Greenhouse Gas Emissions, Ultrasound Imaging And Productive Parameters Changes In Dairy Cows Affected By Ketosis

Ketosis is a metabolic disorder of dairy cows characterized by elevated levels ketone bodies, especially β-hydroxybutyrate (BHB). A BHB concentration of 1.0 mmol/L is the common cut-off for subclinical ketosis. Non-CO2 sources account for 25% of total greenhouse gas (GHG) emissions, with CH4 comprising 80% from livestock. CH4 is produced through microbial fermentation in the rumen. Ketotic cows show elevated CH4 substrates by metabolomics, suggesting a link between metabolic disease and CH4 production. The aim of the study was to assess the link between GHG emissions and ketosis through ultrasound imaging and productive performances in dairy cows. Experimental procedures were approved by Ethical Committee for Animal Welfare of University of Padua (protocol n. 103549/2024). A total of 60 Holstein-Friesian multiparous dairy cows were enrolled from a single farm. All animals were evaluated with blood BHB measurement on field, ultrasound examinations of the liver, longissimus dorsi, and rumen wall at 7, 14, 21 and 28 ±2 days post-partum. Animals were divided into two groups according to BHB: CTR or control (BHB<1.0 mmol/L; n=43); KET or subclinical ketosis (BHB≥1.0 mmol/L; n= 17). Rumen fluid sampling via stomach tube was performed only at the first diagnosis of ketosis to assess rumen pH. Instead, the rumen sampling was performed at 21 days for CTR. Moreover, animals were daily evaluated for GHG (CH4, CO2 and H2) using the GreenFeed system (C-Lock Inc., Rapid City, SD, USA) device for all the study period. Statistical differences among groups were evaluated by mixed model. A Spearman correlation matrix was used to assess relationship among parameters. A p≤0.05 was accepted. The BHB concentrations were higher in KET for all time points. Generally, KET animals produced less milk than CTR with no differences between groups in protein and fat contents. The KET exhibited higher CH4 emissions, and lower CO2 and H2 compared to CTR at all time points. Moreover, KET had lower portal vein diameter and area at 7, 14, and 21 days, and greater liver depth at 14, 21, and 28 days. Back-fat thickness was greatest at 7 days in KET group followed by a marked reduction over time. Instead, the CTR had not differences over the trial. The rumen wall thickness was generally higher in KET, especially at 7 days with a 5.96 of rumen pH. Afterwards, rumen pH increased in KET animals with no difference compared to CTR at 21 days. Positive moderate correlations were observed between portal vein depth and milk production, as well as between BHB and CH4, while a negative moderate one was found between BHB and CO2. The findings of this study highlight the negative impact of subclinical ketosis on both animal performance and GHG emissions in dairy cows. In particular, ketosis reduced milk yield and portal vein diameter and area, and increased CH4 emissions, liver depth, rumen wall thickness, and back-fat loss. In conclusion, these results emphasize the need for ketosis management to improve both animal welfare and environmental impact.