Posted 20 February 2009 - 11:44 PM
Hi PAS,
What is the "proof" of SCID that you speak of in Egypt? The SCID test was not publicly available until 1997. Do you have proof of pedigree mix-ups? I have heard the theory before, Hansi Melnyck speaks of it often, but even she admits she has not proof of this theory. Have you read this speculative article written by Peter Wright? I'm interested to see if it correlates with your theory. It was published in various magazines:
C.I.D. An Assessment of its Significance to the Arabian Horse and a Speculation about its Origin. by P. A Wright CBE MA (1980)
Introduction
COMBINED Immuno-Deficiency, C.I.D., become a very emotive subject in the Arabian Horse world. The cause of this is that its significance to the breeders of Arabian horses has not been assessed. Neither has any attempt been made to discover where it came from nor has any explanation been offered why, if the disease is inherited by transmission of a simple recessive gene, it is still with us. Ignorance always causes alarm and despondency. Val Males' excellent articles on the inheritance of C.I.D. have helped breeders to understand their risks from one generation to the next when they have or use identified carriers. But they do not (and were not intended to) answer the questions posed above.
I admit that I have been guided in my analysis by private knowledge of the identity of certain horses which are proven C.I.D. carriers. However, I will not reveal the identity of these horses or a number of others which, if my analysis is correct, are almost certainly carriers. My hope is that as a result of breeders reading this article, they will lose their fear of C.I.D. and make available any information to further the investigation of the subject and to enable people to breed Arabian horses to minimise the effect of the disease. I also hope that it will stop the witch hunting that has tended to develop because of the fear of C.I.D.
The Data Base for the Analysis
The last three volumes of the British Arab Stud Book are in the same format as Wetherby's Thoroughbred Stud Book Each volume is based on the registered mares whose breeding performance has been returned to the Arab Horse Society over a period of four years. All the mares are listed in alphabetical order and for each of the four years it is stated whether she was barren or slipped her foal, whether the foal was born dead or if it died before it was named at 41/2 months or the foal's sex and name if it survived to be named at 41/2 months. It also states the name of the stallion which covered her.
The stud book also has a list of all stallions used in the four years of the book and their live named produce together with their dams. It is therefore possible to list all stallions and mares that have had foals die between birth and 41/2 months. This has been done for the years l966-1977. This is the data base for the analysis which follows.
General Analysis
Table I immediately shows that infertility is very much more important than deaths, due to any cause, of foals up to 41/2 months of age. When one takes into account the last column, which is probably the percentage loss due - -C.I.D. based upon U.S. findings. infertility is nearly 8 times as important as C.I.D. Much of this infertility can be shown to be genetic.
The last column of Table I produce an apparent mystery. The original work of Studdert et al on the incidence of C.I.D. at Hawksbury Agriculture College, N.S.W., showed with a reason able degree of certainty that the C.I.D gene is a simple recessive. This has been strongly confirmed by the work of Dr Lance Perryman of Washington State University, U.S.A. Using a stud of 1 carrier stallion and 26 carrier mares. he has, over three years, produced 53 foals . Of these, 15 (28%) have died of C.I.D eight being fillies and seven colts. This appears to be conclusive that the C.I.D gene is a simple recessive without sex linkage. Why then does the probable incidence of C.I.D. in the U.K. over the last twelve years stay more or less constant? C.I.D. was probably intro duced by the imports of 100 years, ago. With random mating it should have virtually dissappeared. The only conclusion one can arrive at is that the mating has not been random but that there is a connection between the desirable genes of the Arabian horse and C.I.D. This is emphasised even more when one takes into account that Arabian breeding in Britain is really like one vast stud, as most breeders, even the leading ones, use a range of stallions, most of which are not their own.
If, however, we examine the performance of the most popular stallions defined by those stallions that sired 20 or more live foals at birth, the picture is entirely different.
Table III shows that 76 stallions or 12% of the total stallions used sired 55.5% of the live foals born. They also lost 55% of the foals that died.
Comparing Table IV with Table III, we can see the marked difference between the popular stallions and the rest. 74% of the popular stallions lost foals whereas only 16% of the rest did.
Is C.I.D. a simple recessive gene?
At first sight, Table I suggests that the C.I.D. gene cannot be a simple recessive and yet the researches into specific studs show it to be. If however, we consider how selection for breeding in the U.K. is actually carried out, it is possible to see a way out of the difficulty. If the pedigree which introduced C.I.D. to the U.K. 80- 100 years ago also produced character¬istics which resulted in breeders selecting for horses incorporating this line, it could result in the maintenance of C.I.D. Now in England, as in many other countries, mares have been and are in short supply (hence their price!). So rigid selection only really occurs on the male side. This does not, of course, occur in individual studs, particularly the top ones which select their mares with care, but overall most mares retained in the U.K. are bred from. It is possible to show that the ratio of non-carrier mares to carrier mares can remain constant from generation to generation if we allow the ratio of carrier stallions to be higher than the ratio for the mares and is suitably adjusted. This is not the place to discuss the mathematics of the situation, but if we assume that 27% of all the mares are carriers, we find that for % mare carriers to remain constant the stallion carrier % must be 36%. Furthermore, for the figures given in Tables III and IV, the number of foal deaths due to C.I.D. will be 144, which is 55% of all foal deaths, thus agreeing nicely with the U.S. estimates for % C.I.D. foal deaths. It also means that about 230 of the 644 stallions are carriers.
Only 147 have actually lost foals, but we note from Table IV that 568 stallions have only had an average of 5 3 foals per stallion. As it takes at least 40 matings per stallion to get a reasonable certainty of getting the correct number of foal deaths, it is not surprising that Table IV may be distorted. Table III is probably substantially an accurate picture of the C.I.D. situation.
Where did C.I.D. come from?
The discussion which follows must be regarded as speculative. The starting point is the analysis in the Thompson, Studdert et al paper, based on the Hawksbury data. They state that the evidence points to two imported horses, Sala and Razaz being carriers. This I believe to be a certainty. They point out that these horses have a common grand sire. He is readily identified as Rasim. Now Rasim was sired by a horse bought by Lady Anne Blunt from Ali Pasha Sherif called Feysul. All the stallions which I am certain are carriers have Feysul in their pedigree. Referring back to Table III I have traced the pedigrees of 74 of the 76 stallions. (The two I have not traced I have not been able to do so because I did not have the necessary information). In the two or more lost category, all but one have Feysul as a common ancestor; in the singletons, only three do not trace back to Feysul but in the no loser category 8 out of 20 do not trace back to Feysul.
I have also traced the pedigrees of the first categories of Table IV. Seventeen out of eighteen are descended from Feysul.
By now the reader must be saying to himself "Perhaps all stallions are descended from Feysul!" To test this, I took a sample of the 477 in the last category of Table IV. This was the first 71 stallions in Vol. II of the A.H.S. Stud Book which were in this category. 36 of these did not trace to Feysul. The others did.
Can we take the possible origin of C.I.D. any further? Zobeyni comes twice in Feysul's pedigree but is in my view unlikely to be the source. If he were, C.I.D. would be spread much more widely in the breed as he is in almost every British pedigree. The only other horse that is suspicious is Bint Nura II which was the dam of Daoud. Daoud's sire was Mesaoud. Although I have not got as good evidence of Daoud being a carrier as I believe I have of Feysul, I am almost convinced that the mare, Nasra, was a carrier. Her sire is Daoud. I also find that of the few horses which do not go back to Feysul but which I strongly suspect were or are carriers all go back to Daoud as do many of the descendants of Feysul.
Conclusions
1. C.I.D. is caused by a simple recessive gene. But the line which carries it has other very desirable genes which results in breeders using this line, particularly in the selection of stallions.
2. C.I.D. is not an important disease compared with infertility, much of which is genetic and results in at least 8 times the loss in foals as C.I.D.
3. The maintenance of C.I.D. in the Arabian horse population despite it being a simple recessive gene is probably due to the selection of a greater ratio of carrier/non-carrier stallions than mares because stallions are fewer in number and are selected more rigorously.
4. A holocaust of all C.I.D. carriers would virtually destroy the breed as we know it The foal loss due to it is probably only about 2.5% annually and we should learn to live with it.
5. A simple test for carriers would lead to its reduction because breeders would then have the choice of taking risks and also be able to identify the non-carriers in the resulting foals.
6. C.I.D. has probably been transmitted from a particular line bred by Ali Pasha Sherif from a desert mare, Nura Al Kabir, and introduced into the U.K. by Lady Anne Blunt via Feysul and Bint Nura II. This does not rule out other desert lines which may carry it but I have not yet found any others.
A Final Word
This article must be regarded as informed speculation. There is no proof that the foal losses discussed here are due to C.I.D. They however stand up to statistical tests concerning their links with various classes of horse and also particular horses. It would not be appropriate to include these tests in this article. I intend, however, to write a scientific paper giving the statistical evidence.
I would like to emphasise that because a horse is descended from Feysul or Daoud does not necessarily make him a carrier. At each generation step there is only a 50% chance of the son or daughter being a carrier. Furthermore, Feysul bred two stallions of major significance to the breed, Rasim which was a carrier and Ibn Yashmak which was almost certainly not a carrier. Similarly, Bint Nura II bred two stallions of equal
significance, Daoud and Mahruss II. It is very difficult to believe that Mahrus II was a carrier.
I have not included information on the mares. The labour involved in analyzing their pedigrees is enormous. However, inspection of a sample of the pedigree the mares that have lost foals confirms the data for the stallions.
Lastly, I would like to make general remarks about the 76 stallions, the "20 or more foal" list. A large number of them, probably 40-50% or higher, are either British National Champions or Supreme Champions, major shows. The second important point is that they are not all British bred. They include horses from Egypt, U. S A., Poland and Russia. Buying horses abroad is not a solution unless a detailed investigation is made.
I hope what I have written will chance. Arabian breeders' attitude to C. I. D. If they will, as the Males of Ralvon have already done, let it be known which air the identified carriers, there is considerable hope that what has been speculate: upon above can be established or not an,: then we have hope of reducing the incidence of C.I.D. by discerning breeding.
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Thank you Heidi.
