As the frequency of heatwaves in Australian summers increase, extra management strategies are required to deal with heat stress in grazing dairy cows. Management interventions such as providing shade, sprinklers, fans and adjusting milking times help to mitigate the effects of heat stress but nutritional manipulation of the diet is another tactic to implement.
Work conducted as part of the DairyFeedbase program's Feeding Cool Cows project has quantified the impact of hot Summer conditions on the nutritional characteristics of three commonly grazed forage species - perennial ryegrass, lucerne and tall fescue - that are grown under irrigation in some of Australia’s hotter dairy regions.
The impact of changes in forage quality means that during heat events cows are consuming pasture that is declining in nutritive value as the temperature rises. In addition, the increased levels of fibre in this pasture means that cows will likely have a reduced maximum total daily dry matter intake if the diet remains the same. These factors, in combination with other negative impacts of heat on a cow’s metabolism, will lead to a substantial decline in milk production.
Steps can be taken to modify the diet of cows grazing pasture in summer during periods of heat stress to help to minimize the decline in milk production.
Chicory vs pasture silage during heat events
A higher fibre forage causes the fermentation process within a cow’s rumen to work harder, increasing the heat load the cow is experiencing which can be detrimental to a cow’s milk production. A lower fibre diet during periods of heat stress will reduce the heat produced in this process and mitigate productivity losses.
As part of the DairyFeedbase Feeding Cool Cows project, fresh chicory was compared with pasture silage as a lower fibre forage source versus the average Australian ryegrass silage (typically very high in fibre) during an extreme heat event.
The research provide some key findings for farmers:
- Cows offered fresh chicory in a hot environmental condition had greater milk production in the form of energy corrected milk than cows offered pasture silage; a milk yield advantage of over 4 kg of ECM/cow per day was observed with chicory when offered at a rate of 13 kg DM/cow per day, compared to pasture silage.
- The lower total fibre content in chicory compared to pasture silage appears to reduce the heat load (lower body temperature) of cows under heat stress conditions.
- Use of chicory on a portion of the farm in summer provides an extra option for farmers with grazing dairy herds to mitigate against heat stress
This ability to produce more milk is driven by the impact of the diet on the core body temperature with cows that are fed a significant quantity of chicory having a lower body temperature when compared with their pasture silage counterparts.
Where chicory is not an option farmers should strive to make high quality pasture silage by following the principles of good silage conservation as outlined in the Dairy Australia Top Fodder program and the Successful Silage manual.
Sowing a portion of the farm to chicory for use in summer grazing rotation is a good additional strategy for farmers to consider in consultation with your agronomist.
Betaine as a dietary additive to mitigate heat stress
During a heat event up to 50% of milk yield reduction is attributed to reduced dry matter intake (DMI) and any strategies that helps reduce the decline in DMI will help sustain milk production. Simple changes, like supplementing the diet with an additive such as Betaine can reduce the negative impacts of hot weather.
A naturally occurring extract from sugar beet molasses, Betaine is often used by the ruminant feed industry in Australia. The addition of betaine into the diet can increase a dairy cows resilience to heat exposure assisting animals to recover quicker from periods of heat stress as well as helping optimise reproduction outcomes.
The DairyFeedbase Feeding Cool Cows project examined the role Betaine can play during a heat stress event.
The research provides some key findings for farmers:
- Cows that received betaine as a supplement in their diet tended to produce more milk solids overall than their counterparts who did not receive betaine both during a heat event and subsequent recovery periods.
- Because metabolic adaptation within a cow can take several weeks, if using betaine within your summer diet consider early implementation to allow cows time to adapt and to make the most of the impact betaine can have on production.
- Under Northern Victorian conditions from September to March using Betaine is estimated to provide an additional $30 per cow benefit to the farm.
For more information on the Feeding Cool Cows program and other ways to manage heat stress visit Cool Cows | Dairy Australia.
It is highly recommended that any changes to the herd diet in response to the impact of heat stress on grazed forages are made in consultation with your nutritionist or advisor.
