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RESEARCH
Lincoln University PhD student Cameron Marshall has been researching how cow diet affects the environment for his thesis.
A different perspective By Samantha Tennent
A Lincoln University PhD student has found proof that dairy cows could be part of the solution when it comes to mitigating the environmental impact of farming.
D
airy cows are typically seen as the problem when it comes to environmental impact, but a PhD student at Lincoln University has uncovered how the cow can be used as a solution. As part of his doctoral thesis, Cameron Marshall has identified two promising tools that dairy farmers can use to reduce nitrogen (N) losses and relieve the negative impact on the environment. “Animals tend to be seen as a problem that needs changing and there’s often no consideration that perhaps the system is wrong for the animal,” Marshall, who was studying with the Lincoln University Pastoral Livestock Production Lab, says. “We try to change the system and strategies to try to fix the animal but now we can look at the animal as a solution. “And if we use it in conjunction with other solutions, such as dietary and system management options, we could reduce the overall environmental impact from the dairy sector.”
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His work has explored the milk urea nitrogen breeding value (MUNBV) and how it relates to nitrate leaching and nitrous oxide emissions from cows. “We found with cows that are phenotypically lower for milk urea nitrogen, what they eat and how they eat is important to reducing their environmental impact,” he says. “And that helps us understand how to get the maximum benefit from cows predisposed to urinating lower concentrations of N, resulting in less leaching to waterways.” Milk urea (MU) is a byproduct of the breakdown of dietary protein. It is formed from the normal daily metabolism of N and protein and although most urea is excreted in the urine, some passes into the milk. Dairy cows with differing MUNBVs have been shown to have differences in milk composition, rumen function and urination behaviour. Marshall used MUNBV information for the herd on the Lincoln University Dairy
Farm, which was identified through herd testing from CRV. He noted when they were fed a diet of plantain rather than ryegrass, cows with low MUN phenotypes excreted significantly less N each time they urinated, which reduces the potential N leaching into waterways. He also found cows with differing MUNBV displayed different grazing and ruminating behaviour. They chew their pasture differently, which determines their rumen function and efficiency of N digestion and use in the rumen, and this leads to altering the N excretion patterns to the environment. In previous research, he had demonstrated that cows selected for low MUNBV had a 28% reduction in the urinary urea N loading rate per urine patch than cows with higher MUNBV. The ‘better cows’ also produced a higher milk protein percentage. “With the milk urea nitrogen breeding value we have identified a trait we can breed for that will reduce the
DAIRY FARMER
November 2021
26/10/21 12:58 PM
