Impact Of Subclinical Ketosis On Greenhouse Gas Emissions And Ultrasound Imaging In Dairy Cows

Introduction After calving, cows typically experience a negative energy balance, leading to mobilization of body reserves, especially adipose tissue. Ketosis is a metabolic condition of dairy cows, characterized by increased levels of ketone bodies, particularly β-hydroxybutyrate (BHB). A BHB threshold of 1.0 mmol/L is typically used to diagnose subclinical ketosis. This condition affects up to 56% of cows in early lactation and it is influenced by factors such as body condition at calving. Excessive lipid mobilization is also associated with hepatic fat accumulation and muscle catabolism, both assessable through ultrasonography. Around 25% of total greenhouse gas (GHG) emissions originate from non-CO₂ sources, with methane (CH₄) representing approximately 80% of emissions from livestock. The CH₄ is the major non-CO₂ greenhouse gas produced in the rumen. Metabolomics analyses have shown that ketotic cows possess higher levels of CH₄ precursors, indicating a potential connection between metabolic disorders and CH₄ output. Objective The aim of the study was to determine the impact of subclinical ketosis on GHG emissions and ultrasound imaging of liver, back fat and muscle. Materials and methods Study 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 (CERZOO ltd, Piacenza, Italy). All animals were evaluated at 7, 14, 21, and 28 ± 2 days in milk (DIM) through field measurement of BHB, ultrasound imaging, and GHG monitoring. BHB was assessed using a portable digital meter and specific blood ketone test strips. Based on BHB level, cows were divided into two groups: control (CTR, BHB < 1.0 mmol/L; n = 43) and subclinical ketosis (KET, BHB ≥ 1.0 mmol/L; n = 17). Ultrasound examinations of the liver, back-fat (BFT), and longissimus dorsi muscle were performed using a Mylab™ OneVET portable scanner (ESAOTE S.p.A., Genoa, Italy) equipped with a multifrequency convex probe. The following parameters were recorded: portal vein diameter (PVD), depth (DPV), area (PVA), and liver depth (LD). Daily CH₄, CO₂, and H₂ emissions were measured using the GreenFeed system (C-Lock Inc., Rapid City, SD, USA). Statistical analyses included a mixed model to detect differences between groups. Significance was set at p ≤ 0.05. Results Significant differences in BHB concentrations were observed between groups at all-time points (p < 0.001), with higher levels in KET animals. Ultrasound data revealed lower PVD and PVA in KET cows at days 7, 14, and 21, suggesting impaired hepatic perfusion. In contrast, CTR animals showed a time-related decrease in DPV, with the highest value at 7 DIM (122 mm). The LD was higher in KET cows at 14, 21, and 28 DIM (≥ 156 mm), consistently exceeding the 152.6 mm threshold for hepatic lipidosis. The BFT was initially greater in KET cows but declined markedly over time, unlike CTR animals whose BFT remained stable. This pattern suggests accelerated lipolysis in KET cows, which also had higher pre-partum fat reserves. No significant group differences were observed for longissimus dorsi thickness, indicating muscle reserves were relatively preserved across both groups. Regarding GHG emissions, KET cows emitted significantly more CH₄ (392 ± 27.2 g/day) than CTR (216 ± 16.3 g/day; p < 0.001). CO₂ emissions were lower in KET (10,838 ± 355.03 g/day) than CTR (12,209 ± 215.35 g/day; p = 0.006), and H₂ was also reduced in KET (0.83 ± 0.52 g/day vs. 2.01 ± 0.51 g/day; p = 0.023). Conclusion The findings of this study highlight the negative impact of subclinical ketosis on both GHG emissions and ultrasound imaging in dairy cows. In particular, ketosis reduced portal vein diameter and area, and increased CH4 emissions, liver depth, and back-fat loss. In conclusion, these results emphasize the need for ketosis management to improve both animal welfare and environmental impact.