Hock angles of dairy heifers in twomanagement systems

Br. vet.J. (1996). 152, 237

HOCK ANGLES OF DAIRY HEIFERS IN TWO MANAGEMENT

SYSTEMS

J.J. VERMUNT* and P. R. GREENOUGH Department of Veterinary Anesthesiolo~,, Radiology and Stage,y, Western College of Veterinary Medicine, [hziversitv of Saskatchezoan, Saskatoon, Saskatchewan, Canada S7N OWO

SUMMARY H o c k angles were m e a s u r e d in 30 Holstein heifers in o n e h e r d h o u s e d e i t h e r i n d o o r s on c o n c r e t e slats or out o f d o o r s on dirt. Two e x a m i n a t i o n s were made, i.e. at 12-13 a n d 24-26 m o n t h s o f age. Overall, the heifers h a d straight limbs; the m e a n value o f the h o c k angle was 167.3°+0.7 (sEre) (range 154.3-177.4°). H o c k angles d e c r e a s e d with age in each g r o u p , but the d i f f e r e n c e between the first and s e c o n d e x a m i n a t i o n s was significant only for o u t d o o r - h o u s e d heifers (P<0.05). At the first e x a m i n a t i o n , m e a n hock angles were not significantly different between the two groups (169.5°+1.6 vs 168.1°_+1.6), but at the s e c o n d e x a m i n a t i o n i n d o o r - h o u s e d heifers h a d significantly g r e a t e r m e a n h o c k angles than heifers h o u s e d out o f d o o r s (167.4°+1.0 vs 164.2°_+1.3) (P<0.05). Heifers h o u s e d i n d o o r s on c o n c r e t e slats a p p e a r e d to retain their straight-angled hocks. KE~,orl~s: H o c k angle; c o n f o r m a t i o n ; heifers; cattle; m a n a g e m e n t .

INTRODUCTION In the dai D, industry, lameness d u e to c h r o n i c laminitis and c h r o n i c arthritis is an i m p o r t a n t cause o f p r e m a t u r e culling. C o n f o r m a t i o n o f the h i n d limbs o f cattle, in particular excessively straight hocks (post-legged), is often cited as an i m p o r t a n t predisposing factor in the aetiology o f diseases o f joints, t e n d o n s a n d claws ( G r e e n o u g h et al., 1981). Despite this, t h e r e has b e e n a universal move in the cattle industry to select animals on the basis o f straight hocks ( G r e e n o u g h , 1990). T h e a c c e p t e d criteria for j u d g i n g the straightness o f a h i n d limb is to evaluate the angle o f the hock. However, few studies have b e e n c o n d u c t e d o n the conform a t i o n o f cattle limbs. As early as 1896, an animal was d e f i n e d as having a straight limb if the h o c k angle e x c e e d e d 170 ° (Pusch, 1896; q u o t e d by Habel, 1948; and *To whom correspondence should be addressed at Deparmaent ofVetevinalT Clinical Sciences, Masse}, UniversiF,, Palmerston North, New Zealand. 0007-1935/96/020237-06/$12.00/0

© 1996 Bailli6reTindall

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G r e e n o u g h et al., 1981). Feh6r et al. (1968) measured the hock angle in bulls used for artificial insemination (M) and found that nearly 20% of animals with hock angles greater than 155 ° became lame with advanced age. They also noted that this conformation characteristic was a heritable trait. M t h o u g h of concern for a long time there is still no standard m e t h o d by which objectively to measure the angle of the box4ne hock. T h e purpose of this study was to de t e r m i n e objectively the hock conformation (hock angles) o f Holstein heifers in two m a n a g e m e n t systems.

MATERIALS A N D M E T H O D S

T h e stud), was carried out from January 1989 to April 1990. Data to det erm i ne hock angles were collected twice; the first examination was when the heifers were 12-13 months old and the second immediately after calving at 24-26 months of age.

Animals Thirty Holstein heifers, the replacement for the G reenbrae dairy herd on the campus o f the University of Saskatchewan were used for the study. MI replacem e n t heifers were raised on the farm and sired by different bulls.

Management and nutrition T h e replacement heifers were moved to a breeding group at 12-13 months of age. Th e group was maintained out of doors on a dry lot with a well-bedded, eastfacing, open-fronted shelter. Heifers were artificially inseminated when they reached a body weight of 340 kg or at 15 months of age; they were not bred u n d e r 13 months of age. Heifers in the breeding group received 2 kg of a growing heifer concentrate [67.0% total digestible nutrients (TDN) or 10.21 megajoules (MJ) per kg, and 14.0% crude protein (CP) on an as fed basis] and good quality alfalfa hay (90.0% dry matter, 52.0% TDN or 9.62 MJ kg -j and 14.0% CP) was available ad libitum.

Management groups and experimental design Actual treatments (different m a n a g e m e n t groups) were imposed when heifers were diagnosed p r e gna nt (42 days after conception) and cont i nued until two weeks prior to their expected calving data. With an average gestation length of 278 days for Holstein heifers (Roberts, 1986), all animals spent 222 days in their respective treatment group. Heifers were randomly allocated to one of two groups as they became available until a total of 15 animals had been allotted to each group.

Indoor-housed heifers. These heifers were housed in a separate area of the freestall (cubicle) barn. T he animals had access to cubicles which were b e d d e d with r u b b e r mats plus a limited a m o u n t of cut straw during the winter months. T h e dimensions o f the cubicles were 2.50 x1.10 m -2. At least three-quarters of the floor area o f the alleyways along the cubicles was slatted. T he r e m a i n d e r of the floor was solid concrete and was automatically scraped several times per day. T he animals

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were fed 4.0 kg of chopped, good quality alfalfa hay per day plus barley silage to meet their daily energy requirements. The ration was fed as a complete mixed diet with an average particle length of 2.5 cm. There was always sufficient cubicle and feeding space for all cattle to rest and feed together.

Outdoor-housed heifers. These heifers stayed out of doors and were confined on a dry lot. Straw was used as bedding in the east-facing, open-fronted shelter. In the winter, the ground was snow-covered, icy, frozen and rough. Heifers in this group received the same nutrition on a per head basis as the indoor-housed animals. There was always enough space at the feed bunk for all animals to feed together. Two weeks prior to their expected calving date, all heifers from both groups were transferred to individual, indoor boxstalls which were bedded with a thick layer of straw. The amount of concentrate fed was increased by daily increments so that animals were consuming 2.0kg dairy concentrate (71.0% TDN or 10.80 MJ kg -~, and 19.0% CP) plus 2.0 kg fresh cow concentrate (71.0% TDN or 10.80 MJ-I, and 18.0% CP) by the time they calved. M1 heifers had free access to a commercial 1:1 mineral mix (19.0% calcium:19.0% phosphorus) with trace minerals and vitamins A, D and E. Good quality water was available from drinking bowls at all times. During the experimental period, heifers were observed walking from time to time in order to detect lameness. Evaluation of hock conformation The Conformation Determination System (CDS) (Greenough & Berg, 1989) was used to generate hock angle measurements. In summary, this involved identifying and marking several anatomical landmarks on the animal, followed by taking side-view photographs of the animal and projecting the transparencies onto a digitizing tablet interfaced with a computer. After entering into the computer, the digitized, anatomical landmarks were mathematically analysed by CDS to produce the predefined hock angles (Fig. 1). Transparencies were digitized twice to give average values.

Statistical analysis The data on hock angles were analyzed using SAS (Statistical Analysis System, SAS Institute Inc.) and were described as means+sEM. Group means of hock angles were compared by using the F-statistic. This statistic was also used to test for differences between the means of hock angles at the first and last examination.

RESULTS

Mean values for hock angles of heifers in the two management groups are presented in Table I. In general, the heifers had straight limbs; the overall mean value for the hock angle of all 30 heifers was 167.3°_+0.7. Also, the overall mean hock angle was greater for the indoor-housed heifers than for the outdoor-housed heifers, but the difference was not significant (P>0.05). In both groups, hock angles decreased with age, but the difference between the first and second examination was significant for the outdoor-housed heifers only (P<0.05). At the first

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10

-'<

..i" • ~11:: H" !...

-°

/<12

Fig. 1. Diagram showing some of the points used to generate conformation ineasurements in heifers. The angle beP,~,een line 9-11 and line 12-11 represents the hock angle (H°).

Table I Means and their standard errors for hock angles (°) o f Holstein heifers (n=30) aged 12-26 months and housed indoors or out o f doors

All Indoors Outdoors

OveraU

Range

PTrsl examination*

Second examination/

167.3_+0.7 168.4_+0.9 166.2_+1.1

(154.3-177.4) (155.5-177.4) (154.3-176.2)

168.8_+1.1 169.5_+1.6 168.1_+1.6§

165.8_+0.9 167.4_+1.0++ 164.2_+1.3++

*At 12-13 months of age. tAt 24-26 months of age. +*Within columlaS, values with identical letters are significantly different (P<0.05). §Comparison within group and between examinations (P<0.05). e x a m i n a t i o n , m e a n h o c k angles were n o t significantly d i f f e r e n t b e t w e e n the two groups, a l t h o u g h the i n d o o r - h o u s e d heifers t e n d e d to start tile e x p e r i m e n t with g r e a t e r h o c k angles. At the s e c o n d e x a m i n a t i o n , the i n d o o r - h o u s e d heifers h a d significantly g r e a t e r m e a n h o c k angles t h a n the heifers h o u s e d o u t o f d o o r s (P<0.05). At tile l a m e n e s s observations, n o n e o f the heifers was d e t e c t e d to be clinically lame.

DISCUSSION T h e r e is little explicit i n f o r m a t i o n in the literature as to the d e g r e e o f a n g u l a t i o n desired in the h o c k j o i n t o f cattle, in spite o f the e m p h a s i s p l a c e d on this p o i n t in

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judging. In AI bulls, an angle greater than 155 ° has been termed steep (Feh6r et al., 1968). Greenough et al. (1981) reported that the no~'mal hock angle should be approximately 145 ° , whereas an angle in excess of 160 ° should be classified as straight. Because of a difference in measuring method, hock angles generated by CDS are likely to be slightly larger than those determined radiographically using the long axis of the tibia and the metatarsus. Nevertheless, it can be suggested that, on average, the heifers studied had straight legs, particularly those housed indoors on slats, although these animals, on average, started off with a slightly greater hock angle. Peterse (1987) reported that cattle confined on slats adopted a stilted gait. It call be argued that such a stilted gait in indoor-housed heifers prevented the decrease ill hock angle which occurred in the outdoor-housed animals, possibly as a consequence of the ageing process. Hock angles decreased with age in all the heifers studied. Changes in claw shape may provide additional explanation for the difference in hock angles found between the two groups of heifers. In another study (Vermunt, 1990), it was found that, due to little wear, outdoor-housed heifers developed long hind claws with smaller toe angles and relatively low heels. Heifers housed indoors on slats maintained a short toe length and steep angle of the toe. As a consequence, the centre of weight bearing within the claw may have moved in a more dorsal direction. This agrees with Murphy and Hannan (1986), who reported that horn abrasion occurred especially at the toe area in cattle on slats. They concluded that, on housing on slatted floors, claws tilt forward. As a result, limbs (and hocks) may remain relatively straight. It is debatable whether certain deviations from an arbitrary norm actually interfete materially with the efficiency of the dairy cow. Traditionally, the late-maturing dairy breeds had a long tibia and were often sickle-hocked, whereas straight hocks and short tibiae were characteristics of early-maturing beef breeds (Habel, 1948). Our experience and all published analyses (McDaniel & Wilk, 1989) indicate that increased angulation of the hock (sickle hock), although often regarded as unsightly and a conformation weakness, thereby handicapping the animal in the show ring, is rarely associated with lameness. The straight or upright hocks of the modern Holstein, on the other hand, are likely to accentuate the impact and friction forces received by tile hind claws. Such forces will have exaggerated effects if the claws are damaged by laminitic change. In a recent study invoh,ing thousands of American Holstein cows, it became apparent that moderately straight hind limbs (with a hock angle approaching 170 °) were associated with increased longevity (B. T. McDaniel, personal communication). Such straight hind limbs, however, may make the animal vulnerable to joint injury and claw problems. Straight-hocked (post-legged) animals often develop degenerative joint disease of tile coxofemoral, femorotibial and tibiotarsal-metatarsal articulations, mainly as a result of indirect trauma (Van Pelt & Langham, 1966; Allenstein, 1981; Bailey, 1985). In these animals, the shock absorption mechanism of the muscles, ligaments and tendons is reduced and, consequently, greater force is received by the stifle and hock joints and ultimately the claws. The conformation of any particular animal is likely to be the result of both genetics and environment. Further studies are required to determine more objec-

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tively the r e l a t i o n s h i p b e t w e e n h o c k angles a n d m a n a g e m e n t systems, a n d the i n c i d e n c e o f l a m e n e s s in cattle. In the m e a n t i m e , it may still be wise to be cautious o f b r e e d i n g bulls that have e x t r e m e l y straight legs, i.e. h o c k angles in excess o f 170 ° .

ACKNOWLEDGEMENTS T h e a u t h o r s a p p r e c i a t e the h e l p o f the staff at the University o f Saskatchewan Animal Science Dairy Unit. T h a n k s are also d u e to Michael O g u n y e l e for his assista n c e in data collection. Sheila M c C o r m a c a n d Colin R o u s s e a u x assisted with the analysis o f the data.

REFERENCES

ALLENSTEIN,L. C. (1981). Lameness in cattle. Canadian I,},te~na~yJourna122, 65-7. BArnEY,J. V. (1985). Bovine arthritides; classification, diagnosis, prognosis and treatnlent. Veterinary Clinics of North America: Food Animal Practice 1, 39-51. FEH~:R, G., HA~SZTI,J. & M~:SZ_-~ROS,I. (1968). Steep posture of the hind legs ill bulls and its harmful consequences. Ma~, Allatmv Lap 23, 277-84. GREr'NOU(:H,P. R. (1990). Observations on bovine laminitis, hi Practice 12, 169-73. GREENOLI(;H, P. R. & BERt;, P. A. (1989). CDS Conformation Determination System. Western College of Veterinal T Medicine, University of Saskatchewan, Saskatoon, Canada. GREENOU(;H, P. R., MA(:CAI.I.U.Xl,F. J. & wE-:wi-., A. D. (1981). Lamem:~s in Cattle. pp. 91-7. Philadelphia:JB Lippincott Company. HABEL, R. E. (1948). On the inheritance of metatarsal inclination ill AyTshire cattle. American Journal of Vete~qnmy Research 3, 131-39. McDAMFt., B. T. & Wu.K,J. C. (1989). Lameness in Dai~y Cattle. Animal Science Departnlent, North Carolina State University, Raleigh, USA. MURPHY; P. A. ~ HA,~NAX,J. (1986). Effects of slatted flooring on claw shape in intensively housed fattening beef cattle. Ill Proceedings of the Vth International ,S),mposium on Disorders of the Ruminant Digit, Dublin, pp. 2-7. PETE~SE, D.J. (1987). Aetiology of claw disorders in dail 3, cattle. Ill Cattle Housing Systems, Lameness and Behaviou~; eds. H. K. Wierenga & D.J. Peterse, pp. 87-91. Boston: Martinns Nijhoff Publishers. PUSCH, G. (1896). Beurteihmgslehre des Rindes. Berlin: Parey Verlag. ROBERTS, S. J. (1986). Veterinary Obstetrics and Genital Diseases (Theriogenology). pp. 104-5. Woodstock, VT: SJ Roberts. VAX PELT, R. W. & LaX(;HA~I,R. F. (1966). Degenerative joint disease ill cattle. Journal of the American Veterinan, Medical Association 45, 633-9. VERMUNT,J. J. (1990"). Lesions and structural characteristics of the claws of daily heifers ill two management systems. MSc Thesis, University of Saskatchewan, Canada.