Effects of propiogenic ingredients on serum concentration of insulin and progesterone in non-lactating cows

Three experiments evaluated serum insulin and progesterone (P4) concentrations in grazing Gir×Holstein cows supplemented with monensin (MON) or propylene glycol (PPG; 2.5 mL/kg of live weight0.75 per drench). Cows were non-lactating, ovariectomized, and received an intravaginal drug-releasing device containing 1.9 g of P4 to estimate treatment effects on hepatic P4 degradation. In Exp. 1, 15 cows received, in a crossover design containing 2 periods of 21 d, 0.1 kg/d of corn in addition to 2 g/d of kaolin (CON) or 0.2 g/d of MON. Blood samples were collected on d 13 and 20 of each period. Cows receiving CON had greater (P<0.05) serum insulin concentrations compared with MON prior to and 6 h after feeding. However, MON cows had greater (P=0.01) serum P4 concentrations compared with CON 18 h after feeding. In experiment 2, 15 cows received, in a replicated crossover design containing 2 periods of 24 h, a single drench of PPG or water (WT). Cows receiving PPG had greater (P<0.01) serum insulin concentrations compared with WT from 0.5 to 3 h after drench. However, PPG cows had reduced (P<0.05) serum P4 concentrations compared with WT at 1 and 2 h after drench. In experiment 3, 13 cows received, in a replicated 3×3 Latin square design containing 3 periods of 24 h, 3 PPG drenches administered 1 h apart (PPG3x), 3 WT drenches administered 1 h apart, or 1 PPG drench+2 WT drenches administered 1 h apart (PPG1x). Serum insulin concentrations increased proportionally to PPG dosage (treatment×hour; P<0.01). However, mean serum P4 concentration was greater (P<0.01) in WT cows compared with PPG1x and PPG3x, but similar (P=0.25) between PPG1x and PPG3x cows. In conclusion, feeding propiogenic ingredients to grazing cows failed to substantially increase serum P4 concentrations.