Abstract #336

Section: Ruminant Nutrition (orals)
Session: Ruminant Nutrition III: Forages, fiber, and grains
Format: Oral
Day/Time: Tuesday 9:30 AM–9:45 AM
Location: Ballroom E

# 336
Effects of dietary undigested and physically effective neutral detergent fiber on dry matter intake, milk yield and composition, and chewing behavior of lactating dairy cows.
Wyatt A. Smith^*1, Kyohei Ishida², Jeffrey W. Darrah¹, Heather M. Dann¹, Catherine S. Ballard¹, Michael D. Miller¹, Rick J. Grant¹, ¹William H. Miner Agricultural Research Institute, Chazy, NY, ²ZEN-NOH National Federation of Agricultural Cooperative Associations, Tokyo, Japan.

The objective of this study was to evaluate the effect of feeding different dietary concentrations of 240-h undigested neutral detergent fiber (uNDF240) and physically effective neutral detergent fiber (peNDF) on dry matter intake (DMI), milk production and composition, and chewing behavior. Sixteen Holstein cows averaging 123 (SD = 9) days in milk (DIM) were used in a replicated 4 × 4 Latin square design with 4-wk periods. Cows were fed diets formulated to be isoenergetic and isonitrogenous but varying in uNDF240 and peNDF by changing forage to concentrate ratio and particle length of hay. Treatments were (1) 8.6% uNDF240 and 18.4% peNDF (LULP), (2) 8.6% uNDF240 and 19.9% peNDF (LUHP), (3) 10.5% uNDF240 and 16.2% peNDF (HULP), and (4) 10.5% uNDF240 and 19.0% peNDF (HUHP). Cows were housed in individual tie stalls, fed TMR once daily, and milked 3×/d. Feed intake and milk yield were collected daily from d 20 to 26. Milk composition was collected for 6 consecutive milkings on d 25 and 26 and body weight was collected on d 28 of each period. Behavior was collected for 72 h on d 23 to 25. Data were summarized by period and analyzed as a replicated Latin square design with model effects for diet, period, and replicate using the MIXED procedure of SAS (version 9.4). Cow within replicate was a random effect. Greater forage particle size with low uNDF240 diets resulted in DMI, ECM, and chewing response similar to higher uNDF240 diets with smaller particle size (Table 1). Table 1.

Item	LULP	LUHP	HULP	HUHP	SE	P-value
DMI, kg/d	27.5^a	27.3^a	27.4^a	24.9^b	0.6	<0.001
DMI, % of BW	4.02^a	4.04^a	3.99^a	3.73^b	0.10	0.003
Milk, kg/d	46.1^a	44.9^ab	44.0^bc	42.6^c	0.9	<0.001
Milk fat, %	3.68^b	3.66^b	3.93^a	3.92^a	0.10	<0.001
De novo fatty acids (FA), g/100 g FA	0.87	0.85	0.90	0.88	0.03	0.176
Mixed origin FA, g/100 g FA	1.41^b	1.40^b	1.51^a	1.51^a	0.04	<0.001
ECM, kg/d	47.0^a	45.7^ab	46.4^ab	44.6^b	0.9	0.031
ECM/DMI, kg/kg	1.71^ab	1.68^b	1.70^ab	1.79^a	0.04	0.023
Eating, min/d	255.4^b	262.5^b	279.1^ab	300.3^a	12.4	<0.001
Rumination, min/d	523.2	526.5	531.8	544.5	16.4	0.357
Eating time per DMI, min/kg	9.1^c	9.6^bc	10.1^b	11.9^a	0.5	<0.001
Rumination time per DMI, min/kg	18.6^b	19.3^b	19.3^b	21.7^a	0.8	<0.001

^abcWithin a row, different superscripts differ (P ≤ 0.05).

Key Words: digestibility, particle size, undigested fiber