liver or corpus luteum of heifers. For four consecutive estrous cycles, 14 Holstein heifers were maintained in negative or positive energy balance to lose 510 g/d of BW or gain 560 g/d of BW, respectively. The liver was biopsied and the corpus luteum was collected 7 d after fourth estrus. Heifers fed below maintenance had a smaller corpus luteum than did control heifers. Compared with that of controls, negative energy balance increased growth hormone in serum but decreased IGF-I in serum and the abundance of mRNA for growth hormone receptor and IGF-I in liver. In contrast, diet did not affect the abundance of mRNA for the growth hormone receptor or IGF-I in luteal tissue. Negative energy balance increased IGF binding protein-2 in serum but did not affect IGF binding protein-3. We conclude that negative energy balance of cattle decreases IGF-I mRNA abundance in the liver but not in the 7-d corpus luteum. If decreased IGF-I mediates the adverse effect of negative energy balance on luteal growth, the mode of action is likely endocrine, not autocrine or paracrine.