ABSTRACT
Objectives were to determine the effects of supplementing increasing amounts of choline ion on hepatic composition and mRNA abundance in pregnant dry cows subjected to a fatty liver induction protocol. Holstein cows (35 primiparous and 41 multiparous) at mean (± standard deviation) of 211 ± 9.9 days of gestation were blocked by body condition (3.59 ± 0.33) and assigned to receive 0, 6.45, 12.90, 19.35, and 25.80 g/day of choline ion as rumen-protected choline (RPC) as a top-dress for 14 days. Cows were fed for ad libitum intake on days 1 to 5 and restricted to 30% of the required net energy for lactation from days 6 to 14 of the experiment. Hepatic tissue was sampled on days 5 and 14 and analyzed for concentrations of triacylglycerol and glycogen, and mRNA abundance was investigated. Orthogonal contrasts evaluated the effects of supplementing RPC (0 g/day vs. rest), and the linear, quadratic, and cubic effects of increasing intake of choline ion from 6.45 to 25.80 g/day. Results are depicted in sequence of treatments from 0 to 25.8. During feed restriction, RPC reduced the concentration of hepatic triacylglycerol by 28.5% and increased that of glycogen by 26.1%, and the effect of increasing RPC intake on triacylglycerol was linear (6.67 vs. 5.45 vs. 4.68 vs. 5.13 vs. 3.81 ± 0.92% wet-basis). Feeding RPC during feed restriction increased abundance of transcripts involved in choline metabolism (CHKA, PLD1), synthesis of apolipoprotein-B100 (APOB100), and antioxidant activity (GPX3), and decreased the abundance of transcripts involved in hepatic lipogenesis (DGAT2, SREBF1) and acute phase response (SAA3). Most effects were linear with amount of choline fed. Changes in hepatic mRNA abundance followed a pattern of reduced lipogenesis and enhanced lipids export, which help explain the reduced hepatic triacylglycerol content in cows fed RPC. Choline exerts lipotropic effects in dairy cows by altering transcript pathways linked to hepatic lipids metabolism.