Desenvolvimento placentário e termorregulação de ovelhas gestantes mantidas em sistema silvipastoril durante o verão

Abstract

Animals subjected to high temperatures for prolonged periods undergo a series of behavioral, physiological and reproductive changes. Thus, this study aimed to analyze different reproductive aspects, and physiological changes in ewes subjected to heat stress during pregnancy in the summer. This experiment was carried out at the Sheep Research Unit at UTFPR, in Dois Vizinhos, PR. 24 pregnant crossbred Dorper x Santa Inês ewes were divided into two groups: Silvipastoril System (SPS) and Open Pasture (OP), where they were kept throughout pregnancy. During this period, physiological variables and environmental data were registered every two weeks for a total of 6 time points. At the end of pregnancy, the ewes were kept in a suspended pen for better supervision of parturition. At birth, placentas and lambs were weighed. In the laboratory, the placentas were photographed for biometrical analysis. The lambs were also weighed at 10 days postpartum. Considering all microclimatic variables, both systems were found stressful for the sheep, but the Silvipastoral System had lower Air Temperature than Open Pasture (OP= 26.9 ± 0.41 oC, SPS= 26.0 ± 0.38 o C; p =0.0288). Moreover, the radiant thermal load of the two groups presented a difference of 34 Wm-2 (p=0.0288), and the Temperature of the Grass was also different between the systems (PS= 25.6 ± 0.44 oC, SSP= 23.4 ± 0.37 oC; p=0.0043). During the study, no difference was observed regarding the mobilization of white blood cells in both systems (p=0.4777), nor was there any effect of time or interaction between variables (p=0.8109 and p=0.4150, respectively). For the quantification of circulating monocytes, no differences were observed between the groups (p>0.05). Neutrophils were only affected by time (p<0.0001). In the Silvipastoral group, a difference was observed between timepoints 4 and 1, 5 and 1, 6 and 1 (p=0.0174; p=0.0093; p= 0.0065, respectively), between 4 and 2, 5 and 2, 6 and 2 (p=0.0096; p=0.0050; p=0.0035; respectively). While in the Open Pasture group, differences were observed between timepoints 5 and 1 and 6 and 1 (p= 0.0328; p= 0.0204). The Respiratory and Heart Rates of the animals exposed to the sun were higher than that of the sheep that remained in the shade (p<0.001). Regarding the duration of pregnancy, there was no effect of treatment (p= 0.4987). Interestingly, both systems had higher numbers of female lambs (PS: male 40%, female 60%; SSP: male 38%, female 61.54%). Only an effect of the type of pregnancy (single vs. twin) was detected on the body weight of lambs at 10 days (p=0.0273), which was not observed at birth (p=0.9455). Regarding placental biometry, twin pregnancies had a greater membrane area (p=0.0223), but no differences were observed in placenta weight (p=0.1522) and the number of cotyledons (p=0.5457). Therefore, it can be concluded that the type of Sheep Rearing System affects the thermal comfort of pregnant ewes, and the Silvipastoral System can offer more amenable microclimate conditions resulting in more comfort during pregnancy.