144 UTILITY OF RECIPIENT CATTLE AFTER HYDROPS PREGNANCY TERMINATION

Abstract

There is continuing concern over the complications arising in pregnancies resulting from the abnormal development of somatic cell nuclear transfer (SCNT)-derived embryos. Hydrallantois (hydrops), reported widely in the cloning field, is a potentially dangerous condition that can rapidly progress to extreme abdominal distension, anorexia, lethargy, recumbency, and, finally, death of the cow if left untreated. Recipient cattle diagnosed with hydrops are commonly slaughtered or euthanized, resulting in the loss of proven recipients or market value, respectively. This has led to a growing perception that cloning is potentially unsafe for the recipients, which has ethical implications for the commercialization and public acceptance of SCNT cloning (Lassen et al. 2006 Theriogenology 65, 992–1004). Here, we report on the successful use of recipient dams after termination of hydrops pregnancies. Records from over 8 years of non-transgenic SCNT single embryo transfers (n = 1531) into 560 multiparous, mixed age and breed cattle revealed 100 diagnosed cases of hydrops, i.e. 13% (100/765) of all Day 35 pregnancies were eventually diagnosed as hydrops between Days 150 and 220 by rectal palpation. In the early years, 12 of these recipients were slaughtered to recover maternal, placental, and fetal tissues. In later years, after the diagnosis of hydrops between Days 150 and 220 of gestation by repeated rectal palpation, 88 hydrops pregnancies were electively terminated after single IM injections of 25 mg long-acting dexamethasone (dexamethasone trimethylacetate, Dexavet; Bomac Laboratories, Manukau City, New Zealand) followed 5 days later by topical cervical application of prostaglandin F_2α (Berg et al. 2006 7th Int. Ruminant Reprod. Symp., abst ? 10). Following adequate cervical softening and dilation, the commonly found over-sized, abdominally distended fetuses were safely delivered per vaginum prior to fetal death. The recipients were then aggressively treated with intrauterine and systemic oxytetracycline and repeated alternate day injections of prostaglandins until cleared of all retained placenta and membranes. After the minimal 60-day recovery period and assessment of return to cyclicity, 24/40 (60%) of these animals became pregnant within two rounds of single embryo SCNT transfer, with an overall embryo survival of 40% (27/67) at Day 35. This is not statistically different from the embryo survival rate of 50% (765/1531) for the entire herd over the 8 years. These data also confirm that the cause of hydrops resides mainly with the SCNT embryos and is not an inherent recipient problem. Thus, with early diagnosis and termination, and avoiding the exposure of the recipient to necrotic fetal tissues by careful delivery of live fetuses, these animals can successfully recover and be re-used to carry subsequent pregnancies or be salvaged for commercial slaughter. Application of this approach for the treatment of hydrops can considerably reduce the wastage of recipient animals and ameliorate some of the animal welfare concerns with cloning technology.