Breed ruminants

There will usually be pregnant females in the herd at the start of the simulation especially if the controlled mating timing dictates that the start of the simulation would be after the last mating and before births were due. This switch will try to infer the pregnancy status of all breeding females including those that have supplied young individuals into the initial population (see details below).

This parameter will determine what action is taken if there are insufficient resources to perform this activity.

You can report an error and stop the simulation, skip this activity or use the resources available. See What to do when resources are limiting

The Controlled mating component provides all the functionality to manage controlled mating. This component also handles all labour and financial costs of performing the mating as uncontrolled mating is not considered to have any associated costs. You do not require breeding males in the herd to undertake controlled mating.

This activity will occur in every time-step unless timers are used to restrict this activity (see Using timers).

This activity will obey all Ruminant activity group in the simulation tree at and above it's location.

Only one instance of this component is permitted in each Activity.

For uncontrolled mating

Males and females of breeding condition must be in the same location for uncontrolled (natural) breeding to occur. If no Move ruminants activity has taken place the herd will be together in the default general yards and breeding will occur if possible. If the herd has been moved to a paddock you will need to ensure males and females, of breeding condition, are together. This allows for managed seasonal breeding such that a paddock containing all cows may have a number of bulls moved into the paddock for a period (e.g. September until November each year). The bulls will need to be removed or breeding will continue. Alternatively, you can use the Artificial Insemination (AI) setting to achieve this outcome.

At the start of the simulation (and after the herd has been created from the starting population, see Ruminant initial cohorts) the breeding status of all females is determined and suckling calves are assigned to available cows. The initial state of the female requires a number of parameters to be estimated such as number of births experienced during her life and weight at last conception.

Each suckling calf provided in the initial population is assigned to a cow and if insufficient cows are available a warning is provided. The unassigned calves will not have a mother and access to milk, so will have restricted growth from other feed if available. Mothers are not assigned to weaners. A cow is available for breeding if her age allows the minimum breeding age plus gestation period before the start of the simulation.

Inferring pregnancy status

After mothers have been assigned to sucklings at the start of the simulation all other females will be assigned a pregnancy status when the switch to infer pregnancy at start up is on. The model will step back from the start month, each month, for the gestation period minus one month. If controlled mating would have been performed in any of these months, conception is calculated for all females that were of breeding age (age >= minimum age at first breeding) in that month with normalised weight assumed. If uncontrolled (natural) mating is being used, female conception is calculated based on the monthly number that can be serviced by the males present, whether minimum breeding age has been attained and a 15% of breeding herd monthly limit designed to spread conceptions across months. The prenatal mortality is then assigned to determine if the fetus survived to the start of the simulation and ensure birth rates are considered.

Each month during the Animal Breeding event the births and conceptions for each sub-herd (based on location) are determined. This starts with obtaining the list of all breeders (male and female) for each location (paddock) in which the herd is located (note, general yards are the default location if no paddocks and herd moving are provided). For each location, the status of pregnant females is determined and if delivery is expected in the month the new born individuals are added to the population. A number of newborns will not have survived from conception to after birth and these individuals are not added. The process of prenatal mortality is performed monthly and at the time of birth to satisfy the PrenatalMortality value (whole of gestation and birth). This allows for a change in female diet and time before conception calculations if the fetus died mid-way through gestation.

If both males and females are present, calculations of conception will be made for all females that are able to conceive. This is limited if there are insufficient males to mate with the females in the month.

This activity handles the birth of twins based on a user specified parameter (TwinRate).

Dividing continuous processes into discrete time steps can cause issues with tracking states and estimating values. This section documents when different processes occur in the model and assumes the time step is one month, but the concept will work for smaller time intervals if provided in future.

Age at conception

This is the age at the start of the time-step where conception occurs.

Age at last birth

This is the age at the start of the month (time-step) where the birth occurs. This is determined when Age > Conception Age + Gestation interval. This means any offspring will be 0 at birth and age to one time-step interval at the end of the time-step. If the fetus dies before birth the time of death is set as the mothers AgeAtLastBirth, but the SuccessfulPregnancy flag is set to false, so lactation does not occur and the female can conceive after the minimum period between birth and conception.

A full description of the various methods of calculating conception are available at Ruminant conception.