Relationships among Body Condition, Insulin Resistance and Subcutaneous Adipose Tissue Gene Expression during the Grazing Season in Mares.
Obesity and insulin resistance have been shown to be risk factors for laminitis in horses. The objective of the study was to determine the effect of changes in body condition during the grazing season on insulin resistance and the expression of genes associated with obesity and insulin resistance in subcutaneous adipose tissue (SAT). Sixteen Finnhorse mares were grazing either on cultivated high-yielding pasture (CG) or semi-natural grassland (NG) from the end of May to the beginning of September. Body measurements, intravenous glucose tolerance test (IVGTT), and neck and tailhead SAT gene expressions were measured in May and September. At the end of grazing, CG had higher median body condition score (7 vs. 5.4, interquartile range 0.25 vs. 0.43; P=0.05) and body weight (618 kg vs. 572 kg ± 10.21 (mean ± SEM); P=0.02), and larger waist circumference (P=0.03) than NG. Neck fat thickness was not different between treatments. However, tailhead fat thickness was smaller in CG compared to NG in May (P=0.04), but this difference disappeared in September. Greater basal and peak insulin concentrations, and faster glucose clearance rate (P=0.03) during IVGTT were observed in CG compared to NG in September. A greater decrease in plasma non-esterified fatty acids during IVGTT (P<0.05) was noticed in CG compared to NG after grazing. There was down-regulation of insulin receptor, retinol binding protein 4, leptin, and monocyte chemoattractant protein-1, and up-regulation of adiponectin (ADIPOQ), adiponectin receptor 1 and stearoyl-CoA desaturase (SCD) gene expressions in SAT of both groups during the grazing season (P<0.05). Positive correlations were observed between ADIPOQ and its receptors and between SCD and ADIPOQ in SAT (P<0.01). In conclusion, grazing on CG had a moderate effect on responses during IVGTT, but did not trigger insulin resistance. Significant temporal differences in gene expression profiles were observed during the grazing season.
Department of Agricultural Sciences, P.O. Box 28, FI-00014 University of Helsinki, Helsinki, Finland.
Shaimaa
S
Selim
Department of Agricultural Sciences, P.O. Box 28, FI-00014 University of Helsinki, Helsinki, Finland.
Kari
K
Elo
Department of Agricultural Sciences, P.O. Box 28, FI-00014 University of Helsinki, Helsinki, Finland.
Seija
S
Jaakkola
Department of Equine and Small Animal Medicine, P.O. Box 57, FI-00014 University of Helsinki, Helsinki, Finland.
Ninja
N
Karikoski
Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States of America.
Ray
R
Boston
Department of Green Technology, Natural Resources Institute Finland (Luke), Opistontie 10 A 1, FI-32100 Ypäjä, Finland.
Tiina
T
Reilas
Department of Green Technology, Natural Resources Institute Finland (Luke), Opistontie 10 A 1, FI-32100 Ypäjä, Finland.
Susanna
S
Särkijärvi
Department of Green Technology, Natural Resources Institute Finland (Luke), Opistontie 10 A 1, FI-32100 Ypäjä, Finland.
Markku
M
Saastamoinen
Department of Agricultural Sciences, P.O. Box 28, FI-00014 University of Helsinki, Helsinki, Finland.
Tuomo
T
Kokkonen
D000818:Animals; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism; D049628:Body Size; D005227:Fatty Acids / Q000378:metabolism; D005247:Feeding Behavior; D005260:Female; D005786:Gene Expression Regulation; D005951:Glucose Tolerance Test; D065948:Grassland; D006736:Horses / Q000033:anatomy & histology / Q000235:genetics*; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012621:Seasons; D050151:Subcutaneous Fat / Q000378:metabolism*
D001786:Blood Glucose; D005227:Fatty Acids; D007328:Insulin; D012333:RNA, Messenger