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* Department of Animal Science, University of Nebraska, Lincoln 68583-0908
Dakota Gold Research Association, Sioux Falls, SD 57104
2 Corresponding author: pkononoff2{at}unl.edu
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ABSTRACT |
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Key Words: corn bran • ethanol coproduct • milk • lactation
The recently passed Energy Policy Act (EPACT, 2005) mandates up to 7.5 billion gallons of renewable fuel to be used by 2012 and will result in a dramatic increase in the availability of corn milling coproducts. The inclusion of coproducts such as corn distillers grains with solubles (DDGS) into dairy diets has been demonstrated to maintain milk production (Schingoethe et al., 1999) but are usually fed in limited amounts because of the potential to negatively affect milk fat percentage (Leonardi et al., 2005). Traditional corn-ethanol production employs a system in which the whole corn kernel is ground, cooked, and then fermented to produce ethanol. An alternative to this method is separating the kernel into its 3 major components, namely bran, germ, and endosperm, prior to fermentation. These components are then spared the fermentation processes and may be used for animal feed. Compared with traditional DDGS, corn bran is similar in NDF but lower in CP. Because corn bran is not exposed to the fermentation process, it is generally a better quality nutrient source. The objective of this research was to evaluate the effects of increasing levels of a corn bran coproduct on milk production and composition.
Thirty-nine lactating Holstein cows (23 multiparous and 16 primiparous) were randomly assigned to 1 of 3 dietary treatments in a 3-period crossover design. The experiment was conducted in 2 phases, with 20 animals in phase 1 and 19 animals in phase 2. Cows were housed in individual stalls and milked at 0730 and 1930 h. Cows were fed at 0800 h for ad libitum consumption to allow for approximately 5% refusal. During each of the 21-d periods, cows were offered 1 of 3 rations (Table 1
) that differed by the concentration of corn bran that replaced alfalfa hay, alfalfa haylage, and corn silage. Dietary treatments were 1) low, 10% DM bran, 2) medium, 17.5% DM bran, and 3) high, 25% DM bran. The experimental cows were cared for according to the guidelines stipulated by the University of Nebraska–Lincoln Animal Care and Use Committee.
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-amylase and sodium sulphite were used (Mertens, 2002). The Penn State Particle Separator was used to measure particle size for all rations (Kononoff et al., 2003). Body weight was measured on the last 2 d of each period, but BCS (1 – 5 scale) was measured on the last day of each period. Body condition score was measured by a single trained individual and differed from that described by Wildman et al. (1982) because it was reported to the quarter point. Milk production was measured daily, and milk samples were collected on d 20 and 21 of each period during the AM and PM milking and preserved using 2-bromo-2-nitropropane-1,3 diol. Milk samples were analyzed for fat and true protein (AOAC, 1990) using a B2000 Infrared Analyzer (Bentley Instruments, Chaska, MN) by Heart of America DHIA (Manhattan, KS). Daily DMI and milk yield were averaged weekly.
Milk production, milk composition, intake, and BCS data were analyzed using the MIXED procedure of SAS (Version 9.1, SAS Institute Inc., Cary, NC) according to the following model: yijklm = µ + bij + 
k + 
l + 
m + 
n + eijklm, where µ is the general mean, bij is the random effect of the jth cow within the ith sequence, k is the effect of the kth period, l is the fixed effect of the effect of the lth diet, m is the fixed effect of the mth parity, n is the fixed effect of the nth experimental phase, and eijk reflects the random error in the measurement of the response. Linear, quadratic, and cubic orthogonal contrasts were tested using the CONTRAST statement of SAS.
The corn bran coproduct (Dakota Gold Marketing, Sioux Falls, SD) contained 8.2% moisture and 12.9% CP, 30.4% NDF, and 45.0% NFC, 9.9% ether extract, and 0.70% P when expressed on a DM basis. This chemical analysis outlines the major differences in chemical composition that may exist amount corn milling coproducts. Specifically, compared with the corn bran coproduct, DDGS typically contain similar levels of NDF (38.8%) and fat (10.0%) but higher levels of CP (29.7%; NRC, 2001).
Diets were formulated to contain 3 levels of the bran, which replaced a portion of the forages. The chemical composition of the diets fed were similar (Table 1
), containing approximately 18% CP, but increasing the levels of bran resulted in a modest decrease in total diet NDF: 33.1, 32.5, and 31.8% DM for low, medium, and high treatments, respectively. The concentrations of ether extract and NFC were also different (ether extract = 4.9, 5.3, 5.7% DM and NFC = 38.3, 39.0, and 39.7% DM for low, medium, and high, respectively). The diet P content increased from 0.34, 0.38, and 0.42% as corn bran was included in the diet from 10, 17.5, and 25% of the diet DM. The TMR particle size analysis is also presented in Table 1. Ration particle size reflected the amount of bran included in the treatments. Increasing inclusion of bran reduced the proportion of material on the 19.0-mm screen (5.7, 4.8, 4.5%), but increased the proportion retained on the pan (<1.18-mm; 25.2, 27.1, 30.7%).
Increasing the level of bran did not affect DMI, which averaged 23.8 ± 0.73 kg/d across treatments (Table 2). Milk yield tended (P = 0.07) to increase linearly with increasing concentrations of bran: 32.7, 33.4, 35.8 ± 1.30 kg/d for low, medium, and high, respectively (Table 2). As a consequence of lack of effect on DMI and effect on milk yield, feed conversion significantly improved with increasing inclusion: 1.39, 1.39, and 1.55 ± 0.05 kg of milk/kg of DMI for low, medium, and high, respectively. The observation that the feeding of corn milling coproducts may result in increased milk yield but not intake is in contrast to that of Owen and Larson (1991). In that study, DDGS replaced primarily soybean meal and diets were of low protein content. These authors suggested that intakes were increased by feeding DDGS because a greater amount of amino acids were required to maintain maximal milk production. Thus it is possible that in the current experiment intakes were similar across treatments because the coproduct replaced forage, and based on the NRC (2001) model, experimental diets were formulated to be higher in CP and adequate in MP. This suggestion is further supported because a lack of effect of DMI has also been observed when DDGS replace forage in the form of alfalfa haylage (Clark and Armentano, 1993).
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Compared with other studies evaluating health and reproduction (Windig et al., 2005), the current study contained a small number of animals and should be interpreted with caution. During the second phase of the experiment, 3 animals were diagnosed with displaced abomasums, and data from these animals were removed from the data set. Two animals were diagnosed while consuming the high treatments, and one was diagnosed while consuming the medium treatment. The reason for these observations is unclear but may have been a result of a reduction in effective fiber when the bran replaced forage. The NRC (2001) recommends dairy diets contain at least 25% NDF with at least 19% from forage (fNDF) and an upward adjustment in ration NDF content if fNDF content is reduced. In the current experiment, the low treatment consisted of 15.8% fNDF and 33.1% NDF, which is in the recommended range of minimum total and forage NDF. In comparison, the high diet contained 9.9% fNDF and 31.8% NDF, which is below recommended levels. Practically, health results of the current experiment suggest that the bran coproduct is a feedstuff with high nutrient quality but should be included into dairy diets balanced to contain adequate levels of effective fiber.
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FOOTNOTES |
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Received for publication April 11, 2007. Accepted for publication May 4, 2007.
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