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* Department of Animal Science, University of Nebraska-Lincoln, Lincoln 68583-0908
Dakota Gold Research Association, Sioux Falls, SD 57104-4506
3 Corresponding author: pkononoff2{at}unl.edu
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ABSTRACT |
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Key Words: corn milling (co)product • high-protein distillers grains • milk production
Recent growth in the corn-ethanol industry in the United States has resulted in an accompanying change in the livestock feed industry with increased supplies of feed (co)products such as distillers grains with solubles. In 2007, bio-refineries in the United States produced an estimated 14.6 million metric tonnes of distillers grains, 2.6 million metric tonnes more than the year before (RFA, 2008). In the traditional dry-milling process, whole corn is ground and fermented to produce ethanol. Resulting from this process is the corn-ethanol (co)product—wet distillers grains plus solubles. Previous research has indicated that these (co)products are suitable feed sources for dairy cattle as they contain high levels of protein, digestible fiber, and fat (Schingoethe et al., 1999; Kleinschmit et al., 2006). A recently developed process that aims to improve corn-ethanol yield differs from the traditional dry-milling process because the bran and germ are removed from the corn kernel before fermentation. The remaining endosperm and gluten are ground and used as an energy substrate for yeast fermentation and subsequent ethanol production. Given that the bran and germ, which are high in both fiber and fat, are removed before fermentation, the resulting residue is high-protein dried distillers grains (HPDDG), which may be higher in protein than traditional distillers grains plus solubles.
The current NRC publication outlining the nutrient requirements of dairy cattle (NRC, 2001) describes the fate of dietary protein. In that publication, feed protein is characterized as RDP and RUP. Understanding the proportion of protein that is not degraded in the rumen is important because it is a direct source of protein and ultimately AA for the animal. Consequently, RUP represents an important contribution to the total pool of MP. Although the degradability of distillers dried grains plus solubles (DDGS) was determined previously (Erasmus et al., 1994; Kononoff et al., 2007), changes in the corn-ethanol process and perhaps also rumen degradability warrant continued research. In this study, the chemical composition and rumen degradability of HPDDG was determined and then HPDDG was fed to lactating dairy cows. The objective of this experiment was to evaluate the effects of feeding HPDDG on milk production, milk composition, and DMI.
Ruminal degradability of HPDDG (Poet Biorefinery, Coon Rapids, IA) was estimated using the in situ bag technique (Kononoff et al., 2007). Two British breed crossbred steers fitted with flexible ruminal cannulas were housed individually and fed a mixed diet of hay and concentrate twice daily (2.1% of BW) with free access to water. Approximately 1.0-g samples of HPDDG were weighed to the nearest 0.1 mg, placed in preweighed 3.5- x 5-cm Dacron bags (Ankom Inc., Fairport, NY) with a pore size of 50 µm and heat-sealed (Vanzant et al., 1998) before being placed in the rumen at staggered intervals inside a weighted large-mesh bag. Each steer received 8 bags incubated for 16 h and 12 bags incubated for 24 and 48 h. Following removal from the rumen, all bags were machine-washed using 5 cycles with 1 min of agitation followed by a 2-min spin. Each bag was then individually rinsed with distilled water to remove all visible external residue from the seams before being dried in an oven for 48 h at 55°C. Individual dry weight was taken for each bag and again after a 4-h air equilibrium period. Percentage ruminal degradability for each bag was calculated by subtracting the bag weight from the end dry weight and then dividing by original sample weight corrected for DM. The proportion of CP remaining at each time point was assumed to be RUP.
Sixteen lactating Holstein cows (12 multiparous and 4 primiparous) averaging 80 ± 14 DIM and weighing 623 ± 94 kg were used to study the effect of feeding HPDDG on milk production. Cows were randomly assigned to 1 of 2 dietary treatments in a 2 x 2 crossover design. Control and treatment diets were balanced to be similar in CP with a portion of forage and all soy-based protein being replaced with HPDDG (20% DM) in the treatment ration. Cattle were housed in individual tie-stalls and fed ad libitum to allow for approximately 10% refusal over four 21-d periods. Milk production and DMI were recorded daily and averaged for d 18 to 21. Milk samples were collected from 6 consecutive milkings on d 19, 20, and 21, preserved in 2-bromo-2-nitropane-1,3-diol, and analyzed for fat and true protein using a B2000 Infrared Analyzer (Bentley Instruments, Chaska, MN) by Heart of America DHIA (Manhattan, KS). Cows were weighed at the start of the trial and on d 20 to 21 of each period. Body condition score (1–5 scale) was also recorded (Wildman et al., 1982) to the quarter point at the start and end of each period by a single trained individual. All experimental animals in the study were cared for following the guidelines stipulated by the University of Nebraska Animal Care and Use Committee.
Feed samples were collected on d 20 and 21 of each period, and subsamples were analyzed by Dairy One Laboratory (Ithaca, NY). The analyses included DM (AOAC, 2000; method 930.15), CP (AOAC, 2000; method 990.06), soluble protein (Roe and Sniffen, 1990), NDF (Van Soest et al., 1991), ether extract (AOAC, 2000; method 2003.05), and minerals (Ca, P, Mg, and K; Sirois et al., 1994). Neutral detergent fiber was analyzed using the Ankom A200 filter bag technique, with 12 mL of 
-amylase and 20 g of sodium sulfite. Starch was determined using a YSI 2700 Select Biochemistry Analyzer (Application Note 322; YSI Inc., Yellow Springs, OH).
Milk production data were analyzed using the MIXED procedure of SAS (2004, version 9.1; SAS Institute, Inc., Cary, NC) as a 2-period crossover design with fixed effects for treatment, period, parity, and the interaction between treatment and parity, and cow within period as the random effect. Significance for all models was declared at P 
0.05, and trends were discussed at P 0.10. The PDIFF option was used to test treatment differences among LSMEANS, and all means presented are least squares means.
Table 1 lists the chemical composition of HPDDG and other feedstuffs used in the rations. As expected, CP content was higher (44.1%) and NDF was lower (25.6%) than the traditional DDGS listed in the NRC (2001) publication (CP = 29.7% and NDF = 38.8%). The higher CP and lower NDF were expected because the bran and germ were removed from the corn kernel before fermentation. Estimates of RUP determined in situ were 62.0 ± 8.76, 56.1 ± 5.34, and 30.9 ± 5.93% CP for 16, 24, and 48 h, respectively. Compared with the current study, Kononoff et al. (2007) incubated a sample of DDGS for 16 h and observed a lower proportion of RUP (43.0% CP).
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FOOTNOTES |
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2 Written for thesis submission to University of Nebraska-Lincoln Undergraduate Honors Program.
Received for publication December 8, 2008. Accepted for publication January 27, 2009.
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  D. J. Schingoethe, K. F. Kalscheur, A. R. Hippen, and A. D. Garcia Invited review: The use of distillers products in dairy cattle diets J Dairy Sci, December 1, 2009; 92(12): 5802 - 5813. [Abstract] [Full Text] [PDF]
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