Genetic improvement of growth traits in Jebel Akhdar goats, Batinah goats, and Omani sheep in Oman

Al-Subeihi, Saud (2024). Genetic improvement of growth traits in Jebel Akhdar goats, Batinah goats, and Omani sheep in Oman. University of Birmingham. Ph.D.

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Abstract

The objective of the present thesis was to estimate the genetic parameters associated with growth traits, specifically birth weight (BW), weaning weight (WW), six-month weight (W6), and yearling weight (W12), among Jebel Akhdar (JA) goats, Batinah (BA) goats, and Omani sheep (OS) in Oman. In addition, the level of inbreeding and its trend over 13 years were investigated for the three breeds. Finally, a simulation study was carried out to examine the feasibility of implementing genomic selection (GS) in OS sheep with the aim of enhancing the genetic improvement of these traits. The analysis utilised data obtained from the Wadi Qurayyat Livestock Research Station (WQLRS) in Oman over the years 2008 to 2020. The dataset comprises 2,826 records of JA goats, 2,609 records of BA goats, and 3,530 records of OS sheep.
The heritability estimates for BW, WW, W6, and W12 in JA goats were 0.13 ± 0.04, 0.11 ± 0.04, 0.19 ± 0.05, and 0.21 ± 0.06, respectively. In comparison, the values for BW, WW, W6, and W2 were found to be 0.17 ± 0.04, 0.16 ± 0.04, 0.16 ± 0.04, and 0.24 ± 0.04, respectively, in BA goats. In Omani sheep, the observed values for BW, WW, W6, and W12 were 0.16 ± 0.03, 0.15 ± 0.03, 0.28 ± 0.05, and 0.48 ± 0.05, respectively. The three breeds showed a positive genetic trend for all growth traits, although the phenotypic trend was only significant for the W12 phenotype. The annual genetic gain for BW, WW, W6, and W12 in JA goats was measured as 0.01 kg, 0.09 kg, 0.13 kg, and 0.20 kg, respectively. The BA goats exhibited an annual increase in genetic gain of 0.01 kg, 0.08 kg, 0.10 kg, and 0.18 kg for BW, WW, W6, and W12, respectively. The genetic gain for BW, WW, W6, and W12 in OS sheep exhibited annual increments of 0.01 kg, 0.13 kg, 0.22 kg, and 0.39 kg, respectively. The genetic correlations between the different traits in the three breeds were found to be positive and strong, except for the correlations with the BW trait, which had low correlations. The results of this study highlight the potential for significant genetic improvement in the growth traits associated with the investigated Omani breeds, considering their sufficient genetic variability and the favourable genetic correlations seen between them, particularly with respect to post-weaning traits.
The inbreeding levels within the three breeds were found to be very low, with estimations of 0.67% in JA goats, 0.65% in BA goats, and 1.52% in OS sheep on average. The observed levels of inbreeding among the inbred animals were 3.88%, 3.39%, and 6.49% for the respective breeds. However, there has been a notable increase in inbreeding rates, especially in recent years, necessitating the need for continuous monitoring and the implementation of measures to control it.
The simulation study has indicated that the ssGBLUP method demonstrated superior performance on prediction accuracy of breeding values averaging (0.64) across the traits of BW, W6, and W12 in OS sheep compared to the methods of BLUP (0.56) and GBLUP (0.47). The precision of the three methods was enhanced with an increase in heritability. The genomic prediction accuracy of GBLUP and ssGBLUP was enhanced by increasing the reference size. The average improvements were 0.43, 0.48, and 0.50 for GBLUP, and 0.61, 0.64, and 0.67 for ssGBLUP. These improvements were observed at reference sizes of 500, 1000, and 2000 animals, respectively. For traits with low heritability in particular, ssGBLUP may be a useful method for increasing prediction accuracy when compared to BLUP and GBLUP. The outcomes provide a theoretical framework for implementing GS in OS sheep.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):