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Testing Gait Scoring Systems

28 March 2008

As it becomes increasingly important for welfare conditions on farms to meet consumer and legislative demands, new systems are being devised to ensure that animal health is recognised as a priority, writes Chris Harris, Senior Editor, ThePoultrySite.

The new systems are not only measures of the conditions but also used as benchmarks for quality assurance.

One problem found among commercial broilers that is becoming of increasing concern is difficulties with walking and leg disorders.

A study of a new gait scoring system that has been introduced in the US was recently carried out by the University of Georgia, Athens, Mississippi State University in Starkville together with Sanderson Farms.

The study - Validation of a Gait Scoring System for Field Assessment of Walking Ability of Commercial Broilers - was recently presented to the International Poultry Scientific Forum in Atlanta, Georgia.

Prof. Bruce Webster from the University of Georgia told the forum: "Animal Welfare on farms is becoming more and more important. Large problems have been established on walking difficulties among birds, which have welfare, discomfort and mortality repercussions. "A need to establish the depth of the problem has to be established."

He said that one method of establishing the seriousness of the problem was to use gait scoring - a non-invasive method of assessing a large number of birds.

"The Kestin system for gait scoring uses six categories and was used originally for breeder flocks," he said.

"The US system for gait scoring uses a three category system, which has been developed with Sanderson Farms using direct observation of broiler flocks.

"Increasingly gait scoring is being used as a measure of welfare assurance."

In the study the three category US gait scoring system used to evaluate broiler walking ability in welfare audits of commercial flocks was compared with the six category Kestin system.

In two university trials, six week old broilers were gait scored by two observers for each scoring system - a total of 681 broilers. A sub-sample of birds was rescored and used in latency-to-lie (LTL) tests.

"The experiment conducted two trials on Cobb birds. The test went to two different farms to carry out observations and we observed 20 birds in each Kestin group," said Prof Webster.

"We needed heavy birds to be able to observe the problem."

The study showed that too few birds had significant walking difficulties to allow for comprehensive statistical comparison of the two scoring systems, but Prof Webster added that the data were encouraging despite sampling limitations.

He added that there was a significant association between the two systems and both had substantial inter-observer agreement. Both scoring systems had significant correlations with latency-to-lie but the variation of latency-to-lie was too high to give gait score or latency-to-lie much predictive value for each other.

US Gait Scoring System Marking from 0-2
   0    No obvious signs of problems Balance
   1 Obvious signs Clear limp, awkward but can walk 5ft
   2 Severe signs Will not walk 5ft

"The Kestin six category system requires a lot more work to assess the capability of the birds," Prof Webster said.

For the field observations, two teams of observers scored broilers 47 to 61 days of age on five commercial farms each ( in total 1381 broilers). Two pairs of observers scored the same birds, each pair using the US system or the Kestin system. The tests used a handler to move the birds through an open space towards other birds.

Broilers with evident walking problems were oversampled to generate adequate numbers in each gait score category.

Weighted Kappa statistics showed substantial inter-observer agreement in each system, but more so in the US system (K=0.65 vs 0.78, Kestin vs. US, respectively), suggesting that the application of the US system was more consistent between observers, Prof Webster told the forum.

He said that Spearman correlations between US and Kestin scores for individual birds had high statistical significance (P<0.001) and indicated strong correspondence between the two systems.

The simplicity of the US gait scoring system aids inter-observer agreement, making it preferable to more complex systems for use in commercial welfare audits. The strong correspondence between the US and Kestin systems validates the three category system in light of the well-known six category system.

"There are time criteria that have to be considered in the commercial field," Prof Webster said.

"The study found good observer agreement between observers in the on- farm trial both in the Kestin system and the US Gait Scoring system and this validates the US system for Gait Scoring."

Footnote

The study was conducted by A. B. Webster and D. Fairchild, University of Georgia, Athens, B., T. S. Cummings, Mississippi State University, Starkville, P. A. Stayer, Sanderson Farms, Laurel, MS.

March 2008



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