Selection of Poultry Genotypes in Humid Tropics for Meat Quality Traits, Challenges and Opportunities Ahead

Table of Contents

1. INTRODUCTION
2.2 Genetic selection
2.3 Genomic prediction
2.4 Main selection criteria
2.4.1 Carcass traits
2.4.2 Carcass components of poultry meat
2.4.3 Meat Type Chickens
2.4.4 Major genes affecting heat tolerance
2.4.5 Meat traits
2.4.6 Effect of High Temperature on Meat Quality
2.4.7 Effect of High Temperature on heat production
2.4.8 Opportunity of Genetic Selection on the Welfare of Chickens
2.4.9 Challenges of Genetic Selection on the welfare of chickens
2.4,10 Genetic selection methods
2.4.11 Selection Strategies

3. Summary

4. Recommendation

5. References

1. INTRODUCTION

The indigenous village chicken is the most prominent class of livestock in the country and constitutes about 60-80% of the total poultry population (Aryee and Kutame, 1991), their productivity levels are low because of low genetic potential and poor nutrition. To overcome the problem of low productivity in local chickens, high-yielding exotic breeds have been introduced through cockerel exchange program by the government. This intervention is bedeviled with many challenges; prominent among them is the birds’ inability to adapt to the humid and hot environment, resulting in reduced feed intake and retarded growth (Cowan and Michie, 1988).

A number of major heat-tolerant genes or gene complexes like naked-neck, ptylopody, polydactyly and frizzle have been identified in the genome of Ghanaian local chicken populations (Hagan, 2010). These unique genes have been reported to ameliorate tropical heat stress and enhance the performance of chickens under hot and humid environments (Hernandez et al., 2002 and Cahaner et al., 2008). The existence of the naked-neck gene results in 20-30% less feather coverage overall, with the lower neck of the bird appearing almost naked while the frizzle gene but is reported to reduce the insulating properties of the feather cover (reduce featherweight) and make it easier for the bird to radiate heat from the body, (Islam, M. A., 2004).

The most obvious constraint on poultry production is climate. Poultry seems to be special sensitive to temperature-associated environmental challenges, especially heat stress (Bhadauria, P., 2017).

Environmental extremes have deleterious effects on the productive performance and well-being of all domestic animals. Hot ambient temperatures, above the zone of thermo-neutrality for domestic poultry, typify summer in the greater poultry producing area especially in tropical regions and these affect performance and overall adaptation to the climatic region (Ilori et al., 2009).

According to Reece and Lott (1983), these conditions reduce feed intake and growth rate and negatively affect feed efficiency in growing birds. Prolonged periods of elevated ambient temperature stress increase the time to reach market weight and increase mortality (Deaton et al., 1978). When, high temperatures are coupled with high humidity, the combination can become lethal. ‘Heat stress’ not only causes serious welfare conditions of suffering and death in the birds, but also results in reduced or lost production that adversely affects the profit from the enterprise. Birds are heat-stressed if they have difficulty achieving a balance between body heat production and body heat loss.

Birds will die from heat exhaustion if heat production is substantially greater than heat loss either in intensity (acute) or over long periods (chronic). Productive adaptability itself is a phenomenon whereby an animal gives acceptable level of production in a stressed environment (Ibe, 1990). The tropical environment is characterized by such stress factors as excessive heat, poor nutrition, poor housing and disease. Developing poultry stocks that can tolerate such an environment and give acceptable level of production is desirable (Nwachukwu et al., 2006).

Heat stress can result in significant losses to producers with all types of poultry. The most obvious loss is due to mortality (I.2, 2012).

The heat stress period the increase in body temperature has a negative effect on gamete formation, and the fertilization process. As a result, the full genetic potential of the broiler is often not achieved (Bhadauria, P., 2017).

The objective of this paper is to review selection of poultry genotypes in humid tropics for meat quality traits, the challenges, and opportunities including selection of poultry genotypes, breeds of broilers kept by the farmers, selection criteria, and trait preference for meat quality in humid tropics.

General objective

- To review selection of poultry genotypes in humid tropics for meat quality traits, the challenges, and opportunities.

Specific objectives

- To identify poultry genotypes in humid tropics
- To evaluate selection criteria and meat quality trait preference.
- To identify challenges and opportunities in humid tropics

2. Literature review

2.1 National poultry genotype sector policies

There is increased public and consumer recognition of issues related to food safety, product quality, environmental pollution, animal welfare (Douglas and Buddiger, 2002) and genetic diversity (Notter, 1999), particularly in affluent markets. Breeders have adopted improved production and biosecurity practices and have taken a leadership position on food safety issues. Improvement of animal productivity improves the efficiency of conversion of feed to food and indirectly reduces the production of animal waste per unit, although additional methods of reducing nitrogen and phosphorus waste will ultimately be required. Well-being concerns have resulted in greater emphasis on skeletal and metabolic disorders, disease resistance (McKay et al., 2000) and behavioural genetics in commercial breeding programmes (Hartmann, 1989). It is difficult to assign an economic value to these considerations; primary breeders will be expected to develop novel approaches to help provide sustainable solutions to these problems (Muir, 2003).

2.2 Genetic selection

Humid tropic tolerant broilers are a challenge in global poultry production. In tropical and sub-tropical countries, the evaporative systems applied in broilers houses are not fully functional due to increased environmental humidity. In Southeast Asia, crossbreeding between indigenous and exotic breeds is the most popular breeding system of obtaining a commercial hybrid resistant to tropical conditions, and capable of producing a high amount of eggs and meat (Mekki et al., 2005; Aengwanich, 2007; Bekele et al., 2010; Kingori et al., 2010).

Genetic selection is the most appropriate for birds to become the parents of the next generation. The breeding goal determines what “most appropriate” means in practice. At pedigree level, birds are typically selected taking into account information on relatives, whereas at multiplication levels birds are typically rejected based on their own characteristics, as parents are not known.

The groups of birds destined to replace the birds in the pedigree flocks are selected in such a way that the average genetic relationship within the group is as low as possible and the average value for the selection index is as high as possible. This maximizes the genetic gain, while minimizing the rate of inbreeding in the specific pure line. After selecting the birds that will contribute to the next generation, the birds that follow on average genetic merit are allocated to multiplication (Muir, 2003).

In meat chicken breeding the following parameters are essential:

-Growth rate and body weight
-Fertility and hatchability
-FCR (feed/g weight gain) or FCE (weight gain/g feed consumed and
-Low mortality rate

In cross breed between exotic & local chickens, we should pay attention to paternal & maternal effects on performance of main & reciprocal crosses.

2.3 Genomic prediction

Selection decisions need to be based on predictions of additive genetic merit. To accurately predict genetic merit we need to combine information from phenotypes with information from genotypes and from relatives.

The true additive breeding values is unknown random number we use prediction methods to perform this evaluation. There exists a range of different methods to conduct this prediction process. The most common and simple one includes computing a relationship matrix (G) based on genomic information (Van Raden, 2008) and uses this relationship matrix as variance-covariance structure to obtain the best linear unbiased prediction (BLUP) of breeding values. An assumption of this model is that each marker explains the same proportion of total genetic variance.

A relationship matrix is applied the method is easy to implement using standard software for genetic evaluation that used pedigree information. The only change is that pedigree relationships (A) are replaced with genomic relationships (G), (Calus et al., 2014).

2.4 Main selection criteria

Traits associated with welfare of broilers are subject to genetic selection in at least one breeding company (Muir, 2003).

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2.4.1 Carcass traits

The growth of poultry species is related to the body size. Between poultry species there are significant differences in live weights and carcass measurements caused by genetic and environmental factors (Ogah, 2013). Maturity of the birds is accompanied by muscular tissue growth which is a typical occurrence in time series data. Body weights of chicken increased with age in earlier (Baeza et al., 2001; Nahashon et al., 2006, Bernacki et al., 2013). The poultry with higher body weight have more breast and leg muscles, and carcass remainders (Kokoszynski et al., 2011b). Young et al. (2001) reported that growth of wings or drumstick was not consistent with age as compared to breast, thighs, fillets, and fore quarters which increased with slaughter age while females were heavier than males in chickens (Musundire, 2016).

2.4.2 Carcass components of poultry meat

The most important components of commercial poultry meat are:

Breast

-Thighs
-Drumsticks
-Wings
-Back and neck meat
-Giblets (heart, gizzard, and liver).

They are also available as legs (drumstick & thigh attached), leg quarters, breast quarters, breast halves & poultry halves. Chicken products taken from the breast & wing are considered white meat and the products taken from the drumstick and thigh are considered as dark meat.

2.4.3 Meat Type Chickens

Modern meat type chickens have been selected in breeding program, extensively used for high body weight and improved feed conversion efficiency at earlier age, resulting in substantially increased growth rate. As a result of high growth rate, the broilers have become more susceptible tophysiological as well as pathological problems because modern broilers are imported from the west, where environmentally controlled housing, rich ration, vaccines, and drugs are used for the development of this stock. The modern fast growing broilers are more susceptible to heat stress which in turn results in poor performance due to increased mortality and decreased growth rate in tropical climate (Musundire, 2016).

2.4.4 Major genes affecting heat tolerance

There are specific genes which play crucial role in heat tolerance.

These genes are:

-Naked neck gene (Na)
-Sex-linked dwarfism gene (dw)
-Sex-linked slow feathering gene (KS) Frizzle feather gene (F)

I) Naked neck gene (Na)

They have incomplete dominant autosomal gene.

They are characterized by absence of feather follicles on head & neck regions.

The possible genotypes are:

-Homozygous normal (nana),
-Homozygous naked neck (Na/Na) and
-Heterozygote (Na/Na)

Feathers contain approximately 90% crudeprotein and are low in moisture;

Therefore, amino acids crucial to feather formation are expected to influence live weight considerably. Keeping naked neck or completely naked chickens is advantageous from economic point of view.

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