Ruminal in situ nutrient disappearance from alfalfa and cottonseed hulls in goats fed dried distillers grains

R A Allphin, B D Lambert*, T R Whitney* and J P Muir*

Department of Animal Science and Wildlife Management, Tarleton State University, TX USA
* Texas AgriLife Research, Texas A&M University, TX USA
j-muir@tamu.edu

Abstract

Four mature, ruminally cannulated wether goats (Boer × Spanish) were arranged in a 4 × 4 Latin square design experiment and consecutively assigned to one of four complete isonitrogenous and isoenergetic pelleted treatment rations with 0, 6.6, 13.2, or 20% DDG.  Alfalfa and cottonseed hulls (CSH) were incubated in situ for 0, 4, 8, 16, 24, 48 and 96 h and analyzed for dry matter (DM), organic matter (OM), acid detergent fiber (ADF) and neutral detergent fiber (NDF) disappearance.   

Replacing up to 20% of the diet with DDG did not affect ruminal in situ alfalfa or CSH disappearance.  Further research is needed to determine the maximum levels of DDG inclusion in goat diets for optimal nutrient utilization.   

Key words: DDG, tannins, wethers

Introduction

Since the early 1990’s, goats have been the fastest-growing segment in agriculture (Spencer 2008). In January 2011 there were approximately 3 million goats, the majority raised for meat, in the United States with 1.91 million kid crop in 2010 (USDA-NASS 2011). Texas is the primary producer of meat-type goats in the USA (Solaiman 2007).  With a strong market for meat goats and prices for larger carcasses reaching $5/kg BW (VDACS 2011), pressure to identify alternative feed sources to supplement or finish animals efficiently and economically is growing. 

In 2010, the USA produced 50 billion liters of ethanol (Lichts 2011). Currently there are five proposed ethanol production plants in planning stages across Texas alone. Production rates of DDG, therefore, will likely increase in the near future (McElroy et al 2006). The increases of maize ethanol production leave livestock feeders seeking alternative means for energy and protein feed sources to replace maize.  Including DDG (Figure 1) in the diets of goats may offer producers a more economical alternative to maize.  Gurung et al (2009) fed DDG to growing goats and determined that the inclusion of DDG had no negative effects on growth performance; however, feed fiber disappearance parameters were not tested.  The objective of this study was to determine the effects of replacing cottonseed meal with DDG in goat diets on ruminal in situ nutrient disappearance from alfalfa and cottonseed hulls (CSH).

Materials and methods

Tarleton State University Institutional Animal Care and Use Committee approved all experimental protocols.   

Animals

Four mature, ruminally cannulated (Figure 2) wether goats (Boer x Spanish) with an average body weight of 59 kg were arranged in a 4 × 4 Latin square design experiment.  The study was conducted during 4 periods, each consisting of a 14-d adaptation phase and a 7-d data collection phase.  Goats were randomly assigned to 1 of 4 complete pelleted diets.  Rations consisted of cottonseed meal and milo replaced with 0, 6.6, 13.2, or 20% DDG and formulated to be isonitrogenous and isoenergetic (Table 1).  Goats were fed daily at 0800 and feed refusals were collected weekly to estimate feed intake. Goats had free access to water and salt block and were fed their assigned pelleted treatment ad libitum.

In Situ Disappearance.

Alfalfa and CSH were ground to pass a 2-mm screen, weighed (2 g) into dacron bags and subsequently incubated in the rumen for 0, 4, 8, 16, 24, 48 or 96 h. Upon removal from the rumen, bags were stored at –20°C and thawed just prior to laboratory analyses. Bags were rinsed in a commercial washing machine three times using a 5-minute rinse cycle. Bags were then dried in a forced-air oven at 55°C for 48 h and residual material weighed. Degradation profiles of DM and OM were determined by methods described by Ǿrskov and McDonald (1979). Potential degradability (PD) was calculated as: PD = a + b^{(1 – e ˉct-L)}, where  a is the soluble fraction, b potentially degradable insoluble fraction and c the fractional degradation rate of b. 

Laboratory Methods

Before analysis, forage in situ duplicate samples were composited by goat, period, time, and forage type. In situ samples ground to 1 mm were analyzed for DM by placing them in a forced-air oven at 105°C for 12 h (AOAC 2006). Organic matter concentration was determined by incineration in a muffle furnace at 540°C for 4 h (AOAC 2006). The ADF and NDF concentrations were determined using the methods described by Goering and Van Soest (1970). Feed rations were analyzed for DM, CP, DE, Ca, and P concentrations. 

Statistical Analyses

In situ data were statistically analyzed using Proc NLIN of SAS (SAS Inc. 1990; Cary, NC USA) to estimate in situ degradation parameters. Dependent variables included forage DM, OM, ADF and NDF digestibility. The GLM procedure of SAS was utilized to compare a, b, and k. The model included the effects of animal and treatment. Differences were determined using the PDiff of the LS Means statement and a P-value < 0.05 was considered to be significant.  

Results

In situ nutrient disappearance

There were no treatment differences in fractions ‘a’, ‘b’ and ‘k’ for in situ nutrient disappearance from alfalfa and cottonseed hulls (Tables 2 and 3). 

Discussion

Results of the current experiment support data from Gurung et al (2009) who reported effects of dietary DDG on DMI, growth performance, G:F ratio and carcass quality of growing Kiko x Spanish male goats. In their trial, DDG plus solubles replaced maize and soybean meal at 0, 10.3%, 20.6% and 31% of the diet. Dry matter intake, ADG, ADG/DMI ratio, BW, body wall fat thickness or longissimus muscle area were not affected by treatment. Results of this study demonstrated that DDG can replace soybean meal entirely as well as a portion of the maize up to 31% of the diet DM of growing meat goats without impacting animal performance.  Taken with the data from the current study, it is evident that DDG inclusion in meat goat diets can be accomplished without significant impacts on ruminal nutrient disappearance or animal performance. 

The physical form of distillers grains (DG) affects nutrient values. No research has been conducted feeding wet DG to small ruminants, but a great deal of research has focused on DDG fed to large ruminants.  However, it is generally expected that similar results may be observed when feeding wet or DDG to small ruminants. Depenbusch et al (2009) compared cattle diets containing wet and DDG fed along with varied levels of alfalfa hay. Dry matter intake, ADG, and gain:feed ratio were not affected by the form of DG. Apparent total tract digestion of DM and OM were lower for steers fed diets containing DG than those which did not. However, total tract digestibility did not differ between forms of DG. Carcass characteristics were not affected by diet or form of DG. No differences were detected between wet and DDG when included in steam-flaked finishing diets at approximately 15%. Depenbusch et al (2009) predicted that complete removal of alfalfa hay from diets containing DG will result in a reduction in DMI, ADG, and carcass weight. 

Commercial CSH are commonly fed in ruminant diets to supply fiber and consist of almost pure fiber with the outer hull covered with lint fibers. Condensed tannins (CT) are present in CSH and are a defence mechanism against insects and pathogenic mechanisms (Yu et al 1995).  The CSH used in this experiment contained 5.64% CT as measured by the Terrill et al (1992) method using CSH CT to create the standard curve. Condensed tannins originate in the hull of cottonseed; the kernel itself does not contain CT. Condensed tannins can have an anti-nutritional factor effect on ruminants but at low concentrations, they can improve efficiency of protein digestion by forming hydrogen-bonded complexes with proteins in the rumen (Yu et al 1995). Yu et al (1995) determined the effect of CT in CSH upon in situ DM digestion of CSH in ruminally-cannulated sheep. As levels of CSH increased in the sheep diet, in situ DM digestion rate, potential DM digestibility and predicted rumen digestibility decreased (Yu et al 1995). 

In our study, CSH ruminal degradation was not affected by dietary treatments; however, there was an extensive lag time in the rumen before microbial attachment and disappearance occurred. Similar results were observed by Yu et al (1995) with in situ DM digestion of CSH in the rumen of sheep; digestion was very slow for 12 h, and then progressively increased up to 48 h. 

Conclusions

• Replacing CSH with up to 20% DDG did not affect ruminal in situ alfalfa and CSH disappearance.  We can conclude that DDG can be included in goat diets up to 20% without any negative impact on ruminal disappearance of two of the most common goat feed ingredients: alfalfa and CSH. Results from this study will allow producers to more confidently include DDG in their goats’ diets. Including DDG above 20% or using wet DG in goat feed should be studied before these are recommended.

Acknowledgements

This research was supported, in part, by the U.S. Department of Transportation, Office of the Secretary, Grant No. DT0S59-07-G-00053

References

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Received 24 July 2012; Accepted 5 September 2012; Published 1 October 2012

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