GRAZIERS often wonder why in some years their ewes produce significantly more of one sex of lamb than other years.
It turns out the ewes' diet in the approach to joining could be part of what is influencing the sex ratio.
This was among the findings of research conducted by the NSW Department of Primary Industries (DPI) in conjunction with the Graham Centre (an alliance between NSW DPI and Charles Sturt University), which has just completed stage one of a research project which looks at the effects of omega-3 in animals (so far mainly sheep, but stage two aims to look at cattle), plus how the omega-3 fatty acids are passed to the consumer.
NSW DPI livestock researcher Dr Edward Clayton said the project had shown when ewes were on a diet high in omega-3 leading up to joining (for about six weeks) they produced more male lambs.
If they're fed a diet high in grain, which is high in omega-6, they can produce as much as 25 per cent extra ewe lambs, and on average an extra 15pc ewe lambs.
"There's a lot of anecdotal evidence that in times of drought, people get more females," he said.
"It could potentially be that in drought (the ewes) are being fed more grain and it just so happens it coincides with that joining period."
In their studies they fed 1300 ewes with a similar change in each study so they're "pretty certain" about the effect.
He said dry grass may have lower levels of omega-3 than green grass, however, the levels would likely be higher than grain so the effect would be more like that of green grass.
The source of grains in the trial was oats and cottonseed meal "so we can't make rash generalisations about other types of feed yet, because we don't know for sure", Dr Clayton said.
For the green feed component they used ryegrass and cereal (mainly oaten) silage. The trial stages to come will have to look at the effect of different types of feed.
He said for livestock producers, this knowledge could help shift production towards more males for sale, or more females for herd or flock rebuilding.
"We had funding from MLA to do the work with sheep and it's worked out pretty well. The plan was - when we initially talked to MLA - to move into cattle if it looked like it was going to work in sheep... so we're going to hopefully look at that down the track when they get some new money and have some new projects coming through."
All the ewes used in the trials were joined on synchronised oestrus, with no trials done yet on naturally cycling ewes.
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