Evaluation of the sample needed to accurately estimate outcome-based measurements of dairy welfare on farm

Abstract

Dairy welfare assessment programs are becoming more common on US farms. Outcome-based measurements, such as locomotion, hock lesion, hygiene, and body condition scores (BCS), are included in these assessments. The objective of the current study was to investigate the proportion of cows in the pen or subsamples of pens on a farm needed to provide an accurate estimate of the previously mentioned measurements. In experiment 1, we evaluated cows in 52 high pens (50 farms) for lameness using a 1- to 5-scale locomotion scoring system (1 = normal and 5 = severely lame; 24.4 and 6% of animals were scored ≥ 3 or ≥ 4, respectively). Cows were also given a BCS using a 1- to 5-scale, where 1 = emaciated and 5 = obese; cows were rarely thin (BCS ≤ 2; 0.10% of cows) or fat (BCS ≥ 4; 0.11% of cows). Hygiene scores were assessed on a 1- to 5-scale with 1 = clean and 5 = severely dirty; 54.9% of cows had a hygiene score ≥ 3. Hock injuries were classified as 1 = no lesion, 2 = mild lesion, and 3 = severe lesion; 10.6% of cows had a score of 3. Subsets of data were created with 10 replicates of random sampling that represented 100, 90, 80, 70, 60, 50, 40, 30, 20, 15, 10, 5, and 3% of the cows measured/pen. In experiment 2, we scored the same outcome measures on all cows in lactating pens from 12 farms and evaluated using pen subsamples: high; high and fresh; high, fresh, and hospital; and high, low, and hospital. For both experiments, the association between the estimates derived from all subsamples and entire pen (experiment 1) or herd (experiment 2) prevalence was evaluated using linear regression. To be considered a good estimate, 3 criteria must be met: R(2)>0.9, slope = 1, and intercept = 0. In experiment 1, on average, recording 15% of the pen represented the percentage of clinically lame cows (score ≥ 3), whereas 30% needed to be measured to estimate severe lameness (score ≥ 4). Only 15% of the pen was needed to estimate the percentage of the herd with a hygiene score ≥ 3, whereas 30% to estimate the prevalence of severe hock lesions. Estimating very thin and fat cows required that 70 to 80% of the pen be measured. In experiment 2, none of the pen subsamples met our criteria for accurate estimates of herd prevalence. In conclusion, we found that both a higher percentage of the pen must be sampled to generate accurate values for relatively rare parameters and that the population measured plays an important role in prevalence estimates.

Assessment of test–retest reliability of animal-based measures on growing pig farms

“…A lack of accuracy in the sampling strategy would not make reliable the estimated prevalence. According to Endres et al (2011) estimating the proportion of thin and fat cows required that 70-80% of the pens be measured. Therefore, a higher percentage of pen/group of animals must be sampled to generate accurate estimates for relatively rare parameters such as very thin animals in cattle (in European cattle rearing systems) or tail biting in pigs than for more frequent parameters such as moderate bursitis.…”

Management characteristics, lameness, and body injuries of dairy cattle housed in high-performance dairy herds in Wisconsin

“…Survey data were collected using direct observation of the high-producing mature (multiparous) cow group and their environment, from management records and from interviewing the herd manager. On larger farms with more than one pen designated for high-producing mature cows, multiple pens were measured to ensure that at least 30% of the at-risk population was represented (Endres et al, 2014). The pen or pens on each farm to be assessed were identified by interview with the herd manager and confirmed through the use of available on-farm records for mean pen milk production, age, and DIM at the time of the visit.…”

Sampling strategies for assessing lameness, injuries, and body condition score on dairy farms

“…Few studies have evaluated sampling for assessing animal-based measures. For dairy cattle, approaches have included evaluating whether sample estimates fall within a tolerance range relative to the true herd prevalence of lameness (Main et al, 2010;Hoffman et al, 2013) and using linear regression to evaluate how well samples reflect the true prevalence of a wider range of animal-based measures (Endres et al, 2014;Van Os et al, 2018). However, assessment programs are typically less concerned with precise prevalence and more concerned with whether a specific farm meets a predetermined threshold of acceptability.…”

“…Some other programs take intermediate approaches, such as assessing the hospital pen but excluding those cows from the thresholds (i.e., Dairy Well, Walker et al, 2017) or monitoring the pen for only resource-based measures (i.e., Validus, Urbandale, IA, personal communication). Including cows from only certain subgroups has been shown to result in different prevalence estimates compared with selecting from all lactating cows (Endres et al, 2014). To our knowledge, no studies have evaluated the effects of excluding hospital pens on farm classification.…”

“…9, 2019 2). Among recent studies on freestall operations, some reported average prevalence of hair loss on the hock and carpus between 10 to 15% (Zaffino Heyerhoff et al, 2014;Adams et al, 2017), but others report much higher values (38 to 76%;von Keyserlingk et al, 2012;Endres et al, 2014;Cook et al, 2016). Given this variation, we used a threshold of ≤20% for moderate hock and carpal injuries.…”