by-products for growing beef cattle

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Performance, feeding behaviour and rumen pH profile of beef cattle fed corn silage in combination with barley grain, corn or wheat distillers' grain or wheat middlings

ABSTRACT

This study compared growth performance, feeding behaviour and ruminal pH profile of growing beef heifers fed a total mixed ration (TMR) containing corn silage and either (400 g kg dry matter-1 [DM]) barley grain (CTL), corn distillers' grain (CDDG), wheat distillers' grain (WDDG) or wheat middlings (WM). Eighty beef heifers (16 ruminally cannulated; 301 ± 34 kg), were blocked by weight and randomly assigned to eight feedlot pens for a 70-d backgrounding study. Pens were randomly assigned to one of four dietary treatments and equipped with the GrowSafe feed intake system for determining individual feed intake and monitoring feeding behaviour. Dry matter intake (DMI; P < 0.01) and average daily gain (ADG) tended to be lower for CTL (P = 0.06) heifers as compared with heifers on other treatments. Feed conversion efficiency (i.e., gain to feed ratio), feeding behaviour and ruminal pH profile measurements did not differ among treatments. This study illustrates that barley grain can be replaced by corn distillers' grain, wheat distillers' grain or wheat middlings in diets fed to growing beef cattle without compromising feed conversion efficiency, adversely affecting feeding behaviour or increasing incidences of ruminal acidosis.

Key words: beef cattle, distillers' grain, wheat middlings, feeding behaviour

INTRODUCTION

By-products are included in ruminant diets for various reasons such as reducing feed costs, correcting nutrient deficiencies and improving animal growth performance. Distillers' grains are by-products of the rapidly expanding renewable energy sector that ferments grains to ethanol. Distillers' grains contains more crude protein (CP), fat, fibre and P per unit of product compared to the parent grains due to the fermentation of starch to ethanol (Mustafa et al. 1999; Klopfenstein et al. 2008). Distillers' grains were initially primarily used as a protein source (Klopfenstein et al. 1978), but more recently they have been used as an energy source for replacing corn or barley grain in ruminant diets (Firkins et al. 1985; Ham et al. 1994; McKinnon and Walker 2008).

Wheat middlings or mill run is another feed by-product from the processing of wheat to flour. Their nutrient composition is variable depending on wheat type (Cromwell et al. 2000), but is generally higher in CP, neutral detergent fibre (NDF) and P than whole wheat grain (Kunkle et al. 2000). Wheat middlings has also been used as an energy or protein source in ruminant diets and resulted in similar production and growth as compared to diets containing corn or corn-soybean meal based concentrates for lactating beef cows (Heldt et al. 1998) and growing cattle (Horn et al. 1995).

Feeding by-products with less starch and more digestible fibre may lessen the negative impact of associative effects on forage digestion (Ovenell et al. 1991), and feeding fibrous by-products may improve feed conversion efficiency in part due to a reduction in subacute acidosis (Firkins et al. 1985; Larson et al. 1993). The majority of reported research has been on the use of corn distillers' grain for lactating and finishing cattle, with only a few studies reporting on the use of wheat distillers' grain in ruminant diets. Little information also exists on comparing the value of feeding distillers' grains and wheat middlings to growing cattle. It is common practice to feed high-forage diets without or with very little grain supplementation to growing beef cattle. The addition of grain by-products offers the opportunity to increase the energy and protein content of backgrounding diets, which may improve average daily gain (ADG) of growing cattle. Therefore, the objective of this study was to compare the growth performance, feeding behaviour and ruminal pH profile of growing beef cattle fed a corn silage-barley grain based total mixed ration (TMR) with that of cattle fed a corn silage based TMR in combination with corn distillers' grain, wheat distillers' grain or wheat middlings.

Abbreviations: ADF, acid detergent fibre; ADG, average daily gain; AUC, area under the curve; BW, body weight; CDDG, corn dried distillers' grain; CP, crude protein; DCPI, digestible crude protein intake; DM, dry matter; DMI, dry matter intake; DDMI, digestible dry matter intake; NDF, neutral detergent fibre; NH3-N, ammonia nitrogen; TMR, total mixed ration; VFA, volatile fatty acids; WDDG, wheat dried distillers' grain; WM, wheat middlings

MATERIALS AND METHODS

This study was conducted at the beef cattle research feedlot at Agriculture and Agri-Food Canada's Research Centre in Lethbridge, Alberta, Canada. The experimental protocol was approved by the Animal Care Committee at the Research Centre and animals were cared for in accordance with the guidelines of the Canadian Council of Animal Care (1997).

Animals and Dietary Treatments

Eighty continental crossbred beef heifers, including 16 ruminally cannulated heifers, with an average initial body weight (BW) of 301 ± 34 kg were used in a 70-d backgrounding study. Upon arrival, all cattle were ear tagged, fitted with a radio frequency transponder (Allflex USA Inc., Dallas Ft. Worth, TX, USA) in the left ear, implanted (Component E-H, Elanco Animal Health, Guelph, ON, Canada), treated with Ivomec (Merial Canada Inc., Baie D'Urfé, QC, Canada), and vaccinated with Fermicon 7/Somnugen and Express 5-PHM (Boehringer Ingelheim Ltd., Burlington, ON, Canada). Heifers were blocked by initial BW and then randomly assigned to one of eight pens to ensure that each pen of 10 animals had a similar average starting BW. Within this assignment, two ruminally cannulated heifers were randomly allocated to each pen. The pens contained two feeding tubs fitted with an electronic monitoring system (GrowSafe System, Airdrie, AB, Canada), which allowed the estimation of individual feed intake and documented feeding behaviour. All pens were randomly assigned to one of four dietary treatments (Table 1): 1) TMR of barley grain and corn silage (CTL), 2) TMR of corn distillers' grain and corn silage (CDDG), 3) TMR of wheat distillers' grain and corn silage (WDDG), and 4) TMR of wheat middlings and corn silage (WM). All by-products were added to the diet at 400 g kg-1 dry matter (DM). Diets were not formulated to be isonitrogenous to reflect industry practice and to assess the impact of additional protein provided by the grain by-products on animal performance. All diets also included a vitamin and mineral supplement at 50 g kg-1 DM to ensure adequate vitamin and mineral intake. Heifers were fed for ad libitum intake twice daily, 70% of their daily allotment at 0900 and 30% at 1400.

Measurements, Sampling and Calculations

The 70-d study was divided into three periods: Period 1 = d 1-21; Period 2 = d 22 - 42; Period 3 = d 43 - 70. Heifers were weighed before feeding on two consecutive days at the beginning and the end of the study, and on a single day at the end of Period 1 and 2 to determine BW change and ADG. The amount of feed offered was recorded daily for each pen. Diet ingredients were sampled once weekly and analyzed for DM at 60°C for 48 h to adjust diet composition based on changes in ingredient DM content. A sample of each of the four TMRs was collected once weekly and orts from each pen twice weekly. The samples were reduced in size using a riffle splitter and a representative sample of the TMR and orts by pen and period were kept frozen until analyzed for chemical composition. Another sub-sample of the TMRs was dried at 60°C for 48 h each week to determine DM intake (DMI). Individual DMI was determined using data collected with the electronic monitoring system and the DM content of the TMRs.

Feeding behaviour was described in terms of meal frequency (meals d-1), total meal duration (min d-1), average meal duration (min meal-1), average meal size (g DM meal-1), feeding time (min d-1) and feeding rate (g DM min-1). Distinct feeding events were pooled into meals as described by González et al. (2010). To pool feeding visits into meals, the meal criterion was defined as the longest non-feeding interval that could still be considered as part of a meal. The meal criterion was calculated for each individual animal using the method of Yeates et al. (2001). Feeding time was calculated as the time spent at the feeders within a day, without including the time in which heifers were absent from the feeders within a meal. Feeding rate was determined as daily DMI divided by daily feeding time.

Fecal grab samples were taken from all animals at each weigh day, except on the two consecutive weigh days at the start of the study. Samples were pooled by animal over the entire 70-d study. Apparent total tract nutrient digestibility was determined using indigestible neutral detergent fibre (NDF) as an internal marker (Cochran et al. 1986). Indigestible NDF content of the TMRs and feces was determined as the NDF residue remaining after 120-h incubation in buffered rumen fluid (DAISYII Incubator, Ankom Technology, Macedon, NY, USA).

Ruminal pH was measured continuously in the cannulated heifers for two 4-d periods (d 14 to 18 and 56 to 60) using the indwelling LRC pH system (Penner et al. 2006). Ruminal pH data were summarized for each heifer as daily mean pH, maximum and minimum pH, and time and area under the curve (AUC) using pH thresholds of 5.2, 5.5 and 5.8. The AUC was calculated by adding the absolute value of deviations in pH from the threshold pH for each minute within a day. The estimate was then divided by 60 to express the AUC in units of pH ´ h. Duration of subacute and acute acidosis was defined as the duration of time when the recorded pH was below 5.8 or 5.2, respectively. The AUC below pH 5.8 and 5.2 defined the severity of subacute and acute acidosis, respectively.

Ruminal content samples were taken on the same day and at the same time pH meters were introduced (just before morning feeding) and removed (approximately 6 h after morning feeding) to measure ruminal fermentation characteristics (ammonia nitrogen [NH3-N] and volatile fatty acids [VFA]). Approximately 0.5 L of ruminal content was obtained by hand from multiple sites within the rumen and strained through two layers of monofilament polyester screen (PECAP, pore size 355 μm; B & S H Thompson, Ville Mont-Royal, QC, Canada). Strained ruminal fluid (1.5 mL) was added to a 1% sulfuric acid (0.3 mL) and 25% meta-phosphoric acid (0.3 mL) solution for the determination of NH3-N and VFA respectively, and frozen at -20°C until further analysis.

Chemical Analyses

All chemical analyses were performed on each sample in duplicate, and where the coefficient of variation was >5%, the analysis was repeated. Analytical DM was determined by drying the samples at 135°C for 2 h, followed by hot weighing (Association of Official Analytical Chemists (AOAC) 1995; method 930.05). The OM content was calculated as the difference between 100 and the percentage ash (AOAC 1995; method 942). The NDF was determined as described by Van Soest et al. (1991) using heat-stable α-amylase (Termamyl 120L, Novo Nordisk Biochem, Franklinton, NC, USA) and sodium sulfite, and acid detergent fibre (ADF) was determined according to AOAC (1995; method 973.18). For the measurement of crude protein (CP; N Ã- 6.25), samples were ground using a ball mill (Mixer Mill MM2000, Retsch, Haan, Germany) to a fine powder and total nitrogen was quantified by flash combustion and thermal conductivity detection (Carlo Erba Instruments, Milan, Italy).

Ruminal VFA were quantified using a gas chromatograph (model 5890, Hewlett-Packard Lab, Palo Alto, CA, USA) with a capillary column (30 m Ã- 0.32 mm i.d., 1-μm phase thickness, Zebron ZB-FAAP, Phenomenex, Torrance, CA, USA), and flame ionization detection. The oven temperature was 170°C held for 4 min, increased by 5°C min-1 to 185°C, and then by 3°C min-1 to 220°C, and held at this temperature for 1 min. The injector temperature was 225°C, the detector temperature was 250°C, with helium as the carrier gas. Concentration of NH3-N in the ruminal fluid was determined as described by Rhine et al. (1998).

Statistical Analysis

Data were analyzed as a split-plot design as described by St-Pierre (2006), with pens as the main plots receiving the treatments (diets) and cows the subplots receiving all the same subplot treatment. The mixed model procedure of SAS was used (Release 9.1, SAS Institute, Inc., Cary, NC, USA). The REML method was used for estimating the variance components, and degrees of freedom were adjusted using the Kenward-Rogers option. The appropriate variance-covariance error structure was determined by the lowest Akaike information criterion value. The model was as follows:

Yjkl = μ + δk + рj:k + cl:jk + ωm + ωδmk + ωpmj:k + εjklm

where δk denotes the fixed effect of the kth dietary treatment; рj:k is the random effect associated with the jth pen nested in the kth dietary treatment; cl:jk is the random effect of the lth cow within the kth dietary treatment and jth pen; ωm is the fixed effect the mth period; ωδmk is the fixed effect of the interaction of period and dietary treatment; ωpmj:k is the random interaction effect associated with the mth period and the jth pen within the kth dietary treatment; and εjklm denotes the random error.

All measurements, except for initial and final BW, and digestibility measurements were analyzed as repeated measurements. Animals and pens were considered random variables. Treatment effects were declared significant at P ≤ 0.05, tendency at 0.05 < P ≤ 0.10, and means were compared using the PDIFF option.

RESULTS

Performance and Digestibility

Heifers were blocked by BW at the start of the experiment and therefore initial BW did not differ among treatments (Table 3). Final BW, however, tended to differ among dietary treatments. Heifers fed the CDDG and WDDG diets had higher final BW than heifers fed the CTL diet (P = 0.02). Heifers fed the WM diet did not differ in final BW from heifers fed the CTL (P = 0.20), CDDG (P = 0.32) or WDDG diet (P = 0.31). The ADG also tended to differ among treatments. Heifers on the CDDG and WDDG diets had a higher ADG compared to heifers on the CTL diet (P = 0.03), whereas heifers on the WM diet tended to have a higher ADG than heifers on the CTL diet (P = 0.10).

Heifers fed the CDDG, WDDG and WM diets had higher DMI than the heifers fed the CTL diet (Table 3). Apparent total tract DM, OM and NDF digestibility were lower in heifers fed the CDDG and WDDG diet compared to heifers fed the CTL diet. Digestibility of ADF was also lower for the CDDG treatment compared to the CTL treatment, whereas that of the WDDG treatment was similar to the CTL. Apparent total tract DM and OM digestibility in heifers fed the WM diet were similar to that in heifers fed the CTL diet, and therefore higher compared to that in heifers fed the CDDG and WDDG diets. Digestibility of NDF and ADF were higher in heifers fed the WM diet compared to all other dietary treatments. Crude protein digestibility for the CDDG and WM treatments was similar, and higher compared to that of the CTL and WDDG treatments. Digestible DMI for heifers fed the WM diet was higher than for the other three dietary treatments. Heifers fed the CTL and WDDG diets had similar digestible DMI (DDMI), and both had a higher DDMI compared to heifers fed the CDDG diet. Digestible CP intake (DCPI) was the highest for heifers fed the CDDG and WDDG diets, intermediate for WM-fed heifers and the lowest for heifers receiving the CTL diet.

Gain to feed ratio (kg ADG kg DMI-1) were similar for all dietary treatments (Table 3). However, due to the differences in DM and CP digestibility and DDMI and DCPI, the gain to feed ratio expressed as kg ADG kg DDMI-1 and kg ADG kg DCPI-1 differed among treatments. Heifers fed the CDDG diet had the highest gain to DDMI ratio, the WDDG diet intermediate, and heifers fed the CTL and WM diets had the lowest DDMI conversion ratio. However, heifers fed the CDDG, WDDG and WM diets had similar gain to DCPI ratios, which was lower compared to heifers fed the CTL diet.

Feeding Behaviour

Feeding behaviour as characterized by meals d-1, average meal duration and average meal size was similar for all dietary treatments (Table 4). Total duration (min d-1) of meals however, was greater for WM- and WDDG-fed heifers compared to heifers fed the CTL diet, and intermediate for CDDG-fed heifers. Feeding time, which did not include time within a meal spent away from the feeder, was greater for WM- and WDDG-fed heifers compared to heifers fed the CTL and CDDG diets. In contrast, feeding rate (g DM min-1) was the lowest for WM-fed heifers, intermediate for WDDG- and CTL-fed heifers, and highest for heifers fed the CDDG diet.

Rumen Fermentation and Ruminal pH Profile

Total VFA concentration was similar for heifers fed the CTL and WDDG diets (Table 5). Heifers fed the CDDG diet had the lowest total VFA concentration whereas total VFA concentration for heifers fed WDDG was intermediate and similar to the other three diets. Molar proportions of acetate, butyrate and propionate, acetate to propionate ratio and rumen NH3-N concentration were similar among dietary treatments. Ruminal pH profile measurements (minimum, mean, maximum), indicators of acute and subacute acidosis (duration under predefined pH thresholds) and severity of ruminal acidosis (area under curve for predefined pH thresholds) were also similar among dietary treatments.

DISCUSSION

We compared corn distillers' grain, wheat distillers' grain and wheat middlings as alternative energy sources to barley grain in corn silage-based diets for growing beef cattle. Distillers' grains and wheat middlings are more concentrated in protein and fibre content compared to the original grain (Kunkle et al. 2000; Klopfenstein et al. 2008), and thus present an opportunity to increase the CP content of backgrounding diets while providing digestible energy. This was reflected in the higher CP and fibre contents of the respective TMRs. The metabolizable protein (MP) content of the CTL diet was slightly lower than that recommended for growing beef cattle (NRC 2000) due to a lower than expected CP content for the corn silage (7.4%, DM basis) and barley grain (11.7%, DM basis). Despite the low CP content of the CTL diet the rumen NH3-N concentration was adequate for maximum microbial protein synthesis (2 to 5 mg/dL; Satter and Slyter 1975). The distillers' grains diets and wheat middlings diet also provided enough degradable intake protein for maximum microbial protein synthesis, but it was in excess of animal requirements (NRC 2000).

Heifers fed the CTL diet were more efficient in converting digestible intake protein into weight gain compared to heifers fed the by-product diets. This may be explained by the fact that the use of protein in low protein diets is high due to the ability of ruminants to recycle nitrogen (Reynolds and Kristensen 2008). Also, feeding ruminants protein in excess of their requirement does not always result in higher production (Broderick 2003) because there is an energy cost involved in the excretion of excess nitrogen in the urine (Reynolds and Kristensen 2008).

Heifers fed wheat middlings had similar BW gain and feed conversion efficiency compared to heifers fed the control TMR. This agrees with similar growth and feed efficiencies reported for growing beef cattle fed wheat middlings (35% of diet DM) to replace barley (heifers) and corn (steers) (ZoBell et al. 2003). In another study, however, gain and efficiency tended to be lower for WM-fed (53% of diet DM) steers compared to corn-fed steers (Drouillard et al. 1999). Similarly, ADG and feed efficiency decreased when heifers were fed increasing levels of wheat middlings (16 to 52% of diet DM) to replace rolled corn plus soybean meal (Blasi et al. 1998). In that study the decrease in feed efficiency on WM-fed diets was reported when heifers were limit-fed, but not when heifers received full-fed diets. In our study heifers were fed for ad libitum intake and WM-fed heifers achieved similar feed conversion efficiency to heifers on the control diet by increasing the amount of time they spent eating (total meal duration in minutes per day) and their DMI.

Beliveau and McKinnon (2008) reported that when barley grain is replaced with wheat distillers' grain in feedlot backgrounding diets the optimal theoretical inclusion is 27.2% for maximum DMI and 30.8% for maximum ADG. In our study with grain by-product inclusions of 40% of diet DM, feed conversion efficiency (kg ADG kg DMI-1) was similar for heifers regardless of diet. This was because the numerical increase in ADG for heifers fed the grain by-products was offset by an increase in DMI. In agreement with our study, Gibb et al. (2008) reported no difference in feed efficiency when replacing barley grain (40% of diet DM) with wheat distiller's grain (40% of diet DM) in barley silage-based backgrounding diets for feedlot heifers, but in this case it was due to similar DMI and ADG between treatments. In contrast, McKinnon and Walker (2008) reported similar intakes, increased ADG and increased feed efficiency for growing steers fed 25 and 50% wheat distillers' grain compared to the barley grain control diet.

Decreased total tract digestibility of diets containing distillers' grains have been reported by some (Peter et al. 2000; Gibb et al. 2008), but not all authors (Firkins et al. 1985). In agreement with our study, ZoBell et al. (1993) reported similar whole-tract DM digestibility for heifers fed WM and corn-based finishing diets. However, contrary to our study, ZoBell et al. (1993) reported similar ADF digestibility among treatments. The ruminal pH in WM-fed heifers in their study was lower and this could have negatively affected fibre digestibility. In our study ruminal pH was similar among treatments and fibre digestibility was higher for WM-fed heifers compared to barley-fed heifers. The decreased fibre digestibility in our study for CDDG-fed heifers was possibly due to the high fat content of the diet (Palmquist and Jenkins 1980; Jenkins 1993).

When feed conversion efficiency in our study was expressed as kg ADG kg DDMI-1, it would appear that heifers fed the distillers' grain diets were more efficient as compared to heifers fed the CTL diet. This might, however, not be an accurate assessment. Total tract digestibility for distillers' grain diets in the current study might have been underestimated as it was much lower than reported in other studies (Firkins et al. 1985; Peter et al. 2000; Gibb et al. 2008).

Differences in total meal duration, feeding time and feeding rate were related to the DMI of heifers. In general, the greater the DMI the more time heifers spent at the feed bunk and this also resulted in a lower feeding rate. Heifers fed the CDDG diet seemed to be the exception in that they spent less time feeding despite a high DMI and long total meal duration. This was, however, offset by the high feeding rate for CDDG fed heifers compared to heifers fed the WDDG and WM diets, despite similar DMI and total meal durations. It has been suggested that animals fed distillers' grain products may have fewer off-feed problems and reduced subacute acidosis (Firkins et al. 1985). However, there was no evidence in the current study of changes in feeding behaviour in relation to rumen fermentation profiles. Heifers on all treatment diets had similar meal frequencies, average meal durations and meal sizes. The ruminal pH profile of heifers was also similar among treatments and therefore no indication of increased subacute acidosis was evident for heifers fed barley grain as compared to by-products.

CONCLUSIONS

Barley grain can be replaced by corn distillers' grain, wheat distillers' grain or wheat middlings for growing beef heifers fed a corn silage-based backgrounding diet without compromising rumen health, growth performance or feed conversion efficiency. Further research is needed to quantify the energy cost to the animal associated with the excretion of excess nitrogen supplied by distillers' grain products.

Table 1. Dietary ingredients and nutrient composition of TMR containing corn silage in combination with barley grain (CTL), corn distillers' grain (CDDG), wheat distillers' grain (WDDG) or wheat middlings (WM) offered to growing beef heifers

Diet

Item

CTL

CDDG

WDDG

WM

Ingredient, % DM

Corn silage

55

55

55

55

Tempered barley grain

40

-

-

-

Corn dry distillers' grain

-

40

-

-

Wheat dry distillers' grain

-

-

40

-

Wheat middlings

-

-

-

40

Supplementz

5

5

5

5

Diet compositiony

DM, %

50.4 ± 0.30

49.8 ± 1.32

51.2 ± 1.07

49.2 ± 0.58

CP, % of DM

10.0 ± 0.54

17.1 ± 0.88

21.2 ± 0.01

12.3 ± 0.53

Soluble protein, % of CP

27.8

14.6

16.8

30.0

RDP, % of CPx

63.9

57.3

58.4

65.0

NDF CP, % of DM

1.0

2.1

3.6

1.4

ADF CP, % of DM

0.7

1.7

3.1

0.83

NDF, % of DM

27.9 ± 0.33

35.6 ± 0.83

35.5 ± 0.01

37.4 ± 0.88

ADF, % of DM

15.6 ± 0.44

21.0 ± 0.91

23.0 ± 0.00

20.1 ± 0.16

Ether extract, % of DM

2.0 ± 0.04

5.7 ± 0.60

2.6 ± 0.3

2.6 ± 0.1

zAdded to supply per kilogram of dietary DM: 28.3 g of tempered barley grain, 12.8 g of limestone, 5.0 g of canola meal, 1.5 g of NaCl, 1.3 g of molasses, 1.0 g of urea, 29.8 mg of Zn, 11.5 mg of Mn, 7.6 mg of Cu, 1.5 mg of Se, 0.19 mg of K, 0.16 mg of Mg, 0.12 mg of P, 0.10 mg Co, 2 533 IU of vitamin A, 251 IU of vitamin D, and 7 IU of vitamin E.

yMean ± standard deviation (n=3). Means without a standard deviation represents analysis done by Cumberland Valley Analytical Services, Inc. (Maugansville, MD) on a composite sample.

xRDP = rumen degradable crude protein.

Table 2. Nutrient composition of major feedstuffs used in total mixed rations offered to growing beef heifersz

Feedstuffy

Nutrient

Corn silage

Barley grain

Corn DDG

Wheat DDG

Wheat middlings

DM, %

37.1 ± 0.58

87.0 ± 0.24

92.3 ± 0.19

92.7 ± 0.01

92.7 ± 0.12

CP, % of DM

7.4 ± 0.34

11.7 ± 0.16

31.8 ± 1.36

36.5 ± 0.68

17.9 ± 0.53

NDF, % of DM

42.5 ± 1.32

18.1 ± 1.90

29.9 ± 2.23

28.9 ± 1.23

33.7 ± 1.12

ADF, % of DM

26.7 ± 0.78

5.4 ± 0.69

13.4 ± 0.86

16.1 ± 1.30

11.6 ± 0.07

Ether extract, % of DM

2.1 ± 0.25

2.0 ± 0.05

11.6 ± 1.40

4.5 ± 2.46

4.1 ± 0.10

zMean ± standard deviation (n=3 for corn silage and barley grain; n=2 for corn DDG, wheat DDG and wheat middlings).

yDDG = dried distillers' grain.

Table 3. Performance and apparent total tract digestibility of growing beef heifers fed diets containing corn silage in combination with barley grain (CTL), corn distillers' grain (CDDG), wheat distillers' grain (WDDG) or wheat middlings (WM) (n = 20)

Item

CTL

CDDG

WDDG

WM

SEM

Ptreatment

Performance

Initial BW, kg

297

304

302

300

7.72

0.95

Final BW, kg

377

403

403

392

8.13

0.07

ADG, kg d-1

1.16

1.42

1.43

1.32

0.051

0.06

DMI, kg d-1

7.48b

8.74a

8.80a

8.72a

0.215

<0.01

Gain:feed ratio, kg ADG kg DMI-1

0.155

0.165

0.165

0.153

0.0057

0.41

Gain:feed ratioz, kg ADG kg DDMI-1

0.263c

0.389a

0.349b

0.258c

0.0126

<0.01

Gain:feed ratioy, kg ADG kg DCPI-1

3.53a

1.78b

1.92b

2.14b

0.119

<0.01

Digestibility

DM, %

59.7a

43.4c

47.3b

59.8a

1.21

<0.01

OM, %

62.3a

46.6c

51.1b

62.9a

1.09

<0.01

CP, %

44.8b

54.8a

42.5b

58.8a

1.47

<0.01

NDF, %

35.7b

18.2d

31.7c

41.8a

1.30

<0.01

ADF, %

20.9b

11.2c

19.6b

30.9a

1.40

<0.01

DDMI, kg d-1

4.46b

3.66c

4.16b

5.23a

0.172

<0.01

DCPI, kg d-1

0.32c

0.80a

0.80a

0.63b

0.032

<0.01

zDDMI = digestible dry matter intake.

yDCPI = digestible crude protein intake.

a,b,c,d LSmeans in the same row differ, P < 0.05.

Table 4. Feeding behaviour of growing beef heifers fed diets containing corn silage in combination with barley grain (CTL), corn distillers' grain (CDDG), wheat distillers' grain (WDDG) or wheat middlings (WM) (n = 20)

Behaviour

CTL

CDDG

WDDG

WM

SEM

Ptreatment

Meal frequency, meals d-1

13

14

12

15

1.0

0.37

Total meal duration, min d-1

183.4b

200.4ab

210.2a

214.6a

7.06

0.01

Average meal duration, min meal-1

15.2

14.6

17.9

15.1

1.30

0.38

Average meal size, g DM meal-1

627

640

742

618

42.8

0.29

Feeding time, min d-1

59.6b

59.9b

96.4a

115.8a

7.45

0.01

Feeding rate, g DM min-1

143.8ab

181.0a

101.0bc

80.9c

12.44

0.02

a,b,c LSmeans in the same row differ, P < 0.05.

Table 5. Rumen fermentation measurements and ruminal pH profile of growing beef heifers fed diets containing corn silage in combination with barley grain (CTL), corn distillers' grain (CDDG), wheat distillers' grain (WDDG) or wheat middlings (WM) (n = 4)

Fermentation measurement

CTL

CDDG

WDDG

WM

SEM

Ptreatment

Total VFA, mM

94.3a

83.0b

95.7a

90.0ab

2.64

0.03

Acetate, mol 100 mol-1

59.0

58.1

57.6

60.9

1.59

0.54

Propionate, mol 100 mol

21.4

23.4

23.6

21.9

0.98

0.39

Butyrate, mol 100 mol-1

14.8

13.4

13.7

12.9

1.40

0.83

Acetate:Propionate ratio

2.87

2.65

2.50

2.74

0.156

0.43

NH3-N, mM

4.32

5.63

5.44

5.40

0.831

0.69

pH

Minimum

5.26

5.63

5.37

5.25

0.136

0.31

Mean

6.14

6.31

6.14

6.18

0.104

0.63

Maximum

6.88

6.97

6.86

6.94

0.050

0.46

Duration under pH threshold, h d-1

5.2

0.87

0.09

0.23

1.10

0.379

0.25

5.5

2.97

0.93

2.12

2.95

1.218

0.61

5.8

5.97

3.03

5.25

5.79

1.926

0.69

Area under pH threshold, pH Ã- h d-1

5.2

0.20

0.00

0.01

0.17

0.086

0.31

5.5

0.78

0.14

0.32

0.76

0.301

0.37

5.8

2.08

0.71

1.41

2.03

0.781

0.58

a,b LSmeans in the same row differ, P < 0.05.

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