Zealand, Australia and the world when ever cattle/sheep/horses are grazing fresh green pasture without a carbohydrate (energy) supplement. While the problem is often associated with wet weather the real coarse are the high levels of dietary crude protein and a resulting energy deficit inducing sub-clinical acidosis which can result in full acidosis.
Extensive trials in the USA, have confirmed 90% of all lameness in ruminant animals can be contributed to diet. This research has gone further and found that many foot injuries are also indirectly attributed to diet which result in the feet being more susceptible to damage.
In 1980 Dr Bob Scott of the USA, when on a visit to NZ, lectured on the role that Excess dietary Crude Protein (ECP) played in inducing lameness in the form of foot abscess or foot scald. Hot feet or muscle soreness are also a result of ECP. Dr Scott recommended iodine and high levels of vitamin A as a preventative against the incidence of lameness. Dr Scott’s work also showed the connection between ECP and infertility, abortion and full term deaths at lambing or calving.
In Australia and NZ the assumption has always been, we are different here, we have pasture, and our stock are not subject to the same stresses as those fed high rates of grain. In fact our stock have higher dietary stress levels from ECP than those on total grain rations, do to toxic forms of protein or JUNK PROTEIN as it can be known.
Following autumn rains, our autumn pastures can go from being very dry to be in a high growth pattern so become very fresh in a matter of days. This means protein content rapidly increases from a level of 8 or 9% or lower to as high as 40%. The problem here also is that a high percentage of the protein (nitrogen x 6.25) is in the nitrate form which is toxic protein, the reason stock can rapidly loose weight on this fresh green grass. Remember the animal only requires approximately 12% to 16% crude protein in its diet meaning it has to dispose of the surplus.
So we can see higher rates of lameness both autumn and spring.
Pasture composition changes not only from paddock to paddock but also weekly and season to season. A sudden increase in green feed can result in scouring, weight loss, poorer quality milk, calcium, magnesium mineral and vitamin suppression reduces thyroid activity, we see breaks in the wool, reduced fertility as well as lameness.
The real issues leading to these symptoms from high pasture protein include,
reduced rumination time: pastures are highly digestible – this means reduced saliva production due to lack of chewing, saliva is essential for optimum intestinal activity
reduced rumen pH – due to lower saliva production
reduced appetite, due to lower saliva production and lower rumen pH
low vitamin A level: Pastures (green plants do not contain vitamin A they contain the carotene which is the precursor of vitamin A ) high in nitrates effectively limits the conversion of plant carotene into available vitamin A so the animal has lower than desired A levels.
Increase blood to feet: High pastures nitrates whether natural or from nitrogen fertilisers increase body histamine production = artery dilation around the heart and greater flow of blood to the feet = blood pooling in the feet = hot feet = foot scald and foot sole deterioration = lameness
energy depletion: as rumen organisms take part of the dietary energy intake for their own energy use when breaking down the high levels of degradable pasture protein, converting it to ammonia which ends up in the blood. Then we see the loss of body fat as the liver uses it to produce urea from the ammonia and then the urea is dispatched through the kidneys in the urine and we often see pasture burns. That’s when we need to supply a high energy supplement eg maize silage or PK or fibre
Rumination time: This is the reduction in actual chewing due to the higher level of digestibility of high protein pasture. Rumination time is important, more chewing more saliva, less chewing less saliva. Saliva is nature’s nature digestive modifier; it plays an important in maintaining the rumen and digestive environment and helps with optimum health. Reduced salivation time can lead to acidosis and reduced production.
High protein diets also result in the increased production of histamines, high levels of histamines cause dilation of the central arteries around the heart forcing more blood to the outer extremities of the body, e.g. feet, the result being that blood can pool I the feet and often we see animals with hot feet, which can results in infection and foot scald.
Results published from dairy trials in England (2000) showed a direct relationship between ECP and lameness. As dietary crude protein increased above 19%, so did the incidence of lameness. The level of crude protein in winter, spring and irrigated pasture can range between 20% winter and 40% spring. Dry pastures will be lower. Urea applications can result in levels to the higher end of the scale.
It is important to note that crude protein (CP) is the nitrogen content of a plant multiplied by 6.25; this is because protein is 16% N. Another important issue is that the nitrogen in plants can be in different forms, some good and some toxic. Nitrogen readings do not necessary identify these different forms of N present, levels of the different forms of N will vary at times there are higher readings of toxic forms of N present. For ideal pasture growth pasture should contain 4 to 5% N or 25% to 31.25% CP. So there will always be a difference between pasture and animal requirements, the real issue is to understand.
With any infection bacteria are opportunists, blood pooling in the feet results in a breakdown of tissue allowing infection to occur. The infectious agents are secondary and may not be the normal dichelobacter nodosus (Foot rot) organism. Autopsy of foot abscess has shown the presence of soil born staphylococcus or spirochete as well as the common foot rot organism. If given the opportunity soil born organisms will invade hoof tissue. Dietary issues weaken tissue but if healthy will form an impregnable barrier to infection.
One fallacy I often hear is that green pasture/plants are high in vitamin A, when in fact they only contain carotene which is the precursor of vitamin A. The conversion of carotene to vitamin A takes place in the animal but this conversion can suppressed by the presence of excess nitrogen in the body. So the animal is often vitamin A deficient, even when they have a high intake of carotene which is seldom recognised either in animals or humans. This is what we call an induced deficiency. An induced deficiency is where one element in excess will suppress another. Others examples are potassium suppressing magnesium, iron suppressing copper and zinc, molybdenum suppressing copper which is significant problem. And there are many more.
Vitamin: High to excess pasture protein diets will suppress the activity of the thyroid gland which plays an important role in the conversion of carotene to vitamin A, what is happening is that even though the animal is consuming high levels of carotene the conversion to vitamin A is not happening efficiently.
Lameness is an important issue. With the information we have it is possible to prevent or minimise clinical cases if not eliminate them from our property.
· Ensure a fibrous or high carbohydrate supplement is being fed
· Or feed molasses and use vitamin A as a preventative – 60,000 to 80,000iu daily of vitamin A will normally prevent the majority of lameness in dairy cows grazing pasture
Bryan L McLeod firstname.lastname@example.org