If you are a Cal Poly student enrolled in AVS 303, then these notescover
every subject that will be (possibly) be covered on the final examination.
Do not memorize (you won't be able to), try to understand overall concepts
and relationships as much as possible.  Make sure you are familarwith the
calculations we have covered in class, particularly those covered most
recently.  These notes are a little cryptic (since I wrote themto lecture
from, not publish), but you should be able to use them to fill in anygaps
in your own class notes (assuming you took any).  :-)

If you are NOT enrolled in AVS 303, and are just cruising the websitefor
some obscure reason, you're welcome to do so as well. :-)

Good luck!
 
 

Dietary Energy

Not a single nutrient per se, but quantitatively is required in thehighest
amount in livestock rations.
Livestock feeding tables will list this as one of the requirementsof an
animal in addition to protein requirements, vitamins, minerals, etc.

Energy is capacity to do work.  In Europe and UK, the unit of energyused
most often is the joule, in US calorie, kcal or Mcal.

A calorie is the heat reqd to raise one gram of water one degree celsius=
4.1855 joules.
1000 "little" calories = 1 kcal (what we normally refer to as a calorie)and
1000 kcal = 1 Mcal.  Because of large numbers involved, Mcal normallyused
in livestock rations.

Energy can be derived from different dietary sources with varying degreesof
efficiency.

Proteins 5.65 kcals/g
Carbos supply 4.15 kcals energy/g
Fats provide 9.40 kcal/g

If you're trying to supply energy to an animal, you'd supply it thequickest
of you fed fats, as they're densest source of energy.  But fatcan only be
fed in relatively limited amounts.  Proteins are the second densestsource
of energy, but proteins are also the most expensive nutrient and hasthe
highest heat increment = energy loss.  So even though carbos areleast dense
source of energy, this is source of most reqd energy, because it'scheap and
because livestock can utilize forms that cannot be otherwise utilized,ie
range pasture.

Energy in a feed is measured by bomb calorimetry = heat produced whensample
of feed is completely oxidized.  However, this is not necessarilythe amount
of energy available to the animal, because digestion is not 100% efficient.
Total energy contained in a feed when oxidized by a bomb calorimeteris
called gross energy.

Gross energy - fecal energy lost = digestible energy.  Fecal energy=
greatest loss of energy, varies greatly depending on digestibilityof feed
(anywhere from 30% for low quality forage fed to ruminants to over95% for
fats) and species (ie ruminants are more efficient than horses at digesting
fibrous carbohydrates, horses more efficient than pigs)

Digestible energy - gaseous, urine losses = metabolizable energy. Urine,
gas losses about 10% of GE values in ruminants.

ME - heat increment = net energy.  Heat increment is the wasteheat produced
by oxidizing a feed (ie protein 3-6 times more than carbos or fats),also
heat of fermentation produced as a by-product of microbial fermentation.

DE is most commonly used for monogastric species, ME for poultry, NEwidely
used for ruminants

Why use different energy terms for different species?  To measureenergy
losses, you have to collect output.  Manure is greatest loss ofenergy and
relatively easy to collect and measure (though not nice).  Inmonogastric,
losses through urine and gas are much less, so DE is good enough.

In avian spp, gas losses are negligible, but urine and feces are combinedso
can't collect one without the other, so ME is used.

In ruminant species, losses through gas and heat increment are appreciable,
so must be measured, but pain in the butt.  Must use metabolismstalls, very
expensive, very few exist, so NE values for different feeds are very
limited, so nutrition tables for ruminants might contain NE values,but
don't be surprised to see DE or ME values.

TDN - somewhat outdated, but still widely used.

TDN = digestible CP + digestible CF + digestible nitrogen-free extract
(NFE)(starches and sugars) + 2.25 EE.

Tends to overvalue roughages by about 7-8% as compared to NE or ME,but
pretty accurate for highly digestible feeds such as grains.  Itsprimary
limitation is that while it takes into account fecal and urinary losses,it
does not take into account gaseous losses or heat losses.  Therefore,
because these losses occur in higher amount in forages than in concentrate
feeds, TDN is less accurate for forages than for grains.

The lower a TDN value, the less value it has for productive purposes. TDN
is a percentage, so always going to be between 1-100, except for fatwhich
is multiplied by 2.25 to compensate for denser energy value.

Used to estimate NE:
NE Mcal/kg feed = 0.0245 x TDN - 0.12.
Example:
CSM has TDN of 68% => (0.0245)(68) - 0.12 = 1.546 Mcal/kg NE

Energy requirements are directly related to surface area of animal,as size
of animal goes up, metabolism goes down. MBW = BW .75.  Use tocalculate
energy requirements between species of different sizes, ie an animalthat
weighs ten times as much doesn't need ten times as much energy. A larger
animal is going to need more total energy, but less energy per kg ofBW.

Example, a 10 pound cat requires 363 kcals of DE per day for maintenance=
80 kcals per kg of BW.

A 20,000 lb killer whale requires 180 Mcal/d (180,000 kcals) = 19.8kcals/kg
BW.

Why does this matter?  In domestic livestock species, you can takea couple
dozen animals, feed them on a test diet and decide how well they grow. In
exotic species, a nutritionist has to decide how much energy is goingto be
required by a particular (possibly endangered spp) so that you can
adequately manage that animal.  For example, if spp requires aparticular
food that only grows in Thailand during September, you better be ableto
estimate the amount of food you're going to need to order to maintainthat
animal in a collection).  Or in range management, so that youcan estimate
how many animals (both domestic and wild) can be supported without
overgrazing and damaging the rangeland.

Energy requirements for a number of production species have been published
by National Research Council in bulletins.  Includes common domestic
species, also dogs and cats, fish, shellfish, fur species, lab animals,non
human primates and rabbits.

Energy estmates are based on an average population of a given species,BW
(not MBW, just BW), age, and production status.

Does not take into account additional stress, ie disease, parasites,injury,
temperature, humidity or the effects of beneficial feed additives suchas
antibiotics, feed additives (bST) or effect of feed processing.

Most not measured directly, extrapolated from other species

Five production classes on which nutrient requirements are based:
Maintenance
Growth
Reproduction
Lactation
Work (horses and dogs)

Maintenance - state in which an animal is neither gaining nor losingbody
stores.  This is the nutrition required for an animal to juststand around
and breathe.  True maintenance is unusual in most species becausefor
production, we don't want a status quo, we want the animal growing
something.  The exception to this is horses that are mostly standingaround.
For other species, maintenance requirements are used as a baselinevalue.

Growth - requirements per unit of BW are greatest in the newborn and
decrease as the animal approaches mature BW.  Tissues and organsdevelop at
different rates, which in turn have an effect on nutrient requirements.
Feed efficiency per unit of gain is going to be highest during growth(total
weight gain divided by total food intake).  Also, as performancerate
increases, the greater efficiency is—ie, the faster you can get ananimal to
grow, the more efficient the growth is going to be.  Sometimesdesirable, as
in broiler chickens that you want to get as large as possible as quicklyas
possible.  Pigs are another, as you want them to get to marketweight as
quickly as possible.

However, it's not always desirable or economical to try for maximumgrowth
rate.  Example, in fast-growing horses, you have higher incidenceof
developmental orthopedic disease, when body weight is growing fasterthan
the structural tissue can develop to support it (more meat than bones=
lameness).

Or, in raising a replacement heifer—you're not going to be able to breedher
until she's around a year old and while you want her to be a good sizeby
then, she doesn't have to grow at maximum rate. Also, overnutritionmay
delay puberty, decrease fertility.   Slower growth better,plus more
economical.

Lactation - In most species, lactation is going to have highest energy
requirements, the only exception being sustained intense exercise inhorses,
such as endurance.  Because milk composition is about 80% water,increased
need for water and also protein, minerals, etc, because to supply inmilk,
must first supply in diet.  Example in 600 kg dairy cow:

   Maintenance  Peak lactation   % increase
      (50 kg/d, 4% butterfat)

NE, Mcal/d   9.70   48.17    496%
CP, g  406   1744    429
Ca   24   185    770
P   17   116    682

Dairy animals will produce on average 4-5 times their own BW per yearas
milk, some animals as high as 10 times their own BW during 305-daylactation
period.

Milk production in dairy cows peaks around 60-90 days postpartum, then
declines 8-10% per month until day 305, when dried off to prepare fornext
parturition.  Energy requirements follow lactation curve, highestduring
peak production.  In high-producing dairy cattle, it is impossibleto stuff
sufficient energy down the cows throat to meet the energy needs, thusenergy
must be mobilized from body stores.  If energy is limited, lactationis the
first thing to shut down (and once stopped, won't start again untilnext
freshening).

Reproduction - nutrient requirements less critical than during growthor
lactation, but more critical than for maintenance.  If energyis limited
prior to and during pregnancy = decreased number of ovums, longer time
between estrous cycles, decreased litter sizes, failure to establishor
maintain pregnancy.

Energy requirements highest during third trimester, as this is whenmost
fetal growth occurs.  However, increased energy also requiredbecause
metabolic rate of pregnant animal is about 150% that of nonpregnantanimal.
Also must support development of associated tissues, ie mammary tissues,
placenta, fluids, etc.  To support this, pregnant animals willconsume more
food as a percentage of their BW during pregnancy and lactation thanthey
would during maintenance.

Work - really applies only to horses and sometimes dogs.  Nutrient
requirements increase proportional to the intensity of work and howlong
work is sustained.  As work level increases, energy requirementsare going
to increase at the fastest rate.  Mineral requirements are goingto increase
due to electrolytes lost in sweat, primarily Na and Cl, but also K,Mg.  A
horse might normally sweat 25 liters during endurance ride, requirementsto
replace electrolyte losses as compared to standing around during
maintenance:

   Rest   exercise
Na, g  10   93
Cl   10   163
K   25   70
Mg   10   19

500 kg horse:  Maintenance   Intense work  % increase
DE, Mcal/d  16.4    32.8   200%
CP, g/d   656    1312   200
Ca    20    40   200
P    14    28   200

Problem with NRC - work is defined as being either light, moderate or
intense, but definitions for each are ambiguous and sketchy. What's light
work to one person is intense to another, so while okay for estimatingCP,
mineral requirements, is poor estimator of energy requirements forwork.

Better formula developed by Pagan and Hintz at Cornell.
E (cal/kg/min) = e 3.20 + .0065x; where x = velocity in m/min.

Example: A 1000-lb horse carrying a 150-lb rider covers 20 miles in3 hours.
How many Mcals of energy were expended during this exercise bout?

1) Calculate velocity - 1 mile = 1760 m x 20 miles = 35,200 m/180 min=
195.6 m/min

195.6 x 0.0065 = 1.27 + 3.20 = 4.47.  Inverse LN = 87.45 cal/kg/min

Multiply by total kgs: 1000 + 150 lb = 1150 lbs/2.2 = 523 kg

(87.45 cals/kg/min)(523 kgs)(180 min)/1,000,000 = 8.23 Mcals

So, let's say you have a horse that exercises at this level 4 timesa week.
To calculate energy expenditure, take maintenance requirements (15
Mcals/day) x 7 = 105 Mcals.  Multiply 8.23 x 4 times/week = 32.9. Add 105 +
32.9 = 137.9.  Divide by 7 to get average energy requirementson a daily
basis = 19.7 Mcals/d.

According to NRC, a horse at intense work requires 29.8 Mcal/day; orat
moderate work, 22.3 Mcals, at light work, 18.65.