35 Effect of Late Gestational Heat Stress on Placental Characteristics in Dairy Cattle

Abstract

Abstract To determine the effects of late gestation heat stress on placental development, dairy cows were exposed to heat stress (HT, shade) or cooled (CL, shade, fans and soakers) during the final 46 d pre-calving on the University of Florida dairy facility (temperature-humidity index; THI >68). We hypothesize heat stress (or lack of heat abatement) will reduce placental efficiency and in turn increase placental weight, surface area, and volume. At expulsion all placentae were collected and total placental weight was determined as well as individual cotyledonary weights, surface areas, and volume. In addition, the total number of total cotyledons was recorded and cotyledonary color and placental growth abnormalities (i.e. teratomas) were recorded and photographed. All data were analyzed using PROC MIXED in SAS. In addition, associations between parameters were determined by calculating Pearson Correlation Coefficients using SAS. Placentae from HT cows had a higher total placental weight, higher non-vascular membrane weight, higher total cotyledonary weight, higher total cotyledonary volume, and a higher incidence of teratomas than those from CL cows (P < 0.05). HT cows also had placentae with a significantly greater average cotyledonary weight and volume (P < 0.05). HT cows tended to have a greater incidence of color abnormalities in the placenta (P < 0.075). In addition, HT cows had significantly lighter calves at birth (P < 0.05). These data demonstrate that heat stress (or lack of heat abatement) impacts placental growth during the final stages of gestation, resulting in heavier placentae, an increase in cotyledonary weight and volume, but not an increase in the total number of cotyledons or total cotyledonary surface area. These placental alterations ultimately resulted in lighter calves at birth.