P.PSH.1016 - Nitrogen recycling as determinant for feed efficiency of Bos indicus cattle

Summary

Performance of cattle in northern Australia is dependent on the feed efficiency of cattle grazing low-protein diets, which in turn depends on the ability of the animal to conserve nitrogen via nitrogen recycling in the rumen. Despite this, bulls are frequently selected on high-protein diets assuming similar performance on low-protein diets.

This project aimed to establish if there was a correlation between feed efficiency on low-protein diets with nutrient abundant diets. It was found that there was not a correlation between the two, and that feed efficiency could be estimated from nitrogen ratios in tail hair, and that the trait had heritability of 43%.

Objectives

Performance of cattle in northern Australia is dependent on the feed efficiency of cattle grazing low-protein diets, which in turn depends on the ability of the animal to conserve nitrogen via nitrogen recycling in the rumen. Despite this, bulls are frequently selected on high-protein diets assuming similar performance on low-protein diets.

This project aimed to establish if there was a correlation between feed efficiency on low-protein diets with nutrient abundant diets. It was found that there was not a correlation between the two, and that feed efficiency could be estimated from nitrogen ratios in tail hair, and that the trait had heritability of 43%.

Key findings

The project found that there was no agreement in efficiency ranking when steers were consuming a low-protein compared to a high protein diet. More efficient steers used available nitrogen 41% more efficiency, resulting in a distinct N-isotropic ratio in tail hair that can be used to predict feed efficiency in low-protein diets. Additionally, this trait was demonstrated to have heritability of 43% in tropically adapted breeds.

Benefits to industry

The ability to classify cattle for nitrogen efficiency has the potential to drive productivity improvements in the north through the ability to select for cattle that are more feed efficient during the dry season.

MLA action

MLA continues to invest in research to increase production in Northern Australia, with projects focusing on reproductive efficiency and calf survival.

Future research

It was recommended that research continue in to the development and commercialisation of the tail hair test for nitrogen efficiency, and in quantifying the impact of nitrogen use efficiency on cow fertility and calf mortality.