The effects of distillers dried grains with solubles on apparent nutrient digestibility and passage kinetics of Boer×Spanish castrated male goats

Abstract

This study was conducted to evaluate the effects of different inclusion rates of distillers dried grains with solubles (DDGS) on apparent nutrient digestibility, and passage kinetics in meat goats. Four uniform mature Boer×Spanish castrated goats (51.4±0.9 kg BW) were used in a 4×4 Latin square experimental design. Animals had free-choice access to twice daily 36.5% bermudagrass hay (BGH) and 63.5% concentrates containing 0, 12.7, 25.4 and 38.1% of DDGS (dry matter[DM]basis; w/w proportion) replacing corn and soybean meal in the diet. Concentrates were isonitrogenous with 16% crude protein (CP). Each period consisted of 16 days for diets adjustment followed by 5 days of total fecal and urine collection for the digestion and passage kinetics. Concentrate and hay offered and refused, fecal and urine outputs were monitored daily. The ytterbium-marked BGH was used to determine the passage kinetics. Results indicated that with the inclusion of DDGS increased ether extract (EE) concentrations of total diets from 2.91 (0% DDGS) to 4.33% (38.1% DDGS). No differences were observed in DM and neutral detergent fibre (NDF) digestibility (P>0.05) among treatments. However, DDGS supplementation had a quadratic effect on apparent digestibilities of acid detergent fibre (ADF) and EE (P=0.04). Passage kinetics and nitrogen utilisation were unaffected by DDGS inclusion (P>0.05). Results of this experiment indicated that DDGS can replace up to 38.1% of diet DM for Boer×Spanish castrated goats with no adverse effects on nutrient digestion and passage kinetics.

Keywords:

• goats
• distillers dried grains with solubles
• digestibility
• passage kinetics

Introduction

The distillers dried grains with solubles (DDGS) is a corn-based fuel ethanol by-product. It is becoming increasingly available in large quantities and at competitive prices for use by the livestock industries in the USA. Approximately 31.5 million tons of DDGS were produced in the USA in 2008–2009 while 5.8 million metric tons were exported (AgMRC 2009). The DDGS is a unique feedstuff that provides high levels of protein, energy, digestible fibre and minerals (Schingoethe et al. 2009). Its protein is also moderately resistant to ruminal degradation, thus making it a good source of ruminally undegradable protein (RUP) source. The RUP value of DDGS ranged between 47 and 64% of the crude protein (CP) for higher-quality DDGS (Kononoff et al. 2007). The feeding value of DDGS has been evaluated for dairy cattle (Schingoethe 2004), beef cattle (Corners and Williams 2002), swine (Shurson et al. 2004) and poultry (Lumpkins et al. 2005). Of the portions of DDGS used for domestic livestock feeding, 50% is utilised by beef cattle, 38% by dairy and 6% each by the hog and poultry industries (AgMRC 2009). The DDGS is being used either wet or dry and performance is usually similar whether fed as wet or dried products (Koger et al. 2010). The nutrient composition of DDGS makes it appear to be a suitable supplement for ruminants consuming high-forage diets of low to moderate nutrient quality that require additional CP and energy to perform optimally. Because DDGS contains virtually no starch, the negative effects of starch on fibre digestion are not a concern with DDGS supplementation (Schingoethe et al. 2009). Furthermore, DDGS contains intermediate fat concentration and readily digestible fibre which contributes to the high energy concentration.

Meat goat enterprises have enormous potential to become a new market for DDGS, as meat goats are gaining popularity in the USA. However, there is very limited research evaluating the use of DDGS in goat diets. Objectives of this experiment were to determine the effect of various dietary inclusion rates of DDGS on nutrient digestibilities and passage kinetics in mature meat goats.

Materials and methods

Experimental animals

The experiment was conducted at the Tuskegee University Caprine Research and Education Unit (CREU) of George Washington Carver Agricultural Experiment Station, Tuskegee, Alabama, USA. Tuskegee University Animal Care and Use Committee approved all the procedures outlined for the experiment. Goats were selected from the CREU herd. Four uniform mature Boer×Spanish castrated goats (51.4±0.9 kg BW) were randomly assigned to four different experimental diets in a 4×4 Latin square arrangement of treatments as described by Solaiman et al. (2002) and Mir et al. (1999). Goats were weighed and placed individually in stainless-steel metabolism stalls equipped to separate urine from feces.

Experimental diets and methods

The concentrates containing DDGS (Poet Nutrition, Dakota Gold, Sioux Fall, SD, USA) were formulated to be isonitrogenous at 16% CP. For determination of digestion and passage kinetics, each collection period consisted of 21 days. Each 21-day period of the 4×4 Latin square included 16 days for diet adjustment followed by 5 days for total collection of feces and measurement of passage rates of bermudagrass hay (BGH) by goats fed with various concentrations. Goats were offered 40% of BGH and 60% of concentrate (containing 0, 12.7, 25.4 or 38.1% of DDGS – on a dry matter basis – replacing corn and soybean meal in the concentrate portion of the diet) separately each day and fresh feed was provided twice daily at 08:00 and 16:00 h. However, actual intake was 36.5:63.5 for BGH:concentrate. Goats had free access to water and trace-mineralised salt blocks. Goats were offered diets sequentially to obtain over 5% refusals (BGH plus grain mix) and this intake was used as an estimate of ad libitum consumption by each animal. Feed intake was calculated from disappearance of BGH and concentrates. The BGH was chopped into 5- to10-cm particle size for handling ease. The chemical compositions of DDGS and BHG are shown in Table 1. Body weights were recorded every week 4 h after withdrawing feed and water.

Table 1. Chemical composition of distillers dried grains with solubles (DDGS) and bermudagrass hay (BGH; g/kg, dry matter basis).

Item^a	DDGS	BGH
Dry matter	878	883
Crude protein	287	103
Ether extract	119	21
Non-fibre carbohydrate	301	151
Neutral detergent fibre	278	693
Acid detergent fibre	120	349
Hemicellulose	158	344
Ash	48	58
Phosphorus	9.0	2.2
Sulphur	8.9	2.8
^aAll vales are on dry matter basis except dry matter.

Preparation of marked hay

The BGH was labelled with ytterbium (Yb) to measure rate and kinetics of passage of particulate matter through the digestive tract according to the procedures outlined by Ellis et al. (1994), Grovum and Williams (1973) and Goetsch and Owens (1985). The chopped hay (320 g) was soaked in 3.2 L distilled water containing 5.12 g of Yb as Yb acetate [Yb (CH₃COO)₃·4H₂O] for 48 h. The marked hay solids were retained through four layer cheesecloth, and rinsed twice with distilled water, dried at 55°C for 48 h and equilibrated to ambient conditions before being dosed. At 08:00 h of day 1 of each collection period, two gelatin capsules each containing 6 g of marked hay were inserted into the esophagus of each animal using a balling gun, after which they were offered feed. Based on marker concentration, it was expected (based on calculation) that each animal received 192 mg of Yb (16 mg Yb/g hay).

Sample collection for digestion and passage determination

Total feed offered, refused and fecal and urine outputs were recorded daily for 5 days during the collection period. Samples of each feed (concentrates and BGH) were collected daily and pooled to form composite samples. Fecal samples were collected from each goat before dosing to serve as a blank in marker analysis. Total feces were collected from each goat at intervals of 6, 12, 24, 36, 48, 60, 72, 84, 96 and 120 h after Yb-labelled hay was dosed and an aliquot was taken for marker analysis. Fecal samples were dried at 55°C for 48 h, equilibrated to ambient temperature for 24 h, weighed, and ground through a 1-mm screen in a Wiley Mill (Arthur H. Thomas, Philadelphia, PA). Urine, collected daily in 4-L jugs containing 2 mL of 6 N HCl, was weighed and a 100-mL subsample was stored frozen for later analysis.

Chemical analysis

Composite samples of DDGS, BGH and concentrates were analysed for DM, ether extract (EE), CP and ash (AOAC 1990). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were determined using methods outlined by Van Soest et al. (1991) and modified (Komarek 1993) for use in an Ankom fibre apparatus (Ankom Technology Corp., Fairport, NY). Hemicellulose (HC) was calculated as the difference between NDF and ADF. Non-fibrous carbohydrate (NFC) was calculated by difference (NFC=100 – CP – EE – NDF – ash) with no correction for N Concentration of NDF. Urinary N concentration was measured by Kjeldahl method (AOAC 1990).

Marker determination

In a 10 mL of 50:50 mixtures of 3 M HCl and 3 M HNO₃, 1 g of ashed fecal sample was digested for 12 h. After ashing, samples were filtered through Whatman #541 ashless filter paper (Whatman International Ltd., Maidstone, UK) into a 25-mL volumetric flask and diluted to 25 mL with doubly deionised water. Two millilitres of potassium chloride solution (38.2 g KCl/L H₂O) were added to each sample to reduce absorptive interference by other elements and Yb concentration was determined by atomic absorption spectrophotometry (Model 5000, Perkin–Elmer, Norwalk, CT) using a nitrous oxide-acetylene flame. Standards for Yb analysis were prepared by adding known amounts of Yb to fecal samples obtained before it was dosed.

Rate of passage determination

To estimate passage kinetics, Yb collected from each animal at each period was expressed as a cumulative percentage, and these values from 0 to 120 h were subjected to a direct non-linear least squares regression (one compartmental) model that was solved by iteration similar to that used to calculate rate of digestion (Martens and Loften 1980) or that used to calculate rate of passage (Solaiman et al. 1990). Ruminal retention time (ruminal T1/2 = ln2/k) and mean retention time (MRT = 1/k) were calculated using the equation of Grovum and Williams (1973) and transit time (TT) was considered to be the time from marker dosing until the marker was first detected in feces. Total retention time (TRT=MRT + TT) was also calculated. Data were fitted to the one-compartment model of Pond et al. (1982) for estimation of particulate digesta kinetics.

Statistical analysis

The apparent nutrient digestibility and passage kinetics data were statistically analysed using the Proc Mixed Procedure of SAS/STAT® version 9.2 (SAS 2008) for a Latin square design. The relationship between dietary concentration of DDGS and the response variables were evaluated using orthogonal contrasts for equally spaced treatments (Steel et al. 1997). Models included effects due to diet, animal, period and residual errors. Differences were declared significant at P<0.05, unless otherwise indicated.

Results and discussion

Diet composition

The BGH used in the current experiment was comparable in CP% but lower in NDF and ADF to reported values in the literature (NRC 2001). The nutrient composition of DDGS (Table 1) was within the range of reported values. The DDGS ranged from 26.6 to 33.9% in CP, from 10 to 15.9% in EE, from 28.6 to 38.4% in NDF, from 2.45 to 9.25% in starch, from 0.77 to 1.06% in phosphorus and from 0.46 to 0.83% in sulphur (Kononoff et al. 2007). Many factors influence nutrient concentrations of DDGS such as grain quality, milling process, fermentation process, drying temperatures and the amount of solubles blended back into the wet distillers’ grains at the time of drying (Kalscheur 2007). The DDGS for the experiment was received from a single source and single production lot from the Dakota Gold Research Association (Poet Nutrition), Sioux Falls, SD. As with any by-product feed supplement, nutrient variability is one of the concerns with DDGS.

DDGS (38.1%) containing concentrate mix did not require any addition of soybean meal to meet the 16% CP level because the CP level was met with DDGS alone. There was a small amount of soybean meal added in the 25.4% DDGS containing concentrate to meet the CP level of the diet. The different rates of DDGS inclusion resulted in different concentrations of EE in the experimental diets (Table 2). The calculated EE concentrations of diets were 2.7, 3.4, 3.8 and 4.7% for 0, 12.7, 25.4 and 38.1% DDGS diets, respectively.

Table 2. Ingredient and nutrient composition of different concentrates containing varying levels of distillers dried grains with solubles (DDGS; g/kg, dry matter basis).

	DDGS (%)
Item^a	0	12.7	25.4	38.1
Concentrate	630	644	638	628
BGH	370	356	362	372
Ingredient composition
Cracked corn	463	403	325	203
Soybean meal (48% CP)	122	69	14	–
DDGS	–	127	254	381
Molasses (Black strap)	32	32	32	31
Goat premix^b	13	13	13	13
Nutrient composition
Dry matter	883	864	883	883
Crude protein	136	145	135	141
Ether extract	27	34	38	47
Non-fibre carbohydrate	490	472	464	434
Neutral detergent fibre	324	312	328	344
Acid detergent fibre	148	146	151	157
Hemicellulose	177	166	177	187
Ash	43	45	43	44
Phosphorus	3.7	4.2	4.0	4.5
Sulphur	2.0	2.6	2.7	3.2
^aAll vales are on dry matter basis except dry matter.
^bGoat premix contained: (%) Ca 9.0, P 8.0, Salt 41.0, K 0.10, Mg 1.0; (ppm) Cu 1750, Se 25.0, Zn 7500, and (IU/kg) Vitamin A 308,644, Vitamin D 24,251 and Vitamin E 1653.

Although efforts were made to maintain the concentrate:hay ratio of the diet consumed by goats equal to the 60:40 (w/w), actual ratios were different. The concentrate:hay ratios were 63.0:37.0, 64.4:35.6, 63.8:36.2 and 62.8:37.2 for 0, 12.7, 25.4 and 38.1% DDGS diets, respectively, with the overall concentrate:hay mix ratio being 63.5:36.5.

Nutrient digestibility

Table 3 shows apparent nutrient digestibility of diets by Boer×Spanish castrated goats fed various amounts of DDGS. Since the intakes were calculated to estimate apparent digestibility, they are not discussed in the article, however, there was no difference between treatments (P>0.05). Digestibility of DM, CP, NDF, ash, nitrogen free-extract (NFC) and HC was not different (P>0.05) among treatments. The apparent ADF and EE digestibility decreased (P=0.04) in a quadratic manner as DDGS amounts increased in the diets. The ADF digestibility decreased abruptly at the highest level of DDGS inclusion. This may have been due to the higher EE concentration of the diet contributed by DDGS and EE intakes may have exceeded some threshold concentration. Higher EE levels in the diet are reported to reduce total tract digestion of NDF, ADF and cellulose in wether lambs (Zervas et al. 1990) and dairy cows (Palmquist and Jenkins 1980). Nevertheless, the reason for the depression in fibre digestibility is not fully clear (Palmquist and Jenkins 1980). The NDF digestibility was not different among treatments (P>0.05).

Table 3. Apparent nutrient digestibility of Boer×Spanish castrated goats fed varying levels of distillers dried grains with solubles (DDGS).

	DDGS (%)					S.E.M^a	P-value^b
Items	0	12.7	25.4	38.1		Linear	Quadratic
Dry matter	768^a	757^a	764^a	717^a	13.2	0.84	0.14
Crude protein	771^a	790^a	790^a	771^a	24.7	0.29	0.33
Acid detergent fibre	597^a	573^a	551^ab	464^b	28.9	0.92	0.04
Neutral detergent fibre	620^a	589^ab	619^a	535^b	17.0	0.90	0.16
Ether extract	820^b	849^ab	878^a	870^ab	14.7	0.19	0.04
Ash	569^a	535^a	545^a	443^a	54.2	0.99	0.33
Nitrogen free extract	928^a	931^a	935^a	920^a	5.1	0.35	0.61
Hemicellulose	637^a	609^a	683^a	610^a	23.0	0.92	0.35
^aS.E.M = Standard error of mean derived from the model.
^bBased on orthogonal contrasts for equally spaced treatments.
^a–bValues in the same column without a common superscript letter are significantly different (P<0.05).

Passage kinetics

There was no difference among treatments (P>0.05) in passage kinetics of Yb-labelled hay (Table 4). The passage rates ranged from 4.4 to 4.8%/h which were very consistent across treatments. The lack of significance difference among treatments in passage rates can be partially attributed to similar DM intakes between diets. Owens and Goetsch (1986) reported that passage rates for both concentrates and forages were influenced by DM intake. However, these values were slightly higher than those reported by Caton et al. 1988; 3.7–4.0%/h) for low-quality forage supplemented with cottonseed in wether lambs and those reported by Solaiman et al. (2002); 3.0–3.3%/h) for 45% bermudagrass and 55% concentrates containing 0, 15.7, 32.7 and 50.3% whole cottonseed diets fed to mature goats. Higher values observed for rate of particulate passage reported in current experiment are partially attributed to the higher levels of concentrate fed (over 60%) and physical form of DDGS (fine ground). For example, Caton et al. (1988) fed only 189 g of cottonseed per animal daily with ad libitum low-quality forage (50% prairie hay and 50% oat straw mixture) while the control treatment did not receive any supplements. The NDF and ADF levels were 71.1 and 44.0%, respectively, for the basal forages fed to lambs. Similarly, the NDF and ADF values reported by Solaiman et al. (2002) were much higher (ranged from 45.9 to 51.8%) than the values obtained in the current experiment (Table 2). However, the similarity of passage rate of BGH between treatments provided some explanation for the similarity in DMI and DM digestibilities. Owens and Issacson (1977) reported that the rate of passage affects both DM intake and DM digestibility. For example, as rate of passage increases feed intake increases specially when ruminants are fed ground and pelleted forages; however, particle matter digestibility could be reduced because of having less time to undergo fermentation; overall diet digestibility can be enhanced. But Conrad et al. (1964) reported that the gastrointestinal fill and rate of passage are not important factors limiting feed intake when diet digestible dry matter is 67% or more. All the goats in the four diets had > 67% DM digestibility in the current experiment.

Table 4. Passage kinetics of Boer×Spanish castrated goats fed varying levels of distillers dried grains with solubles (DDGS).

	DDGS (%)
Items^a,b	0	12.7	25.4	38.1	S.E.M^c
k, %/h	4.5^a	4.4^a	4.4^a	4.8^a	0.40
MRT, h	23.1^a	23.5^a	23.0^a	21.2^a	1.80
T1/2, h	16.0^a	16.3^a	16.0^a	14.7^a	1.29
TT, h	10.3^a	10.1^a	12.1^a	10.8^a	1.70
TRT, h	33.4^a	33.6^a	35.1^a	32.0^a	1.13
^a k=passage rate constant for particulate matter, MRT = mean retention time (1/k), TT = time when marker first appeared in feces (transit time), TRT = total retention time (MRT + TT).
^bNo significant differences were observed (P>0.05).
^cS.E.M = standard error of mean derived from the model; P-value columns for linear and quadratic response were removed as there was no difference between diets.
^a–bValues in the same column without a common superscript letter are significantly different (P<0.05).

The mean retention times (MRT) were 23.1, 23.5, 23.0 and 21.2 h for 0, 12.7, 25.4 and 38.1% DDGS whereas the total retention times (TRT) were 33.4, 33.6, 35.1 and 32.0 h, respectively. Robles et al. (1981) reported MRT values for mature sheep 34.13, 37.38, 42.31 and 43.87 h when fed vegetative orchardgrass and mechanically separated alfalfa leaves (60:40; w/w), orchardgrass hay at early head, orchardgrass at late head and orchardgrass hay at seed formation, respectively. These values were higher than the values obtained in the current study. The difference may have been due to several reasons including different hay marking techniques used, higher concentrate diet fed to goats and different species of forages and livestock being used. In the present study, the times for the first appearance of markers (10.1–10.8 h) were lower than those reported by Caton et al. (1988); 15.5–16.5 h). Similarly, both MRT and TRT were much lower than the values reported by Solaiman et al. (2002) for goats fed 45% BGH and 55% concentrate diets containing 0, 15.7, 32.7 and 50.3% Easiflo® cottonseed and those reported by Kennedy et al. (1992) for chopped wheaten hay in goats and sheep. The lower MRT and TRT values in the current study could be explained by the lower NDF and ADF values compared with values reported by Caton et al. (1988) and Solaiman et al. (2002).

Table 5. Nitrogen utilisation by Boer×Spanish castrated goats fed varying levels of distillers dried grains with solubles (DDGS).

	DDGS (%)					P-value^c
Items^a	0	12.7	25.4	38.1	S.E.M^b	Linear	Quadratic
Nitrogen (N) intake, g/day	16.9^a	21.1^a	17.3^a	19.4^a	1.23	0.50	0.42
Fecal N, g/day	3.8^a	4.4^a	3.7^a	4.5^a	0.23	0.26	0.55
Urine N, g/day	8.8^a	12.3^a	10.2^ab	10.9^ab	0.78	0.25	0.12
Absorbed N, g/day	13.0^a	16.8^a	13.6^a	15.0^a	1.18	0.11	0.63
Retained N, g/day	4.3^a	4.5^a	3.4^a	4.1^a	1.11	0.73	0.86
Retained N, % of absorbed N	31.1^a	25.0^a	25.0^a	27.1^a	6.85	0.53	0.78
^aDry matter basis.
^bS.E.M = standard error of mean derived from the model.
^cBased on orthogonal contrast for equally spaced treatments.
^a–bValues in the same column without a common superscript letter are significantly different (P<0.05).

Nitrogen retention

The DDGS inclusion rates did not significantly alter (P>0.05) N intake, fecal N and urinary N excretions (Table 4). The N absorption, N retention and N retention as% of N absorption were also unaffected (P>0.05) by DDGS concentration in the diets. The N intake, fecal N, urine N and N retained (g/day) by mature sheep wethers averaged 21.46, 9.49, 7.52 and 4.45, respectively, when they were fed 100 g DDGS/day with ad libitum access to chopped brome grass hay (Archibeque et al. 2008). The fecal N level were lower (3.8–4.5 g/d); while urine N were higher (8.8–12.3 g/d) in our study while N retained values were comparable although sheep and goats have different physiological adaptations as it relates to nutrition (Table 5). The urine N levels were numerically higher with increasing amounts of DDGS in the diet which may be attributed to increasing levels of RUP in the diets due to DDGS inclusion. The fecal N and urinary N, absorbed N and retained N were directly related to dietary N levels. The similarity between treatments can be explained as dietary N intakes were not different among treatments (P>0.05) in the current study. According to Lallo (1996), N retention showed a curvilinear response to energy intake but exhibited a linear response when increasing N levels were fed implying that N retained is more closely related to N-intake than to energy intake for goats fed diets of varying N levels. Similar response was reported with growing lambs based on the results derived from 298 nitrogen balance studies involving male cross-bred lambs from 3 to 38 kg BW (Black and Griffith 1975). In the current study, N intake was not different between treatments; although, ruminally degradable protein (RDP) was lower as the level of DDGS increased in the diets.

Other nutritional and environmental considerations

The DDGS is relatively high in phosphorus concentration. The phosphorus value of DDGS used in the current trial was 0.9% on a dry matter basis (Table 1). Diets containing higher levels of corn-based by-products have generally low calcium and high levels of phosphorus concentrations thus, requiring addition of calcium supplements to maintain calcium:phosphorus ratio. We did not correct for calcium concentrations of the diets; however, no apparent signs of urinary calculi were observed in any of the animals. The low dietary calcium:phosphorus ratio is one of the factors responsible for phosphatic calculi in intact or castrated male goats (NRC 1981). The high phosphorus concentration in DDGS could also contribute to environmental pollution if phosphorus is fed in excess of goats’ requirements. Due to relatively high sulphur concentration, feeding higher amounts of DDGS could cause high sulphur intake that may induce copper or other trace minerals deficiencies or deficiency leading to polioencephalomalacia (Gould 1998). Sulphur is also reported to form insoluble complexes with copper and molybdenum and decrease their utilisation (Suttle 1980).

Conclusion

The increased production of corn-based ethanol has resulted in abundance of DDGS being available for use in livestock feeds. During period of low forage availability and/or while feeding poor quality of forages, or during drought, supplements such as DDGS can play an important role in diets of goats. However, using supplements in large amounts usually results in a substitution effect, such that intake of forage/hay is reduced. Therefore, knowledge on optimum rate of supplements inclusion is desirable for cost-effective feeding. The results of this study indicate that DDGS can be added up to 38% of the diet dry matter of Boer×Spanish castrated goats without any adverse effects on nutrient digestion and passage kinetics. However, the optimum inclusion level of DDGS depends on its price and availability relative to other feedstuffs fed to meat goats.

Acknowledgements

This work was partially supported by Dakota Gold Research Association, Sioux Falls, SD, Alabama Agricultural Land Grant Alliance and George Washington Carver Agriculture Experiment Station, Tuskegee University, Tuskegee, Alabama, USA. We thank Harold Higgins, Mel Jones and Patricia Mueller for their assistance for the care and management of animals and data collection.