Effects of soybean oil inclusion in the pre-lambing diet on udder size, colostrum secretion, and offspring thermoregulation and growth in hair-breed ewes

Dietary inclusion of vegetable oils in pregnant females is beneficial to improve offspring development and growth during its pre- and post-natal life because these oils are rich in polyunsaturated fatty acids. Excessive oil intake can result in contrary effects. To evaluate the effects of dietary inclusion level of soybean oil (SBO) during the last third of gestation on udder size, production and composition of colostrum, newborn thermoregulation, and lamb growth during the pre-weaning period, 30 Katahdin x Pelibuey multiparous ewes (Body weight [BW]= 50.8±0.38 kg, body condition score [BCS]= 3.02±0.04 units) were assigned under a randomized complete block design to 1 of 3 treatments, which consisted in isoenergetic and isoprotein diets containing 0, 30 or 60 g of SBO/kg DM. Diets were offered from d 100 of pregnancy to lambing. All measurements were collected around lambing and first 60 d post-lambing. There was no treatment x time interaction for BW, BCS, production and chemical composition of colostrum, and offspring thermoregulation. Maternal BW and BCS as well as chemical composition were not affected by SBO. Weight and volume of colostrum linearly increased (P = 0.01) as the dietary level of SBO increased from 0 to 60 g/kg DM. Rectal temperature in newborn lambs was not affected by SBO, but eye and muzzle temperatures, as well as coat temperatures from ear, muzzle, loin, right flank, belly, rump, shoulder and leg linearly increased (P < 0.01) with increasing the SBO level in the pre-lambing diet. Treatment x time interaction affected (P ≤ 0.05) udder traits, being higher udder volume and circumference in ewes fed 60 g of SBO/kg DM than in control during the pre-lambing period. At birth, morphometric measures in lambs were unaffected by the treatment x sex interaction or main factors, while male lambs from ewes fed 60 g of SBO were the heaviest (P < 0.01) compared to any of the other treatments. Pre-weaning daily weight gain and weight at weaning showed a quadratic effect (P ≤ 0.05) with increasing levels of SBO. In general, results suggest that dietary inclusion of 60 g of SBO/kg DM during the last third of pregnancy in hair ewes could be an optimal dose to simultaneously increase colostrum production, udder size pre-lambing, newborn thermoregulation and pre-weaning growth of their lambs.