An Investigation of Colostral IgG in the Neonatal Bovine Intestine from Birth to “Gut Closure”
Creators: Hiltz, Rebecca L
Publisher: name: University of Alberta Library
Year: 2024

<p>IgG absorption from colostrum is essential for transfer of passive immunity in the neonatal calf; despite best practices for colostrum feeding – administering 3L of a colostrum with &gt;50 mg/mL IgG content within 6 hrs of life - some calves still have failure of transfer of passive immunity as defined by a serum IgG content of &lt;1000 mg/mL. The aims of this thesis were to investigate IgG absorption at the tissue level in order to better understand the phenomenon of “gut closure”, or the cessation of macromolecule absorption in the calf that occurs around 24 hrs of life. Kinetics and mechanisms of IgG transport have not been investigated at the intestinal tissue level in the neonatal calf, and labeling methods for IgG have not enabled researchers to distinguish between colostrum derived IgG and experimentally supplemented IgG. A novel ELISA system was developed to distinguish between biotin-labeled IgG and non-labeled IgG when they are held in the same ratio. This ELISA system has the potential to be applied to proteins other than IgG. For animals, Holstein × Angus calves were assigned to one of 6 treatment groups, n = 6, 1) non-fed animals euthanized at 1 hr of life, 2) non-fed animals euthanized at 24 hr24 hrs of life, 3-6) animals fed colostrum at 1 hr of life and euthanized at 6, 12, 18, or 24 hrs of life. Intestinal tissue samples from all calves were used in ex-vivo kinetic experiments to determine IgG transport rate and capacity, and additional samples were analyzed for histological features. IgG was measured in the luminal contents, intestinal tissue, via kinetic experiments, and colocalization to the IgG receptor, FcRn, was performed to analyze the passage and absorption of IgG in the neonatal calf from birth to 24 hr24 hrs of life. Data showed that IgG bioavailability in serum reaches levels indicating transfer of passive immunity has been achieved by 12 hrs of life in fed calves. The lumen of the intestine had high IgG concentrations at 6 hrs of life (5 hrs post feeding) but the concentrations dropped close to 0 by 12 hrs of life (11 hrs post feeding), showing that one feeding of colostrum passes through the intestinal tract, away from the absorptive sites in the small intestine, by 12 hrs of life. In the tissue itself, IgG concentration was highest in the proximal and distal jejunum and 6 and 12 hrs of life, corresponding with increased serum IgG data. However, data showed that IgG transport capacity did not differ between birth and24 hrs of life with animals that were fed colostrum, a novel finding, as the gut has previously been considered to be “closed” by 24 hrs of life. Non-fed animals at24 hrs of life lost the capacity to transport IgG through the intestinal tissue, suggesting that age rapidly decreases absorptive capacity, and that feeding retains the absorptive capacity for IgG. In conjunction, 1 hr and 24 hr old non-fed animals exhibited IgG-negative vesicles in the intestinal villi, while 24 hr old fed animals exhibited IgG-positive vesicles in the intestinal villi.  The presence of empty intestinal vesicles did not correspond with intestinal transport of IgG, and thus IgG-negative vesicle number, thought to indicate transport capacity due to physically available space for absorption of IgG, does not have an effect on transport capacity. In the intestinal villi, IgG was colocalized to FcRn. FcRn was strongly colocalized to lymph vessels and weakly to blood vessels, showing that IgG is preferentially transported into the lymphatics in the calf instead of directly into serum, as has been previously reported in other species. These data suggest that “gut closure”, historically defined as the cessation of macromolecular uptake, does not occur at 24 hrs of life in the neonatal calf. This novel finding challenges previous thinking about the timing of colostrum feeding and the benefits of feeding several colostrum meals past 24 hrs of life.</p>