ISSUE FOCUS 28 FEED & ADDITIVE MAGAZINE February 2023 Hence, any diet that can alter the pH can negatively impact fibrolytic species and result in reduced fiber degradation. This decreased pH can further lead to subacute rumen acidosis (SARA). SARA can be influenced by a number of factors such as forage particle size, feeding behavior, starch content of the diet and grain level of the diet. A meta-analysis by Ferraretto et al. (2012) examined factors that affected the digestibility of wholeplant corn silage. As starch levels increased in the diets, the digestibility of dietary NDF decreased by 0.61% units ruminally and experienced a 0.48% unit total-tract per %-unit increase in dietary starch content. The authors suggested this was due to a downward shift in ruminal pH. 2. Particle size The particle size of the ingested forage can play a role in fiber digestibility. Longer particles may increase a lag to digestion due to a lag in hydration and a reduction in bacterial attachment. Bacterial attachment refers to the ability of the bacteria to start the digestion process by attaching to the cut end of the fiber. The bacteria digest the plant material from the inside out and require either a cut point or opening created by fungal digestion or abrasion to start this digestion process. 3. Animal feeding behavior Dairy cattle are foragers. Over the millennia, cattle have grazed on fibrous pastures. Ruminants have the capacity to consume human inedible feed, including the digestion of cellulose, with forages as the main source thanks to grazing and foraging. The grazing/foraging behavior would be spread out over a long period of time with frequent small meals. Considering the modern dairy cow now has access to a total mixed ration (TMR), they typically consume their daily DMI in three to five hours per day, spread between 6 to 10 meals with the largest meal occurring after the delivery of fresh feed (DeVries et al., 2016; DeVries and von Keyserlingk, 2005). Figure 3. Impact of the rumen pH on the NDF digestion rate of a raw material (Fox et al., 2003)
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