Production, Reproduction and Adaptation characteristics of Boran cattle breed under changing climate: A systematic review and meta-analysis

Introduction Climate change has devastating effects on livestock production and productivity, which could threaten livestock-based food security in pastoral and agro-pastoral production systems of the tropics and sub-tropics. Hence, to sustain livestock production in an environment challenged by climate change, the animals must have the ability to survive and produce under extreme conditions. Boran cattle breed is one of the hardiest Zebu cattle reared by Borana Oromo pastoralists for milk and meat production. This paper aims to compile the main production, reproduction and adaptation traits of Boran cattle based on systematic review amd meta-analysis of peer reviewed and published articles on the subject. Methodology Combination of systematic review and meta-analysis based on PRISMA guideline was employed. Accordingly, out of 646 recorded articles identified through database searching, 64 were found to be eligible for production, reproduction and adaptation characteristics of the Boran cattle, twenty-eight articles were included in qualitative systematic review while 36 articles were used for quantitative meta-analysis. Result Boran cattle have diversity of adaptation (morphological, physiological, biochemical, metabolic, cellular and molecular) responses to the effects of climate change induced challenges - notably high temperature and solar radiation, rangeland degradation, seasonal feed and water shortages and high incidences of tropical diseases. Meta-analysis using a random-effects model showed estimates of heritability and genetic correlations for reproduction and production traits. In addition, heritability and genetic-correlation estimates found in the present study suggest that there is high genetic variability for most traits in Boran cattle, and that genetic improvement is possible for all studied traits in this breed. Conclusion The review revealed that Boran cattle exhibit better reproduction, production and adaption potentials as compared to other indigenous zebu cattle breeds in Ethiopia under low-land, poor pasture and water conditions. On other hand, the breed is currently challenged by adverse effects of climate change and other management factors such as high rate of genetic dilution, reduced rangeland productivity, lack of organized breed improvement programs and discriminate selection of gene pool. Thus, we recommend strategic breed improvement and genetic conservation program of Boran cattle breed in collaboration with Borana pastoralists through proper quantification of important traits and estimation of the pure Boran cattle population while controlled cross breeding strategy could be used in urban and peri-urban areas for maximum utilization of adapataion and production pottential of this breed.


Introduction
parameter estimate for the i th trait in k th article that has reported the standard error,nik is the number 144 of used records to predict the published parameter estimate for the i th trait in the k th article that has 145 reported standard error, and n ij is the number of used records to predict the published parameter 146 estimate for the j th article that has not recorded standard error. Since published correlations don't 147 have normal distribution, they were converted to the Fisher's Z scale and all analyses are 148 performed using transformed values. The results, such as the estimated parameter and its 149 confidence interval, would then be back transformed to correlation for presentation [12]. The 150 approximate normal scale based on Fisher's Z transformation [12,13] is as follows: 151 Z ij =0.5[ln(1+r gij )-(ln(1-r gij )], where r gij is the published genetic correlation estimate for the ith trait 152 in the jth article. To return to the original scale, the following equation [12] was used:

Quality control
Where SEɵ͂ is the predicted standard error for the estimated parameter ɵ, given by  were split into seven categories of adaptation traits, which included morphological (11), 222 behavioural (8), physiological (7), neuro-endocrine (6), blood biochemical (7), metabolic (4) 223 cellular and molecular (9) adaptation traits of Boran and other zebu cattle breeds in the tropics .        showing that there is larger phenotypic variation in these traits than in others (Table 2).     Table 3 indicates comparative summary of birth weight (BW) and mature weight (MW) of six 533 Ethiopian cattle breeds. Boran cattle had better performance in both growth traits (Table 3).      corroborates the current study for Boran cattle.

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Heterogeneity among studies were moderate in milk yield traits by I 2 index (50 to 75%) and higher 625 in reproduction, growth and milk composition traits with I 2 index (>75%). These results reinforced 626 the importance of accounting this heterogeneity in selecting random effect model in the meta-627 analysis reviews of the studies (Table 4).

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The weight and milk production performances of Boran calves are also affected by the maternal 629 genetic effect from dam. In general, maternal-heritability estimates for growth traits had a low to medium magnitude (ranging from 0.089 to 0.20), indicating that the genetic progress for these 631 maternal effects is slow in this breed. Similar trend was observed for milk production traits. It is 632 well known that the initial phases of growth traits are influenced by the maternal effect and 633 ignoring these effects may lead to bias in many situations [94].In general, higher heritability 634 estimates were reported in the studies for milk composition traits followed by growth traits and

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On the other hand, heritability for average daily gain and feed conversion ratio were estimated to 644 be medium for other African cattle breeds (Table 5). The summary of ranges of heritability for 645 tropical cattle breeds indicate that they have lower heritability for reproductive traits except for 646 AFC and lower to medium values for production traits. Similar trends were observed in the current 647 meta-analysis for both reproduction and production traits of Boran cattle.

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Genetic-correlation estimates with the respective 95% confidence interval and the I 2 index to 650 quantify the degree of heterogeneity among the studies were shown in Table 6 for each trait pairs. 651  (Table 6). Estimated genetic correlations among some reproduction and production traits in these 665 studies are in line with summary of genetic correlations of fertility and production traits for tropical 666 zebu cattle in East Africa (Table 7). Except for correlation between AFC and CD, the other