Tropical dairy cow breeding under way

Richard Spelman

An artificial breeding bull which caused some of its offspring to be excessively hairy and prone to overheating has led to two world-first scientific discoveries.

The bull, called Matrix, had inherited a previously unidentified genetic mutation from its sire and passed it on to offspring born in 2011 and 2012.

As part of an investigation into the bull, LIC scientists isolated the "hairy" genetic mutation, and also discovered a variation in a Caribbean breed of cattle that allows them to tolerate high temperatures.

The discoveries - published by the prestigious international science journal Nature Communications - pave the way for the farmer-owned co-operative to breed cattle that will maintain high milk production in tropical conditions, and could protect New Zealand's cows from future impacts of climate change.

Dr Richard Spelman, LIC's chief scientist, described the finding as marvellously serendipitous.

"Many farmers will recall the Matrix offspring - they were hairy, heat intolerant and failed to lactate, and when this came to LIC's attention we set out to find an explanation.

"As a result of the investigation, we were able to isolate the gene involved, but this has also led to another discovery that provides an opportunity to develop a new breed of cattle which will continue to graze and produce large quantities of milk at temperatures that would make most dairy cows struggle."

Spelman said the discoveries revolve around the prolactin hormone, a molecule which is best known to initiate lactation in mammals.

"In the Matrix offspring we found that a mutation in the prolactin hormone was impacting milk production and coat length, but we also found it was impacting the animal's ability to sweat, and therefore it couldn't cope with heat."

Dubbed the "hairy" mutation, the effects were identified as being opposite of those seen in the Caribbean beef breed called Senepol, renowned for its short, slick coat and ability to thrive in hot temperatures.

"This got the team thinking about whether prolactin could be involved in Senepol, and after sequencing the DNA of some Senepol bulls, we found a major genetic variation in the prolactin receptor gene. The Senepol variant improves the animal's ability to regulate body temperature, probably because of enhanced sweating, like the hairy animals, but in reverse.

"This discovery provides a genetic and physiological explanation as to how some cattle are able to tolerate high temperatures, providing an understanding of genes and gene pathways whose activity is required for the heat tolerance trait."

As a result of the discoveries, LIC bulls are now screened for the hairy mutation and a breeding programme is under way to cross Senepol animals with New Zealand Holstein-Friesian dairy cattle, to create offspring with the prolactin receptor variation.

Spelman expects these animals will start being milked in 2017 and if successful, enable these new LIC genetics to be used in tropical countries to produce milking cows.

In addition to the breeding programme, the co-op is also working with Dairy SolutioNZ, a Waikato-based company breeding Senepol cross-bred dairy animals, to develop a tropical cow breed.

These discoveries were made in collaboration with scientists at the University of Auckland and several other US and European Universities, and as part of the co-op's DNA sequencing programme of work. This broader programme aims to map genetic variation impacting cow production and health, and use these to improve the accuracy of genomic selection for future sires. The work will continue this year.

The DNA sequencing programme utilises a large dataset developed by LIC scientists and is co-funded by the Ministry for Primary Industries through the Transforming the Dairy Value Chain Primary Growth Partnership programme, led by Fonterra and DairyNZ.

- For more information visit www.dairynz.co.nz/pgp