Last update: January 17, 2011 02:12:27 PM E-mail Print

 

BREEDING PLANS FOR AFRINO SHEEP

RAM SELECTION


Gretha Snyman

Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (E.C.), 5900

 


The Afrino is a white woolled breed developed for slaughter lamb and wool production under extensive conditions. In a dual purpose sheep breed such as the Afrino, the aim of the breeding programme should be to increase the efficiency of both slaughter lamb and wool production. Simultaneous selection for more than one trait therefore seems necessary to increase overall productivity in the flock.

As approximately 80% of the income from Afrino sheep is generated through mutton production, the primary selection objective should be to increase the lifetime weight of lamb produced per ewe. Fleece traits such as clean fleece weight and fibre diameter should also receive attention during selection. With regard to wool production, the quality of the fleece, in terms of particularly fibre diameter, could be considered more important than the amount of wool produced. This is especially true in an arid environment where quantity, but not quality, could pose a serious restriction.

The Afrino is the first South African sheep breed in which the separation of ram and ewe selection objectives was investigated. Ram selection is aimed at increasing the genetic merit of the next generation, contributing very little to the economic optimilization of the current flock. Ewe selection, however, has a dual purpose. In the first place it is aimed at increasing income from the current flock through own productivity and secondly, to contribute genetically to possible superior future generations.

In practice, most selection emphasis is normally placed on rams and little or no attention is given to ewe selection. As discussed by Snyman (1996), ram selection could concentrate on the economically important growth and wool traits, while ewe selection should be done mainly on reproductive performance.

Before any attempt at constructing breeding plans could be made, it is necessary to identify selection objectives for the breed or stud in question. The following multi-trait selection objective was set for Afrino sheep :

After the selection objectives have been defined, it is necessary to identify suitable selection criteria. In order to achieve the set objectives, the following traits were identified as possible selection criteria for Afrino sheep :

Results obtained from analyses of the Carnarvon Afrino data indicated that there are a high genetic correlation between body weight and total weight of lamb weaned. This implies that total weight of lamb weaned can be improved genetically through selection based on body weight. Reproduction can therefore be taken into consideration by the inclusion of body weight in a selection index for Afrino rams. The selection criteria were used in various combinations in order to obtain several possible selection indices which can be used in a selection programme for Afrino sheep.

SELECTION OF BREEDING SIRES

All the information needed for the selection of potential sires are available at an early age. Selection can therefore be based on a selection index incorporating the relevant objective traits. Traits such as breed standards, conformation and wool quality could be assessed subjectively and rams which meet these requirements could then be selected on the basis of one of the four selection indices presented in Table 1. The genetic response obtained per generation in each selection objective with each of the recommended selection indices are summarized in Table 2. For example, if Index 1 is applied, 9-month body weight should increase with 2.19 kg per generation, fleece weight should remain constant, fibre diameter should decrease by 0.42 micron and total weight of lamb weaned per ewe should increase by 5.68 kg per generation.

It should be mentioned that it is the prerogative of each registered Afrino breeder or commercial producer to decide how much emphasis he would like to place on reproduction, growth performance, fleece weight and fibre diameter, as long as he abides to the general breed standards set for the Afrino breed. It is therefore essential that commercial producers buy rams from breeders who have the same selection objectives than they have.

 

Table 1.  Selection indices for Afrino sheep

                    Weaning               9-month               Clean fleece              Fibre

                      weight               body weight               weight                 diameter

 

Index 1             +4                                                           + 1                          -3

Index 2                                          +3                               +2                          -2

Index 3            +1                                                                                           -1

Index 4                                         +1                                                              -1

 

 

Table 2.  Genetic response obtained per generation in the selection objectives with each of the recommended selection indices

                    9-month               Fleece                 Fibre            Total weight

                   body weight          weight              diameter      of lamb weaned

                        (kg)                    (kg)                  (µm)                  (kg)

 

Index 1            2.19                        0                     -0.42                   5.68

Index 2            2.68                        0                     -0.30                   7.42

Index 3            2.10                    -0.01                   -0.56                   5.70

Index 4            2.63                    -0.02                   -0.42                   7.62

 

It is expected from an Afrino sheep to be able to produce and reproduce under extensive conditions. As 80% of its income is generated through reproduction and growth (mutton production), and bearing in mind the negative genetic correlation estimated between fleece weight and total weight of lamb weaned, selection for an increase in fleece weight under extensive conditions, given present price structures, would probably not be advisable. However, due to this negative genetic correlation it is advised that fleece weight should at least be monitored should selection be aimed at only increasing total weight of lamb weaned and direct growth.

Taking all this information into account, the breeder should decide if he wants to include fleece weight in the selection index. If he wants to do so, Index 1 or Index 2 could be used. The difference between these two indices is that Index 1 places more emphasis on fibre diameter and less on reproduction and growth than Index 2, as is evident from Table 2.

Should the breeder choose to ignore fleece weight in his breeding plan, Index 3 or Index 4 are options. In this instance, Index 4 places more emphasis on reproduction and growth and less on fibre diameter than does Index 3. With both these indices a slight decline of 10 - 20 g clean wool per generation can be expected over the long run.

RECORD KEEPING

The feasibility of any breeding plan depends upon the number of records the breeder or producer has to keep. The aim with the recommended breeding plan is to achieve maximum gains with the minimum record keeping.

Afrino stud breeders who are members of the Breed Society should be compelled to keep the following records :

For the purpose of the accumulation of a data basis for a between flock BLUP analysis, it is recommended that records of both ewes and rams for fleece weight and fibre diameter should be kept.

 

[Breeding Plans for Afrino Sheep Selection for Reproduction]