Increased dairy cow productivity in recent years has been mainly driven by higher concentrate use, but with that has come various challenges, including around the amount of phosphorus (P) and nitrogen (N) lost to the environment, an AFBI scientist has suggested.

Addressing a webinar on Tuesday jointly organised by AFBI, AgriSearch and the UFU, Dr Anna Lavery described P from agriculture getting into waterways as “a major problem” in NI, with increasing P levels measured since 2012.

“Historically, dairy cows have been overfed P due to the perception of a high requirement for milk production,” said Lavery.

She quoted AFBI research, which has shown that reducing dietary P by 20% has no impact on performance or health, and resulted in 45% less P being lost in manure.

“It’s about building confidence to reduce P levels or remove that safety margin that will help reduce that P excretion into the environment,” said Lavery.

She maintained that the current industry standard dairy concentrate is sitting around 5.5g to 6g of P per kg of dry matter, but this can be reduced to around 4.5g.

N losses

When it comes to N losses into the environment, excess N due to overfeeding of crude protein (CP) ends up mainly in urine and is lost to the environment as ammonia and nitrous oxide.

However, a four-year project at AFBI showed that reducing CP from 17% to 15% in early lactation (first 180 days) resulted in no difference in performance and improved N use efficiency.

Where dietary CP was cut from 17% to 14%, ammonia was reduced by 64%.

“As a target, if you work closely with your nutritionist, you can lower your dietary crude protein content to about 15%,” said Lavery.

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