Dissecting light turkey syndrome included an intensive field project was conducted by the research group listed above with the primary objective of determining if differences exist in characteristics among heavy (H) and light (L) poults within the same flock. The characteristics that were measured were presence of potential pathogens (bacteria and viruses), lesions in the gut and immune tissue, an indirect measure of nutrient absorptive capacity (Calvert, 2012) and intestinal microbial populations.
The brooding period was emphasized as examination of field data indicated poult weights were near standard at 1 wk but fell behind thereafter. Six commercial flocks and two research flocks were sampled at approximate age periods of 1, 2, and 3 wks of age. Heavy and light weight poults were selected for sampling with weights that were different by 10-15% of the average sample weight. Poults were euthanized and tissues taken for histopathology and intestinal contents taken for bacterial and virus analyses. Nutrient absorption was measured as the amount of xylose in the blood after gavage with xylose solution.
For the most part, flock differences were more apparent than differences among heavy and light poults within the same flock. As previously observed, body weights among flocks started to separate between 1 and 2 wks of age (Figure 1). Positive tests were observed primarily for astrovirus (all flocks), rotavirus (5 of 8 flocks positive) and some reovirus (2 of 8 flocks present). Scoring for histopathology found differences among flocks and weight group. Heavy weight poults appeared to have a faster maturing and healthier immune system because of the presence of gut lymphocytes (Figure 2). In contrast, light poults tended to have increased heterophils in the gut and bursal atrophy probably due to infection. Nutrient absorption as measured by xylose uptake was not consistently depressed in Light weight poults. Differences among flocks were not consistent.
Two of the commercial flocks showed the expected results with a higher concentration of serum xylose in heavy poults than light poults. Light weight poults from four of six flocks did not exhibit decreased nutrient absorption using xylose absorption as an indirect measure. While malabsorption might be a cause for decreased body weight in some LTS flocks, it was not the cause in all cases. Collection of ileum and contents for microbial community analyses found no large differences between heavy and light weight poults within a flock but that differences existed among flocks that performed well or had depressed poult weights at 2 and 3 wks of age.
The results of the research project indicated that in some flocks, light weight poults in comparison to heavy weight poults had more disease challenge and had an immature gut immune system development but this was not consistent across all flocks.
The many differences seen among flocks in the gut and immune tissue demonstrate that this is a complex syndrome that most likely has different combinations of causes for each flock. The results revolve around enteric challenge, gut development and development of microbial communities. A previous paper at this conference last year covered the topic of poult enteritis. The microbial community aspect of the turkey gut is in its infancy and deserves more attention.
From a management view, the delayed immune response in the gut associated with either Light weight poults or poorer performing flocks also deserves attention. The development of the gut in poultry is of tremendous important as related to its function. One as alluded to earlier is that the gut is one of the major immune organs of the bird. Secondly, and probably more obvious is the function of digestion and nutrient absorption.
Several reviews have been written on these topics. An important take-home message from these reviews is that there is a critical window of opportunity both before hatch and shortly after hatch to develop the gut and its functionality.
Provision of nutrition and/or intake of food shortly after hatch is necessary to start the development of the gut and establish the microbial community. Lack of access to feed shortly after hatch or lack of feed intake delays both the development of gut for digestive purposes as well immunity. As such it is important then to get poults started on feed as soon as possible in the brood barn. Feed quality, presentation, access, poult feeding behavior, and environmental conditions will determine actual intake levels. A major determinant of poult feeding behavior will be brooding temperatures and air mixing that achieve the comfort zone of the poult.
A field trial was conducted to examine various characteristics of poults classified as light weight and heavy weight in various commercial and research flocks. Light weight poults tended to show a delay in development of the gut immune system and also to have more evidence of disease challenge but this varied considerably from flock to flock. Development of the gut immune system, digestive capacity, and microbial community are inter-related and the very first step in this development after hatch is assuring the intake of food. Management and nutrition can be modified and fine-tuned but will go for naught if the doesn’t develop properly.
(From Proceedings of the “Midwest Poultry Federation Convention”, St. Paul, Minnesota, U.S.A.)