Transcript Section 5

‫تغذیه دام درمرتع‬
Animal nutrition
on the rangeland
(Part 5)
By: A. Riasi
(PhD in Animal Nutrition & Physiology)
What is the role of energy in animal nutrition?

The nutritional concern for ruminants centers on:
 Energy
 Protein
 Minerals
 Vitamins
 Water
What is the role of energy in animal nutrition?

Energy is the single most important dietary component for an
animal after water.

Energy is derived from carbohydrates, fats, proteins, and from the
animal’s body reserves.

Energy intake maintains body functions and facilitates growth and
development.
GROSS ENERGY
Feces
DIGESTIBLE ENERGY
Urine & Gas
METABOLIZABLE ENERGY
Heat increment
NET ENERGY
Maintenance Gain
Reproduction
Milk Production
Determining Caloric Energy
TDN


An energy index based on a carbohydrate
Calculated from proximate analysis
Calculating TDN

% CP × Digestibility
% EE × 2.25 × Digestibility
% CF × Digestibility
% NFE × Digestibility

SUM



=x
=x
=x
=x
-----TDN
Example (Chemical composition of a feedstuff):






Water
Crude protein
Ether Extract
Crude Fiber
Ash
NFE
12%
12.5%
4%
10%
2%
59.5%
Example (Chemical composition of a feedstuff):







Water
12
CP (2% N × 6.25) 12.5 × 0.8 = 10
Ether Extract 4 × 2.25 × 0.75 = 6.75
Crude Fiber
10 × 0.4 = 4
Ash
2
NFE
59.5 × 0.8 = 47.6
--------------TOTAL (TDN)
68.35
What is the role of protein in animal nutrition?


Crude Protein is calculated from the nitrogen content of the forage.
The CP of forage is important since:
 Protein contributes energy
 Protein provides essential amino acids for rumen microbes as well
as the animal itself.

Protein in forages is most correlated with forage maturity, as more
mature forages have a lower percentage of crude protein.
Kejeldahal method for CP and N analysis
What is the role of protein in animal nutrition?

Cattle require two types of protein in their diet:

Degradable protein in the rumen (RDP)

Undegradable protein in the rumen which passes straight to the
abomasum or stomach for digestion (RUP)
What is the role of protein in animal nutrition?


The microbial degradation of protein is an energy-dependant process.
Generally more microbial protein is synthesized from green forage
diets than from hay or mature forage diets.
Matching nutritional requirements of livestock


Forage supply is not continuous throughout the year.
Cool-season pasture growth begins in the early spring and quickly
produces very large amounts of forage.

Given adequate moisture, cool-season pastures will often produce a
second surge of growth in the fall before going dormant.
Matching nutritional requirements of livestock

Warm–season pasture begins later in the spring and continues into
early autumn when day length shortens and temperatures fall.

A diverse mix of cool- and warm-season pastures benefits
livestock managers by overlapping the growth curves of both
types, meaning more high-quality pasture than otherwise.
When supplementing protein or energy is necessary?

In temperate regions with lengthy grazing season, supplementation
on green, growing, vegetative, well-managed pastures should not
be necessary.

Well-managed grass-legume pastures can be highly digestible with
protein concentrations approaching 25 percent while vegetative.
When supplementing protein or energy is necessary?

The problem on high-quality pastures often becomes one of
inefficient protein use.

Supplementing energy with digestible fiber in these situations can
make the animals utilize protein more efficiently.
When supplementing protein or energy is necessary?

When supplementing ruminants on pasture, consider the following
questions:

Will the added production cover the expense, especially if
the feed is shipped from off the farm?

Is there an inexpensive local source of protein?

Do you raise the feed on the farm?

Do you have necessary harvest, storage, and feeding
equipment?
When supplementing protein or energy is necessary?

Remember:

On high-quality pastures, energy is often the limiting
nutrient.

Supplementation of protein on low quality forages
will increase forage intake, and therefore increase
energy intake.

Digestible fiber feeds are good for ruminants on high
quality forage because they do not reduce intake, and
provide energy for protein metabolism.
Forage sampling and production estimates

If you choose to have your forage analyzed for nutrient content, the
key nutrients to consider are:

CP

TDN

NDF

ADF

Mineral content
Plant toxicity and grazing- related disorders

Graziers must pay careful attention to the negative health effects that
certain plants can cause in livestock:

Bloat

Grass tetany

Prussic acid

Nitrates

Poisonous plants
Plant toxicity and grazing- related disorders

How we can reduce the occurrence of bloat in grazing animals?

Begin grazing in the spring on pastures that are grass or grass-legume (at
least 50% grass) mixtures. This will allow the animal time to adjust to the
pasture.

Make sure that the animal is full when first put onto pasture in the spring.
This reduces the intake of the fresh pasture until the rumen has had time to
adjust to the new feedstuff.

Do not start animals grazing when the forage is wet from dew or rain.
Plant toxicity and grazing- related disorders

How we can reduce the occurrence of bloat in grazing animals?

Start animals on legume pastures gradually. For example, leave cattle on
pasture 1 hour the first day and gradually increase grazing time to 4 hours
by the third day and day-long grazing by day 5.

Be sure that fiber is maintained in the animal ration during initial grazing
periods. Feed some dry hay or corn silage to grazing animals prior to
turning them out to pasture.

Check animals for bloat carefully every 2 hours when beginning grazing.

When rotating cattle or sheep among pastures, be sure that animals are
moved fast enough so that they are not excessively hungry when going
onto fresh pastures.
Plant toxicity and grazing- related disorders

How we can reduce the occurrence of bloat in grazing animals?

Animals with supplemental feed will be less likely to bloat. For example, a
dairy cow, where 40 to 50% of the intake is pasture will be less likely to
bloat than beef cattle, dairy heifers, and sheep, where pasture comprises
100% of the diet.

Where bloat has been a problem, consider seeding using birdsfoot trefoil
as the legume because it is non-bloating.
Plant toxicity and grazing- related disorders
Some signs of bloat: Swollen abdomen on the left side Collapsed sheep with legs and
the head stretched out .
Plant toxicity and grazing- related disorders

The greatest risk for grass tetany is when:

Pastures soils are low in available magnesium,

Pastures soils are high in available potassium,

Pastures soils are high in nitrogen.
Plant toxicity and grazing- related disorders

Several management steps to consider for grazing livestock to prevent
the Prussic acid poisoning:

Do not turn hungry livestock out on lush re-growth. Feed
some hay first, then turn out in the afternoon.

Prevent selective grazing of young re-growth by using high
stocking numbers and rotational grazing.

Do not graze until the re-growth is 18 to 24 inches tall.
Plant toxicity and grazing- related disorders

Several management steps to consider for grazing livestock to prevent
the Prussic acid poisoning:

The plants that continue to tiller may have re-growth at
toxic HCN levels.

Testing for prussic acid content is advised in many cases.
Plant toxicity and grazing- related disorders

Poisonous plants contain:

Resins

Alkaloids, and/or

Organic acids that render them unpalatable.