Two sets of correlated responses were studied in five Romney selection lines and their controls. The lines were from one experiment selecting for yearling body weight or yearling fleece weight since 1967, from a second experiment selecting for weaning weight or yearling fleece weight since 1973, and from a third experiment selecting for yearling body weight since 1973. Overall, the five selection lines were evaluated whilst being run together with controls at a single site. The responses were faecal egg count (FEC) after weaning, using lamb crops born in 1990#x2013;93, and food intake using 1993#x2010;born 7#x2010;month#x2010;old ram lambs. Four or five new sires were used per line per year, with 1471 and 232 animals being recorded for FEC and food intake respectively. The three body weight lines were each 20#x2013;22 heavier than their respective controls in March (6 months of age) and May. Average FEC over this time period was significantly greater by 63 in one of these three lines whereas there was no difference from the control in the other two body weight lines. The two fleece weight lines were 10#x2013;11 heavier in March#x2014;May, with 34#x2013;35 heavier yearling fleece weights, than their respective controls, whereas average FEC was significantly greater (by 35 and 46) in both selection lines. Significant correlated increases in estimated food intake were recorded in all three body weight lines and in one of the two fleece weight lines, and these increases were proportional to the liveweight response. The implications of the correlated responses and their variability are discussed.
展开▼
