Sheep genetics
Which grade of ram to choose?
Ken Wilson, formerly of DPI
Revised by Tony Hamilton and Dr Roger Lewer, DPI's Agency for Food and Fibre Sciences
Key points
- Buy rams from a stud that has a clearly defined breeding objective and is using objective measurement and selection indexes.
- Grade of ram purchased does not affect rate of genetic gain. Rate of gain is determined by the stud's own selection program.
- The lower the grade of ram used, assuming that there are real genetic differences between grades, the greater the time for a commercial flock to any specific genetic level.
- Lag between stud and commercial flocks averages about two generations.
- Weigh up the savings of buying cheaper rams against the lower performance of their progeny compared to more expensive rams, graded on objective measurements.
Introduction
Many studs offer rams for sale on a quality-graded basis. That is to say that, each year's sale drop is divided into categories (first and second grade etc) by the stud's classer on the basis of visual assessment, objective measurement or a combination of both. Naturally enough, the higher the grade of ram, the higher the price tag. For the ram buyer, it is important that higher price equates with higher progeny performance.
How rams are graded - objective vs visual information
Rams should be graded according to the stud's breeding objective, which is a statement of the target for future flock performance. Most studs class their rams visually at about six months of age to remove obvious conformation and wool faults (eg undershot jaws and black wool). After the first adult shearing, a combination of objective and visual assessment is commonly used to further class the rams to remove any culls.
Studs that use objective measurement as a selection tool are in a better position to correctly separate rams into performance grades. A selection index that combines information on the various production criteria can reduce the risk of accidentally culling some of the superior animals.
Where subjective selection is used alone, the accuracy of the grading is dependent on the classers' ability, experience, personal likes and dislikes and poor accuracy of visual assessment as an indicator of objective performance. Irrespective of how competent a classer is, there are certain economically important wool traits that cannot be reliably assessed visually. Fibre diameter is a good example where classers can never accurately select superior sheep using visual assessment.
Genetic gain and lag
Assuming however, that the grading is accurate, the grade of ram that is purchased will not affect the rate of genetic gain in a commercial flock. Sheep breeders who have been with the same stud for some time will have flocks that, on average, make genetic gain at the same rate as that stud.
However, the lower the grade of ram that is purchased, the greater the 'lag' period in reaching a specified genetic level. On average, this lag is about two generations between stud and commercial breeders. Diagram 1 illustrates this point.
Diagram 1. The relationship between a stud and its clients. The situation is shown for commercial breeding clients consistently purchasing average or above average rams.
The horizontal dotted line represents the lag time between stud and client flocks while the vertical dotted line represents the genetic lag between stud and client flocks. The diagonal lines show the rate of genetic gain of the stud, as well as that of commercial flocks using either above average or average grade rams from that stud.
Rate of genetic gain is the same in all three instances, but the time needed for a commercial flock to reach a specific genetic level is greater, the lower the grade of ram.
How much to pay for a ram?
There is of course, also, the economics of the question about which grade of rams to buy. Many people buy lower grade rams because they can't see the value in paying an extra $50 to $100 per ram. Where annual ram purchases are in the order of 20 or more, this can represent a substantial cost saving and is therefore a legitimate option.
But the effect that lower grade rams have on genetic lag should not be under-estimated as this can represent income foregone. The buyer needs to weigh up the savings against the lower performance of progeny of cheaper rams. It may still be good business to buy lower performing rams if the price difference is sufficiently large. On the other hand, where rams are not classed objectively, there may be little difference in progeny performance between expensive and cheaper rams. There is then little point in buying expensive rams when the cheaper grade is likely to be genetically equivalent.
Acknowledgment
The Lamb Boost Project funded by Australian Wool Innovation produced these notes.
Further information
For further information contact the DPI Business Information Centre on 13 25 23 (Queensland residents) or (07) 3404 6999 (non-Queensland residents) between 8 am and 6 pm weekdays, or e-mail callweb@dpi.qld.gov.au.
This DPI Note is also published on the DPI's PrimeNotes CD-ROM.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
File No: SW0077 . Date created: January 2002 . Reviewed: September 2003
