|KOONTZ, ANNE - University Of Kentucky|
|KIM, DO HYUNG - University Of Kentucky|
|MC LEOD, KYLE - University Of Kentucky|
|HARMON, DAVID - University Of Kentucky|
Submitted to: Animal Production Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2014
Publication Date: 9/15/2014
Citation: Koontz, A.F., Kim, D., Mc Leod, K.R., Klotz, J.L., Harmon, D.L. 2014. Effect of fescue toxicosis on whole body energy and nitrogen balance, in situ degradation and ruminal passage rates in Holstein steers. Animal Production Science. 55:988-998. doi.org/10.1071/AN14037.
Interpretive Summary: The majority of research on fescue toxicosis has relied on animal consumption to introduce alkaloids into the system. This experiment used a ruminally dosed animal model to remove the possibility of a reduction in intake altering the quantity of alkaloids ingested by the animal over the course of the experiment. In addition, pair-feeding was utilized to separate the effects of reduced nutrient intake and alkaloid ingestion. The goal of this experiment was to use these methods to evaluate the interaction between consumption of endophyte-infected tall fescue and dietary intake level on diet digestion and ruminal kinetics, as well as whole body nitrogen and energy balance in consideration of changes in fasting heat production. Ingestion of endophyte infected tall fescue seed in pair fed steers did not alter total nitrogen or energy balance at high or low intakes. Endophyte treatment also did not affect in situ degradation of a common feedstuff. Rumen contents % dry matter and dry matter weight increased with endophyte-infected tall fescue seed ingestion, which is likely related to reduced particulate passage from the rumen. This reduction in particulate passage may contribute to the depression in intake common during fescue toxicosis. The ruminal volatile fatty acid profile is altered by alkaloid ingestion, which may be due to reduced absorption and the changes in ruminal kinetics. When taken together, these results indicate that reduced intake is likely the primary cause of the reduced weight gain and poor productivity associated with fescue toxicosis.
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 (1100 (L) or 1800 (H) kJ/kG BW.75). During each period after 8d of feeding level adaptation animals were ruminally dosed twice daily with ground fescue seed for the remainder of the period. One steer per pair was dosed with ground endophyte-infected fescue seed (E+), the other with ground endophyte-free fescue seed. 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 21. Heat production (HP) was calculated using the Brower equation. Retained energy (RE) was calculated as intakeE – (fecalE + urinaryE + gaseousE+HP). 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) 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, DE, ME, RE, and HP were higher (P < 0.03) for H v L. There was no difference in retained N, DE, ME, or HP (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 increased (P = 0.0002) during H intake and decreased (P = 0.02) with E+ dosing. Ruminal liquid passage decreased (P < 0.03) with H feeding, while liquid flow rate tended to be reduced (P < 0.14) with E+ dosing. Total VFA concentration increased with both H feeding (P < 0.01) and E+ dosing (P < 0.0001). Despite these differences, the N and energy balance data indicate that the reductions in weight gain and productivity seen during fescue toxicosis are primarily due to reduced intake.