Effects of caecectomy and dietary antibiotics on the digestibility of dry matter and amino acids in poultry feeds determined by excreta analysis

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Abstract
Digestibility measurements were made with caecectomized or intact adult cockerels offered diets containing maize, or equal amounts of maize and one of six protein concentrates, with and without antibiotics. Dietary antibiotics reduced micro-organisms to less than 2x 103/g dry excreta. Caecectomy and the addition of antibiotics to the diet reduced dry matter digestibility on average by 9% compared with intact birds on diets without antibiotics. The greatest reduction was 20% for soybean meal. The mean apparent digestibility of several amino acids showed no significant change due to caecectomy and/or inclusion of antibiotics in the diets, while that of isoleucine showed an increase. For other amino acids, the response was variable and within each protein supplement, the response of individual amino acids was also variable. The lowest mean digestibility for lysine was 0.63 in cottonseed meal and the highest was 0 92 for fish meal. It was concluded that, although excreta analysis may not always be a reliable method for determining amino acid digestibility of feeds, neither method used to reduce microflora in the hind gut was consistently effective. It was unclear whether this was due to the nature of the protein source or to the inability of the methods used to suppress microbial activity in the hind gut.