Lesnoff M, Lancelot R
Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), Campus International de Baillarguet, 34398 Montpellier Cedex 5, France.
Animal. 2009 Oct;3(10):1347-53. doi: 10.1017/S1751731109990280.
Many parameters have been proposed for evaluating livestock reproduction performances in tropical farming systems. In tropical free-ranged and small-holder systems, where reproduction cycles cannot be individually observed without expensive field surveys, one of these parameters is the average number of parturitions (h) expected by reproductive female, if the female spends the whole year in the herd. A frequent approach for estimating h is to use the ratio hc = m/T, so-called 'crude annual parturition rate', where m is the observed number of parturitions and T is the total time of presence of the reproductive females in the herd during the year. The bias encountered when h is estimated by hc was evaluated in this paper. Six methods of estimation were used, where T was the exact observed time of presence (hc1) or approximated by monthly, quarterly, half-yearly and yearly averages or final size of the reproductive herd size (hc2 to hc6). Data came from long-term follow-up of cattle and small-ruminant herds (with data recorded at animal level) in extensive agro-pastoral systems in Senegal. In general, h was correctly estimated by hc1. Nevertheless hc1 was sensitive to competing risks (e.g. deaths, sales and slaughtering of reproductive females) and was seriously biased when intensive withdrawals of females occurred before or during the parturition peak. Reliability of crude rates progressively decreased from hc2 to hc6, corresponding to the degradation of information used for approximating T. This decrease was much lower for cattle (for which all methods had acceptable reliability) than for small ruminants. Among the compared methods, the lower reliability was observed for hc6 that we do not recommend for small ruminants. Methods hc5 and hc6 are currently used in rapid cross-sectional retrospective surveys based on the recall of the farmers on the demographic events which occurred in the herd over the last past 12 months. The study has showed that such surveys and estimates hc5 and hc6 can generate seriously biased results. More globally, annual parturition rates can be highly variable depending on the 12-month periods considered. Annual parturition rates estimated on short-term data, even with precise herd follow-up surveys, must be considered cautiously.
许多参数已被提出用于评估热带养殖系统中的家畜繁殖性能。在热带放养和小农户养殖系统中，如果不进行昂贵的实地调查就无法单独观察繁殖周期，其中一个参数是繁殖母畜预期的平均产仔数（h），前提是母畜全年都留在畜群中。估计h的常用方法是使用比率hc = m/T，即所谓的“粗略年产仔率”，其中m是观察到的产仔数，T是繁殖母畜在畜群中全年的总停留时间。本文评估了用hc估计h时遇到的偏差。使用了六种估计方法，其中T是确切观察到的停留时间（hc1），或通过月平均、季平均、半年平均和年平均或繁殖畜群的最终规模进行近似（hc2至hc6）。数据来自塞内加尔粗放农牧系统中牛群和小反刍动物群的长期跟踪（数据记录到个体水平）。总体而言，hc1能正确估计h。然而，hc1对竞争风险（如繁殖母畜的死亡、销售和屠宰）敏感，当在产仔高峰前或产仔高峰期间大量母畜退出时会出现严重偏差。粗略比率的可靠性从hc2到hc6逐渐降低，这与用于近似T的信息的退化相对应。牛的这种下降幅度比小反刍动物小得多（牛的所有方法都具有可接受的可靠性）。在比较的方法中，hc6的可靠性最低，我们不建议用于小反刍动物。hc5和hc6方法目前用于基于农民对过去12个月畜群中发生的人口统计事件的回忆的快速横断面回顾性调查。研究表明，此类调查以及hc5和hc6估计可能会产生严重偏差的结果。更普遍地说，年产仔率可能因所考虑的12个月期间而有很大差异。即使有精确的畜群跟踪调查，基于短期数据估计的年产仔率也必须谨慎对待。
