Woolless or finer wool

With increasing shearing costs and low coarse-wool returns, some New Zealand farmers are considering the benefits of changing from a Romney-based flock to a shedding flock.

In 2007, revenue from wool sales formed on average 13% of gross cash income for sheep and beef farms. By 2017 it had decreased to 7% and now some consider shearing an animal welfare necessity rather than a source of income.

Agricultural researchers Dr Lydia Farrell, professors Stephen Morris and Paul Kenyon, and associate Professor Peter Tozer have created a model to change a purebred Romney flock to a fully shedding Wiltshire-Romney crossbred flock. This could be done by breeding non-shedding ewes with Wiltshire rams.

The modelling showed change would take time, with 12 to 15 years of crossbreeding to achieve a fully shedding third- or fourth-cross flock. The model showed a transition from 2580 Romney ewes to a similarly sized flock of fully shedding third- or fourth-cross Wiltshire-Romney ewes, using a farm system based on an East Coast North Island hill country sheep and beef farm.

The researchers found shearing would not be necessary after seven years of transitioning when a Wiltshire ram with a shedding score of five was used. It would take longer if a lower shedding score ram was used.

With less feed demand for wool growth, the post-transition shedding flocks had more ewes producing more lambs and achieving greater annual profit compared with the base Romney flock.

The net present value (NPV) of grading-up transition scenarios were, depending on wool price, up to 12% higher than the maintenance of the base Romney flock. A sensitivity analysis suggested a ‘break even’ farmgate wool price of $4.15/kg, where NPVs of the transition scenarios and maintenance of the base Romney flock were similar.

The transition was completed when the flock of ewes were either 7/8th W, 1/8th R, or straightbred and had a similar feed demand to the base Romney flock. The numbers of ewes in each age class continued to fluctuate until about 25 years from transition start. This affected sheep feed demand, production, and cost operating surplus.

Economically, crossbreeding to a shedding flock compared favourably with farming a full-fleeced flock.

The researchers found data on shedding sheep in NZ was scarce, and more was needed to improve accuracy. Further grading up was modelled to reduce the risk of non-shedding genes in ewes of the desired final cross. When more data becomes available on shedding scores and associated variances of Wiltshire crosses this would improve the ability of the model to predict changes in shedding score for a Wiltshire grading-up transition.

The Romney flock had an average age of 3.45 years, without replacement ewe lambs entering the flock during the grading-up transition, the average age increased to 4.46 years before all remaining Romney ewes were culled.

The analysis assumed there were no production disadvantages of selecting crossbred ewe lambs to enter the ewe flock based on shedding score. This was because there was little data available for this. The researchers felt farmers would be more likely to also select ewe lambs for flock replacement based on other traits, such as liveweight and conformation issues.

• To read more visit: www.mdpi.com and search ‘Modelling transition from Purebred Romney’