5 Computer Programming of Beef Cattle Diets 1995 Beef Cattle Feeding and Nutrition Second Edition
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5 Computer Programming of Beef Cattle Diets 1995 Beef Cattle Feeding and Nutrition Second Edition

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5

Computer Programming
of Beef Cattle Diets

Dale M. Forsyth

Computers have been useful in ration formulation for beef cattle for many
years. Originally, computer formulation was carded out with main-frame
computers that were very expensive and complicated to operate and were only
available to large businesses and universities. Some universities made their
computers accessible to the public so that more people could utilize computer
formulation. Recently, however, with the advent of inexpensive powerful per-
sonal computers and user-friendly software programs, computers have become
available to businesses of any size, including all those that deal with cattle.

Computers are especially useful in the area of least-cost programming (also
called linear programming, because of the mathematical technique used), due to
the complexity of procedures for solving the equations. Least cost rations have
been especially important for large feedlot operators who purchase all feed
ingredients and for feed companies that deal with many feedstuffs. Simpler
programs that do not rely on price for determining the ration ingredients are also
available and are useful for many situations. Spreadsheets, which are general
purpose computer programs (such as Lotus 123, Quattro, or Excel) that relieve
the user from much of the detail of developing computer code, also have been
utilized for formulating livestock rations.

I. SOURCES OF RATION PROGRAMS FOR COMPUTERS

Ration balancing programs are available from commercial software compa-
nies and from universities for various kinds of applications and for use on
everything from main-frame to personal computers. Recently, powerful spread-
sheet programs for personal computers have made it easier for nutritionists to
develop computer solutions without the need for as much programming exper-
tise. Some of the spreadsheet programs, like Quattro-Pro and Excel, even have

Beef Cattle Feeding and Nutrition,
Second Edition 68

Copyright �9 1995 by Academic Press, Inc.
All rights of reproduction in any form reserved.

II. Least-Cost Ration Assumptions and Problems 69

built in optimization for calculating LP solutions, making least cost program
development available to a wider audience.

II. LEAST-COST RATION ASSUMPTIONS AND PROBLEMS

Least-cost rations rely on the assumption that the same level of performance
will be achieved if a minimum level of each required nutrient is met, regardless
of the source of nutrients. For example, one assumes a pound of protein from
cottonseed meal is equally effective as a pound of protein from soybean meal, or
even urea. This assumption is not always correct. Urea as a source of nitrogen
will not always provide for the same performance level as natural protein. Calo-
ries from fat are not always used in the same manner or with the same efficiency
as calories from carbohydrate or protein.

Least-cost procedures are only mathematical methods for solving equations,
and do not always produce the most practical rations to feed to livestock. A
program may add, for example, a large amount of inappropriate feeds. Under
certain conditions, it may be possible to include large amounts of limestone, salt,
or another cheap feed as filler. Careful attention to restrictions can exclude most
of the common problems of this sort. Both minimum and maximum restrictions
on nutrient levels and specific feedstuff amounts can be used. Sometimes, how-
ever, restrictions are not included on feeds that ordinarily are not a major share of
the diet. If wheat were cheap, it might be substituted for all the corn in a ration,
but a nutritionist would recognize that while the feeding value of wheat is close
to that of corn, practical diets would not be based on all wheat. Differences in
palatability of feeds are not usually considered in the least-cost formulation,
except as maximum restrictions of feedstuff inclusion levels. It is important that
the results of least-cost formulated rations be inspected by someone knowledge-
able about beef cattle nutrition to evaluate the practicality of the ration.

Another problem results if prices are not current and accurate. Since the
decision function of which feedstuffs to use is based on price, it is of paramount
importance that the prices used are correct. Similarly, the feedstuff composition
for the feeds used must be accurate or the ration will not provide the nutrients at
the correct levels. For example, the average value of protein in corn is near 8%
but the range will be from 6.7 to 10.0%. Use of average values for feeds will lead
to great amounts of inaccuracy in the ration.

Least-cost procedures do not usually have a mechanism for taking into ac-
count such complications as associative effects of feeds. Associative effects
occur when the response to nutrients in a feedstuff are different in one ration than
in another, depending on the feed ingredients in each ration.

Performance effects arising because of feed processing methods, even when

70 5. Computer Programming of Beef Cattle Diets

feeds contain the same level of nutrients, are known but not considered by typical
least-cost programs. One way of taking this into account is to consider each
processed feed a separate feedstuff, and to use composition values based on
availability rather than total nutrient content.

Determination of the animal's requirements is difficult, given the variability of
animals and all the things which influence requirement needs, but is not a
problem only for least-cost rations. Estimation of voluntary feed intake, how-
ever, is important to ration formulation but difficult to achieve accurately in all
conditions.

Another shortcoming of least-cost rations is that the ration calculated may not
always be the most profitable one. Incorporating other information into the
decision process is the goal of least-cost-of-production rations and of maximum-
profit rations. These programs are not as commonly available, however.

III. NET ENERGY CONSIDERATIONS

Net energy concepts provide a more accurate description of energy use from
feeds than TDN or digestible energy, and better predict performance of cattle
based on energy intake. They are more complicated to handle in ration formula-
tion, though, because each feed has different energy values for maintenance and
for productive functions. The values are not independent; the energy needed for
maintenance must be met before any additional energy is used for production,
and that energy used for production will be used with a lower efficiency than for
maintenance. Computer programs can make the necessary calculations. Simul-
taneous consideration of voluntary feed intake, however, presents another com-
plication.

In the case of mature beef cows, the energy necessary to gain or lose weight
depends on the current body condition of the cow, thin or fat. Equations for net
energy needs in these circumstances are expected to be included in the next
revision (1995) of the NRC Nutrient Requirements of Beef Cattle.

IV. SOLUTIONS FOR RATIONS

Balancing rations by any method requires: (1) knowing the requirements for
nutrients of the animals to be fed, (2) knowing the composition of feedstuffs to be
used with regard to those nutrients, and (3) a procedure for combining feeds to
meet those requirements. The LP procedure allows many feeds to be considered
for the ration, with selection of which feeds and in which amounts to be deter-
mined on the basis of feedstuff prices. Mathematically, where Feed,, represents

V. Use of Spreadsheet Programs 71

the quantity of the nth feedstuff, and NUT,, represents the concentration of the
nth nutrient for which you are balancing, the linear equations are represented by

Feed l + Feed2 + Feed3 . . . + Feed,, = 100
Feedl(NUT1)