Measuring welfare in rearing piglets: test–retest reliability of selected animal-based indicators

The “Welfare Quality protocols” (WQP) were developed in 2009 as objective welfare assessment tools. The WQP are based on four welfare principles: 1) “good feeding”, 2) “good housing”, 3) “good health”, and 4) “appropriate behavior”. The included WQP-indicators were developed for growing pigs and are recommended for rearing piglets, although, to the authors’ knowledge, they have not been tested in this age class. Therefore, the present study tested selected indicators from different welfare assessment protocols with regard to test–retest reliability (TRR), consistency over time, in an on-farm study on rearing pigs. This allows to investigate whether the WQP-indicators developed for growing pigs can be recommended for rearing piglets and whether the additional indicators should be included in the WQP. In total 28 selected pen- or individual-level indicators were used by one observer to assess the animal welfare of rearing piglets on three pig farms. Per batch 40 to 125 piglets were randomly selected and individually marked to record the weekly assessments. This procedure was repeated in three consecutive batches per farm and resulted in a total of 759 rearing piglets being assessed. Spearman’s rank correlation co-efficient (RS), intraclass correlation co-efficient (ICC), and limits of agreement (LoA) were calculated to evaluate their TRR, especially if the TRR was influenced by the group of assessed animals (batch comparisons) or the age of the assessed piglets (age class comparisons). From the 28 indicators, 12 had a very low prevalence of <1% making an assumption about their TRR meaningless. From the pen level indicators, “sneezing” achieved acceptable TRR for both comparisons and “behavioral observations” (BO) achieved in general good values (e.g., “positive social behavior”: (RS: 0.34 to 0.89; ICC: 0.00 to 0.90; LoA ϵ [−2.93; 7.41] to ϵ [−18.9; 11.5]) for both comparisons (batch, age class). The WQP-indicators of sufficient TRR, such as “tail lesions”, “lameness”, “wounds on the body”, “human–animal-relationship test” and “BO”, cannot cover the four welfare principles adequately. In particular, problems remained with the welfare principles of “good feeding”, “good housing”, and partly “good health”. However, these grievances could be overcome by including further indicators from other sources outside the WQP which have acceptable to good results for TRR in this study, such as “back posture”, “ear lesions”, “normal behavior”, and “tail posture”.