Influence of ruminal turnover on site and extent of digestion

Ruminal turnover rate plays a major role in ruminant nutrition. Theoretical considerations have been developed and several excellent models are available. Newer methods in marker technology offer opportunity for collection of accurate data. Few good studies have been published. This paper covers the above considerations and gives a critical evaluation of some published data. Increased ruminal turnover of liquid alters ruminal fermentation toward more acetate, butyrate and methane and less propionate. It also results in a greater rate of passage of small feed particles of any type. The effect on total digestion depends on feed composition and physical form. Total fiber digestion is usually reduced. Ruminal liquid turnover is increased by increased level of intake, addition of coarse fiber to rations, and osmotically active agents. It is reduced by some mineral complexes and monensin, and by reducing average particle size. Solid turnover rate is increased by reduced particle size and by several factors that influence liquid turnover. The rate of particle size reduction to a critical size is important in any description of solid turnover rate. Literature data that relate to ruminal turnover and in vivo digestion are discussed.