Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 24, 1998
Publication Date: N/A
Interpretive Summary: The microorganisms in the cow's rumen (stomach) ferment (convert) feed materials to products that are used by the animal for energy and milk production. Individual species of rumen bacteria differ in their fermentation products, resulting in different mixtures of nutrients available to the cow. We know very little about how differences in the mixture of species of bacteria in the rumen affects production and composition (quality) of milk. We fed four cows each of four diets that differed in the amount of fiber and the source of fiber (alfalfa silage or corn silage). We measured the amount and quality of the milk produced, and the volatile fatty acid (VFA) contents of the contents of each rumen. We also determined the frequency of each of the three main fiber-digesting bacterial species in each rumen. One of the three bacterial species was consistently more abundant than were the other two species. However, despite large differences in the amount and quality of milk produced and i the rumen VFA profiles, changing the amount or source of the fiber in the diet did not consistently alter the frequency of the three species. Some differences were observed in specific populations among different cows, suggesting that each cow may retain its own unique assemblage of fiber- digesting bacterial strains. The results suggest that each cow contains a well-adapted population of rumen bacteria that will be difficult to modify by techniques such as genetic engineering. Recognizing the uniqueness of each cow and its microbial population will enable us to individually optimize its yield and quality of milk.
Technical Abstract: The effects of four contrasting diets were determined on the ruminal populations of three species of ruminal cellulolytic bacteria (Ruminococcus albus, R. flavefaciens, and Fibrobacter succinogenes), using oligonucleotide probes to rRNA . Diets, based on alfalfa silage (AS) or corn silage (CS) as primary fiber source, and formulated to contain either 24 or 32 per cent aNDF (NDF measured after alpha-amylase treatment), were fed twice daily to four ruminally-fistulated, lactating Holstein cows in a Latin square design. The AS diets resulted in higher dry matter intakes and milk yields, and in smaller pH fluctuations than CS diets (0.3 vs. 0.8 units). Total populations of the three cellulolytic species 3 h after feeding ranged from 0.3 to 3.9 per cent of the bacterial domain, with R. albus generally the most abundant of the three species. The data are in general agreement with population assessments obtained by some traditional culture enumeration methods.