Abstract
A study evaluated the effects of phytase, 25-hydroxyvitamin D3 (25OHD), and cocci vaccination on broilers fed a diet reduced in calcium (Ca) and available phosphorus (avP) under Eimeria challenge. A total of 840 one-day-old male broilers were assigned to a 2 × 5 factorial arrangement based on cocci vaccination and dietary treatments. Half of the birds were vaccinated against coccidia on d 1, and all birds were orally challenged with Eimeria spp. (sporulated oocysts: 12,500 of E. maxima, 12,500 of E. tenella, and 62,500 of E. acervulina) on d 14. Dietary treatments included: 1) a nutrient adequate diet (PC); 2) a diet reduced by 0.2% in Ca and avP (NC); 3) NC plus 1,500 FTU/kg of phytase (NC+PHY); 4) NC plus 3,000 IU/kg of 25OHD (NC+25OHD); 5) NC with both PHY and 25OHD (NC+PHY+25OHD). SAS was used for data analysis, with significance set at P ≤ 0.05. Pre-infection growth performance was comparable across the treatments. However, vaccinated birds exhibited higher body weight (BW) and body weight gain (BWG) from 0 to 6 d postinoculation (DPI; P < 0.05). The NC diet reduced BWG from 6 to 12 DPI and increased the feed conversion ratio (FCR) during 6 to 12 DPI and the overall period (0-26 d) compared to the PC birds. In contrast, the supplementation with phytase, 25OHD, or both, returned BWG and FCR to levels seen with the PC diet (P < 0.01). Vaccinated birds also had reduced gut permeability at 5 DPI, increased intestinal villus height, and lower expression levels of the tight junction proteins junctional adhesion molecule 2 (JAM2) and occludin (OCLN) at 6 DPI (P < 0.05). Interestingly, the cocci vaccine resulted in lower E. acervulina but higher E. tenella oocyst shedding at 6 DPI (P < 0.01). Interaction effects were observed for duodenal lesion scores and ileal crypt depth at 6 DPI (P < 0.05). In conclusion, coccidial vaccination improved growth performance, decreased intestinal permeability, enhanced intestinal morphology, and modulated tight junction protein gene expression under Eimeria infection. Reducing dietary Ca and avP levels adversely affected growth performance and FI during the recovery phase, but these negative effects could be mitigated by supplementing with phytase or 25OHD.