Risk Factors Involved in Herd Lameness of Cattle
Lameness is a clinical sign of different diseases or disorders. For each condition, the range of causal risk factors and their severity varies; therefore, each condition has its own epidemiologic study. The importance of each factor differs depending on the system of management, be it total confinement, less restrictive systems, or totally pastoral. Management factors can usually be controlled, whereas factors such as ambient temperature, humidity, and rainfall must be taken into consideration but cannot be controlled entirely.
The diseases and disorders that affect the feet of dairy cows fall into two broad categories: those caused by infectious agents and those attributable to management.
The following variables can be controlled: nutrition/water, walking surfaces, resting and stress (cow comfort, social confrontation, stocking density), cleanliness/hygiene (prevalence of infectious agents/moisture/irritants), human care (hoof trimming, footbathing, lesion recording, farmer education), and genetic considerations.
If lameness has become a significant problem on a farm, it is invariably too late for a quick resolution. The first step is to immediately obtain the services of a competent hoof trimmer who preferably uses a chute side computerized lesion recording system (see Computerized Recording of Digital Lesions in Cattle).
Objective methods to assess risk factors have been developed; progress is needed to develop more objective methods to assess human care, farmer awareness, facility hygiene, and the stressors to which cows are subjected.
Correlations between genetics and lameness are being investigated in several European countries. It is thought that different lesions may have different degrees of heritable susceptibility. There is even some proof that the benefits of hoof trimming have a heritable component.
In Sweden a "Bull Index" has been created so that farmers may select sires whose progeny have a low predisposition for lameness.
Subacute ruminal acidosis (SARA) is a common problem in high-producing dairy herds. Volatile fatty acids (VFAs) produced by microorganisms in the rumen are absorbed by rumen papillae. The papillae shrink during the dry period and need to be developed by lead feeding. If the surface of the papillae is inadequate, the pH of the rumen contents drops.
Successfully managing SARA depends on the quantity and digestibility of the carbohydrate fed. The more rapidly carbohydrate is digested, the more rapidly rumen acidosis will develop. Finely ground or moist grains are more digestible than dry, cracked grain. Corn silage is frequently used in dairy production. Sometimes the energy content of the silage is completely underestimated, with disastrous results. Slug feeding once a day is contraindicated, and the more frequently concentrates are fed the better. Sudden changes in the diet or formulation of the diet are extremely dangerous. Component-fed cows should be given up to 7.5% of their body wt in concentrates around calving. After calving, it is safest if rations are not increased by more than 0.25 kg/day for multiparous cows and by 0.20 kg/day for primiparous cows to a maximum of 14–16 kg (30–36 lb).
The quality and quantity of fiber fed could be more important than the carbohydrate component of the diet. Fiber can, depending on its physical characteristics, stimulate rumination. If the carbohydrate:fiber ratio is >50% carbohydrate, the animal is increasingly at risk of ruminal acidosis. If the percentage of acid detergent fiber for the complete ration is <20%, risk of ruminal acidosis also increases. If the particle length of silage is cut too short (25% cut <5 cm long), the contribution of effective fiber is reduced.
If a nutritional problem is suspected, a "walk around" should be done. Feed storage facilities should be evaluated for clues. For example, different batches of feed may be of different textures or colors. Changing from one silage storage unit to another can indicate a possible sudden change in diet characteristics. Sometimes feed is purchased off-farm even from several different suppliers.
The manure should not contain fiber particles <1 cm of undigested grain. This can be checked by placing 2 cups of manure in a fine mesh kitchen sieve and washing the material through with water from a hose. Feces should not contain mucin/fibrin casts, be foamy, or contain gas bubbles. The feces in the same feeding group should not vary from firm to diarrhea. Rumenocentesis can be performed as a last resort.
There should be a drinking station for every 15 cows. The water supply should be clean and free of static electricity. A high level of iron in drinking water can affect palatability.
Walking surfaces are another important contributing cause of lameness. The Nordic countries have pioneered the use of rubber matting. One UK study showed that cows enter and exit the milking parlor more rapidly on rubber matting than on concrete. In addition, sole horn wears less on rubber than on concrete. Of course, rubber is fully effective only if kept free of slurry. Installing rubber matting is expensive but a reasonable recommendation. The best flooring system from the perspective of lameness is slats with rubber caps, but this is reasonable only for new installations or major upgrades.
These risk factors together with other physical stressors have been referred to as ecopathologic factors or an Animal Suitability Index. These terms refer to an assessment tool for housing conditions based on seven spheres of influence: walking, feeding, socializing, resting and comfort, behavior, hygiene, and care. Ecopathology, therefore, is evaluation of space allowance, cubicle dimensions, stall base, bedding, stall and pen measurements, type of flooring, slipperiness, stocking density, cleanliness, hoof trimming and footbathing, feed bunk space, water supply, walking surface conditions, and mobility locomotion score.
Under normal conditions, a healthy cow rests 10−11 hr/day. Resting periods usually last just longer than 1 hr, during which time the cows ruminate and thus digest their feed. Lameness, depending on its severity, tends to increase both the lying time and the number of lying bouts.
Anything that inhibits a cow from lying down is of particular concern. This can be assessed rapidly by use of the Cow Comfort Index (CCI), which should be calculated 1 hr before milking. The number of cows lying in a stall should be divided by the number of cows standing or in any way touching the stall. It is assumed that cows standing and touching the stall are showing a desire to rest; thus, the higher the CCI, the more probable there is a problem. If the incidence of noninfectious lameness is also high, then cow comfort is a risk factor to be dealt with. Cows not involved in calculating the CCI are those drinking, eating, or just walking. Unwillingness to lie down because of remembered discomfort is another reason for prolonged standing. However, inability to exercise reduces the amount of oxygen and nutrition delivered to the claw.
Stall size is important but varies depending on the frame size of the cows in a herd. The partitions must be of space-sharing design. If the overall slope of the stalls is adequate, the cows will lie with their hindlimbs all running in the same direction.
Cows prefer sand stalls above all other surfaces. The sand keeps cows cool and provides good footing to rise. Mattresses filled with rubber crumbs are acceptable; concrete covered with straw or sawdust and hard rubber mats are less desirable.
When a cow rises, she is forced to lunge forward; anything that makes that difficult should be corrected. Neck rails (never cables) should be 37–43 in. above the stall. A brisket board is important, and flexible structures are available to reduce the risk of hematomas of the brisket. Loose house stalls built facing a wall are a poor configuration. Cows should not be forced to lie or stand with their hindlimbs in the alley.
Stress is a factor that can and has been measured in cows. Stress may play a role in causing lameness, and lameness itself is a cause of stress. Stress may also be an etiologic factor in both reproductive failure and in some types of mastitis infections. Social confrontation may be a surprising cause of stress. The matriarch cows dominate the pecking order. Presumably, a submissive animal is somewhat stressed when confronted by a dominant animal in a narrow alley. Prolonged standing, waiting in line to drink, or spending >3 hr in the holding yard each day are commonly overlooked factors. Overstocking increases the occasions on which cows of significantly different dominance will face one another. This is particularly noticeable when heifers are first admitted to the milking herd. This may also be the first time heifers ever encounter concrete. Heifers should always be given 1 mo to adapt to concrete before the added stress of facing dominant cows. Alleys should never be <12 ft wide, feed alleys 13 feet wide, and loafing alleys 14 feet. There must be more cubicle stalls and feeding standings than there are cows. All too commonly, a building built to hold 50 cows is modified to take 100–150 cows, with resulting catastrophic overstocking.
When the prevalence of digital dermatitis is unacceptably high, contamination should be reduced, especially if the hind ends of the cows are caked in muck. Possibly the most commonly used slurry removal system is the scraper fixed to the front of a tractor. Although this system is acceptable, it is commonly not done often enough. Automatic scrapers are costly to install and subject to mechanical breakdowns. The overall effectiveness of flushing systems remains questionable.
The presence of any slurry during a clinician visit should evoke comment.
Priority must be given to improving farmers’ knowledge and increasing their willingness to implement recommendations, including routine examination (by the farmer) of the herd for lame cows. However, in the UK and France, lack of time and labor are reported as the most important barriers to detecting and treating lameness.
Special efforts should be made to help farmers understand the gravity and complexity of an increasing herd lameness problem. Information pamphlets, regional seminars, and hands-on on-farm demonstrations with a hoof trimmer and nutritionist involved can all be useful.