Carbohydrate Nutrition

Abstract

An understanding of carbohydrate nutrition is essential to optimize production of dairy cattle. Two rations, both of which appear to be balanced, may have dramatically different results when fed to high-producing dairy cattle. Carbohydrates directly affect microbial protein production and therefore protein nutrition of dairy cattle. Energy intake can be maximized by considering the amount and type of carbohydrate in the ration: 1. The fiber level of the ration should be evaluated. NDF levels should be between 25 and 30% for high-producing cows in early lactation. Within this range, less fiber is required with adequate forage particle length and high frequency of grain feeding, and when buffers are fed and slowly fermented NSC sources are included in the ratio. For mid- and late-lactation cows, fiber levels are higher, ranging between 30 and 36% NDF depending upon the energy required to support milk production and restoration of body condition. 2. Provide adequate effective fiber. There should be some forage particles 1.5 in long in the ration. Limit most high-fiber byproducts to 25% of fiber requirements. 3. Feed highly digestible fiber sources. Differences in fiber digestibility of 30% will result in over 4 Mcal of NEL per day with 15 lb NDF intake. In addition, highly digestible fiber has less gut fill effect, possibly increasing dry matter intake. 4. Consider site of starch digestion. Slowly degraded starch sources such as sorghum may require steam flaking to increase ruminal fermentation. Other situations may require the addition of a slowly degraded starch source. 5. Increase frequency of concentrate feeding. Feed grain at least four times per day or include in a total mixed ration. 6. Include buffers. Under some situations (corn silage, early lactation) buffers allow more grain to be fed. 7. Add fat. Fat supplementation to milking cows has become a common practice in high-producing herds. Fat has about three times the energy of cracked corn and is often used to replace a portion of the grain to increase the energy density of the ration. It is important to realize that fat can cost up to two to three times more per megacalorie of energy than grain. Before fat is added to the ration, less expensive ways to increase energy density (listed previously) should be thoroughly explored.