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Abstract: This study determined impacts of a commercial blend of microencapsulated essential oils (EO), fed at increasing dose levels to high yielding primiparous dairy cows, on milk yield and composition. Eight pregnant Holstein heifers, selected to have their parturition within a period of 30d, were kept in tie stalls equipped for individual feeding, and with free access to water, from the 7th month of gestation. At an average of 40d postpartum, cows were assigned to one of four dietary EO levels in a replicated 4×4 Latin square design. The experimental diets (i.e., corn silage, fescue hay and a compound feed, 6.5, 4.4 and 8.7kg DM/d respectively) differed only in the addition level of a microencapsulated EO supplement (RumaXol Feed) mixed at different levels into the compound feed (fed at 1kg/cow day) in order to provide 0, 0.32, 0.64 and 0.96g/d of the EO mixture. The experiment had four experimental periods of 21d, with the last 5d used for collection of faeces and urine, for milk yield and composition recording and measurement of cow biometric data. The dietary EO supplementation had no effect on dry matter (DM) intake, water consumptions or faecal DM, while urine density was (P=0.01) lower at the intermediate EO dosages. Digestibility and biometric measures of cows were not modified by EO feeding. The protein content of milk tended (P=0.06) to be higher at the intermediate EO dosages, as did (P=0.05) the milk energy concentration. However milk and milk component yields were not affected by EO feeding level. [Copyright &y& Elsevier]

Study aims were to investigate associations of hyperketolactia (HYKL) status of Holstein dairy cows between 6 and 60 d in milk (DIM), defined by milk acetone (mACE) and β-hydroxybutyrate (mBHB) content, with daily milk yield and composition. Milk samples (∼5.0 million) were collected over a 5-yr period (2014–2019) within the milk recording system in Poland. Concentrations of mACE and mBHB determined by Fourier-transform infrared spectroscopy were used to categorize samples into 4 ketolactia groups. Based on threshold values of ≥0.15 mmol/L mACE and ≥0.10 mmol/L mBHB, ketolactia groups were normoketolactia (NKL; mACE <0.15 mmol/L and mBHB <0.10 mmol/L), BHB hyperketolactia (HYKL BHB ; mACE <0.15 mmol/L and mBHB ≥0.10 mmol/L), ACE hyperketolactia (HYKL ACE ; mACE ≥0.15 mmol/L and mBHB <0.10 mmol/L), and ACE and BHB hyperketolactia (HYKL ACEBHB ; mACE ≥0.15 mmol/L and mBHB ≥0.10 mmol/L). To investigate ketolactia association with production outcomes, a linear model was developed, including ketolactia group, DIM, parity, their interactions, year-season as fixed effects, and random effects of herd and cow. Among all milk samples, 31.2% were classified as HYKL, and of these, 52.6%, 39.6%, and 7.8% were HYKL ACEBHB , HYKL BHB , and HYKL ACE , respectively. Ketolactia groups differed for all traits studied in all parities and DIM. Among HYKL groups, lowest milk yield was found in HYKL ACEBHB cows, except for 6 to 30 DIM in first- and second-lactation cows. Milk yield of HYKL BHB cows was higher than that of NKL cows until 20 to 30 DIM, and then it was lower than NKL cows. Milk yield of HYKL ACE cows was mostly lower than NKL cows. Energy-corrected milk (ECM) yield of HYKL ACEBHB cows was higher than that of NKL cows until 30 to 35 DIM for second lactation and third lactation or greater, and in the whole study period for first lactation. The yield of ECM for HYKL BHB cows was mostly higher than that of NKL cows, whereas HYKL ACE cows had higher ECM than NKL cows until 15 to 25 DIM and then was lower for the HYKL ACE group. Milk composition differed among HYKL groups. Highest milk fat (MF) and lowest milk lactose (ML) contents were observed in HYKL ACEBHB cows. Cows in HYKL ACEBHB and HYKL BHB groups had higher MF and lower milk protein (MP; except in 6–8 DIM in first lactation) and ML content than NKL cows. Milk fat content was higher in HYKL ACE than NKL cows in first lactation and during the first 30 to 40 DIM in older cows. Lactose content was lower in HYKL ACE than in NKL cows within 30 to 40 DIM; afterward it was higher in NKL cows. Lower MP content was found in HYKL ACE than in NKL cows, except during 6 to 9 DIM for cows in first lactation and third lactation or greater. In conclusion, HYKL is associated with altered milk production in all parities, but a range of these negative relations depends on ketone status addressing both ACE and BHB contents. Further research is needed to ascertain underpinning biochemical defects of HYKL from elevated ACE, alone or in combination with BHB, during early lactation. [ABSTRACT FROM AUTHOR]