ANIMAL AND PLANT BREEDING 3II 



importance in the past. Several important early varieties of maize, such 

 as Learning, and Delta Farm White Dent, were obtained in this way, 

 while probably all our agricultural crops have been improved by rather 

 haphazard mass selection since agriculmre first began. A recent example 

 of successful selection is the production of a sweet lupin. ^ Most wild 

 races produce an alkaloid in the seeds which renders them unsuitable 

 for fodder. Forms containing very little alkaloid were found by German 

 breeders after an intensive search, and pure Hnes bred by selection. 

 Details of the work were not published and the seeds were not allowed 

 to be exported. The entire work was therefore repeated, equally suc- 

 cessfully, in the U.S.S.R. The plants provide a valuable fodder with 

 high protein content. 



Selection of one parent only is still one of the most important 

 methods in animal breeding.^ The world possesses enormous numbers 

 of low-grade stock animals, and since the reproductive rate of animals 

 is comparatively low, they cannot be simply destroyed and the next 

 generation produced entirely from high-grade animals, as could be 

 done with plants. The stock can, however, be improved by "grading- 

 up," that is, by breeding from most of the females, but using a small 

 number of selected males to father the whole of the next generation. 

 The effects of this method of breeding may be very beneficial; at the 

 Iowa Agricultural Experiment Station, the first generation from a poor 

 scrub herd crossed with pure-bred bulls gave 55 per cent more milk 

 and 44 per cent more butter-fat than their dams, the second generation 

 116 and 106 per cent more. That there is plenty of room for improve- 

 ment of this kind is shown by the fact that the average yield of milk in 

 the United States is about 4,000 lb. per dairy cow per year, with 160 lb. 

 of fat, whereas the average production by pure-bred cattle is well over 

 10,000 lb. with 450 lb. of fat, going up to the record performances 

 (probably only realizable under artificial and non-commercial condi- 

 tions) of about 25,000 lb. of milk a year. 



Equally valuable results have been obtained by grading up the 

 enormous beef-producing herds of western United States by using 

 suitable sires. Recently attempts have been made to give greater force 

 to the method by increasing the number of females which can be 

 served by a single superior male. A single ejaculation of semen contains 

 very many times more sperm than are necessary to ensure fertilization, 

 and by performing artificial insemination with diluted semen, a desir- 

 able male can be caused to produce oflfspring with at least a hundred 

 ^ Cf. Hudson 1937. - Rice 1934. 



