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The aim of the present study was to evaluate the substitution of liquid malt extract for propylene glycol in the treatment of ketotic cows and to assess the changes in the patterns of beta-hydroxybutyrate (BHB), insulin, glucose concentrations, and productive and reproductive performance. On day 3 postpartum, blood samples were collected from 327 fresh cows, and cows with serum BHB concentrations ranging from 1.2 to 2.9 mmol/L were identified as subclinical ketosis. One hundred and twenty cows with subclinical ketosis were selected and blocked based on their parity (second, third, or higher parity) and body condition score (BCS: BCS < 3.25, 3.25 ≤ BCS ≤ 3.75, BCS > 3.75). The cows were randomly assigned to one of four experimental groups: 300 ml propylene glycol (PG), 300 ml malt extract (M300), 600 ml malt extract (M600), or 150 ml propylene glycol plus 150 ml malt extract (MPG). The treatments were applied from the time of clinical ketosis diagnosis (days 4 to 8 postpartum) for a period of five days. During the 120 minutes following the administration on day 8 of lactation, the serum BHB concentration in cows from the M600 group was higher compared to the MP300 (P = 0.01) and PG (P = 0.04) groups; however, no significant difference was observed between the M300 and MP300 groups compared to PG (P > 0.05). At 40 minutes (P = 0.01) and 80 minutes (P = 0.01) after administration, the BHB concentration in cows from the M600 group was higher compared to the PG group; however, no significant difference was observed between PG and the M300 or MP300 groups (P > 0.05). The treatment by time interaction showed that, at 40 minutes after administration, cows in the M600 group tended to have lower serum insulin concentrations compared to the PG group (P = 0.08).At 60, 80, and 120 minutes post-treatment, the M600 group had lower serum insulin concentrations compared to the PG group (P < 0.05). On the last day of treatment, during 120 minutes post-treatment, the average serum glucose concentration in the M600 group was lower compared to PG (P < 0.05). However, no difference was observed in glucose concentrations between MP300, M300, and PG groups (P > 0.05). The interaction of treatment by time showed that at 40, 60, and 80 minutes post-treatment, serum glucose concentrations were lower in the M600 group compared to the PG group (P > 0.05).Over the first 21 days postpartum, serum concentrations of BHB, insulin, and glucose were significantly influenced by the treatments (P < 0.05) and time (P < 0.01). Cows in the M600 group had higher BHB concentrations (P = 0.02), and lower insulin (P = 0.03) and glucose (P = 0.01) concentrations compared to those in the PG group. No significant difference was observed in serum BHB, insulin, and glucose concentrations between M300, MP300, and PG groups (P > 0.05). Milk production and milk composition were not affected by the treatments (P > 0.05). In alignment with the BHB serum results, cows in the M600 group had higher molar percentages of butyric acid and, consistent with insulin and glucose findings, lower molar percentages of propionic acid compared to the PG group (P < 0.05). Although ketosis incidence during the treatment period and the first 21 days postpartum was not affected by treatment (P > 0.05), cows in the M600 group showed a higher tendency for subclinical ketosis compared to those in the PG group, with a 2.19 times higher incidence on day 8, 3.25 times on day 14, and 3.28 times on day 21 (P = 0.1). In conclusion, liquid malt extract may influence metabolic changes in ketotic cows, where the administration of 300 ml or 150 ml malt extract plus 150 ml PG resulted in similar effects on BHB, insulin, and glucose concentrations compared to PG. However, higher doses of malt extract resulted in negative effects on blood metabolites compared to PG. Ultimately, it appears that malt extract may have a reducing effect on serum BHB and the incidence of subclinical ketosis.
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