METABOLIC AND LUTEAL SEQUELAE TO HEIGHTENED DIETARY-FAT INTAKE IN UNDERNOURISHED ANESTROUS BEEF-COWS INDUCED TO OVULATE

Two experiments were conducted to evaluate the effects of dietary fat supplementation and a synthetic progestogen on metabolic hormone patte rns and(or) in vitro and in vivo characteristics of induced corpora lu tea (CL) in undernourished, postpartum beef cows. Metabolizable energy intake was restricted in all cows in both experiments before calving to achieve a body condition (BC) score of 4 (thin), with cows fed to m aintain BW and condition after calving. In Exp. 1, 16 cows were fed is ocaloric and isonitrogenous diets after calving with either no added f at (NL, n = 8) or added fat (HL, n = 8;.374 kg of fat/500 kg BW). In E xp. 2, 32 pluriparous cows that had reached targeted body condition we re divided randomly at calving into a 2 X 2 factorial treatment arrang ement: 1) HL-no implant; HL-CON, 2) HL-norgestomet implant d 14 to 21; HL-NORG, 3) NL-CON and, 4) NL-NORG. Forty-eight-hour calf removal on d 21 and GnRH on d 23 were used to induce CL. The HL diet increased (P <.03) serum growth hormone (GH) concentrations, changed the puerperal pattern of serum insulin from cubic (P <.05) to linear (P <.05), and increased (P <.01) the in vitro production of IGF-I by luteal tissue ( Exp. 1). In Exp. 2, both HL diets and NORG treatments (HL-NORG, HL-CON , NL NORG) tended to promote an increased (P <.09) frequency of luteal activity after GnRH, but only HL-CON and NL-NORG enhanced(P <.04) lut eal lifespan. The HL diet modified metabolic hormone status, potentiat ed ovulation induction, and enhanced luteal competence; however, targe ted ovarian responses in vivo lacked expected consistency when HL and NORG were combined.