“Guide to Poultry Mating Systems and Techniques”
The manner in which the selected individuals (both males and females) mate is also of considerable significance in realising response to selection. Mating systems do not change the gene frequency like selection but depending upon the procedure used rearrange the genotypic frequency. Random mating, positive assortative mating, inbreeding and outbreeding are the most commonly used mating systems in poultry.
Random mating means that any individual of one sex has an equal chance of mating with any other individual of the opposite sex in the population and is the most commonly used method in selection experiments as it holds inbreeding to the minimum. Positive assortative mating refers to mating of likes to likes. Initially the response is usually greater than random mating. Positive assortative mating leads to similar consequences as that of inbreeding and hence response to selection slows down as the generations advance.
Inbreeding refers to mating among closely related individuals. The closest form of inbreeding in poultry is full or half brother-sister mating or constant parent-offspring mating. Inbreeding increases the frequency of homozygotes at the cost of heterozygotes. The decrease in fertility and hatchability, increased mortality, delayed maturity, slow growth, decrease in egg production and increase in the frequency of defects due to inbreeding are called inbreeding depression. The primary objective of inbreeding is to develop lines which can be commercially used. A line to be called inbred should have at least 50% of inbreeding coefficient. Three generations of full brother-sister mating or 6 generations of half brother-sister mating produces inbred lines with 50% coefficient of inbreeding.
Outbreeding is opposite of inbreeding and refers to the mating among unrelated individuals. Crossing among breeds, varieties, strains/lines are different types of outbreeding. The main purpose of outbreeding is to overcome the deleterious effects of inbreeding which arise due to small flock size. Outbreeding is sometimes practised to introduce some desirable characteristics not present in the flock.
However care should be taken not to introduce germplasm from an inferior flock.
Crossing among breeds is usually called crossbreeding. Similarly crossing between strains is called strain-crossing and so on. When a cross is made between two inbred lines belonging to the same breed it is called an incross, and between those belonging to different breeds in-crossbred. Top crossing is a method of outbreeding in which inbred males of one line are crossed to females of an outbred population.
Grading refers to the mating of an improved breed to the indigenous mongrel females. Offspring resulting from this cross are called grades. The first cross shows marked improvement over the indigenous stocks.
Halfbred females are sometimes crossed to the males of exotic breeds again and again to increase the inheritance of exotic breeds. Commercial crosses used for egg and meat production may result
from crossing 2 or more lines/strains/breeds. When a cross involves 2 lines only it is a single cross, 3 lines 3-way cross, 4 lines 4-way cross and so on. All other crosses except single crosses are known as multiple crosses. Although single crosses may be superior to multiple crosses in their production performance, multiple crosses are often used for viability of commercial operation. Diallel crossing system, in which the available lines are crossed in all possible combinations, helps to identify the best cross for commercial use, and to identify which line should be used as male parent and which one as female parent.
Methods of Mating
Flock and pen matings are the two commonly used methods. In flock mating a number of males and females are bred together in a large poultry house. Pedigree records are not maintained. One male is mated to 10 to 15 females for egg type stocks and 1 male to 8 to 10 females for meat type stocks, to obtain desired fertility. When mating is done in single sire pens 1 male is mated to 10 to 12 females at the most. Single sire pen mating permits maintenance of pedigree by use of trap nests. When birds are housed in cages mating is done by artificial insemination. Although semen can be diluted, undiluted semen is very often used immediately after collection. In the case of chicken 0-1 ml semen is given. Twice insemination in the first week followed by single insemination in subsequent weeks gives optimum fertility levels. Insemination is usually done in the afternoon when a hard-shelled egg is not in the uterus.