Improving their reproductive performance can make the option of joining both merino and crossbred ewe lambs a rewarding management option. A PDS (Producer Demonstration Site) conducted by Best Wool Best Lamb groups in Victoria showed the effect genetics, live weight and condition score had on conception rates in ewe lambs. It also showed the effect successful ewe lamb joining could have on overall flock performance.
The overall aim of this Meat and Livestock Australia PDS was to improve the reproductive efficiency of ewe lambs in both cross-bred and Merino sheep leading to improvements of at least 10% in flock reproductive performance. Between 2010 and 2012 trials for mating ewe lambs at 7 to 10 months were undertaken on 4 crossbred flocks and 11 merino flocks. It was demonstrated that mating merino and crossbred ewes at 7 to 10 months was an effective way of lifting lamb production by more than 10% in the flocks participating for multiple years in this project. These flocks achieved a 60% conception rate in merino ewe lambs and a 75% conception rate in crossbred ewe lambs. It was found that both the weight and condition score of ewe lambs at joining significantly affected the reproductive rate in both merino and crossbred ewe lambs. In fact the combined analysis of PDS flocks indicated that on average a 1 kg increase in live-weight at joining was associated with a 3.7 and 2.6% increase in reproductive rate (foetuses per 100 ewes joined) for merino and crossbred ewe lambs respectively.
There were also significant additional effects of condition score of ewe lambs at joining on reproductive rate, over and above correlated changes in live-weight, suggesting that early maturing ewes achieve higher reproductive performance when mated as ewe lambs. At a given live-weight an extra condition score at joining increased reproductive rate by 31 and 26% for merino and crossbred ewe lambs respectively.
Genetic parameters were also found to significantly affect reproductive rate of both merino and crossbred ewe lambs, albeit one merino and one crossbred flock had ASBVs on the ewe lambs involved in this project. It was found that per one unit increase in post-weaning weight (PWWT) reproductive rate increased by 17% in merinos and 6% in crossbreds. In addition carcass traits in merino ewe lambs were shown to be positively correlated with reproductive rate, where at a given joining live-weight an increase of one unit in post-weaning fat (PFAT) and post-weaning muscle (PEMD) resulted in a 50% and 27% increase in reproductive rate, respectively.
A number of significant barriers and concerns participating producers had to mating and lambing ewe lambs were overcome in this project. Firstly, it was demonstrated that reasonable reproductive rates could be achieved, second that the majority of pregnant ewe lambs were able to lamb down and rear their lambs successfully, and finally that with targeted management these ewes achieved high reproductive rates on their second mating. In addition a ready reckoner was developed that producers could use to determine the break-even marking rate they would need to achieve with varying grain prices and lamb prices. The merino flocks that participated in the PDS for more than one year achieved an average marking rate of 50%, which in the period from 2010 to 2012 of this PDS proved to be economically viable at the prevailing lamb prices and feeding costs.
