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An Empirical Test of Part-Record Selection for Egg Production
An Empirical Test of Part-Record Selection for Egg Production I. MICHAEL LERNER AND EVERETT R. DEMPSTER
University of California, Berkeley (Received for publication June 18, 19S6)
Calculations of this sort rest on a series of simplifications and assumptions, not all of which are entirely realistic (most of them have been discussed in some detail by Lerner, 19S0). It is, therefore, eminently desirable to subject the conclusions arrived in this manner to empirical verification. Hence, a test was designed in 1950 to compare results of selection on the two bases. It soon became apparent that significant differences between the alternative selection schemes could not be readily established under our particular circumstances without replication of lines or expansion of popula-
tion size. Since pressure of other current research precluded these procedures, the test was terminated after three years. Although the data available by then fell short of proving that the efficiency of part record selection is greater than that based on full records, they definitely pointed in such a direction, and are deemed to be of sufficient general interest to be presented here. There were several factors complicating simple comparisons between the results of the two selection schemes. Thus, the same material used in the test was also involved in an unrelated study on genotype-environment interaction (Lowry, Lerner and Taylor, 1956). Further, the year-to-year environmental fluctuations may have masked gains expected over the short period of the experiment. The highest annual hen-housed production average was, in fact, obtained from a group hatched in the very first year of the test. A contributing circumstance here may be the relatively high level of production of the flock studied; the question whether the population as a whole had reached a plateau in egg production could not be fully answered at the time the test was initiated (Dempster, Lerner and Lowry, 1952). Also to be mentioned is a succession of outbreaks of respiratory diseases previously unexperienced on our plant. Epidemics were diagnosed as being respectively due to atypical coryza (1949), Newcastle disease (1950), infectious bronchitis (1951), and avian encephalomyelitis (1953)—an impressive roll-call for a flock apparently free from all infection bar leu-
1349
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T?OLLOWING the general demonstration *- by Dickerson and Hazel (1944) of the significance of the average interval between generations in evaluating the relative merits of different selection schemes, Dempster and Lerner (1947) analyzed the theoretical expectations of gains from pullet and from hen selection for high annual egg production. They showed that combined family and individual selection based on records of lay to January 1 of spring-hatched pullets should lead to more rapid progress than similar improvement programs based on a full year's production record. In the former case females are mated for the first time when they are about a year old, while in the second instance the minimum interval between the hatching dates of dam and daughter is approximately two years. Maddison (19S4) made similar computations for the conditions prevailing in his flock at Wye College and arrived at basically the same conclusions.
1350
I. M. LERNER AND E. R. DEMPSTER
cosis and coccidiosis for seventeen years. Despite these difficulties, intra-year comparisons were fairly consistent. MATERIAL AND METHODS
The test proper was initiated in 1951, when the flock was divided into two subpopulations, designated respectively as the Pullet and the Hen lines. The Pullet line was established by making a selection of dams entirely from the 1950-hatched group of birds. The Hen line, in addition to utilizing as a base the group hatched in 1949, also included among the foundation dams birds hatched earlier and already progenytested. In 1952, the same population which was the base of the 1951 selection for the Pullet line was subjected to a completely independent selection to yield some of the Hen-line dams. Of the 47 birds thus chosen on their full record performance, 33 had
Downloaded from http://ps.oxfordjournals.org/ at U Colorado AMC Health Sciences Library on April 10, 2015
The University of California (Berkeley) flock of production-bred White Leghorns previously described by Lerner (1950) formed the object of study. The selection methods used from 1950 onwards departed from those discussed in detail by Lerner and Hazel (1947) in a number of ways. Thus, the proportion of progeny tested birds in matings was reduced in accordance with the findings of Dempster and Lerner (1947), and a selection index, incorporating the individual's production and that of the full-sister family average*, weighted in the manner shown by formula (29) in Lerner (1950), was introduced. In addition, extensive use of pullet breeding based on part-record selection was employed in producing the birds hatched in 1950. It may be parenthetically noted that after the end of the experiment under discussion progeny testing in this flock was stopped altogether, a move which, while lowering expected gains, makes comparisons of progress of different experimental populations easier and probably more reliable.
been among the 66 Pullet-line dams selected in the previous year on their part record indexes. Outside of these common female ancestors the two lines were reproductively isolated. The first selection of sires was made from the same base in the two sub-populations. Thereafter the male-selection schemes were identical in both lines, cockerels being chosen on the basis of part record indexes of their full sister families with an occasional use of repeat mating. On the dam side, in the initial selection a somewhat greater pressure was applied to the previously unmated birds of the Hen line than to those of the Pullet line to compensate for the half-generation lag. Hence, it is reasonable to assume that the Pullet line did not have an undue advantage in its starting base over the Hen line. The number of generations elapsed in the course of the test may be estimated by adding together the respective reciprocals of the average ages of the parents (intergeneration intervals) for the three years in each of the lines. In the pullet-bred population this sum was 2.80 (1.00, 0.89 and 0.91), and in the Hen line 1.79 (0.56, 0.63, 0.60). Presumably, the differences in performance between the lines are traceable to the difference between these two figures. Table 1 gives information on selection intensity. Under the heading Previously unmated in the Pullet line numbers of birds one year old selected on the basis of production to January 1 (about 9 months of age) are listed. In the Hen line the same heading relates to two-year old birds selected with respect to production to October 1 {i.e. approximately 18 months of age). The heading Previously mated refers to repeated matings whose value in all cases was judged by the performance of offspring to January 1. The proportion of birds selected for reproduction was, generally speaking, not dif-
1351
PART-RECORD SELECTION
TABLE I.—Comparative selection intensity Number of females from which selection was made
Number of sires
Year of
Line
Percent of base population actually represented by pullets banded in next generation
Percent of base population selected
Number of dams selected
Firstmated
Repeated
Previously unmated
Previously mated
Previously unmated
Previously mated
Previously unmated
Previously mated
Previously unmated
Previously mated
Percent of pullets banded from previously unmated dams
Pullet Hen
6 5
0 1
289 617
0 118
66 47
0 25
22.8 7.6
0 21.2
17.6 4.7
0 13.6
100 59
19S2
Pullet Hen
5 6
1 0
316 289
51 45
61 55
9 5
19.3 19.0
17.6 11.1
17.7 16.3
11.8 11.1
90 87
1953
Pullet Hen
7 6
0 1
444 316
62 52
56 57
17 12
12.6 18.0
27.4 23.0
11.9 16.8
24.1 21.2
80 88
ferent in the two lines. It is possible that the failure of some selected dams to produce female offspring surviving to banding time (about 3£ months of age) was somewhat higher in the Hen than in the Pullet line. However, this difference is not likely to be significant. In any case it would have led to a higher effective selection pressure in the Hen line, since, as it has been shown by Lerner and Dempster (1951), reproductive fitness and genotypic merit for egg production are positively correlated in this population. Hence, if anything, the Hen line was being favored over the Pullet line with respect to selection intensity. REPRODUCTIVE PERFORMANCE Table 2 shows the reproductive statistics for the dams selected, based on a hatching season of four weeks' duration with the approximate average hatching date of April TABLE 2.—A verage Eggs set of mating
Line
1951
reproductive
Percent fertile
1. The most notable fact emerging from this table is the relatively higher reproductive efficiency of the Pullet line. Over the three years of the test the average number of breeding birds needed to replace the flock was of the order of 20 percent lower in the Pullet than in the Hen line. In the former each breeding female produced six daughters surviving to i\ months of age as compared to five in the Hen line. Hence, it would have been possible to use only 16 percent of the population to reproduce it by pullet mating instead of the 20 percent necessary under hen mating. This, of course, would make higher selection differentials feasible in the former instance. The difference observed between the reproductive capacities of the two lines are indicative only, since not all the figures are strictly comparable. In particular, in the Pullet line some of the matings involved performance
{per dam
Percent fertiles hatched
selected)
Chicks hatched
Pullets banded
Firstmated dams
All dams
Firstmated dams
All dams
Firstmated dams
All dams
Firstmated dams
All dams
Firstmated dams
All dams
Pullet Hen
20.2 19.1
20.2 19.4
93.8 89.6
93.8 91.7
68.9 72.3
68.9 72.7
13.1 12.4
13.1 13.0
4.79 4.17
4.79 4.46
1952
Pullet Hen
21.2 22.0
20.9 21.8
97.8 93.2
96.7 93.7
83.2 66.4
82.2 67.3
17.3 13.6
16.6 13.8
6.57 4.73
6.34 4.98
1953
Pullet Hen
18.7 18.9
18.4 18.5
93.4 91.0
94.0 91.4
80.0 73.8
78.7 65.4
14.0 12.7
13.6 12.1
6.84 5.91
6.63 5.56
Total
Pullet Hen
20.1 20.0
19.8 19.8
95.1 91.5
94.9 92.3
77.2 70.5
76.8 70.5
14.7 12.9
14.4 12.9
6.01 4.99
5.95 5.00
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1951
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I. M. LERNER AND E. R. DEMPSTER
whereas here all of the material available is utilized. Only the floor-maintained population from the 1950 hatched flock was considered in the original selection. In subsequent years birds from both floor and cage were used (with appropriate adjustment in the selection indexes when needed). When pullets were selected from the cage population, they were inseminated artificially. There seemed to be no significant differences in the reproductive performance of floor and cage birds, yet with the limited data at hand, it appears to be safest not to draw any conclusions on this point. It is noted here merely to emphasize the gross order of accuracy in the comparison of reproductive efficiency of the Pullet and the Hen lines. EGG PRODUCTION RESULTS Table 3 presents a summary of the egg production performance of the birds in the two lines under both managements. With a single exception (18-months hen-housed production in the 1953 floor flock) the Pullet line exceeded the Hen line in the average hen-housed and survivors' production. On the other hand, with respect to viability the Hen line was superior. The exception
TABLE 3.—Production performance Hen-housed production
Egg weight
to J a n . 1 (approx. 9 mos. of age), eggs
to Oct. 1 (approx. 18 mos. of age), eggs.
Survivors* production to Oct. 1, eggs
Percent mortality to Oct. 1
in Nov. gms.
in Apr. gms.
Year of hatch
Management
Line
Number of pullets
1951
Floor
Pullet Hen
158 166
18.1 16.3
80.0 73.2
233.7 229.0
256.6 249.7
17.1 12.7
51.0 51.3
57.5 58.6
Cage
Pullet Hen
158 150
18.1 16.2
60.7 57.5
210.6 204.6
227.8 212.9
12.0 8.0
53.2 53.3
60.1 60.9
Floor
Pullet Hen
252 172
20.6 17.8
78.7 73.3
218.6 217.1
251.9 240.7
31.0 21.5
50.2 50.5
56.2 56.9
Cage
Pullet Hen
192 127
20.6 17.5
76.8 67.0
231.2 211.4
254.7 219.8
15.6 9.4
51.9 51.8
58.2 58.5
Floor
Pullet Hen
318 240
22.8 17.9
86.4 83.1
214.8 225.2
245.0 242.3
25.8 12.9
49.9 49.4
55.6 55.7
Cage
Pullet Hen
176 144
22.8 17.7
83.5 73.0
229.3 219.8
244.7 233.0
14.8 13.2
51.2 51.6
57.4 57.7
1952
1953
Mean inbreeding coefficient
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artificial insemination. This practice was dictated by an aspect of management which must be noted here. As it has already been stated, the population in the present study was also used for an investigation of genotype-environment interaction. The purpose of that experiment was to determine the magnitude of the genetic correlation between the performance of birds maintained in laying houses (floor management) and in individual cages. Accordingly, in each of the three generations of the test, families of full-sisters were systematically divided into cage and floor groups. The analysis of the cage-floor experiment (Lowry, Lerner and Taylor, 1956) showed that no interaction between genotype and management was detectable in this material. However, since mean values for some traits did differ between the cage and the floor groups, the data for them will be presented separately here. It may be noted that the numbers of birds given in the cited report of the cagefloor comparison differ from those considered in the present instance. The reason for the discrepancy lies in the fact that in the former analysis the data were limited to those for an equal number of full sisters in each family under the two managements,
PART-RECORD SELECTION
The question may be properly asked whether the four-fold difference in the increase of the average inbreeding coefficient is of significance in evaluating the results obtained. Lerner and Hazel (1947) have investigated in a limited way a question of relevance to this point. In computing the intra-generation regression of egg production on inbreeding for four years in this flock, they obtained three negative values. Since only one of these was significant they failed to attach any importance to their finding. However, the problem is now being studied in a more thorough fashion by our colleague, Dr. Gordon Tebb. Though his investigation has not yet been completed, it appears almost certain from the results to date, that higher inbreeding coefficients within a generation show a significant association with lowered performance. Should this, indeed, be the case, an explanation why the Pullet line did not show a cumulative advantage over the Hen line, as might have been expected on theoretical grounds, would be forthcoming. Similarly the higher mortality of the Pullet line might be associated with its higher inbreeding. It is not too profiitable at this stage to speculate at length on this matter. The material available does not readily lend itself to statistical analyses of high power. Perhaps, it may suffice here to express the opinion that it is the difference between the coefficients of inbreeding of the two lines which accounts not only for the absence of a cumulative advantage but, in general, for the slightness of margin of superiority of the Pullet-bred population. More light on the matter will, no doubt, be available at the completion of Tebb's study. It may be of interest to note that after it was decided to abandon the test, the two sub-flocks were reconstituted into a single population. This process was carried out over a period of two years. In 1954 the
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in the ranking of the two lines for egg production averages noted above is without doubt due to the fact that mortality in the floor flock of the Pullet line in 1953 was double that of the Hen line. Egg weight also tended to be somewhat higher in the Hen line but the difference was not a systematic one. Indeed, the emphasis laid on this character in selection was somewhat variable and directed only to maintain an average 2-ounce (56.7 grams) egg in April. As it may be seen this purpose was reasonably well met. One rather important feature of Table 3 needs to be brought into strong relief here. It refers to the coefficient of inbreeding of the two lines. In the Hen line the first mated sires came from a later generation than did the dams, while in the Pullet line the males and females mated were contemporary and hence somewhat more closely related. As a result the inbreeding of the Pullet line rose from the value of 15.7 percent in 1950 to 22.8 in 1953, a difference of 7.1 percent (2.7% per year). The inbreeding of the Hen line in the same period of time increased from 15.7 to 17.8 percent, or only 0.7 percent per year. It may be argued that since the dams of the 1951 Hen-line flock were hatched in 1949, the change in inbreeding in this line should be computed from that year. As it happens, this procedure would not lead to very different results; the F value of the 1949 flock was 16.1, so that an even lower rate of increase would be arrived at by this method than by the other one used. The difference in the rate of inbreeding between the two lines was inherent in the design of the experiment on the restricted scale on which we were operating. In commercial practice, of course, pullet breeding does not have to be confined to such small populations, and rates of inbreeding of the magnitude reported here may be avoided.
1353
1354
I. M. LEENER AND E. R. TABLE 4.--Production
performance of reconstitutedflock(underfloormanagement only)
of hatch
Line
Number of pullets
Mean inbreeding coefficient
1954
Pullet "Hen" P9XHc? H9XPc? All
281 323 72 52 728
22.7 18.1 17.7 18.3 19.9
Hen-housed production to J a n . 1, eggs
to Oct. 1, eggs
Survivors' production to Oct. 1, eggs
85.5 83.9 81.1 75.8 83.6
211.8 221.2 200.7 220.5 215.5
254.0 258.1 253.4 253.6 255.8
TABLE 5.—Hen-housed averages to December 1 of offspring of sires used in line crosses in 1954 Offspring from Pullet-line dams
Offspring from Hen-line dams
Number
Production, eggs
Number
!«
Sire number
Pullet
K18 K22 Total
33 22 55
75.2 54.0 66.7
23 29 52
75.0 50.8 61.5
Hen
Kl K9 Total
30 42 72
60.2 66.1 63.6
30 24 54
59.0 67.2 62.7
Egg weight
Percent mortality to Oct. 1
in Nov. gms.
in Apr. gms.
28.5 24.5 34.7 19.2 26.6
50.8 49.5 51.2 51.0 50.3
56.7 56.0 57.0 56.5 56.4
ment. Further progress of selection for egg production continued from this base, the results obtained from suspending selection, and other phases of this long term experiment, including attempts at artificial induction of new polygenic variation, will be reported upon in due course of time. CONCLUSIONS AND SUMMARY The hypothesis previously arrived at on theoretical grounds, that combined family and individual selection for egg production based on breeding from pullets is a more efficient procedure than one based on breeding from yearling hens, has been put to a limited test. Due to a number of complications (in particular, those produced by the fact that the population under test may be plateaued, by outbreaks of respiratory diseases, by small numbers in the populations used and a consequent difference between the flocks tested in the degree of inbreeding) the hypothesis cannot be considered unequivocally proven. However, nearly all of the data obtained tend to favor it. Both with respect to reproduction and to egg number (on either the hen-housed or the survivors' basis) the pullet-bred line was superior to the hen-bred line under either floor or individual cage management. Laying house mortality, however, was lower in the hen-bred group. It is, hence, possible that a qualification calling for a higher relative weight to be given to viability in pulletas against hen-breeding selection schemes is needed. This point cannot be established with certainty since in the material here reported differences in mortality may not
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pullet-bred population was continued as before, while in the Hen line selection was made both from the 1952-hatched yearlings (previously unmated) and from the 1953hatched pullets. Thus selection pressure was practically doubled, a fact possibly reflected in the performance of the 1954 generation of this line shown in Table 4. The term "Hen" is given there in quotation marks, since the birds whose average performance is shown were in part descended from pullets. In the same year a test was made to determine whether the isolation between the two sub-flocks has possibly led to manifestations of heterosis in crosses between them. From the figures shown in Table 4, there is no reason to suspect that such was the case. This conclusion is borne out by the part-production figures shown in Table 5. In view of the lack of difference between the performance of intra- and inter-line offspring of each of the four sires used in the test, a fuller analysis of these data was not considered to be necessary. The 1955 mating plans were hence based on a single pullet-bred population under floor manage-
Sire line
DEMPSTER
PART-RECORD
be independent from those in inbreeding coefficients of the lines compared. In general, it can be stated that the results obtained are not contradictory to the theoretical conclusions, and do suggest that pullet breeding is a practical and desirable procedure in programs of combined family and individual selection for egg production.
1355
ness of selection on progeny testing performance as a supplement to earlier culling in livestock. J. Agr. Res. 69: 459-476. Lerner, I. M., 19S0. Population Genetics and Animal Improvement. XVIII + 342 pp. Cambridge U. Press. Lerner, I. M., and E. R. Dempster, 1951. Attenuation of genetic progress under continuous selection in poultry. Heredity, 5 : 75-94. Lerner, I. M., and L. N. Hazel. 1947. Population genetics of a poultry flock under artificial selection. Genetics, 32: 325-339. Lowry, D. C , I. M. Lerner and L. W. Taylor, 1956. Intra-fiock genetic merit under floor and cage management. Poultry Sci. 35: 1034-1043. Maddison, A. E., 1954. The use of partial records in poultry selection. Brit. Soc. Animal Prod., Proc, 1954: 109-115.
Biological Studies on Nicarbazin, a New Anticoccidial Agent W.
H. OTT, S. KUNA, C. C. PORTER AND A. C. CUCKLER Merck Institute for Therapeutic Research, Rahway, New Jersey AND D.
E.
FOGG
Merck Sharp & Dohme Research Laboratories, Rahway, New Jersey (Received for publication June 18, 1956)
N
ICARBAZIN, an equimolecular complex of 4,4'-dinitrocarbanilide and 2hydroxy-4,6-dimethylpyrimidine, has been studied extensively and found to be an effective anticoccidial agent for chickens. This paper summarizes the presently available information on this anticoccidial agent. CHEMICAL NATURE OF NICARBAZIN
During the investigation of the therapeutic potentialities of arylureas, Cuckler, Malanga, Basso and O'Neill (1955) observed that molecular complexes of certain substituted carbanilides possessed antiparasitic activity. The complex formed with 4,4'-dinitrocarbanilide (DNC) and 2-hy-
droxy-4,6-dimethylpyrimidine (HDP) was the most effective anticoccidial compound (Figure 1). In addition to HDP, several other compounds form equimolecular complexes with DNC. These include 2-hydroxy pyrimidine, 3-amino-as-triazine, 2-hydroxypyridine, 2mercapto-4,6-dimethyl pyrimidine, formamide, dimethylacetamide, dimethylformamide, tetramethylurea, acetylpiperidine, and the hydrochlorides of pyridine and trimethylamine. Although the complexes formed with DNC and these various compounds had demonstrable anticoccidial activity, none was more potent than nicarbazin. Furthermore, several structural ana-
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REFERENCES Dempster, E. R., and I. M. Lerner, 1947. The optimum structure of breeding flocks. Genetics, 32: S5S-579. Dempster, E. R., I. M. Lerner and D. C. Lowry, 1952. Continuous selection for egg production in poultry. Genetics, 37: 693-708. Dickerson, G. E., and L. N. Hazel, 1944. Effective-
SELECTION
University of California, Berkeley (Received for publication June 18, 19S6)
Calculations of this sort rest on a series of simplifications and assumptions, not all of which are entirely realistic (most of them have been discussed in some detail by Lerner, 19S0). It is, therefore, eminently desirable to subject the conclusions arrived in this manner to empirical verification. Hence, a test was designed in 1950 to compare results of selection on the two bases. It soon became apparent that significant differences between the alternative selection schemes could not be readily established under our particular circumstances without replication of lines or expansion of popula-
tion size. Since pressure of other current research precluded these procedures, the test was terminated after three years. Although the data available by then fell short of proving that the efficiency of part record selection is greater than that based on full records, they definitely pointed in such a direction, and are deemed to be of sufficient general interest to be presented here. There were several factors complicating simple comparisons between the results of the two selection schemes. Thus, the same material used in the test was also involved in an unrelated study on genotype-environment interaction (Lowry, Lerner and Taylor, 1956). Further, the year-to-year environmental fluctuations may have masked gains expected over the short period of the experiment. The highest annual hen-housed production average was, in fact, obtained from a group hatched in the very first year of the test. A contributing circumstance here may be the relatively high level of production of the flock studied; the question whether the population as a whole had reached a plateau in egg production could not be fully answered at the time the test was initiated (Dempster, Lerner and Lowry, 1952). Also to be mentioned is a succession of outbreaks of respiratory diseases previously unexperienced on our plant. Epidemics were diagnosed as being respectively due to atypical coryza (1949), Newcastle disease (1950), infectious bronchitis (1951), and avian encephalomyelitis (1953)—an impressive roll-call for a flock apparently free from all infection bar leu-
1349
Downloaded from http://ps.oxfordjournals.org/ at U Colorado AMC Health Sciences Library on April 10, 2015
T?OLLOWING the general demonstration *- by Dickerson and Hazel (1944) of the significance of the average interval between generations in evaluating the relative merits of different selection schemes, Dempster and Lerner (1947) analyzed the theoretical expectations of gains from pullet and from hen selection for high annual egg production. They showed that combined family and individual selection based on records of lay to January 1 of spring-hatched pullets should lead to more rapid progress than similar improvement programs based on a full year's production record. In the former case females are mated for the first time when they are about a year old, while in the second instance the minimum interval between the hatching dates of dam and daughter is approximately two years. Maddison (19S4) made similar computations for the conditions prevailing in his flock at Wye College and arrived at basically the same conclusions.
1350
I. M. LERNER AND E. R. DEMPSTER
cosis and coccidiosis for seventeen years. Despite these difficulties, intra-year comparisons were fairly consistent. MATERIAL AND METHODS
The test proper was initiated in 1951, when the flock was divided into two subpopulations, designated respectively as the Pullet and the Hen lines. The Pullet line was established by making a selection of dams entirely from the 1950-hatched group of birds. The Hen line, in addition to utilizing as a base the group hatched in 1949, also included among the foundation dams birds hatched earlier and already progenytested. In 1952, the same population which was the base of the 1951 selection for the Pullet line was subjected to a completely independent selection to yield some of the Hen-line dams. Of the 47 birds thus chosen on their full record performance, 33 had
Downloaded from http://ps.oxfordjournals.org/ at U Colorado AMC Health Sciences Library on April 10, 2015
The University of California (Berkeley) flock of production-bred White Leghorns previously described by Lerner (1950) formed the object of study. The selection methods used from 1950 onwards departed from those discussed in detail by Lerner and Hazel (1947) in a number of ways. Thus, the proportion of progeny tested birds in matings was reduced in accordance with the findings of Dempster and Lerner (1947), and a selection index, incorporating the individual's production and that of the full-sister family average*, weighted in the manner shown by formula (29) in Lerner (1950), was introduced. In addition, extensive use of pullet breeding based on part-record selection was employed in producing the birds hatched in 1950. It may be parenthetically noted that after the end of the experiment under discussion progeny testing in this flock was stopped altogether, a move which, while lowering expected gains, makes comparisons of progress of different experimental populations easier and probably more reliable.
been among the 66 Pullet-line dams selected in the previous year on their part record indexes. Outside of these common female ancestors the two lines were reproductively isolated. The first selection of sires was made from the same base in the two sub-populations. Thereafter the male-selection schemes were identical in both lines, cockerels being chosen on the basis of part record indexes of their full sister families with an occasional use of repeat mating. On the dam side, in the initial selection a somewhat greater pressure was applied to the previously unmated birds of the Hen line than to those of the Pullet line to compensate for the half-generation lag. Hence, it is reasonable to assume that the Pullet line did not have an undue advantage in its starting base over the Hen line. The number of generations elapsed in the course of the test may be estimated by adding together the respective reciprocals of the average ages of the parents (intergeneration intervals) for the three years in each of the lines. In the pullet-bred population this sum was 2.80 (1.00, 0.89 and 0.91), and in the Hen line 1.79 (0.56, 0.63, 0.60). Presumably, the differences in performance between the lines are traceable to the difference between these two figures. Table 1 gives information on selection intensity. Under the heading Previously unmated in the Pullet line numbers of birds one year old selected on the basis of production to January 1 (about 9 months of age) are listed. In the Hen line the same heading relates to two-year old birds selected with respect to production to October 1 {i.e. approximately 18 months of age). The heading Previously mated refers to repeated matings whose value in all cases was judged by the performance of offspring to January 1. The proportion of birds selected for reproduction was, generally speaking, not dif-
1351
PART-RECORD SELECTION
TABLE I.—Comparative selection intensity Number of females from which selection was made
Number of sires
Year of
Line
Percent of base population actually represented by pullets banded in next generation
Percent of base population selected
Number of dams selected
Firstmated
Repeated
Previously unmated
Previously mated
Previously unmated
Previously mated
Previously unmated
Previously mated
Previously unmated
Previously mated
Percent of pullets banded from previously unmated dams
Pullet Hen
6 5
0 1
289 617
0 118
66 47
0 25
22.8 7.6
0 21.2
17.6 4.7
0 13.6
100 59
19S2
Pullet Hen
5 6
1 0
316 289
51 45
61 55
9 5
19.3 19.0
17.6 11.1
17.7 16.3
11.8 11.1
90 87
1953
Pullet Hen
7 6
0 1
444 316
62 52
56 57
17 12
12.6 18.0
27.4 23.0
11.9 16.8
24.1 21.2
80 88
ferent in the two lines. It is possible that the failure of some selected dams to produce female offspring surviving to banding time (about 3£ months of age) was somewhat higher in the Hen than in the Pullet line. However, this difference is not likely to be significant. In any case it would have led to a higher effective selection pressure in the Hen line, since, as it has been shown by Lerner and Dempster (1951), reproductive fitness and genotypic merit for egg production are positively correlated in this population. Hence, if anything, the Hen line was being favored over the Pullet line with respect to selection intensity. REPRODUCTIVE PERFORMANCE Table 2 shows the reproductive statistics for the dams selected, based on a hatching season of four weeks' duration with the approximate average hatching date of April TABLE 2.—A verage Eggs set of mating
Line
1951
reproductive
Percent fertile
1. The most notable fact emerging from this table is the relatively higher reproductive efficiency of the Pullet line. Over the three years of the test the average number of breeding birds needed to replace the flock was of the order of 20 percent lower in the Pullet than in the Hen line. In the former each breeding female produced six daughters surviving to i\ months of age as compared to five in the Hen line. Hence, it would have been possible to use only 16 percent of the population to reproduce it by pullet mating instead of the 20 percent necessary under hen mating. This, of course, would make higher selection differentials feasible in the former instance. The difference observed between the reproductive capacities of the two lines are indicative only, since not all the figures are strictly comparable. In particular, in the Pullet line some of the matings involved performance
{per dam
Percent fertiles hatched
selected)
Chicks hatched
Pullets banded
Firstmated dams
All dams
Firstmated dams
All dams
Firstmated dams
All dams
Firstmated dams
All dams
Firstmated dams
All dams
Pullet Hen
20.2 19.1
20.2 19.4
93.8 89.6
93.8 91.7
68.9 72.3
68.9 72.7
13.1 12.4
13.1 13.0
4.79 4.17
4.79 4.46
1952
Pullet Hen
21.2 22.0
20.9 21.8
97.8 93.2
96.7 93.7
83.2 66.4
82.2 67.3
17.3 13.6
16.6 13.8
6.57 4.73
6.34 4.98
1953
Pullet Hen
18.7 18.9
18.4 18.5
93.4 91.0
94.0 91.4
80.0 73.8
78.7 65.4
14.0 12.7
13.6 12.1
6.84 5.91
6.63 5.56
Total
Pullet Hen
20.1 20.0
19.8 19.8
95.1 91.5
94.9 92.3
77.2 70.5
76.8 70.5
14.7 12.9
14.4 12.9
6.01 4.99
5.95 5.00
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1951
1352
I. M. LERNER AND E. R. DEMPSTER
whereas here all of the material available is utilized. Only the floor-maintained population from the 1950 hatched flock was considered in the original selection. In subsequent years birds from both floor and cage were used (with appropriate adjustment in the selection indexes when needed). When pullets were selected from the cage population, they were inseminated artificially. There seemed to be no significant differences in the reproductive performance of floor and cage birds, yet with the limited data at hand, it appears to be safest not to draw any conclusions on this point. It is noted here merely to emphasize the gross order of accuracy in the comparison of reproductive efficiency of the Pullet and the Hen lines. EGG PRODUCTION RESULTS Table 3 presents a summary of the egg production performance of the birds in the two lines under both managements. With a single exception (18-months hen-housed production in the 1953 floor flock) the Pullet line exceeded the Hen line in the average hen-housed and survivors' production. On the other hand, with respect to viability the Hen line was superior. The exception
TABLE 3.—Production performance Hen-housed production
Egg weight
to J a n . 1 (approx. 9 mos. of age), eggs
to Oct. 1 (approx. 18 mos. of age), eggs.
Survivors* production to Oct. 1, eggs
Percent mortality to Oct. 1
in Nov. gms.
in Apr. gms.
Year of hatch
Management
Line
Number of pullets
1951
Floor
Pullet Hen
158 166
18.1 16.3
80.0 73.2
233.7 229.0
256.6 249.7
17.1 12.7
51.0 51.3
57.5 58.6
Cage
Pullet Hen
158 150
18.1 16.2
60.7 57.5
210.6 204.6
227.8 212.9
12.0 8.0
53.2 53.3
60.1 60.9
Floor
Pullet Hen
252 172
20.6 17.8
78.7 73.3
218.6 217.1
251.9 240.7
31.0 21.5
50.2 50.5
56.2 56.9
Cage
Pullet Hen
192 127
20.6 17.5
76.8 67.0
231.2 211.4
254.7 219.8
15.6 9.4
51.9 51.8
58.2 58.5
Floor
Pullet Hen
318 240
22.8 17.9
86.4 83.1
214.8 225.2
245.0 242.3
25.8 12.9
49.9 49.4
55.6 55.7
Cage
Pullet Hen
176 144
22.8 17.7
83.5 73.0
229.3 219.8
244.7 233.0
14.8 13.2
51.2 51.6
57.4 57.7
1952
1953
Mean inbreeding coefficient
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artificial insemination. This practice was dictated by an aspect of management which must be noted here. As it has already been stated, the population in the present study was also used for an investigation of genotype-environment interaction. The purpose of that experiment was to determine the magnitude of the genetic correlation between the performance of birds maintained in laying houses (floor management) and in individual cages. Accordingly, in each of the three generations of the test, families of full-sisters were systematically divided into cage and floor groups. The analysis of the cage-floor experiment (Lowry, Lerner and Taylor, 1956) showed that no interaction between genotype and management was detectable in this material. However, since mean values for some traits did differ between the cage and the floor groups, the data for them will be presented separately here. It may be noted that the numbers of birds given in the cited report of the cagefloor comparison differ from those considered in the present instance. The reason for the discrepancy lies in the fact that in the former analysis the data were limited to those for an equal number of full sisters in each family under the two managements,
PART-RECORD SELECTION
The question may be properly asked whether the four-fold difference in the increase of the average inbreeding coefficient is of significance in evaluating the results obtained. Lerner and Hazel (1947) have investigated in a limited way a question of relevance to this point. In computing the intra-generation regression of egg production on inbreeding for four years in this flock, they obtained three negative values. Since only one of these was significant they failed to attach any importance to their finding. However, the problem is now being studied in a more thorough fashion by our colleague, Dr. Gordon Tebb. Though his investigation has not yet been completed, it appears almost certain from the results to date, that higher inbreeding coefficients within a generation show a significant association with lowered performance. Should this, indeed, be the case, an explanation why the Pullet line did not show a cumulative advantage over the Hen line, as might have been expected on theoretical grounds, would be forthcoming. Similarly the higher mortality of the Pullet line might be associated with its higher inbreeding. It is not too profiitable at this stage to speculate at length on this matter. The material available does not readily lend itself to statistical analyses of high power. Perhaps, it may suffice here to express the opinion that it is the difference between the coefficients of inbreeding of the two lines which accounts not only for the absence of a cumulative advantage but, in general, for the slightness of margin of superiority of the Pullet-bred population. More light on the matter will, no doubt, be available at the completion of Tebb's study. It may be of interest to note that after it was decided to abandon the test, the two sub-flocks were reconstituted into a single population. This process was carried out over a period of two years. In 1954 the
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in the ranking of the two lines for egg production averages noted above is without doubt due to the fact that mortality in the floor flock of the Pullet line in 1953 was double that of the Hen line. Egg weight also tended to be somewhat higher in the Hen line but the difference was not a systematic one. Indeed, the emphasis laid on this character in selection was somewhat variable and directed only to maintain an average 2-ounce (56.7 grams) egg in April. As it may be seen this purpose was reasonably well met. One rather important feature of Table 3 needs to be brought into strong relief here. It refers to the coefficient of inbreeding of the two lines. In the Hen line the first mated sires came from a later generation than did the dams, while in the Pullet line the males and females mated were contemporary and hence somewhat more closely related. As a result the inbreeding of the Pullet line rose from the value of 15.7 percent in 1950 to 22.8 in 1953, a difference of 7.1 percent (2.7% per year). The inbreeding of the Hen line in the same period of time increased from 15.7 to 17.8 percent, or only 0.7 percent per year. It may be argued that since the dams of the 1951 Hen-line flock were hatched in 1949, the change in inbreeding in this line should be computed from that year. As it happens, this procedure would not lead to very different results; the F value of the 1949 flock was 16.1, so that an even lower rate of increase would be arrived at by this method than by the other one used. The difference in the rate of inbreeding between the two lines was inherent in the design of the experiment on the restricted scale on which we were operating. In commercial practice, of course, pullet breeding does not have to be confined to such small populations, and rates of inbreeding of the magnitude reported here may be avoided.
1353
1354
I. M. LEENER AND E. R. TABLE 4.--Production
performance of reconstitutedflock(underfloormanagement only)
of hatch
Line
Number of pullets
Mean inbreeding coefficient
1954
Pullet "Hen" P9XHc? H9XPc? All
281 323 72 52 728
22.7 18.1 17.7 18.3 19.9
Hen-housed production to J a n . 1, eggs
to Oct. 1, eggs
Survivors' production to Oct. 1, eggs
85.5 83.9 81.1 75.8 83.6
211.8 221.2 200.7 220.5 215.5
254.0 258.1 253.4 253.6 255.8
TABLE 5.—Hen-housed averages to December 1 of offspring of sires used in line crosses in 1954 Offspring from Pullet-line dams
Offspring from Hen-line dams
Number
Production, eggs
Number
!«
Sire number
Pullet
K18 K22 Total
33 22 55
75.2 54.0 66.7
23 29 52
75.0 50.8 61.5
Hen
Kl K9 Total
30 42 72
60.2 66.1 63.6
30 24 54
59.0 67.2 62.7
Egg weight
Percent mortality to Oct. 1
in Nov. gms.
in Apr. gms.
28.5 24.5 34.7 19.2 26.6
50.8 49.5 51.2 51.0 50.3
56.7 56.0 57.0 56.5 56.4
ment. Further progress of selection for egg production continued from this base, the results obtained from suspending selection, and other phases of this long term experiment, including attempts at artificial induction of new polygenic variation, will be reported upon in due course of time. CONCLUSIONS AND SUMMARY The hypothesis previously arrived at on theoretical grounds, that combined family and individual selection for egg production based on breeding from pullets is a more efficient procedure than one based on breeding from yearling hens, has been put to a limited test. Due to a number of complications (in particular, those produced by the fact that the population under test may be plateaued, by outbreaks of respiratory diseases, by small numbers in the populations used and a consequent difference between the flocks tested in the degree of inbreeding) the hypothesis cannot be considered unequivocally proven. However, nearly all of the data obtained tend to favor it. Both with respect to reproduction and to egg number (on either the hen-housed or the survivors' basis) the pullet-bred line was superior to the hen-bred line under either floor or individual cage management. Laying house mortality, however, was lower in the hen-bred group. It is, hence, possible that a qualification calling for a higher relative weight to be given to viability in pulletas against hen-breeding selection schemes is needed. This point cannot be established with certainty since in the material here reported differences in mortality may not
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pullet-bred population was continued as before, while in the Hen line selection was made both from the 1952-hatched yearlings (previously unmated) and from the 1953hatched pullets. Thus selection pressure was practically doubled, a fact possibly reflected in the performance of the 1954 generation of this line shown in Table 4. The term "Hen" is given there in quotation marks, since the birds whose average performance is shown were in part descended from pullets. In the same year a test was made to determine whether the isolation between the two sub-flocks has possibly led to manifestations of heterosis in crosses between them. From the figures shown in Table 4, there is no reason to suspect that such was the case. This conclusion is borne out by the part-production figures shown in Table 5. In view of the lack of difference between the performance of intra- and inter-line offspring of each of the four sires used in the test, a fuller analysis of these data was not considered to be necessary. The 1955 mating plans were hence based on a single pullet-bred population under floor manage-
Sire line
DEMPSTER
PART-RECORD
be independent from those in inbreeding coefficients of the lines compared. In general, it can be stated that the results obtained are not contradictory to the theoretical conclusions, and do suggest that pullet breeding is a practical and desirable procedure in programs of combined family and individual selection for egg production.
1355
ness of selection on progeny testing performance as a supplement to earlier culling in livestock. J. Agr. Res. 69: 459-476. Lerner, I. M., 19S0. Population Genetics and Animal Improvement. XVIII + 342 pp. Cambridge U. Press. Lerner, I. M., and E. R. Dempster, 1951. Attenuation of genetic progress under continuous selection in poultry. Heredity, 5 : 75-94. Lerner, I. M., and L. N. Hazel. 1947. Population genetics of a poultry flock under artificial selection. Genetics, 32: 325-339. Lowry, D. C , I. M. Lerner and L. W. Taylor, 1956. Intra-fiock genetic merit under floor and cage management. Poultry Sci. 35: 1034-1043. Maddison, A. E., 1954. The use of partial records in poultry selection. Brit. Soc. Animal Prod., Proc, 1954: 109-115.
Biological Studies on Nicarbazin, a New Anticoccidial Agent W.
H. OTT, S. KUNA, C. C. PORTER AND A. C. CUCKLER Merck Institute for Therapeutic Research, Rahway, New Jersey AND D.
E.
FOGG
Merck Sharp & Dohme Research Laboratories, Rahway, New Jersey (Received for publication June 18, 1956)
N
ICARBAZIN, an equimolecular complex of 4,4'-dinitrocarbanilide and 2hydroxy-4,6-dimethylpyrimidine, has been studied extensively and found to be an effective anticoccidial agent for chickens. This paper summarizes the presently available information on this anticoccidial agent. CHEMICAL NATURE OF NICARBAZIN
During the investigation of the therapeutic potentialities of arylureas, Cuckler, Malanga, Basso and O'Neill (1955) observed that molecular complexes of certain substituted carbanilides possessed antiparasitic activity. The complex formed with 4,4'-dinitrocarbanilide (DNC) and 2-hy-
droxy-4,6-dimethylpyrimidine (HDP) was the most effective anticoccidial compound (Figure 1). In addition to HDP, several other compounds form equimolecular complexes with DNC. These include 2-hydroxy pyrimidine, 3-amino-as-triazine, 2-hydroxypyridine, 2mercapto-4,6-dimethyl pyrimidine, formamide, dimethylacetamide, dimethylformamide, tetramethylurea, acetylpiperidine, and the hydrochlorides of pyridine and trimethylamine. Although the complexes formed with DNC and these various compounds had demonstrable anticoccidial activity, none was more potent than nicarbazin. Furthermore, several structural ana-
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REFERENCES Dempster, E. R., and I. M. Lerner, 1947. The optimum structure of breeding flocks. Genetics, 32: S5S-579. Dempster, E. R., I. M. Lerner and D. C. Lowry, 1952. Continuous selection for egg production in poultry. Genetics, 37: 693-708. Dickerson, G. E., and L. N. Hazel, 1944. Effective-
SELECTION