Bioavailability of Rumen Protected Histidine in Blood Plasma of Lactating Dairy Cows

• Martha Mueller, Pre-Veterinary Medicine and Animal Biosciences, University of Delaware

• Tanya Gressley, Animal and Food Sciences, University of Delaware

Mueller, M. Tobat, B. Albaugh, S. Torgerson, M. Bhandari, Z. Hobson-Gladney, T. Gressley

Reducing dietary crude protein in the dairy cow diet has been shown to increase nitrogen efficiency, reducing feed costs and improving environmental sustainability on dairy farms.  However, reducing dietary crude protein causes the cow to rely on rumen microbes to supply amino acids, thus limiting some essential amino acids needed for milk production.  In addition to Lysine and Methionine, Histidine is a potential limiting essential amino acid in low crude protein diets. Previous studies demonstrated histidine supplementation improved milk production by increasing milk yield and milk true protein concentration and yield. Supplemented histidine must be protected from rumen microbes that degrade it and limit availability in the intestine. This study evaluated the relative bioavailability of rumen protected histidine (RPHis) compared to a non-rumen protected histidine control. Four ruminally-canulated multiparaous lactating dairy cows were assigned to a 2 ✕ 2 replicated Latin square design across 2 experimental periods. Treatments included histidine HCL monohydrate as the control and a rumen-protected histidine product (RPHis1).  The unprotected histidine control was administered via abomasal infusion and RPHis1 was dosed into the reticulum.  Blood samples were collected prior to infusion at 0 hours and 1, 2, 3, 4, 6, 9, 12, 24, and 48 hours post-infusion.  10 mL of blood were collected through jugular catheters, deposited in 10 mL test tubes, and transported in an ice-filled container.  The blood samples were centrifuged at 2000 x g for 20 minutes at 4°C.  Once centrifuged, the separated plasma was pipeted into two cryovials per sample and stored at -80°C.  Histidine concentrations across sampling times will be evaluated using AUC and dose response modeling to determine it’s bioavailability.  It is expected that RPHis will be more available in the intestine than the control treatment.