Western College of Veterinary Medicine, 52 Campus Drive,
University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5B4, Canada
E-mail: greenough@admin3.usask.ca
Take Home Message
The incidence of lameness in dairy cows is increasing, the underlying cause being the introduction of new technologies related to nutrition and management. The hidden cost of lameness is considerable. Producers must learn to recognize the various disease problems and understand the many different factors that contribute to the appearance of these diseases.
Introduction
Lameness is the clinical sign of many different diseases and, therefore, there are a multitude of causes of lameness (9, 46). This paper will review laminitis and the various circumstances contributing to its occurrence. Diseases directly associated with laminitis are, collectively, the most important group of conditions confronting the dairy farmer today. The increasing incidence of this problem can be directly associated with the increasing intensity of the technologies of management and nutrition, both of which impose stress on the high-producing dairy cow.
Laminitis is a condition in which the tiny blood vessels supplying the horn-producing tissues are compromised. The horn produced by a claw affected by laminitis is soft and prone to physical damage and infection. Laminitis is seen in three forms.
Acute Laminitis
This is a very painful condition that is relatively rare in dairy cows unless they accidentally consume very large quantities of grain. An acute form of founder (laminitis) may be seen in feedlot animals (30, 37, 38).
Chronic Laminitis
Chronic laminitis, or slipper foot, is believed to result from prolonged episodes of acute or sub-acute laminitis. The condition is characterized by an abnormally wide, flat, square-ended, bent, and heavily rippled claw(s).
Subclinical Laminitis
Subclinical laminitis (21, 34, 49, 52, 67, 68, 69, 73) will be the major topic of this paper. The pain associated with this form of the condition produces only subtle changes in the way an animal walks or stands. In dairy cattle, hemorrhages into and softening of the horn of the sole are characteristic occurrences and are followed by a number of secondary diseases which affect mostly hind lateral claws. These conditions severely limit the longevity of the animals involved.
The cause of subclinical laminitis is not simply the result of a digestive upset, which has been thought to be the case until recent years. Inappropriate nutrition still remains the most important consideration, but the sensitivity of animals to bad nutrition increases in response to the influence of a number of 'risk factors'. In other words, stresses associated with management and the environment reinforce the negative effects of inappropriate nutrition. Laminitis is now considered to be a multifactorial disease.
Reading the Story Book in the Claw
Dairymen spend a great deal of time looking at cows' feet as they pass by the milking pit. The health history of the animals is written right there in the claws and is passing many of you by virtually unnoticed.
The coronary band is a strip of soft horn bordering the skin (cuticle of man) that is approximately 1 cm wide. The claw slides out from beneath the coronary band at the rate of about 5 mm (1/8") per month. When there is an upset in horn production, the appearance of the horn changes for a short or long period. This change in appearance runs more or less parallel to the coronary band. Therefore, if you measure the distance from the 'changed' horn to the coronary band and divide the distance by 5 mm, it is possible to calculate the date of the event that caused the change (management or nutrition). If the change in the appearance is a groove (hardship groove), then the event was one of short duration, such as a bad calving or a sudden change in the quality of fiber. If the change in the appearance lasts for several centimeters, it may reflect changes in the general level of nutrition. For example, a dry cow will produce claw horn different in appearance from a cow in peak lactation. In other words, it is quite normal for the claw to appear lightly rippled. When the rippling takes the form of bands of horn of differing quality, then the management of nutrition may be questionable.
When cows are introduced to concentrate over one or two days, the claw horn may grow faster than normal for a short time and a bump or ridge may be felt running around the claw parallel to the coronary band. This is not a good sign because there may be associated changes inside the claw (e.g., dropping of the sole) which are permanent defects that are prejudicial to the longevity of the animal.
The dairyman should learn to recognize normal claw horn. Remember that any change you will see will be an historical one and that the cause of the change will have taken place several months before you are aware of it. Nevertheless, the observer will learn to become acutely aware if the changes become more noticeable than normal and, more particularly, if several animals rather than a single cow are affected. This may be all that is needed to tip off a review of the management and nutrition of the herd.
Another sign for which the dairyman should be looking is puffiness and pinkness of the skin around the coronary band and the dew claws. This usually occurs within days of a sudden increase in concentrate consumption. When this occurs occasionally in single animals shortly after calving, the sign can be accepted as normal. On the other hand, if it is seen in several recently calved cows, then it is a clear indication that the animals are being introduced to concentrate too rapidly.
It would be too much to say that individually these changes are clinical signs of laminitis. However, good observation can reflect the extent or magnitude of change over time which, if significant, would substantiate a diagnosis of laminitis. Grooves or ridges in several animals can indicate a time period during which they have been abnormally stressed. This relationship can be associated with climatic changes, related to calving, related to a change in nutrition, or to some other event.
The Signs of Subclinical Laminitis
Alterations in the way an animal stands (posture) or walks (gait).subclinical
When pain is present inside the claw, a cow will alter its posture (or way of walking) to relieve that pain as much as possible. If the pain is in the toe, the foot will be moved forward; if it is in the heel, the foot will be held further back than normal. If the pain is affecting the inside claw, the animal will walk or stand with its feet close together. Unskilled observers are often confused between a posture and defective conformation.
Pain in the feet is an obvious sign of acute laminitis, but in the case of subclinical laminitis, lameness is not a clear-cut sign of the disease. This is partly because animals may be equally affected in all claws and the pain in one claw is cancelled out by that in another. Nevertheless, animals with subclinical laminitis tend to walk 'carefully', they plod, they may walk with the feet further forward than normal, or with their feet closer together than normal.
Subclinical Laminitis Associated Diseases
The most convincing confirmation that subclinical laminitis exists in a herd is a high incidence of the following conditions:
Because the strength of the claw horn is reduced in laminitic animals, it is believed that there will be a higher prevalence of other miscellaneous conditions such as heel erosion (18, 56), interdigital dermatitis, and sole trauma. However, these conditions are also more prevalent under moist unhygienic conditions.
How Laminitis Develops
The classic theory suggests that when there are sudden increases in the intake of highly digestible carbohydrate there is an alteration of the organisms that inhabit the rumen. Once the wrong type of organisms take over, the carbohydrate is fermented and the environment of the rumen becomes extremely acidic. Under these conditions, it is thought that some of the organisms die, releasing substances that are poisonous and especially damaging to blood vessels. In the early phase of subclinical laminitis, small arterioles dilate. Blood pressure in the claw increases, damaging the walls of the vessels, and blood seeps from them giving the sole a typical blood-stained appearance (16).
A number of workers (5, 45, 48, 49, 59, 70, 71) have found the smallest vessels to be blocked by blood clots. Presumably, the vessel walls are so damaged and roughened that clots cling to the sides. Once the vessels are blocked, the tissues supplied by the tiny blood vessels lose vitality because they are starved of nutrients and oxygen. A period of recovery then follows, circulation from adjacent areas invades the damaged tissue and a scar is formed. The animal may apparently recover and resume walking normally. From practical experience, we know that once an animal has had laminitis it is more susceptible to subsequent insults, and the more scarred the tissue the more likely will there be recurrences. Changes in the horn-producing cells result in the quality of the horn being degraded over time. The claw then becomes susceptible to damage and disintegration. It is these secondary conditions that cause problems of significant economic importance.
Investigating Laminitis (24, 25, 46, 56)
Establish if a Problem Exists
If there is a collective annual incidence of conditions associated with subclinical laminitis in 10% of the milking cows in a dairy herd, it should be assumed that laminitis exists. A similar conclusion might be reached if the prevalence of sole ulcer exceeds 5% at any given time. When examining this criteria, the incidence of hairy wart disease and foot rot should be ignored.
Identify the Animal Age Group First Affected
Examine the soles of the claws of a representative number of animals (maximum 10 animals) in each of the following risk groups:
A thin layer of horn is removed from the soles of all claws. Fresh horn is exposed and hemorrhages evaluated, if they are present. Hemorrhages are scored from one to five; with five being the severest discoloration. The scores for each of the claws for each animal are added together. If the average score for all of the animals in the group is greater than five, then that group of animals should receive special consideration. Although this is an arbitrary method at present, this technique will reveal the relative degree of severity of the condition within the groups. It is then possible to concentrate further investigation towards the risk factors applicable to that group.
It should be appreciated that hemorrhage takes up to three months to grow out to be visible on the surface of the sole. This, of course, means that the cause of the problem must be looked for in an historical perspective namely:
Identify the Date of Onset and the Severity of the Insult
The changes that can be observed in the claw have already been described. Once it has been established that a problem exists, the same methodology is applied to collect objective data. This may be referred to as a baseline study. It is known that the growth of the wall occurs at the toe at the rate of 0.5 - 0.6 cm/month in dairy cows (26, 27). The rate of growth is slightly faster at the heel. The investigator measures the distance from the coronary band to the groove and calculates the point in time at which the insult took place.
Because the hardship or horizontal groove represents what is often a change in management, the horn produced furthest away from the groove may show different characteristics than that between the groove and the hair line. This may give the observer a hint as to how well the animal has adapted to the change in nutrition after it has occurred. A horizontal groove represents the least intrusive insult. Nevertheless, it is an area of weakness. As the groove moves further down the claw, it reaches a point at which the claw will bend, particularly if the toe is long. In dairy cows it is more usual for a series of minor grooves to develop, in which case the claw will bend slightly at each groove and a 'buckled claw' will develop.
A horizontal fissure, on the other hand, indicates a severe insult. In this case, the production of horn will have ceased completely for a short period (days) and a major fault is present. As a fissure moves towards the toe, the portion furthest away from the groove may become partially detached and form a 'thimble'. A thimble can be compared to a hang nail and is just as painful. Finally, the groove or fissure will grow to the tip of the claw and break away. This is referred to as a 'broken toe'.
Collectively, the groove, fissure, buckled toe, thimble, and broken toe are manifestations of the same phenomenon. Subjectively, they represent the duration or repetitive nature of an insult as well as a measure of its severity.
Investigate Risk Factors
When it was first appreciated that subclinical laminitis was the underlying cause of lameness in dairy herds, it was believed inappropriate nutrition was the only cause of the disease. Nutrition remains the most important risk factor, but it has become apparent that intensive management practices have greatly exacerbated the problem. A number of additional 'risk factors' have been identified as contributing to the animal's stress and, by so doing, make it more susceptible to poor nutritional practices.
Nutrition.
Energy. It is well known that sudden ingestion of carbohydrate originating from grain will induce extreme ruminal acidosis and acute laminitis (30, 40, 41, 47, 54, 55, 62). This is most likely to occur either before or soon after calving. If a total mixed ration is fed, the bulk tends to restrict the amount of carbohydrate an animal can consume. On the other hand, if a cow is given the choice of eating concentrate or forage, she will invariably prefer the concentrate. Acidosis also results if the rate of starch degradation is too fast, which is often the case with barley. If barley is fed, it should be limited to 35% of the non-structured carbohydrate (NSC) (37, 38). The same applies to wet, finely ground corn.
Fiber. When considering claw health, the fiber content of a ration is more important than the carbohydrate delivered by the concentrate component. Fiber has natural buffering properties, that is to say, it helps to neutralize the acid that forms in the rumen. Ideally, the concentrate-to-forage ratio should not exceed 60:40. Good quality fiber stimulates salivation, particularly when the animal ruminates. As much as thirty gallons of saliva can be produced each day. Saliva is very high in buffers and consequently plays a very major role in controlling acidosis. Alfalfa is believed to have the most potent buffering properties of any of the forages.
Fine chopping reduces the 'effective' fiber content of forages. Silage should be chopped to contain 25% of the particles over 5 cm long. It is believed that it is useful to have perhaps 5% of the forage chopped to lengths of 15 cm because these so-called 'sticks' will provide mechanical stimulus directly to the wall of the rumen. It is important to have forage tested for the various components. This is particularly the case if the forage is not produced on the farm. Instances can be seen where the acid detergent fiber (ADF) can vary between batches by more than 5%. If there is a sudden change in the quality of the ration brought about by a sudden drop in the level of ADF, the buffering properties of the ration can fail and acidosis will occur very rapidly. Acid detergent fiber is mainly composed of lignin which cannot be digested and, therefore, provides bulk which slows down the passage of food through the gut.
It is worth noting that in a pit silo each layer may have been added at a different time or at a different stage of growth. Therefore, silage removed from the pit will be a mixture of different qualities, but is likely to be consistent throughout the pit. On the other hand, bagged silage may have been filled with sequential layers of forage. Therefore when it is used there may be changes in the quality if the bag is emptied from one end.
Protein. Several reports, some unsubstantiated, have suggested that feeding high levels of protein may cause laminitis (36, 39). Forage (or pasture) that has a high nitrate content may cause a 'laminitis-like' reaction, but objective evidence is lacking. In our own work, we found that feeding crude protein levels in excess of 15% did not increase the incidence of laminitis. From this observation, it seems unlikely that the quantity of protein consumed constitutes a risk factor, but allergic reactions to protein quality cannot be precluded.
Recommendations.
Behavior. It has been shown that there is a relationship between the behavior of dairy cattle and lameness (18, 19, 61). This relationship is based on a cow's unwillingness to lie down. A cow that is lying down is more likely to ruminate and produce saliva. More blood passes through the udder than when she is standing. Therefore, a cow may be producing more milk if she is lying down than if she is standing. If she is standing for prolonged periods, the blood pressure inside the claws will rise and reduced perfusion of blood will follow. This will result in inadequate oxygenation and nutrition of the horn-producing tissues which will lose vitality. Reduced circulation of blood through the foot will mean that poisons present will not be removed.
Cattle need to lie for 11 to 14 hours daily (50). The following factors tend to reduce lying time:
Inadequate numbers of cubicles.
Cow comfort. This is a term used to indicate that cubicles are unattractive to cows:
Social confrontation. Occurs when a submissive animal alters its natural behavior when confronted with a more dominant animal. This factor is important when competing for bunk space and the use of computerized feeders.
Space will not permit an adequate exploration of the importance of housing about which there has been considerable information provided in the literature (3, 4, 6, 15, 31, 32, 44, 75, 76, 77). Let it suffice to say that housing design should be based on animal needs (to accommodate behavior) rather than human convenience.
Exercise. Beneath the coronary band is a complex of veins and elastic tissues. When the animal walks, the vessels are squeezed between the horn of the claw and the toe bone. It seems probable that this arrangement functions as a pump. Stale blood is drawn from the claw and returned to other organs to collect oxygen and nutrients. As well, poisons will be swept out of the foot. If this is the case, exercise becomes very important. We, therefore, must interest ourselves in any management system that restricts exercise. For example, if young animals accustomed to free range are suddenly confined, their opportunities to move around may be restricted. This may also be the time when the ration is changed. Standing in line also reduces exercise. Therefore, if there are too few automatic feeders, cows will stand in line, blood will pool in their feet, and foot problems may become more common.
Claw Trimming. If performed correctly, claw trimming can have a very positive effect on the longevity of a herd. Judicial removal of sole horn stimulates horn growth, thus poor quality horn may be replaced by new more durable material.
For the dairy cow, maintaining the stability of the foot is an important concept. The bearing surface of the medial hind claw has much greater slope towards the cleft than the lateral claw. Nevertheless, in the normal animal, weight is born evenly between the two claws. When this balance exists, the foot is considered to be 'stable' (51, 63, 66).
However, weight-shifting on concrete surfaces is mainly a function of the lateral claw. In modern dairy units, cows spend much time walking on concrete. This allows claw stability to gradually deteriorate because increased loading of the lateral claw causes it to wear more rapidly than the medial. A compensatory reaction of increased horn production should result in a return to natural balance, but this is not the case. Instead, there is a tendency for growth of the lateral claw to be greater than wear. The outer claws then slowly, but gradually increase in thickness beneath the bulb which is said to become overburdened (66). Overburdening of a lateral claw usually causes the animal to become cow hocked. If stability of the claw is lost, slipping may occur and/or more pressure will be exerted on one area of the sole than another. Diseases, such as sole ulcer, may result or the abnormal pressure may play a part in the etiology of laminitis. These observations have provided the basis for the 'Dutch system' of functional claw trimming, the objective of which is to distribute weight equally over the normal weight-bearing areas. Fear of slipping is reduced. While there is no doubt that proficient claw trimming is beneficial, it is equally certain that trimming performed by poorly trained individuals can be extremely counterproductive (65).
Macro/micro Nutrients (74). Copper and zinc are essential elements for the growth of good quality claw horn. Iron, cobalt, and manganese may also be needed elements. However, stress and pain reduce the reserves of essential elements, particularly zinc, thereby making them less available to the keratogenic tissues. On the other hand, if nutritional supplements formulated to counteract stressful circumstances are fed to unstressed animals, imbalance can result.
Nutritional supplementation is regarded by some producers as the miracle solution to claw problems. At the other extreme, other producers consider supplements to be valueless as there has been no improvement in lameness in the herd despite copious offerings of expensive product. Serious claw problems are unlikely to be caused by a trace element deficiency. However, mineral imbalance can be a secondary contributor to the severity of changes in the condition of the claw horn. The unfortunate fact is that there does not seem to be a reliable method of evaluating a marginal mineral deficiency in the field and recommending an appropriate course of action.
Evaluating trace mineral levels in blood provides unreliable information. Testing liver biopsy samples generates accurate data, but is too expensive to be of routine practical value. Analyzing horn trimmings is also of no value because the information is many months out of date (1, 12). Anyway, the mineral content of claw horn is variable, depending on the region from which the sample is taken. Subjective evaluation of the appearance of the coronary band and claw horn may be useful. If the coronary band is rough and the external surface of the wall is dull, finely striated or irregular in appearance, it is worthwhile to investigate the trace element status of the diet.
Forage samples should be analyzed as part of a herd lameness investigation protocol. The levels of Ca, P, Zn, Cu, Co, and Mn should be evaluated. Some elements act as conditioning agents for other elements. A conditioning agent is an element that can affect the availability of one or several other minerals. Farmers like their minerals to be colored so the manufacturer adds iron oxide. Forage is high in iron and sometimes water has a high iron content. In this case, iron will have a conditioning effect on the uptake of other minerals. Molybdenum is the best known conditioning agent in its role of reducing the availability of copper. Molybdenum is found at higher levels in legumes than in pasture grasses. Selenium is a conditioning agent for zinc. In practice, producers often feel the need to use nutritional supplements high in selenium as well as provide injections of vitamin E and selenium even if there is no history of selenium deficiency.
Despite a large volume of published research findings, it is difficult to make recommendations with confidence to individual producers about the most appropriate nutrient supplements to meet the needs of cattle. Officially recommended minimum requirements are generated under controlled, environmentally stable conditions. Therefore, these recommendations can only be considered as a base-line standard. Inappropriate supplementation of minerals can create interactions and imbalances that will exacerbate a deficiency or even create a toxicity.
Bioavailability is that proportion of a trace element compound available to an animal. The percentage of an element published on the label of a bag of supplement does not necessarily mean that it is available to the animal. The value of chelated, complexed, or proteinated minerals is controversial. The more important chelated minerals are those of copper and zinc, but the bioavailability appears to differ according to the method of manufacture and the protein or amino acid involved. It is reasonable to assume that if copper or zinc is called for, at least 50% of the requirement should be supplied in the highest quality chelate available.
It is suggested that a 'strategic' approach to micronutrient supplementation should be developed.
Replacement-stock Management. An increasing number of producers appear to be concerned that laminitis is appearing in dairy heifers soon after they calve. The primary problem may be that young animals are being forced to an abnormally high average daily weight gain during puberty (21, 22, 33). Weight gains in excess of 0.75 kg per day between 3 and 16 months can be prejudicial to long-term claw health. We have been able to correlate average daily weight gain to the severity of sole hemorrhages at calving (23).
A popular recommendation is to calve heifers for the first time when they are 24 months of age or younger. In addition, arbitrary withers-height and body-weight standards have been established for a specific age. It may be worth considering an alternative point of view. What may be possible for a large-framed animal may be impossible for one with small frame size. The use of rations high in carbohydrate can suppress growth hormone production and lead to counterproductive fat deposition in the udder. Furthermore, there is a significant growth in the size of a heifer's claws between 20 and 30 months of age.
Recommendations:
Footbaths (11). A footbath should be an essential component of an effective dairy unit. The main benefit of its use is to reduce the microbial population on the skin of the foot as well as reduce the effects of irritating slurry. If formalin is used, some benefit accrues from the resulting hardening of the horn of the claw (57).
Genetic Selection. Resistance to disease is variable in any population of animals and there is no reason to believe that laminitis is any exception, although the literature gives very little support to such a concept. However, conformation is an important risk factor over which some control could be exercised.
Claw. The shape and size of the claw are hereditable characteristics which have been shown to have some correlation with production in dairy cows (2, 8, 13, 14, 29, 42, 58, 62). The length of the toe of the average mature Holstein cow measured from the apex of the toe to the coronary band is 7.5 cm (42). Recently, there has been a trend to measure the claw diagonal length from the apex to the skin/bulb junction (42). The normal heel height is approximately 3.75 cm and may be less as the animal ages or is affected with laminitis. Presently, there is no consensus as to how claw size (volume or bearing surface) should be measured objectively. There would be benefits to genetic selection methodology, particularly for beef cattle if claws could be evaluated in terms of kg body weight per cm2 or cm3 of bearing surface or volume respectively. Trauma and/or rapid pressure changes inside the claw are important risk factors in the etiology of laminitis.
Hock angle. A steep or post-legged conformation of the hind limb increases the forces of concussion acting on the claw. Instead of being absorbed by muscle, the impact of each step if borne by the bones of the joint. Joint disease may be associated with increased forces on the joint surfaces. It is recommended that animals selected for breeding purposes should have a hock angle of 175° or less.
Farmer Knowledge (43). In one study (72) it was found that the more training that a farmer had in recognizing and treating disease of the digits, the lower was the prevalence of lameness. Training and the availability of suitable training literature are extremely important. Knowledge goes hand in hand with the keeping of accurate records which play a major part in the investigation of an incident of herd lameness.
Discussion
This paper has summarized the currently perceived underlying causes of non-infectious herd lameness. The most important, perhaps least well understood, disease is laminitis. Laminitis has become the disease of intensive management and one that flourishes in the stressed animal. Laminitis itself is not the major disease problem, but the numerous diseases associated with it are becoming increasingly prevalent.
There is strong reason to believe that claw health is compromised during the formative years of heifer and bull development. It is exacerbated by the lack of knowledge of producers about foot diseases and the emergence from research of a multiplicity of risk factors that have some influence on claw health.
References