How to start a linked ewe productivity trial

Introduction

Flock comparison trials are designed to assist you to better benchmark, or compare, your flock’s productivity against that of other flocks. They are designed to remove most of the effects of management and environment, leaving you with a better comparison of the genetic merit between your flock and the other flocks for production. Usually you can only compare teams at one site. However, by including a link team in the trial you can compare the performance of all the teams at your site with all teams tested at another site which also has a link team. As link teams come from a single flock with a common genetic base, they allow you to compare your flock with a much larger range of flocks.

Participation in flock benchmarking exercises can help you identify genetically superior ram sources from which you can source superior rams to achieve your breeding objective more rapidly. You can then use on-farm ram comparisons to check the performance of these ram sources against the performance of your current ram source.

Wether trials have helped raise the awareness of the differences in performance that exist between ram sources. However, wether trials provide information on body weight and wool production traits only. This has led to some criticism because lambs and surplus animals contribute to income. Using ewes instead of wethers and adjusting the trial design can accommodate these criticisms.

Below we outline how to organise and run a ewe productivity trial. You can customise your trial within these guidelines. 

Getting a group together

The first step in establishing a ewe trial is to assemble all interested participants. A protocol, which covers conduct of the trial and compensation of the host, is agreed upon at a group meeting. You can customise you trial within the boundaries of the guidelines, however some of the components of the protocol are ‘mandatory’ (marked with an asterisk below).

Participants provide a team of randomly selected sheep from their largest mob of weaner ewes and assist in data collection. The host farmer is responsible for providing the resources to run the sheep in the trial, the husbandry required to maintain them, and for collecting the information needed to compare the teams. The protocol includes a method of compensating the host for his involvement in the trial. Normally there is a data presentation day and often follow-up field days are organised.

Basic requirements of a linked ewe trial

• *Team size: for ewe trials, 50 sheep is the minimum required in order to achieve reasonable estimates of reproduction and lamb performance in addition to wool traits.
• Number of sheep the host farmer can run: a flock size that will suit the host farmer’s infrastructure will determine how many farmers can participate in the trial.
• Sheep are normally run under the host farmer’s management system: a steering committee of participants could be involved in a decision to manage the flock.
• *Participants on a ram source for less than seven years: the results are not as accurate in terms of representing the ram source as someone who has been on a ram source for longer. However, the results will still provide a good indication of the performance of the current flock and will assist to decide whether to buy rams from other superior ram sources.
• *Length of trial: three shearings (one as hogget and two adult shearings to give two lambings) are normally sufficient but the group can resolve to continue longer, particularly if poor reproduction rates were experienced in one particular year.
• *Tagging sheep: the recommended tagging system is continuous tagging by using tag numbers from one to say 400 (depending on the number of animals). The trial will also benefit by using a different sequence of numbers for each team (that is, 1–50 for team one, 51–100 for team two etc.). If electronic tags are not used, then different coloured tags for different teams are very useful when drafting sheep.
• Health: the host farmer must be comfortable with the health protocol as he is bringing the sheep onto his property, so it is at his risk. All participants must fill out a health declaration before sending sheep onto the host property. Sheep should be drenched on arrival with a current recommendation from a veterinary officer and held in a quarantine paddock for a week or two. Feet should be checked for footrot preferably by a stock inspector if available.
• *Drafting participant teams: weaners are used because these are the animals least affected by environment (since they are the youngest) on entry to the trial. The team should be drafted from the largest weaner mob available, which should have had less than 10% culled previously. Participants should not draft their own sheep to avoid potential bias, and other participants could participate in drafting fellow members’ sheep.
• Value adding: there is an opportunity for the trial to add value to the results with additional measurements. For example, additional body weights could be recorded once or twice a year or staple strength measurements taken etc.

The link team

A link team, selected at random, can be entered in all trials commencing with a particular drop. The performance of the link team across environments allows one to combine all of the data from different trials. This is particularly valuable where more teams are entered than the host can manage. Thus the trial can be split across two properties and linked with a common team. The way in which a link team works is shown in this simple example of three teams in two trials (note: kilograms = kg):

At face value Team 2 and Team 3, run in different trials on different properties, are of equal performance (6kg). However relative to the link team, Team 2 is only 1kg better (6-5=+1) while Team 3 is 2kg better (6-4=+2) in performance. So Team 3 is the better performer.

The contact at the bottom of this page can advise participants on setting up different teams joined with a common link team.

Measurements

Fleece sampling

Fleece sampling should be completed between two and four weeks before shearing so you already have yield and micron recorded on the shearing cards. Fleece samples should be sent to a fleece testing laboratory and tested for the normal fibre diameter traits with the Optical-based Fibre Diameter Analyser (OFDA) or Laserscan. Percentage clean yield of the wool should also be tested to calculate the amount of clean wool. At least two weeks is needed between sampling and shearing so that the fleece testing laboratory can get results back in time. You may choose either the midside or pinbone position for fleece sampling but the site chosen should be used consistently throughout the trial. Greasy fleece weight and classer comments for fleece valuation must be recorded at shearing.

Reproductive performance

At joining, trial ewes should be syndicate mated as a mob to 2% of rams for at least five to six weeks. This group can change between years and may be a group of terminal (meat) sires if desired.

There are two options for measuring reproductive performance:

• The most accurate is for the ewes to lamb in their individual team groups. Two weeks prior to lambing, draft the ewes into their teams and run them in individual team paddocks until lambs are born and tagged. Lambs can be tagged either at birth or at marking, provided groups are kept separate. A similar tag numbering system should be used for the lambs as for their mothers (e.g. if mothers are tags 1–50, their lambs should be tags 1–50).
• A less accurate but more practical method is to use a mothering technique such as udder painting. The marked udder method or MUM (Davis et al 1981 Proc. NZ Soc. Anim. Prod. 41: 229-232) or creep systems (Wilkins and Cox 1980 Aust. Soc. Anim. Prod. 13: 497) can be used to identify lambs to ewe teams.

For the lambs, there are two options:

• Sell the lambs (or the wether portion) at a specified age or when they are finished. Weigh the lambs at marking and retain all records as the more records collected the better.
• Keep the lambs for wool production but record liveweight (growth rate). Carcass traits (back fat and eye muscle diameter) can also be determined from ultrasonic scanning if meat production is important. Record fleece production and quality parameters.

Liveweight

The more weights collected the better the information on the trial. A minimum would include a weight at mating, weaning weight and post shearing. It is recommended that more weights are collected during the year to get a better picture of differences in weight changes between teams.

Other information

Sheep should be scored for wrinkles, face cover and hocks and a range of different wool and body conformational traits. A standard visual sheep score classing system is available on the Sheep Genetics website. These scores may provide additional indirect information on the visual appearance of the different teams.

A sample protocol for conducting a linked ewe productivity trial is available in the side menu.