Concentrations of Progesterone and Insulin in Serum of Nonlactating Dairy Cows in Response to Carbohydrate Source and Processing

Two experiments were conducted to investigate the effects of carbohydrate source and processing on serum progesterone (P4) and insulin concentrations of nonlactating dairy cows. In experiment 1, 12 ovariectomized grazing Gir × Holstein cows were stratified by body weight and body condition score, and randomly assigned to receive a supplement containing either finely ground corn or citrus pulp in a Latin square crossover design. Diets were fed individually, twice daily at a rate of 10.9 kg of dry matter per cow. Cows received a controlled intravaginal P4-releasing insert before the beginning of the study, and inserts were replaced every 7 d. During the first experimental period, cows were adapted to treatments from d 0 to 13 and blood was collected on d 14, whereas during the second experimental period cows were adapted to treatments from d 0 to 6 and blood samples were collected on d 7. In both periods, blood samples were collected immediately before and at 1, 2, 3, 4, 5, and 6 h after the first supplement feeding of the collection day. In experiment 2, the cows utilized in experiment 1 were randomly assigned to receive a supplement based on finely ground corn, coarsely ground corn, or high-moisture corn in a Latin square crossover design. Cows were fed and received the controlled intravaginal P4-releasing insert as in experiment 1. Within each of the 3 experimental periods, cows were adapted to diets from d 0 to 6, and blood samples were collected on d 7 as in experiment 1. Time effects were detected in experiments 1 and 2 because insulin concentrations increased by 1 h (4.6 ± 0.90 vs. 7.4 ± 0.91 μIU/mL for 0 and 1 h, respectively) and P4 concentrations decreased by 3 h (1.8 ± 0.12 vs. 1.2 ± 0.11 ng/mL for 0 and 3 h, respectively) after supplements were offered. In experiment 2, insulin concentrations were greater in cows fed high-moisture corn compared with those fed coarsely or finely ground corn (8.8 ± 1.05, 5.7 ± 1.05, and 6.1 ± 1.05 μIU/mL, respectively). Data combined from both experiments indicated that cows with median insulin ≥4.5 μIU/mL before supplement feeding had greater P4 concentrations at 1 h, but lesser P4 concentrations at 5 h compared with cows with insulin <4.5 μIU/mL. Carbohydrate processing, but not carbohydrate source, affected serum insulin of nonlactating dairy cows.