Reliability of a Twelve-Month Retrospective Survey Method for Estimating Parturition and Mortality Rates in a Traditional African Livestock Farming System

Abstract

Parturition and mortality annual rates are basic data for quantifying productivity of livestock populations in tropical extensive farming systems. Herd monitoring with ear-tagged animals is a gold standard for estimating these parameters in the field. Alternatives are cross-sectional retrospective surveys, based on farmers’ interviews and their short- or long-term recall of the herds’ demography. The present study evaluated a retrospective method (12MO) for estimating parturition and mortality rates over the last twelve months before the survey. The bias of different approximation methods was calculated for different available databases on cattle and small ruminants monitored in Senegal. The main result was the potentially high bias variability (particularly for the mortality rate of small ruminants for which the relative bias ranged from -60 to 96% in age class “0 to 1 year”), although the median bias remained acceptable (the median relative bias was ≤ 6% in absolute value). Retrospective surveys such as 12MO should be used sparingly (for instance to approximate immediate impacts of large shocks or of innovations) and their results interpreted with caution. Whenever possible, herd monitoring surveys (with or without animals’ identification) over a period of several years should be preferred.