nimal sciences
COOPERATIVE EXTENSION SERVICE, PURDUE UNIVERSITY, WEST LAFAYETTE INDIANA 47907
Selection Guidelines lor the Swine Breeding Herd
K.J. Drewry, Animal Sciences Department
The purpose of this publication is to assist the swine producer in the proper selection of herd boars and replacement gilts. This publication setsgoals and outlines those traits which should maximize economic returns to the swine production enterprise.
GOALS
The goals in swine production, whether purebred and commercial, are as follows:
•	100 percent conception and farrowing rates.
•	10 to 11 vigorous pigs, weighing 2.75 to 3.00 pounds, farrowed per litter.
•	100 percent livability to market.
•	18- to 20-pound pigs weaned at 3 weeks with ability to be reared in confinement production systems.
•	150 days or less to reach market weight.
•	3 pounds feed per pound gain or lower for pigs from 50 to 220 pounds.
•	Over 80 percent of hogs grading USDA No. 1 at marketing.
breeds
The genetic material to be used in maximizing economic returns to labor and management is found in our existing swine breeds. Pertinent information concerning performance of the eight major breeds of swine in the U.S. is presented in Tables 1-4.
Those breeds which rank high in litter size grow the fastest with the least feed and have the longest carcasses (Table 2). Those breeds ranking lowest in litter size rank highest for traits used in measuring carcass quantity and quality (Tables 3 and 4). The averages and rank of those breeds for the various traits give some indication of the way the breeds can De used in production programs to reach the goals outlined above.
SELECTION
Selection is the process of culling certain animals that do not meet requirements used in evaluating potential breeding stock. These requirements may be based on the individual's own records or the records of his parents or grandparents.
Amount of selection or "reach” that the producer makes determines his genetic potential lot improved production. If he is to continue to make genetic progress, the replacement animals must be above the average of the previous pig crop. Not all of the "reach" made through selection of boars and gilts will be transmitted to the next pig crop, due to the way genes act and to the fact that the traits are not determined completely by genetics.
Genes passed from parent to offspring may give either additive response or heterosis response. Genes giving the additive response are: permanent, give their response regardless of other genes present and determine the amount of "reach" that will show in the offspring. Genes giving the heterosis response might be considered temporary, since their response depends on specific gene combinations which must be formed each generation.
Pig performance is due to both types of gene responses. The additive response sets the lower limit of performance. Heterosis response represents added performance that maybe obtained with certain traits.
Relative size of the additive and heterosis response for several swine traits is presented in Table 5. Both types of gene responses, combined with the economic importance of the various traits, determine the emphasis a producer should give each trait when selecting herd replacements and choosing the mating system that will maximize returns to labor and management in his swine production program.