The study set out to disentangle the genetic and non-genetic factors that shape milk composition and cow metabolism under real field conditions. The researchers analysed 230 Czech Holstein and 289 Czech Simmental cows, sired by 122 bulls and housed on five farms operating free-stall systems. Milk samples were collected during routine performance testing, meaning the animals were handled exactly as they would be in ordinary commercial practice. Roughly half of the cows were sampled twice within the same lactation, allowing the team to build a dataset of 814 individual test-day records spanning the first through sixth lactations and covering days 1 to 305 of milk production.

The analytical toolkit was deliberately broad. In an accredited laboratory of the Czech–Moravian Breeders Association, the team used Fourier transform mid-infrared spectroscopy to measure fat, crude protein, lactose, urea, citric acid, acetone, β-hydroxybutyric acid (BHB), somatic cell counts, and a panel of fatty acids in every sample. DNA was extracted non-invasively from the milk itself, and the cows were genotyped for polymorphisms in five candidate genes central to milk fat synthesis: AGPAT6, SCD1, FASN, LEP, and DGAT1. These genes encode enzymes and regulators of lipid metabolism and have repeatedly been implicated in previous studies as potential markers for milk fat content, fatty acid composition, and susceptibility to metabolic disease.

Statistically, the researchers applied a linear mixed model with repeated measurements, treating gene variant, farm, parity, lactation stage, and breed as fixed effects while accounting for the sire and the permanent environment of each cow as random effects. Two-way interactions among genotype, farm, lactation stage, and parity were also tested. Post hoc comparisons were performed with Scheffé’s test, and Pearson correlations quantified the relationships among milk components. This design allowed the team to ask, with unusual resolution for a field study, which factors truly matter when the messy realities of commercial dairying are taken into account.

The verdict was unambiguous: farm and lactation stage were the most significant factors influencing nearly every milk parameter measured, along with their interaction. The effects of parity and breed were much weaker, a result the authors attribute in part to the partial overlap between breed and farm, since most of the participating herds kept only one breed. Notably, the significance of parity increased once lactation stage was included in the model, suggesting that properly adjusting for the physiological trajectory of lactation reveals genuine differences between first, second, and later calvings that would otherwise be masked by lactation-related variability.

The candidate genes, by contrast, largely failed to leave their mark. The impact of the five polymorphisms on milk parameters and the fatty acid profile was very low, as were the interactions between gene and farm, gene and lactation stage, and parity and lactation stage. This stands in tension with earlier work reporting significant associations between FASN, SCD1, and DGAT1 variants and milk fat traits or fatty acid composition. One caveat concerns the rare FASN genotype, the AA variant, which was detected in only two animals, potentially reducing the statistical power to detect effects for that allele. The authors also note that four of the five loci deviated significantly from Hardy–Weinberg equilibrium, a pattern consistent with the selection pressure and non-random mating that characterise managed livestock populations.

The metabolic story centred on BHB, a ketone body produced when cows mobilise body fat during the negative energy balance of early lactation. BHB levels in milk were significantly influenced by farm in all models, and by parity in the models including AGPAT6, SCD1, and DGAT1, with concentrations rising from 0.046 millimoles per litre in first lactation to 0.062 in second. Intriguingly, lactation stage itself did not significantly affect BHB in any model, unlike its pervasive effect on other components. BHB correlated strongly and positively with acetone, a relationship reflecting shared ketone metabolism, and correlated significantly with the fat-to-protein ratio, confirming earlier reports linking this ratio to energy status.

Yet the study delivers a sobering message about individual-level diagnosis. Although the association between BHB and the fat-to-protein ratio was statistically significant, the authors conclude that predicting ketosis in individual cows from this ratio does not appear reliable. Previous work has shown that while the fat-to-protein ratio can indicate negative energy balance at the herd level, no threshold provides acceptable sensitivity and specificity for identifying hyperketonaemia in a single animal. Instead, the researchers propose that milk BHB itself, which is routinely assessed during standard milk performance testing, may serve as a practical field predictor of clinical or subclinical ketosis, particularly as automatic in-line milk composition recording becomes more widespread.

Other correlations painted a coherent picture of high-producing cows under metabolic strain. Daily milk yield correlated negatively with most milk components, while urea content and milk yield were significantly positively correlated, hinting at higher metabolic intensity in the most productive animals. Lactose content showed a significant negative correlation with the somatic cell score, reinforcing its role as an indicator of udder health, and a weak but significant positive correlation emerged between the somatic cell score and BHB. Milk urea, the authors caution, should be interpreted as a herd-level tool for evaluating protein nutrition rather than as an individual diagnostic, since it is influenced by a wide variety of factors including health status.

The study’s limitations are acknowledged by the authors themselves: the animals came from a limited number of farms, and some genotypes were represented by very few animals. Even so, the central conclusion is robust and actionable. In the contest between genes and environment for control of milk composition, the environment wins decisively under field conditions, with feeding regimes, housing, milking management, and the natural arc of the lactation curve overwhelming the modest contributions of individual lipogenic gene variants. For dairy producers, the practical takeaway is that routine milk recording, especially when it includes BHB measurement, offers a powerful and increasingly automated window into herd metabolism, one that may ultimately catch ketotic cows earlier than any single genetic marker or ratio ever could.

Subject of Research: Genetic and non-genetic factors affecting milk composition and metabolic status in dairy cows

Article Title: Genetic and non-genetic factors influencing milk composition and cow metabolism

Article References: Čítek, J., Samková, E., Brzáková, M., Hanuš, O., Večerek, L., Jozová, E., Hasoňová, L., Baldíková, E., Iliyasu, S. M., & Rost, M. (2026). Genetic and non-genetic factors influencing milk composition and cow metabolism. Archives Animal Breeding, 69(4), 541-552. https://doi.org/10.5194/aab-69-541-2026

Image Credits: AI Generated

DOI: 10.5194/aab-69-541-2026

Keywords: dairy cattle, milk composition, ketosis, beta-hydroxybutyrate, lipogenic genes, fatty acids, lactation stage, fat-to-protein ratio, animal genetics, metabolic health, FT-MIR spectroscopy, Holstein

The research, published in Food Science of Animal Resources, followed 400 lactating Holstein cows across three commercial dairy farms in Jeju City over 47 months, from January 2021 to November 2024. During this period the farms progressively replaced their conventional concentrate feeds with commercially manufactured methane-mitigating concentrates, allowing the researchers to compare milk records before and after the transition under genuine production conditions. Two products were involved: one containing a yeast-based additive, garlic-derived diallyl disulfide, and condensed tannins, and another built around a commercial essential-oil blend marketed as Agolin. The full composition of the additives is proprietary, a common feature of the emerging methane-mitigation market that itself complicates independent scientific evaluation. All cows received a total mixed ration formulated to Korean feeding standards, delivered twice daily, with free access to water and minerals.

The headline result is straightforward: milk volume survived the transition intact. Across all statistical models, including multifactorial general linear models and linear mixed-effects models that treated individual cows as random effects, methane-mitigating feeding showed no significant effect on daily milk yield. For dairy farmers weighing whether to adopt climate-friendly rations, this is the single most commercially consequential finding, because any drop in milk output would translate directly into lost revenue and would likely doom adoption regardless of environmental benefits. The result also aligns with earlier experimental work showing that additives such as 3-nitrooxypropanol, which can cut enteric methane by 24 to 40 percent, and the red seaweed Asparagopsis, which has suppressed methane by more than 80 percent in controlled trials, generally leave production untouched.

Beneath the calm surface of total yield, however, the milk itself changed. Cows receiving the methane-mitigating concentrate showed significantly lower concentrations of milk protein, solid non-fat, and milk urea nitrogen, along with a modest but statistically consistent increase in somatic cell count, an indicator of udder health and immune activity. Milk urea nitrogen is a window into nitrogen metabolism: when rumen microbes capture dietary nitrogen inefficiently, excess ammonia is converted to urea and appears in blood and milk. Lower MUN in the methane-mitigating group therefore hints that the additives altered rumen fermentation in ways that shifted how the animals handled nitrogen, a plausible consequence of additives that redirect hydrogen away from methanogenic archaea and thereby reshape the entire microbial economy of the rumen.

The somatic cell count finding deserves careful handling. The increase was moderate and does not indicate clinical mastitis, and the authors explicitly caution against causal interpretation. Still, the signal appeared across all three farms, reaching statistical significance everywhere, which lends it weight. One mechanistic explanation involves the gut-immune axis: dietary components that alter rumen fermentation can shift ruminal pH and microbial turnover, promoting the release of lipopolysaccharides, molecular fragments of bacterial membranes that act as inflammatory triggers and can elevate somatic cell counts even in the absence of infection. Previous trials with 3-nitrooxypropanol and Asparagopsis have reported similarly inconsistent somatic cell outcomes, suggesting this may be a recurring, if subtle, trade-off in methane-mitigation feeding.

Perhaps the most striking feature of the study is how context-dependent the responses proved to be. Milk fat fell significantly on Farm A but not on the other two. Milk protein dropped on Farm C alone. Solid non-fat declined on Farms B and C but not on A. Interactions between feed type and farm, parity, and month were significant for nearly every compositional trait, meaning the effect of the same additive family depended on where the cow lived, how many lactations she had completed, and what time of year it was. Farm-level differences in forage quality, hygiene protocols, microclimate, and baseline nutrition likely explain much of this heterogeneity, and the authors argue that any policy or implementation framework must account for it.

Parity emerged as a particularly powerful moderator. Milk yield climbed steadily from the first through the fifth lactation before plateauing and declining, while protein, solid non-fat, and MUN drifted downward with age, consistent with the cumulative metabolic stress and reduced hepatic and mammary efficiency of older cows. Against this backdrop, the methane-mitigating feed produced parity-specific effects: milk yield rose significantly in sixth-parity cows but fell in third and fourth parity animals, solid non-fat declined consistently across parities three through six, and somatic cell counts rose in several mid-life parities. MUN was lower across all parities, though significance faded after the second. These patterns suggest that younger, more metabolically resilient cows absorb dietary perturbation more easily, while older animals, already operating closer to their physiological limits, respond more visibly.

Seasonality added another layer of complexity. Milk protein and solid non-fat dipped during the hot summer months of June through August, a classic heat-stress signature reflecting reduced feed intake and impaired rumen function. Yet the methane-mitigating group’s solid non-fat decline progressed gradually from summer into winter rather than showing a sharp heat-driven drop, and MUN differences persisted across most months with only scattered exceptions. The monthly patterns therefore do not map neatly onto thermal stress alone, implying that individual cow variability, forage quality, and intake dynamics modulate how the feed expresses itself through the calendar. Notably, somatic cell counts remained stable across months, suggesting mammary health in these herds was governed more by parity structure and farm hygiene than by climate.

To distill these tangled effects, the team ran stepwise regression guided by the Schwarz Bayesian Criterion, testing whether methane-mitigating feeding independently explained variation in each trait once farm, parity, and month were considered. The answer was nuanced. Feed group was not retained for milk yield, fat, or protein, indicating those traits are governed by structural factors. But it was retained with strong statistical support for solid non-fat, MUN, and log-transformed somatic cell count, and its inclusion improved model fit, most notably for MUN. The overall explanatory power of the models was modest, with adjusted R-squared values between roughly 0.07 and 0.20, which the authors attribute to the enormous unmeasured variability inherent in field data, from genetics and individual intake to rumen microbial communities.

The study carries an important caveat that tempers its climate message: no methane was actually measured. The feeds were formulated with mitigation in mind, but the research assessed downstream consequences on milk, not upstream effects on emissions. The authors are explicit that the results should not be read as proof of methane reduction. What the study does establish is feasibility and safety at scale: commercially available methane-mitigating concentrates can be deployed across real farms for years without sacrificing milk volume, while producing detectable, context-sensitive shifts in nitrogen-related milk traits and a modest rise in somatic cell counts. The next generation of research, the authors argue, must pair direct methane measurement with rumen fermentation analysis, inflammatory marker monitoring, and cow-level physiological profiling. Until then, the Jeju experiment stands as a rare and valuable bridge between the optimistic world of controlled methane trials and the messy, variable reality of the commercial dairy farm, where the climate solution ultimately has to work.

Subject of Research: Field evaluation of methane-mitigating concentrate feed effects on milk production, composition, and udder health in commercial Holstein dairy cows

Article Title: Impact of methane-mitigating concentrate feed on milk production, composition, and udder health in Holstein cows

Article References: Lee, S., Ko, K., Kim, G., Park, J.-E., & Ryu, Y. (2026). Impact of methane-mitigating concentrate feed on milk production, composition, and udder health in Holstein cows. Food Science of Animal Resources, 46(1), Article 49. https://doi.org/10.1007/s44463-025-00033-w

Image Credits: AI Generated

DOI: 10.1007/s44463-025-00033-w

Keywords: methane mitigation, dairy cows, Holstein, milk composition, milk urea nitrogen, somatic cell count, enteric fermentation, feed additives, greenhouse gas emissions, udder health, commercial dairy farms, sustainable dairy production

The research team, led by scientists from Mengniu Dairy’s Ambient Product Research and Development Centres, purchased sixteen commercial UHT whole milk products from the Chinese e-commerce platform Jingdong Mall. Six samples were produced in China, five in Western Europe, drawn from the Netherlands, Germany, Austria, Ireland, and Spain, and five from Australia and New Zealand. Imported products explicitly labeled as grass-fed or pasture were preferentially selected to maximize the likelihood that they represented grazing-based production systems, although the authors caution that label claims do not guarantee the annual diet of any herd. All samples contained only raw milk or organic raw milk with no additives, and all were packed in aseptic cartons.

The analytical arsenal deployed on these sixteen cartons was formidable. Gross composition, including fat, protein, lactose, solid-non-fat, and total solids, was measured by mid-infrared spectroscopy. Fatty acids were quantified by gas chromatography with flame ionization detection according to the Chinese national standard GB 5009.168. Fat-soluble vitamins A and E were determined by high-performance liquid chromatography with diode-array detection, while riboflavin was measured by HPLC with UV/visible detection. Niacin, pantothenic acid, and folic acid were assessed with commercial assay kits, choline by ion chromatography, and a panel of minerals, including calcium, potassium, sodium, magnesium, zinc, selenium, and iodine, by inductively coupled plasma mass spectrometry. Phosphorus was determined spectrophotometrically. This breadth matters because single-nutrient comparisons can be misleading; milk quality is a multivariate property.

The macronutrient results revealed a subtle but telling pattern. Measured fat and lactose levels of the domestic samples were significantly higher than those of the imported milks, and the domestic products showed the highest fat, vitamin E, vitamin B3, zinc, and iodine content, while milk from Australia and New Zealand had the lowest levels of fat, solids, and vitamin A. Interestingly, the measured fat and protein values for domestic milk exceeded typical raw-milk averages reported for China, pointing to standardization practices in dairy processing, particularly for domestic products claiming 3.6 grams of protein per 100 milliliters. Minerals tied to casein micelles, such as calcium, phosphorus, and magnesium, showed no significant regional differences, likely because protein standardization counteracts the feed-driven variation that previous studies have documented for grazing versus total mixed ration systems.

The vitamin findings may be the study’s most counterintuitive result. Fresh and ensiled grass is an excellent source of fat-soluble vitamins, so one might expect pasture-fed European and Oceanian milk to contain more vitamin A and vitamin E. The opposite was observed. The researchers attribute this to the harsher thermal reality of imported UHT milk: longer transportation distances demand longer shelf lives and higher heat loads, and quality reports cited in the paper show imported UHT milk carried markedly higher heat-load indicators such as furosine and lactulose between 2021 and 2023. Vitamin A degrades through isomerization of its unsaturated isoprenoid side chain during thermal processing, and vitamin E loss increases with temperature and holding time. Degradation continues even under refrigeration, with losses of roughly 8 percent for vitamin A and 11 percent for vitamin E after thirty days of storage. In contrast, water-soluble vitamin B2 was higher in imported milk, consistent with its origin in green leafy forage, while vitamin B3, derived mainly from cereal grains, was higher in domestic milk, matching expectations for grain-heavy total mixed rations.

The fatty acid analysis produced perhaps the clearest separation between regions. Total saturated and monounsaturated fatty acids did not differ significantly, but the polyunsaturated fatty acid picture split sharply along the n-3 and n-6 families. Domestic Chinese milk was richer in n-6 fatty acids, including C18:2n-6c, C18:3n-6, C20:3n-6, and C20:4n-6, whereas imported milks carried higher levels of n-3 fatty acids such as C18:3n-3, C20:3n-3, and C20:5n-3. The imported samples achieved an n-3/n-6 ratio of approximately 0.31 to 0.32, compared with only 0.12 for Chinese milk. The biochemistry behind this split is well understood: pasture is rich in alpha-linolenic acid, an omega-3 precursor, while maize silage, cereals, and oilseeds in mixed rations supply abundant linoleic acid, an omega-6. These dietary fatty acids are then elongated and desaturated in the mammary gland, amplifying the regional differences in long-chain polyunsaturates.

Shorter-chain fatty acids told the same story from a different angle. Imported milk contained significantly higher levels of C4, C6, C12, and C14, reflecting the fact that high-fiber pasture diets stimulate de novo fatty acid synthesis in the udder, whereas the high-starch rations of confined systems lower ruminal pH and suppress this synthesis. Odd-chain fatty acids, C11, C15, C17, and C21, were also significantly elevated in imported milk, and these compounds are recognized biomarkers of pasture-based feeding because they arise from rumen microbial fermentation of forage. The paper notes that omega-3 fatty acids are associated with reduced risk of cardiovascular disease, diabetes, cancer, and mental disorders, and that the dietary n-3/n-6 ratio of Chinese consumers is suboptimal. However, the authors are careful to add a crucial caveat: milk products account for only about 2.3 percent of Chinese food intake and roughly 1 percent of daily milk fat consumption, so switching to imported milk alone cannot transform the overall dietary fatty acid profile. Pairing milk with omega-3-rich foods such as deep-sea fish, nuts, and flaxseeds remains essential.

Sensory evaluation added a human dimension to the chemistry. Eight trained, certified assessors evaluated the samples in duplicate on a nine-point hedonic scale after a structured three-day training program. Imported milks scored significantly higher for cowy and tea flavors and for astringency, while domestic samples appeared brighter in color and sweeter. The yellow-cream hue of grass-based milk reflects high carotenoid and riboflavin levels in forage, whereas total-mixed-ration milk tends toward white. The cowy note is linked to compounds such as p-cresol, a consistent marker of pasture diets, and the higher sweetness scores for domestic milk align with its higher measured lactose content. Notably, despite the heavier heat treatment of imported products, no significant difference in cooked flavor emerged between groups. The authors candidly acknowledge a limitation: Chinese assessors unfamiliar with imported milk may score attributes differently from their Western counterparts, and previous cross-cultural work has shown Irish and Chinese panelists interpreting the same pasture-milk attributes in opposing ways.

Principal component analysis wove all these threads together into a single picture. Two principal components explained 56.7 and 18.2 percent of the variance respectively, and the first component cleanly separated domestic from imported milk. Domestic samples clustered tightly, characterized by higher vitamin E, fat, and n-6 fatty acids, while the imported samples scattered more widely, positively correlated with vitamin B2, n-3 fatty acids, short- and medium-chain fatty acids, long-chain fatty acids, astringency, and tea flavor. That dispersion, the researchers suggest, reflects the diversity of feeding systems, processing technologies, and storage conditions across Western European and Oceanian countries, in contrast to the large-scale standardized farming and industrial production that dominates the Chinese dairy sector.

The study concludes with practical recommendations that extend beyond shopping advice. Because average dairy intake among Chinese adults was only 27.6 grams per day in 2018, less than a tenth of the 300 grams recommended in the national dietary guidelines, the authors argue that even meeting the current recommendation would not fully satisfy needs for calcium, selenium, and vitamin B2, and they suggest that intake above 500 grams per day of milk and dairy products may be needed. They also call for exogenous vitamin A fortification, better retention of vitamins during storage and transport, and regulation of grass-fed and pasture label claims in the Chinese market, including nutrient indicators such as n-3 fatty acid content. The work was funded by the China government guides local funds for scientific and technological development under grant number 2024ZY0146, and the authors declare no competing interests. For consumers, the takeaway is refreshingly even-handed: neither domestic nor imported milk is simply better. They are products of two different agricultural philosophies, and understanding that difference is the first step toward an informed choice.

Subject of Research: Comparative nutritional composition, fatty acid profiles, and sensory characteristics of commercial UHT bovine milk from China, Western Europe, and Australia/New Zealand sold in the Chinese market

Article Title: Nutritional composition, fatty acid profiles, and sensory characteristics of commercial bovine milk from different global production regions in the Chinese market

Article References: Yang, J., Wang, M., Hu, P., Li, S., Qian, W., & Li, H. (2026). Nutritional composition, fatty acid profiles, and sensory characteristics of commercial bovine milk from different global production regions in the Chinese market. Food Science of Animal Resources, 46(1), Article 80. https://doi.org/10.1007/s44463-026-00086-5

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00086-5

Keywords: UHT milk, dairy nutrition, fatty acids, pasture feeding, total mixed ration, vitamins, sensory analysis, China dairy market, omega-3, food science, milk composition, principal component analysis