Plasma β-endorphin, cortisol and immune responses to acute exercise are altered by age and exercise training in horses

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Abstract

Reasons for performing study:

Ageing appears to affect immune and neuroendocirne function in horses and response to acute exercise. No studies have examined the combined effects of training and ageing on immune and neuroendocirne function in horses.

Hypothesis:

To ascertain whether training and age would affect the plasma β-endorphin (BE) and cortisol (C) as well as immune function responses to acute exercise in Standardbred mares.

Methods:

Graded exercise tests (GXT) and simulated race tests (SRT) were performed before and after 12 weeks training at 60% HRmax. BE and C were measured at rest and at 5, 10, 20, 40, 60 and 120 min post GXT. Leucocyte cell number, CD4+ and CD8+ lymphocyte subsets, and mitogen stimulated lymphoproliferative response (LPR), were measured in jugular blood before and after the SRTs.

Results:

Cortisol rose by 5 min post GXT in young (Y) and middle-age (MA) mares (P<0.05) and remained elevated until 40 and 60 min post GXT, respectively during both pre-and post training GXT. There was no rise in C in old (O) mares after either GXT (P>0.05). Pretraining BE rose (P<0.05) by 5 min post GXT in all mares. After training, BE was higher in Y and O vs. MA (P<0.05) at 5 min post GXT. Post training BE was higher at 5 min post GXT in Y and O vs. pretraining (P<0.05). After SRT, lymphocyte number rose in all mares (P<0.05); however, lower lymphocyte numbers (P<0.05) were seen in MA vs. Y and O vs. MA (P<0.05). The O had reduced LPR to Con A and PHA stimulation (P<0.05) compared to Y and MA after the SRT after both pre- and post training SRT. LPR to PWM was lower (P<0.05) in O vs. Y and MA after the pretraining SRT. Training caused an increase in resting LPR to PWM in MA only (P<0.05).

Conclusion:

Both age and training altered the plasma β-endorphin and cortisol responses as well as and immune responses to acute exercise.

Potential relevance:

This study provides important information on the effects of ageing and training that will aid in the management and care of an increasing number of active older horses.

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