Grow ruminants (Protein and Fat)

A critical requirement for integrating a ruminant growth model into the larger CLEM framework was that it be both simple and sufficiently precise to predict livestock production outcomes under local field conditions. While many models exist for predicting ruminant live-weight gain, most require information on forage passage rates through the rumen or were developed for European cattle breeds. The former data is not readily available for many of the feedstuffs commonly used by smallholders and the latter models could not be confidently applied to many tropical breeds which are small in comparison to European breeds. For example, Bali cattle are well adapted to heat, can work up to 5 hours per day without apparent physical distress and survive well on poor forages. Moreover, Bali cattle have higher fertility rates than many other cattle breeds and buffalo when raised under similar conditions, but have poorer milk production and suffer higher calf mortality rates. Nevertheless, the key determinant of animal growth, reproduction and mortality rates is animal nutrition. Forage quality, measured by digestibility and protein content, commonly limits production, but smallholders have an array of different feed sources of varying quality available at intermittent intervals; e.g. native and introduced grasses and legumes, field crop residues, plantation residues (leaf, stem, fruit), tree leaves etc.

The ruminant model combines published data and field data relating to animal live-weight, live-weight gain, milk production, breeding details, as well as the quality, composition and quantity of the various sources of feed. The model is largely based on published energy functions with coefficients adjusted for various breeds.

This animal production model uses published allometric equations that relate various measures and rates to the size of the individual relative to its normalised weight for age, the standard reference weight (weight of adult female breeder in average condition), and relative condition (live weight as a proportion of normalised weight). While it is acknowledged that this relies heavily on the published relationships that may not represent improved breeding or all breeds, the approach has been improved by tracking protein and fat in the animals to allow other metrics to be used in management decisions and provide a better representation of the herd.

Intake is determined from the age (normalised weight) and current or previous highest weight of the animal. This growth rate is adjusted for the effects of available forage (for grazing), forage quality, whether the animal is lactating, high relative condition, and the increasing intake of juveniles.

For more information and equations see the Details section below.

The change in crude protein and fat as the result of the protein and energy gained from intake are summarised in the following diagram. This conceptual diagram is proposed to describe the various pathways for energy and crude protein to be used in a time-step. The diagram does not represent any single individual on a given day as it needs to describe pathways for pregnancy, lactation, and wool, as well as times where crude protein or energy available for gain is either in surplus or deficit. The size of flows are also not specific but designed to show broad magnitude of each resource use.

This section steps through the process from feeding to a change in weight for an individual ruminant in a given time-step with the relevant section identified in the diagram.

1. Feed types

The various feed types available to the animal are stored in the Animal food store or Graze food store. Each feed type follows the Animal Feed (Interface) to ensure the required quality parameters are provided. These types determine the energy and crude protein content of the feed.

2. Feed activities

The feed activities provided will determine the amount of each feed provided based on the feeding style specified. This can consider the current state of the individual to provide the potential intake, or the amount needed to satisfy the individual. Feeding can also ignore these limits and provide a specified amount when comparing simulated output with field-based feeding trials.

3. Potential intake

The maximum potential intake is a function of the normalised weight for age of the individual and will generally restrict intake to this level.

4. Intake modifiers

A number of intake modifiers are applied to the maximum potential intake to determine the final amount consumed. Lactating breeders will have intake increased to account for the lactation demands, while individuals will have their intake reduced as relative condition increases thus reducing demand. Intake can also be reduced as a function of the feed quality when multiple solid feed types are present in the diet with a proportion of very high quality intake not available. Finally juveniles (sucklings) will increase the amount of solid feed consumed as a function of age.

Once the feed is supplied and the amount of intake that can be consumed determined, the mix of feed determines the Digestible Protein Leaving the Stomach (DPLS) and Metabolisable Energy from intake which is available for various uses including growth. These are removed in the following order.

a. Maintenance

Energy required for maintenance is the combination of basal metabolism, heat production form the viscera, and any energy required for movement and grazing. This energy use is the highest priority for sustaining the individual.

Crude protein for dermal requirements is considered in maintenance as well as the crude protein lost through endogenous urinary protein and faecal protein.

b. Pregnancy

Any energy and protein required for the development of the conceptus and fetus is next supplied. The protein provided is added to the conceptus and fetus store (13).

c. Lactation

Any energy and protein required for lactation is next accounted for. See section 5. for more details.

d. Fleece

The energy and protein demands of fleece production are next removed if the ruminant produced a fleece. The protein is deposited in the clean fleece store (12).

5. Lactation reduction

For lactating breeders, a shortfall of available crude protein after maintenance will reduce lactation proportionally and return the energy saved for other purposes.

6. Protein deficit

A shortfall of protein after the animals requirements (4 a-d) needs to be covered by body protein stores and will be removed from the current protein pool.

7. Protein available for gain while energy is limiting

Currently this protein is lost as urinary nitrogen.

8. Energy deficit

A shortfall of energy after the animals requirements (4 a-d) needs to be covered by body fat stores and will be removed from the current fat pool.

9.-11. Energy and protein available for gain

When both energy and protein are available after all other needs are accounted for the protein is provided as body protein with a given energy requirement for this gain. If energy is limiting, some protein can be converted to energy to provide for the remaining as gain (see section 7.). Energy remaining after all protein has been accounted for is available to be converted to fat reserves.

 

A Ruminant herd with at least one Ruminant type. The ruminant herd must have an initial population defined using Ruminant initial cohorts

A Ruminant parameters grow PF (protein & fat) within the Ruminant Parameters holder of the Ruminant type provides all settings for this activity.

Any ruminant methane activity will produce methane emissions that will be provided to a Greenhouse gas type in the Greenhouse gases store either specified above or by assuming a store named Methane if provided.

See Ruminant enteric methane (Charmley)

To include mortality one or more of the Ruminant death activities need to be included in the simulation tree.