Serum metabolite concentrations and enzyme activities in finishing bull calves fed different types of high-grain diets

Abstract. Between the ages of 23 and 35 weeks, various serum metabolites and enzymes were monitored in three 10-animal groups of double-muscled Belgian Blue bull calves maintained in a feedlot in Galicia (NW Spain) on high-grain finishing diets that mainly differed in whether the grain used was predominantly maize (group M), predominantly barley (group B), or a mixture of maize and barley in approximately equal proportions (group MB). The parameters determined were glucose, non-esterified fatty acids (NEFA), total serum protein concentration (TSP), albumin, serum urea nitrogen (SUN), creatinine, aspartate aminotransferase (AST), and gamma-glutamyltransferase (GGT). Throughout the study period, all these parameters remained within the physiological ranges for beef under intensive conditions, and no animal ever showed clinical symptoms of ruminal alterations; indicating that none of these highgrain diets were detrimental to animal health. Although average serum NEFA, creatinine, albumin, AST and GGT levels all differed among groups, only AST can be considered as possible age-independent marker of grain-type-related metabolic alterations, since the other parameters all showed significant time × group interaction. In terms of this parameter, animals fed a MB diet behaved similarly to those fed a B diet. The absence of between-group differences in blood glucose level may reflect a genetic characteristic of this double-muscled breed. Our results, in conjunction with the best productive results obtained in animals fed de B-diet, aim us to suggest that the risk of an acidogenic diet would depend strongly on the nutritional management (in terms of crude protein (CP) and quality of straw in the ration) and not only the type of grain.