Differential responses to dietary carbohydrates and fat of turkeys kept at various environmental temperatures

Adaptation to hot climate and strategies to alleviate heat stress in livestock production

Despite many challenges faced by animal producers, including environmental problems, diseases, economic pressure, and feed availability, it is still predicted that animal production in developing countries will continue to sustain the future growth of the world's meat production. In these areas, livestock performance is generally lower than those obtained in Western Europe and North America. Although many factors can be involved, climatic factors are among the first and crucial limiting factors of the development of animal production in warm regions. In addition, global warming will further accentuate heat stress-related problems. The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems. These strategies can be classified into three groups: those increasing feed intake or decreasing metabolic heat production, those enhancing heat-loss capacities, and those involving genetic selection for heat tolerance. Under heat stress, improved production should be possible through modifications of diet composition that either promotes a higher intake or compensates the low feed consumption. In addition, altering feeding management such as a change in feeding time and/or frequency, are efficient tools to avoid excessive heat load and improve survival rate, especially in poultry. Methods to enhance heat exchange between the environment and the animal and those changing the environment to prevent or limit heat stress can be used to improve performance under hot climatic conditions. Although differences in thermal tolerance exist between livestock species (ruminants > monogastrics), there are also large differences between breeds of a species and within each breed. Consequently, the opportunity may exist to improve thermal tolerance of the animals using genetic tools. However, further research is required to quantify the genetic antagonism between adaptation and production traits to evaluate the potential selection response. With the development of molecular biotechnologies, new opportunities are available to characterize gene expression and identify key cellular responses to heat stress. These new tools will enable scientists to improve the accuracy and the efficiency of selection for heat tolerance. Epigenetic regulation of gene expression and thermal imprinting of the genome could also be an efficient method to improve thermal tolerance. Such techniques (e.g. perinatal heat acclimation) are currently being experimented in chicken.

The response of broiler chickens and turkey poults to steam-pelleted diets supplemented with fat or carbohydrates

The responses of growth and feed efficiency to pelleted feed was investigated in 4- to 7-wk-old broiler chickens, and in 8- to 12- and 16- to 20-wk-old turkeys. In all cases, the growth and feed efficiency responses were linear within the ranges of dietary energy tested. When energy was added by carbohydrate supplementation, weight gain and feed efficiency responses were parallel for both mash and pellets, but due to the growth response to pellets, the elevation was higher for pellets than for mash. When energy was added by fat, the growth response to pellets also resulted in an increase in function elevation but the slope of the response was lower than in mash feeding, possibly due to a decline in pellet quality as dietary fat increased. Grinding of pellets completely abolished the growth and feed efficiency responses observed when the physical form was preserved. In chickens, comparisons of ground pellets to mash suggested some decline in nutritional quality due to the process of pelleting when either carbohydrates or fat were increased in the diets. In both chickens and turkeys, the feeding of pelleted diets resulted in an increase in abdominal fat.

The response of broiler chickens and turkey poults to dietary energy supplied either by fat or carbohydrates

The efficacy of fat and carbohydrates as energy sources was compared in 1- to 4- and 4- to 7-wk-old broiler chickens and in 16- to 19-wk-old turkeys. An increase in dietary energy by carbohydrate was made by a graded replacement of wheat bran by wheat. Energy was increased by fat through a graded replacement of soybean hulls with refined soybean oil. In the experiments with broiler chickens, the feed efficiency responses to added energy were observed within the entire range of dietary energy tested, with no significant differences between the responses to carbohydrate and fat as energy supplements. The growth response to energy from either source appeared to be characterized by diminishing returns in the chicken. In the 16- to 19-wk-old turkeys, the growth and feed efficiency responses were linear within the range from 2,650 to 3,250 kcal/kg. In chickens and in turkeys, the growth and feed efficiency responses to energy supplied by fat were indistinguishable from those of carbohydrates. In chickens, the fractions of abdominal fat and pectoral muscle were not affected significantly by the energy density and source.

Differential responses to dietary carbohydrates and fat of turkeys kept at various environmental temperatures

Interactions between environmental temperature and dietary energy sources were evaluated in 6 to 9-wk and 9 to 12-wk-old turkeys using weight gain, feed efficiency, and carcass fat as response criteria. The dietary variables (soybean oil or glucose) were added in five or six increments at the expense of each other or of the fiber supplements, keeping the minima for protein and amino acid/energy constant. The resulting diets were fed to birds kept at 10 and 27 C. Duplicate experiments were conducted for each mode of dietary variable addition. Parallel increases in body weight gain and feed efficiency were obtained at the two temperatures when fat replaced carbohydrates or fiber, thereby raising dietary energy density. Some responses of weight gain and feed efficiency at the two temperatures were obtained also with a graded isocaloric addition of fat but the response was significant only at 27 C and not at 10 C. A greater response of gain and feed efficiency to energy supplied by dietary glucose was obtained at 10 C as compared with 27 C. Dietary fat supplementation resulted in increased deposition of carcass fat when given together with energy or isocalorically regardless of environmental temperature. Carcass fat was increased by glucose-energy at the low temperature only.