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The objective of this study was to estimate the genetic parameters of reproductive traits in heifers and adult cows and to elucidate the genetic correlations of these traits between heifers and adult cows as well as across different parities. This study collected a total of 84 061 reproductive records， including calving， insemination， and pregnancy diagnosis， from 37 329 Holstein cows in 6 large-scale dairy farms in Jiangsu Province between 2020 and 2024. Among these， 31 689 records were from heifers and 52 372 records were from cows. Genetic parameters were estimated using the average information restricted maximum likelihood （AI-REML） procedure implemented in the DMU software based on animal and repeatability models. The results showed that the heritability estimates of reproductive traits in heifers ranged from 0.04 to 0.52， with the highest value observed for age at first service （0.52±0.01）， while the heritability of the other traits ranged from 0.04 to 0.22. In heifers， the genetic correlations among age at first service， age at last service， and age at first calving were high， ranging from 0.73 to 0.98. In cows， the highest genetic correlations were observed between days open and the number of services and interval between first and last service， with values ranging from 0.95 to 0.96. The genetic correlations of reproductive traits between adjacent parities were relatively high， with values ranging from 0.62 to 0.68 between heifers and primiparous cows. By contrast， the correlations between heifers and multiparous cows were low （0.05-0.15）. Furthermore， phenotypic correlations across different parities were generally low， ranging from 0.01 to 0.18. In addition， the absolute genetic correlations of number of services and interval between first and last service with other traits were relatively high， ranging from 0.28 to 0.97， suggesting that these traits could serve as important indicators of reproductive performance in both heifers and cows. This study systematically elucidated the genetic parameters of reproductive traits in Holstein cattle in Jiangsu Province， providing a theoretical basis for the genetic improvement of reproductive traits in this population.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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