PSIV-2 Gestational heat stress and its impact on placental weight, colostrum production, and milk production on Columbia-Rambouillet ewes

Heat stress during pregnancy causes placental insufficiency and resduces fetal growth by reducing the oxygen and nutrients availability. In lactating production animals, heat stress during gestation lowers performance by decreasing milk yield and impairing reproduction. The study objectives were to understand the consequences of the exposure to warm environmental conditions during pregnancy on placental weight, colostrum production, and milk production of ewes utilizing heat chambers. Columbia-Rambouillet pregnant ewes with singletons (n = 11) were assigned to one of two environmental treatments: 1) heat stress (HS) or 2) thermoneutral (TN; 22°C) during mid-gestation (d 40 to 80) for a duration of 40 d. Heat stress consisted of 12 h at 40°C/55% humidity and 12 h at 35°C/45% humidity. Dry matter intake (DMI) and water intake (WI) were measured daily for both treatment groups. Feed and water were given ad libitum for HS ewes and TN ewes were pair fed to HS ewes for the entire duration of study. At lambing, the offspring were separated from dams. Measurements were taken of placental weight and colostrum production. The placental weights from HS ewes had a mean of 218 g compared with the placental weights of the TN group at a mean of 396 g (P < 0.01). Colostrum was measured for the first 24 h post lambing. The mean colostrum production of TN was 718 mL and for the HS group it was 882 mL. The colostrum production differences between control and HS groups were nonsignificant. Following lambing, ewes were milked twice a day for a 21-d period to evaluate milk production. Daily milk production for HS ewes was a mean of 1.16 kg/d while the TN group ewes had a mean of 1.31 kg/d (P < 0.01). Exposure of HS during mid-gestation had a significant impact on placental weight and 21-d milk production.