Effects of maternal factors during pregnancy on the birth weight of lambs in dairy sheep

Abstract

The aim of the present study was to evaluate the influence of physiological and productive factors of ewes (age and type of pregnancy and level of milk production) during pregnancy on birth weight of lambs. The study was carried out in a single commercial farm on 334 Lacaune dairy sheep, classified by age (187 mature and 147 maiden ewes), pregnancy type (155 single vs 179 multiple pregnancies), milk production average milk yield per day (YDIM),from conception to drying off; 45 Low yielding, LYDIM, <1.37 l/d; 70 Average yielding, AYDIM, 1.37 to <1.8l/d; 72 High yielding, HYDIM, >1.8 l/d; and average milk yield per day during month of conception (Yc); 45 Low yielding, LYc, <0.91 l/d; 70 Average yielding, AYc, 0.91 to <1.3 l/d; and 72 High yielding, HYc, >1.3 l/d). Lambs body weight was recorded in 576 lambs (253 males, 323 females) at birth and at 18 days old. Differences among groups were evaluated with ANOVA and Kruskal-Wallis test when non-normal distributed. The lambs born to mature ewes were heavier than those from maiden ewes both at birth (4.2±0.8 vs 3.5±0.8 kg; P<0.0001) and at 18 d-old (8.8±2.0 vs 6.8±1.6 kg; P<0.0001). Newborns from single pregnancies were heavier at birth than those born from multiple pregnancies (4.3±0.9 vs 3.8±0.8 kg; P<0.0001), but no difference was found at 18 d-old (8.0±2.1 vs 7.9±2.1 kg; P>0.05). The birth weight of lambs was similar in the groups HYDIM and AYDIM and heavier in these both groups than lambs from the groups LYDIM (4.3±0.8; 4.3±0.8; 4.0±0.8 kg; P<0.05); there were no differences at 18 d-old. Concomitantly, lambs of the groups HYc and AYc were heavier than lambs in the group LYc at birth (4.4±0.8; 4.2±0.7; 4.1±0.8 kg; P>0.05), but values were similar among the three groups at 18 d-old. The present study suggests that, age, type of pregnancy and level of milk production during gestation in ewes are determinants of lamb birth weight.