Whole body insulin responsiveness is higher in beef steers selected for increased muscling

Abstract

The aim of this experiment was to evaluate the impact of selection for greater muscling on whole body insulin responsiveness in cattle, as reflected by greater uptake of glucose in response to constant insulin infusion and greater glucose disappearance following an intravenous glucose tolerance test. This study used 18-month-old steers from an Angus herd visually assessed and selected for divergence in muscling over 15 years. Eleven high-muscled (High), 10 low-muscled (Low) and 3 high-muscled steers, which were heterozygous for a myostatin polymorphism (High Het ), were infused with insulin using the hyperinsulineamiceuglyceamic clamp technique. Insulin was constantly infused at two levels, 0.6 mIU/kg per min and 6.0 mIU/kg per min. Glucose was concurrently infused to maintain euglyceamia and the steady state glucose infusion rate (SSGIR) indicated insulin responsiveness. An intravenous glucose tolerance test was also administered at 200 mg/kg live weight. Sixteen blood samples were collected from each animal between 230 and 130 min relative to the administration of intravenous glucose, plasma glucose and insulin concentration was determined in order to analyse insulin secretion and glucose disappearance. Insulin-like growth factor-1 (IGF-1) was also measured in basal plasma samples. At the low insulin infusion rate of 0.6 mU/kg per min, the SSGIR was 73% higher for the High muscling genotype animals when compared to the Low (P , 0.05). At the high insulin infusion rate of 6.0 mU/kg per min, these differences were proportionately less with the High and the High Het genotypes having only 27% and 34% higher SSGIR (P , 0.05) than the Low-muscled genotype. The High-muscled cattle also had 30% higher plasma IGF-1 concentrations compared to the Low-muscled cattle. There was no effect of muscling genotype on basal insulin or basal glucose concentrations, glucose disappearance or insulin secretion following an intravenous glucose tolerance test. The increased whole body insulin responsiveness in combination with higher IGF-1 concentrations in the High-muscled steers is likely to initiate a greater level of protein synthesis, which may partially explain the increased muscle accretion in these animals.

Beef carcasses with larger eye muscle areas, lower ossification scores and improved nutrition have a lower incidence of dark cutting

“…Shift in fibre type proportions is likely to lead to metabolic changes in muscle, as has been shown by McGilchrist et al (2011aMcGilchrist et al ( , 2011b and Martin et al (2011) who demonstrated that more muscular cattle and lambs are more responsive to insulin, less responsive to adrenaline and had a higher storage of muscle glycogen (McGilchrist, et al, 2011a). Therefore younger cattle and more muscular cattle are both likely to have increased glycogen at slaughter and a reduced incidence of dark cutting syndrome.…”

“…McGilchrist et al (2011b) has shown that Angus cattle selected for high muscling had increased whole body insulin responsiveness. This may enhance the uptake of glucose into muscle tissue in the postprandial period and allow for an increased rate of glycogenesis, allowing these animals to have higher resting concentrations of muscle glycogen (McGilchrist, et al, 2011a).…”

Causes and Contributing Factors to “Dark Cutting” Meat: Current Trends and Future Directions: A Review

“…Cattle that have predominantly β (Type I)‐red and α (Type IIA)‐red muscle fibers tend not to be heavily muscled, because β‐ and α‐red muscle fibers are smaller than α‐white (Type IIB) glycolytic fibers (Schiaffino ); therefore, cattle that are small and lightly muscled may be at heightened risk of DC because their muscle fibers are more easily depleted of glycogen with the same level of activity or stress compared with an animal with α‐white muscle fibers (McGilchrist and others. ,b). Also, Tarrant () indicated that muscles most likely to be dark in a beef carcass due to physical stress, were those that had the largest proportion of fast glycolytic muscle fibers, such as the longissimus thoracis et lumborum (LTL) and semitendinosus (ST), whereas those that responded to adrenaline administration, and hence most likely to be depleted by anxiety, were the slow‐twitch β‐red muscle fibers.…”

Genetics of Marbling in Wagyu Revealed by the Melting Temperature of Intramuscular and Subcutaneous Lipids

“…However, in spite of numerous studies [ 10 – 19 ], it has not been possible, hitherto, to identify markers which allow a breeder to quantify superior genetics in individual sires and dams. Some of the explanations for the slow progress include the following: Complexity due to interactions of several metabolic processes and their regulatory mechanisms [ 6 , 20 , 21 ]. Contribution of many genes with small effects [ 22 ].…”

“…Complexity due to interactions of several metabolic processes and their regulatory mechanisms [ 6 , 20 , 21 ].…”