Birth weight responses to shearing ewes in early to mid gestation

Abstract

This study compared the effect on foetal growth of shearing ewes in very early pregnancy (day 50) with the effect of shearing later in pregnancy (day 70 or 100). One hundred and sixty ewes were allocated at day 49 of pregnancy to four ‘time of shearing’ treatments — pregnancy day 50 (P50), P70, P100 (no. = 45 ewes per treatment) and unshorn (shearing of this group occurred 43 days after weaning) (no. = 25); two methods of shearing (by standard comb and cover comb); and two levels (1 or 2) of pregnancy/rearing rank. All ewes had been mated over a 28-day period and grazed pasture throughout the trial. The mid point of lambing was 27 August 1996. Live weights of ewes (corrected for fleece weight) were not influenced by shearing time at any stage except at day 45 of lactation when ewes shorn at P50, P70 or P100 were about 3⋅0 kg lighter than unshorn ewes. Shearing method had no effect on ewe live weight. Time of shearing and shearing method had no effect on ewe greasy fleece production or wool tensile strength. Shearing significantly (P < 0⋅05) influenced the birth weight of single- (by 0⋅7 to 0⋅8 kg) but not twin-born lambs. Maternal plasma triiodothyronine concentration increased proportionately by 0⋅47 to 0⋅85 (P < 0⋅05) and lasted for at least 20 days in response to shearing irrespective of time of shearing. No difference in plasma insulin concentration was detected between shearing groups but plasma glucose concentration proportionately increased by 0⋅06 to 0⋅16 (P < 0⋅05) for 10 to 20 days after shearing. These results indicate that shearing between day 50 and 100 of pregnancy can increase lamb birth weights and that the response is associated with an increase in thyroid hormone concentrations in the maternal circulation.

Epigenetics and developmental programming of welfare and production traits in farm animals

“…Shearing pregnant ewes has consistently been reported to increase lamb birthweight, particularly if conducted during early to mid-gestation ( Figure S3). Associated with this response are increases in maternal feed intake, gestation length and maternal plasma glucose concentrations (Symonds et al 1988;Morris et al 2000;Keady and Hanrahan 2009;Banchero et al 2010). Although shearing is associated with a robust stress response in the ewe, these data suggest that its primary effect on birthweight is through increased feed intake, and hence nutrition of the developing lamb.…”

Thyroid hormones in small ruminants: effects of endogenous, environmental and nutritional factors

“…On the other hand, cold stress in ewes (Hocquette et al, 1992) ram lambs (Ekpe and Christopherson, 2000; Doubek et al, 2003) and shearing (Morris et al, 2000;Merchant and Riach, 2002) induced increases in blood TH levels. The seasonal pattern of blood TH levels often showed maximal values during winter (cold months) and minimal during summer (hot months) (Salem et al, 1991;Webster et al, 1991;Okab et al, 1993;Menegatos et al, 2006).…”

Birth weight effect in twin‐born lambs from mid‐pregnancy shearing is associated with changes in maternal IGF‐I concentration

“…A similar relationship was observed by Revell et al (2000) who suggested the reduction may reflect an increase in the expression of the IGF-I receptor. The IGF-I receptor is regulated, in part, by thyroid hormones, which, in mid pregnancy shorn ewes, display a period of elevation for up to several weeks (Morris et al 2000). However, under conditions in which mid pregnancy shearing tended to increase twin-lamb birth weight, neither short-or long-term elevation of maternal thyroid hormones had any effect (Kenyon et al 2005).…”