The condition of freemartinism occurs in the bovine heterosexual twin foetuses and refers to the resulting infertile female. Vascular anastomoses of the foetal membranes are the major reason of this anomaly. This study examines whether single born heifers following induced twin reduction at 28-34 days of pregnancy could develop normal reproductive functions. The study population derived from 367 lactating dairy cows carrying: unilateral twins (n = 178), bilateral twins (n = 174) or triplets (n = 15), in which manual embryo reduction was performed. The final study population was constituted of 95 single born twin females that reached 12 months of life and entered into the AI period. Of these heifers, 40 have had one unilateral co-twin, 49 one bilateral co-twin, and 6 two contralateral co-twins. A total of 1688 heifers inseminated during the same period were used as controls to compare the rates of pregnancy at 15 months of age, culling due to infertility and birth before the age of 24 months. No differences were detected between groups. With an accepted incidence rate of 50% heterosexuality for all twin sets, we should assume that half of our study population had a male co-twin. Our results indicate lack of effect of the male co-twin on normal development of the gonads and genital tract of his female partner during the late embryonic period.
Keywords: cattle; dairy cattle; double ovulation; leuko-chimerism; twinning rate.
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