WINTER BONUS MAGAZINE 2026

Under the maize silage cover: Why every newmaize silage stock is a new feed Stephan van der Westhuizen – Technical Specialist: Dairy Under themaize silage cover lies one of themost underestimated yet repeatable risks inmodern dairy nutrition: the assumption that a new maize silage pit or bunker will be the same as the one it replaces. Froma management perspective, this assumption is understandable. The crop remains maize, the bunker system is unchanged, and the ration formulation often appears familiar. Froma biological perspective, however, this assumption is fundamentally flawed. Each newmaize silage pit or bunker represents a distinct feed with altered physical, nutritional, and fermentative characteristics, and these changes directly influence intake regulation, rumen function, and ultimately, milk production. This article is based on a hypothetical evaluation designed to illustrate what typically happens when a dairy operation moves from one maize silage bunker to another without a full nutritional reformulation. The evaluation specifically considers a transition from Bunker A (containing a 32% dry matter maize silage) to Bunker B (containing a more mature 38% dry matter maize silage). The intention is to demonstrate, using realistic ration data, how common on-farm practices create predictable nutritional outcomes. While dry matter concentration is the most visible difference between the two silages, table 1 shows that the underlying nutritional shifts are far more significant. The 38% DM silage contains substantially more NDF (414 vs 382 g/kg DM), lower sugar content, reduced organic matter digestibility, and a lower energy value (925 vs 968 VEM/kg DM). Although starch concentration is slightly higher, the overall fermentability of the silage declines, resulting in slower rumen fermentation and reduced microbial efficiency. These changes directly affect rumen fill dynamics and voluntary feed intake. Nutrient 32% DM – Maize silage (Bunker A) 38% DM – Maize silage (Bunker B) VEM (g/kg DM) 968 925 Crude protein (g/kg DM) 82 81 NDF (g/kg DM) 382 414 Sugar (g/kg DM) 18 12 Starch (g/kg DM) 292 306 OM digestibility (%) 76,1 73,3 Table 1: Key nutrient differences between maize silage bunkers used in the hypothetical evaluation www.agribonus.co.za Winter 2026 BONUS 117