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"The Significance of an Achondroplasia-Like Condition Met With in Cattle"

Part VIII

by F.A.E. Crew

in Proceedings of the Royal Society of London, volume 95, 1923, pages 228-255.

Page 248 (Cont'd)

VIII - Suggestion as to Methods by which the Monstrous Calf might be Eradicated

According to the scheme that has been elaborated in this paper there are Dexters which, though of excellent characterisation from the point of view of the breeder, will not throw monstrous calves when mated with others of a similar genetic constitution. If the breeder altered his standards of excellence there would soon be no problem; there are true-breeding races of domesticated mammals which present certain characters very closely akin to many of those which, in combination, constitute the condition of achondroplasia - the dachshund, Natas cattle and Yorkshire pigs are examples perhaps - and in such races it would seem that the amplifying lethal mutations have not occurred as they seem to have done in the case of the Dexter and of the Breton cattle. It is biologically possible to “fix” a degree of achondroplasia as a racial character. But the Dexter breeders are seeking to attain the biologically impossible – a highest grade “achondroplast” which is viable. Hydramnios and

Page 249

dystocia render their efforts of no avail. They must be content to modify their standards somewhat; an SS + L₁ + L₂ individual cannot be produced, but an (S + L₁ + l₂) (S + L₁ + 1₂) or an (S + l₁ + L₂) (S + l₁ + L₂) can, and these are very excellent Dexters. The methods suggested are as follows:

First Step - To get a herd in which all the individuals carry the factor S in the duplex condition.

Theoretically, the quickest way to do this is to mate several Dexter bulls and as many Dexter females as possible to Kerries and to retain only those which yield none but Dexter-type offspring. It must be remembered that the “foundation stock” Dexter is always Dexter by Kerry bred and so must always be heterozygous for its bodily conformation characters. If this is impracticable then the next best thing to do is to obtain Dexters which have never thrown “off-type” calves. There are such. In this way SS males and females will be secured.

Second Step - To remove either the L₁ or the L₂ factor from the herd.

The males retained following the first step may have one of the following constitutions:

     A = (S L₁ 1₂) (S L₁ 1₂).
     B = (S l₁ L₂) (S  l₁  L₂).
     C = (S  l₁  1₂) (S L₁ 1₂).
     D = (S  l₁  1₂) (S l l₁  L₂).
     E = (S  l₁  1₂) (S  l₁ 1₂).

The females retained may be A, B, C, D or E.

Choose the best male and choose as young a one as possible. Mate him to as many females as possible. Discard all the females which, after repeated matings, produce a “bull-dog” calf. It is probable that either A or B will be the type chosen in the case of the sire. In the case of the females, types A and B are equally good Dexters, and C and D though not so good are by no means “off-types.”

A mated with A will give no “bull-dog” calves.
A mated with B will give all “bull-dog” calves.
A mated with C will give no “bull-dog” calves.
A mated with D will give 50 per cent “bull-dog” calves.
B mated with B will give no “bull-dog” calves.
B mated with C will give-50 per cent “bull-dog” calves.
B mated with D will give no “bull-dog” calves.
C mated with C will give no “bull-dog” calves.
C mated with D will give 50 per cent “bull-dog” calves.
D mated with D will give no “bull-dog” calves.

Page 250

If the type E is used at all then it will not throw a monstrous calf in any mating, but it is assumed that the breeder wishes to get as low-set and bulky animal as possible.

Keep to one sire and discard every female that produces a “bull-dog”: obtain a son of the sire out of a female that, after repeated matings with the sire, has not produced a monster and mate the son with the females which have not been discarded. Mate the sire to his daughters and discard all, and their mothers also, that produce a monstrous calf. In this way, if the sire is an A individual the B and the D females will ultimately be removed from the herd; if he is a B type animal then the A and the C type females will become removed. When this is accomplished, the monstrous calf will no longer appear.
 

On to Part IX