AS-417 • 1975
K.J. Drewry and W.L. Singleton. Animal Sciences Department
The two most important factors affecting economic returns from a swine breeding herd are: (1) number of pigs weaned per sow exposed to the boar, and (2) ability of these pigs to convert nutrients into quality pork economically. And both factors are directly influenced by breeding stock selection and herd management.
The genetic profit potential of a swine herd is established when the operator selects his
replacement gilts and boars, and when he decides on the mating system to use. Once these decisions are made, then his management and husbandry practices determine the absolute profit or loss potential of the herd.
This publication deals with how to maximize economic potential of pork production through proper selection of replacement gilts and management of the breeding herd.
Selection of Replacement Gilts
Factors to consider when selecting replacement gilts include: their source, health, litter size, dams' productivity, structural soundness, conformation, teat number and placement, femininity, growth rate, backfat, age and number, and the breeds and mating system to be used. Following is a discussion of each of these factors.
SOURCE AND HEALTH
Most producers prefer replacement gilts that are "home-raised." This permits selection from the top end of the group of potential replacements, which probably would not be possible if gilts were purchased. In addition, the animals are already acclimated to the health condition of the farm.
If gilts are purchased, you should pay particular attention to the health of the herd from which the gilts come. Those selected should either be blood tested and found negative for brucellosis or be from a validated brucellosis-free herd. Purchased gilts should be from the top half of the herd.
All replacement gilts, regardless of source, should be vaccinated for erysipelas at 6 to 8 weeks of age if it is a problem in your area. Also treat for internal and external parasites at this time or at weaning.
LITTER SIZE, UNDERLINE AND SOW PRODUCTIVITY
In selecting replacement gilts, whether purchased or from your own herd, give special attention to litter size, the gilts' underline and their dams' productivity.
At weaning, identify those gilts that (a) are from litters of 8 or more pigs farrowed, (b) have 12 or more evenly-spaced, functional teats (at least six per side), and (c) are from sows possessing the following productivity traits:
1.	No problems at farrowing.
2.	Largest number of live, uniform-sized pigs at farrowing.
3.	Weaning the highest percentage of live pigs farrowed.
4.	Litters with the heaviest weights at weaning.
5.	Least amount of skeletal structure-related problems during farrowing and nursing.
6.	Desirable temperament and disposition.
7.	From "sow-lines" exhibiting good longevity.
The job of selecting the best gilts can be simplified by some way identifying potential replacements at farrowing (i.e., those from litters of 8 or more pigs). For commercial producers, the 1-3-9-27-81 ear notching or tag system is suggested. Then
Selection and Management of the  Sow  Herd
animal sciences  swine

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