Effects of dietary changes on heat stress in broiler and Kampung chickens

Poultry meat production has increased drastically over the last 35 years. Most developing countries are in the tropics and often have high ambient temperatures. At high ambient temperatures, chickens exhibit a slower growth rate due to a reduced feed intake. In order to limit the reduction in feed intake, a feeding strategy should be applied which decreases the level of heat production and/or increases the possibilities for heat dissipation. Such a feeding strategy can be based on feed that gives less heat because of lower energy costs of digestion or provides fewer nutrients that lead to a high heat production. This thesis studied how birds subjected to chronic heat stress change feed intake of especially crude protein and total energy. In addition, a wet feeding strategy that might alleviate the adverse effects of heat stress on performance was applied. Chickens exposed to choice feeding responded similarly at normal and at high ambient temperatures. They composed from a choice of a control diet, an energy rich diet and a protein rich diet a diet with a higher energy (HE) content and a lower protein content compared to the standard control diet. At high temperatures, chickens will reduce feed intake because they want to avoid or reduce a high body temperature. When the chickens were fed a wet-HE diet, feed intake and BW gain were higher in broiler chickens compared with feeding a dry-HE diet. The most beneficial effects of a wet diet occurred with a high energy diet. The indigenous Kampung chickens have been acclimatized to a high ambient temperature and did not benefit from a wet diet. In the present study, temperature had a major effect on relative lengths and empty weights of gastrointestinal tract segments in broiler chickens on day 42. Relative lengths of most gastrointestinal tract segments were affected by diet formulation at day 21 and 42, but not relative empty weight. Control-fed birds had shorter relative lengths than HE-fed birds, suggesting that the higher BW gain of control-fed birds were not accompanied by a similar increase in length of the gastrointestinal tract. Wetting the diet did not increase empty weights of intestines both at days 21 and 42. In Kampung chickens, effects of diet formulation on gastrointestinal tract development disappeared when the birds grew older, suggesting that this type of bird adapts easily to changes in dietary nutrient content. A positive effect of the relative weight of the intestine of birds fed a wet diet was observed in Kampung chickens. In general, it seems that the Kampung chickens grow proportionally but broiler carcass is growing faster than its gastrointestinal tract in control- and wet-fed birds. Key words: Self-selection, temperature, wet diet, broiler, indigenous chicken