Abortion in dairy cattle with advanced twin pregnancies: Incidence and timing.

This study examines incidences and timing of abortion in Holstein Friesian dairy cows with advanced twin pregnancies in north-eastern Spain. The study population consisted of 1,194 twin pregnancies in two herds recorded from 2010 to 2015: 522 bilateral and 672 unilateral. The presence of live twins was determined by transrectal ultrasonography between 55 and 61 days post-AI and pregnancy confirmed 60 days later. Abortion was recorded in 278 (23.3%) cows before Day 260 of pregnancy: 7 (1.3%) in bilateral and 271 (40.3%) in unilateral twin pregnancies. Using binary logistic regression procedures the following were excluded as risk factors for abortion: herd, year, heat stress (temperature-humidity index values >72), lactation number and right versus left side for unilateral twins. Based on odds ratios, cows carrying unilateral twins were 49.9 (right unilateral twins) and 49.3 (left unilateral twins) times more likely to suffer abortion than cows with bilateral twins. The average time of abortion for unilateral twins was 173 ± 32 days and ranged from 135 to 249 days, 43% of abortions occurring between 135 and 154 days of gestation. The authors suggest prevention or reduction of unilateral twin pregnancies by follicular puncture and drainage of subordinate follicles at AI or manual rupture of the amniotic vesicle of one of the two twins at the time of pregnancy diagnosis.