Exam #2 Study Guide

Question 1

What is the average % digestibility of cell contents of ruminants on all forage diets?

Answer 1

98%

Question 2

What are the 2 main factors that affect degradability of the cell wall constituents?

Answer 2

1. Crystallinity of cellulose
2. Lignification of the cell wall (Cementing agent)

Question 3

Why are herbivores well suited to forage diets?

Answer 3

Relative proportion or volume of digestive tract devoted to microbial degradation

~2/3 in horse and cow

Question 4

Horses (other equids) are known as what kind of fiber fermenter?

Answer 4

Hindgut fiber fermenters

Question 5

Cows (other ruminants) are known as what kind of fiber fermenter?

Answer 5

Foregut fiber fermenters

Question 6

How does regurgitation of forage and chewing of cud (bolus) improve forage digestion in ruminants?

Answer 6

• 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

Question 7

What happens when excessive amounts of soluble CHOs reach the hindgut of a horse?

Answer 7

Excessive amounts of soluble CHO’s cause excess lactic acid

Question 8

Compared to a ruminant, horses need a diet higher or lower in crude protein? Why?

Answer 8

Horses needs higher protein diet compared to ruminants, because most of the AA synthesized by microbes in the large intestine are excreted

Question 9

How does the intake and rate of passage of forage through the digestive system compare between a horse and ruminants?

Answer 9

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

Question 10

Unlike the horse, ruminants perform better on what type of forage? Why?

Answer 10

• Perform better on lush vegetation better. Due to rapid digestibility and rapid rate of passage

Question 11

What is the primary source of protein for ruminants?

Answer 11

Protein from both feed and microbes

Question 12

Forage utilization limited by N intake if diet less than 6-7% CP – Why?

Answer 12

• Not enough N to maintain microbial population in rumen
• Reduced digestive capacity, rate of passage

Question 13

At what level of CP in the diet is N wasted? What happens to excess N?

Answer 13

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

Question 14

How do ruminants survive on low quality (low CP) diets?

Answer 14

• Highest efficiency of protein utilization on low quality diets
• N recycles through liver and back through saliva

Question 15

How do tannins in certain forages affect protein availability?

Answer 15

• Tannins bind with proteins to reduce solubility

Question 16

What is bypass protein? Where is it absorbed in the animal?

Answer 16

• 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

Question 17

Where is the bottleneck in the ruminant digestive tract compared to the horse?

Answer 17

Ruminant
* In the rumen

Horse
* Cecum, colon

Question 18

Understand the relationship between increasing fiber content in forages and its effect on digestibility and intake

Answer 18

• Increasing fiber content, decreases digestibility
• As digestiblity goes down, intake also goes down

Question 19

What is RFV a measure of?

Answer 19

Relative energy

Question 20

What is RFQ a measure of?

Answer 20

Energy, but also includes digestibility of protein

Question 21

What is the %DDM equation?

Calculation of digestibility

Answer 21

%DDM = 88.9 – (0.779 * %ADF)

Question 22

What is the %DMI equation?

Calculation of intake

Answer 22

DMI = 120 / %NDF

Question 23

What is the RFV (relative feed value) equation?

Why is 1.29 used?

Answer 23

RFV = (%DDM * %DMI) / 1.29

1.29 is an adjustment factor to scale RFV to be 100 at full bloom alfalfa

Question 24

What are some problems with RFV?

Answer 24

• DDM and DMI assumed constants for all forages
• Based only on ADF and NDF values
• Assumes that ADF has a constant relationship to digestibility

Question 25

In the RFQ equation, DDM is replaced with what estimate?

Answer 25

TDN

Question 26

Why is RFQ a better measure? (i.e. What factor does it take into account when estimating the 2 parameters in the equation?)

Answer 26

RFQ uses in-vitro estimates of digestible fiber

RFQ more representative of actual animal performance, can be used in diet formulation

Question 27

What are the implications if RFQ is higher than RFV for the same sample?

Answer 27

• Hay seller could have gotten more for the hay or the buyer got a good deal
• Premium for quality forage worth $0.90/ton for every
  point change in RFQ

Question 28

What are the implications if RFQ is lower than RFV for the same sample?

Answer 28

• Cattle won’t perform as expected

Question 29

What technology makes it possible to easily estimate the variables needed to calculate RFQ?

Answer 29

Near Infrared Reflectance Spectroscopy

(NIRS)

Question 30

What is a major factor affecting forage quality?

Answer 30

Maturity

Question 31

What changes happen within the plant with advancing maturity?

Answer 31

• Increase in cell wall (CWC)
• Decreased digestibility

Question 32

What happens to CP content as the plant matures?

Answer 32

Crude protein decreases due to dilution as the plant matures