Reproductive cycle of goats
The reproductive cycle of goats is similar to sheep but there are sufficient differences for goats to require different reproductive management. The recommendations for goats are:
Table 1. Reproductive characteristics of goats and sheep
The reasons for these recommendations is explained below.
Normally does start their cycle between February and March and it lasts to June or July. However, it is possible to induce cycling by introducing bucks. The response of the doe to the buck is sudden, ovulation occurs within two to ten days after the buck has been introduced.
If does which mate in the first two to three days do not fall pregnant, they will return for service five days later. These short oestrous cycles are very common in goats. Therefore, unlike ewes, most does will have been mated, and be pregnant, by the tenth day. This "synchronized" mating, and the fact that conception rates are normally very high, means the length of joining need only be five weeks.
Out of season breeding
Both Merinos and goats can be mated out of season. However, the success of these matings varies considerably, the pregnancy rates in sheep is generally much greater than for goats.
Some herds with a small number of goats have achieved reasonable levels of fertility but an experiment in New South Wales at Wollongbar (Dr B.J. Restall) produced low pregnancy rates (12 per cent) to a September mating. Dr Restall concludes that the fertility part of the reproductive system ceased to function for this September mating, even though most of the does (88 per cent) were mated.
In both goats and sheep, pregnancy is maintained by the hormone progesterone. Progesterone in the ewe is produced first by the corpus luteum (structure formed on the ovary when an egg is shed) and then the placenta in the last - third of pregnancy. However, in goats the sole source of progesterone throughout pregnancy is the corpus luteum. Stress which upsets the function of the corpus luteum will cause abortion. Such stresses include trucking, dog worry, yarding or unaccustomed animals and declining nutrition.
As the mating is so synchronized, most kids are born in the first two weeks of kidding.
Does 'plant' their young during the first few days of their life, leaving them in sheltered positions while they graze.
The birthweights of kids born at Avondale in 1986 are shown in Figure 3 and Figure 4. In comparison with lambs, average mortality rates of the kids are very low (see Table 2), nominally less than 10 per cent for either singles or twins.
Because kids are born at a time coinciding. with the spring flush of feed, the doe should be able to meet her lactational requirement easily. Supplementary feeding during pregnancy has not increased kid birthweights or survival.
A major problem at birth is predation by foxes. The doe, by planting its kid, leaves it "unprotected". Also the vixen is giving birth too and rearing cubs in spring, and presumably is attracted to the kidding paddocks for food by the foetal fluids, placenta and dead kids. Death rates in new-born kids at Avondale have increased two to three-fold in recent years due to foxes.
Table 2. Birthweights and mortality rates of kids and lambs
As with sheep, the age at which the buck and doe reach puberty (starts to produce sperm or 'cycle') depends on liveweight and birthday. Does born in spring will begin to cycle in autumn to early winter at five to seven months of age and a minimum of about 13 kg for Cashmere does and 16 kg for Angora does. Animals born in summer may not reach puberty until about 18 months of age.
Because it is common to leave many of the male kids entire, it is possible for young does to be mated by their brothers (or older does by their sons) if they are neither weaned nor the sexes separated until five to six months of age, that is, February or March.