Nutritional anestrus in beef cows: concentrations of glucose and nonesterified fatty acids in plasma and insulin in serum.

Twenty-two nonlactating Hereford cows exhibiting normal estrous cycles were fed either maintenance (M) or restricted (R) diets until most of the R cows became anestrus; R cows then were fed 160% of the M diet until estrous cycles resumed. Concentrations of progesterone, glucose, insulin and nonesterified fatty acids (NEFA) were determined in weekly blood samples. Blood also was collected frequently, before and after i.v. infusion of 300 ml of a 40% glucose solution, to evaluate responses in blood concentrations of glucose and insulin when cows were exhibiting normal estrous cycles, when R cows were initiating anestrus, during anestrus, and at the reinitiation of estrous cycles. Losses in BW and body condition score in R cows were associated with reduced (P less than .01) concentrations of glucose and insulin and greater (P less than .01) concentrations of NEFA in blood plasma compared with those of M cows. During normal estrous cycles, disappearance of infused glucose from plasma and concentrations of insulin in serum were similar for R and M cows. Glucose disappearance from plasma was retarded and serum concentrations of insulin remained increased for a longer time after glucose infusion in R at the start of anestrus compared with M cows (P less than .01). Similarly, during anestrus, the rate of glucose disappearance was slower for R cows (P less than .01). During refeeding of R cows, disappearance of infused glucose was similar for R and M cows. In conclusion, reduced concentrations of glucose and insulin and increased concentrations of NEFA in blood were associated with nutritional anestrus and the glucoregulatory effects of insulin were compromised during nutritional anestrus.