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APPENDIX B: ASSUMPTIONS OF THE MODEL
Inherent within the model used to make future projections are a number of assumptions.
These assumptions are listed below.
Breeding herds give birth once annually; cows first calve at two or three years of age, and ewes or does first give birth at one or two years of age.
Breeding and weaning occur at distinct times during the year.
All enterprises last at least one month.
Weight gain occurs linearly.
Average gestation lengths are 285, 147 and 152 days for cattle, sheep and goats respectively.
Average birth weights are 36 kg, 5 kg and 5 kg for calves, lambs and kids respectively.
The energy requirements for offspring are included in the needs of their lactating dams until 3.5 months for calves and 12 weeks for lambs and kids.
Purchased animals have the same reproductive calendar, mortality rates, culling rates, daily energy requirements and reproductive statistics as similar animals already in the herd.
Supplemental feeding for stockers and feeders is distributed in proportion to time spent in the enterprise during each year.
Changes in animal populations occur at discrete times and in a prescribed order of occurrence.
Stockers and feeders are sold within 24 months of the inventory date of the year they are obtained, and those present on the inventory date are sold within twelve months.
Feeders are shorn no more than once between being obtained and being sold, and it occurs, if at all, in the year they are sold.
For animals leaving an enterprise, direct costs are incurred in proportion to time spent in the enterprise.
