- Why Performance Testing?
|Last update: March 29, 2012 10:49:41 AM|
Why Performance Testing?
It is compulsory for Afrino breeders to participate in the National Mutton Performance Testing Scheme.
Why is it compulsory?
The main aim in breeding Afrino’s is to market as many good slaughter lambs at the earliest age on natural pasturage as possible. The important selection traits are therefore reproduction and growth rate in a natural environment. This objective applies to the breeder as well as to the commercial farmer. Although the breeder sells his rams and therefore not gains his income from slaughter lambs, he should select for the traits which are important to the commercial farmer. A beautiful ram with an ideal head and other conformational traits, but one with a slow growth rate, could mean money for the stud breeder, but to the commercial farmer it has no significance. The progeny of the ram would be slaughtered before their beautiful conformation and heads could develop.
The value of growth rate or mass for age is twofold. Firstly, the lambs can reach the desired slaughter mass at an early age and secondly the young ewes can also reach the desired mating mass and thus reproduce at an earlier age. According to overseas and local literature, growth rate is highly hereditary (Lasley, 1972 and Van der Merwe, 1975) and can be improved through selection. Illustrating evidence of this is the progress which has been made in the barbeque chicken industry. A few years ago it took 14 weeks for the chicken to reach the desired slaughter mass whilst presently it takes about 8 weeks to reach the same mass.
Post-wean mass increase and mass at 12 – 18 months have a higher heredity than 100-days mass which is estimated by the Performance Testing Scheme. Although heredity of 100-days mass is low, it is reasonably highly correlated with l2-month mass. From research on the Carnarvon Experimental Farm involving autumn- and spring-born ram-lambs over two years, a correlation of 0,608 to 0,820 between 100-days mass and l2-months mass was found.
Only 13% of the ram lambs that were below average at weaning, weighed more than the average at 12 months. Corrected 100-days mass index can, therefore, serve as a preliminary selection guide while final selection is based on post-weaning growth on 12 - 18 months mass. According to Van der Merwe (1975), 18-months mass of Dormers is genetically positively correlated with 100-days mass. This means that the progeny of rams that weighed the heaviest at 18 months, also weighed the heaviest at 100 days.
Carcase quality is also of economic importance. The only way in which it can be improved, is by progeny testing or by selecting for correlated characteristics in the live animal. The latter seems to be more acceptable. According to Hobenboken and Hillers (1974) the genetic correlation of all growth characteristics (pre-weaning mass gain and post-weaning mass gain) are highly positively correlated with the carcase mass per age and mass of desirable cuts. These results are the summary of various experiments which have been carried out on the American experimental farm in- Idaho. It seems that selection for growth rate does not adversely affect the carcase quality although it is not clear whether it does improve it. More trials in these aspects should still be conducted.
Within a breed various types, such as the short legged, blocky type and rangy type can be found. Due to the Afrino’s countrywide distribution it is impossible for all to look alike. The type that adapts well to intensive conditions will appear differently from the type that is well adapted to an extensive environment. Various people have various views on the same matter. The one may prefer the bloch-Y type while another may give preference to, the rangy type. Usually the type preferred by the person with the strongest arguments is accepted as desirable. After a few years a more persuasive person appears on the scene and his type of animal would in turn be accepted. There is a continuous chopping and changing and the economically important characteristics are being ignored. When performance testing is applied, the breed itself will indicate which type performs best under certain specific conditions. The animal with the highest growth rate has to be the best adapted one. At the final grading of a sheep, its performance results are the determining factors and not someone's personal taste, which is sometimes very far from the mark.
Performance testing for the Afrino is compulsory because it ensures purposeful selection for traits of economic importance. It also serves to control the personal element so as to ensure that the Afrino remains a well-adapted breed and not merely becomes only a visually attractive breed. It is, justly, accepted that the sheep with the best performance testing results will be the best adapted one. Furthermore, growth rate is highly hereditary and carcase mass for age can be increased by performance testing without reducing carcase quality. Any person who is familiar with the breed's standards would discover that the performance of the animal is not the only characteristic which is to be kept in mind.
In this article no attention was paid to the important selection trait, namely fertility. Selection for multiple births or selection based on the breeding performance of the mother ought to produce positive results for this trait.
Hobenboken, W.D. & Hillers, J.K., 1974. Phenotypic and genetic correlations. In Genetic improvement of carcass merit in sheep Ed. by M.P. Botkin & D.A. Cramer. Agriculture Experimental Station. Bulletin 616. pp 50-55. New Mexico State University.
Lasley, J.F.; 1972 Genetics of Livestock improvement. Prentice-Hall, Inc. New Jersey.
Van der Merwe, C.A., 1975. Genetiese en nie-genetiese faktore wat die produksie en reproduksie-eienskappe van die Elsenburgse Dormer skaapkudde beïnvloed. PhD - Verhandeling Univ. Stellenbosch.
Afrino Manual 2