Dear support, How do I...

We need to simulate a grazing system in southern Australia for a case study on genetic merit. How do we implement a herd where breeders are managed such that joining is undertaken in September and October with calves weaned and males castrated at 7 months of age. All males are sold as well as any females over 8 years of age. Females are also preg-tested in December and sold if dry. Female breeders are only replaced from offspring with excess sold with the males.

Set up herd management

The task of managing a herd is complicated as it relies on a suite of tasks all timed around the dynamic reproduction cycle of the herd. This How To section will cover some of the components you will require in your simulation and the range of considerations needed to setup the simulation. The requirement that the model can provide all the management needs of each user necessitates the use of either generic tasks capable of informing the range of decisions, or a number of properties to set the scope of functionality needed. Managing herds requires a good understanding of CLEM and the various assumptions and implications of the components used. While the individual ruminant activity components are self explanatory and some encapsulate most of the tasks you need (e.g. Manage ruminants) , the ability to use component order in the simulation tree to define functionality means you need to understand the implications of various decisions and when particular tasks are performed with the model events.

The following sections will guide you through some of the components and related decisions needed manage your herd. We will assume a herd of a single breed with Managing ruminants providing further details.

The example farm to simulate

In this walk through we will simulate a cattle breeder herd (Bos indicus parameters from the grazing example) with bulls brought in for mating over a two month window in September and October. Individuals are weaned with all male offspring castrated and sold and young females either assigned as replacement breeders or sold. Females are sold when 8 years old and pregnancy tested each December and sold if not pregnant.

It is easy to overlook the implications of when the simulation starts, with the decision of what month to start potentially simplifying the simulation setup. Your farm simulation is a snap-shot realisation of a virtual farm trying to represent a real world situation with many states reliant on the period of time leading up to the start of your simulation. Some simulation models use a spin-up period to allow temporal processes to get to some equilibrium before the period of interest starts. While this spin-up period can be useful, you can never be certain that the state at the start of the run is correct and other measures may have moved away from what you require at the start. One of the factors important here is rainfall leading to pasture production that overtime changes the health and composition of the herd. Even the condition (initial weight) of individuals at the start of the simulation is hard to predict. Whether individuals have just encountered a drought or period of good growth will impact their performance in the proceeding months. While the model will let you set the initial weight and even have infer pregnancy and conception timing of breeders, the month to start your simulation is important.

If your system uses controlled mating in a given month (or range of months) starting the simulation in the month prior to breeding means you do not have to consider the conception of breeders at the start of the simulation. This also means you do not need to have suckling calves in your initial herd cohorts.

The start month of the simulation will be set to August. We therefore do not need suckling individuals in the herd at start up and all females of breeding age will be ready to mate in the following month (assuming their initial weight is set at a healthy size).

The Breed ruminants activity is the best component to start with as the timing and style of breeding will determine much of the herd management.

Uncontrolled mating needs no setup or timing defined. The breeding cycle will be strongly influenced by the make-up of the initial herd with suckling juveniles determining the last month of conception and births with other conceptions predicted by the model if required. This breeding will continue while males and females of breeding condition are located in the same paddock (or yards). Uncontrolled mating will also result in the spread of births over time. This may start to sync with pasture availability and quality over time as this influences health and the probability of conception.

Adding the Controlled mating component below your Breeding activity will dictate the months of conception and therefore births, weaning and timing of individuals reaching age of sale.

This component requires a Month range timer or Interval timer to set when controlled mating occurs.

There are implications of allowing controlled mating to occur over multiple months. As expected this will result in a spread of births, but also affects the calculation of conception. This does not relate to the conception based on body condition, but the other condition calculations use an expected annual conception rate. This needs to be adjusted for the multiple months so that the expected overall conception rate is realised.

A few options are available:

1. Use controlled mating with a timer for September and October.

2. Use uncontrolled mating but manage a herd of bulls in a separate paddock and move them into the breeder paddock each September and move them back to the other paddock in October.

3. Use uncontrolled mating and purchase bulls (using Managing a trade herd) in September and sell them in October. Pricing may be included in the transaction and any additional attributes can be supplied with the purchased individuals.

We will use the easiest first option.

Births will automatically occur (handled by the Breed ruminants activity) after the specified gestation period.

Births will occur 9 months after breeding; in June and July

Weaning is either managed by Wean ruminants activities or allowed to happen naturally at the specified time after birth (default is gestation length).

Weaning needs to be performed before our upcoming herd management so that the weaners are ready to be castrated and sold if male, or marked as replacement breeders or sold when in excess when female.

The Manage ruminants activity handles much of the management of the herd size and has numerous properties to set. It also requires a timer to define when it happens and this activity assumes it runs once per year otherwise a range of tasks will be repeated unnecessarily.

The Manage ruminants activity is used to handle the purchase and sale of breeders to maintain the breeder herd. It also manages castration and sale of young males and selling of young females surplus to replacing the breeder herd. The following properties are those important for this simulation:

Maximum number of breeders kept: This needs to be set based on the carrying capacity of the land and pasture. You must also consider the additional calves, weaners and any grow out males above this number.

Minimum number of breeders kept: Set to zero. This will ensure breeders are not purchased.

Mark old breeding females for sale: True (checked box)

Maximum female breeder age in months: 8 x 12 = 48

Maximum number of male breeders kept: 0. Males will be brought in for joining

Mark those reaching age/weight for sale every time step: False (not checked) We only want to perform sales when this main activity occurs .

Perform grow out of young males True (checked box). We want to separate this group for sale

Castrate grow out males: True (checked box). This will influence subsequent growth but we will be selling them immediately anyway

Male selling age: 7 months. This will ensure any weaned males are sold as weaning will have occurred before this task even in the same month (due to events)

Perform grow out of young females True (checked box). We want to separate this group for sale if not needed as replacement breeders

Female selling age: 7 months. This will ensure any weaned females are sold as weaning will have occurred before this task even in the same month (due to events). This activity will mark any weaned individuals as replacement breeders as required.

GrazefoodStoreToPlace xxxx in: These should all be set to the main pasture (paddock) in the model.

Adjust breeding females/sires at start up: False (unchecked) . In this simulation we will start with the specified initial herd.

No additional sub components are required.

The Mark ruminants for sale activity is used to identify and sell all dry breeders with an Interval timer set for the month to perform and a Ruminant group defining the dry breeders.

We will mark for sale all females of breeding age that are not pregnant in December (2-3 months after conception). We can apply a Pay herd fee component below the Mark for sale activity if we need to account for the cost of each pregnancy test. To select the dry breeders we add a Ruminant group with the following Filter by property components below the Mark for sale activity. 1) IsPregnant equals false and 2) IsBreeder equals true. As IsPregnant is a property of the Female ruminant, this filter group will only consider females in the herd and the IsBreeder property will ensure we don't sell young females identified as replacement breeders. Depending upon timing we also wish to exclude heifers (females up to first lactation) to ensure we don't sell young females, weaned, but may have missed mating in first year of breeding 3) IsHeifer equals false.

A Buy and sell ruminants activity is supplied to arrange the purchases and sales. It does not include a timer so it will operate in any month where purchases or sales are requested

We add a single Buy and sell ruminants activity to manage sale (no purchases in this simulation) of any individuals identified in any month. We can also add Apply trucking component to manage trucking load rules and track costs and emissions. Any number of Pay herd fee can also be added under the Trucking to account for commissions and any additional charges. This DOES NOT have a timer to ensure it is ready to sell in any month as the mark for sale tag does not carry over between time-steps.

Care needs to be taken selling animals in any month. In this simulation, only the Manage ruminants activity has the ability to take animals from the sale herd if still needed for herd replacement. This is especially true if individuals are sold as weaners or calves before they are considered for herd replacement in the Manage activity.

Other components needed in this simulation