It’s Time for Winter Lick – Minerals

AS MENTIONED before, the protein and energy content of veld grazing depends on the condition of the grass sward, specifically the abundance and diversity of climax grass species.

This under-appreciated fact means that veld in good condition offers grazing cattle and sheep more kilograms protein and megajoules energy per hectare than degraded veld. Therefore, farmers with good veld have less use of lick and spend less money on supplements than farmers with poor veld. In the long run, improving veld condition is more sustainable and will be more profitable than investing in ever more and better nutrient supplements.

The recently completed, MCA-N funded “Baseline Survey of Livestock Nutrition in Namibia’s Northern Communal Areas (NCA)” found that only a grass sward containing an abundance and diversity of the NCAs most common climax grasses can satisfy growing cattle’s requirement of 7% crude protein in the diet with a digestibility of 55% in the rainy season.

In winter, only a good grass sward can meet the maintenance requirement of cattle of 5% crude protein in the diet with a digestibility of 48%, and then only just. Where climax grasses have been decimated, the sward no longer contains sufficient protein and energy for growth in summer and maintenance in winter. To uphold animal production, these nutrients have to be supplemented from the lick bag.

This is more expensive than maintaining veld in good condition. In different areas of Namibia, the grass species involved may differ, but the principle is the same! How to improve veld will be explained in future articles but today, we look at something that cannot easily be controlled: minerals, which derive from the soil.

Minerals like calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), potassium (K) and chlorine (Cl) are needed in relatively large amounts (grams) frequently (e.g. weekly). They are called macro-minerals, not because of their size but because animals need to consume lots of them. Micro-minerals such as copper (Cu), zinc (Zn), manganese (Mn), selenium (Se), iron (Fe), iodine (I), molybdenum (Mo), cobalt (Co) and fluorine (F) are needed in minute amounts (milligrams) occasionally (e.g. a few times a year). All minerals fulfil vital functions in the animal body and a deficiency reduces production considerably.

Na and K occur in cellular fluids that transport nutrients and waste products across cell membranes, a function without which higher animals could not survive. Fortunately, K is abundant in plant matter and has never been found wanting in Namibia. Na and Cl occur in salt and are lost from the body mainly as sweat.

The more an animal sweats, the more salt it needs. In most parts of Namibia, animals need weekly access to salt, preferably even daily. Salt should always be available, even if no other lick is fed. Rock salt made along Namibia’s coast has the added aantage of containing iodine (I), which is involved in regulating the metabolic rate of the body.

An iodine deficiency causes the body’s metabolic rate to slow down and animal output drops. Iodine is deficient in all of the NCA. Rock salt addresses this deficiency in livestock successfully. However, farmers in the Oshikoto region collect their own salt from the numerous inland salt pans and the iodine deficiency persists. People of the north used to be deficient in iodine too in days gone by, developing goitre (“swollen throat”). This deficiency was alleviated when table salt was iodised, but livestock is still suffering it.

Large amounts of Ca are needed by an animal, mainly to keep its bones and teeth intact. Ca has never been found to be deficient in free-ranging grazing ruminants in Namibia. In fact, it is often too much and antagonizes the uptake of other minerals like P, Mg, Cu, Zn and Mn. When feeding lick to grazing ruminants, always choose those that contain least Ca with a Ca:P ratio as close as possible to 11frasl2 :1.

The situation is different in intensive livestock production systems where most feeds come from the bag. Grains and many layer hen feeds in Namibia for example contain too little Ca, resulting in weak egg shells and broken eggs. The farmer could supplement his backyard chickens with some ground limestone or sea shell grit if they produce eggs with soft shells.

Omalindilindi are an excellent source of Ca, protein and energy, too. The crop farmer would do well to release village chickens into his crop fields now, when the dikpense are assuming pest proportions but the grains are high and safe.

Worldwide, a phosphorus deficiency seriously limits the productivity of livestock, more so of grazers (cattle, sheep, donkeys) than of browsers (goats) that utilize mineral-rich tree leaves. More than 90% of the world’s rock phosphate is used in agriculture, mainly as fertilizer or animal feed supplement because so many soils across the world contain too little P to sustain high levels of plant or animal production.

In Namibia too it is deficient in all but the most loamy, fertile soils and is the most seriously deficient mineral in animal nutrition. Its most obvious deficiency symptom is “pica”, the deviating appetite of animals who lack sufficient P.

They try eating anything, from fence posts to tar on roads, plastic bags, discarded cool drink cans, abandoned pieces of clothing and old shoes, tortoise shells and old bones. The latter may contain pathogenic bacteria and infect the animal with botulism, a deadly disease.

Phosphorus is an essential element of the mammalian cellular energy cycle. A deficiency results in slow growth even if the dietary protein and energy level is adequate. It causes general listlessness: livestock stop foraging early and have poor feed intake that slows growth even more.

The hair coat is rough and animals become lame easily. A P deficiency also results in poor conception despite coming on heat and being mated. If it lasts for generations as in the NCA, it leads to a leggy appearance (= poor carcass conformation) and can reduce pelvic size (causing difficult births = dystocia) in dams.

Despite being quite common in earth’s crust, large phosphate deposits that can be mined are relatively scarce and the world is fast running out of conventional rock phosphate. Alternative sources are guano (sea bird droppings) and marine sediments, where P is concentrated by upwelling ocean currents after originally entering the sea as eroded soil.

Decaying organic matter adds P to marine deposits, which are also found along Namibia’s coast. It is therefore relevant that we seem to have been over-feeding P to livestock. P requirements are currently graded downwards to 0,1% of the diet, although the science on this is not yet conclusive. In more intensive agricultural systems, the over-use of P is not only wasting a scarce resource, but also a major cause of environmental pollution (ground and fresh water).

Namibian farmers need to find the fine balance between feeding enough to make high animal production possible and feeding too much, which is unsustainable and an environmental burden.

P is one of the few minerals whose concentration in plants varies with plant age. Since it is abundant in actively growing plants, P supplementation can be scaled down in summer but increased in the dry season.

I believe that we are overfeeding P in summer by not separating it from salt. The salt hunger of livestock in summer is much greater than their P requirement. If both are fed in the same lick, livestock looking for salt have no choice than eating too much expensive P, much to the financial disaantage of the farmer. Rather always avail rock salt in addition to whatever lick you are feeding. This is contrary to the aice of most feed manufacturers.

Magnesium is a macro-mineral that was earlier assumed to be deficient all over Namibia but the recent MCA-N nutrition survey found it to be adequate in livestock in most parts of the NCA, for example. Because Mg is closely linked to the metabolism of P in the animal body, a P deficiency could have been mistaken for Mg problems. Geologically, Mg is abundant in basaltic soils (e.g. in southern and central Namibia) and easily leached from sandy, freely drained soils (e.g. Kalahari sands). Nevertheless, it is abundant in plant matter and appears less of a problem than was thought earlier.

In summary, it is vital to supplement P in winter, Na year-round and to reduce the dietary concentration of Ca. Since our geological environment and vegetation are highly variable, mineral supplements that “work” on one farm may not “work” on the neighbouring farm. If you are not happy with a general recommendation, only analysis of seasonal blood and liver samples obtained from your livestock will give a specific answer.

Source : The Namibian