Agriculture Reference
In-Depth Information
fi ber increases, but it is reduced as a percent of GE when
energy intake increases. Consequently, methane losses are
less when animals have high feed intakes or consume
either high-concentrate diets (Johnson and Johnson, 1995)
or when browse comprises an important dietary compo-
nent (Woodward et al., 2001). Components of browse
including essential oils or unsaturated fatty acids might
inhibit protozoa or methanogenic bacteria to reduce GasE.
Loss of energy in UE and GasE are quite predictable and
result in a high correlation between DE and ME. The ME
for ruminants generally is calculated as ME = DE
deposited. Gender of the animal also can infl uence the
pattern that animals deposit protein or lipid. Deposited
water plus protein (lean) requires less energy (1.2 Mcal/kg)
than deposited fat plus water (8 Mcal/kg). Other factors
such as genotype, rate of gain, or energy density of diet
may affect energy requirements for gain.
Energy required for reproduction depends on the stage
of pregnancy, number of fetuses carried, and development
of mammary tissues. The additional energy required for
pregnancy typically is so small that they can be ignored
until about 100 days in gestation. Most of the fetal and
mammary growth occur during the last 50-60 days of
gestation for goats. Data are insuffi cient to determine
requirements for pregnancy of goats accurately. Estimating
or measuring the energy requirements for and effi ciency
of lactation also are complicated because animals mobilize
body energy reserves to produce milk while, later in lacta-
tion, body energy reserves are replenished simultaneous
with lactation. Effi ciency of converting energy from feed
to energy in milk for ruminants averages 0.62; however,
effi ciency can be higher (0.84; ARC, 1980) when mobi-
lized energy is used for milk production.
Energy requirements for fi ber growth in Angora or other
fi ber-producing goats depend on rate of fi ber growth, the
amount of energy in the fi ber, and energetic effi ciency of
fi ber growth. Energy also is expended for exercise or work.
According to the NRC (1981b), additional energy needs
for low, medium, and high activities are 25, 50, and 75%
of maintenance energy requirements, respectively.
0.82
for forage-based diets; however, this may be an underesti-
mate with diets rich in concentrate or browse that tend to
have lower gaseous losses.
Because suffi cient data are not available to calculate the
net energy (NE) of feeds or the net energy requirements
of goats, NE is used less commonly than DE, TDN, and
ME for formulating diets. The NE considers an additional
loss of energy, heat increment (HiE). Heat increment is
subtracted from ME as NE = ME
×
HiE. Heat increment
is defi ned as the increase in heat production following feed
consumption in a thermoneutral environment (NRC,
1981a). It includes both the heat of fermentation in the GI
tract and the heat of metabolism (i.e., heat released when
nutrients are metabolized). Heat increment is useful to keep
animals warm when they are exposed to low environmental
temperatures but presents a burden otherwise, and must be
dissipated. Heat increment losses account for 25-40% of
GE, increasing as fi ber content of the diet increases, and
as feed intake and tissue gain increase. Net energy relates
more closely to animal performance than DE, TDN and
ME, each of which overestimate energy value of feeds.
−
E
NERGY
S
OURCES
Energy is released during oxidation of nutrients in the
body, being produced with oxidation of carbohydrates,
fats, proteins, and other organic compounds by the body.
Any organic compound capable of being fermented and
converted to VFA, or of being digested and absorbed as a
monosaccharide or fat from the digestive tract can enter
the Kreb's cycle and be converted to energy. One gram of
carbohydrate or protein upon oxidation will produce 4-5
calories of energy while a gram of fat, with a higher energy
density, can produce 9 calories. With most practical diets,
carbohydrates provide the majority of energy for rumi-
nants with only a small portion coming from fats. Proteins
generally are the most expensive part of the diet and are
fed to meet protein (amino acid) requirements, but excesses
will be oxidized yielding energy.
N
ET
E
NERGY
R
EQUIREMENTS
Net energy required for maintenance is that portion of
energy used for basal metabolism, muscular activity, tissue
repair, involuntary metabolic processes, and voluntary
activities that are necessary to sustain life. Life-sustaining
activities account for walking to seek and obtain food,
browse, shade, feeders and waterers, or other related activ-
ities such as social activities specifi c to goats like jumping,
playing or fi ghting. Maintaining body temperature under
extreme environmental conditions also will impact the
maintenance energy requirement. Energy available in
excess of maintenance is available for a wide variety of
activities such as tissue gain, reproduction, lactation, hair/
wool production, or physical work.
Composition of tissue gain varies depending on the age
of the animal. Younger animals tend to gain more water
and protein, but as animals age, more water and fat are
Carbohydrates
Carbohydrates, also called polysaccharides, usually com-
prising 60-70% of ruminant diets, are the main source
