It’s cool to be a slick cow
Humans haven’t been the only ones feeling the heat this summer – as global temperatures rise, heat stress is becoming more common in dairy cattle.
But New Zealand scientists are moving closer to helping farmers breed more heat-tolerant cows, after a trial found dairy cows with the ‘‘slick’’ gene were less affected by heat stress than those without.
Discovered by herd improvement and agri-tech co-operative LIC in 2014, the slick gene produces a short coat and improves heat tolerance.
The gene was discovered after LIC scientists first identified a genetic variation that made cows very hairy. Realising the likelihood that an opposite gene might exist resulted in the eventual discovery of the slick gene.
LIC chief scientist Richard Spelman said the slick gene could be a valuable tool for improving the overall wellbeing of New Zealand dairy cows.
‘‘Heat stress has significant welfare implications for animals,’’ Spelman said. ‘‘For dairy cows it can also impact feed intake, milk production, fertility and calf birth weight.’’
As the gene was originally found in a Caribbean beef breed named senepol, LIC had been working on a breeding programme to incorporate it into elite New Zealand dairy animals, Spelman said.
‘‘The aim of the breeding programme is to provide New Zealand farmers the opportunity to have high genetic merit dairy cows with improved heat tolerance.
‘‘Over the past seven years we have been crossing senepol beef sires with New Zealand dairy cows to breed slick bulls that could potentially produce a more heat-tolerant dairy herd in the future.’’
Esther Donkersloot, an LIC scientist, led the trial, monitoring 18 dairy cows, nine with the slick gene and nine without, at LIC’s dairy farm on the outskirts of Hamilton.
The trial found cows with the slick gene had lower rumen temperatures (0.5-1.0 degree Celsius) compared to their nonslick counterparts when the Temperature
Humidity Index (THI) exceeds 73 (around an ambient temperature of 26C and a humidity of 60 per cent).
THI is a commonly used metric used for heat stress and combines temperature and humidity.
‘‘In cattle, the rumen generates a lot of heat when processing food and adds to their internal heat load,’’ Donkersloot said. ‘‘Although a one-degree temperature decrease doesn’t sound significant, it goes a long way to helping cows feel cooler overall.’’
Donkersloot said the value of the slick gene to dairy farmers would only increase.
‘‘Temperatures in parts of New Zealand already reach uncomfortable peaks for cows in the summer and they will increase if we keep up with current global warming.’’
Modelling by Niwa has shown that by 2040, Waikato could have around 38 days a year with temperatures above 25C, compared to the current 24 days.
‘‘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,’’ Donkersloot said.
Spelman said the trial findings were a step in the right direction but increasing the slick animals’ genetic merit and milk production would take time.
The trial showed slick heifers (which are 87.5 per cent dairy) produced around 18 per cent less milk 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,’’ he said.
‘‘If the breeding programme continues to progress as expected, Kiwi farmers will be able to breed heat-tolerant cows by 2029.’’
Spelman said genomic technology had enabled the co-op to speed up the process as it could screen an animal’s DNA at birth to find out whether it possessed the slick gene.
‘‘Instead of requiring years of back-crossing and progeny testing, with genomics we can generate animals on the ground, evaluate them quickly and utilise them once they reach maturity.’’