Abstract #677

# 677
Effect of high or low P4 during ovulatory follicle development on fertility of dairy cows.
Joao Paulo N. Martins*1, Dongliang Wang2, Nanheng Mu2, Guilherme F. Rossi3, Vinicius R. Martins1, Ana Paula Martini4, Gilson A. Pessoa4, J. Richard Pursley1, 1Department of Animal Science, Michigan State University, East Lansing, MI, 2Shuozhou Vocational and Technical College, Shuozhou City, Shanxi, China, 3Department of Preventive Veterinary Medicine and Animal Reproduction, FCAV-UNESP, Jaboticabal, SP, Brazil, 4Department of Large Animal Clinical Science, Universidad Federal de Santa Maria, Santa Maria, RS, Brazil.

The objective was to determine the effect of high vs. low progesterone (P4) during early and late stages of the ovulatory follicle development in lactating dairy cows. Cows that ovulated a d 7 1st wave dominant follicle were assigned to treatments. Ovaries were manipulated to induce high (H) or low (L) circulating concentrations of P4 during 0 to 4 d (early stage) and/or 5 to 7 d (late stage) of the wave forming 4 treatments: H/H, L/L, L/H and H/L. Luteolysis was induced with PG on d 7 of the treatment period. Ovulation of the dominant follicle was induced with GnRH 56 h following PG. All cows received AI 16 h later (n = 559). Pregnancy was determined 35 and 56 d after AI by ultrasonography and 117 d (±3) and 194 d (±3) by detection of pregnancy-specific protein B (PSPB) in milk. Data were analyzed with chi-squared analysis. Pregnancy/AI 35 d post AI was 43.2, 51.1, 53.6, and 60.4 for HH, HL, LH, and LL, respectively, and was greater for LL than HH cows. However, there was no difference on P/AI 56 d (HH = 42.4%, HL = 46%, LH = 51%, and LL = 51.1%), 117 d (HH = 38.3%, HL = 45.6%, LH = 48.3%, and LL = 48.9%), and 194 d post AI (HH = 36.8%, HL = 43.9%, LH = 44.4%, and LL = 46.3%). Pregnancy losses between 35 and 56 d post AI was 1.8, 10, 4.9 and 14.5% for HH, HL, LH, and LL, respectively, and was greater for LL than HH. There was no difference in pregnancy losses between 56 and 117 d post AI (HH = 5.8%, HL = 0%, LH = 2.8%, and LL = 2.9%) and between 117 and 194 d post AI (HH = 0%, HL = 0%, LH = 5.9%, and LL = 3.1%). Percentage of cows with double ovulations to the last GnRH was greater in LL (49%) compared with HH, HL and LH (12, 33, and 34% respectively). Cows that had double ovulation after the last GnRH had greater P/AI 35 d (45 vs. 66%) and 56 d post AI (43 vs. 57%) compared with cows with single ovulation. Pregnant losses between 35 and 56 d after AI was greater in cows with double ovulation compared with cows with single ovulation (4 vs. 14%) and tended to be greater if the ovulations were on the same ovary. In summary, low P4 during development of the ovulatory follicle increased the percentage of cows with double ovulations and P/AI 35 d post AI, but decreased embryonic survival between 35 and 56 d post AI.

Key Words: follicle, fertility, progesterone