B Matton, D Siebert, A Verhelle, B Saremi
Immune challenge can alter the amino acid (AA) requirements. Histidine (His) is an essential AA for broilers, supports multiple physiological functions and may become limiting in reduced CP diets. However, His requirements in modern broilers have been sparsely investigated, particularly across a full production cycle and under immune challenge conditions. Therefore, a 35-day, 3-phase His requirement study was conducted with 1680 one-day-old male Ross 308 broilers allocated to fourteen treatments (n = 8). Equally divided, a first group, comprised seven treatments without challenge (unchallenged, UC) and a second group comprised seven treatments with immune challenge (challenged, C). The challenge consisted out of an in feed coccidiosis challenge on d6 and d14, followed by an oral bacterial challenge on d21, d22, and d23. In both groups, birds received either a basal diet (BD) containing 0.3 % standardized ileal digestible (SID) His, or a BD supplemented with graded levels of l-His to achieve 0.33, 0.36, 0.39, 0.44, 0.49, 0.54 % SID His in starter, grower, and finisher phases. Histidine requirements were estimated using an exponential asymptotic model. First, the minimum SID His required to achieve 98 % of the maximum performance under immune challenge conditions was determined and used as a reference for comparison between the UC and C group. Over the 35-day period, the estimated SID His requirement for C birds to optimize BW and feed conversion ratio (FCR) was 0.407 % and 0.375 %, respectively. To reach the same performance UC birds only required 0.387 % and 0.325 % SID His, respectively. Second, the UC bird's requirement was estimated using the same model. Over the 35-day period, the estimated SID His requirement for UC birds to optimize BW, ADG, and FCR was between 0.389 - 0.448 %, whereas the requirement to optimize breast weight and breast yield (relative to live weight) was 0.513 and 0.524 %, respectively.