Lesson 4. SYSTEMS OF BREEDING FOR DAIRY CATTLE
SYSTEMS OF BREEDING FOR DAIRY CATTLE
Breeding systems play a significant role in the livestock production depending upon the purpose. The type of the breeding system depends upon the size of the herd, likes and dislikes of the farms/entrepreneur and need for any breed registry/herd registry scheme etc. Basically there are two systems of breeding. Pure breeding is used for registry in the breed associations and these animals will perform better than non-pure breeds. Cross breeding is used mostly by many commercial producer and animals also have good performance because of hybrid vigour.
4.2 Systems of Breeding
A number of breeding systems are available for improving the performance of dairy animals in terms of growth, production and reproduction. The aim of breeding systems is breed improvement. The system of breeding to be used depends on livestock operation, goals of the farmer or breeder and size of the herd etc.
The method of mating between individuals which are more closely related, such as brothers and sisters and of sires with daughters is called inbreeding. After many years of inbreeding it is possible to obtain lines which produce uniform offspring. Commercial and purebred producers exploit this method to obtain hybrid vigour by crossing between two or more inbred lines. Inbreeding increases the genetic purity of the stock produced, but reduces performance. After several generations of inbreeding, both desirable and undesirable traits become more visible. A good program of selection of desirable traits and culling of undesirable traits results in a breeding stock with more desirable traits. The ill effects of long term inbreeding are lowered production in terms of milk yield and fat %, increased susceptibility to diseases resulting in more mortality. All the effects are due to undesirable recessive genes becoming homozygous.
4.2.2 Out breeding
It is a practice of breeding the farm animals which are not closely related within the same breed. It is popular system of breeding the dairy herds with average production and small livestock owners. Out crossing combined with selection is responsible for most of the changes and improvements in most of purebreds of dairy cattle. The effect of outbreeding are opposite to the inbreeding since without breeding heterozygosity is increased.
4.2.3 Cross breeding
It is the mating of the animals belonging to two different breeds. It is done to take advantage of good qualities of two or more breeds. Extensive research on cross breeding of dairy cattle is under taken by military dairy farms in India. The out come of all the crossbreeding studies showed that combination of 50 percent exotic inheritance and 50 percent indigenous inheritance excelled in terms of growth rates, production traits and adaptability to Indian climate. It contributed to make India to stand first in milk production in the world. The level of exotic inheritance should never exceed 62.5% to exploit the full genetic potential of the animal for a sustainable production. The cross breeding programme was under taken to exploit the milk yield potential of the exotic breeds combined with heat tolerance, disease resistance of indigenous breeds. Cross breeds of Jersey, Holstein Fresian and Brown Swiss are early maturing, yielding more milk compared to indigenous breeds. All India Coordinated Research Project on cattle resulted in development of synthetic breeds like Karan Swiss, Karan Fries, Frieswal, and Sunandini etc. Crossbreeding usually results in improved traits in the offspring. Superior traits that results from cross breeding are called hybrid vigor or heterosis.
4.2.4 Grading up
It is mating of pure bred males of a established breed with nondescript females successively over several generations to produce a progeny that resembles and performs similar to the pure breed. Grading up is the system of breeding mostly adopted for genetic improvement of the buffaloes. It is to be taken up in areas having more number of the non descriptive female population. After seven generations of crossing, the non-descriptive females acquire the characters of a pure breed. Murrah buffalo bulls are used on local buffaloes for genetic improvement in India. The amount of improvement that results is dependent on the quality of sire used for the breeding programme. Godavari breed of buffalo is developed by crossing of the local buffalos of coastal region of Andhra Pradesh breed with Murrah breed over several generations.
4.2.5 Out crossing
Mating of the unrelated pure breed animals, within the same breed is called out crossing. The animals mated have no common ancestor on either of their pedigree up to 4 to 6 generations and the offspring of such a mating is called the outcross. The purpose out crossing is to bring into the breeding programme traits that are desirable but not present in the original animals. This results in few undesirable genes being fixed in the population. For traits with high heretabilities like growth rates, this is the most effective method. Out crossing is useful procedure when a drastic change in the type of either seed stock or commercial herd is desired.
4.2.6 Back crossing
The cross bred females obtained by crossing two breeds are mated to males from one of the two parental breeds.
4.2.7 Rotational crossing
In rotational crossing, males from one of the pure breeds are used in alternate generations to breed the cross bred females. This rotational crossing could be between two breeds is called crisscrossing and among three breeds is called triple crossing. The heterosis among crossbreds produced by rotational crossing will not be 100 percent after several generations of rotational crossing: The individual heterosis is about 67 percent in the rotational crossing, while it is about 85 percent in triple crossing. Triple crossing offers maximum individual heterosis and maternal heterosis.
Cross breeding is the system of breeding mostly used for genetic improvement of cattle where as Grading up is the method used for genetic improvement of the buffalos.