Effects of dietary protein reduction and enzyme supplementation on growth performance in fattening period

Abstract

[EN] The effect of a decrease in the dietary crude protein level from 16% to 14%, maintaining the supply of the most limiting amino acids above the recommended levels, and the addition of proteases to the feed during the growing period was investigated. Two diets were formulated to contain 16% or 14% CP and maintaining the same level of total lysine, methionine and threonine (0.77, 0.50 and 0.58%, respectively) by adding synthetic amino acids (14% CP + AA's). To study the effect of protease supplementation, 1 g/kg of commercially available PESCAZYME 5602¿ was added to the diet containing 16% CP. The three experimental diets were offered ad libitum from weaning (35 d of age) to slaughter (63 d) in two growth trials. One hundred and eighty (60 per diet) rabbits were individually housed and 480 rabbits were collectively housed in 120 polyvalent cages (40 cages per treatment) in the growth trials. Forty rabbits (20 per treatment), were assigned to two experimental diets 16% CP and 14% CP + AA's and used to determine total anaerobic bacteria in the ileum and Clostridium perfringens in the caecum. There was no mortality either in the individual or collective trial and Clostridium perfringens was not detected. However, a reduction of total anaerobic bacteria was detected at ileum (15.9 x10 8 ± 3 vs. 7.7 x108 ± 0.3 CFU/g on average for diets 16% CP and 14% CP+AA's, respectively). There was no effect neither for the addition of proteases no for the dietary CP level on growth performances either in the 35 to 49 d period or in the 49 to 63 d period. There was no interaction between type of diet and type of housing. However animals individually caged showed better growth rate and feed conversion rate than animals collectively caged in the whole growing period (55.6 vs. 46.1 g/d and 2.19 vs. 2.45, respectively). From the results of this study it can be concluded that protein concentration in the diet can be reduced to a level of 14% maintaining the levels of most limiting amino acids above recommended levels and supplying 10g digestible protein per MJ digestible energy without any impairment of growth performance.