A Population Genetic Study on Yaks, Cattle and Their Hybrids in Nepal Using Milk Protein Variations

Milk protein polymorphisms in yaks, cattle and their hybrids in Nepal were examined in order to measure their genetic variability, to do a genetic characterization of cattle, and to test the possibility of gene flow between yaks and cattle. Simultaneous phenotyping by isoelectric focusing detected five molecular types (B, C, E, X and Y) of αS1-casein, two molecular types (A2 and B) ofβ-casein, three molecular types (A, B and X) of κ-casein, two molecular types (A and B) of α-lactalbumin and four molecular types (A, B, E and X) of β-lactoglobulin. The degree of genetic variability within populations measured by average heterozygosity for the milk protein loci was higher in cattle (24-33%) than in yaks (16%). Principal component analysis suggested that yaks were genetically much differentiated from cattle, and that there was substantial genetic differentiation among local populations of cattle in Nepal. In the comparison with cattle breeds in Europe, Japan and India, Nepalese cattle were basically similar to the breeds of Indian cattle. The distribution of three alleles (αS1-CnE, κ-CnX and β-LgE) which were suspected to occur uniquely in yaks showed no possibility of gene flow from yaks to Nepalese cattle through traditional production of hybrids by the Sherpa and other mountain tribes. Anim. Sci. Technol. (Jpn.) 63 (6): 563-575, 1992 key words: Nepal, milk proteins, yak, cattle, hybrid, isoelectric focusing Hybrids between yaks and cattle, used as pack or milking animals, have traditionally been bred by the Sherpa and some other mountain-dwellers in the Nepal Himalayas9,16,18). Anim. Sci. Technol. (Jpn.) 63 (6): 563-575 563 1992 KAWAMOTO, NAMIKAWA, ADACHI, AMANO, SHOTAKE, NISHIDA, et al. These animals are distributed widely in the society of Himalayan highlanders and have had prominent roles in trans-Himalayan and domestic trades9,10). The rearing range of yaks is restricted into high altitudes, usually more than 2700m, while the lowlands are occupied mainly by local breeds of cattle6). We conducted a population study in 1988 and 1989 in order to do a morphological and genetic characterization of native livestock in Nepal15,19,20,28) Milk protein was employed as a genetic marker in this study. Genetic polymorphisms are known for the major milk proteins in cows and yaks2,7,12,13,14,23,24). GROSCLAUDE et al.13) investigated a local population of yaks in Langtang, Nepal, and reported species-specific variations in β-lactoglobulin and αS1-casein. In this study, variations in major milk proteins were examined with the aims of i) quantification of genetic variations within and between the populations of yaks, cattle and their hybrids, ii) genetic characterization of Nepalese cattle in view of milk proteins, and iii) assessment of genetic interaction between yak and cattle populations in relation to the traditional production of hybrids by the Sherpas and other local people. Materials and Methods Milk samples were collected from four localities in Nepal (Fig. 1). Those of yaks and hybrids were taken from Khumjung and its surrounding villages in the Solukhumbu district. Those of cows at different altitudes were obtained from the Dhaulagiri zone (highland), Pokhara (midland), and Sauraha (lowland). Sodium azide was added to the milk samples for preservation during transportation, then skim milk prepared by centrifugation was stored at -70°C until examination. Milk proteins examined in this study were as follows; αS1-casein (αs1-Cn),β-casein (β-Cn), κ-casein (κ-Cn), α-lactalbumin (α-La) and β-lactoglobulin (β-Lg). Simultaneous phenotyping was performed by isoelectric focusing with a thin layer of urea-polyacrylamide gel, Fig. 1. A map showing sampling localities in Nepal . The milk samples were collected at Khumjung and its surrounding villages in the Solukhumbu district. Those from the Dhaulagiri zone were obtained at the villages of Dana, Lete, Tukche, Marpha, Syang and Jharkot.