W. THORPE, G.D.M. d'IETEREN, A. FERON, M. MUNDIA, D. ROSS, M. SHERIA, R. SPOONER and J.C.M. TRAIL
If the genetic improvement of livestock production through within-population selection is to be effective, then the criteria of selection must be heritable and easily and cheaply measurable. The estimation of genetic parameters, including heritabilities, requires information on parent-offspring relationships, which in many African livestock systems can only be reliably identified for dams and their calves. Information on sire-offspring relationships is far more difficult to obtain, limiting the opportunities for estimating heritabilities using paternal half-sib groups. Blood grouping is a technique offering the possibility of identifying the sires of many progeny which have been and are currently recorded at various sites collaborating in the ATLN. A pilot study was carried out to test the technique at a site where several bulls were possible alternative sires.
The study was carried out at the Mvuazi research station, Bas-Zaire Province, Zaire, which is one of the research stations of the Institut National pour l'Elevage et la Recherche Agronomiques. The station borders on Kolo Ranch, one of the ATLN sites, with which it shares the same ecological environment. It is stocked with N'Dama cattle derived from cattle imported from Guinea around 1930. The station also has some N'Dama x Red Sindhi. Three breeding herds are maintained with a total of six sires which are not permanently allocated to a specific herd. The station is therefore typical of many sites in the ATLN in which multi-sire herds are common and the dams, but not the sires, of progeny are known.
For the study, blood samples were taken from 389 animals for red-cell antigen typing against 53 blood group antigens. Table 1 presents the number of samples taken. After discounting the dams with no known progeny and the unusable samples, 325 animals remained: 6 bulls, 87 dams with progeny, the 87 progeny of these dams and 145 progeny without dam identification. Of these, 291 were N'Dama and 34 were crosses.
Table 1. Number of animals sampled in each category.
|
Category |
No. |
|
Bulls |
6 |
|
Progeny of these bulls |
232 |
|
Dams of these progeny |
87 |
|
Dams with no progeny identified |
49 |
|
Unidentified/samples lost |
15 |
|
Total sampled |
389 |
The blood typing was carried out in a laboratory in Harare, Zimbabwe in collaboration with staff of the AFRC Institute of Animal Physiology and Genetics Research, Edinburgh, United Kingdom.
The results of the sire identification based on blood typing are presented in Table 2. When the dam identity was known, 62% of the progeny could be accurately linked to a single sire. When the dam identity was not known, 51% of the progeny could be accurately linked to a single sire. If the samples had been examined by polyacryl gel electrophoresis for protein polymorphisms, then a 15-20% improvement in sire identification could have been expected, giving up to 74% sire identification for progeny of known dams and up to 61% for progeny with no dam identification.
Table 2. Results of sire identification based on blood typing.
|
Animals |
No. |
% | |
|
87 |
Progeny - dam pairs | ||
|
|
1 Bull possible (5 excluded) |
54 |
62 |
|
|
2 Bulls possible (4 excluded) |
31 |
36 |
|
|
More than 2 bulls possible |
2 |
2 |
|
145 |
Progeny - dam unavailable | ||
|
|
1 Bull possible |
74 |
51 |
|
|
2 Bulls possible |
51 |
34 |
|
|
More than 2 bulls possible |
18 |
12 |
|
|
None possible |
2 |
2 |
In a situation where any of six bulls could have been the sire of a large group of calves, red-cell antigen typing identified the actual sire of a high proportion, 61%, of those calves with a known dam. The proportion would have been even higher, nearly 75%, if a complementary protein polymorphism analysis had been carried out. These results clearly show that blood typing is a valuable technique for identifying parentages in field situations from which, as a result, performance records can be utilized for genetic parameter estimation.
The technique will prove particularly useful in the ATLN at those key sites with multi-sire herds where potential criteria of trypanotolerance are being evaluated. The identification of paternal half-sib groups will allow the estimation of genetic parameters of trypanotolerance criteria and of production characters, for example growth rate, using past records and those currently being collected.
For matings planned in 1988, a large improvement in the accuracy of sire identification could be achieved by blood typing all selected sires and grouping them for use in multi-sire herds in such a way as to give the maximum possible differentiation between the blood groups of their progeny. At a higher cost and with sufficient bulls of the right BoLA types, BoLA typing alone could identify the sire of a calf. Another technique that may be applicable in the future is DNA "fingerprinting", the typing of DNA polymorphisms, which is now accepted in disputes over human paternity. In the meantime more extensive, rapid and efficient analysis of red cell antigens than is currently possible in Africa can be organized by sending blood samples to the AFRC's Quarantine Station in Pirbright, United Kingdom, for testing by the staff of the AFRC's Institute of Animal Physiology and Genetics Research.
This pilot study of the blood grouping technique has clearly demonstrated its effectiveness for parentage identification in a situation typical of many African livestock systems and, representative of several sites in the ATLN. The success of this pilot study will allow the estimation of the genetic parameters of potential criteria of trypanotolerance and may open the way to the development of effective selection programmes for livestock.
