Washington State University researchers are looking at strategic methods for lameness sampling on dairies. In their report “Rationale for a Dairy Herd Lameness Investigation Strategy,” the authors offer different sampling scenarios.
Dale Moore, DVM, MPVM, PhD, Washington State University, believes that locomotion scoring all of the cows on a regular basis is an onerous task. “A large herd could look at several pens a month to get an idea of what is happening on the farm if they wanted individual cow information,” she says.
“I think that estimating the prevalence on an annual basis would be sufficient for a ‘snapshot’ of the herd. The estimate only tells you grossly whether the herd is ‘high’ or not or above the herd goals. It starts the conversation if looking at lameness is not already addressed as it is on many farms. I do think that every day cow pushers can find limping cows that need immediate attention.”
Moore and others at Washington State have been looking at back arch of cows in the lock-ups as a predictor of lameness. Although the sensitivity of this “test” is only about 65%, if the observations are done on a regular basis when cows are locked up for another management reason (breeding or pregnancy diagnosis), it can help find cows that might need help, Moore explains.
“Scoring all the cows can really get at pen-level prevalence and what factors might be influencing lameness in the herd.” If all of the cows on the dairy can’t be lameness score, Moore says attention should focus on the lactating cows first.
“I think that estimating herd lameness prevalence can help a producer and veterinarian decide if that level is acceptable or not,” she says. “If not, they can start to identify the reasons.”
Strategic herd sampling
Washington State University researchers tested sampling strategies on five farms and determined a few methods that can be used to sample cows for locomotion scoring that accurately (within 95% confidence) estimate herd lameness prevalence.
1. Score all the cows – This can be done as cows exit the milking parlor or by releasing cows individually from the lock-up if the pens are small enough. This is time consuming in a large herd. However, scoring all the cows allows for identification of severely lame cows that need treatment. Additionally, it allows for epidemiologic analysis of lameness for the individual farm, which may be useful in determining problem areas and/or etiology.
2. Score the middle third of the pen as they exit the milking parlor. This strategy is based on work by Main, et al 2010 and was validated by WSU researchers (Hoffman, 2011). The advantage of this strategy is that it can determine pen level prevalence. The disadvantage is that it depends on milking parlor times, and requires the observer to be present for the milking of the entire herd if all pens are to be locomotion scored.
3. Calculated sample size of cows, distributed throughout the herd: This strategy is the one employed by the national Dairy F.A.R.M. (Farmers Assuring Responsible Management) program. A calculated sample of cows is weighted across pens and distributed evenly within each pen. The advantage of this strategy is that it does not rely on the milking parlor times. In some cases, it may be difficult to observe cows walking freely in pens while keeping track of which cows have been scored already. This strategy has been easily implemented while the herd is locked up for regularly scheduled herd checks, but requires an assistant releasing individual cows from the head-lock as needed to allow for locomotion scoring. The disadvantage of this strategy is that it does not accurately estimate pen-level prevalence, only herd-level prevalence. For more of Washington State University’s materials on dairy lameness, visit www.wsu.edu and search for “dairy lameness”.