Exam #2 Study Guide Flashcards
What is the average % digestibility of cell contents of ruminants on all forage diets?
98%
What are the 2 main factors that affect degradability of the cell wall constituents?
- Crystallinity of cellulose
- Lignification of the cell wall (Cementing agent)
Why are herbivores well suited to forage diets?
Relative proportion or volume of digestive tract devoted to microbial degradation
~2/3 in horse and cow
Horses (other equids) are known as what kind of fiber fermenter?
Hindgut fiber fermenters
Cows (other ruminants) are known as what kind of fiber fermenter?
Foregut fiber fermenters
How does regurgitation of forage and chewing of cud (bolus) improve forage digestion in ruminants?
- Increased surface area for attachment of bacteria
- Bolus may be chewed up to 40 times before swallowed
- Increase surface area - aid in absorption of nutrients
What happens when excessive amounts of soluble CHOs reach the hindgut of a horse?
Excessive amounts of soluble CHO’s cause excess lactic acid
Compared to a ruminant, horses need a diet higher or lower in crude protein? Why?
Horses needs higher protein diet compared to ruminants, because most of the AA synthesized by microbes in the large intestine are excreted
How does the intake and rate of passage of forage through the digestive system compare between a horse and ruminants?
Horses
* Rate of passage through cecum and large intestine is 36 to 72 hrs
* 20-30% higher intakes compared to ruminants
Ruminants
* Rapid rate of passage
Unlike the horse, ruminants perform better on what type of forage? Why?
- Perform better on lush vegetation better. Due to rapid digestibility and rapid rate of passage
What is the primary source of protein for ruminants?
Protein from both feed and microbes
Forage utilization limited by N intake if diet less than 6-7% CP – Why?
- Not enough N to maintain microbial population in rumen
- Reduced digestive capacity, rate of passage
At what level of CP in the diet is N wasted? What happens to excess N?
Diets with greater than 12% CP
* Most excreted in urine
* Some recycled in saliva
* Excess absorbed through rumen wall
* Some absorbed by microbes for growth
How do ruminants survive on low quality (low CP) diets?
- Highest efficiency of protein utilization on low quality diets
- N recycles through liver and back through saliva
How do tannins in certain forages affect protein availability?
- Tannins bind with proteins to reduce solubility
What is bypass protein? Where is it absorbed in the animal?
- By-pass protein absorbed in lower gut
- The portion of the protein from a feedstuff that escapes from being broken down or digested in the rumen by microbes.
AKA undegradable protein
Where is the bottleneck in the ruminant digestive tract compared to the horse?
Ruminant
* In the rumen
Horse
* Cecum, colon
Understand the relationship between increasing fiber content in forages and its effect on digestibility and intake
- Increasing fiber content, decreases digestibility
- As digestiblity goes down, intake also goes down
What is RFV a measure of?
Relative energy
What is RFQ a measure of?
Energy, but also includes digestibility of protein
What is the %DDM equation?
Calculation of digestibility
%DDM = 88.9 – (0.779 * %ADF)
What is the %DMI equation?
Calculation of intake
DMI = 120 / %NDF
What is the RFV (relative feed value) equation?
Why is 1.29 used?
RFV = (%DDM * %DMI) / 1.29
1.29 is an adjustment factor to scale RFV to be 100 at full bloom alfalfa
What are some problems with RFV?
- DDM and DMI assumed constants for all forages
- Based only on ADF and NDF values
- Assumes that ADF has a constant relationship to digestibility
