Body condition at parturition and postpartum weight gain influence luteal activity and concentrations of glucose, insulin, and nonesterified fatty acids in plasma of primiparous beef cows.

Effects of body condition score (BCS) at parturition and postpartum weight gain on luteal activity and concentrations of glucose, insulin, and NEFA in plasma were evaluated during the breeding season in 242 primiparous beef cows over 3 yr (Y) at three locations (L). At approximately 90 d prepartum, cows were blocked by breed, expected calving date, and BCS and randomly assigned to diets so that cows would calve in BCS of 4, 5, or 6. At calving, cows were blocked by breed, calving date, and BCS and randomly allotted to gain .45 (M) or .90 (H) kg/d, from parturition to the start of breeding (postpartum nutrition; PPN). During the 60-d breeding season, weekly blood samples were obtained from cows, and progesterone, insulin, glucose, and NEFA were quantified. Progesterone concentrations greater than 1 ng/mL for more than 1 wk indicated luteal activity. To determine the possible value of blood constituents as predictors of luteal activity, categorical data analyses were performed. Cows with greater BCS at parturition had greater concentrations of glucose during breeding (P < .07). Similarly, PPN influenced glucose at the beginning of breeding, but the differences were minimal after d 28 (PPN x day; P <.001). Cows with greater BCS at parturition and M-PPN had greater concentrations of insulin during the breeding season (BCS x PPN; P < .02). Cows with a BCS of 6 at parturition had the lowest concentrations of NEFA; however, cows on H-PPN had greater concentrations of NEFA (BCS x PPN; P < .03). Location, BCS, PPN, and day affected luteal activity (P < .002). Location differences in luteal activity were associated with the interval from calving to the start of breeding. In general, a greater percentage of cows with BCS of 5 or 6 at calving had luteal activity by the end of the breeding season. Concentrations of metabolites in blood during breeding were not predictive of luteal activity. We conclude that BCS at parturition and postpartum nutrition influence concentrations of glucose, insulin, and NEFA in blood and the onset of luteal activity in primiparous beef cows.