Milk fat response and milk fat and urine biomarkers of microbial nitrogen flow during supplementation with 2-hydroxy-4-(methylthio)butanoate

Abstract

2-Hydroxy-4-(methylthio)butanoate (HMTBa) is a methionine analog that has been observed to attenuate biohydrogenation (BH)-induced milk fat depression (MFD), possibly through reducing the shift to altered BH pathways. It has also been suggested that HMTBa increases microbial protein synthesis in the rumen. Our objectives were to stimulate BH-induced MFD and (1) verify HMTBa inhibition of BH-induced MFD and changes in milk fatty acids (FA) associated with altered rumen BH (i.e., trans-10 C18:1); and (2) determine the effect of HMTBa on milk fat (i.e., odd-and branchedchain FA) and urine biomarkers related to microbial N flow. Twenty-four multiparous cows (45.6 ± 8.5 kg of milk/d; mean ± standard deviation) and 12 primiparous cows (32.8 ± 3.1 kg of milk/d) were arranged in a crossover design. Treatments were unsupplemented control and HMTBa fed at 0.1% of diet dry matter intake. The experiment was 80 d and included a 10-d pretrial covariate period. Each experimental period included 2 phases that differed in risk for BH-induced MFD, including a 28-d low-risk phase (31.6% neutral detergent fiber, 21.8% starch, and no oil) and a 7-d moderate-risk phase (28.7% neutral detergent fiber, 28.1% starch, and 1.0% soybean oil). We found no interaction of treatment and parity. Milk fat yield (1.43 ± 0.51 kg/d) and milk fat trans-10 C18:1 (0.42 ± 0.08 g/100 g of FA) did not differ between treatments during the low-risk phase. However, during the moderate-risk phase, HMTBa maintained higher milk fat concentration (3.91 vs. 3.79%), tended to maintain higher milk fat yield (1.44 vs. 1.38 kg/d), and decreased milk fat trans-10 C18:1 (0.61 vs. 0.93% FA) compared with control. Additionally, HMTBa increased milk fat concentration and secretion of odd-and branched-chain FA by 5.3 and 10.2%, respectively, but urinary biomarkers of microbial N flow (i.e., purine derivatives) did not differ between treatments. However, rumen bacterial samples were not available to provide cow-or treatment-specific microbial protein-to-marker ratios, which is a critical source of variation. Additionally, transfer of odd-and branched-chain FA to milk is dependent on several factors that may affect interpretation of these biomarkers. In conclusion, HMTBa decreased absorption of alternate BH intermediates and maintained higher milk fat when feeding a diet with moderate-risk for MFD.

Effect of 2-hydroxy-4-(methylthio) butanoate (HMTBa) supplementation on rumen bacterial populations in dairy cows when exposed to diets with risk for milk fat depression

“…Third, in agreement with the findings by Baldin et al (2019) and M. Baldin, G. I. Zanton (USDA, Madison, WI), and K. J. Harvatine (unpublished data) that no differences were noted in cis-9,trans-11 CLA isomers between control and HMTBa groups, no bacterial populations revealed any significant positive or negative associations with this isomer. For example, the genus Butyrivibrio, known for its role in BH (Lourenço et al, 2010), stayed consistent between treatment groups and did not have positive or negative correlations with FA isomers.…”

“…A challenge model has been useful in testing the effect of feed or supplements on induction of diet-induced MFD. Baldin et al (2018Baldin et al ( , 2019…”

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

“…Taken together, investigations of the effect of HM-TBa in conditions of BH-induced MFD indicate that it may act as a rumen modifier and stabilize rumen BH (Baldin et al, 2018b(Baldin et al, , 2019. The hypothesis of the current experiment was that HMTBa would stabilize rumen BH by modifying rumen environment or protozoa abundance when risk of BH-induced MFD was increased by increasing dietary starch and UFA.…”

“…A first goal of this study was to replicate HMTBa inhibition of BH-induced MFD when dietary starch and UFA were increased (see Baldin et al, 2018bBaldin et al, , 2019. The current study focused on a moderate-risk challenge diet (29.3% starch, 3.80% UFA, and 29.1% NDF on DM basis) targeting approximately a 20% reduction in milk fat and increasing milk fat trans-10 18:1 to approximately 1% of FA because this challenge was sufficient to see an effect of HMTBa in the previous studies and more closely represents on-farm scenarios where small modifications in the diet increase the risk of BH-induced MFD.…”

“…A meta-analysis reported by Zanton et al (2014) observed increased milk fat yield with supplementation of the methionine analog 2-hydroxy-4-(methylthio) butanoate (HMTBa). More recently, supplementation with HMTBa has been demonstrated to attenuate BHinduced MFD when increasing dietary starch and UFA (Baldin et al, 2018b(Baldin et al, , 2019. The first experiment demonstrated that HMTBa decreased trans-10 BH intermediates associated with BH-induced MFD in milk fat in high-producing cows when fed diets high in starch and UFA.…”