Relationship Between Fermentation Acid Production in the Rumen and the Requirement for Physically Effective Fiber

Abstract

The content of ruminally fermented OM in the diet affects the fiber requirement of dairy cattle. Physically effective fiber is the fraction of feed that stimulates chewing activity. Chewing, in turn, stimulates saliva secretion. Bicarbonate and phosphate buffers in saliva neutralize acids produced by fermentation of OM in the rumen. The balance between the production of fermentation acid and buffer secretion is a major determinant of ruminal pH. Low ruminal pH may decrease DMI, fiber digestibility, and microbial yield and thus decrease milk production and increase feed costs. Diets should be formulated to maintain adequate mean ruminal pH, and variation in ruminal pH should be minimized by feeding management. The fraction of OM that is fermented in the rumen varies greatly among diets. This variation affects the amount of fermentation acids produced and directly affects the amount of physically effective fiber that is required to maintain adequate ruminal pH. Acid production in the rumen is due primarily to fermentation of carbohydrates, which represent over 65% of the DM in diets of dairy cows and have the most variable ruminal degradation across diets. The non-fiber carbohydrate content of the diet is often used as a proxy for ruminal fermentability, but this measure is inadequate. Ruminal fermentation of both nonfiber carbohydrate and fiber is extremely variable, and this variability is not related to the nonfiber carbohydrate content of the diet. The interaction of ruminally fermented carbohydrate and physically effective fiber must be considered when diets for dairy cattle are evaluated and formulated.

Effect of forage particle length on rumen fermentation, sorting and chewing activity of late-lactation and non-lactating dairy cows

“…Accordingly, large particles are believed not to be immediately available for passage from the rumen, having a greater ability to stimulate chewing activity in addition to the chemical composition of feeds. Increasing forage particle length increases chewing time (Kononoff and Heinrichs, 2003;Yang and Beauchemin, 2006), which stimulates saliva secretion (Allen, 1997) in lactating cows. Beauchemin et al (2008) observed that greater proportions of forage dry matter (DM), NDF and longer particle length in a Present address: Novus International, Inc., 20 Research park Drive, St. Charles, MO 63304, USA.…”

“…Nasrollahi et al (2012) observed an increase in TC time for greater particle length and no differences in ruminating. However, comparisons of the current results to these experiments should take into consideration differences between experiments that affect chewing behavior: F : C (De Boever et al, 1990;Tafaj et al, 2005), cows' physiological stage (De Boever et al, 1990), level of feed intake (De Boever et al, 1990;Beauchemin, 1991), forage quality (Welch and Smith, 1970;Zebeli et al, 2012), feeding method (Maekawa et al, 2002) and rumen fermentability of the diet (Allen, 1997;Nasrollahi et al, 2012;Zebeli et al, 2012). To reduce particle length of forage, cows can either increase time spent eating and ruminating, increase rate of chewing or both (Yang and Beauchemin, 2006).…”

“…In the study by Nasrollahi et al (2012) where the effects of particle length where compared within grain degradability, it is suggested that forage length role is more critical when rapidly degradable starch diets are fed. Moreover, Allen (1997) suggested an interaction between rumen fermentability of ration carbohydrates and physically effective fiber. It is likely that diets and DMI in this study did not represent a challenge to proper rumen fermentation.…”

Increasing sodium bicarbonate level in high-concentrate diets for heifers. II. Effects on chewing and feeding behaviors

“…However, saliva production is the main source of bicarbonate in the rumen environment (Erdman, 1988). Thus, eating and ruminating activities are important components of the digestive function because they are associated with increased saliva output (Bailey and Balch, 1961;Allen, 1997). The amount of daily BICARB secretion through saliva is greater than that entering the rumen through dietary buffers (Erdman, 1988).…”

“…However, other management factors may alter the eating patterns and become the cause of low ruminal pH, e.g. factors that increase meal size and eating rate may result in lower ruminal pH and greater risk of acidosis (Allen, 1997;Owens et al, 1998;Schwartzkopf-Genswein et al, 2003). Feeding BICARB increased ruminal pH and osmolality (Rogers and Davis, 1982).…”