The course of pregnancy changes general metabolism and affects ruminal epithelium activity pattern in Zebu beef heifers

Abstract

The present study aimed to investigate metabolic and physiological changes induced by pregnancy, as well as the expression of key genes linked to the absorptive and proliferative activity of the ruminal epithelium towards the end of the gestational period in zebu beef heifers. Twelve ruminally cannulated Zebu beef heifers were randomly assigned into two experimental treatments: a pregnant group (n = 7) and a control group (non-pregnant; n = 5). All heifers received the same diet throughout the experiment. Respiratory and heart rates and plasma glucose levels were assessed just before and four hours after morning feeding at 110, 171, 206, 242, 266, and 286 days of pregnancy (DOP). Blood samples were collected for serum non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), and urea analysis prior to the morning feedings at 110, 206, 266, and 286 DOP. At 215 and 272 DOP the ruminal epithelium was biopsied to evaluate the mRNA expression of key genes involved in remodeling, inflammation, and transport. The respiratory rate was similar (P ≥ 0.79) between groups over days. However, the heart rate increased (P = 0.01) in late-pregnant heifers compared to controls. Blood concentrations of NEFA (P = 0.11) and BHB (P = 0.67) did not vary over the gestation period in pregnant heifers. Glucose concentrations, before morning feeding, were similar during all collection periods with an exception at 286 days (DOP × physiological status interaction; P = 0.05) when glucose was lower in pregnant (83 mg/dL) compared to non-pregnant (107 mg/dL) heifers. The mRNA expression of genes related to cellular remodeling (PCNA and CASP3), inflammation (KLK9 and KLK10), and transport of volatile fatty acids (SLC16A1 and SLC16A3), H+ (SLC9A1), HCO3− (SLC26A3 and SLC26A6), and glucose (SLC5A1) in the ruminal epithelium were downregulated at late gestation. These results suggest that the ruminal epithelium saves energy at late pregnancy to benefit fetal development. In addition, the increase in heart rate coupled with tissue mobilization can be considered homeorhetic mechanisms that help meet fetal nutrient requirements.