FAMILY PERFORMANCE AS A BASIS FOR SELECTION 



IN SHEEP 



By E. G. RiTZMAN, Animal Husbandman, New Hampshire Agricultural Experiment 

 Station, and C. B. Davenport, Station for Experimental Evolution, Carnegie 

 Institution of Washington 



Two contrasted methods of selecting mates are in current use. The 

 commonest is that of picking out the best individuals or those that 

 exhibit the traits which are desired in the offspring. This method 

 depends on the principle that the somatic traits of the parent are the 

 best index of its germinal determiners; so that in selecting somatically 

 we are at the same time selecting gametically. This principle is, however, 

 false in so far as the soma is usually a very inadequate index of the germ 

 plasm. In animals that are heterozygous in any trait the germ cells 

 are of two kinds in respect to that trait: (i) those carrying determiners 

 for the trait and (2) those for its absence, or for its allelomorphic trait. 

 Practically it has been found by many breeders of animals and plants 

 that progress is made slowly or not at all by this process. 



The other method of selecting mates recognizes the principle that the 

 individual's somatic traits constitute a partial and imperfect index to 

 its germ plasm. A better insight into that germ plasm is gained by 

 considering the traits shown by as many close relatives as possible. 

 Naturally the qualities of the proposed mates are considered, but only as 

 members of their families. 



The foregoing principles have been applied in the sheep-breeding 

 experiments at the New Hampshire Experiment Station. The aim of 

 these experiments is to produce a race of sheep that will combine 

 good qualities of conformation, size, and wool. As criteria of these 

 three points we used the following quantities and assigned to each the 

 factor or weight indicated : 



Weight. 

 CONFORMATION 



Ratio, head width : length 3 



Ratio, neck length: circumference . . 2 



Ratio, foreleg length: trunk length. . 10 



Ratio, chest width: depth 5 



Ratio, chest width: trunk length. ... 5 



Ratio, loin width: trunk length 5 



Ratio, croup length: trunk length. . . 5 



Weight. 



SIZE 



Body weight (pounds) 5 



Height at shoulder 5 



Chest circumference 5 



Loin width 5 



Hindleg circumference : 5 



Total size 25 



WOOL 



Weight of fleece 10 



Length of staple 10 



Diameter of fiber 10 



Crimp of wool 10 



Total wool 40 



Total. 



35 



Joximal of Agricultural Research, 

 Washington, D. C. 



(93) 



Vol. X, No. 2 



July 9, 1917 



Key No. N. H.— 3 



