ISSUE FOCUS 34 FEED & ADDITIVE MAGAZINE November 2023 ing (also known as ad libitum, ad lib, or full feeding), where the animals always have feed available. The other is restricted feeding (or limited feeding), where producers dictate when and how much feed animals receive. Each has benefits and drawbacks, and the producers must decide which strategy is most appropriate based on their equipment and management ability. ACIDOSIS The lamb's digestive system is not designed to handle large amounts of grain. When suddenly introduced to grain, the rumen microbes will produce large amounts of lactic acid that cause severe animal metabolic stress. The animal controls rumen acidity during eating and rumination by secreting saliva. When lambs eat, saliva containing sodium bicarbonate helps neutralize the acidity caused by microbial action. The quantity of saliva secreted depends largely on time spent eating and ruminating, as this is when saliva production is the greatest. Lambs can produce more than six liters of saliva in a day. The amount of acid produced from fermentation is directly proportional to the digestibility of the feed. Therefore, only about half the acids are made from fermenting straw compared to the same weight of cereals. Because grain feeding requires less chewing and rumination time, the animal produces less saliva when fed cereal grain than when fed straw. The result is that if large amounts of cereal grains are fed to lambs, the rumen pH will drop to about 5.4 to 5.2. Diets with a lot of grain but lacking fiber usually lead to rumen acidosis. The primary carbohydrate of cereal grains is starch. Cereal grains differ greatly in their starch content, with wheat and corn having the highest values (average 76%), followed by barley and oats (average 61% and 42%, respectively). The rate and extent of starch fermentation in the rumen differ significantly between grains and varieties of grains. Also, lambs differ from cattle in their ability to chew their food, impacting starch digestibility. Armstrong and Beever (1969), showed that when rolled barley, or ground corn, is fed to sheep, the total starch digestibility was 99,9%, and the proportion of starch disappearance before the small intestine was 91,8%, while when fed to cattle, the total starch digestibility was 98,5%, with 68% of the starch disappearing before the small intestine.
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