16 MASS. EXPERIMENT STATION BULLETIN 307 



The Introduction of Outside Stock 



From the genetic standpoint almost an>- flock of birds is very heterogeneous, 

 especially with respect to genes concerned in the inheritance of high fecundity. 

 The fact has already been pointed out, however, that close inbreeding is detri- 

 mental to increasing the egg production as a rule. The method of improving 

 the station flock has avoided inbreeding; at the same time, there has been no 

 outside stock introduced since 1915. Under this system of breeding there arises 

 a high degree of relationship which may eventually produce the same effects as 

 close inbreeding. Limited experimental studies on the value of introducing 

 outside production-bred males have given negative results so far. 



Practical breeders desire to know how long they may continue breeding within 

 their own flocks and what specific developments indicate that outside stock 

 should be introduced. In answer to these question, experience here tends to 

 show that there are two specific indications that new blood may be beneficial. 

 (1) If hatchabiiity is on the decline e\en though incubation methods are good and 

 attention is given to hatchabilit\ in selecting breeders, it is probable that the 

 stock is too closely related. (2) If there is excessive mortality in the families 

 on the range and in the pullets during the first laying year from no specific disease 

 outbreaks but largely from many functional disturbances, this is evidence of 

 close relationship. Close inbreeding very often produces low hatchabiiity and 

 late sexual maturity as well as lack of persistencx . 



When there is evidence that outside stock is needed, it is especially important 

 that such stock should be selected from flocks bred s>steniatically for the charac- 

 ters being sought, and that the birds should be free from undesirable defects. 

 Probably the most satisfactory procedure is to obtain pedigreed hatching eggs 

 from two or three different sources and to hatch and rear the chicks with the 

 regular flock. Pullets may then be housed with the home flock and trapnested 

 until the hatching season to obtain some evidence of their behavior under existing 

 conditions. Preliminary crosses can be made between those families that appear 

 to be satisfactory, and the off^spring checked against the home flock. Crossing 

 should not be undertaken on too large a scale until there is evidence of its value, 

 yet numbers should be sufficiently large to give a true measure of results. 



The Types of Records Kept 



One of the essentials in a successful breetling program is a complete and accurate 

 system of records. Such records should be kept up to date and should be con- 

 stantly used as a guide to the breeder. Trapnesting and record keeping are 

 expensive and are of little value unless the records are studied and analyzed 

 regularly. The two greatest essentials of a good set of records are simplicity and 

 completeness. 



The record forms used for the experimental flock are rather complete and are 

 presented here not as suitable for conmiercial flocks, but rather as suggestive 

 material to guide the breeder. It is easily possible to modify and combine 

 these record forms to reduce labor and \et meet practical needs. 



