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)+ Feed2(NUT~) + Feed3(NUT~) + �9 �9 �9 + Feed,,(NUT1) > NUT1 
Feedl(NUT2) + Feed2(NUT2) + Feed3(NUT2) + . . . + Feed,,(NUT2) > NUT2 
Feedl(NUT,,) + Feed2(NUT n) + Feed3(NUT,,) + . . . + Feed,,(NUT,,) > NUT,, 
In the representation above, all of the feedstuffs add up to the whole of the 
ration. Each feedstuff amount multiplied by its nutrient composition (NUT), for 
each nutrient, adds up to, or exceeds, the amount of that nutrient required in the 
ration. Typically the variable nutrients balanced for include protein, energy, 
calcium, phosphorus, and other nutrients that are individually considered. The 
restrictions can be made to be equal to, less than (<) or greater than (>) the 
given fight hand side member (RHS), or requirement. Typically the nutrient 
composition of the feedstuffs and the RHS values are arranged in tables. The 
software package then combines the values according to the restrictions, calcu- 
lates the solution to the equations, and presents the solution, displaying the ration 
cost, the feedstuff amounts, and often additional information. Other useful infor- 
mation includes penalty cost, which is the added cost of using a feedstuff that is 
not part of the solution, and shadow price, which is the incremental cost of 
increasing the value of a nutrient amount. 
V. USE OF SPREADSHEET PROGRAMS 
Spreadsheet programs have become very popular for keeping financial re- 
cords, for doing what-if planning, and for making other calculations. Three of 
the most popular spreadsheet programs with which the reader might be familiar 
are Lotus 123, Quattro Pro, and Excel. These programs have become powerful 
tools that can be used with relatively less programming expertise than is required 
for the use of computer programming languages such as FORTRAN, Pascal, and 
Basic. 
Templates have been developed for use with spreadsheet programs for check- 
ing and for balancing beef rations. Templates contain the words, instructions, 
and equations to provide the specific application to be used with the spreadsheet 
program. They have been especially useful to consultants for checking the ade- 
quacy of a client's ration, and for making adjustments to bring a ration into better 
balance. 
Powerful spreadsheets have built-in procedures for matrix algebra calcula- 
tions, and therefore can easily solve simultaneous equations. Considering a 
specific case of the generalized equations presented earlier, one can see that 
72 5. Computer Programming of Beef Cattle Diets 
solving for crude protein and TDN with hay, corn, and soybean meal (SBM) can 
be done directly and easily. 
100 = Corn + SBM + Hay 
CP = Corn(CPcom) + SBM(CPssM) + Hay(CPHay) 
TDN = (Corn)(TDNcorn) + (SBM)(TDNssM) + (Hay)(TDNHay) 
Let the requirements be represented by matrix R. R is a matrix of n rows and 1 
column, where n = the number of requirements. Let the feedstuffs analysis 
values be represented by matrix C. (C is a matrix of n rows and n columns, where 
n = the number of nutrients that also must equal the number of requirements). 
Let the feedstuff amounts, i.e., the answers, be represented by B. Then, in 
matrix notation, R = B C. Therefore: B = C -~ R. In other words, to get the 
amount of each feedstuff to feed, multiply the inverse (the matrix algebra equiva- 
lent of dividing) of C (the composition table) by R (the requirements). Use the 
matrix inversion procedure of the spreadsheet to obtain the C inverse and then 
use the matrix multiply procedure to obtain the answers. 
There are precautions that must be noted. The solution can include negative 
feedstuff amounts when a nutrient is present at a higher level than needed. 
Therefore, it often does not work well for cattle rations containing alfalfa, which 
is high in protein. Expanding the procedure to more than two nutrients is easy but 
not often practical because, again, the likelihood of the correct solution contain- 
ing negative numbers becomes too great. For example, if one includes calcium 
and phosphorus as nutrients for which to solve, alfalfa may contain more calcium 
than required and negative amounts of limestone will be the result. 
VI. OTHER COMPUTERIZED METHODS 
Least cost of production and maximum profit procedures have been mentioned 
previously. Nonlinear programming procedures have been described, to accom- 
modate situations in which one-to-one relationships between feedstuff levels and 
responses do not exist. Stochastic programming procedures have been described 
for taking into account in a systematic way the uncertainty associated with 
requirements or the composition of feedstuffs. This procedure may be relatively 
more important for commercial feed mills where a minimum nutritional value 
must be guaranteed. Computer modeling programs are also in use in research, to 
explore relationships between the rumen, animal growth, and nutritional require- 
ments.