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Effect of 2-hydroxy-4-(methylthio)butanoate (HMTBa) on risk of diet-induced milk fat depression
Dietary polyunsaturated fatty acids (FA) and diet fermentability are key risk factors for diet-induced milk fat depression (MFD). A role for HMTBa in increased milk fat yield has been proposed, but the interaction of HMTBa and dietary risk factors for MFD have not been investigated. The objective was to evaluate the effect of HMTBa (ALIMET® feed supplement, Novus International, Inc., St. Charles, MO, USA) on milk fat synthesis when feeding diets with increasing risk for MFD. Thirty multiparous Holstein cows [227 ± 88 DIM, producing 38 ± 17 kg milk/d (Mean ± SD)] were used in a randomized block design. Treatments were control (corn carrier) and HMTBa (HMTBa fed at 0.1% of the diet DM provided with a corn carrier). The experiment was 70 d and included a 14 d covariate period followed by three phases that fed diets with increasing risk of MFD. During the low-risk phase (28 d) the base diet was balanced to 33.5% NDF and had no exogenous oil, during the moderate-risk phase (14 d) the diet was balanced to 31% NDF and contained 0.75% soybean oil, and during the high-risk phase (14 d) the diet was balanced to 28.5% NDF and contained 1.5% soybean oil. Milk yield, DMI, and BW were measured daily. Milk was sampled every 7 d and analyzed for fat and protein concentration. Data were analyzed using PROC Mixed with repeated measures and the effect of treatment was tested at each time point. There was no overall effect of treatment or treatment by time interaction for DMI, BW, milk yield, and milk protein concentration and yield. A treatment by time interaction was observed for milk fat concentration (P = 0.02) and yield (P = 0.01). HMTBa increased milk fat percent during the high-risk phase on d 63 (2.83 vs 3.55, P < 0.0001) and d 70 (2.91 vs 3.43%, P = 0.005) and increased milk fat yield on d 63 (821 vs 1093 g/d, P = 0.002) and d 70 (771 vs 951 g/d, P = 0.018). In conclusion, HMTBa increased milk fat yield when cows were fed a diet with a high risk of diet-induced MFD.
Keywords: HMTBa, milk fat depression