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«Measurements of Trackways as a Method for Assessing Locomotion in Dairy Cows Evgenij Telezhenko Thesis (Licentiate) Sveriges Lantbruksuniversitet ...»

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The self-chosen speed of the cow walking on different floors is an important indicator of her reaction to a specific floor. It should be noted that locomotion parameters obtained at different speeds are much more complicated to interpret (Paper II). Still it seems that a particular cow uses more or less the same speed when she walks on the same floor type and in the same direction (Paper I). The speed of locomotion may also have a close relationship with the motivation for movement. Usually cows are more motivated to move from the milking parlour to the cubicles than in the opposite direction, which can result in differences in speed and other speed-related parameters (Telezhenko, unpublished). Analysis of repeatability and reproducibility of trackway elements revealed significant withintest variation. Although cows walked apparently smoothly, some speed variation did occur and contributed to variation of speed-related gait parameters (i.e. stride length). The walk itself may be a less consistent gait than e.g. trot. In one study horses walked less consistently on the treadmill and needed more habituation time than at a trot (Buchner et al., 1994).

The low reliability of step asymmetry suggested non-systematic changes in inter-limb coordination in non-lame cows. The within-test variation was very high and can be explained both by within-test speed inconsistency and by tactics adopted to avoid falling and slipping.

Quality of gait Definition of good locomotion Gait quality in cows has usually been evaluated in terms of presence or absence of lameness (Manson & Leaver, 1988; Whay & Main, 1999). In sport horses, however, associations between stride kinematics and subjective assessment of movement quality have been found (Clayton, 2001). Horses with good movements showed more retraction in the forelimbs and more protraction in the hind limbs, a prolonged swing phase and ability to achieve a particular speed using a long stride length and a low stride frequency. Impaired locomotion in cows has been described as stride shortening and a “stiff gait” and has also been described in terms of the degree of abduction or adduction in the hind limbs (Whay, 2002).

Still, no detailed description of “good locomotion” in cows measured using quantitative methods has been published.

Indicators of cow locomotion comfort Stride length When assessing gait quality, we used the trackways on sand as a standard surface with properties for the best locomotion comfort (Paper II). The most informative parameter for locomotion comfort assessment was stride length. The stride length was significantly decreased in moderately lame cows, and non-lame as well as lame cows increased their strides on the yielding surfaces. The stride shortening during lameness is characterised by shortened swing durations and longer stance durations, which is an important method of reducing the peak loads on the lame limbs (Buchner, 2001). In Paper II it was suggested that stride lengthening is a more efficient way to increase speed during walking than is increasing stride frequency. However, effectiveness of stride lengthening during walking is limited by the effectiveness of the pendulum-like energy exchange between kinetic energy and gravitational potential energy. The effectiveness of the exchange depends on the angle the legs make from vertical (Alexander, 2003). Too long a stride would imply a too large angle for the legs and therefore not enough potential energy to be transformed to kinetic energy, which would raise the metabolic energy cost of transport. Under normal conditions animals choose the walking speed and stride length which corresponds to the most optimal exchange between potential and kinetic energy (Biewener, 2003). Therefore it was concluded that maximal stride lengthening on the sand surface at cows’ own chosen speed constitutes natural movement with minimal energy expenditure. It has also been shown that cows increase their stride length when the COF of the floor is satisfied for unconstrained walking (Phillips & Morris, 2000, 2001). Walking with shorter strides on a slippery floor is an adaptive mechanism for preventing slipping, in which the COF required for walking is kept below the available COF (Van der Tol et al., 2005).

However, maintaining the speed by increasing frequency with shortened strides is an attribute of inefficient walking (Paper II). Slippery floors force animals to modify their posture and develop a “stiff” gait, which can remain even when a cow walks on a floor with acceptable friction (Herlin & Drevemo, 1997).

Overlap Overlap distance describes the lengthwise position of the rear foot imprint in relation to the imprint of the same side’s front foot. It was repeatedly stated that cows normally put their rear feet on the same spot that the front feet has just been lifted from (Tranter & Morris, 1991; Whay, 2002). Usually positive or cloze to zero overlap characterises the good, progressive movements; and lameness and slippery floor cause an under-reaching of the rear foot in relation to the front foot, or a negative overlap (Paper II). However, we found that some degree of lameness could be associated with an over-reaching (large positive overlap) as well (Paper II).

The overlap characterises the extent of hind limb protraction and in Paper I was associated with the stride increasing. However, the negative correlation between overlap and body length (Paper I) implies that when evaluating the overlap attention should be paid on proportions of the animals, i.e. a long body with short legs will result in placement of the rear foot imprints further behind the front ones (negative overlap) and a short body with long legs will result in placing the rear imprints in front of the front ones (positive overlap). The between-breed differences in overlap found in Paper II were most probably due to such differences in animal proportions.

Step length and step asymmetry The contribution of step length alone to the assessment of locomotion comfort is no greater than that of stride length. The two measurements are highly correlated but step length can be less reliable as a measure of progression because it is influenced by the width of the support base (step width, step angle) and step abduction-adduction. The important derivative we can obtain from the step length measurements is step asymmetry. Step asymmetry arises primarily from shortening of one step, but varied step abduction can contribute to bigger step asymmetry as well. Step asymmetry showed good agreement with the subjective assessment of lameness and, besides, was proof of increased walking comfort for lame cows on the yielding floors (Paper II). A similar decrease in foot lameness expression on soft surfaces has been shown in horses (Ross, 2002). Nevertheless it may be complicated to use step asymmetry as an exact tool for determination of the site of the pain. Even in cases of only supporting lameness (caused by the pain associated with weight bearing), where a cow will shorten her step shifting from, e.g., the right limb to the left, it may mean a problem with weight acceptance of the left limb, or a problem with propulsion of the right limb. Increased asymmetry in nonlame cows on the slippery floor showed the possible implementation of the measurement as a parameter of altered stability. Consequently asymmetric steps may be a parameter for presence of gait abnormality, without being a diagnosis.

Width of walking posture The width of the posture during walking can be described either by measuring step width or by measuring step angle, the latter method having an advantage in determination of landmarks for measurements (Paper I). Step angle correlated positively with stride length and big angle (narrow walking posture), usually a characteristic of a more efficient gait due to minimal lateral displacement of the centre of gravity (Alexander, 1985). On the other hand, with a small step angle the centre of mass is placed centrally within a cow’s base of support and a more balanced position is provided. Step angle was not a very informative parameter of locomotion comfort on different floors in non-lame cows (Paper II). Only on the slippery slatted concrete floor was it considerably diminished. On the hard concrete surfaces lame cows walked with a significantly smaller step angle compared with non-lame cows, while on the soft surfaces the step angles of lame cows were no different from those of non-lame cows (Paper II). The difference in step angle between lame and non-lame animals could be explained by more hind limb abduction in the lame cows.

All the described parameters mostly reflect one single element of cow locomotion – steady-state, straight level walking, which is only one part of the repertoire of cow movements. Other types of movement, such as accelerating, stopping and turning, put higher demands for locomotion comfort on the environment (Van der Tol et al., 2005). Also, we need to develop methods for objectively and more comprehensively analysing gait quality in cows.

Conclusions It was concluded that a trackway measurement system is suitable for evaluating locomotion comfort in field studies. The system is able to measure differences in kinematics on different floors if the quality of floors is very different. Because of the relatively high inconsistency of cow walking it is beneficial to use several strides to obtain a representative gait pattern. Future studies in cow biomechanics should focus on the development of simple yet sensitive methods to comprehensively assess locomotion comfort of cattle in different flooring systems.

Svensk sammanfattning Med ökad medvetenhet om djurens välbefinnande har husdjurens hälsa och möjlighet till naturligt beteende satts i fokus i djurskyddslagen och inom mjölkproduktionen. Kornas rörelsekomfort är en viktig del av djurens naturliga beteende och välfärd, och klöv- och benhälsan är ofta en indikator på den miljö de exponeras för. Behovet av rörelse tillfredställs bättre i lösdriftsystem än i uppbundna system och intentionen inom mjölkkohållningen är att uppbundna system successivt ska ersättas med lösdriftsystem. Men, trots att kor i lösdriftstall har större rörelsefrihet och större möjlighet till sociala kontakter än uppbundna kor, innebär lösdrift större risk för och högre förekomst av skador på framförallt ben och klövar, med rörelsestörningar och hälta som följd. Större exponering för en undermålig miljö i form av snävt tilltagna rörelseytor, dålig hygien och hårda, halkiga, onaturliga golv bidrar till dessa problem.

Diskussion om förbättrade golvsystem i lösdrift har pågått länge. Dock saknas studier med objektiva uppskattningar av kors rörelsekomfort i olika golvsystem.

Det är vanligt med subjektiva betygskalor för att gradera hälta, men sådana metoder är inte anpassade för att värdera skillnader i rörelsemönster hos icke halta kor. Dessutom är de vanligaste förekommande metoderna för biomekaniska undersökningar kostsamma och kan vara svåra att tillämpa i de stallmiljöer som korna befinner sig i.

Vid tillämpning av olika metoder för att beräkna hur kor rör sig på olika underlag är det viktigt att beräkna i vilken grad en ko behåller sitt rörelsemönster från ett undersökningstillfälle till ett annat. Likadeles är det viktigt att beräkna rörelsemönstrets variation mellan och inom individ för uppskattning av mätningarnas tillförlitlighet.

I denna avhandling beskrivs en ny metod för att studera mjölkkors rörelsemönster genom att mäta djurens fotspår på olika golvunderlag. Syftet med studien var att testa tillförlitligheten hos de gångparametrar som erhölls från mätningar av kors klövavtryck, att studera samspelet mellan hälta och golvmaterial samt att studera möjligheten att använda mätningarna för att beskriva rörelsemönster hos kor med och utan rörelsestörningar på olika golv.

För att göra klövspåren synliga beströks gångarna med ett tunt lager släckt kalk (Ca(OH)2) som blandades med befintlig gödsel. För att beräkna tillförlitligheten i metoden studerades 32 icke halta kor. Korna testades två gånger med tre veckors intervall och fyra rörelsecykler mättes vid varje testtillfälle. Följande mätningar av fotspår användes vid tillförlitlighetsstudien: dubbelsteglängd (avstånd mellan två följande fotavtryck av samma fot), stegvinkel (vinkeln mellan linjerna som förbinder tre följande fotavtryck), stegbredd (tvärgående avstånd mellan höger och vänster sidas fotavtryck), steglängd (avstånd mellan två följande fotavtryck), stegasymmetri (skillnaden mellan två steglängder i rad), övertramp (avstånd mellan fram- och bakavtryck på samma sida), abduktion-adduktion (tvärgående avstånd mellan fram- och bakavtryck på samma sida). Mätningarnas tillförlitlighet skattades som en procent av inter-individvariationen av den totala variationen, vilken inkluderade mellan-test- och inom-testvariation samt variationen för testindividsamspel.

I golveffektstudien användes både måttligt halta (n=6), lätt halta (n=5) och icke

halta kor (n=25). Rörelsemönstret hos varje ko undersöktes på fem olika underlag:

betongspalt och helt golv med och utan mjuka, 20 mm tjocka gummimattor (Kraiburg Gummiverk GmBH) samt på ett naturligt, eftergivande underlag i form av fuktig, packad sand. Graden av hälta uppskattades enligt ett system med fyra klasser, anpassat efter Sprecher m. fl. (1997). Samma mått användes såväl i golveffektstudien som i tillförlitlighetsstudien med undantag för abduktionadduktion och stegbredd.

Dubbelsteglängd, stegvinkel, stegvidd och övertramp hade måttlig tillförlitlighet (52-65 %), medan abduktion-adduktion och steglängd hade ganska låg tillförlitlighet (25,4 respektive 37,8 %). Tillförlitligheten hos stegasymmetri var mycket låg (18,1 %), vilket kan förklaras med icke-systematiska förändringar i inter-benkoordinationen hos icke halta kor.

Ökad dubbelsteglängd hade samband med ökad stegvinkel, ökad steglängd och större övertramp. Ökad abduktion hade samband med minskad stegvinkel, ökad stegbredd och något ökad stegasymmetri. Mankhöjd visade positivt samband med dubbelsteglängd och stegvinkel, och negativt samband med stegbredd och abduktion-adduktion. Kroppslängd var positivt korrelerad med dubbelsteg- och steglängd, och tenderade att korrelera negativt med övertramp.

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