New Zealand veterinarian Neil Chesterton made the following statement some years back, "The veterinary practitioner faced with a lameness problem on a farm needs to examine farm management in a herd rather than merely treating a long series of individual cows." The truth in that statement holds the key to understanding the ramifications of herd lameness today as well as herd health in general.

I wrote a book on lameness that was published in 1996. Ten years later I shall publish another book on the same subject and the content will be remarkably different. Of course, diseases such as foot rot don't change much. What has changed dramatically is basic knowledge about the impact management has on the constitution of a high-production dairy cow and how this has increased the incidence of lameness.

The milk yield of intensively managed high-production, Holstein dairy cows has probably doubled in the lifetime of most contemporary dairy farmers. At the same time, the functional life of the same dairy cows has become increasingly shorter and is now recognized as being economically unacceptable. It has been said that 'hig-production cows in an environment of intensive management are on the verge of failing to attain their genetic potential for production.' This problem of 'longevity,' expressed in many different ways, fills much of the literature published today.

For years, it has been known that the three most important health problems in dairy cows are mastitis, reproductive failure, and lameness. Up to fifty percent of cows culled in Europe are lost because of lameness. Now it has been clearly shown that the higher the incidence of lameness in a herd the more serious will become the problem of reproductive disorders. There are recognized linkages between these two types of disorders. Stress features prominently in both. Geneticists have found that single-trait selection for production has a negative long-term affect on functional non-production traits such as feet and legs. Workers in Ireland have concluded that reproductive performance has declined in recent years and attribute this partly to selection for higher milk yield.

The longevity rate was studied using several million records from herds in nine different regions of the United States. It was found that the days from first calving to culling differed considerably from region to region with an overall variation being 73 days. It was concluded that factors such as herd size, housing facilities, feeding programs, and heat stress affect the voluntary and involuntary culling policies of individual herds. From this, it can be concluded that although selection for milk production is of primary importance, differences in nutrition, management, and the environment can make matters worse. The variable risk factors involved in nutrition and management will be discussed briefly in this paper.

It is frequently said that feeding high-production dairy cows too much carbohydrate in the form of cereals is a major cause of lameness or at least laminitis. Strictly speaking, this is an incorrect assumption. When carbohydrates are fermented in the rumen, a considerable amount of acid is produced. If this went on unchecked, the wall of the rumen would become inflamed, poisons would pass through it, and the liver would be affected. Most producers have seen the damage done when a cow accidentally gets unrestricted access to the grain bin. The way that nature manages acid production is to provide the antidote in the saliva of the cow. The cow can produce up to 80 US gallons of saliva each day. There are several tricks to this equation.

1. The production of acid can get out of control. This can happen in several ways. First the digestibility of the cereal varies considerably. Oats has the fastest rate of digestion, followed by wheat, then barley, then corn, and finally sorghum. However, when a cereal is processed, effective ruminal digestibility is increased. For example, 45% of coarsely cracked corn is digested. If the shell is fully cracked, the digestibility could rise to 53%, but if the corn is finely ground, 75% would be digested. Finally, if the corn is steam-flaked, up to 90% of it might be digested. The extent of digestion also increases with the higher the moisture content in the grain.
   
   A problem, that can slip by unnoticed, occurs with corn (maize) silage. Depending on the stage at which corn is harvested, there can be a huge variation in the carbohydrate contribution to the cow's diet. Obviously, if there is a sudden jump in the energy in the silage and the producer goes on giving the same amount of cereal, the rumen will receive more carbohydrate than it can handle.
   
   
2. The other side of the equation is the saliva or more particularly what can reduce saliva production. A large amount of saliva is produced when cows ruminate (chew the cud). It is the quality of the fibre in the forage that stimulates eructation (bringing up a cud from the rumen). Lush grass, for example, has very low levels of suitable fibre, so it passes though the rumen very rapidly, landing on the ground as an undigested puree. On the other hand, long hay stays in the rumen for some time. The rough stalks scratch the wall of the rumen and stimulate it to churn and bring up the cud. Long hay forms a floating mat on the rumen contents, and the feed stays for a longer period before it is passed on to the hind gut. Incidentally, the longer carbohydrates stay in the rumen, the more completely they are digested. Seeing undigested grain in the manure is a sign that it is not being completely digested. A good tip is to borrow the wife's 8" sieve from the kitchen, place a handful of manure in it and wash it with a hose. Undigested grain will be obvious, but also it is possible to see how well the forage has been broken down since it went into the cow's mouth.

Not many farmers aiming for high production will be using very much long hay. Silage mixed with cereals makes the modern total mixed ration (TMR). The length to which the silage is chopped changes the effective fibre of the total ration. The finer the chop, the less will be the stimulation of the rumen. This will result in an inadequate flow of saliva. The effectiveness of fibre is also reduced if the feed is overmixed. The important message is: 'Use good quality fibre, make no sudden changes in forage, and ensure that the ratio of concentrate to forage never exceeds 60:40.'

There is considerably more to be said about feed and feeding behaviour. However, the composition of the ration is only part of today's story of lameness or, more specifically, laminitits. The term 'cow comfort' has entered the vocabulary of the dairy industry. There is even a cow comfort index (CCI) which is an innovative method for a dairyman to monitor the level of cow comfort in a herd. The CCI should be calculated (one hour before milking) as the proportion of cows standing. The average CCI on sand-based stalls has been recorded as 15% and on hard-based stalls as 25%. A 10% CCI is ideal and 15% is a desirable objective. There is a correlation between the CCI and the incidence of lameness in a herd.

Under completely natural conditions, a cow will lie down for up to 14 hours each day. A lot of the time will be spent chewing the cud. Chewing the cud stimulates salivation. Not only does a lying cow produce more saliva, but more blood passes though the udder than it would do if the cow were standing and this means more milk.

Although adequate time spent lying down is beneficial, it is also important that a when a cow is on her feet she should be moving around. Exercise is essential to force blood to move through the feet. Blood brings nutrients and oxygen to the tissues of the claw and carries away irritant waste products. Anything that causes a cow to stand around, such as lack of space, waiting to be milked, lining-up to drink, or being confronted by a dominant cow reduces movement and compromises foot health.

The following table has been modified from that appearing in the section on cow comfort in this website.