Development of Breeding Strategies to Improve Growth and Egg Production in a Dual-Purpose Native Chicken Breed in Thailand

Abstract

<p>This thesis examines the methods to improve the productivity of a dual-purpose native chicken breed in Thailand. Five generations of body weights and egg production data on Lueng Hang Kao Kabinburi (LHKK) chickens were used for estimation of genetic parameters in chapters 3 and 4. Traits considered were body weights, measured at four-weekly intervals from hatch to 24 weeks of age (BW1D, BW4, BW8, BW12, BW16, BW20, and BW24), body weight at first egg (BWFE), age at first egg (AFE), egg weight at first egg (EWFE), and egg number (EN).There were 11,588 chickens from 486 cocks and 1,461 hens that had records for growth and egg production traits. Relationships between growth rate and egg production traits were also explored. The level of inbreeding and its effect on growth and egg production were explored. In chapter 5, hatchability (HAT), rate of lay (RL), average daily gain (ADG), and survival rate (SUR) were identified as economically important traits and were used in a selection index to optimize the genetic response to selection. Finally, in chapter 6, population sizes and mating ratios were explored to optimize the genetic response in HAT, RL, ADG and SUR while minimizing the rate of inbreeding in the nucleus flock of LHKK chickens by simulating 20 generations of chickens for recurrent selection.</p> <p>Univariate and bivariate analysis were used to estimate genetic parameters in body weight and egg production traits. Fixed effects of year and hatch within year were significant for all traits and sex was significant for all body weight traits, except for BWFE. The direct additive genetic effect was significant for all traits and the maternal genetic effect was significant only for growth traits, except BWFE. The maternal permanent environmental effect was significant for all growth traits, except for BW24 and BWFE. The estimates of heritability for direct additive genetic effect ranged from 0.10 to 0.47 for body weight traits and ranged from 0.15 to 0.16 for egg production traits. High positive genetic correlations were estimated between all traits, except for negative genetic correlations between EN and other traits. Inbreeding effect on growth and egg production traits was not significant, except for BW1D, where BW1D reduced by 0.09 g when the rate of inbreeding increased by 1% per generation.</p> <p>Univariate random regression model was used to estimate genetic parameters for body weight traits along the growth trajectory from BW1D to BW24. A quadratic Legendre polynomial was identified as the best model to estimate variance structure for all random effects fitting heterogeneous residual variances based on six growth periods. Heritability estimates ranged from 0.34 to 0.54 and 0.04 to 0.06 for direct additive and maternal genetic effects, respectively. Estimated variance ratios ranged from 0.19 to 0.48 and 0.10 to 0.12 for direct and maternal permanent environmental effects, respectively. All genetic correlations between body weight traits were high and positive.</p> <p>Genetic relationships between growth rates, measured at four-weekly intervals, and AFE and EWFE were estimated using bivariate analysis. Estimated heritabilities for growth rates ranged from 0.06 to 0.28. Estimated heritabilities for AFE and EWFW were 0.24 and 0.16, respectively. Genetic correlations between growth rates and AFE ranged from -0.22 to 0.02, and between growth rate and EWFE ranged from -0.05 to 0.40. The result suggested that selecting chicken with a high growth rate at an early growth period (at 28 days of age) would improve the body weight and egg weight at sexual maturity while reducing the age at sexual maturity. </p> <p>Breeding strategies to improve the meat and egg production of the LHKK chickens under intensive (IPS) and extensive production system (EPS) were explored. A bioeconomic model was developed to calculate economic weights for HAT, RL, ADG and SUR. Estimated economic weights and the response to selection showed that LHKK chicken production was economically viable under the IPS and the EPS in Thailand. Annual economic return per hen in the EPS (621THB) was higher than the annual economic return per hen in the IPS (132THB) due to the lower cost of production under the EPS than the IPS. Calculated combined economic weights from the IPS and the EPS were 21.01THB for HAT, 56.52THB for RL, 106.52THB for ADG, and 15.76THB for SUR. The estimated relative economic weights showed that RL was the most important economic trait in LHKK chicken production. Decreased feed price and increased fattening chicken price is expected to increase the monetary return from the native chicken farms. Using the multi-trait selection index resulted in predicted responses of 0.97% in HAT, 2.41% in RL, 1.38g in ADG and 0.73% in SUR. Thus, implementing a single breeding objective strategy in the nucleus flock of the LHKK chickens will improve the productivity under both IPS and EPS.</p> <p>A stochastic simulation using an optimal contribution selection (OCS) approach with a target of 25º for mate selection was used to minimize the level of inbreeding and maximize genetic gain in LHKK nucleus flock. The level of inbreeding and genetic gain for a range of population sizes and mating ratios were compared after 20 generations of recurrent selection. The predicted level of inbreeding indicated that increasing the population size by 30% from the current population size would reduce the level of inbreeding in LHKK flock by around 1% per generation. Reducing the nucleus size by 30%, in comparison to the current nucleus size, will increase the level of inbreeding by 1.55% per generation. The highest level of inbreeding was found in the higher mating ratios of one cock to floating hens (one to 10 hens) and the lowest level of inbreeding was found in the lowest mating ratio of one cock to three hens. The predicted genetic responses obtained across the four mating ratios were not significantly different to each other.</p> <p>In summary, this study found that the growth and egg production traits in LHKK chicken are heritable and also have high genetic correlations between them. Therefore, both meat and egg production of LHKK chickens can be improved by implementing a multiple traits selection strategy. Furthermore, implementing a common selection strategy in the nucleus flock of LHKK chickens is expected to increase the monetary return under an intensive and extensive production system in Thailand. However, the effects of using a system specific selection strategy for IPS and EPS on the profitability under each production system need to be explored. Increasing the current nucleus flock size and reducing the mating ratio will fulfil the main objective of the current LHKK breeding program by further improving the meat and egg production, while maintaining the breed characteristics of LHKK chickens. </p>