Select skeletal muscle mitochondrial measures in Thoroughbred weanlings are related to race earnings and sire

Guy, CP, CM Latham, RN Owen, AL Fowler, SH White-Springer. 2020. President’s Oral Pick:

Abstract

QuanPfiable, cellular differences of individuals are not widely used in breeding and training decisions in the equine industry. Our objecPve was to determine if mitochondrial parameters in weanling Thoroughbreds were related to sire or lifePme race earnings. We hypothesized that weanling skeletal muscle mitochondrial capacity would be posiPvely correlated with race earnings. Gluteus medius muscle samples were collected from racing-bred Thoroughbred weanlings (n=139; mean±SD; 6.0±0.4 mo) from 40 different sires over 3 years at 5 different farms and evaluated for mitochondrial volume density (citrate synthase acPvity; CS) and funcPon (cytochrome c oxidase acPvity) by colorimetry, and oxidaPve (P) and electron transport system (E) capaciPes by high resoluPon respirometry; two- and three-year-old race earnings were available for a subset of 13 horses. Data were analyzed using mixed linear models with sire, sex, year of collecPon, and farm as fixed effects. CorrelaPons between lifePme race earnings and mitochondrial measures were determined using Pearson CorrelaPon StaPsPcs. A main effect of sire was observed for weanling intrinsic (relaPve to CS acPvity) P with complex I substrates (P=0.04) and the contribuPon of mitochondrial leak to O2 consumpPon (FCRL; P=0.04). A trend was observed for the effect of sire on intrinsic mitochondrial leak (P=0.09). Race earnings were posiPvely correlated with integrated (relaPve to mg protein) leak (r=0.7684, P=0.009) and FCRL (r=0.7035; P=0.02). A trend for a negaPve correlaPon between E with complex II substrates and race earnings was also observed (r=-0.4775, P=0.09), No other measures were influenced by sire, nor were correlated with race earnings. Our previous work has indicated a preferenPal use of complex I in breeds bred for short- duraPon racing (Thoroughbreds) compared to distance racing breeds (Standardbreds) that relied more heavily on complex II. Mitochondrial measures in weanlings may be uPlized to inform future breeding and training decisions in horses.