Due to its high production performance levels (78% carcass muscle, mean daily weight gain > 2 kg/d), the double-muscled Belgian Blue bull has specific digestible amino acid (AA) requirements that are unlikely to be satisfied by the common practice of feeding maize silage with soybean meal as a protein source. The lack of one single essential AA inevitably prevents any additional protein accretion and thus limits the animals’ growth potential. Precise ration formulation is therefore essential if the impact of future genetic progress is not to be restricted. Providing a ruminant with supplementary digestible AA often requires the AA to be protected from ruminal fermentation, so as to ensure their availability in the small intestine, the animal’s main source of nutrient absorption. However, the low rumen volume in the growing Belgian Blue combined with a high level of free AA enables the degradation of free AA to be greatly limited (60 to 65%), obviating the need for protection and making it economically unprofitable in the case of common AA such as methionine and lysine.
Objectives
The primary aim of the project was to identify the limiting AA, that is, the AA most lacking in relation to the animals’ requirements, in a conventional maize silage and soybean meal based ration, in the growing Belgian Blue bull. A secondary aim was to determine the best method of administration in order to provide supplementary digestible AA without protecting the AA from ruminal fermentation. Two methods were tested: continuous ruminal AA supplementation over a 24?hour period and instantaneous supplementation, also called flash treatment. The third aim, lastly, was to formulate an amino acid enriched additive based on the deficiencies observed and test it in a conventional fattening test.
Results obtained
The first trial showed histidine to be the principal limiting AA when the animals were fed a ration of maize silage (50%), soybean meal (20%), sugar beet pulp (20%) and hay (10%). Methionine and lysine were also limiting, though to a lesser degree. It was also found that the flash treatment, which provided an instant supply of methionine (40 g/d) and lysine (60 g/d), produced a better AA output rate than continuous treatment (40 as opposed to 16%), for an equal quantity of AA. Based on the results, an additive was formulated to make up part of the deficit of the total essential AA. This was tested in conventional fattening conditions in two rations with a low (12%) or normal (17% - same as the previous trial) protein content. Mean daily weight gain under each treatment over the whole growing/fattening period is shown in Figure 1. The effect of the additive was most marked at the beginning of the growing period, with the ration providing 17% protein (improved mean daily weight gain of 300 g/d in the presence of the additive, P < 0.001). For the time being the cost of the additive is high, as histidine is an expensive amino acid. Future research should lead to cheaper production techniques (microbial synthesis) or, failing this, development of cheap protection to make the additive competitive economically.
Contribution
Project leader - coordinator
Partners
o CRA-W o Comptoir de Gîves S.A. o Gembloux Agricultural University, Animal Science Unit o Centre Wallon de Biologie Industrielle
