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Meat Yield from Live, Dressed, and Eviscerated Rhode Island Red Chickens During Growth and at Maturity*
Meat Yield from Live, Dressed, and Eviscerated Rhode Island Red Chickens During Growth and at Maturity* E. H. MCNALLY AND N. H. SPICKNALL U. S. Department of Agriculture, Agricultural Research Service, Animal and Poultry Husbandry Research Branch (Received for publication April 27, 1954)
T
Since it was observed with the cockerels that only linear relationships were found on plotting the various dressed conditions,
* Report of a study made under Research and Marketing Act of 1946.
145
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
RESULTS AND DISCUSSION
it was considered important in the present study to select only those relationships which were of the most practical importance, giving the smallest standard error. Calculations of dressed from live weight, eviscerated from dressed weight, weight of eviscerated with giblets from dressed weight and edible meat weight from eviscerated weight were chosen as most suitable. These calculations, since they were each in order of the least treatment of the carcass in the steps of dressing poultry, also gave the smallest standard error of estimate. For example, the calculation of yield of edible meat from the eviscerated weight was more accurate than calculation of yield of edible meat from either live or dressed weight. The relations described above were plotted to obtain the general trend of the scatter diagram. The scatter diagrams for the pullets, hens, and cocks were similar to those for the cockerels and showed linear relationships. Regression equations were calculated by the method of least squares. Since similar equations were observed for the various dressed weights of both sexes and also for young and mature birds, overall equations were also calculated for all the birds together to compare with the equations for a single sex and age. The regression equations are given in Table 1. A comparison of the equations for the cockerels, pullets, hens, and cocks with the over-all equation is plotted in Figure 1.
HE meat yields from live, dressed, and eviscerated Rhode Island Red cockerels were reported by McNally and Spicknall in 1949. Since linear relationships and equations were found suitable for use with these birds, it was considered worth while to continue the study with pullets and mature birds of both sexes to determine if the sex and age differences were important in the determination of yield in this breed. The effect of age is especially interesting, since in the growing birds each individual is increasing in weight and thus passing from one weight group to another. In the mature birds the growth has stopped and the musculature has become balanced. The smaller bird will not change into the larger one at some later time. The difference between small and large growing birds, therefore, might be much greater or much less than between mature birds that are small and large. The birds were reared and fed the same as the cockerels previously reported (McNally and Spicknall, 1949). They were killed, plucked, and eviscerated under similar conditions to keep the procedure for all the birds as much the same as possible. In the study, 125 pullets, 85 cocks, and 30 hens were used. The pullets were from 10 to 16 weeks of age. The hens and cocks were about 38 weeks old when killed.
146
E. H. MCNALLY AND N. H.
TABLE 1.—Regression equations in grams for weights of various market-dressed Rhode Island Red chickens T,- j >
Cockerels Pullets Cocks Hens All
Regression equation, live—dressed (Dressed = b l i v e - C )
Standard error of estimate
Ey = 0.8923a; -- 54.9 .8750*-- 5.2 .9363*- -164.4 .9616*- -129.4 .9052*- - 58.3
±42.1 +42.4 ±62.7 ±42.4 ±52.4
±19.8 + 28.1 + 54.6 ±51.0 ±21.5
TABLE 2.—Average observed and calculated dressed, in grams, of a small random sample of chickens of different ages and sex
TI:-A„ ..*„,! Birdsused
jj-um iT~ ber
Average Average Average Average obcalcuobcalcuserved
lated
weight weight1 Dressed weight
swved
uted
weight weight Eviscerated weight2
Cocks Hens Pullets Cockerels All
8 7 7 7 29
gms. gms. gms. gms. 3,261.3 3,249.6 2,516.6 2,493.1 2,216.3 2,140.3 1,577.6 1,684.4 1,405.1 1,425.5 1,064.8 1,039.5 1,148.3 1,140.0 861.9 837.1 2,048.2 2,032.3 1,540.1 1,547.3 Edible-meat Eviscerated+Giblet weight3 weight4
Cocks Hens Pullets Cockerels All
8 7 7 7 29
2,155.3 2,141.3 2,625.3 1,353.1 1,334.4 1,667.3 892.7 891.7 1,130.6 726.4 717.1 917.4 1,312.0 1,301.1 1,620.9
2,615.0 1,772.8 1,109.6 900.3 1,634.4
i Dressed=0.9052 Live—58.3. Eviscerated=0.7935 Dressed—74.1. »1 Edible meat =0.8607 Eviscerated—24.8. Eviscerated+Giblets=0.8157 Dressed—36.5. 2
Dressed—Eviscerated and Giblets (Eviscerated with Giblets=b Dressed+Q Cockerels E y = 0 . 8 2 3 6 * - 36.3 ±38.4 Pullets .8739*-104.7 ±37.8 Cocks .7542*4-158.9 ±54.5 Hens . 7 8 9 0 * - 73.0 ±54.5 All . 8 1 5 7 * - 36.5 ±49.2 Eviscerated—Edible Meat (Edible Meat=b Eviscerated—C) Cockerels £ y = 0 . 8 4 2 0 * - 4.6 Pullets . 8 8 8 1 * - 38.8 Cocks . 8 7 9 4 * - 64.2 Hens .9747*-184.9 All . 8 6 0 7 * - 24.8
±17.4 ±20.6 ±37.6 ±17.7 ±22.6
While some differences due to sex and age are apparent, these differences are so small that for practical purposes the over-all equations may be used, greatly simplifying the correction for weight and calculations of yield within a single breed. One equation may be used with fair accuracy in place of four, except when the calculation must be made with the greatest precision possible. To show the variation that may be found under practical conditions in using the different equations, a random sample was selected from each group, and the observed and the calculated yields, using the over-all equations, are shown in Table 2. Since the over-all equations were found to give results which are satisfactory for most uses, a single table was prepared
which may be used for either sex without regard to age. Such calculations for quarter-pound intervals from 2.50 to 8.00 pounds are given in Table 3. To show the change in percentage of yields over this range, representative calculations have been made, using the equations for each age and sex and the over-all equations. These figures are given in Table 4. I t will TABLE 3.—Calculated dressed yield of Rhode Island Red chickens from 2.5 to 8.0 pounds live weight
Lbs.
.50 75 00 25 50 75 00 25 50 .75 00 25 50 75 00 25 ,50 .75 ,00 .25 .50 .75 .00
Live weight gms. 1,134.0 1,247.4 1,360.8 1,474.2 1,587.6 1,701.0 1,814.4 1,927.8 2,041.2 2,154.6 2,268.0 2,381.4 2,494.8 2,608.2 2,721.6 2,835.0 2,948.4 3,061.7 3,175.1. 3,288.5 3,401.9. 3,515.3 3,628.7
dressed
Dressed to eviscerated
Dressed to evis- Eviscercerated ated to with edible Giblets
gms. 968.2 1,070.8 1,173.5 1,276.1 1,378.8 1,481.4 1,584.1 1,686.7 1,789.4 1,892.0 1,994.7 2,097.3 2,200.0 2,302.6 2,405.3 2,507.9 2,610.6 2,713.2 2,815.8 2,918.5 3,021.1 3,123.7 3,226.4
gms. 694.2 775.6 857.1 938. S 1,020.0 1,101.4 1,182.9 1,264.3 1,345.8 1,427.2 1,508.7 1,590.1 1,671.6 1,756.7 1,834.5 1,915.9 1,997.4 2,078.8 2,160.2 2,241.7 2,323.1 2,404.6 2,486.0
gms. 753.3 837.0 920.7 1,004.4 1,088.2 1,171.9 1,255.7 1,339.3 1,423.1 1,506.8 1,590.6 1,674.3 1,758.0 1,841.7 1,925.5 2,009.2 2,093.0 2,176.6 2,260.3 2,344.1 2,427.8 2,551.5 2,595.3
Live to
gms. 572.8 642.8 713.0 783.0 853.1 923.2 993.3 1,063.4 1,133.5 1,203.6 1,273.7 1,343.8 1,413.9 1,487.2 1,554.2 1,624.2 1,694.4 1,764.4 1,834.5 1,904.6 1,974.1 2,044.8 2,114.9
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
Dressed—Eviscerated (Eviscerated = b Dressed+C) j E y = 0 . 7 8 9 8 * - 58.8 Cockerels .8446*-133.6 Pullets .7318*4-126.5 Cocks .7783*-144.7 Hens . 7 9 3 5 * - 74.0 All
SPICKNALL
MEAT YIELD FROM LIVE, DRESSED, AND EVISCERATED CHICKENS
147
2,500
2,000
S 1,500
1,500
1,000
500
2,000 DRESSED WEIGHT
3,000
2,500 (GMS)
FIG. 1. Plotted lines for age and sex compared to over-all yield of eviscerated based on dressed weight.
be seen that while 7.4 percent difference between small cockerels and large cocks is found in the dressed weight based on live weight, only 3.9 percent difference is found in yield of eviscerated plus giblets of the dressed weight of small pullets and large cocks. The over-all equations give less differences in percentage of yield than the equation for a single sex age group.
SUMMARY
The regression equations for the interrelation of weights of live, dressed, and eviscerated Rhode Island Red chickens and the edible meat were calculated for 125 pullets, 85 cocks, and 30 hens ranging from 1134 to 3628 grams live weight. The pullets were 10 to 16 weeks of age and the hens and cocks, 38 weeks.
TABLE 4.—Calculated dressing weights and percentages of various weights T y p e of birds
1,000 gms.
%
2,000 gms.
%
3,000 gms.
%
1,000 gms.
%
731.0 711.0
73.10 71.10
91.15 91.85 88.57
85.80 91.31 85.24
1
Cockerels Pullets Cocks Hens All
837.4 869.8
83.74 86.98
846.9
84.69
Cockerels Pullets Cocks Hens All
837.4 849.3
83.74 84.93
835.9
83.59
1 2 8
Dressed weight 1,729.7 86.49 1,744.8 87.24 1,768.2 88.42 1,793.8 89.69 1,752.1 87.61
2,734.5 2,755.4 2,657.3
Edible meat weight* 1,697.4 83.97 86.87 1,737.4 84.73 2,574.0 1,694.6 88.23 2,739.2 1,764.5 84.83 2,557.3 1,696.6
Live—Dressed. Dressed—Eviscerated. Eviscerated—Edible meat. * Dressed—Eviscerated-|-Giblets.
2,000 gms. Eviscerated 1,520.8 1,555.6 1,590.1 1,411.9 1,512.9
%
3,000 gms.
%
719.4
71.94
weight* 76.04 77.78 79.51 2,321.9 70.59 2,190.2 75.64 2,306.2
77.59 73.01 76.87
787.3 769.2 913.1 742.7 779.2
Eviscerated with giblets weight* 78.73 1,610.9 80.55 76.92 1,643.1 82.15 83.37 2,421.5 2,374.1 77.92 77.92 1,594.9 79.75 2,420.6
80.72 79.13 80.69
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
1,000
148
B. W. HEYWANG, H. R. BIRD AND M. G. VAVICH
accurate method of calculation of the various yields. The equations for the cockerels, pullets, cocks, and hens were similar enough so that over-all equations could be used on most occasions for both the young and mature birds of either sex. REFERENCE McNally, E. H., and N. H. Spicknall, 1949. Meat yield from live, dressed, and eviscerated Rhode Island Red males of broiler, fryer, and light roaster weights. Poultry Sci. 28: 562-567.
The Level of Protein in the Diet of Laying White Leghorns During Hot Weather 2 BURT W. HEYWANG, H. R. BIRD 1 AND M. G. VAVICH Agricultural Research Service, U. S. Department of Agriculture, Animal and Poultry Husbandry Research Branch, Glendale, Arizona, and Bellsville, Maryland, and Department of Nutrition, College of Agriculture, University of Arizona, Tucson, Arizona (Received for publication April 27, 1954)
T
HE National Research Council (1950) recommends that diets for laying chickens contain 15 percent protein. However, the feed intake of laying chickens decreases appreciably during periods of high environmental temperatures, such as during several months of the year in the region where the Southwest Poultry Experiment Station is located. Because this decrease in feed intake results in a decrease in the nutrients needed for egg production, it seemed possible that the level of protein in the diet of laying chickens should be higher during hot weather than during cool or moderate weather. Heywang (1947) reported the results of
1 Present address: Department of Poultry Husbandry, University of Wisconsin. 2 Arizona Agricultural Experiment Station Technical Paper No. 337.
several experiments in which the main object was to determine the effect of the dietary level of protein on the mortality rate among laying chickens during hot weather, with casein in their diets as the only protein concentrate. Egg production was a little higher when the protein level in the diets was 23.5-25.5 percent than when it was 15.5-18 percent, but those results do not seem indicative because the diets were not necessarily suitable for satisfactory egg production. Accordingly, two experiments were conducted at the Southwest Poultry Experiment Station, Glendale, Arizona to obtain information on the subject. One of these experiments was in progress during only hot weather, while the other was in progress during cool and moderate weather as well as hot weather. The data obtained in the experiments are presented and discussed in this paper.
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
While a number of different interrelations may be calculated between various dressing methods, those equations were computed which gave the relation after the smallest amount of manipulation of the carcasses, as live to dressed weights, dressed to eviscerated-body weights, and eviscerated-body to edible meat weights. The advantages of this are they have the smallest standard error of estimate of the several equations that could be calculated. Linear equations were found to give an
T
Since it was observed with the cockerels that only linear relationships were found on plotting the various dressed conditions,
* Report of a study made under Research and Marketing Act of 1946.
145
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
RESULTS AND DISCUSSION
it was considered important in the present study to select only those relationships which were of the most practical importance, giving the smallest standard error. Calculations of dressed from live weight, eviscerated from dressed weight, weight of eviscerated with giblets from dressed weight and edible meat weight from eviscerated weight were chosen as most suitable. These calculations, since they were each in order of the least treatment of the carcass in the steps of dressing poultry, also gave the smallest standard error of estimate. For example, the calculation of yield of edible meat from the eviscerated weight was more accurate than calculation of yield of edible meat from either live or dressed weight. The relations described above were plotted to obtain the general trend of the scatter diagram. The scatter diagrams for the pullets, hens, and cocks were similar to those for the cockerels and showed linear relationships. Regression equations were calculated by the method of least squares. Since similar equations were observed for the various dressed weights of both sexes and also for young and mature birds, overall equations were also calculated for all the birds together to compare with the equations for a single sex and age. The regression equations are given in Table 1. A comparison of the equations for the cockerels, pullets, hens, and cocks with the over-all equation is plotted in Figure 1.
HE meat yields from live, dressed, and eviscerated Rhode Island Red cockerels were reported by McNally and Spicknall in 1949. Since linear relationships and equations were found suitable for use with these birds, it was considered worth while to continue the study with pullets and mature birds of both sexes to determine if the sex and age differences were important in the determination of yield in this breed. The effect of age is especially interesting, since in the growing birds each individual is increasing in weight and thus passing from one weight group to another. In the mature birds the growth has stopped and the musculature has become balanced. The smaller bird will not change into the larger one at some later time. The difference between small and large growing birds, therefore, might be much greater or much less than between mature birds that are small and large. The birds were reared and fed the same as the cockerels previously reported (McNally and Spicknall, 1949). They were killed, plucked, and eviscerated under similar conditions to keep the procedure for all the birds as much the same as possible. In the study, 125 pullets, 85 cocks, and 30 hens were used. The pullets were from 10 to 16 weeks of age. The hens and cocks were about 38 weeks old when killed.
146
E. H. MCNALLY AND N. H.
TABLE 1.—Regression equations in grams for weights of various market-dressed Rhode Island Red chickens T,- j >
Cockerels Pullets Cocks Hens All
Regression equation, live—dressed (Dressed = b l i v e - C )
Standard error of estimate
Ey = 0.8923a; -- 54.9 .8750*-- 5.2 .9363*- -164.4 .9616*- -129.4 .9052*- - 58.3
±42.1 +42.4 ±62.7 ±42.4 ±52.4
±19.8 + 28.1 + 54.6 ±51.0 ±21.5
TABLE 2.—Average observed and calculated dressed, in grams, of a small random sample of chickens of different ages and sex
TI:-A„ ..*„,! Birdsused
jj-um iT~ ber
Average Average Average Average obcalcuobcalcuserved
lated
weight weight1 Dressed weight
swved
uted
weight weight Eviscerated weight2
Cocks Hens Pullets Cockerels All
8 7 7 7 29
gms. gms. gms. gms. 3,261.3 3,249.6 2,516.6 2,493.1 2,216.3 2,140.3 1,577.6 1,684.4 1,405.1 1,425.5 1,064.8 1,039.5 1,148.3 1,140.0 861.9 837.1 2,048.2 2,032.3 1,540.1 1,547.3 Edible-meat Eviscerated+Giblet weight3 weight4
Cocks Hens Pullets Cockerels All
8 7 7 7 29
2,155.3 2,141.3 2,625.3 1,353.1 1,334.4 1,667.3 892.7 891.7 1,130.6 726.4 717.1 917.4 1,312.0 1,301.1 1,620.9
2,615.0 1,772.8 1,109.6 900.3 1,634.4
i Dressed=0.9052 Live—58.3. Eviscerated=0.7935 Dressed—74.1. »1 Edible meat =0.8607 Eviscerated—24.8. Eviscerated+Giblets=0.8157 Dressed—36.5. 2
Dressed—Eviscerated and Giblets (Eviscerated with Giblets=b Dressed+Q Cockerels E y = 0 . 8 2 3 6 * - 36.3 ±38.4 Pullets .8739*-104.7 ±37.8 Cocks .7542*4-158.9 ±54.5 Hens . 7 8 9 0 * - 73.0 ±54.5 All . 8 1 5 7 * - 36.5 ±49.2 Eviscerated—Edible Meat (Edible Meat=b Eviscerated—C) Cockerels £ y = 0 . 8 4 2 0 * - 4.6 Pullets . 8 8 8 1 * - 38.8 Cocks . 8 7 9 4 * - 64.2 Hens .9747*-184.9 All . 8 6 0 7 * - 24.8
±17.4 ±20.6 ±37.6 ±17.7 ±22.6
While some differences due to sex and age are apparent, these differences are so small that for practical purposes the over-all equations may be used, greatly simplifying the correction for weight and calculations of yield within a single breed. One equation may be used with fair accuracy in place of four, except when the calculation must be made with the greatest precision possible. To show the variation that may be found under practical conditions in using the different equations, a random sample was selected from each group, and the observed and the calculated yields, using the over-all equations, are shown in Table 2. Since the over-all equations were found to give results which are satisfactory for most uses, a single table was prepared
which may be used for either sex without regard to age. Such calculations for quarter-pound intervals from 2.50 to 8.00 pounds are given in Table 3. To show the change in percentage of yields over this range, representative calculations have been made, using the equations for each age and sex and the over-all equations. These figures are given in Table 4. I t will TABLE 3.—Calculated dressed yield of Rhode Island Red chickens from 2.5 to 8.0 pounds live weight
Lbs.
.50 75 00 25 50 75 00 25 50 .75 00 25 50 75 00 25 ,50 .75 ,00 .25 .50 .75 .00
Live weight gms. 1,134.0 1,247.4 1,360.8 1,474.2 1,587.6 1,701.0 1,814.4 1,927.8 2,041.2 2,154.6 2,268.0 2,381.4 2,494.8 2,608.2 2,721.6 2,835.0 2,948.4 3,061.7 3,175.1. 3,288.5 3,401.9. 3,515.3 3,628.7
dressed
Dressed to eviscerated
Dressed to evis- Eviscercerated ated to with edible Giblets
gms. 968.2 1,070.8 1,173.5 1,276.1 1,378.8 1,481.4 1,584.1 1,686.7 1,789.4 1,892.0 1,994.7 2,097.3 2,200.0 2,302.6 2,405.3 2,507.9 2,610.6 2,713.2 2,815.8 2,918.5 3,021.1 3,123.7 3,226.4
gms. 694.2 775.6 857.1 938. S 1,020.0 1,101.4 1,182.9 1,264.3 1,345.8 1,427.2 1,508.7 1,590.1 1,671.6 1,756.7 1,834.5 1,915.9 1,997.4 2,078.8 2,160.2 2,241.7 2,323.1 2,404.6 2,486.0
gms. 753.3 837.0 920.7 1,004.4 1,088.2 1,171.9 1,255.7 1,339.3 1,423.1 1,506.8 1,590.6 1,674.3 1,758.0 1,841.7 1,925.5 2,009.2 2,093.0 2,176.6 2,260.3 2,344.1 2,427.8 2,551.5 2,595.3
Live to
gms. 572.8 642.8 713.0 783.0 853.1 923.2 993.3 1,063.4 1,133.5 1,203.6 1,273.7 1,343.8 1,413.9 1,487.2 1,554.2 1,624.2 1,694.4 1,764.4 1,834.5 1,904.6 1,974.1 2,044.8 2,114.9
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
Dressed—Eviscerated (Eviscerated = b Dressed+C) j E y = 0 . 7 8 9 8 * - 58.8 Cockerels .8446*-133.6 Pullets .7318*4-126.5 Cocks .7783*-144.7 Hens . 7 9 3 5 * - 74.0 All
SPICKNALL
MEAT YIELD FROM LIVE, DRESSED, AND EVISCERATED CHICKENS
147
2,500
2,000
S 1,500
1,500
1,000
500
2,000 DRESSED WEIGHT
3,000
2,500 (GMS)
FIG. 1. Plotted lines for age and sex compared to over-all yield of eviscerated based on dressed weight.
be seen that while 7.4 percent difference between small cockerels and large cocks is found in the dressed weight based on live weight, only 3.9 percent difference is found in yield of eviscerated plus giblets of the dressed weight of small pullets and large cocks. The over-all equations give less differences in percentage of yield than the equation for a single sex age group.
SUMMARY
The regression equations for the interrelation of weights of live, dressed, and eviscerated Rhode Island Red chickens and the edible meat were calculated for 125 pullets, 85 cocks, and 30 hens ranging from 1134 to 3628 grams live weight. The pullets were 10 to 16 weeks of age and the hens and cocks, 38 weeks.
TABLE 4.—Calculated dressing weights and percentages of various weights T y p e of birds
1,000 gms.
%
2,000 gms.
%
3,000 gms.
%
1,000 gms.
%
731.0 711.0
73.10 71.10
91.15 91.85 88.57
85.80 91.31 85.24
1
Cockerels Pullets Cocks Hens All
837.4 869.8
83.74 86.98
846.9
84.69
Cockerels Pullets Cocks Hens All
837.4 849.3
83.74 84.93
835.9
83.59
1 2 8
Dressed weight 1,729.7 86.49 1,744.8 87.24 1,768.2 88.42 1,793.8 89.69 1,752.1 87.61
2,734.5 2,755.4 2,657.3
Edible meat weight* 1,697.4 83.97 86.87 1,737.4 84.73 2,574.0 1,694.6 88.23 2,739.2 1,764.5 84.83 2,557.3 1,696.6
Live—Dressed. Dressed—Eviscerated. Eviscerated—Edible meat. * Dressed—Eviscerated-|-Giblets.
2,000 gms. Eviscerated 1,520.8 1,555.6 1,590.1 1,411.9 1,512.9
%
3,000 gms.
%
719.4
71.94
weight* 76.04 77.78 79.51 2,321.9 70.59 2,190.2 75.64 2,306.2
77.59 73.01 76.87
787.3 769.2 913.1 742.7 779.2
Eviscerated with giblets weight* 78.73 1,610.9 80.55 76.92 1,643.1 82.15 83.37 2,421.5 2,374.1 77.92 77.92 1,594.9 79.75 2,420.6
80.72 79.13 80.69
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
1,000
148
B. W. HEYWANG, H. R. BIRD AND M. G. VAVICH
accurate method of calculation of the various yields. The equations for the cockerels, pullets, cocks, and hens were similar enough so that over-all equations could be used on most occasions for both the young and mature birds of either sex. REFERENCE McNally, E. H., and N. H. Spicknall, 1949. Meat yield from live, dressed, and eviscerated Rhode Island Red males of broiler, fryer, and light roaster weights. Poultry Sci. 28: 562-567.
The Level of Protein in the Diet of Laying White Leghorns During Hot Weather 2 BURT W. HEYWANG, H. R. BIRD 1 AND M. G. VAVICH Agricultural Research Service, U. S. Department of Agriculture, Animal and Poultry Husbandry Research Branch, Glendale, Arizona, and Bellsville, Maryland, and Department of Nutrition, College of Agriculture, University of Arizona, Tucson, Arizona (Received for publication April 27, 1954)
T
HE National Research Council (1950) recommends that diets for laying chickens contain 15 percent protein. However, the feed intake of laying chickens decreases appreciably during periods of high environmental temperatures, such as during several months of the year in the region where the Southwest Poultry Experiment Station is located. Because this decrease in feed intake results in a decrease in the nutrients needed for egg production, it seemed possible that the level of protein in the diet of laying chickens should be higher during hot weather than during cool or moderate weather. Heywang (1947) reported the results of
1 Present address: Department of Poultry Husbandry, University of Wisconsin. 2 Arizona Agricultural Experiment Station Technical Paper No. 337.
several experiments in which the main object was to determine the effect of the dietary level of protein on the mortality rate among laying chickens during hot weather, with casein in their diets as the only protein concentrate. Egg production was a little higher when the protein level in the diets was 23.5-25.5 percent than when it was 15.5-18 percent, but those results do not seem indicative because the diets were not necessarily suitable for satisfactory egg production. Accordingly, two experiments were conducted at the Southwest Poultry Experiment Station, Glendale, Arizona to obtain information on the subject. One of these experiments was in progress during only hot weather, while the other was in progress during cool and moderate weather as well as hot weather. The data obtained in the experiments are presented and discussed in this paper.
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 10, 2015
While a number of different interrelations may be calculated between various dressing methods, those equations were computed which gave the relation after the smallest amount of manipulation of the carcasses, as live to dressed weights, dressed to eviscerated-body weights, and eviscerated-body to edible meat weights. The advantages of this are they have the smallest standard error of estimate of the several equations that could be calculated. Linear equations were found to give an