Balancing the eggs in your basket

By Nicola Dennis

As a scientist, so much of the job is interpreting what farmers already instinctively know into firm, concrete numbers. Years of battling through the elements and farm accounts give farmers an brilliant gut feeling for the relationship between an action and its likely result.

Today’s topic is an excellent example of this. Most people reading this article know that there is a tipping point in lambing percentage: a point where those extra lambs are just not worth the effort. A point when the dreams of large lamb cheques turn into bigger slinks piles, smaller weaning weights and barer pastures. You did not have to sit through seminars about datasets and statistical regressions you “just know” that increasing lambing percentage beyond a “certain point” is a bad idea.

The genetic trend for number of lambs born per ewe is 0.01. This means that over 10 years, scanning percentage would increase by 10%. That is a very exciting prospect if you have a lower lambing percentage than you would like and you are confident this is because you have a low number of lambs being born. However, for a lot of other farmers, the rams they are using are liable to push them up and over their tipping point.

The trouble is that the profit ranking tools that breeder use to select for increasing lambing percentage, as they stand, do not easily allow them to stop selecting at the “certain point”.

The profit for number of lambs born (NLB) is currently linear. In a linear world, every extra lamb born is worth the same value no matter how many lambs you started with or how many lambs you wanted. In this world, triplets are three times the fun! This means that within the all-powerful-bean-counting-machine rams with excessively high breeding values for NLB (and perhaps lower values for other traits) have high scores and can outrank rams that may have a better balance of traits.

All this is about to change!

The economic value of NLB in the profit ranking (New Zealand Maternal Worth) is going to dump its linear ways and take up a life as a capped trait.

What this means is that scientists (my colleagues Tim Byrne, Cheryl Quinton, Peter Amer and the team at Beef and Lamb genetics) have identified the average tipping point for a commercial farm. Using economic modelling they have found the point at which an additional increased in NLB results in a net monetary loss per extra lamb.

They have also found that there are diminishing returns per lamb when a farm begins to approach the tipping point. The economic value for NLB will now reflect this and there will be a cap on the value for NLB that a ram can reach in the profit ranking (the NLB breeding values themselves will be unchanged).

Once a ram’s breeding value surpasses the tipping point, they receive no extra points in the profit index for increases in NLB.  

The great thing about the capped system is that only the rams with very high values for NLB are affected by this change; rams with low and moderate NLB values will still have very similar rankings as they do in the current linear system.

Under the new system, there is no incentive for producing rams with extremely high breeding values for NLB and this has to be a good thing for everyone. Not least of all, because pumping the brakes on NLB frees up some space in the index to maintain or improve other traits. This will give progressive breeders the opportunity to provide you with rams that will increase your future profit in other areas (e.g. other maternal traits, weaning weight, parasite resistance, yield, growth) while holding on to the great gains you have made in NLB.

This article was reproduced from the Country-Wide magazine, August 2017 issue. To view the article page, please click here