Getting your lambs off to a fast start

The first influencer is the maternal effect as your ewes set half of the potential of the lamb born. Over the past 15 years what traits and genetic potential have you been selecting for in your maternal sires? Has selection for higher lamb weaning weight (WWT) alongside higher lambing percentages been a focus?

The second major influencer is the sire effect. Are you taking full advantage of hybrid vigour by using terminal sires to their full potential? Do you assess the genetic potential for lamb growth in your terminal ram purchase? Is your ram budget ($) shooting you in the foot by severely limiting the growth potential of their progeny? B+LNZ genetics have some excellent tools to make finding rams and assessing their merit easier. In your discussion group, or alongside your farm advisor, take some time to go through FlockFinder and RamFinder and to gain an understanding of key estimated breeding values (eBV), the NZ Maternal Worth Index, and the NZ Terminal Worth Index.

So many different strategies are out there. The one question I would ask you is “Does the feed demand brought on by your lambing date regularly result in average pasture cover dropping below 1200-1300kgDM/ha in the post-lambing period?” If the answer is “yes” then you are shooting yourself in the foot twice over – first because you have started to limit the daily feed intake of lactating ewes, reducing their milk production and therefore lamb growth rates; and second because grazing pasture this low has now started to impact on pasture growth rates, limiting your total pasture production for the spring. Your choice of lambing date may have created a hole and now you will struggle to grow out of it. An eye-opening experience through the spring is to record average pasture cover at weekly or fortnightly intervals in blocks with early lambing ewes versus later lambing ewes. Do you see areas with low post-lambing covers translate into lower pre-weaning growth rates?

The target is for ewes to lamb at a BCS of 3. Every attempt should be made to avoid BCS loss in late pregnancy. Ewes with low BCS and ewes that have lost body condition in late pregnancy have been shown consistently to give birth to smaller lambs with poorer survival. They tend to produce less colostrum, to have lower total milk production, and to wean lighter lambs.

Too much emphasis is placed on the single topic of pre-lamb, long-acting treatments for ewes. These are just one of the tools available to you and their use should be considered in light of a heap of other information.  In previous articles I have written about how stocking policies, sheep:cattle ratio, young:mature stock ratio, use of alternative forage crops, and sheep genetics influence the contamination of pasture with parasite larvae. Developing a detailed animal health plan, putting in place monitoring steps, and clearly articulating how you will reach a decision on whether to treat or not treat stock classes at different times is incredibly valuable, brings a lot of clarity and confidence, and leaves you less susceptible to spending money out of fear or habit.

You should know your farm’s selenium status and have an evidence based supplementation programme if required. Selenium deficiency will impact on lamb growth rates and on lamb survival.  In my experience cobalt/Vit B12 deficiency in lambs leading into and after weaning is common, although in the locations I have worked in, deficiency in ewes is uncommon. Trace element requirements are farm specific, so spend the time developing a comprehensive animal health plan with an advisor you trust.

Generally speaking, pasture quality in late winter and early spring tends to look after itself and the focus during this period is simply the quantity of feed available to support lactating ewes. As temperatures lift, and pasture covers stabilise and rise, the driver of animal performance shifts to the quality of the sward. With heat, grass species increase their fibre content and the feed quality of grass drops. Increasing the legume and herb content of the feed on offer helps maintain a higher quality pasture mix to help drive lamb growth rates as they transition from a milk-only diet to becoming more and more reliant on pasture.