Slip-resistance of solid concrete floors in cattle buildings

J. agric. Engng Res. (1990)45, 137-147

Slip-resistance of Solid Concrete Floors in Cattle Buildings R. W. ALBUTr;* J. DUMELOW;* J. P. CERMAK;'I"J. E. OWEN:[: A new method for determining the slip-resistance of floor surfaces for cattle has been developed. Horizontal foot movements were measured using a motion analysis system and a force plate interfaced to a microcomputer. The force plate was positioned beneath the centre of a walkway and covered with a panel of the floor surface to be tested. Pairs of infra-red light emitting diodes (LED) were attached to both of a cow's left feet. Two infra-red photodetectors then recorded the positions of the LEDs as the cow walked over the force plate. The co-ordinates of each LED's position and the output from the force plate were sampled by the microcomputer at intervals of 0-01 s. A bare soil surface was more slip-resistant than any of the concrete surfaces tested. Tamped concrete was more slip-resistant than grooved concrete. The direction of tamping or grooving had no significant effect upon slip magnitude. The front feet of cows slip outwards from the direction of travel more than back feet. 1. Introduction Slippery floors are considered to be one of the main causes of leg lameness in dairy cattle (Baggottl), with it mainly occurring in the hind limbs above the hock joint (Russell et al.2). The objective of this work was to develop a technique for evaluating the slip-resistance of solid floor surfaces. With the current and probable continuing dominance of concrete as the most widely used flooring material for farm use, this study concentrates on concrete surface texture design. H o w e v e r , a soil surface was also included in the experiment to establish if there were any differences in the slip-resistance of hard, unyielding concrete surfaces and that of a softer soil surface. The most c o m m o n l y r e c o m m e n d e d texture for new concrete floors for cattle is a tamped finish made by forming grooves with the corner of a board at 50 to 75 m m intervals along the slab (Mitchell, 3 Kelly4). For existing worn concrete floors, slipresistance can be improved by either grooving, mechanical roughening or the application of proprietary anti-slip c o m p o u n d s (MAFFS). Inevitably there is some form of contamination of the floor surfaces in a cattle building in the form of a slurry, consisting of faeces, urine, some bedding material and often added water from washing operations. Contaminants drastically alter the coefficient of friction of materials (James6), it being a c o m m o n experience that combinations of dirt and water make walkway surfaces slippery. Whilst profiled floor surfaces improve the situation the best solution is removal of the contaminant. Keeping floors clean and dry solves m a n y slipping problems. H o w e v e r , this is impractical in dairy cattle buildings w h e r e cows defecate and urinate freely. Many investigations of the slip-resistance of floors in livestock buildings have been carried out. W e b b and Nilsson 7 have c o m p a r e d the results of these studies and found them to be in p o o r agreement. This is almost certainly due to their failure to simulate the cow foot and floor interaction sufficiently accurately. The hoof pressures exerted by a * ADAS Farm Buildings Development Centre, 77-81 Basingstoke Road, Reading RG2 0EF t ADAS, Government Buildings, Gabalfa, Cardiff CF4 4YH :~ Department of Agriculture, University df Reading, Early Gate, Reading RG2 2AT Received 12 May 1989; accepted in revised form 17 September 1989

137 0021-8634/90/020137 + 11 $03.00/0

t~) 1990 The British Society for Research in Agricultural Engineering

138

SLIP-RESISTANCE

~

OF CONCRETE

FLOORS

Instrument cabin ~

Infra-red photodetectors~

Cow

turning

I I I,I I I-~,l I I I I

area

Cow entrance door Fig. 1. Plan oiew of layout in building used for tests cow, the rate and direction of loading, the h o o f material properties and contact area of the hoof must all be accurately simulated by a friction or slip tester for the results to be consistent and therefore meaningful.

2. Experimental methods A biomechanical approach to the study of the slip resistance of floors in cattle buildings was adopted. Rather than use an indirect method of measuring how slippery floors are, such as a floor friction tester, the amount of foot m o v e m e n t was measured directly and used as an index of a floor's slip-resistance. The floor surfaces were tested in a walkway. Fig. 1 shows the walkway positioned so that there is room for cows to turn easily at either end of the building. The walkway measured 8 m by 0-85 m in plan and comprised a n u m b e r of removable trays containing the surface under test. The large panels are 0.85 m wide, 0.75 m long and 75 m m deep. One of the two smaller panels, measuring 0-6 m long and 0.4 m wide, was bolted to a force plate. The other smaller panel was connected to a d u m m y plate alongside the force plate. A tubular steel rail 0-9 m above floor level formed a race to constrain the cows to walk over the surface under test. Full details of the experimental rig and recording equipment are given in Albutt. a

2.1. Instrumentation The force plate (Kistler Instruments A G , Switzerland) was used to measure the forces exerted by the cows' feet during floor contact. It was bolted to a steel frame set in concrete beneath the centre of the walkway. To measure cow foot m o v e m e n t an optoelectronic motion analysis system, called Selspot (Selcom AB, Sweden), was used. The system uses infra-red light emitting diodes ( L E D ) for determining the positions of objects to which they are attached. T w o pairs of L E D s were attached to both of a cow's left feet in order to determine the position and m o v e m e n t of those feet. The L E D s were connected to a light control unit m o u n t e d on a strap running around the cows girth. This in turn was connected by an overhead cable to a m i c r o c o m p u t e r which carried out data collection. The positions of the L E D s were determined in three dimensions using two infra-red photodetectors beside the walkway. An analog-digital converter was used to sample the eight force plate outputs every 0.01 s. D a t a recording was triggered when a cow's leg broke an infra-red b e a m projecting perpendicularly across the walkway approximately 1 m before the force plate.

2.2. Test procedure The L E D s were attached to the outside of both the front and rear left feet. It is assumed that symmetrical results would be obtained for the right feet. One L E D was

R. W. A L B U T T ET AL.

139

Fig. 2. Cow stepping on the force plate during a test run on dry steel float concrete

placed close to the rear of the foot and the other as far forward as possible. Care was necessary in positioning the front L E D since the curvature of the front of the hoof m e a n t that an L E D placed too far forward would not be visible to both infra-red photodetectors. The L E D s were attached to the feet using a cyanoacrylate adhesive. The cows were driven, not led, down the walkway. Fig. 2 shows a cow during a run with its front left foot on the force plate. The two infra-red photodetectors can be seen standing behind a row of straw bales. The light control unit on the cow's back was connected to one of the photodetectors by the overhead cable and hence to the rest of the instrumentation system. A successful run was achieved if the cow placed either the front left foot or the back left foot fully on the force plate. If both feet o v e r l a p p e d or missed the plate then it was noted as having been an unsuccessful run. Ideally the cow placed both left feet completely on the force plate so that there was a complete data set for that run. Approximately 20 runs were made in each session with a cow. Having completed this number of runs the cow would usually appear to be tiring and became increasingly reluctant to move or difficult to handle. Of these 20 runs only approximately 25% were suitable for later analysis. The discarded runs were usually due to the foot not being placed completely on the plate and occasionally due to L E D disconnection or breakage. It was not practical to randomize the floor surfaces for testing purposes as changing a floor surface in the walkway t o o k approximately 4 h. T h e r e f o r e , all m e a s u r e m e n t s were completed on one surface before moving on to the next. Fourteen cows of varying ages, weights and stages of lactation were used throughout the test period. H o w e v e r , as few of the cows were available for all of this time not all of the cows were used on all of the surfaces.

3. Calculation of slip Any foot m o v e m e n t can be broken down into three constituent parts as follows: (a) slip, a horizontal translational m o v e m e n t occurring in a horizontal plane; it is a vector having both magnitude and direction;

140

SLIP-RESISTANCE

OF C O N C R E T E

FLOORS

(b) twist, a turning movement in a horizontal plane about a vertical axis; (c) rotation, a turning movement in a vertical plane about a horizontal axis. The vertical force output from the force plate was used to determine when a foot was in contact with the floor surface under test. Ideally, the vertical force output would have been zero just before the foot made contact with the plate. However, noise or a residual charge invariably meant that the vertical output was not always zero. It was therefore necessary to find the threshold value of vertical force above which the foot would be taken to be in contact with the floor. If too low a threshold was used, noise could trigger the instrumentation too early, before the foot actually made contact with the force plate. To find the optimum vertical force threshold, five runs by one cow were analysed using seven different threshold values. A threshold value of 20 N was selected as being the lowest vertical force which ensured that premature triggering by noise could not occur. The time for which the foot was in contact with the floor was subdivided into short time intervals. A F O R T R A N program was developed which calculates the movements of a cow's foot when in contact with the force plate. A two letter subscript is used when referring to L E D s in the subsequent analysis. The first letter indicates whether it is the initial or later (~ or ~) L E D position in a time interval. The second letter shows whether it is the front or back (f or b) L E D on a foot.

3.1. Slip magnitude The imaginary line joining the front and back L E D positions on each foot is referred to as an L E D line. At an instant in time during a footstep, the position of a cow's foot can be represented by the L E D line, such as A in Fig. 3. During one time interval the foot has moved to the position represented by L E D line B. In doing so some foot rotation, twist and slip has occurred. To determine the slip that occurred the rotation and twist are calculated and then removed from the overall foot movement. The rotation that occurred is found by calculating the angles between the lines A and B and the horizontal plane, p and ty respectively in Fig. 3. p = t a n - ' ((Zih --

Zif)/((Yih

- - yif) 2 + (Xih -- Xif)2) I/2)

ty = t a n - ' ((Zlh -- Zif)/((yih -- yif)2 + (Xih -- Xif)2) '/2)

Z,

A,,, / ~ 1

/ /

I

z

Xib ' Yib' Zib

I

X

Fig. 3. Schematic diagram of changes in foot position represented by LED lines

R. W. ALBUTT

ET AL.

141

Xib' Yib

A ~

Xkb' YLb

Yif

iX

,,<, T

Fig. 4. Plan view o f twist in horizontal plane

Then the rotation is given by "~ =

O'-- p

Fig. 4 is a plan view of Fig. 3. The amount of twist that occurred in a time interval is given by the horizontal angle, y, f o r m e d between L E D lines A and B. Angle L E D line A makes with the y axis at the start of the interval: tr = tan -1 ((Xib - Xif)/(Yib -- Yif)) Angle L E D line B makes with the y axis at the end of the interval: /3 = tan -l ((xi, - x i f ) / ( y i , - Yif)) So the twist is given by y=/3-

~r

The rotation and twist can now be r e m o v e d in order to find the slip. The twist is removed by turning the initial L E D line through the angle ), to lie in the same vertical plane as the later L E D line. It is then necessary to find the co-ordinates (x,, Y t ) of the point of intersection, T, of the normal to the bisector and of the later L E D line, B. Bisector of initial and later L E D lines: 09 = a~ + y/2 Thus, the gradient of the normal to the bisector is - 1 / t a n ( 9 0 - ¢o). The equation of the L E D line at the end of 0.1 s interval is y = tan ( 9 0 - / 3 ) . x + c.

(1)

Similarly, the equation of the normal to the bisector is y = - x / t a n (90 - to) + c.

(2)

c~ and c. can be found by inserting known x and y values in Eqn (1) and Eqn (2), so that Cl = Ytf - - X l f ' tan (90 - fl) c. = Yif + &f/tan (90 - co)

142

SL|P-RESISTANCE

OF CONCRETE

FLOORS

Eliminating y f r o m E q n (1) and E q n (2) gives x . tan (90 - fl) + cl = - x / t a n (90 - to) + cn x ( t a n (90 - fl) + 1/tan (90 - co)) = c. - cl T h e r e f o r e the x c o - o r d i n a t e of the intercept: xt = (Cn -- c 0 / ( t a n (90 -- fl) + 1/tan (90 -- co)) Yt is found by substituting the value of x, in E q n (1). T h e height of the floor plane relative to the d a t u m used by the m o t i o n analysis system is fp. T h e r e is a point C on the floor plane a b o u t which the initial L E D line can be r o t a t e d to bring it parallel to the later L E D line with both lines the s a m e vertical distance f r o m the floor plane, see Fig. 5. T h e angle of rotation, 0, a b o u t C is not the s a m e as the angle of foot rotation, ~. T o find the co-ordinates (xr, Yr) of the point R shown in Fig. 5: sin q~l =

ziO/a

(3)

sin 492 = (fp - zlO/a

(4)

(fp

-

0 = q,, - 4,2

(5)

Substituting for q~t in E q n (3) using E q n (5): sin (0 + q~2) = (fv - ziO/a sin 0 . cos ~z + cos 0 . sin dP2 = (fo - ziO/a Eliminating q~2 using Eqn (4): sin 0. (a 2 - (fp - ztf)2)"2/a + ((fp - z , O / a ) , cos 0 = (fp - zif)/a Solving for a: a = ((fp - z,0 2 -

2(fp

ztO(fo - zi0 cos 0 + (fp

-

--

zlf)2)t/2/sin 0

Z

•-

fp

~ Rk

[

I

i i

I I

dl

d2

xtf'Ytf' ztf

Slip

magnitude

c 0

Fig. 5. Slip magnitude in a vertical plane

R. W. A L B U T T

143

ET AL.

Now if: dr = d2 - dt dr = (a 2 - (fp - zIf)2) 1/2 - (a 2 - (fp - zif)2) 1/2 So the x and y co-ordinates of the front L E D after rotation removed are: xr = x, + dr. cos (90 - / 3 ) Yr = Y, + dr. sin (90 - / 3 ) where/3 is the angle between the later L E D line and the y axis, see Fig. 4. The slip that occurred in a time interval is then given by the horizontal distance between the two parallel L E D lines, see Fig. 5. Slip magnitude = ((xlf - xr) 2 + (Ylt -

y r ) 2 ) 1/2

Preliminary analysis of early runs showed that large errors in slip magnitude were caused by system noise if a 0.01 s time interval was used, 100 Hz being the sampling frequency of the instrumentation. T h e r e f o r e each foot step was split up into 0.1 s intervals, each containing 10 frames of data. Mean L E D positions for each interval were then used in subsequent analysis. 3.2. Slip direction The position of the foot at any point in time is represented by one point whose co-ordinates are given by the mean of the x, y and z co-ordinates for the two L E D s on that foot. For example, the co-ordinates of the foot's initial position in Fig. 3 are (Xib + X i f ) / 2 , (Yib q" Yif)/2, and (Zib + Zif)/2. The direction of slip is given by the line joining the initial and later foot positions. It is represented by the angle formed between this line and the direction in which the cow was walking, t h e y axis. Positive angles were measured in an anti-clockwise direction and negative angles clockwise, when viewed from above.

4. Results and analysis

4.1. Slip magnitude Slip is the horizontal movement of a foot that occurs during its contact with a floor surface. In this study it has been used as an index to indicate a floor's slip-resistance. Low slip values indicate slip-resistant surfaces. Mean front foot slips on each surface are given in Table 1. Less slip occurred on soil than on the dry concrete surfaces (P < 0-001). Concrete surfaces were more slippery when slurry-covered than when dry (P < 0.001). Surprisingly, less slip occurred on steel float concrete than the textured surfaces when slurry-covered (P < 0.001). The tamped surfaces were more slip-resistant than the grooved ( P < 0 . 0 1 ) . The most slip-resistant of the textured concretes when slurry-covered was the laterally tamped surface (P < 0-05). Mean back foot slips are given in Table 2. Less slip was measured on soil than on the dry concrete surfaces (P < 0.05). Concrete was more slippery when slurry-covered than when dry (P < 0.001). More slip occurred on slurry-covered steel float concrete than any of the textured concretes (P < 0-001). The tamped surfaces were more slip-resistant than the grooved surfaces (P <0.01). The slurry-covered longitudinally tamped concrete was more slip-resistant than any other slurry-covered surface (P < 0.001). A t-test of 271 paired difference values for slip magnitude showed that there is no significant difference between the amount of slip occurring between front and back feet.

SLIP-RESISTANCE OF CONCRETE FLOORS

144

Table 1 Mean slips for front foot Surface

Condition

Mean slip, mm

No. o f runs

Sandy loam soil

Dry

18.6

22

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Dry Dry Dry Dry Dry

33.6 31.3 32.2 41.0 44-4

31 29 37 37 57

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Slurry Slurry Slurry Slurry Slurry

41.7 46.1 50.8 62.7 56.1 (s.d. = 19-25)

38 27 42 25 52

F o r b o t h front a n d b a c k feet, the results s h o w that less slip o c c u r s on soil t h a n o n c o n c r e t e . This is p r o b a b l y d u e to the soft, resilient n a t u r e o f soil a l l o w i n g the h o o f to " p l o u g h " into the soil surface t h e r e b y i n c r e a s i n g the r e s i s t a n c e to h o r i z o n t a l m o v e m e n t . H i g h e r slip m a g n i t u d e s w e r e m e a s u r e d on d r y c o n c r e t e t h a n w e r e e x p e c t e d . T h i s m a y be d u e to the m e t h o d o f slip c a l c u l a t i o n which starts to m e a s u r e slip f r o m t h e first m o m e n t a f o o t m a k e s c o n t a c t with the floor. A t this t i m e t h e c o w ' s w e i g h t is still o n a n o t h e r foot. If the t i m e at which w e i g h t t r a n s f e r o n t o the f o o t u n d e r o b s e r v a t i o n o c c u r s had b e e n d e t e r m i n e d this m a y h a v e b e e n a b e t t e r p o i n t at which to start slip measurement. Slips in excess o f 500 m m a r e c o m m o n l y o b s e r v e d on s l u r r y - c o v e r e d s m o o t h c o n c r e t e in cattle buildings ( M i t c h e l l 9) a n d y e t the m e a n f r o n t a n d b a c k f o o t slips on t h e s l u r r y - c o v e r e d steel float c o n c r e t e used in this e x p e r i m e n t w e r e o n l y 41-7 m m a n d 80.7 m m r e s p e c t i v e l y . This d i s c r e p a n c y is p r o b a b l y d u e to the g e n e r a l l y u n i f o r m s p e e d at which the cows m o v e d o v e r the w a l k w a y in this s t u d y . In c o n t r a s t , the large slips e n c o u n t e r e d on f a r m s o c c u r w h e n cows a r e e i t h e r b e i n g m o u n t e d o r j o s t l e d by o t h e r cows o r f r i g h t e n e d into s u d d e n m o v e m e n t . Table 2 Mean slips for back foot Surface

Condition

Mean slip, mm

No. o f runs

Sandy loam soil

Dry

21-3

20

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Dry Dry Dry Dry Dry

41-2 27-7 29-7 31-5 40-1

29 26 30 25 32

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Slurry Slurry Slurry Slurry Slurry

80-7 46-3 34.3 43.5 63.4 (s.d. = 22-44)

29 22 33 33 53

R. W. ALBUTT E T A L .

145 Table 3 Mean slip directions for front foot

Surface

Condition

Mean slip direction, °

No. o f runs

Sandy loam soil

Dry

46-3

22

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Dry Dry Dry Dry Dry

19.1 18.4 31.1 38-1 24-9

31 29 37 37 57

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Slurry Slurry Slurry Slurry Slurry

18.1 29-7 29.5 25.2 23.9 (s.d. = 15-48)

38 27 42 25 52

The tamped and grooved concrete surfaces were expected to be significantly more slip-resistant than the steel float owing to the greater drainage capacity of the rougher surfaces. H o w e v e r the results for the front foot did not bear this out. Nor did the results show a consistent effect of groove or t a m p direction.

4.2. Slip direction The mean slip directions for the front foot are shown in Table 3. The direction of slip is significantly greater on soil than on dry concrete (P < 0 . 0 0 1 ) . T h e r e was no significant difference between the concrete surfaces dry and slurry-covered. C o m p a r i n g the concrete surfaces when slurry-covered, the direction of slip was greater on textured surfaces than steel float (P < 0-01). The mean slip directions for the back foot are shown in Table 4. In contrast to the front foot there was no significant difference in the direction of slip between soil and the dry concrete surfaces. The angle of slip was greater on the concrete surfaces when Table 4 Mean slip directions for back foot Surface

Condition

Mean slip direction, °

No. o f runs

Sandy loam soil

Dry

9-4

20

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Dry Dry Dry Dry Dry

12-0 -3-1 6.5 -0-8 1.9

29 26 30 25 32

Steel float concrete Lat. tamped concrete Long. tamped concrete Lat. grooved concrete Long. grooved concrete

Slurry Slurry Slurry Slurry Slurry

24.7 2.4 7.3 -2.2 13.8 (s.d. = 16.84)

29 22 33 33 53

146

S L I P - R E S I S T A N C E OF C O N C R E T E F L O O R S

Table 5 Mean direction of horizontal force maxima, *

Forward (s.d.) Front Foot Back Foot

29.2 17.7

(14-52) (11-60)

Backward (s.d.) 167.0 165-2

(9.38) (10-19)

No. o f runs 462 455

slurry-covered than when dry (P < 0.01). The angle of slip was greater on slurry-covered steel float concrete than the other slurry-covered concrete surfaces (P < 0.001). There is a significant difference (P < 0-001) in the direction of slip between front and back feet. A paired t-test on front and back foot m e a s u r e m e n t s showed that the front foot slips outwards from the direction of travel 18.6 ° more than the back foot (s.d. 26.27 °, 270 d.f.).

4.3. Horizontal force The direction in which the m a x i m u m horizontal force exerted by a cow's f o o t acts may have an important bearing upon the direction of any linear features, such as grooves or tamps, in a floor surface. Vertical, longitudinal and lateral force data were m e a s u r e d by the force plate at intervals of 0-01 s, from which the resultant horizontal force was calculated. Graphs of the lateral and longitudinal forces on a cow's foot have been described by Webb and Clark. TM The resultant horizontal force has two maxima, one forwards and one backwards. The mean directions that both front and rear feet are pushing in when these maxima occur are given in Table 5 for both forward and backward directions. The mean maximum backward horizontal force acts at 167.0 ° on the front foot and 165.2 ° on the back. This result is significantly different to that of W e b b and Clark's 1° who found that the forward (longitudinal) thrust during push-off was the same as the sideways (lateral) thrust for both front and back feet, implying that the net resultant force acts at 135 ° to the direction of travel. However, the latter result was based on data from only one cow with known gait problems.

5. Conclusions It has been shown that the m e a s u r e m e n t of horizontal foot m o v e m e n t during contact with a floor surface can be used as an index of that floor's slip-resistance. Significant differences in slip magnitude were measured on the surfaces tested. Results for the surfaces were similar for front and back feet. The bare soil surface was m o r e slip-resistant than any of the concrete surfaces. T a m p e d surfaces were m o r e slip-resistant than grooved. No consistent effect of the direction of tamping or grooving was found. An unexpected result was the finding that, for the front foot, steel float concrete was more slip-resistant than either grooved or t a m p e d surfaces. Significant differences between surfaces in the direction of slip were observed. Front feet slip outwards more from the cow's direction of travel than the back feet.

Acknowledgements Thanks are due to the Ministry of Agriculture, Fisheries and Food for funding this work at the ADAS Farm Buildings Development Centre.

R. W. ALBUTT E T A L .

147

The authors wish to thank the Director and staff of the A F R C Institute for Animal Health, Compton for kindly allowing them the use of a building and their stock. We are also grateful to Bill Morgans, University of Reading, for his valuable assistance with the manufacture and repair of a number of items of equipment. References

1 Baggott, D. G. Losses due to lameness caused by physical contact with buildings. Farm Buildings Association Journal 1982, 30:12-15 2 Russell, A. M.; Rowlands, G. J.; Shaw, S. R.; Weaver, A. D. Survey of lameness in British dairy cattle. Veterinary Record 1982, 111:155-160 3 Mitchell, C. D. Non-slip finishes for concrete floors. Farm Building Progress 1975, 39:11-12 4 Kelly, M. Good dairy housing design--a form of preventitive medicine. Veterinary Record 1983, 113:582-586 s Ministry of Agriculture, Fisheries and Food. Repairing farm floors. Leaflet 825, MAFF, Alnwick, 1982 e James, D. i. Rubber and plastics in shoes and flooring: The importance of kinetic friction. Ergonomics 1983, 26(1): 83-99 7 Webb, N. G.; Nilsson, C. Flooring and injury--an overview. In: Farm Animal Housing and Welfare (Baxter, S. H. et al., eds). Martinus Nijhoff Publishers, 1983, 226-261 a AIbutl, R. W. An investigation of the slip-resistance of floor surfaces for dairy cattle buildings. M.Phil. Thesis, University of Reading, 1987 (unpublished) 9 Mitchell, C. D. Are the passageways in your cubicle buildings too slippery? Farm Building Progress 1974, 37:17-20 lo Webb, N. G.; Clark, M. Livestock foot-floor interactions measured by force and pressure plate. Farm Building Progress 1981, 66:23-36