Effects of dietary rumen-protected, ruminal-infused, or abomasal-infused choline chloride on milk, urine, and fecal choline and choline metabolite yields in lactating cows.

Current approaches to study choline bioavailability do not account for the ruminal or postruminal bacterial degradation of choline to trimethylamine (TMA) and TMA N-oxide (TMAO). To evaluate choline bioavailability, 8 multiparous Holstein cows (184 ± 109 d in milk) were enrolled in a study with a 4 × 4 Latin square design. Treatments were (1) 0 g/d of supplemental choline chloride (CTR), (2) 16.8 g/d of unprotected choline chloride (CC) delivered as a continuous ruminal infusion (12.5 g choline ion/d; UPC), (3) 27.9 g/d of rumen-protected CC (12.5 g choline ion/d; RPC), or (4) 16.8 g/d of unprotected CC delivered as a continuous abomasal infusion (ADC). Cows were fed every 4 h and milked twice per day. Choline and choline metabolites were analyzed using liquid chromatography and mass spectrometry. Each cow was administered 4.08 L of infusate daily for 5 consecutive days in each period, followed by a 2-d washout period. The statistical model included the fixed effects of treatment, square, period, treatment × square, and the random effect of cow. Mean comparisons of UPC, RPC, and ADC vs. CTR were conducted using the Dunnett test. Milk choline and betaine concentrations and yields (4% and 5% of infused choline for ADC), and plasma choline and betaine concentrations, were greatest for ADC (trt, P < 0.01). Urinary TMAO concentrations were greater for ADC vs. CTR (~4% of infused choline for ADC; P = 0.03). Urinary choline and betaine concentrations and yields were greatest for ADC (~3% and 9% of infused choline for ADC, respectively; trt, P < 0.01). Fecal TMA concentration and yields were highest for ADC (P < 0.01 and P = 0.07, respectively), while fecal betaine concentrations and yields were also greatest for ADC (P = 0.07 and P = 0.03, respectively), whereas fecal choline concentrations and yields were highest for RPC (P = 0.07 and P = 0.02, respectively). Our findings emphasize the importance of measuring choline and choline metabolite concentrations and yields when evaluating choline bioavailability.

Key Words: bioavailability, choline, trimethylamine N-oxide (TMAO)