Research and Reviews: Dairy

Special Circular 163-99

Effects of Replacing Forage Fiber or Nonfiber Carbohydrates With Dried Brewers Grains

R. S. Younker
S. D. Winland
J. L. Firkins1
B. L. Hull
The Ohio State University
Department of Animal Sciences
Department of Veterinary Clinical Sciences

1 For more information, contact at: The Ohio State University, 223 Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210; 614-688-3089; fax: 614-292-1515; e-mail: firkins.1@osu.edu

Abstract

Substituting dried brewers grains for forage (reducing forage NDF from 23.5 to 17.0% of DM), for concentrate (to reduce nonfiber carbohydrates from 45.0 to 34.1%), or both forage and concentrate had minor effects on ruminal characteristics or site of NDF digestion by cows in late lactation. However, gut fill appeared to be limited by brewers grains fiber when total NDF exceeded 35% of the dietary DM. Because of the short (14-day) periods, milk fat percentage was the only production response affected by treatment. Milk fat percentage was reduced in low forage diets unless brewers grains replaced both forage and grain. Although chewing was not measured, dried brewers grains appeared to be a successful replacement for a portion of the forage in the diet.

Introduction

Brewers grains are moderately high in fiber but have been used mostly as a protein source. Wisconsin research showed that they were relatively effective at stimulating chewing by cows and should, therefore, be a good replacement for forage when forage supplies are low or the price is high. It was hypothesized that brewers grains would be able to replace forage but that a lower ruminal pH or faster ruminal passage rate would reduce NDF digestibility in the rumen or total tract, but this has not been ascertained previously.

Materials and Methods

Four primiparous Holstein cows in late lactation were used in a 4 x 5 Youden square design. Each cow was fitted with ruminal, duodenal, and ileal cannulas. Treatments were a control diet with a high concentration of forage, a control diet with a low concentration of forage, and three diets in which dried brewers grains replaced a portion of the forage, concentrate, or both (Table 1). The NRC recommends about 21% forage NDF in lactation diets. The high forage control (HFC) was above this recommendation, but the low forage control (LFC) decreased forage NDF from 23.5 to 17.0 % of DM. Cows were fed and milked twice daily in 14-day periods. Chromic oxide and Yb (acid-soaked) were used as markers for digesta flow and rate of passage, respectively.

Results and Discussion

No significant differences in ruminal pH or rates of passage were detected due to treatment. Although brewers grains had slower digestion rates of NDF in situ and faster passage rates than did alfalfa, feeding brewers grains had minor effects on site of NDF digestion (Table 2). Intake of DM (Table 3) was depressed by the higher NDF concentrations in diets in which brewers grains replaced concentrate. Concentration of NDF in the diets was correlated moderately (r = -0.40, P = 0.08) with dry matter intake (DMI). Therefore, because of the coarseness of BG, DMI appeared to have been limited by gut fill. Although NEL concentrations of the diets varied from 0.80 to 0.91 Mcal/lb of DM (Table 1), NEL intakes (Table 3) followed patterns similar to DMI. Despite the range in NEL intake (7.4 Mcal/day), only a range of 3.7 lb/day difference in milk production was obtained.

Table 3. Least Squares Means for Lactation Performance by Cows Fed Control Diets or Diets Containing Brewers Grains (Bg) to Partially Replace Forage, Concentrate, or Both.
Item	Diets1
	HFC	LFC	BGF	BGC	BGB	SE	P <2
DMI, lb/day	40.3ab	43.1a	42.2ab	36.5c	39.4bc	0.9	0.05
NEL Intake, Mcal/day	31.9b	35.7a	34.4a	28.3c	31.5b	0.8	0.06
BW, lb	1,155	1,135	1,118	1,155	1,133	13	NS
DMI, % of BW	3.50b	3.80a	3.78a	3.14c	3.49b	0.09	0.07
Milk, lb/day	47.7	49.3	48.8	45.5	46.0	3.5	NS
Milk protein, %	3.63	3.72	3.66	3.54	3.56	0.05	NS
Milk fat, %	4.06a	3.45b	3.45b	3.88a	3.79a	0.10	0.05
a,b,c Means in the same row with different superscripts differ according to the P value indicated. 1 HFC = high forage control; LFC = low forage control; BGF = BG replacing forage; BGC = BG replacing concentrate; BGB = BG replacing both forage and concentrate. 2 Probability of a treatment response; NS = not significant (P > 0.10).

Production of milk, 4% fat-corrected milk, milk fat, and milk protein, and percentage of milk protein were not significantly different among treatments. Cows fed the HFC, BGC, and BGB diets produced milk with a higher (P < 0.05) fat percentage than did cows fed the LFC or BGF diets, which is in general agreement with the ruminal acetate to propionate ratio but not pH. Wisconsin researchers noted that BG stimulated chewing time relatively more than other nonforage fiber sources. They also noted that with BG the milk fat percentage was relatively less than with other nonforage fiber sources. The lack of difference in milk fat percentage between cows fed the LFC and BGF diets supports this conclusion. Differences in DMI and, therefore, ruminally fermentable carbohydrate intake appear to prevent our corroboration of their results for effectiveness of BG to stimulate chewing in our study (chewing was not measured in our study).

Changes in DMI occur more quickly than do changes in milk production and composition; additionally, in short-term studies, lactation responses generally represent differences that are based on a small window of time. Because DMI and NEL intake in the current study demonstrate such distinct differences, efficiencies of milk production reported should be different as well; however, differences were lacking. Therefore, short-term studies may mask treatment differences because cows may still be adapting when sampling occurs. Although BG did not appear to be very effective at stimulating milk fat percentage, DM intake was maintained when BG replaced forage, and it appears that brewers grains can successfully replace a portion of the forage NDF in the diets of lactating cows.