The effect of nutrition in mid pregnancy and ewe liveweight change on birth weight and management for lamb survival in highly fecund ewes

Abstract

The effect of moderate undernutrition in mid pregnancy on lamb birth weight and survival of single- and multiple-bearing ewes is reported. A total of 1220 ewes of 3 crossbred types with different fecundity, Booroola Merino x Dorset (BD), Trangie Fertility Merino x Dorset (TD) and Border Leicester x Merino (BLM), were examined over 2 years. The treatments were low (L) and high (H) nutrition at pasture for 4 weeks from about day 75 of pregnancy. Ewe liveweight of the L group at the end of the treatments was 5 kg lower in 1984 and 8 kg lower in 1985 (P<0.01) than the H group. The differences were smaller by late pregnancy and post-lambing. The L treatment increased (P<0.01) birth weight by 0.16 kg in 1984 but had little effect in 1985. Litter size had the greatest effect on birth weight (P<0.01). Ewe crossbred type and lamb sex effects were also significant (P<0.01), although they tended to be reduced for higher order births. Nutritional treatment had no effect on gestation length. Ewe liveweight at joining and weight gains before and after the treatment period significantly affected birth weight and accounted for the large difference in birth weight between years (0.7 kg). Ewe weight gain during the treatment period in mid pregnancy had no significant effect on lamb birth weight. Nutritional treatment in mid pregnancy had no effect on lamb survival. Litter size significantly affected lamb survival, although inclusion of birth weight in the model reduced the effect. Weather conditions, as measured by chill index, significantly (P<0.01) affected lamb survival in 1984 but accounted for less variation in 1985 (P<0.05). Lamb survival for ewes was ranked BLM > TD > BD. Maximum survival was achieved at birth weights of 4-5 kg from BD and TD ewes and 5-6 kg from BLM ewes. The L treatment reduced (P<0.01) ewe greasy fleece weight by 0.15 kg but did not affect staple strength. Plasma glucose concentration at the end of treatment was lower (P<0.01) for L ewes, but there was no difference between L and H ewes in late pregnancy. Glucose declined with increasing fetal number. Plasma B-hydroxybutyrate concentration was lower for the H group than for L, and also for BLM than TD and BD ewes (P<0.01).

The birthweight and survival of Merino lambs can be predicted from the profile of liveweight change of their mothers during pregnancy

“…Hence, it was not surprising that the overall survival to 48 h after birth (86% for singles and 65% for twins) was towards the top end of the published data for Merinos (Lax and Turner 1965;Atkins 1980;Fogarty et al 1992). Nonetheless our data showed a typical quadratic relationship, lamb survival increased up to a birthweight of 4.5 kg and only declined for single lambs when they weighed more than 6.5 kg at birth as previously reported by Atkins (1980) and Knight et al (1988).…”

“…The birthweight of single (5.1 kg) and twin (3.8 kg) lambs in this study were in the optimum range (3.5-6.0 kg) for survival of Merinos (Atkins 1980;Hinch et al 1985;Fogarty et al 1992). Hence, it was not surprising that the overall survival to 48 h after birth (86% for singles and 65% for twins) was towards the top end of the published data for Merinos (Lax and Turner 1965;Atkins 1980;Fogarty et al 1992).…”

“…Restricting the level of nutrition to the pregnant ewe can reduce lamb birthweight dependent on the timing and severity of the restriction (Holst et al 1986), although others suggest changes in ewe liveweight were not associated with effects on birthweight (Fogarty et al 1992). Nonetheless, where there are adverse effects of nutrition during early and mid pregnancy they can be overcome by adequate nutrition during late pregnancy (Taplin and Everitt 1964).…”

Opportunities for genetic improvement of lamb survival

“…Under less inclement lambing conditions in other years, no association between lamb survival and birth coat was observed (Mullaney 1966). Future studies will fit wind chill as a covariate (to be calculated from meteorological data recorded at all IN sites) in analyses of IN data, similar to studies by Donnelly (1984) and Fogarty et al (1992) to better ascertain the importance of birth coat and other factors to lamb survival.…”

Growth and carcass characteristics of lambs sired by Dorper and Dorset rams1

“…High triplet and quadruplet death losses have often been reported in lambs from prolific Booroola Merino crossbred ewes. In Australia, death losses in offspring of Booroola Merino crossbred ewes ranged from 14 to 16% for singles, 14 to 33% for twins, 34 to 67% for triplets, and 60 to 61% for quadruplets (Owens et al, 1985;Kleemann et al, 1990;Fogarty et al, 1992). In a large New Zealand study including 1,776 triplet and 538 quadruplet lambs (Hinch et al, 1985), death losses to weaning in lambs born on pasture averaged 9.9% for singles, 19.1% for twins, 44.7% for triplets, and 53.6% for quadruplets; 78% of these deaths occurred within 2 d of birth.…”