Rabbit Fertility:
The ability of animals to produce living young is obviously of the greatest importance. Although rabbits are often the subject of jokes about great fertility, the rabbit breeder may sometimes be faced with difficulties in getting his stock to produce regularly.
On occasions permanent sterility, from one of a number of causes may occur, but this is generally not of such importance to the rabbit breeder, for the animal may be eliminated without serious loss. Even more occasionally a strain may become infertile, when of course there is little which can be done except to introduce new blood,or recommence with another strain. It is generally temporary sterility with which the breeder must contend. Fertility and good bodily condition are closely related.One of the first bodily functions to suffer from poor management, and in particular, poor feeding, is the reproductive system. Excessive fatness and very poor condition both lead to sterility, however it should be remembered when the reasons for sterility are being sought, that sterility itself will often lead to excessive fatness.
Apart from nutrition, probably the most important factor (excluding disease) is under or over use:
- In the buck periods of rest may result in a temporary sterility, which however, usually ceases after the first services.
- Long rests,or more frequently very much delayed first litters in does may result in difficulty of does becoming pregnant.
- It often occurs that a doe being shown for a year or possibly two, is then unsuccessfully mated. The reason is that the ovaries do not function normally and the solution in both cases is to ensure that the animals are bred at the proper times.
- A doe will be extremely fertile immediately after kindling and likewise;
- A doe will be of above average fertility immediately following the termination of pseudo-pregnancy, and she will kindle more easily immediately after weaning. A difficult doe should therefore be bred at one of these times.
As to the causes of other types of sterility, there are abnormalities of the reproductive system, but these are rare. In-breeding may cause one of two types of sterility. In one type sterility is permanent, and the majority of the animals produced are completely infertile. In the other type, some early breeding is possible, but then a permanent sterility occurs. An in-breeding degeneracy to sterility should therefore be closely watched.
A buck whose testicles have failed to descend into the scrotal sacs is known as a cryptorchicl or rig, and is invariably sterile. In some cases one testicle only descends and then the animal, a half rig, may or may not be sterile, although usually he is capable of producing sperm.
Temporary sterility may be produced in bucks by high temperature. In Britain temperatures are rarely high enough for this to occur, but it is a fairly common cause of temporary sterility in other countries with a hot climate.There are infrequent cases of sterility between two animals.That is a doe may never hold to a particular buck, but is fertile to other bucks. The buck itself is fertile to other does. A type of sterility in which the embryos do not survive until birth is inherited.
There is some evidence that sterility in a strain may be associated with some forms of vices such as cannibalism or desertion of young, and also that good maternal characteristics usually go together. Good mothers are generally speaking highly fertile.
It is probable that hormone treatment may result in the clearing up of some cases of sterility, but generally speaking this approach to the problem would be expensive, and the better way to tackle the matter is to breed for good fertility in the same way as for other desirable characteristics. Apart from the question of permanent or temporary sterility there is the problem of infertile matings. In some studs, where the standard of management is high, the number of matings per hundred litters may be as low as two, whilst in some studs the average may be about 300. On average throughout the year probably half the matings are infertile. Infertile matings are a great inconvenience to the rabbit breeder, no matter what his ultimate aim. In the case of the commercial breeder there is loss financially due to decreased output with the same overheads. For the fancier there maybe a missed chance of exhibiting at a particular show. For the laboratory there may be some disarrangement of experimental work.
The highest percentage of fertile matings occurs during the early summer. This is probably the result of improved nutrition, which gives an indication of the methods of maintaining good fertility. Good feeding, good management,and regular use are the most important.
