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Sunday, November 28, 2010

Nutritional Value: The Calculations

In a recent conversation on Twitter, an interesting topic arose questioning the value of feeding cattle on grass or grain. So instead of looking around on the internet Answers sites or taking second-hand info off someone's website, I looked up the information myself, with a little help from Anna.

Cattle nutrition is a complex subject and there are entire university programs based on the subject, so I'm going to take a very pointed look at the subject.

Our bodies require a specific amount of energy for maintenance of body systems and gain of body tissues. This is similar in cattle. Foodstuffs contain a measurable amount of caloric energy. This energy is measured in Net Energy Value (NE); the amount of energy remaining after digestion, urine, gas, and heat losses. This is further broken down into NE maintenance (NEm) and NE gain (NEg) values. NEm is the amount of energy available for basal metabolism, maintenance activity, and maintaining body temperature. NEg is the amount of energy available for retention in body tissues. (Now that you are thoroughly confused, NEm is the amount of energy your body requires to function. NEg is the amount of energy your body requires to perform activities above maintenance.)

Let's use the table below to compare the NE requirements of a  500-pound growing calf and common high quality feedstuffs.



NE maintenance
NE gain
500-lb calf req for 1-lb of gain
4.84 Mcal/day
1.5 Mcal for 1 lb of gain
Values of Feedstuffs
Alfalfa Hay
0.59
0.33
Bermuda Grass Hay
0.42
0.17
Corn
1.03
0.67
Whole Cottonseed
1.09
0.77

Mcal/lb
Mcal/lb

A 500-lb growing steer has a requirement of 4.84 Mcal of NEm per day for body maintenance. For that animal to gain one pound requires 1.5 Mcal of NEg energy. For that same animal to gain 3 pounds per day, the NEg requirement increases to 5.0 Mcal per day.

To figure the amount of each feedstuff required to meet the daily NEm requirements, take requirement divide by NEm value of feedstuff.
Example: The NEm requirement is 4.84 Mcal/day. To supply sufficient NEm with Bermuda grass hay (0.42 Mcal/lb) the animal would need to consume 11.5 lbs of Bermuda grass hay.
To supply efficient NEm with Whole Cottonseed (1.09 Mcal/lb) the animal would need to consume 4.4 lbs of Whole Cottonseed.
In this scenario, the animal could consume 2.6 times more grass than cottonseed to supply NEm requirements. The higher the NEm value of the feedstuff, the less needed to meet nutritional requirements for maintenance.

To figure the amount of each feedstuff required to meet the desired NEg requirements, take desired rate of gain divide by the NEg value of the feedstuff.
Example: For a desired rate of gain of 1 lb per day the animal requires 1.5 Mcal of NEg. To supply efficient NEg with Bermuda grass hay (0.33 Mcal/lb) the animal would need to consume 4.5 lbs of Bermuda grass hay.
To meet a rate of gain of 1 lb per day with Whole Cottonseed (0.77 Mcal/lb) the animal would need to consume 1.9 lbs of Whole Cottonseed.
In this scenario the animal requires 2.4 times more grass than cottonseed to meet NEg requirements for 1 lb rate of gain per day. The higher the NEg value of the feedstuff, the less needed to meet nutritional requirements for rate of gain.


Animals must first meet maintenance requirements before meeting requirements for gain. Add the two values for each feedstuff to get the total amount of feedstuff to meet requirements for maintenance and desired gain.
Bermuda grass hay: 11.5 lbs for NEm + 4.5 lbs for NEg = 16 lbs to meet maintenance and 1 lb desired rate of gain.
Whole Cottonseed: 4.4 lbs for NEm + 1.9 lbs for NEg = 6.3 lbs to meet maintenance and 1 lb desired rate of gain.
By figuring the requirements for NEm and NEg of a 500-pound steer for 1 lb/gain/day, the animal requires 2.5 times more grass than cottonseed to meet desired performance.

When a producer puts a dollar value to these feedstuffs, he/she can find which is of greater value. After a little research I found Whole Cottonseed costs $0.567/hd and Bermuda grass hay costs $0.80/hd to meet desired performance.

To make a really long, confusing story short, by doing these calculations a cattle producer can find which feedstuff will be cheaper and more effiecient when looking for a desired performance and rate of gain. This scenario shows that using a feedstuff with a higher NEm and NEg value (such as many grains and grain by-products) the desired performance can be met cheaper and more efficiently.