BETA-HYDROXYBUTYRATE PROFILE OF HIGH-YIELDING DAIRY COWS OF A BRAZILIAN INTENSIVE SYSTEM

Abstract Text: This study aimed to investigate the beta-hydroxybutyrate (BHB) profile of high-yielding primiparous and multiparous cows according to milk yield level.  A total of 174 Holstein cows was evaluated and divided as: (1) primiparous with mean milk yield equal to or higher than 35 kg/d (42.92±0.78 kg/d) (HP group, n=37); (2) primiparous with mean milk yield lower than 35 kg/d (26.44±0.91 kg/d) (LP group, n=50); (3) multiparous with mean milk yield equal to or higher than 35 kg/d (44.28±0.87 kg/d) (HM group, n=37) and (4) multiparous with mean milk yield lower than 35 kg/d (24.87±0.91 kg/d) (LM group, n=50). The animals belonged to a commercial herd located in São Paulo State, Brazil, and were kept in free stall barns, according to their production level, and were given high-concentrate diet based on NRC recommendations (NE_L: H groups: 1.74 MCal/kg DM and L groups: 1.56 MCal/kg DM). Blood samples were collected from the coccygeal vein to evaluate BHB by an enzymatic method using a commercially available kit (Randox-Ranbut Laboratories, Oceanside, CA). The mean lactation period of all evaluated cows was 216±12. Statistical analysis was performed using SAS software by One-way ANOVA and Pearson Correlation Test. The mean dry matter intake of each free stall barn during the period in which blood samples were collected was similar between groups (HP: 24 kg/d; LP: 22.7 kg/d; HM: 26.9 kg/d and LM: 22.7 kg/d). There were no statistical differences between groups (P>0.05). The BHB concentrations for primiparous groups were: HP 0.45±0.05 mmol/L, and LP 0.48±0.08 mmol/L; for the multiparous ones, HM 0.42±0.04 mmol/L, and LM 0.42±0.09 mmol/L. When the same production level was compared, HP and HM tended to have a negative correlation, and so did LP and LM (Pearson´s correlation coefficients: -0.26 and -0.22, respectively); when the same category was compared, both HP – LP and HM – LM combinations tented to have a positive correlation (0.21 and 0.40, respectively). The results suggest that the cows with the mean lactation period in this study did not show a negative energy balance (NEB), probably due to the fact that milk production requirements were provided by their diet, which did not alter BHB concentration levels, an NEB marker.

Keywords: beta-hydroxybutyrate; dairy cows; negative energy balance.