Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows

We postulated that daily drenching of propylene glycol to cows in early lac tation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to tr eatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples fo r glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N wer e collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks . Blood samples were collected for progesterone analysis and cows were palp ated three times per week until 11 weeks to assess ovarian status. Propylen e glycol did not affect dry matter intake (DMI), milk yield or energy balan ce in treatment cows. After drenching, propylene glycol increased (P < 0.01 ) plasma glucose and insulin and decreased (P < 0.01) NEFA; plasma urea N o f the treatment group tended (P = 0.07) to be higher than that of the contr ol group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first in semination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurr ed earlier than that of control cows (32.3 versus 44.5 days, P = 0.06) and the length of the first luteal phase was longer in treated cows (13.1 versu s 7.3 days, P < 0.05). These data are consistent with the hypothesis that i nsulin is important for normal ovarian function. During negative energy bal ance, treatment with propylene glycol, which induced small increases in pla sma concentrations of insulin, prevented the short luteal phase characteris tic of the first estrous cycle in control cows. (C) 2001 Elsevier Science B .V. All rights reserved.