Behavioral, physical, and physiological variation among litters of cloned pigs

Abstract

The variability of behavioral, physical, and physiological characteristics among cloned animals has yet to be studied. Through a series of behavioral, physical and physiological measurements, we quantified the variation in food preference, temperament, time budgets, weight, shoulder width, nose to tail length, growth rate, a serum chemistry panel, and two hormone concentrations (cortisol and T₃). The subjects consisted of two genetically identical Duroc litters (n = 5, 4) and their naturally bred age matched controls (n = 4, 4). All litters of pigs were tested for their food preference using apples, bananas, crackers, and carrots. Variation in temperament was determined by timing latency to remove a towel (Towel Test) and by counting vocalizations and escape attempts during Back and Pick-up Tests. Two hundred sixteen hours of time lapse video were used to determine time budgets of the pigs consisting of the following behaviors: lying in bedding, lying on concrete, standing, feeding, and play/fighting. Weights, shoulder widths, and nose to tail lengths were determined between the ages of 8 and 9, 14 and 15, and 20 and 21 weeks of age. The average daily gain from one growth point to the next was quantified for these physical traits as well as an overall average daily gain. Blood was collected from the pigs at 15 and 27 weeks of age for a serum chemistry panel and determination of cortisol and T3 concentrations. The clones were similarly or more variable (P < 0.05) than the naturally bred controls: in their preference for the foods in 13 of the 16 comparisons; in five of the eight comparisons during the Towel Test; in all four comparisons in the Back and Pick-up tests; and in all 10 comparisons in the time budget analysis. The clones were also similarly or more variable (P < 0.05) than the natural bred controls: in all 18 physical measurement comparisons; in 17 of the 18 growth rate comparisons; and in 19 of the 28 physiological comparisons. Overall, clones were also similarly or more variable (P < 0.05) than the natural bred controls in 87 of the 102 comparisons in this study. These results reinforce the importance of epigenetic and environmental effects on animal behavior and question the use of cloning by nuclear transfer to replicate animals with specific behavioral, physical, or physiological characteristics.