Changes in hepatic microsomal triglyceride transfer protein and triglyceride in periparturient dairy cattle

We determined the relationship between microsomal triglyceride transfer pro tein (MTP) (activity, mass, and mRNA) and liver triglyceride concentration in 16 dairy cows (13 multiparous and three primiparous) from 27 d before ex pected calving (d -27) to 35 d postpartum (d 35), the time period when fatt y liver is most likely to develop. In addition, dry matter intake, plasma n onesterified fatty acids (NEFA), and plasma glucose were monitored. There w ere no significant parity x time interactions. Dry matter intake, plasma NE FA, plasma glucose, and liver triglyceride were significantly affected by d ay of sampling. Dry matter intake was 10.7, 8.0, and 19.5 kg/d on d -27, 2, and 35, respectively. Plasma NEFA concentration was higher on d 2 (1113 mu Eq/L) compared with d -27 (201 mu Eq/L) and 35 (358 mu Eq/L). Plasma gluco se concentration was 63.3, 54.3, and 57.8 mg/dl on d -27, 2, and 35, respec tively. Hepatic triglyceride (TG) concentration increased from 1.8 to 11.8% liver TG (DM basis) on d -27 and 2, respectively. There was no difference between hepatic triglyceride concentration on d 2 and 35. There was a signi ficant effect of day of sampling on hepatic MTP activity and mRNA. Hepatic MTP activity decreased from 2.08 to 1.79 nmole triolein transferred/h per m g of microsomal protein on d -27 and 2, respectively, and increased from 1. 79 to 2.17 nmole triolein transferred/h per mg of microsomal protein on d 2 and 35, respectively. Hepatic MTP mRNA increased from d -27 to 2 and remai ned elevated from d 2 to 35. There was no effect of day of sampling on MTP mass. There were no significant correlations between hepatic MTP activity, mass, or mRNA with either liver TG or plasma NEFA on any of the sampling da ys. The cause of a decrease in hepatic MTP activity and increase in mRNA on d 2 is unknown. However, the lack of correlation between MTP activity, mas s, or mRNA with either liver TG or plasma NEFA on d 2 postpartum suggests t hat MTP probably does not play a role in the etiology of fatty liver that o ccurs in dairy cows at calving.