CLINICAL AND PATHOLOGICAL STATUS OF CLONED CALVES BORN PRE-

CLINICAL AND PATHOLOGICAL STATUS OF CLONED CALVES BORN PRE-TERM

M. Taneja,¹ R. French,² H. Levine,³ D. Tauro-Miller⁴ and X. Yang¹

¹Department of Animal Science, and ²Department of Pathobiology, University of Connecticut, Storrs, Connecticut 06269, USA; ³Tufts University Ambulatory Service, Woodstock, Connecticut 06267, USA; ⁴Fairvue Farms, Woodstock, Connecticut 06281, USA

Incidence of pre-term labor in natural pregnancies is very high in humans; however, a much lower incidence is reported in most farm animal species including cattle. In the present study we examined the efficacy of clinical management of pre-term born somatic cell cloned calves and associated pathology.

Pregnancies were established through non-surgical transfer of 2-nuclear transfer (NT) generated cloned embryos per synchronized Holstein recipient maintained under standard feeding and management conditions. NT was performed using fibroblasts or cumulus cells derived from a 13-yr old Holstein cow. Eight pregnant heifers delivered 10 cloned calves, vaginally or through cesarean section (CS), at 266.6+2.0 d (range 253-273d) of gestation. The parturition was either spontaneous (S) or induced (I) with an im injection of 20 mg dexamethasone (Butler Co., Rochester, NY) 17 h before a planned CS (Wells et al., Biol Reprod 1999; 60:996-1005).

In the S-group, two singles and a pair of twin calves (n=4) were born with a mean birth weight of 33.0+4.0 kg at 263.0+3.8d of gestation. One of the twin calves was delivered unsupervised and found dead, and the other dead twin was pulled out soon thereafter. No significant findings were observed at their necropsies; however, it was confirmed that both the calves were born dead. Another calf delivered through CS, showed symptoms of stress and hypothermia at birth. It had to be hospitalized 36 h later due to high fever. Arterial blood gas analysis showed low O₂ concentration. Radiograph of the chest revealed immaturity of lungs. On day 6 this calf was operated for an umbilical abscess and a patent urachus, after which it completely recovered and survived. The last calf in this group that was delivered vaginally with some assistance developed hypothermia and low blood O₂ concentration and died 12 h after birth. At necropsy, signs of immature lungs, bacteremia and septicemia were evident. In the I-group, 4 singles and a pair of twin calves (n=6) were born with a mean birth weight of 43.3+4.8 kg at 269.0+1.8d of gestation. Dexamethasone induced the parturition earlier than expected in 2 cases, resulting in unassisted birth of a surviving healthy calf 8 h post-injection, and birth of another calf 15 h post-injection. The latter calf died 3 h after birth due to hypoxia confirmed from immature lungs at necropsy. A twin and a single calf delivered through CS survived, while another twin and a single calf delivered through CS, died soon after birth and their necropsy revealed atelectatic lungs and presence of intrapulmonary meconium.

In this study, body temperature and blood O₂ saturation of calves ranged from 100.0 to 103.4°F and 69 to 94% at birth, respectively. All but one of the 8 live pre-term calves required clinical support, which ranged from supplemental O₂and symptomatic neonatal treatment on the farm, to surgery and intensive care in hospital. Overall, 4 of 8 live-born cloned calves survived and are living and healthy to date. Immature and incompletely inflated lungs appeared to be the primary cause of mortality in cloned calves born pre-term.

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