Effects of short-term administration of a glucogenic mixture at mating on feed intake, metabolism, milk yield and reproductive performance of lactating dairy ewes

The effects of the intra-ruminal dosing of a glucogenic mixture including 70% glycerol, 20% propylene glycol and 10% water was studied on thirty late lactation dairy ewes of Sarda breed. The animals were divided in two homogeneous groups receiving by gavage either 200 mL of water (CTR group; body weight 40.9 ± 1.5 kg) or 200 mL of the above mixture (GLY group; body weight 39.4 ± 1.3 kg) twice daily from d 16 to d 19 of the oestrus cycle, synchronised by “ram effect”. The ewes were then mated and their reproductive responses to the synchronised mating evaluated by scanning on d 50 and at lambing. During the treatment, the ewes were housed in an open hut, machine milked twice daily and fed concentrate and hay to meet their nutrient requirements. During the treatment, concentrate intake was markedly reduced in GLY when compared with CTR (P < 0.001), without any effect on ewe body weight or body condition. The administration of the glucogenic mixture increased plasma osmolarity and blood volume as estimated by serum total protein concentration. Moreover, it increased plasma content of glycerol, glucose (P < 0.001) and insulin (P < 0.01) while decreasing plasma level of NEFA (P < 0.001) and urea (P < 0.05). Milk yield (P < 0.01) and milk lactose content (P < 0.001) were decreased by the glucogenic treatment, whereas milk protein and casein contents were increased (P < 0.001). As for reproductive performance, the glucogenic treatment numerically increased ewe's conception rate, but the difference was not statistically significant. Prolificacy did not change between groups. In conclusion, the administration of a glucogenic mixture to late lactation dairy ewes caused significant changes both in plasma and in milk composition during the treatment. However, reproductive performances were unaffected by the treatment.