This study investigated whether heterosis was present when crossing sheep from four closed Romney flocks selected for increased fleece weight. Three of the flocks had been developed by AgResearch (C, W and H) and one by Massey University (M). Each ewe was joined with a single ram according to a diallel design to generate single-line, two-line and four-line cross progeny. The trial ran from 1988 to 1996 with 599 records available for analysis. In rank order, the mean (± standard error of mean) greasy yearling fleece weight (kg), adjusted for year, sex, pre-shearing live weight and days of wool growth was W (3.41 ± 0.08), H (3.39 ± 0.12), C (3.31 ± 0.10), M (3.10 ± 0.15) for the "single-line" groups, WC (3.40 ± 0.09), MW (3.36 ± 0.10), CH (3.24 ± 0.08), WH (3.16 ± 0.11), MH (3.14 ± 0.11), MC (3.14 ± 0.10) for the "two-line" crosses and 3.26 ± 0.06 for the four-line cross. Combining sheep from two or more flocks independently selected for increased fleece weight resulted, on average, in no heterosis in wool production among resultant progeny.

RMW, Sumner, JN Clarke, HT Blair, NG Cullen, and HV Henderson

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 195-199, 2006
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