Abstract #502

# 502
Lactation performance and energetic metabolism of transition cows fed rumen protected glucose.
Carrie S. McCarthy*1, Brooke C. Dooley1, Emily H. Branstad1, Anthony J. Kramer1, Erin A. Horst1, Edith J. Mayorga1, Mohmmad Al-Qaisi1, Megan A. Abeyta1, Gabriela Perez-Hernandez2, Brady M. Goetz1, Alejandro R. Castillo3, Mark R. Knobbe4, Charles A. Macgregor4, Juan P. Russi5, J. A. D. R. N. Appuhamy1, 1Iowa State University, Ames, IA, 2Universidad Autónoma Chapingo, Chapingo, México, 3University of California, Cooperative Extension, Merced, CA, 4Grain States Soya, Inc, West Point, NE, 5Rusitec Argentina, General Villegas, Buenos Aires, Argentina.

Carbohydrate supply and availability in the small intestine may limit milk production in transition dairy cows. Thus, experimental objectives were to evaluate the effects of rumen protected glucose (RPG) on milk production and post-absorptive metabolism in transition dairy cows. Fifty-two multiparous cows were blocked by previous 305ME and randomly assigned to one of 2 iso-energetic and iso-nitrogenous treatments: (1) control diet (CON, n = 26) or (2) a diet containing RPG (RPG, pre-fresh 8.4% RPG DM basis, post-fresh 9.5% RPG DM basis; n = 26). Cows received their respective dietary treatments from d −21 to 28 relative to calving via individual feeding gates. Weekly BW, BCS, milk samples and fecal pH were recorded until 28 DIM, whereas milk yield was recorded through 105 DIM. Blood samples were collected on d −7, 3, 7, 14, and 28 relative to calving. Data were analyzed using repeated measures in the MIXED procedure of SAS. Fecal pH was similar (P = 0.87) among treatments; however, compared with pre-calving, both treatments had a reduction in pH following calving (7.2 vs 6.6; P < 0.01). Milk yield was similar among treatments (P = 0.37) for 1 to 28 DIM (42.8 ± 1.2 kg/d), as well as through 105 DIM (P = 0.92; 47.3 ± 1.3 kg/d). Dry matter intake pre-calving (12.0 ± 0.7 kg/d) and post-calving (22.0 ± 0.7 kg/d) were unaffected by treatment (P ≥ 0.65). Milk fat, protein and lactose were similar among treatments (P ≥ 0.40; 4.36 ± 0.13%, 3.66 ± 0.11% and 4.73 ± 0.06%, respectively). Plasma concentration of BUN and glucose were similar (P ≥ 0.57) among treatments; however, postpartum concentration of circulating BHBA tended (P = 0.13) to be 0.24 mmol/L lower with a concomitant reduction (P < 0.01) in NEFA concentration in the RPG-fed cows compared with CON (630 vs. 456 ± 68 µEq/L). Circulating insulin tended to be increased (P = 0.06; 27%) in RPG-fed cows compared with CON. Based upon circulating hormones and metabolites, it appears that treatment influenced energy partitioning pathways in the periparturient period such that RPG-fed cows mobilized less adipose tissue compared with the control cows while maintaining milk yield.

Key Words: bypass carbohydrates, ketosis, transition period