Energy and Protein

Energy is not a nutrient, but managers evaluate diets and animals' requirements on an energy basis. Usually, optimal economic return from this conversion is predicated upon maximizing consumption of forage; the more forage they eat, the better. Managing forages as energy and protein sources centers on managing the agronomic aspects of the forage to take full advantage of its nutrient potential, and on predicting the nutrient content of a given forage at the time it is grazed or harvested as hay. Knowing nutrient content (Table 2) and accurately predicting forage consumption allow a good manager to formulate a supplement that complements the forage nutrient supply to meet nutritional requirements and minimizes feed costs. Nutrition-related diseases, such as grass tetany, acute bovine pulmonary emphysema, or nitrate toxicity, can have lethal effects on grazing ruminants.[1'2] Legumes, such as alfalfa and clover, are good sources of energy and protein for beef cattle; however, beef cattle may die from bloat caused by rapid consumption of legumes.[1]

An important aspect of beef production is the use of byproducts as feedstuffs. By-products such as recycled poultry bedding, whole cottonseeds, and soybean hulls are cost-efficient sources of energy and protein. In fact, many of these unusual feed sources are rated for their value relative to corn grain, soybean meal, or alfalfa hay, which allows managers to make intelligent feed purchase decisions.1-3-1

Beef cattle gain weight rapidly on high-grain diets, but excessive consumption of grain can upset the fermentation balance in the rumen, which can lead to potentially lethal acidosis.1-1-1 Acidosis is controlled by feeding approved compounds (ionophores, buffers) as well as by astute management of feed composition and supply to the animals.

The relatively high cost of supplemental protein obliges a manager to consult technical information and formulate diets that meet but do not exceed the animal's requirements. Degradability of dietary protein in the

Table 1 Nominal daily dry matter intake and nutrient requirements for beef cattlea

Weaned calf Growing finishing,

200 350 kg BW 350 500 kg BW Mature cow Mature bull

Table 1 Nominal daily dry matter intake and nutrient requirements for beef cattlea

Weaned calf Growing finishing,

200 350 kg BW 350 500 kg BW Mature cow Mature bull

Dry matter, kg

4

10

10

12

6

12

6

9

Nutrient

Water, L

15

56

28

78

23

61

30

78

Protein, g

400

1000

600

1000

500

1300

800

1000

Metabolizable energy, Mcal

12

17

15

27

12

27

21

28

Calcium, g

12

35

15

29

12

42

27

33

Phosphorus, g

9

18

13

21

12

31

22

33

Sodium chloride, g

10

20

10

15

36

15

36

'Specific requirements'4' for a given type of animal and productive purpose should be used for formulating and evaluating diets.

'Specific requirements'4' for a given type of animal and productive purpose should be used for formulating and evaluating diets.

rumen varies among feedstuffs.[4] Managers can mix protein sources of differing ruminal degradabilities to optimize efficiency of nutrient use for weight gain. Concern about the contribution of animal waste to nutrient loads in ecosystems encourages managers to tightly manage nitrogen supply and use.

Energy and protein requirements vary with age, environment, and productive state (Table 1). In general, if forage intake equals 2 3% of the animal's live weight, the forage will be close to providing the animal's maintenance energy needs, and if that forage contains at least 8% crude protein, it will be close to providing the animal's maintenance protein needs.

Minerals

Several essential minerals may be limited in beef cattle diets. Supplemental feeds usually contain minerals to meet nutritional requirements (Table 1). Supplements usually provide salt (NaCl), Ca, P, and trace minerals such as Mn, Cu, Co, Zn, I, and Se. Concentrations of each mineral are based on estimates of voluntary intake and daily requirements.'2' Supplements can contain supplemental protein or energy as well as minerals, or can contain other compounds (e.g., ionophores) that modulate fermentation to improve nutrient use or reduce the chance of a nutrition-related disease, depending on the management scheme.

Mineral deficiencies or imbalances are the most likely problems, but isolated areas may have toxic levels of minerals, such as Se.[5] In most instances, problems linked to improper mineral nutrition are subtle, such as slightly reduced weight gain and reduced probability of pregnancy in breeding females. Effective managers need to know local conditions and need to routinely analyze feedstuffs to distinguish problems caused by improper mineral nutrition from problems with other causes unrelated to nutrition. Blood, liver, and hair samples are taken from cattle to pinpoint potential problems with mineral status.

Vitamins

Essentially all the water-soluble vitamins (B-vitamins) and fat-soluble vitamin K required by beef cattle are synthesized by the ruminal microbes.[3] These vitamins are provided in mother's milk to young calves before their rumens begin functioning. At normal intakes, fat-soluble vitamins A, D, and E are adequate in common feedstuffs. In most situations, animals are exposed to sufficient sunlight to adequately synthesize vitamin D to supplement

Table 2 Dry matter (DM) and nutrient composition of examples of feedstuffs for beef cattle

Recycled

Soybean Whole poultry

Bromegrass Bermudagrass Alfalfa Corn grain meal cottonseed bedding

Recycled

Soybean Whole poultry

Bromegrass Bermudagrass Alfalfa Corn grain meal cottonseed bedding

DM, g/kg

270

920

290

900

200

910

770

890

890

900

870

900

770

820

Protein, g/kg DM

60

171

70

140

149

225

890

112

477

540

200

244

225

320

Metabolizable energy,

1.8

2.8

1.5

2.3

2.1

2.4

3.2

3.7

2.9

3.4

3.2

3.5

1.5

2.1

Mcal/kg DM

Calcium, g/kg DM

2.6

3.8

4.2

5.5

11.9

16.9

0.2

0.3

2.9

4.0

1.5

2.0

15

40

Phosphorus, g/kg DM

1.6

2.6

1.8

2.7

2.1

3.3

3.3

6.8

7.1

5

7.5

7

25

Source: Ref. [3], personal experience of authors.

Source: Ref. [3], personal experience of authors.

dietary sources. Managers need to respond to unusual conditions, when the diet or ambient conditions are not compatible with adequate supplies of vitamins. For example, animals fed poor-quality, old hay, or animals that have access to sparse, mature grass in pastures may need supplemental vitamin A. Animals housed indoors may need supplemental vitamin D. Animals eating forages in geographic areas with soils low in Se may need supplemental vitamin E. The relatively low cost and minimal risk of toxicity of vitamins A, D, and E prompt many managers to routinely include them in completely mixed diets or supplements to meet requirements.1-2-1

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