The study, published in the Journal of Agriculture and Food Research, is unusual because it treats climate, milk quality, and money as a single connected system. Most previous work has examined heat stress effects on milk yield or composition in isolation, leaving a gap between the biology of the cow and the economics of the bulk tank. By integrating all three dimensions, the Brazilian team set out to ask a deceptively simple question: when the climate changes the milk, does the paycheck change with it?

To answer it, the researchers assembled an unusually complete dataset. Hourly records of air temperature and relative humidity from the Agronomic Institute meteorological station in Piracicaba, totaling 25,920 observations, were aggregated into monthly means to match the resolution of milk-quality data from the Milk Quality Reference Laboratory. Fat and protein percentages were measured by near-infrared reflectance spectroscopy, somatic cell counts by Fourier-transform infrared spectroscopy, and standard plate counts of bacteria by flow cytometry. Gross milk prices came from the Center for Advanced Studies in Applied Economics at ESALQ-USP, and quality bonuses and penalties were calculated using the published pricing criteria of the processor Piracanjuba, aligned with Brazilian Normative Instructions 76 and 77. After harmonization, the final analytical dataset consisted of 36 consecutive monthly observations from January 2016 to December 2018, with no missing values.

The seasonal patterns were striking. Air temperature averaged 25 degrees Celsius in summer and 23.6 in spring, well above the roughly 24-degree upper critical temperature generally cited for lactating dairy cows, while fall and winter averages of about 20 degrees remained within the thermoneutral range. Relative humidity hovered between 64 and 73 percent, high enough in the hot seasons to limit evaporative heat dissipation, the primary cooling mechanism available to cattle. Milk fat told the mirror-image story: it peaked at 3.62 percent in fall and fell to 3.23 percent in spring, while protein followed the same trajectory. The final milk price averaged R$ 1.48 per liter in the cool seasons against R$ 1.23 in the hot ones, a gap driven largely by composition-linked bonuses. Notably, somatic cell count and standard plate count showed no significant seasonal differences, which the authors attribute to the strict, standardized milking hygiene protocols all participating farms followed, including pre- and post-dipping and standardized cup handling.

The multivariate analyses reinforced the picture. Principal component analysis showed the final milk price negatively associated with air temperature and bacterial count, and positively associated with fat and protein. Canonical discriminant analysis separated the four seasons with 88.9 percent classification accuracy, with air temperature, milk fat, and final price contributing most strongly to the discrimination. Canonical correlation analysis then quantified the link between the thermal environment and the milk-quality-economic variable set, revealing approximately 36 percent shared variance between the two canonical variates. The authors are careful to stress that this figure represents shared variation between linear combinations of variables, not the proportion of total milk-quality variation caused by climate; genetics, nutrition, lactation stage, hygiene, and management all contribute substantially. Within the environmental set, air temperature dominated the canonical relationship and was negatively associated with milk fat and its economic component, while relative humidity played a comparatively weak role in this particular dataset.

To look forward, the team fitted both ordinary least squares regression and a deliberately constrained Gradient Boosting Regressor, using an expanding-window temporal validation in which each of the 12 months of 2018 was predicted using only preceding data. The nonlinear model consistently outperformed the linear one, but the authors emphasize that performance metrics from a 36-month series are exploratory evidence, not externally validated forecasts. When the fitted relationships were combined with the IPCC RCP4.5 warming scenario, the clearest directional signal was a decline in milk fat: a statistically significant negative coefficient, with the conditional trajectory falling from roughly 3.31 percent in 2025 to 3.21 percent by 2100. The fat-linked bonus approached zero over the same horizon, and the final milk price was projected to slip from about R$ 1.21 to R$ 1.12 per liter, an absolute decrease of roughly R$ 0.09, or about 7.4 percent.

Milk protein, by contrast, showed only a weak and statistically non-significant negative trend, drifting from about 3.14 to 3.11 percent, and the protein bonus barely moved. The microbiological story was different in kind. Standard plate count rose along the warming trajectory, from approximately 0.99 million to more than 1.13 million colony-forming units per milliliter by 2100, though the low explanatory power of the model indicates that climate accounts for only a small share of the variation in bacterial load. Somatic cell count showed no significant relationship with warming. The most provocative finding, however, was economic: within the evaluated payment structure, the SPC- and SCC-linked payment components remained essentially flat and statistically unrelated to the warming trajectory, even as the underlying bacterial counts climbed.

That asymmetry between biological deterioration and economic signal may be the study’s most consequential message. If quality-based payment schemes respond strongly to compositional traits like fat but weakly to gradual increases in microbiological counts, then the market may fail to warn producers about a climate-driven hygiene risk until it crosses a penalty threshold. The authors suggest that more responsive pricing could incorporate progressive penalties or bonuses tied to microbiological indicators and climate-related risks, but they caution that simply raising penalties could disproportionately burden smallholders with limited capital for cooling, sanitation, and infrastructure. Any redesign of incentives, they argue, should be paired with technical assistance and access to adaptation technologies. They also note that the findings are specific to one Brazilian payment structure and cannot be generalized to processors or markets with different thresholds and weights.

The authors are equally candid about the limits of their projections. Extrapolating relationships estimated from three years of data to the end of the century assumes that those relationships remain stable, ignoring future genetic selection for heat tolerance, changes in nutrition, housing, cooling technology, and market policy. Environmental exposure was characterized by a single external weather station rather than on-farm sensors, and no physiological or behavioral measures of heat stress were collected, so the results describe system-level associations rather than cow-level mechanisms. The trajectories should be read for their direction and relative magnitude, not as precise predictions for any given year. Even so, the study offers a rare integrated view of how a warming, humid tropics will press simultaneously on milk composition, hygiene, and farm income, and it makes a compelling case that climate adaptation in dairy farming must be designed around the whole chain, from shade and silage to somatic cells and the fine print of the milk check.

Subject of Research: Climate change effects on milk quality and farmer remuneration in humid tropical dairy systems

Article Title: Climate–milk quality–remuneration relationships in humid tropical dairy systems: an exploratory assessment under climate-change scenarios to 2100

Article References: Silveira, R. M. F., de Castro Júnior, S. L., Roma Junior, L. C., McManus, C., & da Silva, I. J. O. (2026). Climate–milk quality–remuneration relationships in humid tropical dairy systems: an exploratory assessment under climate-change scenarios to 2100. Journal of Agriculture and Food Research, Article 103369. https://doi.org/10.1016/j.jafr.2026.103369

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103369

Keywords: climate change, dairy farming, milk quality, heat stress, Holstein cows, milk fat, somatic cell count, standard plate count, quality-based payment, RCP4.5, Brazil, tropical agriculture

The research team worked with nine rumen-cannulated Holstein cows in their third lactation, using a changeover design with two three-week experimental periods separated by a three-week washout. The animals were assigned to four treatments: a control diet containing 40 percent concentrate, the same control diet plus a daily abomasal infusion of three kilograms of starch to induce hindgut acidosis, a high-concentrate diet containing 65 percent concentrate, and the high-concentrate diet combined with the starch infusion. Infusing starch directly into the abomasum, the cow’s true stomach, was a clever experimental trick: it bypassed the rumen entirely, allowing the researchers to isolate the effects of starch fermenting in the hindgut from the effects of a starch-rich ration fermenting in the rumen.

The physiological measurements confirmed that both insults did what they were designed to do. Cows on the high-concentrate diet spent an average of 249 minutes per day with ruminal pH below the critical threshold of 5.8, compared with just 69 minutes per day for cows on the control diet, and their mean ruminal pH dropped from 6.26 to 6.09. Meanwhile, the abomasal starch infusion lowered fecal pH from 6.58 to 6.33, a hallmark of hindgut acidification, and shifted hindgut fermentation toward greater propionate and lactate production. In other words, the study successfully created subacute ruminal acidosis and hindgut acidosis in the same animals, sometimes simultaneously, setting the stage for a metabolomic showdown.

To read the chemical story, the team analyzed rumen fluid, feces and blood serum using high-performance liquid chromatography coupled to tandem mass spectrometry, with anion exchange chromatography linked to high-resolution mass spectrometry reserved for carboxylic acids, sugar-related compounds and nucleotides in serum. The data were processed with rigorous quality controls, including blank-to-sample filtering and drift correction, and analyzed in MetaboAnalyst with false-discovery-rate adjustment. The statistical power of the design, estimated at 78 to 95 percent with an average of 85 percent, gave the researchers confidence that the differences they detected were real rather than noise.

The ruminal results were strikingly one-sided. Only the diet mattered here: the high-concentrate ration reshaped the ruminal metabolome, while the abomasal starch infusion left it essentially untouched. Cows on the high-concentrate diet showed elevated concentrations of adenosine, histidine, inosine, guanine, citrulline, arginine and a lipid-related compound, 1,2-dilinoleoyl-3-palmitoylglycerol. Pathway analysis revealed enrichment of purine metabolism, the urea cycle, aspartate metabolism, methyl histidine metabolism, and arginine and proline metabolism. The authors interpret this as evidence of intense microbial turnover: when ruminal pH falls, microbes die and lyse, releasing their nucleic acids and proteins, while the extra energy and roughly 700 additional grams of daily protein in the high-concentrate ration fuel faster microbial growth and protein synthesis.

Some of these ruminal shifts carry warnings for long-term health. The enrichment of the urea cycle suggests a heavier workload for the liver and kidneys, which must convert microbial ammonia into urea for recycling or excretion. If ammonia is not efficiently detoxified, the authors note, chronic subclinical ammonia overload could impair nervous system function, hormonal activity, reproduction and blood pH regulation. The increased citrulline, produced by rumen bacteria converting arginine under low-pH conditions, is itself a survival strategy: the reaction generates ammonia, which helps buffer the acidic rumen environment that threatens the bacteria. It is a vivid example of the microbial community fighting back against the chemistry its host’s diet has created.

The fecal metabolome told a different story, one in which both dietary treatments left fingerprints, but the abomasal starch infusion was by far the stronger force. Starch infusion altered 48 fecal metabolites, including increases in linoleic acid, ethanolamine, oleoyl ethanolamide, linoleoyl ethanolamide, xanthine, alpha-linolenic acid, stearoyl ethanolamide and pentoses. The high-concentrate diet affected 10 metabolites, several of them overlapping with the infusion effects. Enriched pathways included bile acid biosynthesis, arginine and proline metabolism, linoleic acid and alpha-linolenic acid metabolism, glycine and serine metabolism, purine metabolism, the urea cycle and biotin metabolism. The bile acid finding is particularly intriguing, because bile acids are not merely fat-digesting detergents but powerful signaling molecules that regulate glucose and lipid metabolism; their enrichment may reflect the activation of energy homeostatic mechanisms in response to the starch overload reaching the hindgut.

Among all the fecal metabolites, one stood out as a potential diagnostic prize: ethanolamine. This compound rose under both high-concentrate feeding and abomasal starch infusion, meaning it marks acidity in either the rumen or the hindgut. Ethanolamine is derived from phosphatidylethanolamine, abundant in the membranes of shed intestinal cells, so its accumulation likely reflects gut lining damage and dysbiosis, consistent with the elevated fecal lactate observed in the companion microbiome study. More troubling still, ethanolamine can serve as a nitrogen source for pathogenic bacteria, including enterohemorrhagic Escherichia coli O157:H7, and research has shown that Salmonella enterica and E. coli can exploit it to outcompete beneficial commensal microbes. Chronic accumulation may also damage gut permeability, promote inflammation and disrupt glucose metabolism. A simple fecal marker that flags dual-site acidosis would be a genuinely valuable tool for dairy veterinarians.

The blood metabolome delivered the study’s most counterintuitive result. Despite the dramatic changes in the gut, hindgut acidosis left the serum metabolome essentially unchanged, and the high-concentrate diet produced no major overall profile shift, only specific decreases in hippuric acid, 3-phenylpropionic acid, 2-hydroxybutyric acid, acetic acid and 3-hydroxybutyric acid. The authors suggest this is because hindgut fermentation products are only partially absorbed and partly excreted, whereas ruminal fermentation end-products are extensively absorbed into portal circulation. Yet the pathways enriched in the blood favored the control diet: amino sugar metabolism, aspartate metabolism, fatty acid biosynthesis, propanoate metabolism, branched-chain amino acid degradation and, notably, the malate-aspartate shuttle, the most efficient mechanism for shuttling cytosolic NADH into the mitochondrial electron transport chain. The authors speculate that high-concentrate diets may force cows into less efficient cellular energy use, with potential consequences for feed efficiency.

Taken together, the study draws a clear chemical map of two acidotic conditions that dairy nutritionists have long struggled to disentangle. High-concentrate feeding dominates the ruminal metabolome through nitrogen and purine metabolism, both treatments converge on the fecal metabolome with ethanolamine as a shared signature, and only diet reaches the bloodstream in a meaningful way. The work also carries honest caveats: the washout period was relatively short, milk data lacked sufficient statistical power, ruminal ammonia was not measured, and increasing concentrate changes more than just starch. Even so, the findings emphasize that maintaining adequate gut health is not simply about preventing a drop in pH; it is about protecting an entire interconnected metabolic network that links rumen microbes, hindgut fermentation, liver function and cellular energy economy. For an industry in which subacute ruminal acidosis affects an estimated 10 to 26 percent of commercial dairy herds, a fecal biomarker like ethanolamine could transform how silently sick cows are found, long before production losses become visible.

Subject of Research: Metabolomic impacts of high-concentrate feeding and hindgut starch flow on rumen, fecal and blood metabolism in Holstein dairy cows

Article Title: Metabolome analyses of the rumen, feces and blood reveal separate and simultaneous impacts of increased dietary concentrate and hindgut starch flow in Holstein cows

Article References: Castillo-Lopez, E., Aigensberger, M., Atif, R. M., Biber, P., Hartinger, T., Raykova, S., Guerrero-Lavin, A., Reisinger, N., Schwartz-Zimmermann, H. E., Berthiller, F., & Zebeli, Q. (2026). Metabolome analyses of the rumen, feces and blood reveal separate and simultaneous impacts of increased dietary concentrate and hindgut starch flow in Holstein cows. Metabolomics, 22(5), Article 163. https://doi.org/10.1007/s11306-026-02519-0

Image Credits: AI Generated

DOI: 10.1007/s11306-026-02519-0

Keywords: dairy cattle, metabolomics, ruminal acidosis, hindgut acidosis, Holstein cows, starch fermentation, rumen, fecal biomarkers, bile acids, ethanolamine, animal nutrition, gut health