http://www.agric.gov.ab.ca/agdex/400/00053003.html#Energy

Digestible energy per kgs of feed for cattle

Kilocalories per kg of feeds about 2.5

kilocalories per pound of grass, hay, etc about 1

grains -- 3.5 per KG 1.5 per pound

Fats -- about 2.5 of carbohydrates

Energy

Animals require energy for maintenance, growth, work, and for the production of milk and wool. Feeds are
evaluated in terms of the amount of energy an animal can obtain from them. The digestible energy (DE) is the
gross (total) amount of energy in the hay and grain fed an animal less the amount lost in the feces. Energy is
usually reported in mega calories (Mcal) per kilogram. (One kilocalorie is equal to 1,000 calories. One
megacalorie is equal to 1,000,000 calories).

Amount of DE needed by an animal per day varies according to body size, weight gain, milk production, and
work. The amount of energy required to maintain an animal for one day without loss of body weight is called the
energy required for maintenance. Most symptoms of slight energy deficiency are not very noticeable: slightly
reduced gains, less than maximum milk production and small increases in calving interval. The more severe
the energy deficiency, the more noticeable are the symptoms described. Excess energy is stored as fat.

Table 1 gives the digestible energy values of some common feeds.

The most common energy source is from the carbohydrates contained in feeds. These are the sugars,
starches, cellulose and hemicellulose which have been stored in plant tissues. Chemical reactions which take
place in the animal release the energy in the feed (originally trapped from the sun by the plant) and convert it to
other forms of energy which the animal can use.

Lipids are another energy source found in plants. They are fats and compounds closely related to them. They
contain about two and a half times as much energy as carbohydrates.


Feedstuff
Digestible
Energy
(Mcal/kg)
Digestible
Energy
(Mcal/lb)
Crude
Protein
(%)*
HAY
Alfalfa
2.60
1.1 8
17.7
Alfalfa-grass
2.46
1.12
14.5
Native
2.13
0.97
9.0
Brome
2.24
1.02
9.9
GREENFEED
Barley
2.64
1.20
10.0
Oats
2.53
1.15
9.4
SILAGE
Barley
2.64
1.20
10.9
Oats
2.53
1.15
10.0
STRAW
Barley
1.98
0.90
4.7
Oats
2.16
0.98
4.5
Wheat
1.80
0.82
3.9
GRAINS
Barley
3.65
1.66
12.3
Oats
3.34
1.52
11.6
Wheat
3.87
1.76
15.8

* Since protein is listed in percentage, 1 lb of alfalfa hay will contain 0.177 lb of protein 1 kg of alfalfa hay will contain 0.177 kg protein.