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| Strategy for sheep and goat breeding | | | Dr. Vikas Mahajan | 3/31/2012 11:15:37 PM |
| Sheep development activity was undertaken as early as the early 19th century by the East India Company, which imported exotic breeds for cross-breeding with the indigenous breeds. Subsequently, with the establishment of the Imperial (now Indian) Council of Agricultural Research, research and development programmes were taken up on a regional basis; they included selective breeding within the indigenous breeds and cross-breeding them with exotic fine-wool breeds, and covered almost all the important sheep-rearing States. Major emphasis was however placed on sheep development after the country attained independence and initiated its Five-Year Development Plans. During the Third Plan, a large number of sheep and wool extension centers were established, and a wool grading and marketing programme was initiated in Rajasthan. During the Fifth Plan, a large number of breeding farms were planned to be established in the central and State sectors to produce genetically superior breeding stocks. It was also planned to reorganize and strengthen the existing sheep-breeding farms in the States as well as to expand and reorganize sheep and wool extension centres, and to set up scientific sheep shearing and wool-grading programmes. A number of sheep development programmes were undertaken under specialized programmes, such as DPAP, small-farmer (SF), marginal-farmer (MF) and agricultural labourer schemes. Setting up of wool boards in important wool producing States like Jammu and Kashmir was also foreseen.
The breeding strategy is different for different regions of the country. In the north temperate and northwestern regions, it involves breeding for apparel wool through cross-breeding indigenous breeds with exotic fine-wool breeds. For the northwestern and central peninsular regions and Bihar, selection among better carpet-wool breeds and crossing extremely coarse and hairy indigenous breeds with exotic fine-wool and dual-purpose breeds to improve carpet-wool production and quality and mutton production has been recommended. For improving mutton production in the southern peninsular region, the strategy contemplates selection within better indigenous breeds such as Nellore and Mandya, and upgrading of inferior breeds with these two breeds.
So far, there has been very little systematic emphasis on goat development. Some State governments have been distributing bucks of superior indigenous breeds, mostly Jamnapari and Beetal, or stationing them in veterinary dispensaries for natural service. The Sixth Plan envisages the establishment of large goat-breeding farms for the production of studs of important breeds as well as breeding bucks of exotic dairy breeds to be used for cross-breeding for improving milk production. There is some emphasis on improving pashmina production in the Ladakh area of Jammu & Kashmir, where state government has established pashmina goat farms for the production of studs. For devising any breeding plan for sheep and goat selection and mating system are the two tools in the hands of a breeder on which emphasis should be laid for the genetic improvement of these two species.
Breeding Strategies
Animal breeding is a branch of animal science that addresses the evaluation of the genetic value of domestic livestock. A breed is a group of domestic animals with a homogeneous appearance, behavior, and other characteristics that distinguish it from other animals.
Pure-breeding
Pure-breeding is the mating of rams and ewes of the same breed or type. A purebred flock can be managed as a single flock because all ewes and rams are of the same breed. The goal of purebred sheep production is to provide superior genetics (seedstock) to the commercial sheep industry. The National Sheep Improvement Program (NSIP) collects performance data from purebred producers and provides them with across-flock EPDs. "EPD" is short for "Expected Progeny Difference." An EPD is an estimate of the genetic merit of an animal for a given trait. It is the expected difference between the performance of an animal's progeny (offspring) and the average progeny performance of all the animals in the breed for that trait. For example, if a lamb has a weaning weight EPD of 2.0 lbs., this means that its progeny will be 2.0 lbs. heavier than the average lamb in the breed.
Out-breeding
Within pure-breeding, there are several types of mating systems. Out-breeding is the mating of animals of the same breed but which have no closer relationship than at least 4 to 6 generations. Outbreeding is the recommended breeding practice for most purebred sheep.
Inbreeding
Inbreeding is a system of breeding in which closely related animals are mated. This includes sire to daughter, son to dam, and brother to sister. Technically, inbreeding is defined as the mating of animals more closely related than the average relationship within the breed or population concerned. The primary genetic consequence of inbreeding is to increase the frequency of pairing of similar genes. Inbreeding is essential to the development of prepotent animals - animals that uniformly "stamp" their characteristics on their progeny. Inbreeding may also be used to uncover genes that produce abnormalities or death - genes that, in outbred herds, are generally present in low frequencies. Inbreeding is suggested for only highly qualified operators who are making an effort to stabilize important traits in a given set of animals. Line breeding : Line breeding is a system of breeding in which the degree of relationship is less intense than in inbreeding and is usually directed towards keeping the offspring related to some highly prized ancestor. The degree of relationship is not closer than half-brother half-sister matings or cousin matings, etc. Line breeding is a mild form of inbreeding. Cross breeding : Crossbreeding is the mating of rams and ewes of different breed compositions or types. However, it does not denote indiscriminate mixing of breeds, but rather is a systematic utilization of different breed resources to produce crossbred progeny of a specific type. Crossbreeding is used extensively in the commercial sheep industry and the majority of slaughter lambs are crossbred.
Breed complementarity
The second major advantage of crossbreeding lies in the ability to utilize breed complementarity. All breeds have strengths and weaknesses. No one breed excels in all relevant traits. Thus, production can be optimized when mating systems place breeds in roles that maximize their strengths and minimize their weaknesses.
Crossbreeding Systems
There are several systematic crossbreeding systems. Terminal crossing makes maximum use of both heterosis and breed complementarity. It may utilize two, three, or four breeds, and can be as simple as crossing two pure breeds.
Terminal crossing
In terminal crossing, all of the crossbred offspring are sold and replacement ewe lambs must be purchased or produced in the flock by mating a proportion of the flock to rams of the same breed. In a three or four breed terminal crossbreeding system, crossbred ewes and crossbred rams can be utilized in the system to maximize heterosis.
Rotational crossing : Rotational crossing will also maintain high levels of heterosis. Rotational crossing involves alternating the use of rams of two, three, or more breeds. Ewes are mated to rams of the breed which they are least related. It works best when breeds which function acceptably as both ram and ewe breeds, are utilized. Roto-terminal crossing : Roto-terminal crossing involves both terminal crossing to produce market lambs and rotational crossing to produce ewe lambs. The best ewes in the flock would comprise the nucleus flock. They would be used to produce replacement ewes. The rest of the ewes in the flock would be bred to a terminal sire to produce market lambs. Grading up: Grading up denotes the repeated crossing of ewes and their female progeny to rams of a single breed, with the ultimate objective of creating a flock that is indistinguishable from purebred flocks of the ram breed. It is used when only rams of the breed of interest are available or affordable. |
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