Fifty hens and five cocks from a random mating population of light local chicken ecotype (LLCE) were mated and the fertile eggs hatched to obtain the parent generation (G0) used for this study aimed at improving egg production traits in the LLCE using a selection index. The hens were monitored for short-term (90-days from first day of lay) egg production traits namely: Body Weight at First Egg (BWFE), Average Egg Weight (AEW) and Total Egg Number (TEN). Data obtained were subjected to statistical analysis using SPSS (2001) and paternal half-sib model with Harvey (1990) to estimate descriptive statistics and genetic parameters respectively. These were employed in constructing the selection index. Selection for all the selection criteria (BWFE, AEW and TEN) was in the positive direction. Selected parents were mated to produce next generations – G1 and G2. Selection differentials, selection intensities and genetic response due to selection were also estimated. A control population which spanned for three generations (each generation had its own control population) was used to monitor environmental changes and to estimate the genetic changes due to selection. There were significant increases (P<0.05) in BWFE, AEW, and TEN in the selected populations over the three generations of study such significant increases (P<0.05) were not observed in the control population. Heritability estimates for all traits in all generations and populations were moderate to high. The heritability of the index was also moderate. Such moderate to high heritability estimates indicate high additive genetic variances, implying that these traits were most passed on from the parents to their offspring. Low to high positive genetic and phenotypic correlations was observed between BWFE and AEW in all populations of study. The genetic correlation and phenotypic correlation between BWFE and EN, and between AEW and EN, was moderate to highly negative for all generations and populations of study. A positive genetic correlation was observed between AEW and TEN in G2 of the selected population. A cumulative selection differential of 269.38g, 1.58g and 3.88 eggs were obtained for BWFE, AEW and TEN respectively. Selection response for traits increased over the generations in a fairly linear manner. Realized response per generation was estimated to be 94.22g, 0.84g and 4.85eggs for BWFE, AEW and TEN respectively. It is evident that the simultaneous inclusion of BWFE, AEW, and TEN in a selection index generally improved the performance of selected birds over the generations in the Light Local Chicken Ecotype.
1.1 BACKGROUND OF STUDY
The report of the 4th Food and Agriculture Organization (1973) expert consultation on Animal Genetic Resources presented two important objections concerning the endeavour to improve and conserve the local chicken. The first was as to whether the local strains still possess genes, which are useful to the vastly improved exotic strains given the centuries of genetic screening, which the latter have undergone. The second objection pointed to the fact that the process of further screening of the local chicken will be long, laborious and very expensive. However, the results of recent research using local chicken (Ikeobi and Peters, 1996; Ayorinde et al., 2001; Udeh and Omeje, 2001) indicate that the local chicken is a repository of advantageous genes. Secondly, with molecular genetic techniques, genetic improvement of the local chicken is fast and less expensive. Incidentally, third world countries, which established breeding programmes based on the dilution of indigenous germplasm by extensive crossbreeding programme, suffered failures. Those failed efforts have made livestock breeders aware of the importance of indigenous breeds in overall food production systems – because of their adaptation to the environmental stress of the tropics.
In spite of the large number of livestock and poultry in the nation, the animal protein intake per caput per day still falls below the minimum requirement level recommended by UN/FAO (Ayodele and Ajani, 1999). This has been traced to the low production of animals, which could be due to genetic and/or environmental constraints. The above underscores the need to improve the level of animal protein production in Nigeria. Of greater importance is the improvement of the poultry sector since it has a number of advantages – including short generation interval, and production of large number of offspring, due to its peculiar reproductive traits (Ibe, 2001). Furthermore, poultry meat is generally accepted by all religions and societies.
In many countries the development of agriculture and breeding programmes has resulted in serious changes in poultry breeding stocks during the last decades. The establishment of breeding institutions has led to a pronounced supra-regional propagation of certain chicken breeds due to improvements in performance. As a consequence the local breeds have decreased continuously to the same extent as the preferred high performance breeds have expanded. For instance, it was in a bid to satisfy the need for increased production and profitability in intensive production systems to meet the increase in demand for animal protein by the populace that new high yielding and fast growing poultry breeds were introduced into the existing poultry production systems in Nigeria since the late 1950’s (Obioha, 1992). Incidentally, such introduction has resulted in non-integration of the local breeds considered as ‘low producers’ into large-scale poultry production.
Nigeria has rich chicken genetic resources. A good number of workers have documented the characteristics of the local chicken, in terms of morphological, physiological, behavioral and production attributes. Nwosu (1990) gave a review of these. Ibe (1990a, b) identified some major genes of tropical relevance in Nigerian local chicken populations. Perhaps, the most distinguishing feature for physical characterization at present is the body weight of the local chicken found in the various ecological zones of the country (Olori and Soniaya 1992). Observations have shown that local chicken found within the swampy rainforest and guinea savanna regions are lighter in weight than those found within the highlands and sudan savanna regions (Nwosu, 1979). Such differences in body weight can be used to categorize the local chicken broadly as Light Ecotype – those with lighter weight and Heavy Ecotype – those with heavier weight.
Research data on the local chicken in the past 50 years (Hill, 1954; Oluyemi, 1979; Omeje and Nwosu, 1982; Nwosu, 1987; Udeh and Omeje, 2001) indicate that the Nigerian local chicken has useful genetic attributes that can be harnessed in crossbreeding programmes for the development of egg-type and meat-type chickens. However, there exist limitations to the realization of total heterosis in such crosses with the exotic because – the local chicken is unpedigreed, unselected and unsegregated (Omeje, 1985) hence, unlike the exotics the local chicken cannot be considered a purebred. Furthermore, crossbreds from purebred parents show heterosis to the extent that their gene frequencies differ unlike hybrids from similar lines that manifest total heterosis, (Pirchner, 1983).
In order to incorporate the local chicken as a parent breed to produce strains of chicken that are adaptable to the local environment as well as achieving the much desired goal of making Nigeria self-sufficient in the sourcing of poultry breeding stock and boosting her poultry industry, there is need for selective breeding. The practice of selective breeding among local strains has been found advantageous (El-Issawi, 1975). The concept underlying selective breeding is variation. For within a group of individuals there exist allelic variations that affect the outcomes of quantitative traits such as growth, egg production and egg quality traits.
1.2 STATEMENT OF PROBLEM
Not much study has been done on selection of local chicken for meat or egg production; most of the studies have been on crossbreeding with exotic birds. Oluyemi (1979) after seven generations of mass selection on 12-week body weight of the local chicken concluded that the local chicken is not a potential broiler strain. Although the local chicken has been termed a low producer with regards to egg production (40-80 eggs /bird/year under extensive management system), studies relating to the development of the local chicken as a potential layer have shown appreciable improvement in egg production traits of the birds under improved management system (Hill and Modebe, 1961; Nwosu et al, 1979, Omeje, 1985; Tule, 2005). Nwosu and Omeje (1985) further noted that the local chicken has a genetic potential of producing 128 eggs /bird/year. It should be noted that the results of these studies were from random-bred populations. It is quite possible that the local chicken subjected to selection and improved management can do better. This has prompted the present selection study of the local chicken using a selection index approach.
1.3 OBJECTIVES OF STUDY
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