As temperatures rise globally, heat stress is becoming more common in New Zealand's dairy herd.
Kiwi scientists are one step closer to enabling farmers to breed more heat-tolerant cows after a trial found dairy cows with the ‘slick' gene are less affected by heat stress compared with their non-slick counterparts.
Back in 2014, herd improvement and agritech co-op LIC discovered the slick gene, which produces a short-hair coat and boosts heat tolerance and realised that an opposite gene might exist, leading to the eventual discovery of the slick gene.
LIC chief scientist Richard Spelman says the gene could be a hugely valuable tool for improving the wellbeing of Kiwi cows.
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"Heat stress has significant welfare implications for animals. For dairy cows it can also impact feed intake, milk production, fertility and calf birthweight.
"The aim of the breeding programme is to provide farmers the opportunity to have high genetic merit dairy cows with improved heat tolerance."
As the slick gene was originally found in a Caribbean-based beef breed named Senepol, Spelman says LIC has been working on a breeding programme to incorporate it into elite New Zealand dairy animals.
LIC scientist Esther Donkersloot led the trial to see the impact of the slick gene in dairy cows. She monitored 18 dairy cows, nine with the slick gene and nine without, at LIC's dairy farm on the outskirts of Hamilto.
The trial found cows with the slick gene had lower rumen temperatures (0.5-1.0°C) compared with their non-slick counterparts when the Temperature Humidity Index (THI) exceeds 73 (around an ambient temperature of 26C and a humidity of 60per cent). THI is a commonly used metric used for heat stress and combine temperature and humidity.
"In cattle the rumen generates a lot of heat when processing food and adds to their internal heat load. Although a one-degree temperature decrease doesn't sound significant, it goes a long way to helping cows feel cooler overall."
Donkersloot says the value of the slick gene to Kiwi dairy farmers would only increase.
"Temperatures in parts of New Zealand already reach uncomfortable peaks for cows in summer and they're going to increase if we keep up with current global warming."
Modelling by NIWA has shown that, by 2040, Waikato can expect to have around 38 days a year which top 25C, compared with 24 now.
"Farmers want their cows to be healthy and happy - and being more comfortable in the heat is an important part of that," she says.
"Introducing the slick gene into New Zealand's dairy herd could allow for a significant improvement in dairy cow performance in hotter temperatures in the long term."
Spelman says the trial findings are a step in the right direction but increasing the slick animals' genetic merit and milk production will take time; the trial showed slick heifers produced around 18 per cent less mi than high genetic merit dairy heifers without the slick variation.
"Genetics is a long-term game. Before we offer heat tolerant genetics to farmers we want to make sure cows that have the slick coat also have high genetic merit and milk production expected of New Zealand dairy cows. If the breeding programme continues to progress as expected, Kiwi farmers will be able to breed heat tolerant cows by 2029."
