Growth performance and changes in physiological, metabolic and hematological parameters due to outdoor heat stress in hair breed male lambs finished in feedlot.

The aim of this study was to evaluate the effect of seasonal heat stress (HS) on productive performance, physiological responses, metabolism, and hematological profile of hair breed male lambs finished in feedlot. Twenty Dorper × Katahdin male lambs (body weight = 34.6 ± 1.4 kg and age = 4.5 months) were housed in individual pens and exposed to environmental conditions of summer HS (n = 10, temperature = 28.3 ± 4.0 °C and THI = 77.2 ± 5.4 units) or winter thermoneutrality (n = 10, temperature = 19.2 ± 2.6 °C and THI = 64.0 ± 3.0 units). Each season, a 30-day feeding test was conducted to measure study variables. Compared to thermoneutral lambs, heat-stressed lambs had lower (P < 0.01) growth rate and feed efficiency without changing dry matter intake. Heat-stressed lambs presented higher (P < 0.01) rectal temperature and respiratory rate through the daytime than termoneutral lambs. On most sampling days, summer HS caused lower (P < 0.01) serum concentrations of glucose, cholesterol, total protein, urea, potassium, and thyroid hormones, but higher (P < 0.01) serum triglyceride and chlorine values. Overall serum concentrations of cortisol and insulin were unaffected by summer HS. The blood of heat-stressed lambs showed lower (P ≤ 0.03) erythrocyte and platelet counts, hemoglobin, and hematocrit, but higher (P ≤ 0.03) erythrocyte size and leucocyte count than the blood of thermoneutral lambs. In conclusion, hair breed male lambs in response to chronic conditions of summer HS had slow growth but avoided hyperthermia due to the activation of physiological, metabolic and endocrine adjustments.

Ferulic acid supplementation for 40 days in hair ewe lambs experiencing seasonal heat stress: short-term effects on physiological responses, growth, metabolism, and hematological profile.

Free ferulic acid (FA) is a natural compound with antioxidant properties which mitigates the negative effects of cold stress in sheep; however, its impact on thermoregulatory responses in heat-stressed sheep has not been defined. The objective was to evaluate the effects of FA supplementation on physiological responses, serum analyte concentrations, and the hematological profile of heat-stressed hair ewe lambs. Twenty-two Dorper × Katahdin ewe lambs (initial body weight = 23.5 ± 2.8 kg and age = 4 months) were housed in individual pens for 40 days and assigned under a randomized complete block design to the following treatments (n = 11): basal diet with 0 (control) or 250 mg of FA/kg of feed. The FA × sampling day interaction only affected serum concentration of some metabolic hormones; particularly on day 20 of the trial, FA increased (P < 0.01) insulins and the insulin to glucose ratio while decreased (P = 0.05) thyroxine. Overall, supplemental FA did not affect rectal temperature, respiratory rate, most body surface temperatures, feedlot performance, and serum concentrations of metabolites, electrolytes, triiodothyronine, and cortisol. In addition, FA only tended to decrease (P ≥ 0.09) erythrocyte count and plaquetocrit and to increase (P = 0.08) mean corpuscular volume. In conclusion, FA supplementation did not improve the growth nor thermoregulatory capacity of heat-stressed hair ewe lambs. Still, it partially modulated the metabolism to reinforce some energetic adaptive mechanisms when the ambient temperature was ≥ 35 °C.