EFFECT OF PHOTOPERIOD AND DIETARY STRATEGIES ON CROP MICROBIAL ECOLOGY AND HEALTH OF BROILER CHICKENS
Dalal, Sangeeta 1979-
Increased restriction of antibiotic use in the poultry industry has focused research efforts towards alternative strategies to promote bird health. Photoperiod and nutritional management strategies are recognized as major factors affecting bird health and were investigated here as strategies to modulate immune status and intestinal microbial abundance. In the first study four experiments, each comprising more than 5,000 broiler chickens, were conducted to examine the effect of photoperiod duration on immune parameters and livability assessed by mortality incidence. All birds were exposed to 23L:1D (23L) photoperiod from 0-7 d of age prior to photoperiodic treatment allocation. In the first two experiments, broiler chickens (Ross 308 and 708) were housed under 14L:10D (14L), 17L:7D (17L), 20L:4D (20L) and 23L:1D (23L) and raised on used litter. Photoperiod treatments included 15L:3.5D:2L:3.5D (15L), 17L, 23L in experiment 3 and 13L:11D (13L), 18L:6D (18L), 23L in experiment 4. In experiment 3 and 4, Ross 308 were fed different dietary amino acid levels (Low-Lo, Medium-Med and High-Hi). Several immune parameters (relative organ weight, heterophil:lymphocyte (H:L) ratio, response to systemic lipopolysaccharide, systemic vaccination antibody response, and a whole blood chemiluminescence (WBCL) assay) were used to monitor immune status of birds across these experiments. Near continuous photoperiod (23L) reduced liver and bursa relative weight concomitantly with increased incidence of total and infectious mortality. However, there was no consistent evidence of compromised innate or acquired immunity nor of altered response to systemic inflammatory challenge. In a second study, the effects of photoperiod (13L, 18L and 23L) and dietary amino acid level (low, medium, high) on performance, breast meat yield and crop microbial ecology were measured in 39 d-old broiler chickens. Increased photoperiod duration of ≥18L reduced the relative crop size and increased crop pH compared to 13L. Increased photoperiod (23L) and the highest amino levels increased final body weight and breast meat yield. Short photoperiod (13L) increased feed efficiency and microbial abundance in the crop, mainly of Lactobacillus spp. as evaluated here by T-RFLP profiling and qPCR enumeration techniques. The final experiment was a growth trial where broiler chickens were fed three diets with three primary ingredients (corn vs wheat vs pea), ground using a 350 mm (fine) or 1000 mm (coarse) hammer mill screen size, and offered ad-libitum or in three meals per day. Final body weight of broiler chickens was not affected by dietary ingredients or grind size except meal-fed broilers had the lowest body weight compared to ad-libitum fed counterparts. 16S rRNA gene based T-RFLP profile analysis of crop contents and crop mucosa associated community revealed broilers fed corn- or wheat- based diets segregate from broilers fed pea diets, however, no clustering of ileal content T-RFLP profiles was observed. Quantitative PCR analysis of crop content further revealed higher abundance of Lactobacillus spp., L. johnsonii and L. salivarius in broilers fed corn and pea-based diets, while in crop mucosa pea diets promoted increased abundance of L. gallinarium versus corn and wheat-fed birds. Three times per day meal feeding increased ileal counts of L. johnsonii, L. gallinarium and L. reutri compared to ad-libitum fed broiler birds. This study demonstrated that easily digestible substrates (e.g. available starch, amino acids) might serve as an important substrate for the proximal broiler chicken intestinal microbial community, particularly Lactobacillus species which further can be stimulated by diet composition, processing and feeding strategies. Overall, findings here suggest the importance of photoperiod management and dietary composition on bird health, emphasizing a possible important role of crop microbial composition.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentAnimal and Poultry Science
CommitteeMutsvangwa, Tim; Classen, Henry L.; Laarveld, Bernard; Gomis, Susantha
Copyright DateAugust 2016