32 CHARACTERISTICS OF BOVINE CLONE OFFSPRING (F1): COMPARISON WITH CLONES

Abstract

Information on clone offspring (F1) remains limited, especially in species with a long intergeneration interval such as cattle. In the present study, we report data on calves born from cloned females at the INRA experimental unit. Characteristics of these offspring are compared to that of clones or AI control animals born and raised in the same farm. Currently, 39 F1 have been obtained after AI of 64 cloned heifers from 3 different Holstein genotypes, with semen from 6 different Holstein sires. All calves were naturally delivered at term with a mean easy calving score of 1.58 and a normal pregnancy length of 282 days. There were 20 males and 19 females, resulting in a normal male/female sex ratio of 51/49%. Male calves were euthanized during the first 3 months after birth, and a group of 18 Holstein single-born female F1 were further considered and compared to female AI controls (n = 68) or clones (n = 50) all Holsteins. The mean birth weight of the female F1 was 40.28 ± 3.32 kg (range 35–44), not significantly different from that of AI controls: 40.57 ± 5.55 kg and significantly lower (P < 0.05) and less variable than that of the clones: 49.27 ± 10.93 kg. No case of large offspring syndrome was observed in the F1 group. Postnatal survival in the clone offspring group was normal as 17/18 of the females (94.4%) remained alive and healthy by 6 months of age. This was comparable to survival in the AI control group: 64/68 (94.1%) and higher than for clones at the same age: 35/50 (70.0%). Animals were weighed every month. There were no statistical differences between the clone offspring group and the AI controls raised in the same conditions, with a total body weight of 188.25 ± 15.17 kg v. 185.30 ± 18.94 kg by 6 months of age and a daily weight gain of 0.820 and 0.803 kg day^–1, respectively. The oldest F1 heifers are now mature and their reproductive function is being evaluated. Some animals are already used as recipients in an embryo transfer program. As enlarged internal organs had been reported for clones, we analyzed the data from euthanasia of 20 male F1 by weighing the different organs after postmortem examination. The mean ± SD relative organ weight (% of body weight) was compared to that of somatic clones (n = 18) and a limited number of AI control calves (n = 5) previously autopsied in our institute at similar ages. Figures were very similar between F1 and controls, but significant differences (t-test, P < 0.05) were observed between F1 and clones. F1 had a smaller (and less variable) liver ratio than clones (0.022 ± 0.004 v. 0.028 ± 0.009, respectively), a smaller kidney ratio (0.005 ± 0.001 v. 0.007 ± 0.002), and a lower heart ratio (0.008 ± 0.002 v. 0.010 ± 0.003) than clones. No significant difference was observed between groups for thymus/body ratio. None of the F1 calves presented any of the pathologies observed in clones. Altogether, these results indicate that clone offspring F1 develop similarly to AI controls and differ from the clones themselves.