374 L. M. WINTERS 



experimental results, we will be in a better position to bridge this gap. My 

 experiences have convinced me, however, that it is a mistake not to take 

 seriously the observations made by competent practical men in the field of 

 operations. I am inclined to believe that very often these men see more, al- 

 though they measure less accurately, than we in the field of research, with 

 our eyes glued carefully to the job of measuring certain details. 



In this experiment we used four standard measurements for appraisal of 

 the pigs' worth. These were: number of pigs born alive, number of pigs 

 weaned, rate of gain, and feed per unit of gain. Since then we have added a 

 fifth measure — appraisal of body form on the basis of judgment. When we 

 took the first four factors and compared the performance of the crosses with 

 the comparable purebreds, we obtained an advantage of the crosses over the 

 purebreds of 6.3 per cent for the first cross, 7.5 per cent for the backcross, 

 and 11.7 per cent for the three-breed cross. This was obtained by throwing 

 the four factors together as equal in importance. 



By another method of comparison, wherein more factors were thrown into 

 the pool, we obtained an advantage for the first cross of 7 per cent, the back- 

 cross 6 per cent, and the three-breed cross of 17 per cent. If, however, we 

 were to take litter weight at weaning, which in one sense is comparable to 

 yield in corn, we would have an advantage of the first cross of approximately 

 25 per cent, the backcross 39 per cent, and the three-breed cross 61 per 

 cent. If we were to take total litter weight at the close of the experiment, the 

 advantages of the crosses would be still greater. In my opinion, total litter 

 weight as a sole measure of merit exaggerates the diliference. On the other 

 hand, I do not consider the method we have used entirely satisfactory. I do 

 not know of an entirely satisfactory measure of performance in livestock. 

 We in the livestock field need to do a great deal in the matter of perfecting our 

 methods of measurements. The important question to the practical man is 

 whether one procedure is better than another, rather than whether this pro- 

 cedure gives me exactly 20 per cent or 18 per cent increase. 



ROTATIONAL CROSSBREEDING 



On the basis of these results, we developed and put forward our plan of 

 rotational crossbreeding. Even at the time that I started to analyze the data, 

 I did not believe that our three-breed cross had given us any worth-while 

 advantage over the single cross. I mention this merely to show how strongly 

 entrenched the old teaching had become regarding the limitations of cross- 

 breeding in livestock production. The results of the experiment were, how- 

 ever, very definite. I calculated and recalculated, and the results were always 

 essentially the same- — the three-breed cross possessed distinct advantages 

 over the first cross and over the backcross. 



Simple calculation shows that, on the average, the first cross will possess 

 50 per cent of the chromosomes, or more properly speaking, linkage groups 



