Breeding more efficient cows results in animals capable of producing more milk for their relative liveweight, so more nitrogen is used for this with less going out as waste in urine.
“Genetic gain in itself has environmental benefits almost by default, even when not specifically targeting that as an outcome,” he said.
He believes daughter-based or genomic approaches to readily identify low-nitrogen cows in the near future are heavily dependent on readily available phenotypic measures.
“At a simple level, herd testing provides great and vast phenotypic measures for milk production traits to get at the heart of genetic components,” he said.
“For the genetics of nitrogen use efficiency, measuring and using milk urea nitrogen information as the phenotypic measure might be a good approach to explore”.
The best example of work studying the effect of breeding on nitrogen efficiency was a recent DairyNZ trial indicating high genetic merit or high Breeding Worth cows had significantly higher milksolids yield with significantly more nitrogen taken up in milk and a reduction in urinary nitrogen losses.
So a farmer would need fewer high genetic merit cows to achieve the same level of production with fewer cows meaning fewer urine patches and less nitrogen returned to the soil.
