protein digestion and absorption in ruminants - chapter 10

ANS215 exaam 3

What happens to proteins and NPN in the rumen?

Rumen microbes degrade them into ammonia (NH₃), which is used to synthesize microbial protein (MP).

What is Rumen Degradable Protein (RDP)?

The fraction of feed protein that is degraded by rumen microbes to produce NH₃ for microbial protein synthesis.

What is Rumen Undegradable Protein (RUP)?

The portion of protein that escapes rumen degradation and is digested in the small intestine.

What is Microbial Protein (MP)?

Protein contained in rumen microbes (bacteria & protozoa) that provides 60–80% of a ruminant’s amino acid needs.

What percentage of microbial protein comes from bacteria vs. protozoa?

Bacteria ~55% crude protein; protozoa ~40% crude protein.

What are the two main sources of protein reaching the small intestine in ruminants?

1. RUP (undegraded feed protein) 2. Microbial protein (MP)

How is protein digested in the small intestine of ruminants?

Similar to monogastrics — using pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidases) and intestinal peptidases.

What factors affect protein degradation in the rumen?

1. Type of protein source 2. Rumen pH (low pH ↓ proteolytic bacteria → ↓ RDP)

How does rumen pH affect RDP and RUP?

pH 6.7 → 70% RDP, 30% RUP; pH 5.4 → 45% RDP, 55% RUP.

What are typical RDP and RUP percentages in soybean meal?

RDP = 70% of CP, RUP = 30% of CP.

What are typical RDP and RUP percentages in fish meal?

RDP = 40%, RUP = 60%.

What are typical RDP and RUP percentages in blood meal?

RDP = 20%, RUP = 80%.

What are the two fates of ammonia (NH₃) in the rumen?

1. Used by microbes to form microbial protein. 2. Absorbed into blood and converted to urea in the liver.

What are the two fates of urea made in the liver?

1. Excreted in urine. 2. Recycled back to the rumen via blood or saliva.

What are the sources of ammonia (NH₃) in the rumen?

1. Degradation of dietary protein (RDP, NPN). 2. Recycled urea from blood or saliva.

Why don’t horses or pigs benefit from microbial protein?

Their microbial fermentation occurs in the large intestine, after the small intestine — so amino acids can’t be absorbed.

What are the main uses of abs