Supplementary Feed Additives Can Improve Lamb Performance in Terms of Birth Weight, Body Size, and Survival Rate

SIMPLE SUMMARY: Grazing in arid and semi-arid regions causes ewes to suffer from feed shortages to some degree. This is particularly problematic in late pregnancy, when maximum fetal growth has been reached and the nutritional requirements of the growing fetus exceed maternal nutrient intake. The result is weaker offspring with lower birth weights and survival rates, which in turn affects livestock profitability. Finding an alternative to improve the supply of necessary nutrients to dams during pregnancy will help farm managers achieve healthy lambs with higher survival rates. Using additives involved in the energy status of animals, this study has shown that administration of these additives during late gestation reverses the debilitating effects of feed restriction and improves placental efficiency, thereby enhancing nutrient delivery to the growing fetus, such that lambs from ewes offered diets containing these additives had higher birth weights and subsequently higher survival rates. These results will help livestock producers in arid and semi-arid regions to benefit from the combined administration of the three substances, namely propylene glycol, rumen-protected choline chloride, and monensin sodium, when feeding pregnant ewes. ABSTRACT: To evaluate the effects of supplementation of feed additives in the last trimester of pregnancy on placental characteristics and offspring performance, this study was conducted with 48 estrous-synchronized Ghezel ewes that had randomly been assigned to one of the following six groups (n = 8): ad libitum feeding (AL); feed restriction (RF; 60% of ad libitum intake); feed restriction + propylene glycol (PG); feed restriction + propylene glycol + monensin sodium (MS); feed restriction + propylene glycol + rumen-protected choline chloride (RPC); feed restriction + propylene glycol + monensin sodium + rumen-protected choline chloride (PMC). Birth weight, body size, and rectal temperature of lambs were determined within 24 h of birth. The presence of lambs at 87 days of age was used as an index of survival to weaning. The outcome of this study was that the average placental weight of ewes in the AL and MS groups was the highest and lowest, respectively, among the treatment groups (p < 0.01). RPC ewes presented higher placental efficiency compared to AL, RF, and MS ewes (p < 0.05). The largest and smallest crown-to-rump lengths (CRLs) were observed in PMC and RF lambs, respectively (p < 0.01). In addition, lambs born from PMC, RPC, and PG ewes had a longer curved crown-to-rump length (CCRL) than those born from AL and RF ewes (p < 0.01). The concurrent administration of propylene glycol and rumen-protected choline chloride resulted in the highest birth weight among treatment groups (p < 0.01). Lambs born to PMC and RPC ewes had a higher survival rate and rectal temperature than those born to RF ewes (p < 0.05). It can be concluded that although dietary restriction does not have adverse effects on lambs’ performance compared with ad libitum intake, the combined administration of propylene glycol and rumen-protected choline chloride in the ewes’ restricted diet can improve placental characteristics and subsequently amend lambs’ birth weight and body size. Therefore, the combined administration of these additives can be practiced during feed restriction.