ARTICLE 92 FEED & ADDITIVE MAGAZINE July 2025 REDEFINING FORAGE PARTICLE SIZE FOR RUMINANTS William Woodley Dairy Consultant Woodley Dairy Direction Dairy cow rumination is a complex process involving eating, cud chewing, and recumbent chewing—all of which are influenced by forage particle size. Recent research challenges long-held beliefs about longer forage being better. Could reducing particle size actually enhance milk yield and digestion? Discover how fibre structure, chewing behaviour, and forage quality intersect to impact performance and health. There has always been a strong association with long forage particles and an improvement in rumination and consequentially rumen health – but is this always the case? To better understand the impact of particle size on cud chewing and rumen health, we need to fully understand rumination. Although dairy cow rumination is often equated strictly with cud chewing it is actually a more complex process consisting of eating, cud chewing and recumbent cud chewing. EATING AND PARTICLE SIZE The dairy cow uses a grinding action with the molars to reduce the particle size of the forages – resulting in a shearing effect rather than cutting (Beauchemin, J. Dairy Sci. 101:4762–4784 2018). This is critical because the material needs to be reduced in particle size to be swallowed and then regurgitated as a bolus (cud). Innovative research by Italian researchers (Schadt et al., 2012) demonstrated that the dairy cow, during eating, chews the forages just enough to reduce the forage particle size to be able to swallow the bolus – no more; no less. Longer or poorer quality material would increase eating time due to the increase difficulty in reducing particle size. Schadt’s research demonstrated that, regardless of the particle size of the ingested material, the particle size of the regurgitated bolus (cud) remained similar (see Table 1 and Image 1). Recent research has shown an inverse relationship between time spent eating and resting. Long material, such as long dry hay, increases eating time but may reduce resting (lying) time – depending on the quality of the forage. Jiang et al., 2017 compared diets with increasing levels of forage – from 40% forage to 70% forage (Figure 1). As the forage content increased, peNDF (physically effective NDF) and uNDF240 (undigested NDF) levels also increased. Forages that are higher in NDF concentration or have longer particle size effectively lengthen the time required to consume feed. There was a significant increase in rumination time (eating and cud chewing)
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