Actions to be taken
The following approaches are classified by the target objectives pursued when cows are exposed to heat stress conditions.
The use of shade is an important resource to mitigate heat stress. Shade is a requirement in any environmental management programme for dairy. In an experiment cows under shade yielded 10% more milk, had lower rectal temperatures and slower respiratory rates.
It is recommended to provide shade in all areas, 4.5 to 5 square metres per cow oriented to cover most of the sun path during the hottest season. It can be provided either by solid roofs or by sheds. Feeding and watering areas should provide a shade refuge - holding pens, maternity pens, cows in lactation, managing areas and if possible also pathways.
Reformulate diets to account for reduced DMI, adjust increased requirements to cope with heat, reduce heat increment and avoid any excess in nutrient supply. Avoid excess nitrogen as energy might be distracted to produce NH2. Feed low fibre diets since acetate is not efficiently used in hot weather conditions.
Low forage and higher concentrate diets increase total DMI, so measures to manage a low DMI should be taken while providing the right amount of nutrients. To compensate this, the dietary neutral detergent fibre content needs to be adjusted to keep DMI at the desired level.
Reduced DMI requires an increase in the dietary mineral concentrations. Cation and anion should be increased (Na and K), as well as trace minerals (Z, Mn, Cr and Cu) to reinforce the antioxidant status and also to prevent problems derived from tissue weakness like pododermatitis.
In facilities with low mechanised cooling capacities, try to feed cows at a time when temperature is comfortable, early and late in the day. Provide a well-balanced diet with an accurate energy supply calculated according to the production stage and weather (DMI).
Mechanised ventilation has shown to be a useful resource to improve comfort, especially when combined with the use of sprinklers or foggers. Fans running at 6.5 to 9.7 km per hour, depending on the season and facilities, would provide sufficient cooling. Fans should be placed at the most efficient height (2.40 to 2.50 m). Fan companies provide the service of calculating the optimal capacity for the area.
Frequent maintenance to fans is also essential. All must be good working order before the hot season starts. A thermostat should be calibrated and cleaned frequently.
The use of sprinklers on the cows has shown to provide comfort as they increase their evaporative heat loss. Low pressure coarse droplets sprinklers (1.8-2.8l per minute, 1.25l per cow) are preferred, as the less the air is moving the more times the cow needs to be soaked. Once the cow is wet, time should be allowed for the water to evaporate. Humid weather requires more frequent soaking. An 11.6% improvement in milk yield was obtained when cows were sprayed for 1.5 minutes every 15 minutes. Give proper maintenance to nozzles and flush pipes.
Care must be taken to avoid manure accumulation creating muddy areas. Due to metabolic acidosis that develops during heat stress, vasoactive changes usually weaken claws (hooves). Lameness can result from the softening and later wear of the claw.
Provide full water access (linear water access: 1.0-1.2m per cow), preferably in shaded areas, in free stall barns and parlour exit lanes. Keep water tanks clean and check water flow rates at peak hot times. When providing cooling ponds, allow 4-5 square meter per cow. Downside is of course the tremendous amount of water use.
Supplementation of vitamins A and C and trace minerals lost and depleted during heat stress, would be helpful. Minerals can be provided from high bio-available sources like complex trace minerals, Zn, Cu, Mn and Cr. This would also help to reinforce the immune system and reduce infectious problems. By providing sodium bicarbonate to replenish the carbonates lost in the urine would also prevent metabolic acidosis.
It is desirable that animals have the benefit of being exposed to lower temperatures during night time.
Despite high ambient temperatures during the day, a cool period of less than 21o Celsius for three to six hours will minimise the decline in milk yield.
To summarise, utilisation of management as well as nutritious strategies can significantly reduce heat stress with lactating dairy cows. Careful consideration should be given to water quantity and quality, feed and micronutrient nutrition before and after heat stress.
References are available on request.
* This article is an edited version of a presentation by Jeffrey DeFrain, research nutritionist, Zinpro Corporation, at the Global Feed and Food Congress in South Africa, and an article by his Zinpro colleague Marco Rebollo, which was first published by AFMA Matrix and re-used with permission.