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 patterns and(or) in vitro and in vivo characteristics of induced corpora lutea (CL) in undernourished, post-partum 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 maintain BW and condition after calving. In Exp. 1, 16 cows were fed isocaloric and isonitrogenous diets after calving with either no added fat (NL, n = 8) or added fat (HL, n = 8; .374 kg of fat/500 kg BW). In Exp. 2, 32 pluriparous cows that had reached targeted body condition were divided randomly at calving into a 2 x 2 factorial treatment arrangement: 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) luteal lifespan.(ABSTRACT TRUNCATED AT 250 WORDS)