Diurnal rhythm and effects of feeding, exercise and recombinant equine growth hormone on serum insulin concentrations in the horse

Noble, G.K. & 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(6), pp. 745-750.

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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. Study design

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. Potential relevance

This therapy is not recommended to address obesity in insulin-resistant equids.

Impact and interest:

5 citations in Scopus
5 citations in Web of Science®
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ID Code: 63446
Item Type: Journal Article
Refereed: Yes
Keywords: Horse, Weight Loss, Laminitis, Hyperinsulinaemia, Metabolism, Diurnal Rhythm
DOI: 10.1111/evj.12057
ISSN: 0425-1644
Divisions: Current > Schools > School of Earth, Environmental & Biological Sciences
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2013 EVJ Ltd.
Copyright Statement: This is an Author's Accepted Manuscript of an article published in Equine Veterinary Journal 2013 copyright Taylor & Francis, available online at: http://www.tandfonline.com/.
Deposited On: 17 Oct 2013 22:52
Last Modified: 07 Dec 2014 00:02

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