Abstract：
Since the early 2000 s the practice of free-range egg production has increased in developed countries, partly driven by consumer perception that free-range housing is better for hen welfare. While poultry in free-range systems have more behavioural opportunities compared with poultry in caged systems, free-range systems are associated with greater frequencies of infectious disease, predation and \'smothering\', a condition where birds pile on top of one another with death occurring due to suffocation. Although the frequency of smothering deaths in Australian free-range layer poultry is anecdotally high, there is a lack of empirical evidence quantifying smothering cause-specific mortality rates and identifying factors that place birds at higher risk of death from smothering. This was a prospective cohort study of poultry flocks managed by three commercial free-range layer organisations in Eastern Australia. Flocks were enrolled into the study from 1 January 2019 to 29 March 2021 and were followed until the end of lay or until the end of the study on 31 March 2022, whichever occurred first. Throughout the follow-up period flock managers provided production details for each flock and details of smothering events using custom-designed logbooks.A total of 84 flocks were enrolled in the study: 32 from Organisation 1, 35 from Organisation 2 and 17 from Organisation 3. The number of birds per flock ranged from 16,000 to 45,000. The total mortality rate was 1131 deaths per 10,000 bird-years. Smothering mortality rate across the three organisations was 183 (minimum 133, maximum 223) deaths per 10,000 bird-years at risk. Smothering accounted for around 16% (minimum 9%, maximum 22%) of all deaths.We identified no distinctive temporal pattern in daily smothering risk as a function of either the number of days since placement or calendar date. The locations of smothering events in sheds and in the outdoor range were not consistent, with relatively large numbers of smothering events occurring in specific locations for some sheds but not others. To the best of our knowledge, this study is the largest prospective study of smothering mortality in commercial free-range layer flocks conducted to date. Estimates of smothering incidence rate and how that varies within and between flocks and organisations over time provides a critically important benchmark for further investigations into this substantial area of productivity loss.
摘要：
自2000年代初以来，发达国家的散养鸡蛋产量有所增加，部分原因是消费者认为自由放养住房对母鸡福利更好。虽然与笼养系统中的家禽相比，自由放养系统中的家禽具有更多的行为机会，自由放养系统与更高的传染病频率相关，捕食和“窒息”，鸟类相互堆积，因窒息而死亡的情况。尽管澳大利亚自由放养蛋鸡窒息死亡的频率很高，缺乏经验证据来量化窒息性特定原因的死亡率，并确定使鸟类因窒息而死亡的风险较高的因素。这是一项由澳大利亚东部三个商业自由放养层组织管理的家禽群的前瞻性队列研究。从2019年1月1日至2021年3月29日，羊群被纳入研究，并随访至产程结束或至2022年3月31日研究结束，以先发生者为准。在整个后续期间，羊群经理使用定制设计的日志提供了每个羊群的生产详细信息和窒息事件的详细信息。该研究共招募了84只羊群：32只来自组织1，35只来自组织2，17只来自组织3。每群鸟类的数量从16,000到45,000不等。总死亡率为每10,000鸟年1131例死亡。这三个组织的窒息死亡率为每10,000鸟年有风险，死亡人数为183人（最低133人，最高223人）。窒息约占16%(至少9%，最大22%)的所有死亡。我们在每日窒息风险中没有发现独特的时间模式，该模式是自放置或日历日期以来的天数的函数。棚屋和室外范围内窒息事件的位置不一致，在某些棚屋的特定位置发生了相对大量的窒息事件，而在其他棚屋则没有。据我们所知,这项研究是迄今为止进行的最大的商业自由放养蛋鸡群中窒息性死亡率的前瞻性研究.窒息发生率的估计以及随着时间的推移在羊群和组织内部和之间的变化如何，为进一步调查生产力损失的这一重大领域提供了至关重要的基准。
