Keeping a dry cow cool and comfortable is beneficial to it, its calf and a dairy farmers' bottom line, according to US animal scientist Geoff Dahl, who recently presented at a Dairy-SA Heat Stress Management Workshop at Meningie in South Australia.
Dr Dahl outlined that understanding heat stress management was not only important for the whole dairy herd but particularly vital for dry cows, with updated research showing that heat stress resulted both in lower milk production and had a 'generational effect' on future progeny.
More than 40 dairy farmers and service providers attended the session - held at Brad and Karin Fischer's farm - featuring a detailed presentation followed by a walk to the dry cow area and valuable interactive discussion among the group.
Dr Dahl explained how heat stress limited 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.
His research found cooling dry cows increased milk for 40 weeks after calving. Yields from cows cooled during the dry period saw a 4-5 litre increase a day than uncooled cows, despite zero differences in how the animals were treated after calving.
"Across the board, they all show the same thing," Dr Dahl said. "Animals cooled when dry make more milk in their next lactation."
Cooling dry cows increased body weight prepartum, but decreased body weight postpartum. Cooled animals gained weight during their dry period and, because they were making a lot more milk after calving, they were metabolising more body tissue. Research also found that cooling dry cows had positive effects on their immune function, including lymphocyte proliferation and increased neutrophil action postpartum.
Dr Dahl said 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," he said. "The difference is an effect on the proliferation - or growth - of these cells. There are a lot more in cooled cows."
Effect on calves
Heat stress on the cow also impacted the unborn calf, both early in life and when it begins lactating. Dr Dahl 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," Dr Dahl said.
He said cooling the cow increased its calf's 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," Dr Dahl said.
Cooling also improved immunity, measured by the higher circulating Immunoglobulin G (IgG). "In fact, it looked like calves born to hot cows had lower ability to absorb IgG," Dr Dahl said.
His studies also showed that in-utero heat stress decreased reproductive performance, with cooled calves requiring fewer services and achieving pregnancy at an earlier age at pregnancy, by almost a month.
Dr Dahl said it made good financial sense to cool cows, for the present and long term. While the ideal approach would be to build a barn to mediate heat stress, or retrofitting it with a cooling system such as fans or soakers, he recognised this was 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. It makes sense to cool dry cows."
To get practical information and tools to manage heat stress, head to http://coolcows.dairyaustralia.com.au/. Farmers can also sign up for the free Dairy Forecast Service that will alert them to upcoming extreme heat events. D
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.