Excess Dietary Protein and Animal Health
30/05/2011 1:57:22 PM
Bryan McLeod
During autumn and winter, especially after good breaks and in wetter weather, farmers often question vets for the reasons their stock have poor nutritional status.
How many times do you hear the statement, “We have lots of green pasture but our stock is not performing”?
When animals are consuming fresh green pasture, especially if it is a major part of their diet, we often see:
- scouring
- weight loss
- bad temperament – especially horses
- bad feet – foot scald in sheep and cattle and founder in horses
- higher levels of metabolic problems such as milk fever and grass tetany (low Magnesium).
- mis-mothering in all species. A few years back in SA there were cases of cows killing their calves immediately following birth – the reason was good spring pasture growth with the excess pasture protein resulting high levels of blood ammonia resulting in mental instability – prevention - feeding high energy barley before calving.
- full term young being still born, a problem in all species. I have seen it in sheep, cattle and horses. Horses are particularly susceptible to the effects of excess dietary protein prior to foaling. I witnessed a case in New Zealand where a mare was being expected to graze only fresh rye grass/clover pasture coming up to foaling. On seeing the situation I passed a message to the owner that I would expect the coming foal to be still born, no action was taken and the foal was dead at birth. I had another case on a farm where all cows were producing dead calves- my question to the farmer “are the cows grazing fresh regrowth lucerne?” – They were and on changing the diet, it took only a few days and all calves being born were alive.
- poor quality colostrum-the first milk. High protein diets just prior to birth prevent the build up of antibodies in the colostrum – the young miss out on the initial life giving protection. They can die or stay behind in their development and will normally take approximately two years to catch up to their peers.
- discolored/dark cutting meat. This can be a serious problem for many beef producers especially when pastures are showing vigorous growth. In Victoria and SA the problem often occurs following the break of the season when pasture growth is at its best and pasture protein is at its highest. This problem can also be associated with stress and management issues. But animals grazing fresh high protein pasture will always be more liable to suffer from any introduced stress.
Why pasture?
Many things happen in the plant when pastures are green, fresh and in a high growth stage. Firstly plant mineral levels, in relation to daily intake, decrease. Why?
[1] There is a greater volume of plant material due to the higher moisture content and plant dry matter, the portion without the moisture, is reduced. This means that in a grazing day stock have a lower drymatter intake with a reduced intake of essential minerals. The only way to get the extras needed is to increase consumption which doesn’t occur so animals grazing fresh faster growing pasture are actually on a semi starvation diet. Most mineral deficiencies occur or become more acute during periods when grazing fresh growth.
[2] Pasture protein levels increase rapidly as pasture growth increases as does pasture energy. Protein readings as high as 40% are not uncommon during certain growth periods. So what’s the problem? The problem is surplus protein consumed above requirements (most animals only require 10 to 16% dietary protein) needs to be processed by the digestive system. It ends up as ammonia, goes to the blood and is dispatched out of the system via the kidneys as urea and we thus see pasture burns which are a good indication that something is wrong in the diet.
High protein pastures are also very digestible and require little processing so little saliva is produced. Saliva production is an essential part of digestion. Noting that one of the roles of saliva is to maintain an ideal digestive system pH of 6.9 to 7.0. As stock ingest pasture/feed their stomach pH will decrease but as digestion is completed the pH will return to normal. In ruminants pH decreases during consumption and then as they ruminate (chew their cud) saliva is passed into the rumen and the pH is restored. But when pasture is too digestible and the diet lacks fibre, digestion in horses and cud chewing in ruminants is reduced and thus saliva input is also greatly reduced and the end result is a lower than desired intestinal pH. Side effects are reduced appetite, lameness, scouring and trace element deficiencies etc as listed above. Thus we see stock chewing soil, trees and gates to increase their digestive system pH.
Energy
We often read about the high energy (ME) level in fresh green pasture which is true but what is not commonly understood is the energy depletion as a result of the high protein levels. An over supply of protein is detrimental to all species, it depletes energy.
In horses it depletes stamina so they run out of energy before they complete the race or event and breeding ability. I was once called in to help a trainer who had not had a winner for 3 months. I quickly discovered he was feeding a 20% protein diet and on reducing the daily protein to approximately 8% (only for horses in heavy work) his horses started winning again.
In cattle it reduces weight gain, milk production and breeding ability
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Here’s why:
Every unit of surplus protein negates approximately 0.18 ME.
eg.if we are feeding a 35% protein pasture and the animal only requires approximately 12% protein then there is a loss of 35-12x 0.18 = 4 ME of energy which is the reason for stock requiring high levels of low protein high fibre high-energy supplements when in this situation.
The application of trace elements to pasture, as a foliar via boom spray or via irrigation water is a very effective way of over coming the side effects of high pasture protein.
Elements to target are:
[a] Boron, its application as a spray will effectively reduce surplus pasture protein increasing available energy.
[b] Copper: A copper deficiency not only occurs when the level is low but also can be a result of interference by high pasture molybdenum, iron, zinc and cadmium. This means that if any of these minerals are in excess then the desired level of copper intake needs to be increased to compensate.
[c] Cobalt, related to vitamin B12 needed in higher amounts when grazing fresh pasture, not essential for horses but essential for cattle for rumen activity.
[d] Magnesium: Normally low when pasture protein high, suppressed by high pasture potassium that often occurs when pasture protein is high.
[e] Zinc, can be suppressed by high iron intake that often occurs due to soiling of pasture.
[f] Manganese is also required to counter the side effects of high protein.
Some Strategies
Blood testing - is often effective to gain a better insight into your animal’s nutritional status.
Pasture analysis - is required to have a serious look at what your animal is actually receiving. If you don’t know what your pasture contains how can you know what supplementary feed to give?
Feed analysis - again if you don’t know the nutritional status of your supplements, how can you possibly know when to feed them?
A good feeding program requires mix and matching – matching the right supplements to the base diet so that your animal receives the best level of nutrition. Knowing a feeds strengths and deficiencies enables you to choose the right mineral supplement to feed at the right time.
Assumptions - too many assumptions are made about feed quality lucerne being a good example – I have seen lucerne vary in protein from 7% to 23% when most tend to assume it is all high quality. When ever buying a supplement always ask for the analyses results, If you are buying a volume then have one done, I have heard of many buying what they thought was good quality but ending up with bad.
Different pasture species - all green grass is not the same; There significant differences in the nutritional status between species. eg warm climate grasses will often contain lower protein and energy compared to cooler climate species like rye grass that contain much higher levels of protein. Kikuyu contains a sodium suppressant so salt needs to be supplemented.
Protein - protein is nitrogen x 6.25. There are also different forms of nitrogen in a plant, some are good and some are known as “junk protein” which are detrimental to health. eg Nitrate nitrogen
As the provider of supplements to your animals you must take responsibility for their well being. Don’t just wait and see what happens but take control and see it happen.