A COMPUTER PROGRAM TO

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1 01997 Applied Poultly Science, Inc A COMPUTER PROGRAM TO STANDARDIZE FEED EFFICIENCY DATA FOR BROILERS OF DIFFERENT BODY WEIGHTS GENE M. PESTI' and STEPHEN R. ROGERS2 Department of Poultry Science, The University of Geo@tz, Athens, GA Phone: (706) F a (706) Primarv Audience: Poultrv Managers. Researchers DESCRIPTION OF PROBLEM It is well known that younger and smaller broilers use their feed more efficiently than older, larger ones. Poultry producers often compare flocks of broilers killed at different weights that have different feed efficiencies. Researchers usually compare results from flocks processed on the same day, even though producers are interested in results from flocks processed at the same weight. Producers, 1 To whom correspondence should be addressed 2 Present address: B.C. Rogers, Inc., P.O. Box A, Morton, MS however, need a method of extrapolating efficiencies of flocks killed at the same time to estimate the flocks' efficiencies had they been killed at the same weight. There is no widely accepted formal procedure to account for differences in body weight when comparing flocks with different feed efficiencies. Many broiler producers have formulas (rules of thumb) for rewarding contract growers whose birds have superior feed efficiency, but

2 Research Report PEST1 and ROGERS 369 these formulas do not always consider the relationship of body weight to feed efficiency. As birds grow, they become progressively less efficient in utilizing feed, in accord with the law of diminishing marginal productivity [l]. The higher proportion of nutrients needed for maintenance (as opposed to growth) accounts for the apparent decline in efficiency. Knowing a flock's body weight to feed intake production function would enable producers to estimate the expected feed intake at any body weight and vice versa. MATERIALS AND METHODS To establish the production function for a flock with a known body weight and feed intake at some age, it is first necessary to determine the general shape of the production functions for broilers. Figure 1 shows such production functions taken from four editions of the NRC Nutrient Requirements for Poultry [2,3,4,5] and a recent breeder management guide [6]. lho aspects of this figure are notable: 1) Although the overall efficiency of broilers has changed, the basic shape of the curves have remained constant, and 2) there are only small changes in the slopes of the lines over the entire range of slaughter weights for broilers. A spreadsheet template was written for Microsoft Excel to fit a curve with the basic shape shown in Figure 1 through any observed point. By establishing the production function curve, it is possible to estimate feed intake for any body weight and vice versa. The following process will produce an estimate of a flock's efficiency at a particular weight when another efficiency and weight are known. A standard curve is input. It is a quadratic, or second- order polynomial, curve defined by the formula: Body weight = bo + bif + b$ where bo = intercept, bl and b2 are coefficients, and F = feed intake. When an observed body weight and feed intake are input, the program uses the ratio of observed to predicted body weight at the observed feed intake to construct a series of points on a curve going through the observed point. The program then fits a new quadratic curve through the new mer New Ranan h Po c 3.5 w BROILER PRODUCTION FUNCTIONS!3 2.5 * 2.0 n Fp FEED CONSUMPTION (kg) FIGURE 1. A comparison of broiler production functions from several sources (all R2 >.97).

3 370 FEED EFFICIENCY AND WEIGHT points and solves the new curve for feed consumption at any input body weight, using the quadratic formula. Figure 2 shows the input window for the spreadsheet. The program contains standard default values when it is started. The operator need only move the cursor to the number to be replaced, input the new number, and press < Enter >. The results for the new inputs are displayed immediately. The exact calculations can be found in the spreadsheet itself. The spreadsheet described here, filename FCRADJ.XLS, can be downloaded from the UGA Department of Poultry Science Worldwide Web site at h~:llwww.uga.edul-poultryl, or may be obtained by sending a formatted diskette to Dr. Gene M. Pesti, Department of Poultry Science, The University of Georgia, Athens, GA RESULTS AND DISCUSSION Table 1 illustrates the problems involved in comparing different flocks of broilers and the kinds of comparisons that can be made. This table incorporates data for flocks grown in 1995 in the United States. Of the five flocks shown, Flocks B and E would be essentially identical in performance if grown to the same weight. Flock A's performance would differ little from that of Flock B or E at the same weight. Flock D would show the greatest efficiency, eating 50 g less feed to reach 2.2 kg. Flock C broilers would be expected to consume over 100 g more feed to reach 2.2 kg. The feed savings at a standard weight could serve as a basis for awarding feed efficiency bonuses to contract growers. Although the production function curve has changed over time, its basic shape has remained constant (Figure 1). Many factors can affect this line, including genetic stock used, chick size, sex of the birds, general flock health, management practices, metabolizable energy of the feed, use of pelleted or nonpelleted feed, and an especially important factor, environmental temperature. The response lime for any particular flock will be higher as temperature rises and lower as temperature falls. The exact curve for many situa- The standard body weight curve should first be decided upon and input, then the observed feed intake (FI) and body weight (Bw should be input, When the desired "TARGET" body weight is input, The FI and feed conversion ratio for that weight will be calculated. BW=bo+ (bqxfi) - (b,xflxfi) STANDARD ADJUSTED BODY WEIGHT CURVES: bo= bq = bz= OBSERVED TARGET FEED INTAKE: BODY WEIGHT: FEED CONVERSION RATIO: FIGURE 2. The "input" window of the FCRADJ.XLS program template for Microsoft Excel

4 Research Report PEST1 and ROGERS 371 TABLE 1. A comparison of the performance of flocks of broilers by adjusting to standard body weights conversion ratio tions is not known; precisely how the curve changes for the sexes in each season under different management and nutritional environments leaves room for further study. Other, more complex models [7, 8, 91 may predict performance at a given point in time; the FCRADJ program is designed only to extrapolate from one point to another. The function used in FCRADJ has the potential to provide a formal mechanism for rewarding contract growers for truly superior performance (technical efficiency). The best estimate of technical efficiency for growers should be the difference between the mean efficiency of a company (or even the company s best expected efficiency) and the mean efficiency of the grower over several flocks for a similar time period. This avoids the criticism that technical inefficiency is due entirely to a random error. In this case the curve becomes: Body weight = bo - (c-g) + bif + b2$ where c = mean company weight or best expected weight, and G = mean grower weight for several flocks. The value entered into the program for bo is then the sum of bo - (c-g). This functionwill reward or penalize depending on whether the long-term mean efficiency for the grower is greater or less than the long-term mean effi- ciency for the company. Therefore, normalization to a given weight is performed only after correcting for the mean effect for several flocks. In this manner agrower is not penalized for one below-average flock, but will be penalized if below-average flocks (due to random error) are not offset by above-average flocks (due to random error). If the grower is in fact practicing poor management, applying this model over time will result in continued belowaverage contract payment. The time horizon used for G should be sufficiently long to take into account interactions between seasons and grower equipment (for example, a producer s lack of a curtain machine yields poor efficiency in winter only). The error referred to above as random error is really error from unexplained sources. For instance, chick size may not be taken into account when determining how a grower compares to others at the same complex. A grower unlucky enough to get chicks below average in size for all six batches in a given year would be expected to have less than average performance that year. Such irregularities can be ascribed to random error only until their causes are identified, at which time producers or growers can take steps to correct them. CONCLUSIONS AND APPLICATIONS 1. The computer program template discussed here (FCRADJ) provides a formal method of comparing the performance of flocks of broilers with different body weights and feed consumptions. 2. FCRADJ can estimate the feed conversion expected if each flock were killed at the same weight, using the well known shape of the body weight to feed consumption curve. 3. The FCRADJ program may be useful for comparing and rewarding contract growers. 4. The program may be obtained from anywhere free of charge on the Worldwide Web (htlp:llw.uga.edul -poultry) in metric or imperial unit versions.

5 372 JAPR FEED EFFICIENCY AND WEIGHT 1. Heady, EO. and J.L. Dillon, Agricultural Production Functions. The Iowa State Univ. Press, Ames, L4. 2. National Research Council, Nutrient Requirements of Poultly. 6th Rev. Edition. Natl. Acad. 3, Research 1977, Nutrient Requirements of Poultry. 7th Rev. Edition. Natl. Acad. 4. National Research Council, Nutrient Requirements of PoultIy. 8th Rev. Edition. Natl. Acad. 5. National Research Council, Nutrient Requirements of Poultry. 9th Rev. Edition. Natl. Acad. 6. Ross Breeders, Inc., North American Broiler Performance Standards and Nutritional Specifications - ROSS X Ross 208. Ross Breeders, Inc., P.O. Box 155, Elkmont, AL Rogers, S.R., G.M. Pesti, and H.L. Marks, Comparison of three non-linear regression models for describing broiler growth curves. Growth 51: Talpq H., S. Hufuitq J.R. de La Tome, and P.J.H. Sharpe, Economic optimization of a growth trajectoiyfor broilen. Amer. J. AWc. eon. 70: Hrnby, M., M.L. Hamre, and C.N. Coon, Non-linear and linear functions in body protein growth. J. Appl. Poultry Res. 5: