Hand feeding sheep
Different feeding regimes for ewes at conception may influence the sex ratio of their offspring, according to preliminary findings of MLA-funded research, with grain high in omega 6 leading to more female lambs while omega 3-rich silage resulting in more males.
Eighteen months of the research (on top of earlier research funded by the EH Graham Centre) at Wagga in southern NSW has found the supplementary feed type, fed to both first cross and Merino ewes for six weeks prior to joining and for 17 days following, had an impact on the sex ratio of the flock’s offspring and the time it takes to reach oestrus.
Project Leader Dr Edward Clayton, a ruminant nutrition specialist with the NSW Department of Primary Industries (DPI), said the 2011 MLA-funded research, conducted on 600 ewes, found 64% of the Merino offspring were female when ewes were fed an oat grain/ cottonseed meal (CSM) based ration, while the crossbreds produced 62% females.
Ewes fed a silage based ration produced, in both Merinos and crossbreds, between 40 and 45% female offspring.
“Why would producers want to change the sex ratio of their lambs? If you are running a terminal sire flock for prime lamb production more males could be useful or if you are building up your flock, more females could help you get their faster,” Ed said.
The research also found ewes fed the oats/CSM reached oestrus approximately half a day earlier than those fed silage.
While Ed said this may not seem hugely significant, it could be beneficial when seeking greater synchronisation of ewes for a tighter joining period, for AI or for using fewer rams and warranted further investigation.
It could be in the timing
The research is continuing with trials also examining whether the impacts of the timing of supplementary feeding on the sex ratio is from the feeding prior to or following joining.
This year the ewes will be fed the opposite diet to the one received in the first year of the project.
Blood samples have also been taken from all offspring and, this year, the lambs will be measured after slaughter to assess if the diet impacted on the omega 3 or omega 6 levels and other eating quality traits in their meat.
What did they eat?
The two rations were (on a dry matter (DM) basis):
Group 1: 90% cereal/legume silage, 10% molasses
Group 2: 70% whole oat grain, 8% cottonseed meal (CSM), 22% cereal/legume silage
Both groups were fed approximately 1.07 kg/day total DM for the silage group and 0.81 kg/day total DM for the oats/CSM group.
Each group also received 20g/hd/day of a commercial mineral mix.
Source: Argentine Beef Packers S.A.