Efficiency of using identical twins in sheep experiments

Abstract

Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 EFFICIENCY OF USING IDENTICAL TWINS IN SHEEP EXPERIMENTS J.C. GREEFFA and R.W. KELLY B *Wool Program, Agriculture Western Australia, Katanning, W.A. 6317 B Wool Program, Agriculture Western Australia, Albany, W.A. 6330 Studies of environmental factors affecting sheep production are influenced by the genetic variation that exists between animals. Recent technological advances in embryo splitting have increased the ability to produce sufficient identical twins for experimentation so it is now possible to exploit the uniformity that exists between genetically identical twins. Hancock (1951) published a series of papers on the similarity of identical twins in cattle, however, no results could be found for sheep. This paper reports the efficiency of the use of identical twins in wool sheep experiments. Thirty-five pairs of identical twins were produced over 2 years by splitting embryos collected at day 6 of pregnancy and placing each clone in a different recipient ewe. DNA testing has confirmed that the 35 pairs were identical. A wide range of fleece and body weight traits were measured at hogget age. The data were adjusted for the known environmental factors, ie birth year, sex of the lambs and age of the recipient dam and the intraclass correlation between members of a pair estimated. Efficiency was calculated according to the method of Biggers (1986) as defined in Table 1. The results presented in Table 1 indicate that 1 pair of identical twins can replace between 10 and 50 randomly selected animals in experiments without loss of statistical efficiency. Many investigations, however, involve the comparison of more than 2 treatments. Using a randomised block design, twins will allow the comparison of only 2 treatments. Biggers (1986) shows how these figures can be used to determine the most desirable experimental design where more than 2 treatments are involved. Table 1. Intraclass correlation and efficiency of using twins Feeding and maintaining large numbers of sheep is a major cost item in experiments. Identical the potential to reduce the number of animals necessary and maximise the utilisation of data as the reduced variation that exists between twins. If identical twins could be produced at low cost, dramatically increase the cost effectiveness of long term and detailed experiments. We wish to acknowledge the support given to the work by the Australian Wool Research and Organisation. BIGGERS, J. D. (1986). Theriogenology. 26: 1-25. HANCOCK, J. (195 1). N.Z. J. Sci. Technol. 33: 17-29. twins have a result of they could Promotion 419