Abstract #W167

Section: Ruminant Nutrition (posters)
Session: Ruminant Nutrition: Ruminal Fermentation and Gas Production
Format: Poster
Day/Time: Wednesday 7:30 AM–9:30 AM
Location: Exhibit Hall A

# W167
Effects of feeding barley grain on intake, rumen pool size and apparent total tract digestibility in lactating dairy cattle fed pasture-based diets.
M. Dineen^*1,2, B. McCarthy², P. Dillon², S. W. Fessenden¹, P. A. LaPierre¹, R. A. Molano¹, M. E. Van Amburgh¹, ¹Department of Animal Science, Cornell University, Ithaca, NY, ²Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.

The objective of this study was to evaluate the effects of barley grain supplementation on intake, rumen pool size (PS) and apparent total-tract digestibility (TTD) of dry matter (DM), Neutral Detergent Fiber (aNDFom) and undigested Neutral Detergent Fiber (uNDFom) in lactating dairy cattle fed mechanically cut fresh perennial ryegrass indoors. Ten ruminally cannulated Holstein cows averaging 49 ± 23 DIM and 513 ± 36 kg of BW were assigned to one of 2 treatments in a switchback design. Diets contained (DM basis) 100% perennial ryegrass (PRG; DM = 18%, CP = 16%, Starch = 2%, aNDFom = 36%) or 80% PRG and 20% rolled barley (PRG+B; DM = 33%, CP = 15%, Starch = 14%, aNDFom = 33%). The trial consisted of 3 29 d periods where each period consisted of 21 d of diet adaptation and 8 d of data and sample collection. To quantify rumen PS, rumen contents were evacuated on d 28 and 29 of each period, weighed, mixed, and sampled. To estimate TTD, fecal samples were collected during 3 8 h intervals on d 24, 26 and 27 to encompass every 2 h of a 24 h cycle. All data were analyzed using the Proc Mixed procedure in SAS. The inclusion of barley grain increased the rumen PS of DM, aNDFom and uNDFom however reduced pasture intake and apparent TTD of DM and aNDFom (Table 1). Energy corrected milk was not effected by treatment (24.5 vs 24.1 ± 0.8 kg day⁻¹ for PRG and PRG+B, respectively). Table 1 (Abstr. W167). Effects of barley grain on intake, rumen pool size (PS) and apparent total tract digestibility (TTD) in lactating dairy cattle fed pasture-based diets

Item	PRG	PRG + B	SEM	P-value
Pasture intake (kg DM day⁻¹)	15.94	13.02	0.57	<0.0001
Barley intake (kg DM day⁻¹)	—	3.32	—	—
Total intake (kg DM day⁻¹)	15.94	16.34	0.57	0.12
aNDFom intake (kg day⁻¹)	5.76	5.34	0.20	<0.0001
uNDFom intake (kg day⁻¹)	0.58	0.68	0.02	<0.0001
Rumen DM PS (kg day⁻¹)	9.26	10.08	0.55	0.02
Rumen aNDFom PS (kg day⁻¹)	4.81	5.53	0.34	<0.001
Rumen uNDFom PS (kg day⁻¹)	1.54	1.75	0.09	<0.0001
Apparent TTDMD¹ (g g⁻¹)	0.83	0.80	0.003	<0.0001
Apparent TTaNDFomD² (g g⁻¹)	0.83	0.75	0.007	<0.0001

¹TTDMD = total tract dry matter digestibility. ²TTaNDFomD = total tract aNDFom digestibility.

Key Words: rumen, pool size, total-tract digestibility