Last update: November 22, 2010 01:57:53 PM E-mail Print

 

BREEDING PLANS FOR AFRINO SHEEP

 

Dr. 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 optimisation 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. 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 weight

9-month body weight

Clean fleece weight

Fibre 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 body weight (kg)

Fleece weight (kg)

Fibre diameter (μm)

Total weight of lamb weaned (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 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.

 

EWE SELECTION

Not all of the information required for the accurate identification of superior ewes is available at an early age. Adequate information on the productive performance (growth and wool traits) are available and accurate selection based on these traits is therefore possible. These traits, however, contribute much less to total lifetime productivity than the ewe's reproductive performance. At this stage little information on the young ewe's reproductive ability is known. The aim must therefore be to predict from the available information at selection age which ewes will be the highest producers, in order to increase gains in the current flock, as well as in future generations.

Results obtained from analysing the Carnarvon Afrino data indicate that selection for weaning weight (WW) or 9-month body weight (W9) will lead to a correlated genetic increase in total weight of lamb weaned (TWW). However, the low phenotypic correlations estimated between TWW and WW (0.153) and between TWW and W9 (0.242) would not guarantee that the highest producers be selected for the current flock.

At selection age, total weight of lamb weaned by the young ewe’s dam is the best predictor of lifetime reproduction of the young ewe. After the first parity, total weight of lamb weaned by the young ewe herself, also gives the best indication of her lifetime reproduction in the current flock. The high genetic and especially phenotypic correlations estimated between total weight of lamb weaned after the first parity (TWW1) and future performance indicate that selection based on TWW1 will ensure that the highest producers will be selected and therefore that gains in the current flock would be increased. It is therefore recommended that ewe selection should take place in two phases.

In the first phase, ewes could be assessed subjectively for breed standards and conformation or wool faults. Preliminary selection on the basis of WW or W9 could then be done. If preferred, one of the selection indices recommended for Afrino ram selection could be used. Each breeder or commercial producer should decide which selection strategy is most suitable for his specific circumstances and requirements. As the production traits contribute much less to total productivity than the ewe's lifetime reproductive performance, more than the required number of young replacement ewes should be selected during the first phase. These ewes should then be mated and final selection (second phase) could be done after their first parity.

With the second phase of ewe selection, selection should be based solely on reproduction performance. Selection intensity at this phase is dependent upon several factors. The most important of these are the prevailing environmental conditions especially during mating, but also pregnancy and lactation, as well as the age at first mating. In extremely poor years it would be advisable to leave final selection of young ewes till after their second parity.

 

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. For the successful implementation of the discussed breeding plans, Afrino breeders should keep the following records :

For the purpose of the accumulation of a data basis for a between flock BLUP analysis, it is recommended that full parent-offspring identification, as well as records of both ewes and rams for body weight, fleece weight and fibre diameter be kept. The National Small Stock Improvement Scheme has been developed to accommodate all information mentioned above.