|KOONTZ, ANNE - University Of Kentucky|
|FOOTE, ANDREW - University Of Kentucky|
|KIM, DO - University Of Kentucky|
|MCLEOD, KYLE - University Of Kentucky|
|HARMON, DAVID - University Of Kentucky|
Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: 3/8/2013
Publication Date: 7/8/2013
Citation: Koontz, A.F., Foote, A.P., Kim, D.H., Klotz, J.L., Mcleod, K.R., Harmon, D.L. 2013. Effect of fescue toxicosis on ruminal kinetics, nitrogen and energy balance in Holstein steers. J. Anim. Sci. Vol. 91, E-Suppl. 2:92.
Technical Abstract: This study was designed to examine alteration of ruminal kinetics, as well as N and energy balance during fescue toxicosis. Six ruminally cannulated Holstein steers (BW=217 ±7 kg) were weight-matched into pairs and pair-fed throughout a cross-over design experiment with a 2x2 factorial treatment structure. Factors were endophyte (infected, E+ vs. uninfected, E-) and feeding level (1.8 x NEm, H vs. 1.1 X NEm, L). During each period after 8d of diet adaptation one steer per pair was ruminally dosed with ground endophyte-infected fescue seed (E+), the other with ground endophyte-free fescue seed for the remainder of the period. In situ degradation of ground alfalfa was determined on d13-16. Total fecal and urinary collections were performed on d17-21, with animals placed into indirect calorimetry head-boxes during d20 and 21for determination of heat production (HP) using the Brower equation. Liquid and particulate passage rates were evaluated using Cr:EDTA and iADF respectively on d 22 and 23. There was no difference (P > 0.9) in DMI/kg.75 between endophyte treatments, and DMI/kg.75 was different (P < 0.01) between H and L intake by design. Animals on H feeding had higher (P < 0.01) water, N, and energy intakes. Energy and N excretion, as well as retained N, DE, ME, RE, and HP were higher (P < 0.03) for H v L. There were no differences in retained N, DE, ME, HP, or partial efficiency of energy use (P > 0.15) between endophyte treatments. Neither rate nor extent of in situ degradation was altered by intake level or endophyte treatment (P > 0.3). Dry matter percentage and DM weight of rumen contents were increased (P < 0.01) by E+ dosing. Particulate passage was decreased by both intake (P < 0.01) and endophyte (P = 0.02). Ruminal liquid passage rate increased (P = 0.03) with H feeding and tended to be reduced (P < 0.15) with E+ dosing. Total VFA concentration increased with both H feeding (P < 0.01) and E+ dosing (P < 0.01). Despite these differences, the N and energy balance data indicate that reduced weight gain during fescue toxicosis is primarily a function of reduced intake and not secondary effects of alkaloid ingestion.