Ruminant intake

This section considers the supply, management, and conversion to growth of energy (feed) provided to ruminants in the simulation. This is one of the fundamental aspects of managing ruminants on a farm. The details discussed are shown in the conceptional diagram below.

Supply of energy (food)

Energy is provided to individuals in the herd in the form of feed by Feed ruminants and/or Graze ruminants activities. Both the amount and quality of the feed will dictate the energy provided to the individual.

Type of feed

Previously, feed type was only defined as a result of the dry matter digestibility (DMD), nitrogen content, and where it came from (Animal food store versus Graze food store). The new approach is able to consider the different processes in digestion and energy provision of different types of feed. This means that each Animal food store type and Graze food store type will need to be assigned a feed type. This is especially important in separating concentrates from hay and silage which have very different quality. The feed types now available include, concentrate, hay/sillage, tropical pasture, temperate pasture, and milk.

Quality of feed

The quality of the feed is described by a range of parameters which are defined by the CLEM Feed Interface (IFeed) and include the type, metabolisable energy content, dry matter digestibility, fat content, nitrogen content, rumen degradable protein content, and acid detergent insoluble protein. All feed types must provide these details to determine how it is digested and the energy it provides. The list of these parameters is more comprehensive than previously required and will need to be determined for all feed types (see Animal food store type for the full list of properties).

CLEM continues to provide functionality to read pasture inputs and a sub-model to track the decay in quality (DMD and N%) and quantity (detachment) over time. This will continue under the new changes and the Graze food store type will alter nitrogen content and DMD of the pasture pools as they decay before being consumed. This allows the model to track the pasture sward with respect to proportion green and quality by considering each pasture pool available.

Passing food around the model

The Food Resource Packet represents a parcel of feed of given type that is used by the model. These packets conform to the IFeed interface to describe the quantity and also have an Amount property to provide the quantity of the packet.

Each packet defines the gross energy content which was previously assumed constant for all feed (RuminantActivityGrow.GrossEnergy).

Depending upon the feed type and area of the user interface, the user will be present with options of how to provide crude protein content as a value or calculated from nitrogen content.

Each food packet also has methods to determine degradable protein and metabolic energy content from the feed details specified.

This new approach means greater detail is needed for all feed types provided in the model. Most of the values can be obtained from feed quality sheets and a range of common feeds will be provided in the grazing example with CLEM.

Management of food

It is the responsibility of the various feeding activities to arrange the feeding of individuals. This occurs in the GetResourcesRequired event (see Events) which happens after PotentialIntake calculation event and before the AnimalWeightGain event. This ensures all tasks are performed in the correct order.

Each ruminant individual has an Intake property which is a class in the code. This class holds a range of properties that track diet and intake and can be accessed by the user (individualRuminant.Intake) when reporting. It also provides methods which are used to control intake in the simulation.

Potential and actual intake

Potential intake is the amount of food an individual can consume in a time-step and is based on the live weight at the time of intake, determined based on the normalised animal weight (coefficient) and the base weight (weight excluding fleece and conceptus) recorded for the individual. Potential intake is provided in the Intake section of the individual ruminant and is calculated by the Grow activities (see Grow ruminants and Grow ruminants (Protein and Fat) for details). In the latest growth activity, potential intake will be adjusted by the state of the individual in that lactation will add demand and allow more feed to be consumed, while individuals will consume less as their body condition (relative size) increases toward the maximum. This provides a maximum potential intake and an expected intake. Of course, it cannot be assumed that the individual will receive the required amount of feed, or that the quality will provide the necessary energy requirements. The result is the actual intake received. These potential and actual intakes, along with calculations of proportions achieved are tracked in two ExpectedActualContainers in the Intake section.

Solids daily

This ExpectedActualContainer allows the code to track the amount of solid intake expected by the individual as well as the amount received, and the final actual amount achieved. It can also provide feeding activities the amount still needed to satisfy the individual and report the proportion achieved as well as convert from daily amounts used in all calculations to the total amount across the time-step.

Milk daily

This is the same as the Solids daily container but represents the milk intake of sucklings.

Tracking intake

Each animal will have one or multiple Food Resource Stores depending on the type of feed provided. These stores divide the incoming feed by type and track the mixing of each store as feed items are added by Feeding or Grazing activities. They provide the Ruminant Intake component with the current crude protein, degradable crude protein, and digestibility undegradable protein based on feed types, as well as metabolizable energy and fermentable energy. These can be used to provide the DMD of all intake and therefore the portion eaten and resulting energy provided.

As each feed type is tracked as one entity, there is no way of altering the make-up of each feed type once fed.

Modifying intake

The latest Grow ruminants (Protein and Fat) also provides the functionality to reduce intake available as a function of the quality of the total intake. This is important when large amounts of low quality feed are provided and was required to handle cured, tropical pastures in the dry season. This was previously handled by a PastureQualityScalar in the Graze ruminants activity, but is now part of the animal intake. This also decides in what order the feed types are restricted ensuring the concentrates are provided to the individual.

Conversion of energy to growth

The final step involves the growth activities calculating the growth of individuals form the energy and protein details of the feed provided from Intake and updating the weight as well as fat and protein pools.