title: Equine obesity: concepts and mechanisms
Creators: name: Morrison, Philippa
Publisher: name: University of Liverpool Repository
Year: 2015

description: Obesity in the UK leisure population of horses and ponies is a growing problem with major welfare implications. To date, research into the associations between obesity and metabolic disease such as insulin dysregulation and laminitis remain ongoing. To improve our understanding of obesity in this species, the current thesis was designed to address several related objectives ranging from psychological aspects of obesity to the role of key determinants of energy balance in the setting of obesity. Implementing dietary restriction to reverse obesity requires an owner to correctly recognise obesity in their animal, knowledge of which is lacking for the horse. A two-tier internet-based questionnaire was created and distributed through UK equine-based forums. Tier 1 utilised lateral photographic images of horses and ponies and demonstrated that only 11% of respondents (n = 546 total) correctly identified all overweight animals from a panel of 12 images. When assessing the suitability of horses and ponies for taking part in a range of activities, respondents considered it more appropriate for each animal to carry more weight/condition for competing in affiliated showing classes. Tier 2 (n = 177 responses) provided information regarding current management practices of horse-owners in the UK. The ability to quantify internal adiposity in live animals requires imaging technology which is not yet available for the horse. A semi-quantitative regional adipose-depot specific scoring system (EQUIFAT) was developed and tested. Associations between ante-mortem body condition score (BCS) and post-mortem EQUIFAT scores (n = 207 animals) revealed that retroperitoneal EQUIFAT score had strong positive associations with BCS, whilst omental had weaker associations and mesenteric and epicardial scores had no associations with BCS, indicating clear functional differences between regional adipose depots in the horse. Performing in-depth molecular biology studies using abattoir-derived samples requires knowledge of the time-frame of RNA degradation. RNA was found to remain intact up to 30 minutes and 2 hours post-mortem for adipose tissue and skeletal muscle ( n = 3 horses), respectively. The expression of myostatin, a key regulator of skeletal muscle mass and energy balance was evaluated in lean and obese horses and ponies (n = 6/group). Myostatin gene expression was increased in skeletal muscle of obese animals, with no difference at the protein level. Circulating myostatin concentrations were increased in obese animals. Adipocyte area was increased in adipose depots (retroperitoneal, omental, crest and tailhead) in obese animals, except for epicardial WAT. The expression of lipolytic proteins PLIN1 and HSL was reduced in retroperitoneal WAT of obese animals, with fewer differences noted between groups for other depots. Together, findings from this thesis indicate a misperception of obesity exists among horse-owners and enthusiasts. Functional differences between regional adipose depots and altered expression of key regulators of energy balance have been identified in obese horses and ponies.