Dry cows are the up-and-coming milk-makers in your herd – yet when it comes to cooling, they are often overlooked. A study conducted by the National Animal Health Monitoring System (NAHMS) revealed that 74.3 percent of all dairy operations provided fans for their lactating herd, while only 36 percent offered fans for dry cows. The milking herd on 20.3 percent of all operations was also cooled by sprinklers, yet only 4.6 percent of dry cows had access to this cooling method.
Current research indicates that cooling dry cows has a direct impact on milk production in the subsequent lactation. It is also shown to aid in better immune function. Dry cows carry considerable profit potential, and if not kept comfortably cool during the entire dry period, the profitability of your herd could be compromised.
Heat stress is extremely costly. Damages to the dairy industry range from $900 million to $5 billion every year due to lost milk, reproduction problems and various health issues. Depending on the humidity level, cattle can begin suffering heat’s adverse effects at temperatures as low as 72ºF.
How does all of this translate to the dry cow?
Research from the University of Florida is shedding light on the importance of cooling this group of animals. During a three-year study, the effects of heat stress were evaluated in dry cows as it related to milk production, immunity, mammary gland cell proliferation and calf performance.
Cows were either imposed to heat stress (shade, no fans, no sprinklers) or cooling (shade, fans, sprinklers – sprinklers turned on at 71ºF and ran for two minutes, every five minutes) from dry-off until freshening. Upon calving, all cows were moved into a freestall barn with sprinklers and fans. The studies ran until 30 weeks in lactation.
Milk production up
Results from the University of Florida trials showed that cooling cows prepartum improves milk production postpartum. Cows that were cooled during the dry period produced an average of 14 pounds more milk per day in the first 30 weeks post-calving than heat-stressed cows.
Milk production responses ranged from 10.3 pounds to 20.5 pounds of additional milk per day for the three studies. Research also included mammary gland investigation, disclosing that heat stress abatement increased mammary epithelial cell proliferation in the dry period. These milk secretory cells are responsible for milk production and explain the cooled cows’ increase in milk.
Calf performance
Because heat-stressed cows often calve earlier than their cooled counterparts, calves born to these cows weighed substantially less. The calf body weights from University of Florida studies were recorded as follows:
• Year 1: Birth weight of calves born to heat-stressed cows: 68.3 pounds. Birth weight of calves born to cooled cows: 97.0 pounds. Difference: 28.7 pounds (42 percent).
• Year 2: Birth weight of calves born to heat-stressed cows: 87.0 pounds. Birth weight of calves born to cooled cows: 98.0 pounds. Difference: 12 pounds (12.6 percent).
• Year 3: Birth weight of calves born to heat-stressed cows: 91.7 pounds. Birth weight of calves born to cooled cows: 102.4 pounds. Difference: 10.7 pounds (11.6 percent).
Maternal heat stress also reduces the calf’s serum total immunoglobulin (IgG) levels. Cooled dams yielded calves with 2,500 milligrams per deciliter on day one versus just over 1,500 milligrams per deciliter for the offspring of heat-stressed animals and retained a difference of about 500 milligrams per deciliter throughout day 28.
On a follow-up study, the University of Florida evaluated milk production on the first lactation of calves born from cows that were heat stressed or cooled when dry.
Milk production on the first lactation of calves that were born from cows that were cooled when dry was 10 pounds higher than those born from cows that were heat stressed when dry. Heat stress abatement during the dry period improves milk production in the subsequent lactation of the dam and of the offspring’s first lactation.
Strong immunity
The team also evaluated the role heat stress plays on the immune system through close examination of the neutrophils – cells that serve as the first line of defense against infection. These pathogen-eaters attack bacteria, but when an animal is stressed, the neutrophils’ ability to fight infection is impaired.
The studies showed that heat stress reduces neutrophil phagocytosis (ability of the neutrophils to “eat” bacteria) and neutrophil oxidative burst (ability of the neutrophils to “kill” bacteria), thereby limiting this cell’s power to actually kill the bacteria it eats.
Neutrophils isolated from cooled cows had greater ability to eat and kill bacteria at 20 days postpartum than those isolated from heat-stressed cows.
Another cell of the immune system is the lymphocyte (a type of white blood cell). Lymphocytes isolated from cooled cows had greater proliferation (three times more) than those isolated from heat-stressed animals.
Heat-stressed dry cows had greater respiration rates and rectal temperatures as well as much higher water intake – about 5 gallons more per cow per day. Cooled cows took 40 to 50 breaths per minute, while cows experiencing heat stress had more than 80 breaths per minute.
Improve transition success
Dry cows are equally important to lactating cows. Therefore, emphasis on transition success is key. Heat stress abatement in dry cows improves transition into lactation by increasing milk production, mammary cell proliferation and immune function.
It also improves calf performance. The magnitude of response an individual herd can observe from cooling its dry cows is directly related to the heat intensity and load, as these figures alter year to year between the three studies done at the University of Florida.
In addition to using shade, fans and sprinklers for both lactating and dry cows, dairies should employ nutritional strategies for combating heat as well. When feeling heat stressed, cows eat less.
To maintain milk production and overcome other heat-related challenges, a cow must consume the same amount of nutrients year-round. Choose a highly palatable, concentrated energy source to provide equivalent nutrients in a more modest serving size.
The research is clear: If you’re not cooling dry cows, you could be missing out on significant economic potential. When cows experience proper cooling while dry, they are set up to achieve maximum profitability in the next lactation.
References omitted due to space but are available upon request. Click here to email an editor.
