Zinc Animal Nutrition
Written by John Turner Consultancy for Agrifert
Zinc
Zinc is an essential trace element for the nutrition of all ruminant animals.
For many years Zinc deficiency in NZ agriculture has been masked by the fact that Zinc is a significant impurity in superphosphate fertiliser.
Zinc treatments for prevention of facial eczema symptoms have raised soil and pasture herbage zinc level in some areas throughout the northern half of the North Island.
Zinc contamination of soil is common on land previously used for horticulture, particulary avocado orchards however elevated soil zinc levels are not always reflected in pasture and forage crop herbage.
Symptoms of deficiency:
Deficiency of zinc typically results in reduced growth rates of young stock, reduced feed consumption, reduced efficiency of conversion of feed energy to milk or live-weight gains, dermititis or scaley skins, swollen tissue around the hooves and foot problems. Development or growth of testicles and sperm production is likely to be affected. Young animals are typically listless and lack energy .
Zinc is also thought to be requried for the excretion of mucus from the gut lining, this is the barrier to attack by gut parasites so zinc deficiency maybe linked to low resistant to intestinal worms. Healing rate of injury or wounds is reduced and more likely to become chronic infections for zinc deficient animals.
Different classes of livestock have different requrirements for zinc:
Calves and lambs are most susceptible to zinc deficiency and increase the mortality rate of young animals.
Factors that influence the zinc content of pastures:
There is a weak correlation between soil zinc level and the zinc content of pastures so soil testing for this element is used as a general indicator of zinc status and to predict if application of this element to the soil may be worth considering. Plant uptake of zinc from the soil is reduced by cold soil temperature, high pH of recent lime application and high levels of phosphorus.Zinc absorption by animals is reduced when the copper level is high, copper supplementation is not recommended at the same time as high rates of zinc are being supplemented for facial eczema control.
Zinc absorption is reduced when dietary iron and manganese levels are high, soil ingestion in wet muddy conditions will have this effect.
Level of Zinc required in pasture or feed:
The desired range of zinc levels considered adequate in pasture and animal feeds is 30 to 50 mg/kg however for young stock and where symptoms linked to zinc deficiency are a concern, 40 mg/kg is the suggested target level.
To quantify this amount of zinc, 40 mg/kg is the same as 40 grams per 1000 kg dry feed.
Options for Zinc application:
Zinc is still an impurity in superphosphate and fertiliser blends containing this fertiliser, so where there is a long history of application of 'super' soil zinc levels are likely to be OK. Where pasture or forage zinc levels are low, foliar application is good option.
The distribution of zinc over an area fertilised with a bulk blend where zinc sulphate is added to base fertiliser may also be uneven and the timing of application may not be ideal for meeting the spring requirements of sensitive classes of stock.
Zinc applied as a foliar treatment is effictive on all pasture types and there is no time lag between application and when the element is available to grazing animals. The rate required for effective treatment is much lower than for soil application. Application may be targeted onto pastures for young stock in the spring and rams or bulls pre-mating.
Multi-mineral additives to salt blocks or to stock drinking water may be beneficial however the amount of any one element included is usually not adequate for 'deficient' stock. Zinc addition to drinking water tastes bad to sheep and they tend to avoid drinking from treated trough.
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