Influência da capsaicina na fisiologia térmica e desempenho de cordeiros terminados a pasto e em sistema silvipastoril

Abstract

Through this study, we assessed whether capsaicin influences the thermal physiology and performance of lambs finished on pasture and silvopastoral systems. The experiment was carried out in the Southwest region of Paraná, Brazil. Twenty-one lambs (13 males and eight uncastrated females) from the crossbreeding of the Dorper and Santa Inês breeds, aged 6.0±1.0 months, weighing an average of 36.0±1.8 kg and with an average body condition score (BCS) of 4.0±0.5, were divided into two finishing systems on pasture: full sun (PS) and silvopastoral (SSP). The animals were randomly distributed in the proportion of two per paddock (76.0±1.70 kg per paddock). The treatments were: SEP-PS: animals on PS with capsaicin supplementation; CONT-PS: animals on PS without capsaicin supplementation; SEP-SSP: animals in SSP with capsaicin supplementation; CONT-SSP: lambs in SSP without capsaicin supplementation. All lambs were supplemented with 1.5% concentrate about body weight, and in treatments with added capsaicin, 300 mg/day of CAPCIN® were provided. The lambs were weighed, and the ECC was measured to calculate the average daily gain. The microclimatic variables were measured: air temperature, grass temperature, wind speed and relative humidity for 12 h for three consecutive days. From these variables, the values of radiant heat load and mean radiant temperature were obtained with the aid of mathematical models. The physiological responses evaluated were respiratory and heart rates, rectal temperature, and mean surface temperature. They were performed together with the microclimatic measurements at 3:00 p.m. All evaluations had intervals of 14 days. Data analysis used mixed models, analysing factorial interactions as fixed effects. The highest values of air temperatures (PS: 27.4 ºC; SSP: 26.6 ºC), grass temperatures (PS: 33.6 ºC; SSP: 30.1 ºC), mean radiant (PS: 47.0 ºC; SSP: 44.0 ºC) and radiant heat load (PS: 601 W.m2; SSP: 581 W.m2) (P<0.01 for both) and lowest mean relative humidity were obtained in PS (PS: 64%; SSP: 66%; P<0.01). Heart rate was altered (P<0.01) by the system (PS: 123; SSP: 111 beats per minute) and by the use of capsaicin (PS: 120; SSP: 114 beats per minute). For the mean surface temperature, there was an isolated effect of production systems, where PS was higher than SSP (PS: 37 ºC; SSP: 33 ºC; P<0.01). Animals raised in SSP presented lower values (SEP: 131; CONT: 140 movements per minute) than those in PS (SEP: 116; CONT: 119 movements per minute) in the respiratory rate variable (P<0.01). Rectal temperature was higher in CONT-PS (39.8 ºC), followed by SEP-PS (39.8 ºC) (P>0.05); these differed from the values observed in SEP-SSP (39.6 ºC) and CONT-SSP (39.3 ºC). In the performance evaluation, there was a difference in weight, where animals finished in CONT-PS (47.0 kg) presented higher values than the others (SEP-PS: 44.0 kg; SEP-SSP: 44.0 kg; CONT-SSP: 40.0 kg). Therefore, silvopastoral systems present more favourable thermal conditions for sheep production. Capsaicin supplementation allowed a reduction in physiological responses, indicating greater thermal comfort for the animals.