Ruminal digestion of leguminous forage, potatoes and fodder beets in batch culture: II. Microbial protein production

Abstract

Effects of fodder beets and potatoes on microbial protein production were examined in two experiments with 5 h incubations in a 700 ml batch culture system. Effects of the substrates per se, indirect effects from rumen fluid donor cow adaptation to fodder beets and potatoes and effects of the basal silage in incubation diets were studied. Diets in the first experiment comprised a control of silage (S) and a 60:40 (dry matter basis) mixture of silage and one of the carbohydrate supplements: barley/oat grain 1:1 (BO), raw potatoes (RP), boiled potatoes (BP), frozen potatoes (FP), fodder beets (FB) or barley/oats/raw potatoes 1:1:2 (BORP). Rumen fluid was from non-lactating cows fed at maintenance energy intake (MFL) or from lactating cows adapted to fodder beets (BFL) or potatoes (PFL). Silages were alfalfa, grass and a mixture 1:1 on dry matter basis of these two. Incubations were completed in triplicates with each combination of diet, rumen fluid and silage type. With MFL, the FB diet produced most ( P<0.05) microbial protein and had endtime ammonia concentration similar to BO. With adapted rumen fluids, FB, BO and BP produced similar amounts of microbial protein and the BO diet had lowest ( P<0.01) endtime ammonia concentration. Boiling of potatoes increased ( P<0.05) microbial protein production. Microbial efficiencies ranged from 30.3 to 65.1 mg microbial N/g fermented hexoses and 13.8–41.5 mg microbial organic matter/mmole adenosine triphosphate (ATP). Alfalfa silage had a higher ( P<0.001) microbial efficiency than grass silage. The microbial production was better correlated to the amount of fermented substrate than to the calculated ATP supply from fermentation. In the second experiment a grass silage/barley grain diet (60:40 on dry matter basis) was incubated in the same batch culture system with rumen fluid from lactating cows adapted to 0, 1 or 2 kg dry matter potatoes per day. Microbial protein production did not differ with the rumen fluids, but ammonia concentration was lower with rumen fluid from cows adapted to 1 kg dry matter potatoes per day. It was concluded that the capacity of fodder beets to facilitate faster microbial growth than barley/oats grain will be exploited only if end product accumulation do not limit microbial synthesis. Further, adaptation of the rumen microbiota to starch reduce differences between fodder beets and barley/oats. Adaptation effects of potato feeding on the rumen microbiota’s ability to ferment various substrates and produce microbial protein are inconsistent.