EFFECT OF SELECTION FOR GLUCOSE-TOLERANCE IN SHEEP ON CARCASS FAT ANDPLASMA-GLUCOSE, UREA AND INSULIN

Over 5 years (1987-91), the progeny of rams selected for fast (Low T-h alf) or slow (High T-half) glucose clearance after an intravenous gluc ose tolerance test, differed significantly in glucose tolerance. In co mparison with an unselected control, the line differences were mainly in the direction of Low T-half. They appear to have arisen during the establishment period, with little evidence of enhanced divergence over the four subsequent years of continued selection (heritability 0.10 /- 0.03). The Low line had higher plasma insulin concentrations during the glucose tolerance test than the High line. Basal plasma concentra tions of glucose were lower, and urea higher in the Low than the High line. In addition, carcasses of Low line ram progeny had more subcutan eous fat at the same carcass weight than High line carcasses (11% high er GR in the final year of the experiment). Selection of sheep for glu cose clearance appeared to be associated with differential partitionin g of nutrients into adipose tissue, the pooled genetic correlation bet ween T-half and GR being -0.28 +/- 0.13.