Timing of luteolysis and conceptus expulsion after induced pregnancy loss at three different timepoints after maternal recognition of pregnancy in cattle

Benjamin Duran
Graduate (PhD)
Alvaro Garcia Guerra
Animal Sciences

Results from previous research indicate induced pregnancy loss (IPL) on day 36 of gestation in cattle resulted in corpus luteum regression (luteolysis) by gestation day ~45. The aim of this study was to test the hypotheses that IPL at 25, 35, or 55 days of gestation will: 1) result in luteolysis; and 2) interval between IPL to luteolysis is positively associated with days of gestation at time of treatment. Pregnant non-lactating beef cows were randomly assigned to undergo IPL, consisting of an intrauterine infusion of 120 ml of hypertonic saline (7.2%), at day 25 (IPL25, n=15), day 35 (IPL35, n=14), or day 55 (IPL55, n=14). Corpus luteum (CL) volume and embryo/fetal viability were evaluated by transrectal B-mode ultrasonography daily for 19 days following treatment and every other day subsequently until luteolysis was identified or gestation day 91. Blood flow through the CL was evaluated using color doppler ultrasonography and luteolysis was defined as the day there was 25% of the CL represented with color pixels. Data were analyzed using proc mixed in SAS (version 9.4). Luteolysis occurred earlier (P=0.01) in IPL25 (5.3±0.4 days) than IPL55-treated (8.9±1.4 days) cows and tended (P=0.07) to occur earlier in IPL35 (6.6±0.6 days) than IPL55-treated cows, with no significant difference (P0.2) between IPL25 and IPL35-treated cows. Interval between treatment and luteolysis and conceptus expulsion were correlated in IPL35 (r=0.84; P0.01) and IPL55 (r=0.88; P0.01), while there was no correlation in IPL25-treated (r=0.31; P=0.3) cows. Volume of the CL was less (P=0.04) in IPL25 by treatment day 5 compared with IPL55 cows. Additionally, CL volume was less (P=0.03) in IPL25 by treatment day 6 than IPL35, while IPL35 cows had a lesser (P=0.01) CL volume starting at treatment day 10 than IPL55 cows. Induction of pregnancy loss at different times of gestation consistently results in luteolysis, however, interval between treatment and luteolysis tended to increase as gestation days increased. Results from the present study support the working hypothesis of presence of a continuous mechanism for CL maintenance beyond the classical maternal recognition period in cattle.