EXPERIMENTAL AND BASIC RESEARCH STUDIES
Diurnal rhythm and effects of feeding, exercise and recombinant equine growth hormone on serum insulin concentrations in the horse
Article first published online: 4 MAR 2013
© 2013 EVJ Ltd
Equine Veterinary Journal
Volume 45, Issue 6, pages 745–750, November 2013
How to Cite
Noble, G. K. and Sillence, M. N. (2013), Diurnal rhythm and effects of feeding, exercise and recombinant equine growth hormone on serum insulin concentrations in the horse. Equine Veterinary Journal, 45: 745–750. doi: 10.1111/evj.12057
- Issue published online: 14 OCT 2013
- Article first published online: 4 MAR 2013
- Accepted manuscript online: 21 JAN 2013 09:04AM EST
- Manuscript Accepted: 27 DEC 2012
- Manuscript Received: 9 FEB 2012
- Charles Sturt University Small Grants program
- Australian Thoroughbred Racing Board
- weight loss;
- diurnal rhythm
Reasons for performing the study
As growth hormone increases lean body mass, it could be a therapy for obese horses. However, growth hormone use induces hyperinsulinaemia in some species, so further investigation is warranted.
To investigate the effects of feeding, exercise and growth hormone therapy on basal insulin concentrations in healthy horses.
In vivo experimental study.
Blood samples were obtained every 30 min from 12 geldings over 24 h, to establish basal serum insulin concentrations, before they underwent a 3-week exercise programme. Horses were allocated into 2 groups and exercised for another 4 weeks. Group A received daily i.m. injections of recombinant equine growth hormone; 5 mg/day for 5 days, then 12.5 mg/day for 16 days. Blood samples were taken daily before feeding. Insulin vs. time area under curve of Groups A and B were compared using a Student's unpaired t test.
Horses demonstrated insulin peaks within 2 h of feeding of 577 ± 108.3 pmol/l at 09.30 h and 342.4 ± 75.7 pmol/l at 17.30 h, despite receiving the same meal. The nadir was between midnight and 07.30 h. Exercise had no effect on basal insulin concentrations prior to equine growth hormone administrations. The equine growth hormone injections increased serum insulin concentrations (P = 0.01) within Group A, from 44.4 ± 15.3 pmol/l initially to 320.9 ± 238.2 pmol/l by Day 12. Exogenous growth hormone caused variable hyperinsulinaemia, which was alleviated once equine growth hormone administration ceased.
Single serum samples taken prior to the morning meal provide basal insulin concentrations. Exercise did not change basal insulin concentrations. However, equine growth hormone injections increased basal insulin concentrations, which were not ameliorated by exercise.
This therapy is not recommended to address obesity in insulin-resistant equids.