Effect of 2-hydroxy-4-(methylthio)butanoate (HMTBa) on milk fat, rumen environment and biohydrogenation, and rumen protozoa in lactating cows fed diets with increased risk for milk fat depression

Authors: BALDIN, MICHEL - Pennsylvania State University; GARCIA, DAVID - Pennsylvania State University; Zanton, Geoffrey; HAO, FUHUA - Pennsylvania State University; PATTERSON, ANDREW - Pennsylvania State University; HARVATINE, KEVIN - Pennsylvania State University

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2022
Publication Date: 9/1/2022
Citation: Baldin, M., Garcia, D., Zanton, G.I., Hao, F., Patterson, A.D., and Harvatine, K.J. 2022. Effect of 2-hydroxy-4-(methylthio)butanoate (HMTBa) on milk fat, rumen environment and biohydrogenation, and rumen protozoa in lactating cows fed diets with increased risk for milk fat depression. Journal of Dairy Science. 105(9):7446–7461. https://doi.org/10.3168/jds.2022-21910
DOI: https://doi.org/10.3168/jds.2022-21910

Interpretive Summary: Dairy rations that target high yields of milk often increase the risk for milk fat depression which is a reduction in milk fat production caused by bioactive fatty acids (FA) produced during altered rumen metabolism of unsaturated FA. 2-Hydroxy-4-(methylthio)butanoate (HMTBa) has been observed to reduce ruminal formation of bioactive trans fatty acids that inhibit milk fat synthesis. This study substantiates the fact that feeding HMTBa attenuates biohydrogenation-induced milk fat depression and demonstrates a functional effect of HMTBa in benefiting rumen biohydrogenation and increasing ruminal protozoa abundance.

Technical Abstract: Biohydrogenation-induced milk fat depression (MFD) is a reduction in milk fat synthesis caused by bioactive fatty acids (FA) produced during altered rumen metabolism of unsaturated FA. The methionine analog 2-hydroxy-4-(methylthio)butanoate (HMTBa) has been shown to reduce the shift to the alternate biohydrogenation pathway and maintained higher milk fat yield in high producing cows fed diets lower in fiber and higher in unsaturated FA. The objective of this experiment was to verify the effect of HMTBa (ALIMET, Novus International, Inc., St. Charles, MO, USA) on rumen biohydrogenation and milk fat synthesis. Twenty-two rumen cannulated high-producing Holstein cows [168 ± 66 DIM; 42 ± 7 kg milk/d (Mean ± SD)] were used in a randomized design performed in two blocks (1 = 14 cows, 2 = 8 cows). Treatments were control (corn carrier) and HMTBa (0.1% of diet DM). The experiment included a 7-d covariate period followed by three phases that fed diets with increasing risk of MFD. The diet during the covariate and low-risk phase (7 d) was 32% NDF with no additional oil. The diet during the moderate-risk phase (17 d) was 29% NDF with 0.75% soybean oil. Soybean oil was increased to 1.5% for the last 4 d. There was no effect of block or interaction of block and other fixed effects. There was no overall effect of treatment or treatment by time interaction for DMI, milk yield, and milk protein concentration and yield. Overall, HMTBa increased milk fat percent (3.2 vs 3.6%, P < 0.01) and yield (1342 vs 1543 g/d, P = 0.02) and there was no interaction of treatment and dietary phase. Additionally, HMTBa decreased the concentration (1.29 vs 0.81 g/100 g of total FA, P = 0.02) and yield (14.7 vs 10.9 g/d, P = 0.01) of trans-10 18:1 in milk across the entire experiment. Ruminal pH and concentration of total volatile fatty acids were not affected by HMTBa. No treatment difference was observed for nine selected common culturable bacterial species and fungi, but HMTBa increased total rumen protozoa (1.01 vs 1.34 abundance relative to pretrial, P = 0.03). Additionally, HMTBa increased the fractional rate of a-linoleic acid clearance from the rumen following a bolus (0.022 vs 0.034 h-1, P = 0.01). In conclusion, HMTBa prevented the increase in trans FA associated with MFD and maintained milk fat yield when cows were fed a diet with moderate risk of diet-induced MFD through increased biohydrogenation rate and protozoa abundance.