Further Evaluation of 1,25(OH)2D3-Glycosides Inclusion Timing for Reducing Clinical Bacterial Chondronecrosis with Osteomyelitis-Induced Lameness Incidence in Broilers

This experiment compared 14-day and 28-day inclusion schedules of 1,25(OH)2D3-glycosides in the broiler feed on the reduction of experimental clinical bacterial chondronecrosis with osteomyelitis (BCO) lameness, using the aerosol transmission induction model. Eight hundred and forty Cobb 500 chicks were randomly allocated to each of the following treatments at 60 chicks/pen as the initial stocking density and reared over 56 d: T1 (Positive Control-PC, 2 wire-flooring pens)—Basal diet (7166 IU/kg Vit-D3); T2 (Negative Control-NC, 4 litter pens)—Basal; T3 (4 litter pens)—Basal + 14d 1,25(OH)2D3-glycosides (1 µg/kg feed); and T4 (4 litter pens)—Basal + 28d 1,25(OH)2D3-glycosides (1 µg/kg feed). There were three feeding phases: Starter (d0–21), Grower (d22–42), and Finisher (d43–56). Clinical lameness assessment was conducted daily from d21, followed by euthanasia and necropsy of clinically lame birds to determine BCO lesion severity. Cumulative lameness incidence rates between treatments were assessed using binomial logistic regression analysis in a generalized linear mixed model. All statistical significance was determined at p < 0.05. Cumulatively, T4 (55.5%) was significantly lower in clinical lameness incidence compared to T2 (85.0%, relative decrease of 34.71%; p < 0.0001), while T3 (85.5%) was not significantly different (p = 0.89). These results further affirm efficacy of the 28-day inclusion period and the rate of 1,25(OH)2D3-glycosides against experimental clinical BCO lameness incidence.