The finding is important for Indonesia, where many dairy farmers operate smallholder systems and have limited access to expensive cooling technologies such as mechanical ventilation, fans, sprinklers, and climate-controlled housing. Genetic adaptation could potentially provide an additional long-term strategy for helping dairy cattle cope with increasingly hot and humid conditions.
Heat Stress Threatens Tropical Dairy Production
Dairy cows are particularly vulnerable to heat stress when high temperatures are combined with high humidity. Under these conditions, cattle have greater difficulty releasing body heat, forcing their bodies to devote more energy to maintaining normal temperature.
The consequences can extend beyond animal comfort. Heat stress can reduce feed intake, alter physiological conditions, affect reproductive performance, and ultimately decrease milk production.
One commonly used indicator for assessing this environmental burden is the Temperature–Humidity Index (THI). The index combines air temperature and relative humidity to estimate the level of thermal stress experienced by dairy cattle.
For smallholder farmers, the challenge can be especially serious. Holstein Friesian cattle and their crosses, which are widely used in Indonesian dairy production, have high milk-producing potential but can be sensitive to hot tropical conditions.
In lowland areas of Java, where temperatures and humidity can remain high, farmers may need additional cooling measures to protect productivity. However, installing and operating such systems can be difficult for farms with limited financial and infrastructure resources.
This situation has increased interest in biological forms of climate adaptation, including genetic selection for heat tolerance.
What Makes Slick Hair Genetics Different?
The slick hair characteristic is associated with genetic variation involving the prolactin receptor gene, particularly the SLICK1 allele. Cattle carrying the trait generally have shorter and smoother hair coats.
The characteristic is important because a shorter, smoother hair coat can help cattle dissipate body heat more effectively. Previous research has also reported physiological differences between slick and conventional cattle during periods of heat exposure.
Rather than eliminating heat stress completely, slick genetics is expected to reduce the severity of the animal's response to high temperatures.
Brontosantoso incorporated this biological concept into a predictive model designed to examine what could happen to milk production as THI increases in lowland smallholder dairy systems.
Simulation Compared Four Heat Conditions
The study did not collect new field data from Indonesian dairy farms. Instead, Brontosantoso developed a quantitative simulation-based predictive model using climatic, genetic, physiological, and milk-production parameters reported in previous studies published between 2020 and 2025.
Four environmental scenarios were simulated:
THI 71.28: 23°C temperature and 75% relative humidity, categorized as comfortable.
THI 75.37: 26°C and 70% humidity, representing mild heat stress.
THI 82.15: 30°C and 75% humidity, representing moderate heat stress.
THI 90.30: 34°C and 85% humidity, representing severe heat stress.
The model compared predicted milk production between slick and non-slick dairy cows under each condition.
The researchers also examined the interaction between slick genetics and THI to determine whether the genetic characteristic could reduce the production losses associated with increasing heat exposure.
Slick Cows Showed a Smaller Production Decline
The simulation showed a clear pattern: milk production declined as THI increased in both genetic groups, but slick dairy cows experienced a smaller decline.
For non-slick cows, predicted milk production fell from 7.07 liters per cow per day under the comfortable scenario to 6.36 liters under severe heat exposure.
That represented a simulated reduction of approximately 10.11%.
For slick cows, predicted production declined from 7.91 liters to 7.28 liters per cow per day, equivalent to a smaller reduction of approximately 8.04%.
The difference between the two groups also became slightly larger as heat exposure intensified.
At THI 71.28, the predicted difference was 0.84 liter per cow per day. At THI 90.30, the difference increased to 0.92 liter per cow per day.
The results suggest that slick genetics may act as a buffer against heat-related production losses, rather than providing complete protection against heat stress.
Potential Impact Becomes Larger at Herd Level
To illustrate the possible relevance for smallholder farmers, the researchers scaled the simulation to a representative herd of 10 lactating cows.
Under severe heat conditions, the model predicted milk production of:
63.6 liters per day for 10 non-slick cows, compared with 72.8 liters per day for 10 slick cows.
The difference was therefore approximately 9.2 liters per day.
Over a 30-day period, that would correspond to approximately 276 additional liters of milk in the modeled slick-herd scenario.
However, Brontosantoso emphasizes that these figures are predictions from a literature-calibrated simulation, not observed milk sales or farm revenue.
The potential economic value can therefore be calculated using the actual farm-gate milk price. For example, the modeled additional milk value under severe heat exposure would be equivalent to 276 liters multiplied by the applicable local milk price.
The model also suggests that greater milk output could potentially improve feed-cost efficiency per liter and reduce dependence on energy-intensive cooling systems. However, these economic implications require validation using actual feed costs, milk prices, cooling expenses, electricity consumption, and farm-level production data.
THI Appears to Strengthen the Advantage of Slick Genetics
One of the study's important contributions is its treatment of THI not only as an environmental factor but also as a moderating variable.
The simulation estimated a THI coefficient of −0.0376 liter per cow per day for each increase in one THI unit among non-slick cows.
After incorporating an estimated buffering effect associated with heat tolerance, the predicted decline for slick cows became less severe, with a modeled slope of approximately −0.0335 liter per cow per day per THI unit.
In practical terms, both groups continued to lose production as temperatures and humidity increased, but the slick group showed a flatter decline.
Brontosantoso's model therefore provides provisional support for the idea that the potential benefit of slick genetics becomes more noticeable under stronger environmental heat pressure.
Genetic Adaptation Is Not a Replacement for Good Farm Management
Despite the promising results, the study does not suggest that slick genetics can eliminate heat stress or replace conventional farm management.
Adequate drinking water, shade, ventilation, nutrition, housing, animal health management, and appropriate cooling remain important for maintaining dairy productivity.
The study also highlights an important limitation: THI alone cannot explain all changes in milk production.
The calibration data used in the model showed relatively low explanatory values, with R² of 0.124 for morning production and 0.077 for afternoon production. This means many other factors—including lactation stage, nutrition, health, management, and housing—also influence milk yield.
Because the study relied on secondary data, conventional predictive accuracy measures such as RMSE and MAE could not be calculated. The model has also not yet been externally validated using Indonesian dairy cows whose slick genetic status has been confirmed.
For that reason, the reported results should be understood as quantitative predictions rather than statistically confirmed evidence from Indonesian farms.
A Potential Long-Term Climate Adaptation Strategy
The findings nevertheless provide a framework for considering genetic thermotolerance as part of Indonesia's future dairy-development strategy.
For smallholder farmers operating in hot lowland environments, genetic adaptation could potentially offer an advantage because the trait is embedded in the animal and can be transmitted through breeding. Unlike mechanical cooling, genetic adaptation does not directly require continuous electricity consumption.
However, actual adoption decisions would require information on the cost of acquiring slick genetics, breeding programs, herd replacement, milk prices, feed consumption, and comparisons with investments in fans, blowers, sprinklers, and improved ventilation.
The study also raises the possibility of improved carbon efficiency. If cattle maintain greater milk production under comparable management conditions, greenhouse-gas emissions could potentially be distributed across a larger quantity of milk. Yet this does not prove that slick cattle produce fewer total emissions, because feed intake, methane, manure emissions, electricity use, and cooling requirements were not directly measured.
For Brontosantoso, the next step is therefore clear: the predictive model needs to be tested in real dairy farms.
Future research should follow genetically verified slick and non-slick cows over time while recording THI, milk yield, body temperature, respiration rate, feed intake, lactation stage, housing, and farm-management conditions.
If those field studies confirm the simulation's predictions, slick genetics could become one component of a broader climate-resilient breeding strategy for Indonesia's tropical dairy sector.
Author Profile
Budwi Brontosantoso is affiliated with Universitas Trisakti, Jakarta, Indonesia. His research in this article focuses on climate resilience in dairy production, livestock genetics, heat tolerance, predictive modeling, and the sustainability of smallholder dairy systems under changing environmental conditions.
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