Effect of production level and parity on responses of milk fat to supplementation with 2-hydroxy-4-(methylthio)butanoate (HMTBa)

Abstract Text: We previously reported that high producing cows are at higher risk of biohydrogenation-induced milk fat depression (MFD) and that HMTBa reduced MFD in high-risk situations.  The objective was to determine the relationship between production level and parity and responses of milk fat to supplementation with HMTBa (ALIMET, Novus International, Inc., St. Charles, MO, USA).  Twelve primiparous and 24 multiparous Holstein cows were used in a cross over design preceded by a 14 d pretrial period.  The 35 d treatment periods included 28 d of a low risk diet (31% NDF, 27% starch and 4.2% EE) followed by 7 d of a moderate risk diet (29% NDF, 30% starch and 1% soybean oil).  Treatments were control (corn carrier) and HMTBa (0.1% of diet DM). At the end of pretrial period cows averaged 127 ± 33 DIM (Mean ± SD) and 41 ± 9 kg milk/d (min. 27 and max. 61 kg/d).  Milk yield and DMI were measured daily and milk was sampled every 7 d and analyzed for fat and protein concentration.  Data were analyzed using PROC Mixed with repeated measures, with cow by treatment as the subject and the effect of treatment was tested at each time point.  During the low risk phase, no overall effect of treatment or trt*time interactions were observed for DMI, milk yield, milk fat and protein yield and concentration (P > 0.2 for all).  Additionally, no trt*parity or trt*parity*time interactions were observed for milk fat concentration (P = 0.2) and yield (P = 0.9).  During the moderate risk phase, no overall effect of treatment or trt*time interactions were observed for DMI, milk yield, and milk protein concentration and yield (P > 0.4 for all).  HMTBa supplementation maintained higher milk fat concentration (3.67 vs 3.86, P < 0.001) and yield (1.37 vs 1.47, P < 0.001) at the end of moderate risk phase.  No trt*parity or trt*parity*time interactions were observed for milk fat variables (P > 0.4 for both).  On d 35, responses (HMTBa – Control) of milk fat concentration and yield correlated positively with pretrial milk yield (0.35, P = 0.03, and 0.38, P = 0.02, respectively).  In conclusion, HMTBa maintained milk fat yield when cows were fed a diet with moderate risk of biohydrogenation-induced MFD and milk fat response to treatment was correlated with production level but not affected by parity.  

Keywords: HMTBa, milk fat