Altieri, Damiano (2025) Stayability approach to longevity evaluation in Italian Mediterranean Buffalo: genetic parameters and associated traits. [Tesi di dottorato]

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Abstract

The longevity of dairy animals, particularly Mediterranean Italian buffaloes, is a complex trait influenced by multiple factors, with genetics playing a challenging role due to the significant impact of environmental conditions and farm management strategies. This thesis aimed to estimate the longevity of these buffaloes using the Stayability approach in Italian Mediterranean Buffalo (IMB) herds, analysing its genetic parameters for its potential inclusion in breeding programs and to study the relationship with IMB type traits. Data from 276,415 buffaloes born between 1980 and 2020 were provided by the National Farmer Association of Buffalo Species (ANASB), covering 1,025 farms in central and southern Italy. Stayability was assessed across different parities, defined as the probability of an animal remaining in the herd after each calving. Genetic parameters, including heritability and estimated breeding values (EBVs), were estimated using a two-model approach implemented in the BLUPF90 suite. Model 1 accounted for fixed herd effects (Herd), herd-year-season effects (HYS), and an additive genetic effect, while Model 2 incorporated milk production EBVs as a covariate to separate genetic effects from production-related influences. Variance components were estimated using Gibbs sampling via GIBBS1F90+, and post-processing was conducted with POSTGIBBSF90. Results indicate a decreasing stayability trend across parities, with the most significant drop occurring between the first and second parity (0.81 to 0.41), reaching 0.03 by the tenth parity. The culling rate was highest in early lactations and gradually declined in later ones. Heritability estimates ranged from 0.07 to 0.12, with higher values observed in early parities, suggesting that production traits strongly influence culling decisions in younger animals. Genetic correlations between stayability and milk yield EBVs were positive in early parities but weakened in later ones, while negative correlations were observed with fat and protein percentages, potentially due to metabolic constraints on longevity. These findings highlight stayability as a relevant genetic trait for selection, with implications for optimizing breeding strategies to enhance longevity and productivity in IMB herds. A second study investigates the relationships between morphology and stayability in Italian Mediterranean Buffaloes (IMB). Two analytical approaches were employed to explore these relationships. The first method utilized a mixed-effects logistic regression model to analyse binary stayability outcomes, aiming to identify the morphological traits most associated with prolonged productive life. The second approach estimated approximate genetic correlations between stayability estimated breeding values (EBVs) of artificial insemination (AI) bulls and their official EBVs for linear type traits, facilitating the assessment of genetic associations between conformation and longevity. The same dataset from of previous study was used, provided by ANASB, included stayability records from 211,266 buffaloes, spanning parities from stayability 2 to stayability 10. Morphological trait evaluations were available for 51,702 animals from 430 farms. The dataset was merged with test-day milk yield data to control for the confounding effect of milk production. A subset of animals born between 2005 and 2020 and recorded for type traits from 2010 onward was selected. The primary statistical framework applied was a mixed-effects logistic regression model, which incorporated fixed effects for herd-year-season (HYS), age at first calving, and contemporary group, while random effects included the additive genetic effect of the animal. The variance components for stayability were estimated using Gibbs sampling implemented in the BLUPF90 suite, ensuring robust estimation of genetic parameters. Results from the logistic regression model highlighted that body-related traits, including chest width, body depth, and angularity, were significantly associated with higher survival probabilities. A broader thorax and deeper chest were particularly advantageous, supporting higher milk production without compromising health. Conversely, stature exhibited minimal influence on survival. Among feet and leg traits, heel height positively correlated with longevity, while a wider hock angle negatively affected stayability in later parities. Regarding udder conformation, front udder length and rear udder width were positively associated with survival, whereas deeper udders and excessive rear udder height exhibited adverse effects due to increased susceptibility to mastitis. The genetic correlation analysis confirmed the phenotypic findings, showing positive correlations between chest depth and stayability, particularly in early parities. Notably, when milk EBVs were accounted for in the analysis (Model 2), genetic correlations between body size traits and stayability became more negative, suggesting that larger animals are retained longer primarily due to their superior production capacity rather than inherent structural advantages. Similarly, udder traits that were favourable for production showed weaker correlations with longevity once adjusted for milk EBVs, emphasizing the importance of disentangling production effects from conformation-related influences on survival. This study underscores the necessity of incorporating morphological traits in buffalo breeding programs to enhance longevity while maintaining production efficiency. The findings suggest that selecting for animals with optimal conformation, independent of milk production, could improve sustainability by reducing involuntary culling and enhancing overall herd resilience. Future research should focus on refining selection indices that integrate both productivity and structural soundness to optimize buffalo breeding strategies. Results from these studies showed that the genetic analysis of stayability hadlow to moderate heritability values, with an increasing trend for older parities. Productive buffaloes selected during early lactations stay on farms mainly due to their resilience to environmental conditions and good health. The analysis of genetic correlations between longevity and estimated breeding values (EBV) for milk production suggested a possible positive association, although this was less evident in older parities, likely influenced by voluntary culling based on production. Longevity in buffaloes is heavily influenced by environmental factors, making genetic selection more challenging. Genomic selection could be a solution to better exploit genetic potential and reduce generation intervals, thus accelerating genetic progress. The association between longevity and morphology showed that some morphological traits traditionally thought to favour longevity, like larger trunk diameters and udder volumes, were more closely linked to higher production than long-term longevity. In contrast, more compact bodies were associated with greater longevity when milk production was controlled for. The findings suggest that current selection criteria for buffalo morphology should be reconsidered. Advanced genetic models for estimating correlations between longevity, morphology, and productivity can help identify animals with a higher potential for a long, productive career. Achieving high longevity in buffaloes is crucial for sustainability in dairy production, particularly in markets like Mozzarella di Bufala Campana DOP. Accurate selection for stayability could reduce culling rates, the need for replacements, and environmental impact, supporting more sustainable and profitable buffalo farming practices. Integrated genetic selection programs combined with innovative management strategies could play a key role in the future of the buffalo industry.

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