Twin Bearing Ewes

Summary

The pasture growing season was very poor in 2006, such that little pasture growth occurred at the shelter comparison site. There was very little if any typical winter weather to challenge lamb survival at this site. At the other site lambing commenced a month later in late July. A number of typical winter fronts occurred which would have challenged lamb survival, although grain feeding rates were atypically high due to the delay in pasture growth as a result of a late start to the growing season. 
Severe adverse seasonal conditions at both sites resulted in the ewes relying in large part on supplementary feed for their energy requirements. At site 1 ewes obtained close to 100% of their dietary energy from grain supplement. At site 2 the ewes relied on supplement for approximately 60% of their dietary energy. Decisions on supplementation levels in the producer fed groups were based on FOO assessments, knowledge of the ewes requirements for energy, and measurement of their condition score. 
The bodyweight and condition score data confirms that the supplementation decisions were quite accurate in maintaining the ewes in healthy condition. The lamb marking percentages, ewe bodyweight and condition score patterns were very similar at site 1 for the self feeder mob (no FOO) and open paddock with a limited green feed. In practice this meant that feeding costs could be reduced by $17 per ewe for the same performance. Clearly a little green feed makes a huge difference!. At neither site did the provision of a barley rich diet available ad lib increase lamb survival or lamb growth rate. 
This is a similar outcome to a number of field studies done by Agriculture WA in 2002 - 2004. The hypothesis that increased colostrum production in response to a high starch diet (in this case barley) should improve lamb survival and growth as proposed by Milton (pers comm.) was not supported in these field trials and additional work is required to determine how to elicit this response. The ewe bodyweight response to the self feeder differed at the two sites. At site 1 the ewes maintained weight and condition score throughout the study, with a barley/lupin mix and loose hay available ad lib. At site 2 where more green feed was available, the ewes lost 0.4 of a condition score over lambing. Grain intakes were lower at site 2 and a simple mass balance suggests that the ewes chose to lose weight even though the grain was available to increase their energy intake. Thereasons for this are not clear.