Cytogenetic and reproductive studies of bulls born co-twin with freemartins

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Abstract
The XX lymphocytes in peripheral blood of 22 bulls born co-twin with freemartins ranged from 5-95%. The difference of 1.2% between the means of XX percentages at initial and final karyotyping of 14 bulls over periods of 1-5 yr was not significant (P > 0.25). Of the 12 A.I. chimeric bulls, 7 (58.3%) were reproductive bulls as compared to only 5.4% of their 128 controls (P < 0.001). The culled chimeras produced no semen, had a low sperm output or had a high incidence of abonormal spermatozoa. The means for motility, sperm concentration and motile spermatozoa per ejaculate were significantly lower for the 12 chimeric bulls than for a random sample of 12 controls (P < 0.025). The 60-90 day non-return rate for 30,814 services to 8 chimeric bulls was 70% with a -0.1% mean deviation from contemporary breed average (P > 0.5). The 7 chimeric bulls culled for poor reproductive performance had larger and more numerous focal areas of testicular degeneration. Areas of lymphocytic infiltration in testes of many of these bulls suggest a rejection phenomenon or the autoimmune response. No XX germ cells were detected in testes of 11 chimeric bulls, aged 1-9 yr. Differential hemolysis blood typing tests on one bull with 85% XX lymphocytes and 23 of his dam-daughter pairs provided no evidence of germ cell chimerism. One bull with 33% XX cells sired an excess of daughters (71%) in progeny group of 48, a significant deviation from a 1:1 ratio (P < 0.01). A disturbance in normal spermatogenesis in prenatal and postnatal life by transplanted XX primordial germ cells may contribute to the marked reduction in reproductive fitness of many chimeric bulls.