Preliminary Evidence of Heat Stress Effect on Placentome Morphometry in Beef Cows

Abstract

The objective of the study was to evaluate the effect of heat stress on placentome morphometry during the first third of gestation in multiparous beef cows. The experiment was conducted at the Estación Experimental de la Facultad de Agronomía Salto (EEFAS), Uruguay, during the summer 2023. A total of 38 multiparous Hereford cows were randomly divided into two treatments prior to breeding: Sun (S) (n=20) and Shade (SH) (n=18). In the S treatment, cows were kept in a paddock without access to shade, whereas cows in the SH treatment had voluntary access to natural shade provided by a stand of trees within the paddock. Transrectal ultrasonography was performed at the end of the first third of gestation to measure the surface area of the cross-sectional face of the first four placentomes randomly identified adjacent to the cervix. Air temperature (ºC) and relative humidity (%) were recorded using an automated meteorological station. Heat waves were defined as periods of at least three consecutive days with daytime maximum temperatures ≥35.3 ºC and nighttime minimum temperatures ≥21.8 ºC. Four heat waves were identified: 1-12 February, 23 February-2 March, and 18-20 March. Statistical analysis was performed using a linear mixed model. The overall mean area of placentomes was 5.61 ± 0.20 cm². However, cows in S treatment had significantly smaller placentomes areas 5.11 ± 0.28 cm² vs. 6.16 ± 0.29 cm² of placentomes of SH treatment cows (P<0.05). Heat stress during early gestation negatively affected placentome development. These results are preliminary, and data on placentome area in later stages of gestation and additional associated variables are still being analyzed. The potential effect of heat stress on placentome characteristics during mid and late gestation, as well as on offspring performance, remain to be determined. Further research is required to elucidate these impacts.