WHOLE-BODY UREA KINETICS AND FUNCTIONAL ROLES OF UREA TRANSPORTERS AND AQUAPORINS IN UREA SECRETION INTO THE RUMEN IN SHEEP FED DIETS VARYING IN CRUDE PROTEIN CONTENT AND CORN GRAIN PROCESSING METHOD
Date
2023-07-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0008-5585-4210
Type
Thesis
Degree Level
Masters
Abstract
The objectives were to determine the effects of dietary crude protein (CP) content and corn grain processing on serosal-to-mucosal urea flux (Jsm-urea) in ruminal epithelia. Thirty-two Rideau-Arcott lambs were blocked by BW into groups of 4 (i.e., a total of eight blocks) and then randomly allocated within block to 1 of 4 dietary treatments (n = 8) in a 2 × 2 factorial design. Dietary factors were CP content (11% [LP] vs. 16% [HP]) and method of corn grain processing (whole-shelled [WSC] vs. steam-flaked [SFC] corn). Four blocks of animals (n = 4) were used in 4-day continuous infusions of [15N-15N]-urea with concurrent collections of urine and feces to determine whole-body urea kinetics and nitrogen (N) balance. After 23 days of dietary exposure, lambs were killed to collect ruminal epithelia which were mounted in Ussing chambers to determine Jsm-urea. Lambs fed HP had greater N intakes (29.4 vs. 19.1 g/d; P < 0.01) and total N excretion (20.3 vs. 14.5 g/d; P < 0.01) than those fed LP. Endogenous urea-N production (UER) was greater in lambs fed HP compared to those fed LP (29.9 vs. 20.6 g/d; P = 0.02), whereas urea-N secreted into the gut (GER; g/d) and urea-N used for anabolic purposes (UUA; g/d) were similar. Lambs fed LP tended to have greater GER:UER (0.78 vs. 0.66; P = 0.05) and UUA:GER (0.23 vs. 0.13; P = 0.05) ratios, and Jsm-urea (144.7 vs. 116.1 nmol/[cm2 × h]; P = 0.07) compared to those fed HP. Lambs fed SFC had a lower phloretin-insensitive Jsm-urea (87.1 vs. 143.1 nmol/[cm2 × h]; P = 0.02) and tended to have a lower NiCl2-insensitive Jsm-urea (117.4 vs. 178.4 nmol/[cm2 × h]; P = 0.09) compared to those fed WSC, whereas total Jsm-urea and total-insensitive Jsm-urea were similar. Lambs fed SFC tended to have a lower mRNA expression of UT-B (0.89 vs. 1.07; P = 0.08) and AQP-3 (0.90 vs. 1.05; P = 0.07) compared to those fed WSC. These results suggest that urea transport through UT- and AQP-mediated pathways can be upregulated in ruminants by feeding more ruminally-fermentable carbohydrates (manipulated via grain processing).
Description
Keywords
sheep, nitrogen recycling, rumen
Citation
Degree
Master of Science (M.Sc.)
Department
Animal and Poultry Science
Program
Animal Science