The rumen is an acidic environment and it's general function is digestion through fermentation. A healthy rumen is maintained by feeding adequate forage, and too much energy too quickly can damage rumen microflora. The rumen contains many bacteria and protozoa that play an important role in the digestion of fiber which is otherwise highly indigestible by normal digestive enzymes. Simply put, forages are fed to have happy bugs and happy bugs make for a happy cow.
Bacteria and protozoa in a dairy cow rumen:
Bacteria – 25-80 million/ml
- S. bovis, optimum rumen pH 6.4 (can handle 4.5 – 7.7)
- B. fibrisolvens, optimum rumen pH 6.3 – 6.5
- S. ruminatium, optimum rumen pH 6.6
Protozoa – 200,000-500,000/ml
- Equal biomass to bacteria
- Slower growth, longer retention time in rumen
- Stabilize rumen fermentation
Volatile Fatty Acids (VFAs):
Produced through fermentation by rumen microbes, VFAs provide the ruminant with roughly 70% of its energy supply. They are absorbed across the ruminal epithelium, and then proceed through the ruminal veins, the portal vein and the liver. 3 major types of VFAs are acetate, butyrate, and propionate.
VFA removal from the rumen is important for maintaining a healthy rumen pH. Accumulation of VFAs causes a drop in rumen fluid pH, which can cause rumen health problems. When there are too many VFAs (i.e. from grain overfeeding), the rumen’s ability to absorb VFAs is exceeded and the pH of the rumen fluid drops. The increased ruminal acidity causes an increase in lactate formation. Lactate can’t be absorbed by the rumen wall and decreases the rumen fluid pH even more, intensifying the problem (lactic acidosis).
Metabolism:
In ruminants, energy can be derived from carbohydrates (CHOs) and lipids. CHOs can be divided into non-structural carbohydrates (NSC) and structural carbohydrates. NSCs are highly digestible, whereas structural carbohydrates are slowly digestible. Grains are a common source of CHOs.
Energy is derived less from lipids than CHOs, however fats are 2.25x the energy of CHOs. They are readily digestible but in limited amounts. Lipids can be sourced from feeds like vegetable oils and whole soybeans.
References:
Dairy Nutrition Primer Notes, Dr. K. Lissemore
Nutrient Absorption and Utilization in Ruminants, Colorado State University