An inquiry has been made to determine whether shearling rams sire more good-quality offspring than would be expected from the proportion of them used in Swaledale flocks in northern England, 1951–3.

Quality was assessed at two levels, both concerning shearling rams: those passed for registration in the Flock Book, and those making £50 or more at Kirkby Stephen ram sale.

The expected percentage of lambs, and hence good-quality offspring, by shearling rams was estimated from the practice on a sample group of farms, using the formula

where E is the estimated percentage of lambs by shearlings, x the proportion of shearlings to all rams in use, and y the fractional value in numbers of ewes served where aged rams are regarded as having unit value.

The estimated percentage of lambs by shearlings is 28·7, with s.e. = 2·444.

The actual percentage of registered shearlings sired by shearlings in 1951–3 was 35·7 with s.e. = 0·764, and the actual percentage of shearlings sold for £50 or more in the same years was 32·8 with s.e. = 3·313.

That shearlings sire a slightly, but significantly, higher number of registered shearlings than would be expected is probably due to the transmission of earlymaturing qualities, since shearlings of high quality are consistently used in early-maturing, and therefore shearling-producing, flocks. Those likely to sire ‘£50’ shearlings often remain in early-maturing flocks throughout life and, by continuing to sire this high-quality progeny, depress the percentage of such shearlings sired by shearlings to a figure not significantly higher than the ‘expected’ figure.