Effects of pasture consumption and obesity on insulin dysregulation and adiponectin concentrations in UK native-breed ponies.

BACKGROUND

Insulin dysregulation (ID) and hypoadiponectinaemia (total [adiponectin] <7.9 μg/mL) are risk factors for laminitis. They are sometimes, but not always, associated with obesity.

OBJECTIVES

To investigate the effects of pasture consumption and obesity on ID and circulating total [adiponectin] in ponies.

STUDY

DESIGN

Longitudinal.

METHODS

Seven native-breed ponies with normal basal and post-oral sugar test (OST) [insulin] and body condition score (BCS) 4.3-5.5/9 were allowed to graze until they reached BCS 7/9. Ponies were then maintained at BCS 7/9 until completion of the study (week 22). Morphometric measures, OST, insulin tolerance test (ITT), plasma [adiponectin], whole-blood expression of receptors for adiponectin, insulin, and insulin-like growth factor 1, and pasture conditions (height and vigour) were determined fortnightly.

RESULTS

Median (range) BCS increased significantly (p < 0.001) from 5.0 (4.3-5.5; week 0) to 7.2 (5.7-7.5; week 22). Basal [insulin] did not change significantly over the study, but median post-OST [insulin] was significantly higher (p < 0.05) at week 14 (95.2 [17.9-114.0] μIU/mL), week 16 (103.0 [16.4-166.0] μIU/mL), and week 20 (93.6 [10.0-153.0] μIU/mL) than week 0 (25.0 [10.0-64.0] μIU/mL). Compared with week 0, ITT results were significantly lower at weeks 2-6 and 12-20, and [adiponectin] was significantly lower at weeks 10-22 (p < 0.05). [Adiponectin] decreased in all ponies during the study. Both low (3/10) and high (8-9/10) pasture scores were significantly associated with low ITT results. Low pasture scores were associated with low [adiponectin]. BCS was significantly associated with basal [insulin], post-OST [insulin], ITT results, but not [adiponectin].

MAIN LIMITATIONS: No control group with maintenance of ideal BCS; small sample size comprising native UK ponies.

CONCLUSIONS

Six ponies developed hypoadiponectinaemia, and all showed transient or consistent ID during the study. Both short, stressed grass and long, lush grass were associated with decreased tissue insulin sensitivity.