37 ANATOMICAL DEVIATIONS IN APPARENTLY HEALTHY, WEANED, CLONED CALVES

Abstract

Bovine somatic cell nuclear transfer (NT) is associated with increased incidence of abnormal placental and fetal development. NT fetuses often show an overgrowth phenotype involving the liver, kidney, heart, adrenals, and thyroids. About 10% of NT embryos will result in a live calf and only 67% of these will survive to weaning at 3 months of age. Those that survive beyond weaning appear normal but underlying health problems may not be revealed until the animals are stressed, physiologically challenged, or subjected to postmortem (PM) examination. The health and physiology of NT predominantly (75%) Jersey bull calves (n = 11) and Jersey bull control calves (n = 5) derived from artificial insemination (AI) were investigated. Routine blood analyses were carried out at 3 weeks and then at 3 and 6 months of age. The animals were euthanized at approximately 7 months of age and a full PM undertaken, including histological examination of organ tissues. Calf and organ weights were recorded. The bone mineral density (BMD, g cm²) of the left femur was determined by dual energy x-ray absorptiometry (DEXA). The mean values for the various parameters were compared between treatments using one-way ANOVA. One of the calves died at 40 days from acute hemorrhaging in the abomasum, and a second, at 50 days from respiratory infection. The remaining 9 NT and 5 AI calves appeared healthy at the time of euthanasia, and PM results showed no major gross or histological organ abnormalities. Plasma electrolytes of all animals were within the normal range. Mean NT body weight was significantly higher than that of AI calves (169 vs. 141 kg, respectively; P < 0.0001) but this may have been due in part to the minor beef genetic contribution. Comparison of organ weights relative to the total body weight identified the mean relative NT brain (P < 0.0001) and lung (P < 0.01) weights to be lighter than those of controls, whereas the mean relative weight of the chest thymus (P < 0.05), thyroid glands (P < 0.001), and left testis (P < 0.05) were heavier in NT than in controls. Interestingly, mean femur weight (P < 0.01) and mean overall BMD (P < 0.05) were higher in NT than in AI calves. The mean bone shaft BMD of NT calves was greater (P < 0.05) than that of the controls, although no difference in BMD was evident at the growth plate. The current study indicates that surviving NT calves are apparently healthy but still manifest certain organ abnormalities frequently seen in NT fetuses of failing pregnancies. Identification of osteopetrosis of the long bones suggests that osteoclast differentiation or function is altered in NT calves. Modulation of hematopoietic progenitor differentiation by the NT process may explain the osteopetrosis and the reported compromised immune function and response of NT animals subjected to mild stressors since osteoclasts, monocytes, and macrophages are derived from the same progenitor cells. However, further studies are required to test this hypothesis.

This work was supported by NRCGD and FRST contract C10X0311.