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Heat stress expert visits Murray Dairy

Keeping a dry cow cool and comfortable is beneficial to her, her calf and a dairyfarmers’ bottom line, according to US Animal Scientist Geoff Dahl who presented at at a series of workshops in the Murray Dairy region in October. 

Geoff outlined that understanding heat stress management is not only important for the whole dairy herd but particularly vital for dry cows, with updated research showing that it results both in lower milk production and can have a ‘generational effect’ on future progeny.

At the workshops Geoff explained how heat stress limits mammary growth, metabolism and immune function, with these factors setting the stage for a more challenging transition, resulting in lower yield in the next lactation.

Geoff's research found that cooling dry cows increased milk for 40 weeks after calving. Yields from cows cooled during the dry period were 4 - 5 litres/day higher than cows that experienced heat stress, he reported, despite zero differences in how the animals were treated after calving.

'Across the board, they all show the same thing. Animals cooled when dry make more milk in their next lactation,' Geoff said.

Cooling dry cows increases body weight prepartum, but decreases body weight postpartum. Geoff explained that cooled animals actually gained weight during their dry period and, because they are making a lot more milk after calving, they're metabolising more body tissue.

Research also found that cooling dry cows has positive effects on their immune function, including lymphocyte proliferation and increased neutrophil action postpartum.

Geoff noted the effects on acquired immunity and antibody production could be important to vaccination profiles.

“Biopsies revealed that cooling dry cows has a direct impact on their mammary cells. The difference is an effect on the proliferation - or growth - of these cells,” he explained. “There are a lot more in cooled cows,” Geoff observed.

Effect on Calves

Heat stress on the cow also impacts the unborn calf, both early in life and when she begins lactating. Geoff termed this a ‘generational issue’ and not just on the affected animal, likening it to human mothers smoking during pregnancy and its resulting effect on a child's development.

“We have essentially created a situation where calves cannot reach their genetic potential when they suffer heat stress in the dry period,” Geoff said.

Geoff confirmed that cooling the cow increases her calfs birth weight.

"We found the difference persists into weaning, as does the persistence of lower birth weights of hot cattle," he said, citing research that found in-utero heat stress of about six weeks in length reduced calf body weight and height at weaning.

"Cooled calves were heavier and taller," Geoff reported.

Cooling also improves immunity, measured by the higher circulating IgG.

"In fact, it looked like calves born to hot cows had lower ability to absorb IgG," Geoff said.

Geoff’s studies also show that in-utero heat stress decreases reproductive performance, with cooled calves requiring fewer services and achieving pregnancy at an earlier age at pregnancy, by almost a month.

It makes sense to keep cows cool

Geoff emphasised that it makes good financial sense to cool cows, for the present and long term. While the ideal approach would be to build a barn to accommodate heat stress, or retrofitting it with a cooling system like fans or soakers, he recognises this is not always feasible.

“Creating temporary shade structures, providing tree shade, sprinklers or even planning calving patterns that allow cows to be dry in the cool months of the year, will all help,” he said.

“At a minimum we need to be allowing animals to recover from heat stress to ensure core body temperature does reduce, and that will have positive flow-on effects for the whole business,” Geoff added.

“It makes sense to cool dry cows,” he said.

To get practical information and tools to manage heat stress, head to The Cool Cows website. You can also sign up for the free Dairy Forecast Service that will alert you to upcoming extreme heat events.

Professor Geoff Dahl was a Keynote Speaker at the 2018 Australian Association of Ruminant Nutrition Conference held in Victoria, and his visit was thanks to the support of Dairy Australia.

Article produced by DairySA. 

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