Abstract
The current study was performed to evaluate the effects of the dietary inclusion of extra virgin olive oil (EVOO), betaine (BET), lemongrass essential oil (LGEO), gallic acid (GA), vitamin C (VC) and vitamin E (VE) on different body temperature traits and stress hormone and glucose levels in heat-stressed growing rabbits. Rabbits were fed diets with no supplementation (control group) or supplemented with 15 g of EVOO, 400 mg of LGEO, 500 mg of GA, 1000 mg of BET, 500 mg of VC, or 200 mg of VE per kg of diet. All tested feed additives, especially EVOO, had a lowering effect on various rabbit temperature traits. Both triiodothyronine (T3) and tetraiodothyronine/thyroxine (T4) were increased (p<0.05) by the addition of BET, VC, EVOO, and VE. With the exception of the VC group, all dietary groups showed no significant changes in the insulin level compared to the control group level. In contrast, the cortisol and glucose levels were diminished (p<0.05) in all treated groups compared to the control levels. The results suggested that all tested supplementations had positive ameliorating effects on growing rabbits under a severe heat load in terms of lowered body temperatures and a favourable stress hormone balance, with the most favourable results found in the EVOO, VC, and BET supplementation groups.
Highlights
Under the high environmental temperatures in tropical and subtropical regions, farm animals, including rabbits, are subjected to heat stress, which results in poor production traits
The current study was performed to evaluate the effects of the dietary inclusion of extra virgin olive oil (EVOO), betaine (BET), lemongrass essential oil (LGEO), gallic acid (GA), vitamin C (VC) and vitamin E (VE) on different body temperature traits and stress hormone and glucose levels in heat-stressed growing rabbits
The results suggested that all tested supplementations had positive ameliorating effects on growing rabbits under a severe heat load in terms of lowered body temperatures and a favourable stress hormone balance, with the most favourable results found in the EVOO, VC, and BET supplementation groups
Summary
Under the high environmental temperatures in tropical and subtropical regions, farm animals, including rabbits, are subjected to heat stress, which results in poor production traits. High ambient temperatures are a major stress factor for rabbits due to their dense fur and few functional sweat glands, which greatly hinder heat loss (Marai et al, 2002). In tropical and subtropical regions, heat stress is aggravated by high relative humidity, which can reach 85% during hot months (Marai et al, 2007). Alterations in the rectal, skin and ear temperatures; respiration rate; and thyroid and stress hormone, albumin, globulin, total lipid, glucose, sodium, potassium, calcium, magnesium and phosphorus levels are the main physiological responses to heat load in rabbits (Marai et al, 2008). Heat load causes increased oxygen-derived free radicals, which create a condition of oxidative stress (Sahin & Kucuk, 2003)
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