Lipid classes in adipose tissues and liver differ between Shetland ponies and Warmblood horses

Abstract

Fatty acids, as key components of cellular membranes and complex lipids, may play a central role in endocrine signalling and the function of adipose tissue and liver. Thus, the lipid fatty acid composition may play a role in health status in the equine. This study aimed to investigate the fatty acid composition of different tissues and liver lipid classes by comparing Warmblood horses and Shetland ponies under defined conditions. We hypothesized that ponies show different lipid patterns than horses in adipose tissue, liver and plasma. Six Warmblood horses and six Shetland ponies were housed and fed under identical conditions. Tissue and blood sampling were performed following a standardized protocol. A one-step lipid extraction, methylation and trans-esterification method with subsequent gas chromatography was used to analyse the total lipid content and fatty acid profile of retroperitoneal, mesocolon and subcutaneous adipose tissue, liver and plasma. Fatty acids were grouped according to their degree of saturation and their conjugated double bond into the respective lipid classes. In the adipose tissues, saturated fatty acids (SFAs) and n-9 monounsaturated fatty acids (n-9 MUFAs) were most present in ponies and horses. N-6 polyunsaturated fatty acids (n-6 PUFAs), followed by SFAs, were most frequently found in liver tissue and plasma in all animals. Horses, in comparison to ponies, had significantly higher n-6 PUFA levels in all tissues and plasma. In liver tissue, horses had significantly lower hepatic iso-branched-chain fatty acids (iso-BCFAs) than ponies. The hepatic fatty acid composition of selected lipid classes was different between horses and ponies. In the polar PL fraction, horses had low n-9 MUFA and n-3 PUFA contents but higher n-6 PUFA contents than ponies. Furthermore, iso-BCFAs are absent in several hepatic lipid fractions of horses but not ponies. The differences in fatty acid lipid classes between horses and ponies provide key information on the species- and location-specific regulation of FA metabolism, thus affecting health status such as inflammatory responses.

Fig 1. Calculated Desaturase and Elongase Activity Indices.

Product/precursor ratio of the percentages of individual FAs represent desaturase and elongase activity indices: (A) C16:1n-7/C16:0 = Δ9-desaturase (D9D16), (B) C18:1n-9/C18:0 = Δ9-desaturase (D9D18), (C) 18:3n-6/C18:2n-6 = Δ6-desaturase (D6D), (D) C20:4n-6/C20:3n-6 = Δ5-desaturase (D5D) and (E) C18:0/C16:0 = elongase (Elo). Data are shown as whisker plots. Boxes represent the interquartile range (IQR) between the 25^th and 75^th percentiles. Horizontal lines are medians. Error bars show the full range excluding outliers (dots), which are defined as being more than 1.5 IQR outside the box. Lower-case superscripts with different letters indicate significant differences in these values between equine species (P ≤ 0.05).