4 June 2012

3 minute read

Oceania

Dr Lindsay Bell, CSIRO farming systems research scientist says winter cereals are an important winter feed supply in northern mixed crop-livestock production systems, whether they are used as dedicated forage crops, dual-purpose crops or sacrificial grazing of poor grain crops.

Dr Bell says several studies have shown a response to magnesium and/or sodium supplement in sheep grazing forage wheat, but the response in cattle has previously received little validation.

Two recent experiments investigated cattle response to these supplements when grazing wheat in the northern cropping region by comparing two mobs of yearling Angus and Angus-cross steers in side-by-side paddocks.

One paddock was supplemented with a mix of Causmag (MgO):Salt (NaCl) and cracked grain at an allowance of 140 grams/head/day. The second paddock received no supplements.

Dr Bell said a 25pc increase in average steer liveweight gains were recorded across the supplemented herd.

Supplementation increased beef production per hectare by 92 kilograms and returns by $246 at a cost of $22/ha or 6c/hd/day, he said.

“This response occurred across the whole supplemented herd, with some evidence of reducing within-herd variations in liveweight gain,” Dr Bell said.

Dr Bell says supplementing stock grazing on cereals is a sound investment, increasing liveweight gains by 20 to 60pc.

He says growers can reduce the incidence of tetany or magnesium deficiency in stock grazing wheat and some triticale varieties by supplementing with magnesium or sodium.

Dr Bell says growers should provide stock with a mixture of 1:1 Causmag (MgO):Salt (NaCl) at an allowance of 20 grams/head/day for sheep and 140g/head/day for cattle.

“A small amount of added grain or hay, about 20pc of the total mix, may assist acceptance of the supplement initially,” he said.

“This supplement mix of salt and Causmag is a low cost solution for improving liveweight gain for stock grazing wheat.

“It cost one cent/head/day for sheep and six cents/head/day for cattle and is a safe investment with 10- to 25-fold return.”

Additional research by former CSIRO researcher Dr Hugh Dove and others explored fertilising wheat with magnesium to indirectly supplement grazing animals.

“Results showed a rapid increase in magnesium concentration of the wheat after fertilisation with magnesium sulphate or Causmag,” Dr Bell said.

“This increased magnesium content to 50pc above animal requirements, but magnesium concentration declined gradually after fertilisation.

“In the first year, animals grazing the magnesium fertilised crop gained 25pc more liveweight.

“However in the second year higher growth rates were observed in the first two weeks of grazing, when crop magnesium content was higher, but as magnesium concentration declined the difference in growth rate declined so that over the five-week grazing period no difference in liveweight gain was observed.”

Dr Bell said in any case, fertilisation of the crop to indirectly supplement animals was not cost effective.

“The 70kg magnesium sulphate used costs about $574/ha or 60c/sheep/day and this is unlikely to be recouped from increased livestock gains compared to the low cost for direct supplementation,” he said.

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