Forty Romney and Perendale ewes with a history of either high (W+) or low (W-) winter wool growth but similar summer wool growth were selected from a large flock. The ewes were not pregnant and were penned individually indoors and offered either 500 or 1500 g/d of high quality pelleted diet for 8 weeks in both winter and summer. The 2 breeds had similar intakes and live-weight changes, but the Romneys grew more wool. The W+ and W- ewes had very similar intakes and live-weight changes. Intakes on the low and high plane of nutrition respectively were 420 and 1093 g DM/d in winter and 422 and 1222g DM/d in summer. Corresponding live-weight changes were -71 and +54 g/d in winter and -112 and +131 g/d in summer. Summer wool growth rates were on average twice those in winter. Plane of nutrition had a much greater absolute effect on wool growth in summer than in winter (5.5 v 2.3 g/d), but the relative effects were similar (54 v 48%). The W+ ewes grew 38% more wool in winter than the W- ewes (5.8 V 4.0 g/d) and had a 38% higher mean staple strength (2.7 v 1.8 g/tex). Differences between the W+ and W- ewes were similar on the high and low planes of nutrition, and also similar for the Romneys and Perendales. The variation in winter wool growth and hence in staple strength was evidently due to variation in the partitioning of nutrients to wool growth rather than to variation in feed intake.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 217-220, 1985
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