P.PSH.0998 Final Report

Summary

Problem addressed: The Australian feeding standards were developed throughout the 1980s culminating in the publication 'Feeding Standards for Australian Livestock – Ruminants' in 1990 (SCA, 1990). The standards were based largely upon the UK system (ARC, 1980) but adapted and expanded upon to better reflect the livestock and conditions prevalent in Australia. The standards were significantly updated in 2007 with the publication 'Nutrient Requirements of Domesticated Ruminants' (CSIRO, 2007). In the intervening years the genetics of ruminant livestock have changed in response to selecting for higher production rates and the feedbase has also changed. In particular the prediction of empty body weight and protein and fat composition was considered to no longer reflect commercial conditions. There was also poor understanding of the relationship between live body weight and empty body weight. Thus, the conversion of energy in the diet to production of muscle, fat, empty body and, ultimately, live body weight was no longer fit for purpose in defining the energy requirements on modern ruminants.

Objectives

This project will revise the Australian Feeding Standards to:
• include prediction of body composition to inform efficiency metrics and predict market – related attributes of fatness, yield, and MSA score
• better predict nutrient requirements and responses to supplementation of cattle on seasonally and spatially heterogeneous low-quality diets
• account for genetic variation in traits including efficiency of feed utilisation
• further develop and refine a dynamic rumen model utilising new data on rumen function and rumen microbiology in particular on prediction of microbial protein supply and energy digestion.

Key findings

The current project has developed an improved model for estimation of body composition and hence energy requirements for maintenance, growth and reproduction, an improved model for estimation of voluntary feed intake and a technique for measuring the energy cost of activity under extensive grazing conditions. The current approach has greatly improved upon the understanding of energy requirements and advances our understanding beyond a notion of static efficiencies for maintenance and growth. Ongoing model development has expanded the concept to include reproductive ruminants and to account for the energy requirements of activity. This new model can be used with current measures of feed energy values and is capable of being expanded into a full replacement for Australian feeding standards for ruminants at all stages of production.

Benefits to industry

New models will be incorporated into existing programs, for example; GrazFeed, BeefSpecs, Drought and Supplementary Feed Calculator (DASFC) and CSIROs CLEM. Further work is required to link models with other decision support tools (DSTs) and explore adoption/user pathways.

MLA action

MLA to continue to provide support to updates, and further research.

Future research

A number of further models are required to be developed or finalised, including:
• High demand for model to be developed in cattle. We would like to get agreement between CSIRO and DPI and UC Davis (and MLA) to develop.
• Finalise incorporation of lactation and pregnancy into model and develop for cattle.
• Update and finalise incorporation of activity and energy required for grazing.
• Explicitly link rumen model and methane with animal model.

More data is required in a number of areas to improve the models, including:
• variation in mature size and composition by breed/sex
• examine variation in feed intake by genotype
• data from animals at/near maintenance to finalise values for kp and kf more
• better representation of effect of feed characteristics on km and on viscera (not just M/D, but fibre, type of feed or other feed components.