The feeding of high concentrations of fermentable carbohydrate to ruminants has become a common practice in the beef and dairy cattle industry over the last 50 years. The need for improving the production efficiency and quality of meat has led to this trend. Improvements in production have not occurred without certain difficulties. Increasing the ruminant consumption of fermentable carbohydrate by feeding higher levels of cereal grains has resulted in increased incidence of metabolic disorders such as acidosis. The relationship between high concentrate consumption and ruminal acidosis has been well documented in reviews (Dunlop, 1972; Slyter, 1976). Many researchers have shown a decline in ruminal pH following the feeding of high levels of readily fermentable carbohydrate (RFC) to cattle and the subsequent disruption of ruminal microbiota and physiological changes occurring in the animal (Allison, et. al., 1975, Hungate et. al., 1952; Elam, 1976). Most have attributed this decline to an over production of organic acids by ruminal bacteria such as Streptococcus bovis. However, the effect of excessive carbohydrate on the ruminal microbiota that initiates this response has not been well documented.
In the past, intensive management of feeding has been the only method to combat acidosis. More specifically, grains are diluted with roughage and the increase in dietary concentrate percentage is carefully controlled in a step-wise method to ensure smooth transition to high levels of concentrate over a 14-21 day period. Most commercial feedlots formulate and deliver several “adaptation” diets that contain different ratios of grain to forage.
Although intensive feeding management is usually quite effective in controlling acidosis, it is very costly to the producer due to the high cost of producing, transporting, chopping forage, disposing of increased animal waste, and lower production efficiencies. Producers and feedlot managers need to implement strategies that will allow for efficient production of livestock fed high concentrate rations.
Other strategies have been to combine the use of adaptation diets with feeding antimicrobial components such as ionophores. Ionophores inhibit intake and reduce the production of lactic acid in the rumen by reducing the ruminal populations of gram-positive, lactic acid-producing organisms such as Streptococcus bovis and Lactobacillus spp. (Muir et al. 1981).
Although the usage of ionophores have reduced the incidence of acute acidosis in feedlots, consumer concern about the use of antibiotics in meat production and the need for feedlot managers to continually find ways to reduce costs while improving animal performance and carcass composition has led to the examination of alternative methods to reduce acidosis and improve feedlot cattle performance.
The use of direct-fed microbials as a method to modulate ruminal function and improve cattle performance has been gaining increased acceptance over the past 10 years. There are two basic direct-fed microbial technologies that are currently available to the beef industry for the control of ruminal acidosis: (1) using lactic acid producing DFM technology and (2) adding specific bacterial species capable of utilizing ruminal lactic acid. While the reported mode of action of each of these technologies is different, they both attempt to address the accumulation of ruminal lactic acid.
The first approach, i.e., using lactic acid producing DFM technology, attempts to increase the rate of ruminal lactic acid utilization by stimulating the native ruminal microbiota. As reported, the addition of relatively slow growing lactic acid producing bacteria, such as species of Enterococcus, produces a slightly elevated concentration of ruminal lactic acid. The gradual increase forces the adaptation of the ruminal microflora to a higher portion of acid tolerant lactic acid utilizers. However, these Enterococcus strains failed to adequately control and prevent acidosis.
The second approach, i.e., adding specific bacterial species capable of utilizing ruminal lactic acid, is based on the finding that species of Propionibacterium significantly minimize the accumulation of ruminal lactic acid during an acidosis challenge with a large amount of Readily Fermentable Carbohydrate (RFC). Propionibacterium are natural inhabitants of the rumen in both dairy and beef cattle and function in the rumen by using lactic acid to produce important volatile fatty acids like acetate and propionate.
Current DFM technologies developed to date have been developed based upon an antiquated microbiological understanding of the incidence of acidosis in the rumen. Until recently, methods of studying the microbial ecology of the rumen have relied on cultivation techniques. These techniques have been limited due to unknown growth requirements and unsuitable anaerobic conditions for many of the rumen microorganisms. Thus, ecological studies relying on these cultivation techniques have been based on a limited understanding of the rumen microbiota.
Current DFMs when used alone or with yeast to minimize the risk of ruminal acidosis and to improve utilization of a feedlot cattle diet containing high concentrate provide mixed results. However, a study of DFM strains Propionibacterium P15, and Enterococcus faecium EF212, and E. faecium EF212, fed alone or fed combined with a yeast, Saccharomyces cerevisiae, indicated that addition of DFM combined with or without yeast had no effect on preventing ruminal acidosis (Yang, W., 2004).
In view of the foregoing, it would be desirable to provide one or more strains to prevent and/or treat acidosis. It would be advantageous if the one or more strains also improved other measures of ruminant health and/or performance. It would also be desirable to provide methods of making and using the strains.