Three Main Strategies
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Biotechnical Options
Genetically Develop More Heat-Tolerant Dairy Breeds
This can improve both the reproductive ability and adaptability of cows to warmer climates8.
Embryo Transfer
This can bypass the harmful effects heat stress has on the fertility of lactating dairy cows9.
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Management
Nutritional Modification
Decreased feed intake in heat-stressed cows causes a negative energy balance. Also, the energy requirements of heat-stressed cows are higher, because their core body temperature is increased and their heat-dissipation processes are inefficient.
Feeding these animals high-quality forage supplemented with concentrates, additional fats and feed additives can help mitigate some of these adverse effects10.
More fiber and/or fewer concentrates in the ration will increase rumination, and this will compensate for rumen and metabolic acidosis. You can also provide bi-carbonate in the ration to compensate the rumen acidosis.
Environmental Modification
Shade protects from direct solar radiation but does not alter the air temperature or the relative humidity of their surroundings.
Evaporative cooling strategies are costly, but are very useful for alleviating heat stress in animals. Lack of proper ventilation can lead to high moisture levels, manure gases, pathogens and dust concentrations, creating an adverse environment for dairy cows.
However, the selection of cooling systems to improve cow health and performance may vary between humid and arid areas. Options should optimize the combination of increased air velocity and conductive cooling to improve cow well-being by reduce their body temperature11.
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Hormonal Therapy
Hormonal therapy does not address the causes of heat stress, but it can ameliorate some of its direct effects on the endocrine reproductive axis. It can also help to overcome the decrease in reproductive performance in cattle seen during summer and early autumn.
Timed Artificial Insemination (TAI) Protocol
Breeding synchronization protocols for insemination at fixed time-points may reduce the calving-conception interval and the number of services per conception.
The optimal hormone treatment to combat the effects of heat stress should:
- Be suitable for cows in a fixed time-point insemination program and avoid the need for heat detection.
- Resolve anoestrus, including ovarian cysts or anovulatory follicles.
- Have a short duration.
One of the most popular treatments, the OvSynch protocol, consists of the following treatments: GnRH (day 0), prostaglandin F2α (day 7), and GnRH (day 9), with artificial insemination 16-20 hours after the second GnRH treatment. It has been shown that TAI protocol can reduce losses in reproductive efficiency in cattle caused by poor summer estrus detection.
GnRH Administration at Estrus
Induction of ovulation with GnRH not only decreases the incidence of delayed ovulation, but also provides additional luteotrophic support to the early corpus luteum.
GnRH or Human Chorionic Gonadotropin (hCG) Administration Post Artificial Insemination
Administration of hCG or GnRH post insemination supports the function of the yellow body in the ovary, thereby maintaining higher progesteron levels resulting in higher pregnancy rates.