Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2017
Publication Date: N/A
Citation: N/A Interpretive Summary: Reduced milk fat represents an issue on many dairy farms because the milk price is partially based on milk fat content and because milk fat depression may indicate rumen health problems for the cow. Inhibition of milk fat synthesis is normally caused by bioactive trans fatty acids formed during a specific process in the rumen known as ruminal biohydrogenation. Some feed additives may have the potential to decrease the risk of milk fat depression, but interactions may occur with animal and dietary factors. This study demonstrated that feeding the methionine analog 2-hydroxy-4-(methylthio)butanoate (HMTBa) provides a mechanism to prevent or attenuate biohydrogenation-induced milk fat depression and reduces its occurrence in high-producing cows. This information will be helpful to dairy farmers and dairy cattle nutritionists by demonstrating a dietary option for reducing the risk for milk fat depression in higher risk cows.
Technical Abstract: Diet-induced milk fat depression (MFD) is a multifactorial condition resulting from the interaction of numerous risk factors including diet fermentability and unsaturated fatty acids (FA) concentration, feed additives, and individual cow effects. 2-hydroxy-4-(methylthio)butanoate (HMTBa) is a methionine analog that has been observed to increase milk fat in some cases, and interactions with MFD risk factors may exist. The objective was to evaluate the effect of HMTBa supplementation on milk fat synthesis in cows with different levels of milk production fed diets with increasing risk of biohydrogenation-induced MFD. Sixteen high-producing cows (44.1 ± 4.5 kg milk/d; mean ± standard deviation) and 14 low-producing cows (31.4 ± 4.3 kg milk/d; mean ± standard deviation) were used in a randomized block design. Treatments were unsupplemented control and HMTBa-fed at 0.1% of diet dry matter. 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, the base diet was balanced to 33.5% neutral detergent fiber (NDF) and had no exogenous oil (28 d). During the moderate-risk phase, the diet was balanced to 31% NDF and contained 0.75% soybean oil (14 d). During the high-risk phase, the diet was balanced to 28.5% NDF and contained 1.5% soybean oil (14 d). Milk yield, dry matter intake, and body weight were measured daily. Milk was sampled every 7 d and analyzed for fat and protein concentration and fatty acid profile. Data were analyzed using PROC Mixed with repeated measures, and the effect of treatment was tested at each time point. An interaction of treatment, production-level, and dietary phase was observed. Low-producing cows did not experience substantial biohydrogenation-induced MFD, nor did their milk fat respond to HMTBa. In high-producing cows, HMTBa maintained higher milk fat concentration during the moderate (2.94 vs 3.49%, P = 0.03) and high (2.38 vs 3.11%, P < 0.01) risk phases. High-producing cows receiving HMTBa also had greater milk fat yield (0.94 vs 1.16 kg/d, P = 0.02) and lower trans-10 C18:1 (6.11 vs 1.50, P < 0.001) during the high-risk phase. In conclusion, HMTBa increased milk fat in situations with a high risk of biohydrogenation-induced MFD by decreasing absorption of alternate biohydrogenation intermediates.