تعیین ارزش اقتصادی صفات کلیدی تولیدی به منظور بهبود عملکرد و توسعه اصلاح‌نژاد گوسفند افشاری

Introduction
The livestock sector is a fundamental pillar of global food security, providing essential protein sources-including meat, milk, and eggs-for human consumption. In developing countries, this sector faces two interconnected challenges that threaten its sustainability and productivity. First, animal productivity remains substantially below its genetic potential, despite increasing demand for animal products driven by population growth and rising incomes. Second, livestock production in these regions contributes disproportionately to greenhouse gas emissions, accounting for 50 to 65 percent of global livestock-related emissions. Genetic improvement through structured breeding programs offers a sustainable, long-term solution to simultaneously enhance productivity and reduce environmental impact per unit of product. The success of such breeding programs fundamentally depends on accurately defining breeding objectives, wherein traits are appropriately weighted according to their economic contribution to overall farm profitability. Bio-economic modeling provides a rigorous methodological framework for deriving these economic weights by simulating the complex biological and economic relationships within production systems. The Afshari sheep represents an important fat-tailed breed in Iran, primarily raised for meat production under extensive and semi-intensive management systems in mountainous regions. Despite the breed's economic significance to rural livelihoods and national meat production, comprehensive economic analyses to establish quantitative breeding goals for this breed have remained conspicuously absent from the scientific literature.
This study was designed with three primary objectives that build progressively toward establishing a foundation for genetic improvement programs. The first objective was to develop a comprehensive bio-economic model that accurately represents the biological processes, management practices, and economic flows of typical Afshari sheep production systems. The second objective aimed to estimate both absolute and relative economic values for key productive and reproductive traits that influence system profitability. The third objective sought to evaluate the sensitivity of these economic values to potential changes in management practices, input costs, and output prices, thereby providing insights into the robustness of breeding objectives under varying production scenarios.
Method
The research was conducted through an extensive field survey of 480 Afshari sheep flocks in 2024, employing multiple complementary data-collection strategies. Information was gathered through systematic document analysis of farm records, direct observation of management practices across different seasons, and structured in-person interviews with flock owners to capture detailed economic data. The collected information encompassed production parameters (including growth rates and body weights at different ages), reproductive performance measures, comprehensive management practices, and detailed economic accounts of all revenues and costs. A deterministic bio-economic model was constructed and simulated in Excel to calculate the profit function for a representative flock operating under typical management conditions. The model partitioned the flock into six distinct age-and-sex classes—suckling lambs, weaned lambs, replacement females, replacement males, breeding ewes, and breeding rams—with specific biological and economic parameters defined for each class. All revenue streams were quantified, including income from meat sales at various ages, wool production, and manure sales. Cost components were comprehensively categorized into variable costs (encompassing feeding, husbandry, labor, and marketing expenses) and fixed costs (including depreciation and infrastructure maintenance). Feeding costs were calculated based on individualized energy and protein requirements, considering the physiological state of each animal class (maintenance, growth, pregnancy, and lactation). The economic value for each trait was derived mathematically as the partial derivative of the profit function with respect to that trait, representing the change in annual profit per ewe resulting from a one-unit increase in the trait mean, while holding all other factors constant. The traits evaluated through this approach included litter size at birth, total litter weight weaned annually, ewe economic longevity (measured as productive years in the flock), birth weight, weight at three months of age, weight at six months of age, weight at nine months of age, weight at twelve months of age, and annual greasy fleece weight.
Results
The bio-economic analysis revealed detailed insights into the profitability structure of Afshari sheep production systems. The average annual profit per ewe under baseline conditions was calculated at approximately 90.6 million Iranian Rials, providing a reference point for evaluating the impact of genetic changes. Examination of the cost structure revealed that feeding costs represented the dominant expense category, accounting for 61.1 percent of total production costs, underscoring the critical importance of feed efficiency in determining overall profitability. Labor costs accounted for 25.2 percent of total expenses, while husbandry costs (including health management and breeding) accounted for 12.5 percent. Fixed costs comprised a minimal portion of total expenses (less than one percent), reflecting the extensive nature of the production system. Analysis of revenue streams demonstrated the overwhelming importance of meat production to system profitability, with meat sales contributing 95.9 percent of total income. Manure sales provided 3.7 percent of revenue, while wool sales contributed only 0.4 percent, confirming the breed's primary role as a meat producer.
The economic value analysis revealed substantial variation among traits in their contribution to profitability. Litter size at birth had the highest relative economic importance among all evaluated traits, with a value substantially exceeding those of other traits. This finding indicates that improving reproductive performance by increasing the number of lambs born per ewe lambing yields the greatest profit. Total litter weight weaned also showed a high positive economic value, reflecting the combined contribution of both reproductive rate and lamb growth to overall meat production. Growth traits at three, six, and twelve months showed moderately high positive economic values, indicating that genetic improvement in post-weaning growth rates would significantly enhance profitability by increasing meat production from animals sold at various ages. Ewe economic longevity showed a moderate positive value, reflecting the benefits of reduced replacement costs and increased lifetime production from longer-lived breeding females. The economic value for birth weight was negative, indicating that selection for increased birth weight would reduce overall profitability. This negative relationship arises because higher birth weight increases nutritional requirements and management costs without generating corresponding increases in revenue, since birth weight itself is not directly marketed. Annual greasy fleece weight demonstrated the lowest positive economic value among all traits, confirming that wool production is economically marginal within this meat-focused production system and should receive minimal emphasis in breeding programs.
Conclusions
This study successfully developed and applied a bio-economic modeling approach to establish quantitative breeding objectives for Afshari sheep production systems. The results demonstrate conclusively that breeding programs should prioritize genetic improvement in reproductive performance—measured by litter size and total litter weight weaned—followed by growth traits including weights at three, six, and twelve months of age. The estimated negative economic value of birth weight suggests that selection strategies should focus on improving postnatal growth rates without increasing birth weight, thereby avoiding the associated costs and potential complications associated with heavier lambs at birth. The minimal economic importance of wool production suggests that this trait should receive correspondingly minimal emphasis in selection decisions. These empirically derived economic values provide the quantitative foundation for constructing multi-trait selection indices that enable breeders to make economically optimal selection decisions. Implementation of breeding programs based on these objectives has the potential to substantially improve the profitability and sustainability of Afshari sheep production, contributing to enhanced food security and rural livelihoods while potentially reducing the environmental footprint per unit of meat produced by improving biological efficiency.