Effects of starter diets with different neutral detergent fiber levels on gastrointestinal tract development, microbial profiles, nutrient digestibility, and growth performance in Xinong Saanen dairy goat kids.

Starter feeds in pre-ruminant diets help optimize ruminal development before weaning, contributing significantly to lifelong health and performance. This study investigated the effects of varying neutral detergent fiber (NDF) levels in starter diets on growth, serum indices, slaughter performance, nutrient digestibility, gastrointestinal tract (GIT) development, and microbial profiles of dairy goat kids. Sixty 14-d-old Xinong Saanen dairy goat kids were assigned to 3 groups (n = 20/group) with NDF levels of 20%, 25%, or 30%. All kids received milk and starters from day 15 to 84. Body weight (BW) was monitored bi-weekly, and blood was sampled at weeks 2, 6, 10, and 12. At 12 wk, 3 male kids per group were slaughtered for GIT morphology, enzyme activity, microbial profiles, and carcass assessment. The 25N and 30N groups exhibited significantly greater overall BW (P < 0.01) and serum aspartate transaminase (AST; P < 0.01) and β-hydroxybutyric acid (BHBA; P < 0.01). Dressing percentage, duodenum mass, jejunum mass, and total small intestine mass increased linearly (P < 0.05) with higher NDF levels. The ruminal papilla length (P < 0.05) and papilla width (P < 0.05), the villus height/crypt depth (VH/CD) of jejunum (P < 0.01) and the mucosal thickness (P < 0.01) of ileum also increased linearly as dietary NDF levels increased. Enzyme activities, such as cellulase in the rumen (P = 0.071) and small intestine (P = 0.075) tended to increase with increasing NDF content, whereas α-amylase in the rumen (P < 0.05) and small intestine (P < 0.05), pepsin in the rumen (P < 0.01) and trypsin in the small intestine (P < 0.05) decreased. Increasing NDF levels resulted in linear responses (P < 0.05) in ruminal acetate, butyrate, acetate/propionate (A/P) ratio, and total volatile fatty acid concentrations. In the rumen, Lachnospiraceae_UCG-010 and norank_f_UCG-010_o__Oscillospirales, fibrolytic microorganisms were more abundant in the 30N group, while Succinivibrio, a saccharolytic bacterium was enriched in the 20N group. In the jejunum, norank_o__Clostridia_vadinBB60_group and unclassified_f__Lachnospiraceae, were enriched in the 25N and 30N groups. In contrast, Candidatus_Arthromitus, Mitsuokella, and norank_f__F082, involved in host immunity, were significantly enriched in the 20N group. Overall, starters containing 25% and 30% NDF promoted fiber-degrading bacteria and enhanced GIT development, thereby optimizing the growth performance of dairy goat kids.