THE GARDEN AiND FIELD. 



July, 1913^ 



Report of the M»if\e E^xperiment. 



By Dr. Raymond Pearl. 



(Continued from Mav Issue). 



From these tables (published in 

 the May issue, lid. G. & F.) the 

 following matters are to be 

 noted : — 



1. The percentage of infertile 

 eggs is distinctly hig-'h, being r9 

 per cent, in one case and ib per 

 cent in the other. This, however, 

 does not mean, as might at first 

 thought be supposed that there is 

 some weakness on the part of the 

 males or females bred. As a mat- 

 ter of fact the explanation of this 

 poor record of activity is that 

 when the pens were mated up 

 earl}- in February no interval of 

 time was allowed for the estab 

 lishment of fertility before begin- 

 ning to Save eggs for hatching. 

 That is to say, the eggs were 

 saved and, incubated from these 

 breeding pens on the very same 

 day that the male bicd was put m 

 the pen, and in a few instances it 

 is probable that eggs were actual- 

 ly included from hens which had 

 never, been with a male bird at 

 all. Kvery practical iJoultryman 

 knows that on the average it 

 takes from 6 to lo days to estab- 

 lish good fertility in eggs after 

 b rds are mated together. As a 

 result of this incubating of the 

 eggs taken from the time that 

 the male and female birds were 

 put together the record of fertility 

 suffers a hea\y handicap. Actuail}' 

 after fertility was once established 

 (that is, alter the male bird had 

 been in the pen about lo days) 

 the average percentage of infertile 

 eggs for the remainder of the sea- 

 son was about that which is con- 

 sidered normal in the work of this 

 station. This figure is on the 

 average about lo per cent, of the 

 eggs inlertile. 



The reader may be disposed to 

 wonder wh'- eggs which were prac- 

 tically- certain tip be infertile were 

 incubated. The reason was pri- 

 inarilv that it was de.sired to get 

 just as many chicks as possible 

 hatched April ist or within a few 

 days of that time. Kxperience has 

 shown that, under the environ- 

 mental conditions which obtain 

 here, that time is the best to 

 hatch chickens which are to be 

 used in fecundity work. Such birds 

 came into laying at the proper 

 time without eithi r forcing or re- 

 tarding. Now it is a fact thai 

 while, cm the average, it takes 

 Jrom 6 to lo days to get fertility 

 well established after a mating is 

 made, yet there are individuals in 



which the very next egg laid after 

 the first copulation will be fertile. 

 Because of this consideration all 

 possible eggs were saved from the 

 beginning of the matings, with the 

 certain Knowledge that while the 

 relative or percentage fertility of 

 these early eggs would be low, yet 

 absolutely a few chicks would be 

 obtained. The desire to get these 

 chicks far outweighed, any idea of 

 making a maximum record of fer- 

 tility of eggs, the latter, in fact, 

 not entering into consideration at 

 all. 



2. The hatching quality of the 

 eggs as indicated by the per cent, 

 of fertile eggs hatched is again 

 somewhat below what may be con- 

 sidered normal for the Maine Sta- 

 tion stock at the present time. 

 With large numbers of eggs the 

 normal hatching percentage of fer- 

 tile eggs is on the average a little 

 over 6o, taking the whole season 

 through. Toward the last ol the 

 mating season (the month of May) 

 the hatching percentage normally 

 rises considerably. 



Here, just as in the case of fer- 

 tility, the records tabled, bear a 

 rather heavy handicap, which could 

 have been avoided had the only 

 purpose been to bring out the best 

 record of which the birds were cap- 

 able. The factor m question here 

 is the holding of the eggs before 

 incubation from the first week in 

 February on. iNo eggs were put 

 in incubators until March jth. 

 More than half of the eggs set 

 at this time were over, two weeks 

 old when put in the incubator. 

 Everyone who has dealt practical, 

 ly with incubation knows thiat 

 this means a serious reduction in 

 the percentage of fertile eggs 

 hatched. The reason for managing 

 iu this way was again to get the 

 greatest possible absolute number 

 of chicks hatched about April ist, 

 regardless of the relative propor- 

 tion of chicks to eggs set. 



3. Taking all the records toge- 

 ther and using the averages in the 

 computations it appears that, even 

 with the handicap mentioned, in 

 the high fecundity lines it required 

 only 2.6 t-ggs in the incubator in 

 lyil to produce one chicken three 

 weeks old. In the low fecundity 

 lines it requires 3-2 eggs to make 

 one chicken three weeks old (As, is 

 well known three weeks covers 

 nearly the entire chick mortality. 

 The subsequent death rate among 

 chicks which at three weeks of age 



are in full health and vigor is rela- 

 tivelv insigniiicant). These figures 

 are for the whole of the hatchiing 

 season of lyii, that is, from 

 February 1st to .June 1st. They 

 do not represent the normal repro- 

 ducing ability of the stock because 

 of the heavy handicap explained 

 above. In spite of this fact, "how- 

 ever, these records can only be 

 regarded as indicating an excellent 

 performance. 



Certainly these figures for hatch- 

 ing and reaing give no support to 

 the view that the constitutional 

 vigor or vitality of the Station 

 Barred Plymouth Kock has been 

 impaired by .many years of con- 

 tinued artificial incubation and 

 rearing. When it takes but three 

 eggs or less to produce a chick 

 three weeks old the stock cannot 

 be said to be in a condition of re- 

 duced vitality. 



4. It is plain that there is no 

 substantial difierenoe between the 

 females of the high fecundity lines 

 and the females of the low! fecundi- 

 ty lines with respect to hatching 

 records. ' What small differences 

 there are indicate that birds of the 

 high fecundity lines are on the 

 whole somewhat surer reproducers 

 than those of the low fecundity 

 lines. While the percentage of in- 

 fertile eggs is smaller in the low 

 fecundity lines, on the other hand 

 the percentage of fertile ebgs 

 hatched is also lower and a slight- 

 ly larger percentage of chicks died 

 during the first three weeks of their 

 lives. Particular attention is 

 called to this matter here because 

 it has been alleged by one critic 

 that selection for high egg produc- 

 tion was inimical to reproductive 

 capacity in the domestic fowl. 

 As , a matter of fact, a.s, the pre- 

 sent figures show, that is not at 

 all the case. The criticism was 

 ba.sed upon the accepted fact 

 that there is a negative correlation 

 between winter egg production and 

 the hatching quality of eggs in the 

 subsequent breeding sea.son. This, 

 however, is purely a physiological 

 and not a genetic matter. High 

 laying during the winter months 

 undoubtedly tends to bring about 

 a .somewhat fatigued comlition of 

 the whole reproductive system 

 with the result that the eggs in 

 the subsetjuent spring do not hatch 

 tiuite so well as under other cir- 

 cumstances. This, howeuer, has 

 nothing to do with the innate 

 hereditary ca])acity of thcSie same 

 l)irds ill respect to fecundity. 



( In the next section of the report 

 Dr. Pearl discusses the interesting 

 subject of in-breeding as it affected 

 the i>urposc of those experiments. 

 -Ed.) 



