Date Published: October 19, 2018
Publisher: Public Library of Science
Author(s): Zaher Alshamy, Kenneth C. Richardson, Hana Hünigen, Hafez Mohamed Hafez, Johanna Plendl, Salah Al Masri, Arda Yildirim.
The transition to using dual-purpose chickens is an alternative to killing male hatchlings of high performance egg-laying chickens. This study aimed to compare the gastrointestinal tract of a recently developed genetic line of dual purpose male chicken, Lohmann Dual (LD), with that of a broiler line, Ross 308. Eighty birds from each line were grown until they reached an average body weight 2000 g (5 weeks for Ross and 9 for LD birds). Six birds of each line were sampled weekly. Body weight (BW), normalized mass of gastrointestinal segments and relative length of intestine were determined. Histologically the villus height, epithelium height, crypt depth, mucosal enlargement factor and the tunica muscularis thickness were measured in jejunum and ileum. Data were regressed against body weight and genetic line. Jejunal enterocyte microvilli and junctional complexes length were measured. Normalized mass and relative length of the gastrointestinal segments were greater in LD birds than in Ross birds at all ages. After day 7 these decreased steadily over the lifetime of the birds in both genetic lines. The growth curves of the gastrointestinal segments of the LD birds were similar to those of the Ross birds. In birds of the same BW, LD birds had a significantly heavier gizzard, shorter intestine, higher jejunal villi, thicker ileal tunica muscularis and smaller ileal mucosal enlargement factor than were found in Ross birds. The large gizzard in LD chickens presumably increases the degree of food processing and enhances availability of nutrients in the orad part of the intestine leading to a lower nutrient concentration and a smaller absorption surface area in the ileum of the LD compared to the Ross chickens. The anatomical differences between the two lines are important criteria for further selection and should be considered in their feeding management.
The commercial chicken industry is based on the genetic development of highly productive breeds selected for either egg laying or meat production. Since males of laying breeds are slow growing, they are not profitable for meat production and are killed immediately after hatching . This outcome has caused intense ethical debate . One suggested approach to resolve this problem is to raise layer-type males to a live weight of 600 or 2000 g and market them as alternatives to quail or broiler chickens respectively. However, to reach a live weight of 2000+ g, the layer-type males require twice the quantity of feed and triple the time compared to specifically selected broiler breeds . In a public survey conducted by Leenstra et al. (2011), of 5 potential alternatives to killing one-day-old chicks, “transillumination of the fresh eggs to determine the sex of the eggs and not incubate male eggs” and “using dual-purpose chickens” scored best (25% and 24%, respectively) out of the proposed alternatives” .
The breeding of dual production chicken lines with high performance females for laying eggs and males being raised for meat production is an alternative to the culling of one-day-old male chickens of laying lines. Lohmann Dual, a recent commercial dual-purpose breed developed by crossing meat and layer lines and using the sex-linked dwarf gene, has acceptable performances in both meat and egg production . Over the 70 days of their life their feed conversion ratio is 1:2.5 which is better compared to that of Lohmann Brown cockerels 1:4 .
The gastrointestinal tract of the LD birds was not affected by the breeding and selection criteria used in the development of this dual purpose chicken line. At gross anatomical, histological and ultrastructural levels the gastrointestinal tract of the LD birds grew proportionately to the increase in body weight without any abnormalities or deformations being observed. However, there were several anatomical differences between the LD birds and the more rapidly growing birds Ross 308 birds that may contribute to the slower growth rate of LD birds. We suggest that LD chickens have a lower nutrient absorption capacity due to their shorter intestine and smaller intestinal mucosal surface area that result in a slower body growth rate than found in Ross chickens. Moreover, the earlier establishment of the time of a balance between the growth of gastrointestinal tract segments and the overall increase in body weight in Ross chickens compared to LD chickens is noteworthy. The earlier balance time-point in the Ross birds is possibly an indicator of their better growth and performance. Thus anatomical characteristics of the gastrointestinal tract such as the time of body weight-organ balance, intestinal length and intestinal mucosal surface area could be considered as criteria for the ongoing selection of the LD birds to improve their performance and to optimize feeding strategies. However, the interactions between feeding regimens to gizzard and intestine development needs further investigation.