RESEARCH is showing enormous variance in the ability of northern cattle to preserve nitrogen where tropical rangeland diets are lacking in protein.
Animal production scientists from the University of Queensland have also come up with a forensic tool to make it easier to detect animals that are more nitrogen efficient at the crushside.
It's exciting work that has the potential to significantly boost productivity in northern herds during prolonged dry seasons.
Dr Luis Prada e Silva is leading the work looking into nitrogen recycling as a determinant for feed efficiency in Bos indicus cattle and while trials are still underway, answers have already become evident.
Researchers at Gatton have recorded the percentage of nitrogen lost in the urine of 60 Brahmans digesting 50 grams of nitrogen daily.
The best animals used 70 per cent of the nitrogen, while the worst used just 2pc.
"That is a huge variation in the difference between an animal's ability to utilise the available diet nitrogen - what we call the nitrogen use efficiency (NUE) of an animal," Dr Prada e Silva said.
"The idea behind this work is that the traditional way of selecting for feed efficiency is from work measuring intake and body weight gain in a feedlot diet.
"However, a producer of northern cattle grazing tropical rangelands might not be improving anything if selecting on the results of that work because these cattle are not under feedlot rations but rather are on diets lacking in protein.
"The first answer we got is the rankings are completely different to those on a good diet."
The research has shown feed efficiency depends on the ability of an animal to recycle nitrogen back to the rumen.
That creates a big difference in how nitrogen flows in the body, and a different signature in their protein isotope.
That means it is possible to pull a hair from the tail and estimate in a laboratory the NUE of the animal with reasonable accuracy.
"These preliminary results indicate it may be possible to estimate NUE and identify animals which are more efficient while requiring only simple non-invasive sampling on-farm," Dr Prada e Silva said.
"The next step is to see if we can detect the isotope with near infrared technology.
"This would provide a cheaper and faster way to measure NUE, and allow for the use of a portable instrument at the crush."
He emphasised that NUE should be used as part of a suite of selection traits.
"While selecting for only fertility or growth might mean a producer is not selecting the most productive animal in certain conditions, you also would not ever just select for NUE but rather use it together with other traits," he said.
The project was jointly supported by the Department of Agriculture and Fisheries, Queensland Alliance for Agriculture and Food Innovation and Meat and Livestock Australia Donor Company.
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Shan Goodwin
Shan Goodwin steers ACM’s national coverage of the beef industry. Shan has worked as a journalist for 30 years, the majority of that with agricultural publications. She spent many years as The Land’s North Coast reporter and has visited beef properties and stations throughout the country and overseas. She treats all breeds equally. Contact 0427686187. E: s.goodwin@austcommunitymedia.com.au
Shan Goodwin steers ACM’s national coverage of the beef industry. Shan has worked as a journalist for 30 years, the majority of that with agricultural publications. She spent many years as The Land’s North Coast reporter and has visited beef properties and stations throughout the country and overseas. She treats all breeds equally. Contact 0427686187. E: s.goodwin@austcommunitymedia.com.au
