What is the truth about lime and animal health?

Press, 2 November 1984, Page 25

What is the truth about lime and animal health?

Obviously lime can improve the over all health of animals simply by increasing the amount of feed available and raising the level of nutrition.

But a popular view holds that liming can be beneficial to animal health by changing the mineral composition of the pasture. Not a lot of experimental evidence exists to support this view, says the S.A.L.T. team.

In fact, the indications are that if lime does affect animal health by altering the chemical balance in pastures then these effects will be detrimental rather than beneficial (with the exception of possible manganese effects). Many M.A.F. trials have measured the effects of liming on the mineral composition of pastures. These show that the major effects of liming are:

® A decrease in magnesium and manganese.

» An increase in calcium and molybdenum. Liming has very little effect on the concentrations of the macronutrients phosphorous, nitrogen, sulphur, potassium and sodium, or micronutrients copper, boron, calcium over the acidity (pH) range normally encountered in agriculture practice. (The normal pH range is 5.0 to 6.0. The S.A.L.T. authors say that the text books on this subject should be updated.) The decrease in herbage magnesium and the increase in calcium are believed to

be a factor in the increased incidence of hypomagnesaemia in lactating dairy cows which was measured in one trial in Taranaki. Farmers should not be alarmed by this but they should be aware of it and, if hypomagnesaemia is a problem, take the necessary precautions, such as applying fertiliser magnesium or drenching. Similarly, the increase in molybdenum following liming has important implications.

Although molybdenum concentrations are increased generally copper concentrations do not change. Consequently the ratio of copper to molybdenum decreases. This could lead to molybdenum-in-duced copper deficiency in animals. Some evidence indicates that this ratio should be greater than four to avoid copper deficiency. Also, farmers who use molybdenum fertiliser regularly should be careful when they apply lime. They should have a herbage analysis done first. One of the largest effects of liming on plant chemical composition is to decrease manganese concentrations. However, it is unlikely that this will affect animal health.

Work done by Dr Neville Grace at the D.S.I.R. Palmerston North, suggests that manganese concentrations greater than 400 parts per million (p.p.m.) are necessary before sheep growth rates are affected. A recent nationwide summary

of nutrient concentrations by Dr Garth Smith of the M.A.F., Ruakura, indicated that such high concentrations are unlikely. Typically, plant manganese concentrations are in the range of 100 to 200 p.p.m. However, there are some regions of New Zealand, particularly on the East Coast, where high manganese concentrations may occur in summer.

Once again, it would pay farmers to have herbage analyses done before they applied lime. Liming, of course, increases plant clacium concentrations, and clacium is required for bone development and is important to growth in other ways. *

However, calcium concen ; trations in most New Zealand pastures are normally adequate for animals .because of the good soil clacium levels, helped by the addition of large amounts of calcium in superphosphate. At this stage, there is no evidence to show that this effect of liming is important for animal health. The evidence from all of this work indicates that if lime affects animal health by altering the chemical balance in pastures, then these effects will be detrimental rather than beneficial, with the exception of possible manganese effects. The old myth that liming is beneficial to animal health because it releses nutrients is a generalisation which is no longer helpful to New Zealand farmers, say the researchers.