Abstract
Mannan based oligosaccharides and Lactobacillus strains has emerged as a promising bioactive substance to enhance intestinal development and improve early growth in poultry. However, their specific microarchitectural targets and differential microarchitectural role in post-hatch growth of layer pullet have not yet adequately characterized. This study explored the differential effects of in ovo delivery of two variants of mannan based oligosaccharides: D-mannan oligosaccharide (Dman) and Poly-D-mannan oligosaccharide (PolyD) and Limosilactobacillus reuteri DSM 17938 (LBR) on intestinal microarchitectures and growth in layer pullets. A total of 1,260 fertile eggs were divided into five groups: (1) not-injected control (NC); (2) saline-injected control (Sal; 100 μL of sterile saline); (3) LBR (100 μL of suspension containing 10⁸ CFU per egg); (4) PolyD (3 mg per egg); and (5) Dman (3 mg per egg). The solution was injected into amniotic on 17.5 day of incubation. Both mannan oligosaccharides (MOS) variants significantly enhanced early post-hatch growth, with Dman sustaining the effects up to 42 days (P < 0.05), whereas LBR had no significant effect (P > 0.05). In the ileum, both MOS variants increased villus width (VW) and villus surface area (VSA) on day 1, whereas LBR enhanced VW (P < 0.05). These effects persisted to day 7, with PolyD and LBR maintaining higher VW. In the jejunum, Dman increased VW on day 1 and crypt depth (CD) on day 7, while PolyD improved the villus height (VH):CD ratio on both days. By day 21, both VH and CD were elevated in the jejunum and ileum of both MOS variants treated chicks, with a sustained increase jejunal VH observed through day 42 (P < 0.05). Inclusively, these findings suggest that in ovo bioactive substance delivery exerts segment- and age-specific effects on intestinal development, supporting the concept of precision nutritional programming in layer chickens.