Optimizing forage particle size enhances rumen function and body condition in Atlas Brown dry cows under semi-arid conditions.

Optimizing the physical structure of forage remains a central challenge for improving dry-cow nutrition in low input dairy systems. This study evaluated how controlled reductions in particle-size distribution (PSD) within a mixed-forage ration (MFR) influence ingestive behaviour, ruminal physicochemistry, fiber digestibility, metabolic status, and body-condition dynamics in the indigenous Bos taurus “Atlas Brown” breed. Fifteen dry cows were assigned to three MFR treatments differing solely in PSD: long forage (> 50 mm; T1), coarsely chopped forage (10–50 mm; T2), and finely ground forage (5–10 mm; T3). Progressively narrowing PSD significantly increased daily dry-matter intake (8.18 to 9.47 kg; p = 0.004) and reduced the behavioural cost of feeding, as indicated by a 38% decrease in the fibrosity index. Contrary to prevailing assumptions, finely ground rations improved ruminal stability: mean ruminal pH increased from 6.05 (T1) to 6.37 (T3), while the duration below the subacute acidosis threshold (pH < 5.8) decreased by 80% (p < 0.001). Fiber utilization also improved, with apparent NDF digestibility rising from 45.3% to 53.1% (p = 0.012). Metabolic profiling revealed enhanced energy-protein synchrony in T3, characterized by higher plasma glucose and triglycerides alongside reduced plasma urea nitrogen, while mineral homeostasis (Ca, P) was maintained within physiological limits. Cows receiving the finely ground ration also exhibited better body condition recovery (+ 0.19 units) without excessive fattening. Collectively, these findings demonstrate that PSD modulation has enhanced feeding efficiency, ruminal health, and metabolic resilience in a local breed dry cows in semi-arid smallholder systems.