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Journal of Animal Science - Animal Nutrition

Effects of alternate day feeding of dried distiller’s grains plus solubles in forage-fed steers on intake, ruminal fermentation and passage rates, and serum nonesterified fatty acid1

 

This article in JAS

  1. Vol. 93 No. 8, p. 3959-3968
     
    Received: Mar 05, 2015
    Accepted: May 19, 2015
    Published: July 10, 2015


    2 Corresponding author(s): Carl.Dahlen@ndsu.edu
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doi:10.2527/jas.2015-9070
  1. S. I. Klein,
  2. Q. P. Larson,
  3. M. L. Bauer,
  4. J. S. Caton and
  5. C. R. Dahlen 2
  1. Department of Animal Sciences, North Dakota State University, Fargo 58108

Abstract

Four ruminally and duodenally cannulated Holstein steers (BW = 449 ± 7.3 kg) were used to examine the effects of feeding either dried distiller’s grains plus solubles (DG) or grass hay on alternate days (every other day) on intake, ruminal fermentation and passage rates, and serum NEFA in forage-fed steers. Steers were assigned to 1 of 4 dietary treatments in a 4 × 4 Latin square: 1) only hay (CON), 2) hay and 0.4% of BW as DG DM daily (DG7), 3) hay daily and 0.8% BW DG every other day (DG2), and 4) alternate day feeding of hay and 0.8% of BW as DG (DGA). Treatment periods consisted of 13 d of adaptation and 8 d of collecting digesta and blood. Over the entire collection period, DMI was decreased (P = 0.004) for DGA compared with other treatments (13.0 ± 0.8, 12.7 ± 0.8, 13.3 ± 0.8, and 10.9 ± 0.8 kg/d for CON, DG7, DG2, and DGA, respectively). Immediately after feeding on days supplement was fed to DG2 and DGA (supplemented days [SUP]), ruminal pH of DGA was less than other treatments but by the end of the day was greater than other treatments (treatment × time, P < 0.001). At feeding time on nonsupplemented days (NSUP), ruminal pH of DGA steers was greater than other treatments but was similar (treatment × time, P < 0.001) to DG2 and CON by 5 h after feeding. Total concentrations of VFA were similar (P = 0.09) among treatments on SUP; however, on NSUP, total VFA concentrations were least in DGA from feeding until 4 h after feeding (treatment × time, P = 0.02). No differences (P ≥ 0.06) were observed among treatments for apparent ruminal, total intestinal, and total tract DM, OM, or CP digestibility. There were no differences (P = 0.36) in serum NEFA among treatments on SUP; however, on NSUP, steers fed DGA (209.5 ± 12.7 mM) had greater (P < 0.01) NEFA compared with other treatments (84.4 ± 12.7, 88.0 ± 12.7, and 77.7 ± 12.7 mM for CON, DG7, and DG2, respectively). The DGA feeding strategy influenced DMI and ruminal kinetics and circulating NEFA without impacting total tract digestibility.



INTRODUCTION

As feed costs account for >60% of cow costs (Miller et al., 2001), strategies that optimize the use of existing forages can contribute greatly to producer profitability. Dried distiller’s grains plus solubles (DG) is a good supplement for cows consuming forage-based diets and can help reduce forage intake (MacDonald and Klopfenstein, 2004; Morris et al., 2005), increase concentrations of ruminal VFA (Loy et al., 2007), and ultimately increase OM digestibility (Leupp et al., 2009).

Reducing the frequency of supplement delivery can reduce time and labor required for feeding, resulting in cost savings. However, altering frequency of supplementation from daily to 3 d/wk can result in fluctuations in forage intake, ruminal pH, concentrations of VFA (Beaty et al., 1994), and circulating concentrations of NEFA (Moriel et al., 2012). Restricting access to forage can reduce forage intake while still maintaining acceptable levels of performance (Cunningham et al., 2005; Miller et al., 2007), perhaps by increasing digesta retention time and increasing feed digestibility (Dias et al., 2011).

When the concepts of reduced supplementation frequency and limiting forage access were combined in mid- to late-gestation cows, we observed a reduction in forage intake, altered concentrations of NEFA, and altered pattern of feeding (Klein et al., 2014). However, ruminal fermentation patterns were not quantified in our model of eliminating forage from diets on alternating days while supplementing with DG. Therefore, we conducted the following study to determine the effects of feeding only DG and only hay on alternating days on intake, ruminal fermentation and passage rates, and serum NEFA in steers fed moderate quality forage. We hypothesized that alternate day feeding of DG and hay would decrease hay DMI without adversely affecting ruminal fermentation and passage rates.


MATERIALS AND METHODS

All research procedures were approved by the North Dakota State University Animal Care and Use Committee.

Animals and Diets

Four ruminally and duodenally cannulated (T-type cannula) Holstein steers (449 ± 7.3 kg) were used in a 4 × 4 Latin square consisting of four 21-d periods (449, 513, 537, and 559 kg BW and the initiation of periods 1, 2, 3, and 4, respectively). Steers were housed in a climate controlled room in individual pens (3.0 by 3.7 m) during a 13-d adaptation period and transferred to individual tie-stall stanchions (1.0 by 2.2 m) during an 8-d collection period. Diets consisted of bromegrass hay (Bromus inermis), DG, or both (Table 1) in the following treatments: 1) only hay (CON), 2) hay and 0.4% of BW as DG DM daily (DG7), 3) hay daily and 0.8% BW DG every other day (DG2), and 4) alternate day feeding of hay and 0.8% of BW as DG (DGA). Feeding of DG commenced at 0630 h daily to DG7 and on alternate days to DG2 and DGA; all DG was consumed within 30 min. Predominately bromegrass hay (chopped to pass through a 3.8-cm screen) was fed at 0700 and 1900 h daily to ensure ad libitum intake. The daily allotment of hay was based on 110% of the previous weeks’ average daily intake. All hay originated from the same cutting and field and all DG used in the study originated from the same production lot. Steers were weighed before feeding 2 and 1 d before the beginning of each period to determine the quantity of DG to deliver for the entirety of the ensuing period. Calcium in the form of ground limestone was added to DG before feeding to maintain a dietary Ca:P ratio of 2:1. Steers also had ad libitum access to water and a pressed mineral block (Hubbard Feeds, Mankato, MN; 11% Ca, 13% P, 12% salt, 0.5% Mg, 396 kIU of vitamin A/kg, 39.6 kIU of vitamin D3/kg, and 110 IU of vitamin E/kg).


View Full Table | Close Full ViewTable 1.

Composition of forage and dried distiller’s grains plus solubles (DG)

 
Bromegrass hay
DG
Item % of DM
CP 16.2 28.3
OM 85.1 94.5
NDF 64.1 30.6
ADF 35.8 8.7
Sulfur 1.0

Sample Collection

Samples of hay and DG were taken daily (d 14–21) and composited for the entirety of the collection period to determine nutrient composition of feed. Orts were collected daily (d 14–21) at 0615 h and composited for the entirety of the collection period to determine nutrient composition of refusals, and samples were frozen (–18°C) until sample processing and chemical analysis could be performed. Chromic oxide (8.0 g) was dosed through the ruminal cannula in gelatin capsules at 0700 and 1900 h to serve as a digesta flow marker, beginning on d 9 until the end of the collection period (d 21).

Ruminal and duodenal samples were taken so that every 2 h of a 24-h period were sampled. Ruminal contents (500 g) and duodenal samples (200 mL) were taken at 0800, 1400, and 2000 h on d 14 and 15; 0200, 1000, 1600, and 2200 h on d 16 and 17; 0400, 1200, and 1800, and 2400 h on d 18 and 19; and 0600 h on d 20 and 21. Ruminal content samples were refrigerated (7°C) and composited over the duration of the collection period. The fixed, composited ruminal sample was blended for 1 min, strained through 4 layers of cheese cloth, and stored frozen (–18°C) until analysis. Duodenal samples were collected into individual Whirl-Pak bags (532 mL; Nasco, Ft. Atkinson, WI), composited into a 3-L container, and frozen (–18°C) until sample processing and analysis.

Steers were intraruminally dosed with 200 mL of Co-EDTA (1,734 mg of Co; Uden et al., 1980) at 0430 h on d 18 and 21 to serve as a liquid passage marker. Ruminal fluid samples (200 mL) were obtained via a suction strainer from the ventral ruminal sac immediately before Co-EDTA dosing, at feeding, and every 2 h thereafter until 8 h after feeding (0430, 0630, 0830, 1030, 1230, and 1430 h). Immediately after collection, ruminal fluid samples were poured into individual Whirl-Pak bags (532 mL; Nasco), acidified with 2 mL of 6.0 M HCl, and frozen (–18°C) until analysis of ruminal VFA and Co.

Ruminal pH was measured using wireless sensors (Kahne Ltd., Auckland, New Zealand) every 10 min for the entirety of the collection period. Sensors were calibrated on d 13 of each period before inserting them manually into the ruminal ventral sac. Three consecutive pH measurements were averaged to represent every 30 min, giving a total of 48 time points per day. An experimental day was defined as beginning at feeding (0630 h) and ending before the subsequent day’s feeding (0600 h).

Total fecal material was collected into stainless steel pans located directly behind each steer. Total fecal output was weighed once daily (d 14–21) at 0530 h and mixed by hand and 10% (wet weight basis) was composited. Each fecal subsample was composited per steer per period for both supplemented days (SUP) and nonsupplemented days (NSUP). Fecal samples were refrigerated (7°C) until the end of the collection period and then mixed for 3 min in a rotary mixer (model A-200; Hobart Mfg. Co., Troy, OH). Mixed fecal samples were subsampled and immediately taken to be dried.

Blood samples were obtained daily (d 14 to 21) via coccygeal venipuncture into two 10-mL evacuated tubes at 1100 h, placed on ice and allowed to clot for 3 h, and then centrifuged at 1,500 × g for 25 min at 4°C. Serum was pipetted into individually labeled 2-mL microtubes and frozen (–18°C) until analysis for NEFA.

Laboratory Analysis

Feed, ort, and fecal samples were dried in a 60°C forced-air oven for 48 h and then ground to pass a 2-mm screen (Thomas-Wiley Lab Mill, model 4; Thomas Scientific USA, Swedesboro, NJ). Feed and ort samples were analyzed for DM, CP, and ash (methods 934.01, 2001.11, and 942.05 respectively; AOAC, 2010) and NDF and ADF (Goering and Van Soest, 1970; as adapted by Ankom Technology, Macedon, NY). Neutral detergent fiber and ADF were determined using an Ankom 200 fiber analyzer (Ankom Technology). Values used to estimate intake of NEm were 1.279 Mcal/kg DM for hay and 2.116 Mcal/kg DM for DG, respectively.

Duodenal samples were lyophilized. Dried duodenal and fecal samples were analyzed for DM, CP, ash, NDF, and ADF (same procedures as above) as well as concentrations of Cr (Fenton and Fenton, 1979). Ruminal content samples were blended and analyzed for DM and CP (same procedures as above).

For analysis of VFA, ruminal fluid samples were thawed and centrifuged at 20,000 × g for 10 min at 4°C. After centrifugation, 5 mL of supernatant was mixed with 1 mL of 25% (wt/vol) metaphosphoric acid and recentrifuged at 10,000 × g for 10 min at 4°C. The resulting supernatant was used for VFA analysis via gas chromatography (6890 series gas chromatograph; Agilent Technologies, Santa Clara, CA) using a capillary column (15 m by 0.53 mm by 0.5 µm thickness; Supelco, Belefonte, PA) and an internal standard of 2-ethylbutyric acid (1 mL per 5-mL sample).

Cobalt concentrations in ruminal fluid were determined with and air + acetylene flame using atomic absorption spectroscopy (Uden et al., 1980). Fluid passage rate was determined by regression of the natural logarithm of the ruminal Co concentration on time. The absolute value of the slope was defined as the fluid dilution rate. Fluid volume was then determined by dividing the Co dose by the antilogarithm of the marker concentration at time zero (Grovum and Williams, 1973).

Serum NEFA was determined using the acyl-CoA synthetase, acyl-CoA oxidase method (NEFA-HR; Wako Pure Chemical Industries, Richmond, VA).

Statistical Analysis

Data were analyzed using the MIXED procedure of SAS version 9.2 (SAS Inst., Inc., Cary, NC) as a 4 × 4 Latin square. The class statement included steer, period, and treatment and, when data were analyzed over time, time was included as well. The Satterthwaite method was used to determine degrees of freedom and the best fit covariate structure was chosen based on the lowest Akaike, Akaike with small sample size adjustment, and the Bayesian information criterion statistics. For response variables that could be immediately influenced by feeding regime, data were further divided into days when DG7, DG2, and DGA treatments were fed DG (SUP) and days when CON, DG2, and DGA treatments were fed only hay (NSUP). Means were separated using the LSMEANS option of SAS.

The model for hay, DG, total intake, and total NEm intake included treatment, day, and their interaction. Random variables included steer and period, treatment × steer, and day × period. Day was analyzed as a repeated measure and the subject was steer × treatment. For the intake parameters, the best fit covariate structure chosen was the simple variance components structure. Additionally, intake of hay, DG, and total DMI were evaluated separately for SUP and NSUP using a similar model.

Ruminal pH data were analyzed separately for SUP and NSUP. The model for ruminal pH included treatment, time, and their interaction. Random variables included steer, period, and treatment × steer. Ruminal pH was analyzed as a repeated measure and the subject included steer × treatment. Ruminal pH was analyzed as a repeated measure and the subject included steer × treatment and the covariate structure chosen was the first-order autoregressive (ar(1)).

Ruminal VFA were separated to represent SUP and NSUP. The model for VFA included treatment, time, and treatment × time. Random variables included steer, period, treatment × steer, and time × period. Volatile fatty acids were analyzed as repeated measures. The model for total VFA and (acetate + [2 × butyrate]):propionate (A:P) ratio contained treatment, time, and their interaction, and the random variables included steer, period, and treatment × steer. The best fit covariate structure for VFA analyses was ar(1).

Ruminal liquid dilution parameters were analyzed separately to represent both SUP and NSUP. The model included the effect of treatment. Random variables included steer, period, and treatment × steer. The model for digestibility of DM, OM, CP, NDF, and ADF included treatment. Data for blood hormones and metabolites were separated for SUP and NSUP. The model for NEFA included treatment, day, and treatment × day and were analyzed as repeated measures. The best fit covariate structure chosen for NEFA was ar(1). Random variables included steer, period, treatment × steer, and day × period.


RESULTS AND DISCUSSION

Hay, Distillers Grains, and Total Intake

By design, weekly DG intake was similar (P ≥ 0.42) among DG7, DG2, and DGA treatments, resulting in a true test of supplementation strategies. The DGA strategy tested in the current report was designed to alternate between 1 d where steers were allowed ad libitum hay intake and 1 d where steers were fed no hay and only a limited amount of DG. As hypothesized, steers receiving the DGA supplementation strategy had reduced (P < 0.001) hay intake compared with steers receiving other strategies (Table 2). In addition, steers fed DG7 and DG2 had reduced (P < 0.001) hay intake compared with steers fed CON. This reduction in hay intake in steers fed DGA compared with all other treatments reinforces the pattern of reduced forage intake we observed with gestating beef cows using a similar treatment design (Klein et al., 2014). The overall reduction in hay intake by DGA steers compared with other supplementation methods was likely because the DGA strategy restricts access to hay on alternate days. Similarly, when lactating beef cow’s access to round bales of hay was reduced from 24 h to only 4 h daily, a 37% reduction in hay disappearance was measured (Cunningham et al., 2005).


View Full Table | Close Full ViewTable 2.

Intake of bromegrass hay and dried distiller’s grains plus solubles (DG) by steers fed varying frequencies of DG

 
Treatment1
SEM P-value
Item CON DG7 DG2 DGA
Hay DMI, kg/d 13.0c 10.5b 11.2b 8.7a 0.96 <0.001
DG DMI, kg/d 0.0a 2.2b 2.1b 2.2b 0.10 <0.001
Total DMI, kg/d 13.0b 12.7b 13.3b 10.9a 0.95 0.004
Total caloric intake,2 Mcal NEm/d 16.6a 18.1b 18.8b 15.8a 1.06 0.004
a–cMeans within row lacking common superscripts differ (P < 0.05).
1CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG.
2 Values used to determine caloric intake were 2.116 Mcal NEm/kg for DG and 1.279 Mcal NEm/kg for hay.

The reduction (P < 0.05) in hay intake for DG7 and DG2 compared with CON steers was also anticipated. Others (Morris et al., 2005; Leupp et al., 2009) have reported heifers and steers had linear decreases in forage intake with increasing DG intake. In addition, steers offered either daily or alternate day supplementation of a soybean hull and corn gluten feed blend had reduced hay intake compared with steers offered no supplement (Drewnoski et al., 2014). The reduction in forage intake observed for DG7 and DG2 in the current study was likely due to a portion of the energy from the forage being replaced by supplemented DG (i.e., a substitution effect; Caton and Dhuyvetter, 1997).

Total DMI was reduced (P < 0.001) for steers fed DGA compared with CON, DG7, and DG2 treatments, and total NEm intake was reduced (P < 0.001) for CON and DGA compared with DG7 and DG2 (Table 2). When data were analyzed separately for SUP and NSUP, hay intake and total DMI were least in DGA on SUP but greatest on NSUP compared with all other treatments (treatment × feed day, P < 0.001; data not shown). The current experiment was designed to have a reduced overall DMI on alternate days for DGA steers (eating only 0.8% BW as DG), and the pattern of overcompensating the day following a restriction with a greater hay intake and DMI was also observed in gestating beef cows (Klein et al., 2014).

Ruminal pH

A treatment × time interaction (P < 0.001) was present on SUP for ruminal pH (Fig. 1). From 0630 to 0800 h on SUP (i.e., immediately after feeding), ruminal pH was reduced (P ≤ 0.05) in DGA compared with CON, DG7, and DG2. Ruminal pH steadily increased throughout the day for steers in the DGA treatment, and over the last 7 h of SUP, ruminal pH for DGA was greater (P ≤ 0.05) than other treatments. In addition, ruminal pH for DG7 was reduced (P ≤ 0.05) for a 4.5-h period after the 1900-h feeding compared with other treatments but was similar (P ≥ 0.10) to ruminal pH of CON and DG2 for the remainder of the SUP.

Figure 1.
Figure 1.

Ruminal pH on supplemented days starting at feeding (0630 h) in forage-fed steers supplemented with various frequencies of dried distiller’s grains plus solubles (DG). CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG. Treatment × time (P < 0.001). †DGA differs from other treatments (P ≤ 0.05). ‡DG7 differs from other treatments (P ≤ 0.05).

 

A treatment × time interaction (P < 0.001) was also present on NSUP for ruminal pH (Fig. 2). At feeding on NSUP, ruminal pH was greater (P ≤ 0.05) for DGA than for other treatments, whereas DG7 was less (P ≤ 0.05) than all other treatments until 3 h after feeding and from 5 to 7.5 h after feeding. At 8 h after the 1900-h hay feeding (0300 to 0600 h) on NSUP, ruminal pH was greater (P ≤ 0.05) for DG2 compared with other treatments.

Figure 2.
Figure 2.

Ruminal pH on nonsupplemented days starting at feeding (0630 h) in forage-fed steers supplemented with various frequencies of dried distiller’s grains plus solubles (DG). CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG. Treatment × time (P < 0.0001). †DGA differs from all other treatments (P ≤ 0.05). §DG2 differs from all other treatments (P ≤ 0.05). ‡DG7 differs from all other treatments (P ≤ 0.05).

 

Increasing ruminal pH throughout the feed day when only DG was delivered to the DGA treatment was likely due to a decrease in readily fermentable substrates in the rumen as the day advanced. This is reasonable because when only DG was delivered it was consumed in approximately 30 min, resulting in a ruminal pH of less than 6 at1 h after feeding and nearly 6.8 at 24 h after feeding. Consequently, ruminal fermentation and VFA concentrations were altered as the feed day progressed. The following morning at feeding (i.e., on NSUP), ruminal pH was still greater for DGA compared with other treatments but began a steady decline after consumption of hay ensued. The steady decline observed was likely due to increased microbial fermentation as substrate in the rumen was digested.

Although data from indwelling ruminal probes evaluating frequent pH changes in response to a feeding strategy such as DGA are lacking, patterns of ruminal pH throughout the feeding day for CON, DG7, and DG2 dietary treatments were comparable to previous reports. For example, no differences were observed in ruminal pH in grazing beef steers supplemented with cottonseed meal and corn compared with unsupplemented steers (Caton et al., 1988). Furthermore, no differences in ruminal pH were observed among treatments when protein concentration in supplement increased from 13 to 39% (DelCurto et al., 1990b).

Ruminal pH was reduced, as expected, for steers fed DG7 compared with other treatments when DG7 steers were fed DG and steers on other treatments were not supplemented DG (NSUP). Similarly, on days when steers fed an alternate day soybean hull and corn gluten feed blend supplement regime did not receive supplement, ruminal pH was greater after feeding compared with steers that received daily supplementation (Drewnoski and Poore, 2012). Ruminal pH was reduced in steers receiving supplement 7 d/wk compared with those receiving supplement 3 d/wk on days when only the 7 d/wk group was supplemented (Beaty et al., 1994). Overall patterns of pH changed observed in the current report were likely indicative of experimental treatments causing alterations in VFA concentrations.

Total VFA and (Acetate + [2 × Butyrate]): Propionate Ratio

On days when DG7, DG2, and DGA received DG (SUP), no differences (P = 0.09) were observed among treatments for total VFA (84.0 ± 1.4, 83.2 ± 1.4, 82.6 ± 1.4, and 84.6 ± 1.4 mM for CON, DG7, DG2, and DGA, respectively). However, on NSUP, a treatment × time interaction (P = 0.02) was observed for total VFA concentrations. Total VFA on NSUP was less (P < 0.01) in DGA from feeding until 4 h after feeding compared with other treatments (Fig. 3).

Figure 3.
Figure 3.

Total VFA concentration on nonsupplemented days for steers fed varying frequencies of dried distiller’s grains plus solubles (DG). CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG. Treatment × time (P = 0.019). †DGA differs from all other treatments (P < 0.01).

 

The similarities among our treatments for total ruminal VFA on SUP were also observed on days when steers on an alternate day supplementation scheme received their soybean hull and corn gluten feed supplement (Drewnoski and Poore, 2012). However, Bohnert et al. (2002) reported that on days when steers were given protein supplements, total concentration of VFA linearly increased as frequency of protein supplementation decreased from daily to every third day to every sixth day. The decrease in concentrations of total VFA in DGA steers on NSUP until 4 h after feeding compared with other treatments could possibly be explained by the fact that it had been several hours since the animal last received feed; therefore, ruminal substrate or microbial fermentation were likely limited. Due to the time between feedings and lack of substrate in the rumen, the concentration of total VFA were decreased, which may be correlated with a decrease in microbial population for DGA before feeding on NSUP (Owens and Goetsch, 1988). Therefore, when hay was delivered at 0700 h on NSUP, there was a large influx of substrate into the rumen that would not begin to ferment until the microbial population multiplied, attached, and colonized the new substrate. This process led to a 6-h lag before total VFA concentration in DGA increased to concentrations similar to those of CON, DG7, and DG2.

On SUP, a treatment × time interaction (P = 0.03) was present for the ratio of A:P (Fig. 4; calculated on a mmol:mmol basis). At feeding and 2 h after feeding, DGA had a lower (P ≤ 0.05) A:P ratio compared with DG7 and DG2. In addition, on SUP, the A:P ratio for DGA was lower (P ≤ 0.05) compared with all other treatments at 8 h after feeding. On NSUP, the A:P ratio was reduced (P ≤ 0.01) in DGA (2.72 ± 0.12) compared with CON (3.06 ± 0.12) and DG2 (3.17 ± 0.12), whereas DG7 (2.89 ± 0.12) was intermediate. Furthermore, the ratio of A:P was greater (P ≤ 0.01) for DG2 on NSUP compared with DG7, whereas CON was intermediate.

Figure 4.
Figure 4.

The (acetate + [2 × butyrate]):propionate ratio on supplemented days for steers fed varying frequencies of dried distiller’s grains plus solubles (DG). Ratio calculated as [acetate + (2 × butyrate)]/propionate. CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG. Treatment × time (P = 0.03). £DGA differs from DG7 and DG2 (P ≤ 0.005). DGA differs from all other treatments (P ≤ 0.04).

 

Our observation that control steers had A:P ratios similar to DG7 and DG2 steers on SUP conflicts with other reports documenting differences in the A:P ratio among supplemented and unsupplemented cattle. As supplemental DG increased from 0, 0.3, 0.6, 0.9, and 1.2% of BW daily in beef steers consuming moderate quality hay, the ratio of A:P linearly decreased (Leupp et al., 2009). Differences among reports are likely due to large daily variations in amount and timing of supplement offered across experiments. Due to the scarcity of information pertaining to our DGA treatment, it is unclear why the ratio of A:P is decreased on SUP in this treatment. We speculate that to acclimate to the DGA treatment, ruminal microorganisms were becoming more efficient at utilizing substrate. On NSUP, the ratio of A:P was least in DGA and greatest in DG2. It is well documented that in ruminants, the A:P ratio generally decreases with the inclusion of a supplement in a forage-based diet (Horn and McCollum, 1987). Because the DGA treatment was not receiving DG on this day, it is unclear why the ratio of A:P was decreased in DGA compared with CON and DG2 as all 3 of these treatments were receiving only hay.

Ruminal Fluid

Ruminal fluid parameters on SUP (Table 3) including fluid dilution rate, fluid flow rate, rumen fluid volume, and turnover time were similar (P ≥ 0.08) among all treatments. On NSUP, fluid dilution rate, rumen fluid volume, and turnover time were also similar among treatments (P ≥ 0.08) but fluid flow rate was decreased (P < 0.05) for DGA compared with CON, DG7, and DG2 (Table 3).


View Full Table | Close Full ViewTable 3.

Ruminal fluid dynamics in steers consuming hay and dried distiller’s grains plus solubles (DG) at varying frequencies

 
Treatment1
SEM P-value
Item CON DG7 DG2 DGA
SUP2
    Dilution rate, %/h 10.0 12.6 12.5 9.7 1.2 0.08
    Flow rate, L/h 5.97 5.62 5.62 5.29 0.80 0.70
    Volume, L 62.4 45.2 47.0 53.6 7.1 0.27
    Turnover, h 11.7 8.0 8.1 10.5 1.7 0.21
NSUP3
    Dilution rate, %/h 11.7 12.1 11.9 12.8 0.5 0.54
    Flow rate, L/h 5.03b 4.79b 4.65b 3.94a 0.59 0.02
    Volume, L 42.8 40.9 39.2 31.4 5.8 0.08
    Turnover, h 8.6 8.4 8.5 7.9 0.4 0.61
a,bMeans within row lacking common superscripts differ (P < 0.05).
1CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG.
2SUP = supplemented days (days when DG7, DG2, and DGA received DG).
3NSUP = nonsupplemented days (days when DG2 and DGA did not receive DG.

The pattern of supplementation increasing passage rates in forage-fed cattle observed by other authors (McCollum and Galyean 1985; Caton et al., 1988; DelCurto et al., 1990a; Bohnert et al., 2002) was not observed in the current study on either SUP or NSUP as liquid passage rate parameters were similar for CON, DG7, and DG2 treatments. Similarly, liquid dilution rates were unaffected by either increasing concentration of CP in supplements (10, 20, 30, or 40%) or supplementation frequency (daily or 3 d/wk) in forage-fed steers (Beaty et al., 1994). Several other instances of supplementation not impacting liquid dilution parameters in forage-fed cattle have also been reported (Gilbery et al., 2006; Islas and Soto-Navarro, 2011).

In a previous report, increasing the forage level to achieve 30 to 120% of maintenance energy requirements resulted in a linear increase in fluid passage rate (Scholljegerdes et al., 2004). Therefore, our observation of reduced ruminal fluid flow for DGA steers on NSUP compared with other treatments is conflicting. The disparity in reports is likely related to the design of specific experiments. Whereas Scholljegerdes et al. (2004) used heifers that were adapted to specific forage concentrations in the diet, the DGA strategy tested in the current report used a design where large quantities of hay intake on NSUP were preceded by a day where steers were fed no hay and a limited amount of DG. With limited ruminal fill from SUP, steers in the DGA treatment responded on NSUP with hay intake that was greater than all other treatments. The large influx of hay likely absorbed a larger proportion of available ruminal fluid compared with other treatments and was ultimately manifested as a reduction in fluid flow rate for DGA steers on NSUP.

Apparent Ruminal, Total Intestinal, and Total Tract Digestibility

Daily DMI was decreased (P < 0.01) in DGA compared with other treatments (Table 4). Both OM and CP intake were similar (P ≥ 0.07) among all treatments. Neutral detergent fiber intake and ADF intake were least (P < 0.01) in DGA and greatest (P < 0.01) in CON among treatments. Furthermore, both NDF intake and ADF intake were similar (P ≥ 0.18) for DG7 and DG2, and NDF intake was similar (P = 0.09) between CON and DG2.


View Full Table | Close Full ViewTable 4.

Intake and digestibility of dietary components by steers consuming hay and dried distiller’s grains plus solubles (DG) at varying frequencies

 
Treatment1
SEM P-value
Item CON DG7 DG2 DGA
Intake, kg/d
    DM 13.0b 12.7b 13.3b 10.9a 0.8 0.004
    OM 11.1 10.6 11.2 9.5 0.7 0.07
    CP 2.1 2.2 2.3 2.0 0.2 0.28
    NDF 8.3c 7.3b 7.7bc 6.2a 0.6 0.004
    ADF 4.6c 4.0b 4.2b 3.3a 0.3 0.001
Apparent ruminal digestibility, %
    DM 46.1 49.6 45.6 44.5 2.3 0.22
    OM 52.7 56.4 51.9 53.4 1.9 0.20
    CP 23.3 30.6 19.9 25.3 5.0 0.30
Total intestinal digestibility, %
    DM 6.1 5.8 12.4 15.7 3.5 0.18
    OM 5.2 4.3 11.5 12.5 2.6 0.08
    CP 31.5 29.5 44.6 40.8 5.5 0.06
Total tract digestibility, %
    DM 52.2 46.3 58.0 60.2 5.7 0.36
    OM 57.8 53.4 63.3 65.9 4.9 0.32
    CP 54.7 55.7 64.5 66.1 4.7 0.26
    NDF 71.0 59.8 70.3 71.5 6.0 0.46
    ADF 66.9 52.1 64.5 63.7 6.6 0.42
a–cMeans within row lacking common superscripts differ (P < 0.05).
1CON = only hay; DG7 = hay and 0.4% of BW as DG DM daily; DG2 = hay daily and 0.8% BW DG every other day; DGA = alternate day feeding of hay and 0.8% of BW as DG.

Although dietary treatment influenced intake, no differences were present among treatments for apparent ruminal (P ≥ 0.20) or total intestinal digestibility (P ≥ 0.06) of DM, OM, or CP or total tract digestibility (P ≥ 0.26) of DM, OM, CP, NDF, or ADF. Whereas total NDF digestibility linearly increased with increasing supplemental DG (0.2, 0.4, or 0.6% BW) fed to heifers grazing small grain pastures, no differences were observed in OM and CP digestibility (Islas and Soto-Navarro, 2011). Similarly, no differences were reported in NDF total tract digestibility when wethers consuming low-quality forage were supplemented with a corn and soybean meal mix (Howard et al., 1992) or in DM digestibility when ewes were supplemented to provide low, medium, or high amounts of ME (Reese et al., 1990). In contrast, true ruminal OM digestion and total tract OM digestibility were increased with increasing supplementation of DG (Leupp et al., 2009). Although the DGA strategy did alter intake, VFA concentration, ruminal pH, and fluid flow rate in the current study, we could not detect coincident changes in digestibility parameters.

Serum NEFA

No differences (P = 0.36) were detected among treatments for serum NEFA on SUP (72.6 ± 7.0, 81.1 ± 7.0, 84.1 ± 7.0, and 75.3 ± 7.0 mM for CON, DG7, DG2, and DGA, respectively). However, on NSUP, concentrations of serum NEFA were greater (P < 0.01) in DGA (209.5 ± 12.7 mM) compared with other treatments (85.4 ± 12.7, 88.0 ± 12.7, and 77.7 ± 12.7 mM for CON, DG7, and DG2, respectively). The increase in NEFA on NSUP in steers fed DGA is indicative of mobilization of body fat in the animal and suggests that steers were in a negative energy balance (Erfle et al., 1974). Because steers in DGA were receiving only a limited amount of DG without forage, the increase in NEFA for DGA reflects that their energy requirements were being met by mobilizing body fat stores. Using a model of mid- to late-gestation beef cows, we previously reported that all treatments receiving supplement (DG7, DG2, and DGA) had reduced serum NEFA compared with control on days they received supplement, whereas CON and DGA strategies had greater serum NEFA on days they did not receive supplement (Klein et al., 2014). A combination of low-quality forage (5.9% CP) and the gestating cow model (greater NEm requirements than steers) likely contributed to differences observed between the previous study (Klein et al., 2014) and our current report.

No differences in concentrations of serum NEFA were observed among CON, DG7, and DG2 treatments. Similarly, providing supplemental RDP and RUP to beef cows did not affect plasma NEFA concentrations (Rusche et al., 1993). However, greater NEFA concentrations have been reported in unsupplemented cattle and sheep compared with those that were supplemented (Krysl et al., 1987; Cheema et al., 1991; Barton et al., 1992). Lack of differences in serum NEFA among our DG2, DG7, and CON treatments in the current report is likely a result of the hay quality being sufficient to meet NEm requirements of steers used in our model so no additional body fat mobilization was required.

In summary, feeding only distiller’s grains on alternate days decreased hay and total DMI without negatively impacting ruminal kinetics, liquid dilution rate, and digestibility. However, increased concentrations of NEFA in steers on the day when only distiller’s grains was fed may indicate possible changes in body composition over a feeding period of longer duration.

 

References

Footnotes


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