Pigs to Pork
BREEDING
Applied Swine Breeding Practices
C. W. Foley and Richard Hollandbeck, Animal Sciences Department
Most of the important economical traits in swine are affected by many pairs of genes. Since one pair of genes may result in six different genetic combinations; and since 243 possible combinations may result from five pairs of genes; the total number of possible genetic combinations becomes almost inconceivable because swine have nearly 50, 000 different genes. The many possible combinations partially explain why it is so difficult to develop breeding principles for rapid improvement.
Nevertheless, basic research in genetics and animal breeding has led to great progress in livestock improvement through approved breeding practices.
Improvements in heredity are permanent--each generation builds upon the previous one. But, genes cannot express themselves to their fullest without an excellent environment. Genes establish the blue-print of maximum capabilities of the animal. The environment determines the degree of maximum capability which is realized.
Neither, alone, can do the job; but, collectively, the horizons are unlimited.
The basic tools of genetic improvement are selection, crossbreeding and in-deeding. How much a swine breeder can Use these tools depends upon his basic understanding of genetic principles and the factors involved in each method.
selection
Major emphasis is placed on selection ecause the average breeder can still make
more progress through selection than with crossbreeding or inbreeding. And, when crossbreeding or inbreeding, selection must still be emphasized.
Selection is defined as causing or allowing certain animals to reproduce offspring. Two kinds of selection are often discussed--natural and artificial. Natural selection occurs in nature and has played an important role in the development of our species. Artificial selection has been practiced by man with domestic animals. Here, it must be remembered that man does not create new genes; he merely changes the frequency of certain genes and attempts to generate superior combinations of genes in one individual.
Individuality--an Aid in Selection
Artificial selection is based upon three points--individuality, pedigree and progeny tests. An animal's individuality includes type (physical characteristics) and performance. This is phenotypic selection.
One disadvantage of using individuality in selection is that environmental effects could easily be mistaken for genetic effects . For example if one beef calf is creep fed and suckles a nurse cow and another has only dry pasture and the milk supplied by its mother, creep fed calf will appear superior. But, the creep fed calf might be genetically inferior to the non-creep fed and transmit less desirable characteristics to his offspring.
AS-318 Sept. 1964