Tuesday, September 14, 2010
Cross breeding coming to the Egg industry, will the eggs be kosher?
Chapter 7: Breed Improvement
Strategies to develop poultry breeds suitable for family poultry smallholders in tropical countries must differ from those used in intensive production, and should focus on improving indigenous breeds while also making use of pure exotic and cross-bred chickens where appropriate.
Conservation of local breeds possessing genetic variations specific to the particular environment is essential for sustainable development. Although they exist as numerically small populations, local breeds are not only highly adapted to the natural environment, but are also an integral part of the lifestyle of the rural people. People, livestock and environment form a delicately balanced but sustainable ecosystem, and thus the potential impact of any intervention to improve production in the traditional system should be predetermined. The situation is less sensitive in peri-urban, industrial and small-scale intensive poultry production, in which rapid improvements can be achieved through well-designed development programmes. The intensive poultry production sector, however, is generally much smaller than the family poultry sector in virtually all developing countries.
STRATEGIES FOR BREED IMPROVEMENT
The following two rules should be incorporated into breeding strategies:
Germplasm in traditional conditions should not be modified until management and housing have been improved and, even then, selection should be restricted to local breeds.
When technical conditions are optimum and a ready market exists for the products, then improved breeds, crosses and hybrid strains that have been selected for high performance can be introduced into the peri-urban system, even at small-scale levels.
The most common method of improving the local gene pool is crossing indigenous and exotic birds, and then leaving the hybrid offspring to natural selection. Pure-bred or hybrid cockerels (or pullets) selected for greater meat or egg production are introduced into local flocks, usually in order to increase egg production. It is important to note that improved growth (for meat production) and high egg production are genetically incompatible in the same bird. The genetic traits are negatively correlated, which means that selection for one trait will reduce the other.
Cockerel or pullet exchange
An example of this type of strategy is a flock of indigenous local hens laying 50 eggs a year and beginning to lay at 25 weeks of age, crossed with “improved breed” cockerels, which have a genetic breed potential of 250 eggs a year, with hens beginning to lay at 21 weeks. The results are cross-bred hybrid pullets beginning to lay at 24 weeks, with a genetic potential of laying 200 eggs per year. The first generation hybrid cross-breed has a higher theoretical genetic potential (genotype) than the average (150) of the two parent breeds, due to the effect of hybrid vigour. However, unless management (especially in the area of nutrition) is improved, this genetic potential will not be realized by the hybrid cross-breed in actual practice in the environment.
If subsequent generations of the hybrid cross-bred pullets are mated (back-crossed) again with the same “improved breed” cockerel, the genetic potential for increased production is raised, although at a slower rate (as hybrid vigour only works with first-time crossing). With each generation, higher levels of management (including the provision of properly balanced feeds) are required to achieve this potential.
If the hybrid cross-breeds mate among themselves, however, potential production falls in the very next generation to the average potential of the two original genotypes, even if management could support the higher hybrid level.
The use of cockerels in this way is the basis for the Cock or Cockerel Exchange Programme (CEP) or Opération Coq, which has been implemented in almost all tropical countries. Households exchange all their local cockerels for a few improved cockerels, which are then raised to maturity to allow them to adapt to local conditions.
In some cases, a Pullet Exchange or Hybrid Hatchable Eggs Programme is used. These approaches were used extensively from the early 1930s until the 1960s, by which time urban development had begun to give rise to peri-urban, intensive, small- to medium-scale poultry production, which makes use of imported commercial breeds and technology.
The gradual replacement of local genes through cross-breeding and artificial selection has been the basis of initial development in many countries (Omeje and Nwosu, 1986; Coligado et al., 1986).
Although many strategies deemed appropriate for smallholder poultry production systems have been implemented, most have not succeeded, due to a lack of management input to support the improved potential.
Replacement of all indigenous breeds
The use of hybrid chickens under free-range rural conditions has often been studied, notably in Zimbabwe (Huchzermeyer, 1973), and in Sri Lanka, Zambia and Nicaragua (Roberts and Senaratne, 1992; de Vries, 1995).
It has consistently been found that entire flock replacement programmes lead to increased egg and meat production, but only where management supplies good nutrition and veterinary hygiene. There is, however, one great disadvantage, in that the use of commercial hybrids to increase egg production necessarily eliminates broodiness of hens, due to the negative genetic correlation between these two factors. For this reason, complete replacement of local birds should not be considered unless a reliable local supply of day-old chicks (of an appropriate breed) is available.
Selection within local breeds
Production traits of local breeds
The genetic development of local breeds and varieties in developing countries first requires proper documentation of their productive and reproductive performance. The main production characteristics of local breeds are:
small body size (low nutritional maintenance requirement);
lateness in maturing (up to 36 weeks of age);
low performance in egg numbers (20 to 50) and egg size (25 to 45 g);
small clutch sizes (two to ten eggs); and
long pauses between laying of clutches and a predominant inclination to broodiness.
For rural smallholder extensive systems, meat production cannot be separated from egg or chick production, and thus a highly broody (with consequent low egg production), low body-weight (low-feed requirement) bird is best for survival under these conditions. Surplus cockerels, whatever they weigh, are usually sold for meat when they reach sexual maturity at three to four months of age. Under rural smallholder extensive systems, there is little reproductive control of the hens, as they brood their own chicks for continuous regeneration of the flock. The egg brooding (incubation) and chick rearing activity increases the reproductive cycle length by 58 days to about 74 days in total:
16 days for egg laying and clutch formation + 21 days for hatching + 37 days (5.3 weeks) for chick rearing = 74 days
Source: Horst, 1990b
Thus, most hens can produce chicks about four to five times per year, and only four times if the rearing period is extended to eight weeks. As malnutrition, infections, predators and accidents result in mortality rates of 60 to 70 percent during rearing, virtually all eggs are used for reproduction. With four to five reproductive cycles per year, only about nine replacement pullets may be obtained.
Fertility and hatchability are also high in local birds. They generally adapt well to unfavourable management conditions, and resistance to prevailing diseases is usually assumed to be high, although juvenile and sometimes adult mortality rates can be high in extensive production systems.
Considerable genetic differences exist between different regional and continental populations of indigenous chickens, and production rates of local populations should be evaluated before introducing development programmes.
Selection programmes for local breeds
Although better management procedures can significantly improve the performance of local birds, some feel there is also a need for genetic selection (Nwosu, 1979). Pure-breeding and selection programmes have been developed in Bangladesh (Ahmad and Hashnath, 1983), although not implemented in the field. Both of the above groups concluded that although improvement of local poultry breeds would be beneficial, it is essential to evaluate breeds and their crosses before undertaking a breeding strategy.
Research conducted in the United Republic of Tanzania (Katule, 1991) concluded that selection for dual-purpose characteristics within individual local populations is both time-consuming and costly. Cross-breeding with improved breeds is recommended, followed by selection in the composite population.
Although consumer preference in most developing countries is for dual-purpose breeds, it is important to restate that in the same bird, the traits of increased egg production and increased broodiness are genetically incompatible, as are the traits of high egg production and high meat production. Selection for any trait within these pairs will reduce the other trait of that pair.
Modifying local breeds using major gene types
The use of single or combined dominant genes for feather restriction (Na) and feathering structure (F), as well as the sex-linked recessive gene for reduced body size (dw), has been found to be particularly relevant for the tropics (Horst, 1989; Haaren-Kiso et al., 1995). Research into the effects of these genes on economic factors has been undertaken in Malaysia (Khadijah, 1988; Mathur and Horst, 1989). For example, the feather restriction (Na) or Naked Neck gene results in 40 percent less feather coverage overall, with the lower neck appearing almost “naked”. This considerably reduces the need for dietary nutrition to supply protein input for feather production, and protein is a limiting factor in many scavenger feed resource bases. Barua et al., (1998) has reviewed the available information on the performance of indigenous Naked Neck fowl in the hope that it will draw the attention of scientists worldwide to its interesting characteristics and facilitate future research.
The incorporation of such genes could be significant in the development of appropriate breeds and strains for smallholder poultry production in the tropics. There are now seven potentially useful major genes:
Na - naked neck (autosomal -A);
Dw - dwarf (sex-linked -S);
K - slow feathering (S);
Fa - Fayoumi (A);
F - frizzle (A);
H - silky (A); and
Fm - fibro-melanosis (A).
The use of major genes to improve productivity in smallholder poultry breeding programmes has been researched in various tropical countries (including Indonesia, Malaysia, Thailand, Bangladesh, Bolivia, India, Cameroon and Nigeria).
Other morphological traits that allow better heat dissipation include large combs, large wattles and long legs. Gene coding for these traits, which are not major genes but the result of multiple genes and their interactions, could also be considered for incorporation into the development of high performance local birds for the tropics.
BETTER PRODUCTION: BY BREEDING OR MANAGEMENT?
Family poultry is well integrated into most village farming systems, with local breeds representing 40 to 70 percent of the national meat and egg supply in most tropical countries. Because of their scavenger adaptability, production ability and low cost, local breeds are kept by rural smallholders, landless farmers and industrial labourers. It is difficult to imagine birds better adapted for survival under scavenger free-range conditions than the breeds that have already evolved under those very same conditions, and are still surviving as proof of their ability to do so. However, there does remain a considerable and largely unexploited potential for increased production from local breeds through improved management.
The critical management objective for scavenger free-range systems is to reduce the high mortality in both growing and adult age groups, but especially the 60 to 70 percent mortality in the growers. This high mortality means that many eggs laid by the hen need to be used for reproduction to maintain flock size, instead of for sale or consumption. It also means that many birds that die could instead be sold or consumed as meat.
The problem with local breeds, as outlined above, is not inherently low egg production or low meat production, but high mortality. Breed improvement to increase meat or egg production would not solve the health and nutrition management problems. However, increased egg production (by breed improvement) would create a new problem - lack of broodiness in the flock - which would force the smallholder to buy stock rather than have the hen brood and rear her own.
Mortality can be significantly reduced through increasing farmer awareness of health needs, through the provision of vaccine (especially for Newcastle Disease) and through improving the nutrition of growing stock (for example, by providing creep feeding systems). These are the most important improvements to management activities that will enable to the farmer to best exploit the existing potential of local breeds under scavenging free-range conditions.
If management resources available to the smallholder or landless farmer increase to the extent of a local supply of balanced poultry feed, the options open to his income-generating ability are increased. However, the answer is not to confine local breeds in intensive management systems. The performance of local breeds will increase slightly under cage or deep litter management (Akinokun, 1975; Oluyemi, 1979; Nwosu, 1979) but, because the genetic potential for egg production (or meat production) of local breeds is lower than that of commercial hybrids, the same investment in intensive management will achieve a much higher production result by using commercial hybrids.
If balanced feed, good health-care supplies and day-old chicks of hybrid varieties are locally available, then intensive poultry management is an option. If these are not available, raising local breeds under scavenger free-range systems is still the best choice.