Nutritional strategies for mitigating wooden breast and white striping myopathies of the Pectoralis major muscles in broiler chickens
Type of DegreePhD Dissertation
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Throughout the last decade, broiler producers have increasingly noted the presence of wooden breast (WB) and white striping (WS) in the Pectoralis major muscles (breast fillet) of broilers. Non-genetic factors, such as environment and nutrition, may contribute a substantial portion of the observed variance in myopathy incidence, and could be suitable targets for practical interventions aimed at reducing the incidence of myopathy. Therefore, a series of 4 experiments was conducted to determine whether WB and WS may be ameliorated by modulating nutrient intake. The first experiment utilized a quantitatively controlled feeding program to obtain differences in growth trajectory aimed at reducing the incidence and severity of WB and WS. Linear decreases in feed intake resulted in linear decreases in WB and WS at 33, 43, and 50 d of age, indicating that controlled feeding programs have the potential to reduce myopathies. The second experiment attempted to replicate the nutrient intake of the quantitative feeding program in a qualitative manner by altering dietary AA and AMEn densities. However, broilers responded to the reduced density diets by over-consuming feed, eliminating the differences in dietary density. To mitigate compensatory intake, the third experiment investigated the use of diets that only reduced the concentrations of digestible Lys (dLys), but did not alter energy density or maintain AA ratios to dLys. Reducing dLys to 75% (18 to 26 d) and 85% (28 to 40 d) of primary breeder recommendations substantially decreased the incidence of severe WB and WS at 48 and 61 d of age, respectively. These results indicated that the intended market weight of a flock must be taken into account when determining the timing and intensity of a reduction in dLys density. The fourth experiment utilized a diet formulated at 75% of primary breeder recommendations for dLys concentrations from 15 to 25 d of age in order to produce broilers within the same flock that were differentially affected by WB as a suitable model for an in vivo comparison of myofiber CSA and the relative populations of myogenic cells known to play critical roles in muscle growth and repair. The size and activity of Myf-5+ and Pax7+ myogenic cell populations were increased in the presence of severe WB. Additionally, broilers affected by severe WB had different distributions of myofiber CSA. Altogether, these results indicated that targeted modification of the growth trajectory using reduced dietary dLys is a viable strategy to reduce the severity of WB and WS. Future research should strive to establish a basic understanding of the etiology of WB and WS in order to develop practical nutrition and management interventions aimed at reducing the prevalence of these myopathies in the broiler industry.