Thermoregulatory responses and blood parameters of locally adapted ewes under natural weather conditions of Brazilian semiarid region

Abstract

The effect of the natural weather conditions on respiratory rate, rectal temperature and hematologic parameters such as glucose, total cholesterol, triacylglycerol, total protein, albumin, globulin, red blood cells, microhematocrit, mean corpuscular volume, serum triiodothyronine (T3) and thyroxine (T4) levels was evaluated in red (RMN) and white (WMN) coat colored Morada Nova ewes, of different class of body condition score (CBCS), during the dry (from july to december) and wet (from january to june) seasons, which exhibited different (P<0.05) air temperature, relative humidity and radiant thermal load averages. Tukey’s test was used and the difference considered was to P<0.05. Significant greater averages of respiratory rate were observed in the dry period compared to the rainy period (42.26±8.96 and 36.89±8.20 breaths min-1, respectively), mainly in the RMN (45.54±8.23 breaths min-1) compared with the WMN (39.27±8.57 breaths min-1). No differences were observed in rectal temperature measurements between the dry and the wet periods (38.59±0.58 and 38.60±0.56 oC, respectively), but the WMN had higher values than the RMN (38.77±0.54 and 38.40±0.54 oC, respectively). The glucose and total cholesterol were higher in the wet season, with no variation due to breed variety and CBCS. The triacylglycerol did not change between breed varieties and seasons. The albumin was similar between varieties and in different seasons, being different in CBCS. Total protein and globulin serum were higher during the wet season, but total protein was higher and globulin was lower in better CBCS. T3 and T4 levels were higher in the rainy season (0.25±0.07 and 6.74±11.37 ?g dL-1, for T3 and T4, respectively) than in the dry season (0.18±0.08 and 6.31±1.64 ?g dL-1, for T3 and T4, respectively). The red blood cells showed no difference, but microhematocrit was higher in WMN and in the better CBCS and mean corpuscular volume was higher in the dry season. The concentration of T3 was lower in the RMN than in the WMN (0.19±0.07 and 0.24±0.08 ?g dL-1, respectively), while T4 did not differ between them (6.53±1.51 and 6.52±1.46 ?g dL-1, respectively). The Morada Nova sheep showed positive physiological responses to the heat stress, notably an increase of respiratory rate and a reduction of T3 and T4 levels. All another hematologic parameters analyzed were within the normal range for all sheep, indicating a good ability to cope with the climatic changes of the Brazilian semiarid region. Both varieties were heat tolerant, but the red variety required major adjustments to maintain homeothermy.

Keywords

• Adaptation
• Blood metabolites
• Blood parameters
• Sheep
• Thermoregulatory responses
• Thyroid hormones.