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LIVESTOCK BEEF PRODUCTION Nitrate – a possible alternate dry season supplement? During the dry season in northern Australia’s pastoral regions, nitrogen is often the primary limiting nutrient in the low quality, tropical forages available to cattle. To counteract this, graziers usually supplement cattle with urea. But in recent years, researchers have been looking at the feasibility of using nitrate salts as an alternative supplement, which reduces methane production by animals and may offer better feed conversion efficiency than urea. By Pamela Lawson NITROGEN NEED Sufficient dietary nitrogen is needed for ruminants to provide a source of ammonia to support microbial growth and protein production in the rumen. This process in turn increases pasture intake and therefore liveweight gain. Although supplementing cattle with non-protein nitrogen (such as urea) generally results in only small liveweight gains, it is a common and practical strategy to reduce production losses during the dry season. Cattle grazing on low quality, tropical pastures produce high amounts of methane during digestion. About half the methane emissions from cattle can be attributed to cattle in extensive grazing systems in Queensland and Northern Territory. www.farmingahead.com.au Although naturally occurring, methane emissions represent an inefficiency in the conversion of feed to protein and energy. They can however be reduced by improving the diet quality and therefore production per animal, which in turn reduces the emissions of methane per kilogram of animal product. In intensive or small-scale grazing operations, managing livestock so they are grazing on younger pastures with some legume content will improve diet quality and productivity whilst reducing methane production. But this is not possible for the extensive grazing systems of northern Australia without significant capital investment and changes to current management practices. This has prompted the University of New England (UNE) to © Kondinin Group – Reproduction in whole or part is not permitted without permission. Freecall 1800 677 761 AT A GLANCE ▸▸ Recent research has flagged nitrate as a possible alternative dry season supplement to urea for northern Australia beef cattle herds. ▸▸ While nitrate feeding holds similar risks to urea supplementation, it reduces methane emissions from cattle significantly. ▸▸ Financial considerations and the current lack of monetary reward for methane abatement may limit the use of nitrate at present. Graziers in northern Australia typically supplement their cattle with a non-protein nitrogen such as urea to maintain production during the dry season. Photo: Pamela Lawson. No. 293 June 2016 Farming Ahead 57 lead a number of projects looking at nitrate as a potential alternative source of nonprotein nitrogen to urea, whilst reducing methane emissions in livestock. FEEDING NITRATE Most northern Australian graziers have had experience with feeding urea supplements during the dry season, and feeding nitrate as a supplement is very similar. Like urea, nitrate salts can be fed as part of a molassesbased mix, low-intake loose lick or lick block. Feeding nitrate carries similar risks to feeding urea, as excessive consumption of either can cause toxicity in cattle. Once eaten, nitrate is converted to nitrite and then ammonia, which is used by rumen microbes to make protein. If nitrate intake is excessive, nitrite can accumulate faster than it can be turned into ammonia. This results in nitrite being absorbed through the rumen wall into the blood, where it reduces the ability of blood to transport oxygen around the body and causes poisoning. Toxicity generally occurs when nitrate concentrations in the diet exceed nine grams per kilogram of dry matter. But other variables that influence the extent of toxicity include the rate of nitrate intake, the rate of feed digestion (release of nitrates into the body), the rate nitrite is converted to ammonia and diet quality. But UNE researchers are confident the risks of toxicity when feeding nitrate can be minimised by careful management. Feedlot studies have shown feeding a given dose of nitrate over several feeds rather than as a single dose each day reduces the risk of poisoning occurring, as does feeding nitrate as part of a total mixed ration or with pelletised grain or oaten hay. In general, higher digestibility diets have an increased conversion rate of nitrate to nitrite to ammonia so toxicity is less likely to occur. While current research suggests that nitrate can replace urea in an extensive grazing system with no additional risk, research continues to determine how to best manage risk mitigating factors. IS IT WORTH IT? With similar risks to feeding urea, producers may question the benefits of feeding nitrate over urea. In terms of production benefits, a UNE feedlot study showed a 3% better feed conversion efficiency from feeding nitrate rather than urea. However similar results have yet to be shown in an extensive grazing situation. There are also financial considerations when deciding which supplement to feed, as nitrate salts have a lower nitrogen content than urea which means it has to be fed at greater rates for a similar result. This is likely to increase daily feeding costs by 58 Farming Ahead June 2016 No. 293 Supplement bar: Cattle licking nitrate blocks late in the 2014 dry season during a UNE supplement trial in northern Queensland. Photo: Joseph Miller. about 2.5 times compared to the current urea-based supplement feeding regime. The UNE researchers found feeding cattle nitrate in an intensive system can reduce methane emissions by 10-30%. Significantly lower mitigation levels have been shown in extensive grazing systems. While methane production is normal and advantageous, it would be far more productive for beef producers if methane energy could instead be converted into growth. Reducing methane as an inefficiency in livestock systems will also become more important as food demand and climate change impact government policy and ultimately result in product prices that factor in methane abatement. But for the time being it is unlikely that current government policy will adequately reward graziers financially for reducing greenhouse gas emissions. FEEDING SUPPLEMENTS Regardless of which source of non-protein nitrogen is used to supplement livestock during dry seasons, graziers are also faced with the conundrum of deciding the best supplement strategy to employ. In extensive grazing systems, ruminants have to have the capacity to use a wide range of forages with changing mineral contents and crude protein levels. It is therefore very difficult to predict the mineral and nutrient requirements of cattle grazing dry pasture because of factors such as seasonal variability and its effect on the stage of pasture growth and the effect of leaching on pasture crude protein and mineral composition. Ruminants have evolved to survive periods of nutrient deficiencies by developing the ability to find and try materials to remove a metabolic discomfort and correct the deficiency. Individual sources of urea, sulphur, phosphorus or even trace minerals will be sought by grazing animals as these substances become deficient in the available feed. Research has shown that animals self-medicate by selectively seeking out materials that supply the deficient nutrient or prevent the harmful effects of toxins in their feed. Examples of this include chewing bones or the bark of certain trees, detoxifying feeds by consuming clay minerals to bind toxins, selecting higher protein diets when pregnant or lactating or consuming more of a medicated block when infected with internal parasites. The UNE researchers set up a free-choice based self-medication program under an extensive grazing system near Richmond, Queensland. Although the trials are continuing, early results indicate the most effective program was to offer year-round availability of mineral and urea/nitrate supplements. Essentially three separate supplements are needed for free choice supplementation, with a background of other minerals also on offer. One supplement should be high in nitrogen (usually non-protein like urea or nitrate), one high in sulphur, and fed as three separate lick supplements. Under this program, the researchers found that animals seem to be able to balance their needs and the disappearance of blocks signals the onset of deficiency. UNE researchers are now using remote pastoral management technologies such as walk-over weighing, GPS collars and supplement intake monitoring equipment, to refine their findings. By conducting station-based trial testing the effects of urea, nitrate and free choice mineral supplement systems on productivity and emissions the researchers are now hoping to quantify the variation in individual animal grazing, supplement intake and watering behaviour and their affect on animal productivity. Contact: Joe Miller Project Officer, Animal Nutrition UNE 0477 374 424 [email protected] © Kondinin Group – Reproduction in whole or part is not permitted without permission. Freecall 1800 677 761 www.farmingahead.com.au