Activity of glutamate dehydrogenase and protein content in the breast of broilers fed diets containing different sources and levels of glycerine.

According to scientific literature, glycerol in the diet can spare glucogenic amino acids by inhibiting the activity of enzymes, such as glutamate dehydrogenase, thereby promoting protein deposition in muscle tissues. Therefore, the objective of this study was to evaluate the effect of three sources of glycerine (crude glycerine from soybean oil--CGSO, mixed crude glycerine from frying oil and lard--MCG and a semipurified glycerine from soybean oil--SPGSO) in four concentrations in the diet (17.5, 35.0, 52.5 and 70.0 g of each type of glycerine/kg of feed) on the activity of hepatic glutamate dehydrogenase, performance and protein content in the breast of broilers, during 22-35 days of age (experiment I) and 33-43 days of age (experiment II). In both experiments, an increase in MCG induced a linear decline in glutamate dehydrogenase activity (p < 0.05). In contrast, increasing the concentration of SPGSO in the diet caused a linear increase in enzyme activity (p < 0.05). There was no (p > 0.05) isolated effect of glycerine on the enzyme activity in either evaluated phase; however, during 33-42 days of age, MCG inhibited (p < 0.05) the glutamate dehydrogenase activity by up to 34.43%. During 22-35 days of age, the diet containing SPGSO induced a higher protein content (p < 0.05) in the breast, and regardless of the source utilized, the maximum protein deposition was estimated (p < 0.05) when broilers were fed with 55.08 g glycerine/kg of diet. There was no (p > 0.05) interaction or isolated effects of the sources and levels of glycerine on the protein content in the breast of broilers at 33-42 days of age, and moreover, all diets containing glycerine promoted a similar protein deposition in the breast compared with birds that received the diet without glycerine. The bird age also showed to influence the feed intake and weight gain of broilers fed diet containing glycerine. It is concluded that for both rearing phases, an increase in glycerine in the diet did not necessarily reduce the glutamate dehydrogenase activity, and the protein deposition in the breast of broilers may not be strictly correlated with the activity of this enzyme.

Content of plasmatic glycerol and activity of hepatic glycerol kinase in broiler chickens fed diets containing different sources and concentrations of glycerine.

The objective of this study was to evaluate the effect of three sources of glycerine (crude glycerine from soya bean oil - CGSO, mixed crude glycerine from frying oil and lard--MCG, and a semipurified glycerine from soya bean oil--SPGSO) in four concentrations in the diet (17.5, 35.0, 52.5 and 70.0 g of each type of glycerine per kg of feed) on the levels of plasmatic glycerol and the activity of the hepatic enzyme glycerol kinase in broilers of 22-35 days old (experiment I) and 33-42 days old (experiment II). The highest (p < 0.05) plasmatic glycerol level was detected in broilers fed diet containing CGSO. Independent of the source, increasing the concentration of glycerine led to a linear increase (p < 0.05) in the plasmatic glycerol concentration. In experiment I, all the diets containing glycerine resulted in increased concentrations of plasmatic glycerol, in relation to the control diet without glycerine. However, in experiment II, only the diet containing 17.5 g of CGSO per kg of feed and the diets formulated with any of the three types of glycerine in the inclusion concentrations of 35, 52.5 and 70 g/kg of feed resulted in higher plasmatic glycerol levels than those observed in the control broilers. The source of glycerine influenced the glycerol kinase activity only in experiment II, where the use of CGSO in the diet increased the enzyme activity. For both experiments, the glycerol kinase activity increased with the inclusion of glycerine in the diet. In conclusion, based on the absence of saturation of the glycerol kinase activity for the three glycerine sources and for both rearing periods evaluated, the broilers can metabolize the glycerol (at the level of the phosphorylation of the glycerol to glycerol-3-phosphate in the liver) present in the glycerine when the diet is supplemented with up to 70 g of glycerine per kg of feed.