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Reduced high-intensity training distance in growing horses had no effect on IGF-1 concentrations, but training onset interrupted time-dependent IGF-1 decline

In: Comparative Exercise Physiology
Authors:
L. Johansson Swedish University of Agricultural Sciences, Department of Anatomy, Physiology and Biochemistry, Ulls väg 26, Uppsala 75007, Sweden.

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S. Ringmark Swedish University of Agricultural Sciences, Department of Anatomy, Physiology and Biochemistry, Ulls väg 26, Uppsala 75007, Sweden.

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E. Skiöldebrand Swedish University of Agricultural Sciences, Department of Biomedical Sciences and Veterinary Public Health, Ulls väg 26, Uppsala 75007, Sweden.

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J. Bergquist Uppsala University, Department of Chemistry-BMC, Analytical Chemistry and Neurochemistry, Husargatan 3, Uppsala 75237, Sweden.

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A. Jansson Swedish University of Agricultural Sciences, Department of Anatomy, Physiology and Biochemistry, Ulls väg 26, Uppsala 75007, Sweden.

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Open Access

This study investigated plasma insulin like growth factor (IGF)-1 concentrations in 16 young Standardbred horses introduced to systematic high-intensity training at two different levels of intensity. Growth and locomotion asymmetry and correlations between these and plasma IGF-1 concentrations were also examined. From September as 1-year olds to March as 2-year olds (Period 1), all horses were subjected to the same submaximal training program. In March (start of Period 2), the horses were divided into two groups (n=8) and one group was introduced to regular high-intensity training. The other group was introduced to a program where the high-intensity exercise distances were reduced by 30%. These two training programs were maintained for the remaining 21 months of the study (Periods 2, 3, and 4). There was no effect of training group on plasma IGF-1 concentrations. A continuous decline in IGF-1 levels was observed throughout the study (P<0.0001), with one notable interruption in Period 2 when the IGF-1 concentration remained at the level seen at the start of Period 1. Growth rate of body length was equally high in Periods 1 and 2 (P>0.05). Front and hind limb asymmetry was elevated in Period 2 compared with Period 1. There were positive correlations between IGF-1 concentrations and changes in body condition score, and a negative correlation between IGF-1 concentration and weight. These results indicate that introduction to high-intensity training induces IGF-1 release in horses, but that a 30% difference in the distances used in high-intensity training does not affect IGF-1 levels. The temporary interruption in decline in IGF-1 release with the onset of high-intensity training may influence growth pattern and locomotion asymmetry, but further studies are needed to assess causality.

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