The timing of nutritional restriction during reproduction influences staple strength

Abstract

The staple strength of wool from Merino ewes (liveweight 41 kg; condition score 1.5) was assessed in response to a short-term nutritional restriction at different stages of pregnancy and lactation. Single- and twin-bearing ewes were fed to maintain maternal liveweight (control) or restricted to lose 2 kg in maternal liveweight between Days 85 and 98, 113 and 126, or 141 and 154 of pregnancy, or Days 169 and 182 in early lactation. Unmated control ewes were fed to maintenance, and a group of unmated ewes was restricted between the equivalent of Days 141 and 154 of pregnancy. All groups were maintained in group-feeding pens from Day 8 of pregnancy to 4 weeks after weaning of lambs. The ewes were fed lucerne hay.

Control ewes fed to maintain liveweight produced sound wool (unmated 52.7, or single-rearing 46.0, and twin-rearing 43.0 N/ktex). Nutritional restriction only reduced the staple strength of wool produced by unmated ewes by 2.2 N/ktex (P > 0.05), but reduced that of reproducing ewes by 0–26.8 N/ktex. The decline in staple strength of reproducing ewes increased as the time of restriction during pregnancy advanced. Restriction during lactation did not significantly (P > 0.05) influence staple strength. The effect of restriction appeared to be mediated via changes in diameter along fibres. The results indicate that there is variation in the sensitivity of staple strength to short-term nutritional restriction, with both pregnancy status and the stage of pregnancy at which the restriction is imposed influencing the impact on staple strength.