MFD is a nutritional disorder in dairy cattle characterized by a reduction in milk fat content despite a normal or increased milk yield. This review synthesizes current knowledge on the biological mechanisms and nutritional factors contributing to the development of this condition. Disruptions in rumen fermentation and alterations in fatty acid biohydrogenation (particularly the formation of trans-10 fatty acids) are recognized as central contributors to MFD. Several theories have been proposed to explain its pathophysiology, including the glucogenic, volatile fatty acid, trans fatty acid, and biohydrogenation theories. MFD is most commonly associated with diets low in fiber and high in polyunsaturated fatty acids or starch, which promote the accumulation of fatty acid intermediates that inhibit mammary lipogenesis. Among these, trans-10, cis-12 conjugated linoleic acid is particularly notable for its potent suppression of de novo fatty acid synthesis in the mammary gland. While proper dietary formulation remains the most effective preventive strategy, nutritional interventions such as magnesium-based alkalinizers, sodium bicarbonate, intravenous arginine, and vitamin E have shown promise in mitigating established cases. This review underscores the importance of nutritional management in preserving milk fat synthesis and promoting overall animal health.

Climate change is intensifying heat stress conditions in livestock systems, posing significant challenges to animal welfare, productivity, and food quality. This study aims to investigate the combined effects of seasonal heat stress and postpartum physiology on the milk fatty acid (FA) profile of Holstein dairy cows in Galicia, Spain. Forty milk samples were collected during winter and summer and at 1 week and 1 month postpartum. Fatty acid composition was analyzed via gas chromatography (GC-FID), and heat stress exposure was quantified using the temperature–humidity index (THI). Results revealed that heat stress significantly altered the milk lipid profile, with increased concentrations of short- and medium-chain fatty acids (SMCFA) such as C10:0 and C14:1 (n-5), and conjugated linoleic acids (CLAs), suggesting enhanced de novo lipogenesis and shifts in rumen fermentation. Conversely, unsaturated long-chain fatty acids (LCFAs), including cis-11 C18:1 and cis-13 C18:1, decreased with lactation progression and thermal exposure. Notably, certain LCFAs remained stable under combined seasonal and physiological stress, indicating potential metabolic regulation. These results show how milk composition is sensitive to environmental stress and emphasize the need for climate-resilient management to protect milk quality under global warming.

Heat stress is a physiological challenge for dairy cattle, linked to oxidative imbalance and immune dysregulation. This study evaluated seasonal heat stress effects on systemic redox and inflammatory status in healthy dairy cows and tested saliva as an alternative diagnostic fluid to serum. A total of 114 clinically healthy Holstein cows were sampled across summer, autumn, and winter (38 cows per season). Environmental exposure was quantified using the temperature–humidity index (THI). Paired saliva and serum samples were analyzed for total oxidant status (TOS), total antioxidant capacity (TAC) and adenosine deaminase (ADA); the oxidative stress index (OSI = TOS/TAC) was calculated. In saliva, TOS, TAC and ADA were significantly lower in summer than in autumn and winter, while salivary OSI remained stable across seasons. In serum, summer was characterized by increased TOS and OSI together with reduced ADA activity, indicating systemic oxidative stress accompanied by diminished ADA-linked immune activation under heat stress. Although salivary markers correlated with THI, saliva did not mirror the systemic oxidative imbalance detected in serum. Under the conditions and biomarkers evaluated, serum provided a more reliable assessment of heat-stress-related redox and immune disturbances in dairy cattle, whereas saliva showed limited utility as a substitute for monitoring.

This study examined dietary determinants of enteric methane (CH4) emissions in high-yielding Holstein Friesian dairy cows across different physiological stages. Emissions were estimated using the IPCC Tier 2 methodology during peak lactation, the full lactation cycle, and the dry period in two commercial groups with distinct productivity. Group A (38–40 kg milk/day) showed higher peak dry matter intake and fiber content than Group B (32–35 kg milk/day), which had greater ether extract (EE) levels. Peak-lactation CH4 emissions were significantly higher in Group A (P < 0.05), while dry-period values did not differ (P > 0.05). Dietary EE was inversely associated with CH4 output, suggesting a potential mitigation pathway. Phase-specific regression models (adjusted R2 = 0.88–0.93) confirmed diet composition and physiological stage as major drivers of emissions. Digital twin simulations based on these models offer a non-invasive, reproducible tool for predicting emission scenarios, which is particularly valuable in farms where direct measurements are impractical. These findings highlight the feasibility of integrating diet optimization and predictive modeling into herd management strategies, enabling substantial reductions in CH4 emissions while sustaining milk yield and overall productivity in intensive dairy systems.

BACKGROUND: Bovine milk is a major dietary source of lipids whose fatty acid (FA) profile shapes its nutritional and technological quality, yet its natural variation is commonly described using fixed days‐in‐milk windows that ignore individual peak‐yield timing and parity‐specific metabolism. We used routine milk‐recording data and Fourier transform mid‐infrared spectroscopy (FT‐MIR) to characterize parity‐ and stage‐dependent dynamics in milk composition, defining lactation stages relative to each cow's model‐based peak yield. RESULTS: A total of 10 209 test‐day records from 677 Holstein cows (160 primiparous; 517 multiparous) from a commercial herd in Galicia (Spain) were analyzed for milk components, FA groups and individual FAs, β ‐hydroxybutyrate (BHB) and udder‐health traits using linear mixed models. Multiparous cows had higher milk fat, BHB and somatic cell count and higher concentrations of most FA fractions, whereas primiparous cows had higher lactose, protein and urea ( P < 0.05); peak‐referenced stage effects were larger and more coherent in multiparous cows. Disaggregating multiparous cows by lactation number revealed consistent gradients with advancing parity (declining de novo synthesized FAs and rising BHB and somatic cell count) superimposed on, but not overturning, the primiparous–multiparous contrast. CONCLUSION: Parity structure and peak‐referenced lactation staging are practical, FT‐MIR‐measurable determinants of raw‐milk fat quality; accounting for them supports more precise milk characterization and stage‐ and parity‐informed standardization of dairy products for human nutrition. © 2026 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

While the myostatin (MSTN) gene is responsible for the double-muscled phenotype in cattle and has been associated with alterations in metabolism and energy homeostasis. its potential effects on sperm function and fertility remain poorly understood. This study evaluated whether the MSTN genotype affects post-thaw sperm cryotolerance and its relationship with field fertility in Asturiana de los Valles bulls. Frozen-thawed semen from 15 homozygous MSTN-mutated (mh/mh) and 15 wild-type (+/+) bulls were assessed after 30 and 240 min of incubation at 37 °C. Sperm motility and kinematic parameters were analyzed by computer-assisted sperm analysis (CASA), whereas sperm functionality variables were evaluated by flow cytometry. Fertility was assessed using 90-day non-return rates (NRR) from 10,416 artificial inseminations. Post-thaw incubation significantly reduced sperm motility and altered all CASA kinematic parameters. Although total motility declined more markedly over time in MSTN carriers, most kinematic descriptors did not differ between genotypes. In contrast, flow cytometry revealed clear genotype-dependent differences. Sperm from MSTN carrier bulls showed lower acrosome integrity, increased membrane lipid disorder, reduced intracellular calcium levels, and altered oxidative status, together with significant Genotype × Time interactions for reactive oxygen species, superoxide production, and calcium dynamics. These findings indicate reduced functional stability and lower cryotolerance in sperm from MSTN carriers. Fertility analyses further showed that post-thaw sperm viability after prolonged incubation was positively associated with fertility at first service in MSTN carriers, whereas CASA-derived kinematic traits exhibited weaker and non-genotype-specific associations. In conclusion, the MSTN genotype negatively affects post-thaw sperm cryotolerance and functional stability. Reduced fertility in double-muscled bulls appears to be more closely related to impaired resilience to cryopreservation-induced stress than to alterations in conventional sperm kinematic parameters.