51 PHENOTYPIC VARIATION IN CLONED SWINE IS CORRECTED IN THE F1 GENERATION

Abstract

Systematic studies of cloned animals generated from adult somatic cell nuclei are critical in assessing the utility of somatic cell cloning in various applications, including the safety of food products from cloned animals and their offspring. Studies in mice show that abnormalities seen in the cloned parents are not transmitted to the siblings. To our knowledge, however, there are no studies on the F1 progeny of clones from food animals. Previously, we compared somatic cell derived cloned pigs with naturally bred control pigs on a series of physiological and genetic parameters. Phenotypic and genetic analyses indicated that there are two classes of traits, one in which the cloned pigs have less variation than controls and another characterized by variation that is equally high in cloned and control pigs. We have extended our studies to the F1 progeny of these clones to see whether these phenotypic differences are transmitted to the next generation. Age-, sex-, and breed-matched cloned and control pigs, housed together since weaning, were used in this study. Starting with their second estrus cycle, standing gilts were mated two consecutive days. All gilts were mated to the same boar. Pregnant cloned (n = 9) and naturally bred (n = 5) gilts (F0) were allowed to farrow naturally, and number and sex of live offspring at birth (F1) recorded. There was no difference in the average litter size between litters from cloned gilts and naturally bred controls (7.78 ± 2.6 and 7.40 ± 3.0, respectively; mean ± SD) or in the degree of litter size variation (coefficients of variation of 33.4% and 40.5% for litters of clones and controls, respectively). Similarly there were no statistical differences between sex ratios from cloned litters (51%:49%; M:F) and control litters (59%:41%; M:F). Blood profiles among cloned pigs, control pigs, and their progeny were compared at two time points, i.e. 15 and 27 weeks, to quantify the effect of cloning on various blood parameters and their transmission to next generation. Although the range of values for all traits overlapped between different classes, the variation differed between F0 clones and F0 controls. In the clones there were two groups of traits: one in which cloned pigs had less variability than controls, and the other in which clones had the same variability as control pigs. In contrast, the variability between all of the traits in F1 progeny of both the clones and the control pigs was similar at 15 and 27 weeks, with one exception. Combined, our data and previous results in mice strongly support the hypothesis that offspring of clones are to all intent and purposes indistinguishable from offspring of naturally bred animals, and as such there should not be any increased risks associated with consumption of products from these animals.

This work was supported from NIH grant HL 51587 to JAP.