Physiological responses of Santa Inês x Dorper ewes and lambs to thermal environment of silvopasture and open pasture systems

Abstract

The silvopasture is a sustainable livestock system, which has great potential for sheep, mainly focused on the thermal comfort and welfare of animals. However, there is a lack of information regarding the thermal environment and physiology of ewes and lambs raised in this system. This study was therefore aimed at assessing the influence of microclimate on the thermal comfort of postpartum ewes and lambs kept in silvopastoral (SP) or open pasture (OP) systems during the summer. Postpartum crossbred ewes (Santa Inês x Dorper; n = 24) and their lambs (n = 24) were randomly allocated to SP or OP group, being distributed into four paddocks per group (three ewes and three lambs per paddock). The microclimate characterization measured were dry-bulb ambient temperature (Ta, ºC), black globe temperature (Tbg, ºC), relative humidity (RH, %), grass temperature (Tg, ºC) and wind speed (WS, m s−1). These variables were then applied to calculate the temperature and humidity index (THI), black globe temperature and humidity index (BGHI), and radiant heat load (RHL). To assess the thermophysiology response, the respiratory rate (RR, breaths min−1), heart rate (HR, beat min−1), rectal temperature (RT, ºC), and hair coat surface temperature (ST, ºC) were analyzed. Regarding the microclimate variables, Ta and Tg were higher in OP than in SP (P = 0.008 and P < 0.001, respectively), while SP presented higher RH values (P = 0.037). There was no significant difference in WS between the systems (P = 0.288). As expected, all indices showed lower mean values in SP compared to OP, mainly the radiant heal load (P < 0.001). Regarding the thermophysiology response, the RR of ewes was significantly higher in OP (129 ± 4.5 breaths min−1) than in SP (85 ± 4.7 breaths min−1) (P < 0.001). The RT was higher in the OP, but only in the afternoon (P < 0.001). Meanwhile, lambs in OP also presented higher RR (105 ± 3.5 breaths min−1) and RT (39.9 ± 0.1 °C) values than in SP (74 ± 2.8 breaths min−1 and 39.9 ± 0.1 °C, respectively). Following the prior trends, during the afternoon lambs showed higher values of RR than in the morning. However, the difference between those periods was small for RT. The ST of ewes in SP was lower compared to ewes in OP (P < 0.001). In the afternoon, the difference of ewes in SP had ST 4.3 °C lower compared to OP, while for lambs, the ST in the afternoon increased by 5.3 °C more in OP than in SP. The study suggests that the presence of trees reduced hyperthermia for both ewes and lambs further supporting the SP as a sustainable farming system that promotes thermal comfort and welfare for small ruminants.