I have received the following reply to my enquiries to the Dept of Ag New South Wales and I thought it might be of interest to you.
Thanks very much for your email. It is very interesting the sex ratios you observed after feeding a grain-based diet. This is consistent with some of the results we have obtained from pen feeding studies here in Wagga. We have seen up to 65% female lambs when Merino ewes were fed a high-grain diet leading up to joining, which is very similar to what you observed. We think that feeding a high grain diet (about 70% of the total ration) that is high in omega-6 fatty acids (relative to omega-3) for 6 weeks prior to joining can result in a higher proportion of females. This means that you would have to start feeding shortly for a February joining.
We have less evidence about skewing the ratio back towards males. However, I was involved with a study where ewes were fed fresh lucerne prior to joining and this was associated with a sex ratio skewed significantly towards males. Our recommendation at the moment (without having all the evidence required) would be in order to try to increase the amount of male lambs, feed some type of green feed (lucerne seems to work, but we don’t know about hay compared with fresh). We have fed silage in our pen trials (oaten, wheaten or ryegrass silage in our trials, I can see no reason why lucerne silage would not have a similar effect) and have usually seen a skew towards males (around 55% males).
We will see how we get on this year.
Thanks very much for your email. It is very interesting the sex ratios you observed after feeding a grain-based diet. This is consistent with some of the results we have obtained from pen feeding studies here in Wagga. We have seen up to 65% female lambs when Merino ewes were fed a high-grain diet leading up to joining, which is very similar to what you observed. We think that feeding a high grain diet (about 70% of the total ration) that is high in omega-6 fatty acids (relative to omega-3) for 6 weeks prior to joining can result in a higher proportion of females. This means that you would have to start feeding shortly for a February joining.
We have less evidence about skewing the ratio back towards males. However, I was involved with a study where ewes were fed fresh lucerne prior to joining and this was associated with a sex ratio skewed significantly towards males. Our recommendation at the moment (without having all the evidence required) would be in order to try to increase the amount of male lambs, feed some type of green feed (lucerne seems to work, but we don’t know about hay compared with fresh). We have fed silage in our pen trials (oaten, wheaten or ryegrass silage in our trials, I can see no reason why lucerne silage would not have a similar effect) and have usually seen a skew towards males (around 55% males).
We will see how we get on this year.