Limestone and Salt

Perhaps the two most abundant compounds on the face of the earth, yet our cows are deficient in both, with significant implications to health, fertility and milk production. Why, perhaps due to their commonness, and we tend to take little notice of things that are very common.

Salt is an essential compound in a cow’s diet for a number of metabolic functions, but also for buffering capacity of saliva in the rumination process. Apart from these important functions, salt will make cows drink water, and there is a direct correlation between water intake and dry matter intake; which naturally drives milk production. Salt should be in the dairy grain mix, but also offered free choice as the cows’ needs can vary daily.

The subject I really want to address is calcium in our cow’s diet. Limestone dressing on pastures is another subject that requires urgent attention. No, or low, calcium in soils will seriously retard plant growth and mineral content of plants. Calcium is the transport system of other minerals in both our soil and our cows’ rumens.

Gary Oetzel, DVM, professor of dairy science at the University of Wisconsin, during a seminar stated: “You ought to respect hypocalcemia, you ought to be afraid of it, and you ought to do everything you can to minimise it”. Hypocalcemia is low blood calcium. Milk Fever in clinical form, but we’ve made massive inroads on milk fever with anionic lead feeds and good transition management reducing incident rates to 2% – 3% of the herd. Despite this, sub-clinical milk fever is reported to run around 60% of all second-plus lactation cows. Heifers are not immune either.

The clinical milk fever cow can be recognised, treated, and back in production relatively easily. The consequences of sub-clinical hypocalcaemia have far more serious effects than we realise, and far more reaching into lactation production, health and fertility. Blood tests are the only real indicator of the degree of hypocalcaemia. Initially, at calving, there are big benefits in oral calcium supplements (drenches or boluses) to help cows cope with “lactational osteoporosis”. This is virtually unavoidable to meet the 300% increase in calcium that fresh cows require. Oetzel estimates sub-clinical hypocalcaemia at four times the cost of clinical milk fever. When research has identified up to 60% of mature cows suffer sub-clinical hypocalcaemia, at four times the cost of clinical milk fever, then this is a very significant cost to farm profit.

Sub-clinical hypocalcaemia is well documented as the prerequisite to a numerous diseases common around calving: obviously clinical milk fever, but add to that, retained membrane, metritis, mastitis, ketosis, and a major industry problem, fertility. Productive life as milking cows can be unnecessarily cut short as a result of sub-optimal calcium nutrition. Our clients that have been proactive in calcium nutrition have seen major decreases in fresh cow mastitis, metritis, and very significant improvements in fertility.

My concern is, in our low calcium ryegrass pastures, this hypocalcemic disorder goes on well past early lactation. A cow producing 30 litres of milk is exporting 36 gm of calcium daily in milk. That’s the calcium content of 100+ gms of limestone. Then there are urinary loses, reabsorption of calcium into bones and metabolic functions requiring calcium. The immune system alone has a high calcium demand.

Dietary calcium deficiencies are common in ryegrass pastures which frequently have little or no clover content these days. Milk protein production is also limited by calcium deficient diets. Ryegrass contains typically around 0.3% calcium. Clover is around 1.4% and Lucerne 1.7%. A recent article in the Australian Dairyfarmer highlighted the need for a return to 30% to 40% clover content in grazing pastures. This article was more about pasture production and soil health and their need for clover, rather than cow nutrition.

Soils have a high need for calcium to function well (transport other nutrients). Obviously, legumes have a high need for soil calcium availability for growth, and their high calcium content. The author of the Dairyfarmer article stated “we’ve lost our way” in pasture production with the neglect of clover. Losing our way is correct. When I started share farming in the 1970’s, applying lime was an annual autumn event. Where I live in SW Victoria we sit on top of a limestone mountain, yet I see very little spreading of lime on pastures. Certainly SW Vic would benefit immensely from gypsum applications. Gypsum will supply sulphur as well as calcium, another element lacking in our soils as a legacy of high analysis fertilisers and urea. Gypsum will restore soil structure allowing for better water and air penetration.

I think the massive uptake of urea use, the demise of super applications, the spraying of broadleaf weeds have all contributed to clover’s departure from our pastures. These are all reversible including broadleaf sprays that are now available and harmless to clover. A return to lime applications must precede sowing of clover. It is not just a soil pH issue, but a locking up of other nutrients that only calcium can undo that needs to happen to ensure good clover establishment and perseverance.

Reestablishment of clover in our pastures will not just increase calcium in the diet of our cows with major benefits to production, health and fertility, but increase pasture harvested per hectare, improve soil nutrient availability to plants, improve soil structure and reduce soil compaction problems prevalent on most dairy farms.

I profess no expertise in agronomy and strongly advise consultation with sound agronomists. Calcium is not a stand-alone cure-all. It is intimately involved with numerous other elements in both soil and animal nutrition. However, calcium is called a macro element, meaning, it is required in large amounts and our capacity to meet this need through grain mixes alone is limited. Increasing calcium in our forages through good pasture clover content will go a long way in improving both pasture and cow health and production. As the Dairyfarmer article said; “we’ve lost our way”. This is not rocket science, but was standard, good-farming practice of 50 years ago.

Leafy summer fodder crops like sorghum have a high need for calcium and respond in yield very significantly when calcium is not a limitation. As one of my clients says; lime is a fertiliser.

John Lyne

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