Bioavailability of Different Formulations of Rumen-Protected Lysine in Dairy Cattle

• Dylan Friedman, Pre-Veterinary Medicine and Animal Biosciences, University of Delaware

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

Lysine is an essential amino acid critical for milk protein synthesis. Dairy cattle diets are often deficient in absorbed lysine, and supplemental dietary lysine can improve lactational performance. Unprotected lysine will be degraded in the rumen by rumen bacteria. As such, it is necessary to supplement dietary lysine using rumen-protected lysine (RPL) forms that are protected from rumen degradation but available for intestinal absorption. There is a need to identify RPL products with high bioavailability. The objective of this experiment was to determine the lysine bioavailability of three different formulations of RPL. The study used four lactating, ruminally cannulated Holstein dairy cows (days in milk from 181 to 312 and milk yield from 25 to 48 kg/d at the start of the study) to measure the bioavailability of each RPL treatment. A 4 x 4 Latin square design was implemented where each cow received each treatment over four back-to-back experimental periods (P), each lasting two days with a three day rest separating P2 and P3. Treatments were ruminal administration of three different RPL test products or abomasal administration of unprotected lysine hydrochloride, all administered as a single pulse dose at the start of each P providing 120 g of lysine. Blood samples were taken at 0, 1, 2, 3, 4, 6, 9, 12, 24 and 48 hours after administering the treatment. Samples were centrifuged and are being analyzed for plasma lysine concentration. Bioavailability of each test product will be determined by comparing the plasma lysine response of each RPL to that of the unprotected lysine control. We hope to identify a product with high lysine bioavailability so that our findings can be used to develop the product for commercial use.