Effect of increasing levels of glycerin on growth rate, carcass traits and liver gluconeogenesis in young bulls

This study aimed to evaluate performance, carcass traits, glycerol kinase 1 (GK1) and cytoplasmatic phosphoenolpyruvate carboxykinase (PCK1) gene expression, and glycerol kinase activity in liver of young bulls receiving different levels of crude glycerin. Forty-four crossbred young bulls (initial body weight of 368 ± 4.2 kg) were used in a completely randomized design, with four treatments and 11 replicates. The experiment period lasted 84 days, preceded by an adaptation period of 28 days. The basal diet was composed of corn silage (300 g/kg) and concentrate (700 g/kg) containing corn and soybean. The experimental treatments were as follows: without glycerin or including 60, 120 or 180 g/kg of crude glycerin in the diet. Blood samples were collected on the last day of the experiment period to evaluate biochemical parameters. After slaughter, carcass traits were measured and liver samples were collected to analyze gene expression and glycerol kinase activity. There was no effect (P = 0.21) of glycerin on glucose blood concentrations. However, liver glycerol kinase activity was greater (P < 0.01) and GK1 and PCK1 genes expressions were down regulate (P < 0.01) as glycerin levels in the diet increased. Glycerin did not affect (P > 0.17) performance and most of the carcass traits. However, there was a greater (P = 0.02) marbling score in the carcass of animals fed 120 and 180 g/kg of crude glycerin. In conclusion, the use of glycerin at a level of up to 180 g/kg is recommended in diets of feedlot beef cattle, and it increases liver glycerol kinase activity, feed efficiency and beef marbling.