Influence du procédé d'hydrolyse des protéines de poisson sur leur utilisation par le veau de boucherie. Comparaison avec les protéines de lait et celles de soja

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Abstract
The utilization of 3 protein concentrates (fish A, fish B and soybean) was studied in the veal calf. The fish concentrates were prepared from white fish by partial hydrolysis, using a mixture of plant (A) or bacterial (B) enzymes. The soybean concentrate was a soybean oil-meal treated by moist heating and cleared of its sucrose and .alpha. galactosides by alcohol extraction. Four milk replacers containing 24% crude protein and 18% fat on a dry matter basis were prepared. In the control diet, the proteins were almost exclusively provided by skim milk. In the 3 other diets (fish A, fish B and soybean) 59% of the proteins were supplied by 1 of the protein concentrates studied, the rest by skim milk powder, lysine and methionine. Each diet was offered to 12 Friesian bull calves from 3-16 wk of age. The performances of the calves were lower with fish A diet than with the control diet but only the difference in feed conversion ratio (6.5% for the whole trial) was significant. The results obtained with fish B diet were less satisfactory than those concerning fish A diet (-8.6, and -4.0 and -5.1% for live weight gain, feed conversion ratio and carcass weight). The performances of the calves fed the soybean diet were very similar to those of the calves given fish B diet and lower than those of the calves fed control and fish A diets. The hematocrit value decreased less with fish B and soybean diets than with control and fish A diets. The adverse effect of replacing milk protein by that of the protein concentrates studied may be partly due to an insufficient protein supply, at least during the 1st weeks of the trial, as indicated by the lower uremia in the calves fed fish A, fish B and soybean diets or by essential and semi-essential amino acid deficiencies, mainly in fish A and fish B diets, as suggested by measurements of blood levels of free amino-acids in the calves. Poorer utilization of fish B compared to fish A may be due to a lower valine availability. Protein utilization prepared by enzymatic hydrolysis of white fish might replace large proportion of skim milk powder in milk replacers fed to veal calves. To avoid any adverse effect, the substitution level must not exceed 35%; it is also useful to mix these fish concentrates with whey powder to get a better essential amino acid composition. The kind of enzymes used for hydrolysis has an important effect on protein utilization. The soybean concentrate studied in this trial was not as well used as the fish A concentrate.