COMMERCIAL RABBIT RAISING 



tions arise. It consists of strict 

 brother-sister matings usually done 

 without selection (since successful 

 reproduction and uniformity are 

 the major objectives) for at least 

 20 generations. This leads to the 

 complete set of many genes of the 

 breed being alike, pair for pair, 

 except for that part which deter- 

 mines sex. It will continue to be 

 so as long as such breeding is con- 

 tinued except for possible occa- 

 sional mutations which under nor- 

 mal environmental situations rarely 

 occur. New genes must never be 

 introduced or the 20-generation 

 procedure must be repeated and 

 then the chances of having the 

 identical gene pool are very small. 

 The major difficulty with in- 

 breeding, and this the breeder must 

 weigh carefully before undertaking 

 such a program, is that during the 

 first 10 to 12 generations sterility, 

 mortality, and undesirable abnor- 

 mal variations are certain to be 

 high, rendering the undertaking 

 economically costly and even vul- 

 nerable to complete loss. Unless 

 sufficient offspring are produced in 

 each generation to insure that only 

 the absolute best are retained (that 

 is, some selection is exercised), the 

 program may be hazardous. Where 

 selection is practiced, inbreeding 

 progresses more slowly from gen- 

 eration to generation, but more 

 safely. Once deleterious genes are 

 fixed in an inbred generation the 

 damage can be repaired only by 

 some form of outbreeding. Once 

 the program is initiated, new genes 

 cannot be added in any generation 

 without undoing all uniformity 

 previously achieved. It is there- 

 fore most important that the ini- 

 tial stock be of the highest quality, 

 that is, contain the maximum num- 

 ber of favorable genes. Should 

 there be any question as to this 

 quality of foundation stock or its 

 ability to produce, line breeding 



(the mating of animals of less close 

 relationship) may be desirable for 

 a few generations. This will ac- 

 quaint the breeder with his un- 

 known recessive gene pool and at 

 the same time, by selection, pro- 

 vide some form of concentration 

 of the best genes. It can be done 

 most rapidly by keeping the rela- 

 tionship to some one desirable an- 

 cestor high. Because a prolific 

 male can affect many more off- 

 spring than a female in a given 

 time period, several generations of 

 backcrosses to any exceptionally 

 vigorous and prolific male may do 

 much to strengthen the initial gene 

 pool before full brother-sister 

 mating is begun. 



It should be pointed out that a 

 number of attempts have been 

 made to inbreed the rabbit in this 

 country and abroad over the past 

 25 years but thus far no completely 

 isogenic strain exists. Achieve- 

 ment of inbred lines is the onl^ 

 means of securing genetic uni- 

 formity and, although it is a hazard- 

 ous undertaking, the breeder who 

 has obtained some degree of suc- 

 cess by any system of close breed- 

 ing will find inbreeding a chal- 

 lenging approach to further breed 

 improvement. With the increas- 

 ing usefulness of the rabbit in 

 medical and biological research, 

 the demand for truly isogenic 

 strains is almost certain to become 

 greater and greater; and breeders 

 who do undertake production of 

 such might find it not only a pro- 

 fitable investment, but would ren- 

 der a most valuable service to 

 medical and biological science. In 

 such an undertaking the value and 

 importance of some training in 

 genetics, nutrition, animal hus- 

 bandry, and health cannot be over- 

 emphasized. Young people who 

 are interested in such efforts will 

 do well to seek such training as 

 early in their education as possible. 



424-402 O - 71 - 2 



