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 70.0g 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 22-35days of age (experiment I) and 33-43days 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 33-42days of age, MCG inhibited (p<0.05) the glutamate dehydrogenase activity by up to 34.43%. During 22-35days 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 55.08g 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 33-42days 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.
