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Every year about 50 million one day old male chicks of egg-laying hens are killed in Germany because their growth rates are significantly less than that of meat-producing chicken breeds. Ethical and cost factors suggest that an alternative to the current cull is to use dual-purpose chickens. The aim of this study is to compare anatomical characteristics of the gastrointestinal tract of dual-purpose chickens (Lohmann Dual, LD) with broiler chickens (Ross 308) raised under conditions typical for meat production.
MATERIALS AND METHODS
Sixtysix (LD) and 54 (Ross) chickens were housed until 5 (Ross) or 9 (LD) weeks of age, under the same husbandry conditions. At roughly 7 day intervals 6 birds from each line were weighed and then euthanized by decapitation. The length of each intestinal segment, and the weight of the empty gizzard and intestinal segments were measured.
The jejunum was examined histologically and morphometrically. Villus and epithelial heights, crypt depth, and the tunica muscularis thicknesses were measured. Digitalized live pictures were analyzed using an image analysis program NIS-Elements AR (Nikon Instruments Inc., U.S.A.).
The allometric relationships between the organ masses and body mass were determined. Data was examined using the Mann–Whitney U test, by analysis of variance and multiple linear regression analysis. P values lower than 0.05 were considered statistically significant.
The Ross birds were about 2.6 times heavier than the LD birds by day 35. The normalized gizzard mass was greater in the LD than in the Ross. A multiple regression analysis showed that both the BW and the chicken line had an influence on the mass of the gizzard, p ≤ 0.001.The length of the intestine of Ross birds increased faster than in the LD birds. The normalized intestinal mass showed that the two lines were similar, peaking at day 7 and decreasing to plateau between days 21-35. From day 35-63 the intestinal mass of LD birds dropped dramatically.
Multiple regression analysis showed that both the BW and the genetic line had an influence on the entire intestine length and mass. The light microscopic studies showed that villus height was higher in Ross than LD in the jejunum from day 7-35.
Whilst Lohmann Dual birds took 63 days to reach 2000 g BW, compared to the 35 days by Ross birds this is faster than found in other slow-growing lines.
The higher normalized organ masses reported here in LD suggest that a greater portion of nutrients are used for organ development than for BW. A larger gizzard in LD than in Ross corresponds to an increased food processing, which could influence intestinal morphometry. Smaller intestines and smaller jejunal villus surface areas in LD suggest a lesser area for digestion and absorption than in Ross. This could represent an adaptation of the lower portions of the digestive to the gizzard size.