Original Research
Effects of Ω-3 (n-3) Fatty Acid Supplementation on Insulin Sensitivity in Horses

https://doi.org/10.1016/j.jevs.2012.07.007Get rights and content

Abstract

The objective of this study was to examine the effects of dietary ω-3 fatty acid supplementation on insulin sensitivity (SI) in horses. Twenty-one mares were blocked by age, body weight (BW), and body condition score (BCS) and randomly assigned to one of three dietary treatments. Treatments consisted of (1) 38 g of n-3 fatty acids via fish and algae supplement and diet (MARINE), (2) 38 g of n-3 fatty acids via a flaxseed meal from the supplement and diet (FLAX), and (3) control (CON) no supplemental fatty acid. Treatments were supplemented for 90 days. Frequent sampling intravenous glucose tolerance tests were performed on days 0, 30, 60, and 90. Blood samples were analyzed for glucose and insulin. The minimal model was applied for the glucose and insulin curves using MinMod Millennium. SI increased 39% (P < .007) across all treatment groups. Acute insulin response to glucose decreased 22% (P < .006) between days 30 and 60 and increased (P = .040) again at day 90. Disposition index (combined SI and β pancreatic response) increased (P = .03) by 53% in the MARINE- and 48% in the FLAX-supplemented horses and did not change with time in the CON group. In insulin-resistant mares, MARINE- and FLAX-treated horses had an increase in SI (P = .09). It would be interesting to test this supplement in a larger group of insulin-resistant horses. If proven effective, supplementation with ω-3 fatty acids would help to reduce problems associated with insulin resistance in horses.

Introduction

Insulin resistance in horses has been linked to the development of laminitis, osteochondrosis, and metabolic syndrome [1], [2], [3], [4] and is therefore considered a problem in the equine industry. These diseases can result in a loss of function and performance of the horse. Several factors may predispose a horse to develop a decreased sensitivity to insulin, such as diet, age, breed/genetics, and obesity [5], [6], [7]. Supplementation with certain dietary components could increase insulin sensitivity (SI) in animals that have decreased sensitivity or insulin resistance, reducing the risk for the development of diseases such as metabolic syndrome and laminitis.

Dietary supplementation with n-3 polyunsaturated fatty acids (PUFAs) has been shown to increase SI in pigs and rats [8], [9]. Dietary eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been shown to incorporate into cell membranes, increasing membrane fluidity owing to greater unsaturation of the membrane and improving glucose transport function [10], [11]. Incorporation of EPA and DHA into muscle cell membrane has been shown to increase binding of insulin [12] and m-RNA expression of glucose transporter type 4 (GLUT-4) in rats [13]. Supplementation with EPA and DHA has shown to improve SI in rats [12], in pigs [8], and in humans [14]. The current study was designed to investigate the effects of feeding a marine source of n-3 PUFAs (algae and fish oil pellet), a direct source of EPA and DHA, or a plant source of n-3 fatty acids (ground flaxseed), on glucose and insulin dynamics in a group of 21 adult mares.

Section snippets

Horses and Treatments

Twenty-one nonpregnant mares of mixed stock horse breeding were acclimated to a basal diet of free-choice alfalfa/bromegrass mixed hay for 1 month before this study. Horses were maintained according to the policy of Colorado State University’s Equine Sciences Program and by following the protocol approved by the Institutional Animal Care and Use Committee. Horses had been dewormed and vaccinated before the start of the study. Initial and monthly assessment of BCS was made by three trained and

Horses Weights and Body Condition Scores

Weights and BCS were evaluated on a monthly basis and are presented in Table 3. Because no differences were seen among treatments, results were pooled and averaged across all treatments. Horses weighed 585 ± 41.5 kg at day 0, then weight decreased (P < .001) progressively from day 0 to day 60 (565.0 ± 35.6 kg), and then increased (P < .010) from day 60 to day 90 (576.1 ± 36.8 kg). BCSs ranged from 5 to 8 and decreased (P = .02) from day 0 (6.74 ± 0.85) to day 90 (6.38 ± 0.82). Horses remained

Discussion

Insulin sensitivity, β pancreatic response, and glucose-mediated glucose disposal were not affected by fatty acid supplementation in the current study. DI was higher in the FLAX than in the CONT group at day 90. DI is a measure calculated from SI and β pancreatic response; however, no other measures for SI were significantly different between treatments. If an individual does not secrete enough insulin (AIRg) for insulin sensitivity, DI will be higher, and it may be used as an indication of

Conclusions

No effect of treatment with fatty acid supplementation was able to be detected in the current investigation; however, a number of exogenous factors may have reduced the ability of a significant effect of treatment to be detected, and further investigation in this area is necessary. In horses classified in the lowest quintile for insulin sensitivity, there was a trend for a treatment effect, where MARINE and FLAX horses had higher SI compared with the control treatment. The results of the

Acknowledgments

The authors thank United Bionutrition for the donation of the Magnitude supplement (JBS United, Sheridan, IN), Horse Tech for the availability of the Nutra-Flax (Horse Tech, Laurens, IA), the Equine Reproductive Center at Colorado State University (CSU) for the lease of the mares, the undergraduate Equine and Animal Science students, Dr Zumbrunnen for statistical assistance, and the Department of Animal Science at CSU for the funding of the study. Kibby Treiber for help with the analysis of

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