Ruminants....

The nutrients presented to the cow or steer by the rumen are Feed In VFA Microbial Protein Vitamins The nutrients presented to the cow or steer by the rumen are very different than those entering the rumen as feed.

Digestion Fermentation All CHO must pass through Pyruvate to become VFA

Some Basics Pyruvate Lactate VFA, H+ Nonstructural polysaccharides Structural polysaccharides Pyruvate Lactate VFA, H+ Rumen pH must be defended in the face of organic acids and H+ production to prevent acidosis.

Rumen papillae epithelium performs at least 3 major functions: protection metabolism absorption VFA are absorbed passively; thus, the concentration gradient from lumen to blood supply must be maintained. Metabolism of some VFA within the cells of the papillae help ensure a gradient.

Some Basics II. Rumen Development A. Newborns are not functional ruminants 1. Lack sucrase 2. Limited amylase 3. Lactase: galactose, glucose 4. Ability to digest non-starch polysaccharides precedes that for starch

Some Basics B. Rumen Development Begins Early 1. Depends on: a. fibrous diet b. inoculation c. VFA stimulation

Some Basics C. Inoculation occurs by: 1. Feed 2. Inter-animal contact (saliva) 3. Manure, soil *occurs with isolation, but much slower and less completely

Ruminants.... N metabolism vs. Protein metabolism... The quality and quantity of protein (amino acids) fed to the rumen is very different from that delivered to the small intestine because microbes within the rumen fix nitrogen and modify in- coming proteins.

Ruminants....

Ruminants.... Incorporation of recycled nitrogen in the form of ammonia allows the daily flow of nitrogen into the duodenum to EXCEED nitrogen intake when the dietary protein content is held low.

Ruminants.... Synthesis of microbial protein ammonia (NH3) is a key molecule R

Ruminants.... Rumen bacteria use NH3-nitrogen as a source of amino nitrogen for synthesizing amino acids. ~40% of the bacterial protein nitrogen passes through the rumen ammonia pool.

Ammonia enters the rumen from multiple sources Dietary NH3 Sources Endogenous Sources Diffusion Saliva Recycled urea NPN (urea) Degradable protein All of these contribute to the pool of ammonia in the rumen

Ammonia enters the rumen from multiple sources... The “urea cycle” Carbomyl Phosphate + Aspartate + 3 ATP + 2 H2O Urea + Fumarate + 2 ADP + 2 Pi + AMP + PPi

CO(NH2)2 O C Ammonia enters the rumen from multiple sources... NH2 NH2 Urease produced by SOME rumen microbes adhered to the rumen epithelium cleaves amino nitrogen from blood urea and releases it as free ammonia. The ammonia in the acid conditions of the rumen is ionized (NH4+) and trapped. C NH2 NH2 Urease

Ammonia enters the rumen from multiple sources... Trapped ammonia-N exits the rumen as protein, or ammonia for recyling NH3 As microbial protein < Absorption by rumen wall >> Flushing to omasum

Ruminants.... Ruminants do not require amino acids in their diet Instead they require N This N can come from amino acids or non-protein N (NPN) sources such as urea

Rumen undegradable proteins... One of the challenges in formulating ruminant diets is that the AA ratio fed does not reflect the AA profile available to the animal Therefore, there is interest in “Rumen Undegradable Proteins” (RUPs, RBPs)

Rumen undegradable proteins... RUPs cannot be degraded by the microbes in the Rumen Therefore, the amino content of the RUP represents what is being presented to the small intestine of the animal