Commodities have become more common or more flexibly used in dairy rations in the past two decades. Fibrous by-products (FBP) that formerly were locally or regionally used started competing nationally. Of course, many factors contributed to the increased reliance on commodities in rations, including herd expansion. However, I think that the expansion in our knowledge also has helped nutritional advisors know how to use FBP more efficiently and cost effectively.
The concept of "effective fiber" of FBP has evolved to help lower the reliance on forages, while still minimizing rumen health issues. The 1995 Alternative Feeds Symposium and a symposium from the 1995 ADSA meetings (Allen, 1997; Armentano and Pereira, 1997; Firkins, 1997; Grant, 1997; Mertens, 1997) laid a sturdy foundation. The NRC (2001), particularly Chapter 4, has reviewed this information and standardized the relationship between forage neutral detergent fiber (NDF) and nonfiber carbohydrates (NFC). As can be seen from Table 1, these two factors should counter-balance each other in a sliding scale; the more fermentative acids produced (generally related to increased NFC), the more neutralization is needed from salivary buffers (generally related to increased forage NDF). The variance associated with particle size of forages and the degree of processing of grains was recognized by Varga et al. (1998) and qualifies the data in Table 1, but our ability to model and thereby prevent depressions in ruminal pH (Allen, 1997) still seems to limit more sophisticated systems based on effective fiber. Broadly defined, effective fiber 1) stimulates chewing and 2) dilutes the concentration of fermentative acids in the rumen. I will relate these processes to "physically effective" fiber (Mertens, 1997) and "chemically effective" fiber (Ipharraguerre and Clark, 2003), respectively, in this paper.
|Minimum Forage NDF||Minimum Total NDF||Maximum NFC|
|1Taken from NRC (2001). These recommendations were for cows fed TMR with adequate forage particle size and ground corn as the predominant grain. Nonfiber carbohydrate (NFC) = 100% – NDF – protein – fat – ash.|
My objectives are to focus on the current role of FBP as partially physically effective fiber sources and as low-starch feedstuffs that help reduce variability in dairy rations, providing some parallel contrasts to beef situations at the end. I will include some reference to various common FBP sources, but my intention is not to discuss each one separately other than to tie in common characteristics. Readers are referred to more complete descriptions of FBP in the 1995 Alternative Feeds Symposium proceedings and to Stern and Ziemer (1995).
Numerous studies have shown that FBP are intermediate between grain and forage when related to the response in milk fat percentage. This response criterion has been adapted to assess the "effective NDF" (i.e., the total response from physical and chemical effectiveness) of these FBP (Mertens, 1997); however, we now know that milk fat percentage, while related to our perception of chemically effective NDF, leads to inherent difficulties (Krause et al., 2002; Beauchemin et al., 2003). Physically effective NDF coefficients for the same FBP can be quite variable among studies (Table 2). Different particle size and passage rates in different diets explain some of this variation (Varga et al., 1998), and more can be explained by interactions of FBP with different forage sources (Grant, 1997). Such variation is difficult to predict for ration balancing, leading to headaches for nutritional advisors. Despite this variability, though, the physically and chemically effective NDF from various FBP can be successfully used to lower forage or reduce hoof problems in low-forage rations (Pereira et al., 1999). Therefore, the rest of this paper will discuss factors that will help nutritional advisors adjust or troubleshoot rations containing significant quantities of various FBP. For example, based on differing digestion kinetics, chewing activity, and ruminal mat consistency, Grant (1997) proposed a decision tree for soybean hulls (Figure 1). Also, another method for adjusting rations based on various feeding conditions can be constructed (Figure 2).
|Trial 1||Trial 2||Trial 1||Trial 2|
|Corn gluten meal||0.71||0.41||0.63||0.04|
|1Data from Mertens (1997). These factors from milk fat and chewing responses can be multiplied times the NDF percentage in the feed to obtain effective (eNDF) and physically effective (peNDF) NDF concentrations, respectively.|
Increasing particle size of haylage or provision of coarsely chopped hay can help compact the ruminal mat, slowing the passage rate of FBP and potentially stimulating rumination (Grant, 1997). Chop length of forages is certainly related to rumination and ruminal pH. However, within a normal range representative of that seen on dairy farms, the benefits of particle size are not always clear-cut. Different forages, silage management, and other factors must be considered. Because of the importance of the forage-FBP interactions documented by several recent research reports from Nebraska, a brief discussion must be included in this paper.
Increasing particle size of alfalfa (Clark and Armentano, 2002) or barley (Soita et al., 2000) silages increased total chewing time, which should increase ruminal pH (Krause et al., 2002). In contrast, others have shown minor effects of particle size on ruminal pH or chewing activity for corn silage (Clark and Armentano, 1999) or brown midrib corn silage (Schwab et al., 2002). Moreover, does increased chewing necessarily increase milk production? More forage materials on the top screen of the Penn State separator are better until you reach the magic number, right? That’s consistent with our other concepts of "requirements." Allen (1997) even modeled a breakpoint mean particle size. However, although forage particle size can be linearly related to rumination activity (Clark and Armentano, 2002), lack of linearity might be difficult to ascertain with few treatments within studies. I am suggesting that the relationship between forage particle size and rumination probably is not linear and does not necessarily even influence ruminal pH when forage NDF is adequate (Kononoff and Heinrichs, 2003b). Based on my readings, chewing activity (minutes of chewing per unit of forage NDF intake) tends to increase as we provide less effective fiber in the diet. That is, even though total chewing time decreases with decreasing forage particle size, the smaller amount of forage NDF remaining is chewed more. Particle size of alfalfa silage increased chewing much more when forage NDF was low than when high (Beauchemin et al., 1994). Therefore, as forage NDF is replaced by FBP, we might consider that the FBP themselves become more effective at stimulation of chewing, but in reality, the forage NDF could be more efficiently ruminated (and we are crediting the FBP).
Many nutritionists assume that increasing the chop length of silage or provision of long or coarsely chopped hay should stimulate chewing and increase ruminal pH, yet research findings are equivocal. Long hay could be more difficult to handle on some farms and could lead to more variable TMR composition or wastage if fed separately. Coarser silages might not pack as well and could have poorer silage recovery or other related problems. Ruminal pH was affected more by alfalfa hay particle size than by the ratio of alfalfa silage to alfalfa hay (Beauchemin et al., 2003). Provision of long hay maintained or increased dry matter intake (DMI) in some studies with low forage NDF diets (Pereira and Armentano, 2000; Krause et al., 2002; Kononoff and Heinrichs, 2003b). In contrast, DMI was decreased with increasing particle size of alfalfa hay (Yang et al., 2002) or BMR corn silage (Schwab et al., 2002). I will explain later why increased chop length (or feeding of hay) seems to be more beneficial with diets containing considerable amounts of FBP replacing forage but seems to provide much less benefit when forage NDF is adequate, especially if FBP replace grain.
Although forage particle size has been researched considerably in the past 10 years, care must be exercised in the interpretation of results from individually fed cows, especially when dry hay is used. Wisconsin workers (Leonardi and Armentano, 2003) showed that adding long hay increased sorting against those long particles in a TMR fed to grouped cows. The quality of the hay did not affect the sorting rate. They also showed that there was considerable variation among animals, which would present situations on farms in which some cows eat too much grain and, conversely, some eat too much of the leftovers. The former might exhibit signs of poor hoof health or acidosis, while the latter ones might have lower body condition or milk production.
Whole cottonseeds (WCS) provide physically or chemically effective NDF, both of which can help stabilize ruminal pH. Research has documented that linted WCS or WCS products provide superior physical effectiveness compared with other FBP. Other attributes are outlined in the review of Arieli (1998). The physical effectiveness factor for NDF from WCS is about 80% (Harvatine et al., 2002). However, Mooney and Allen (1997) documented that this factor increases dramatically as the physical effectiveness of the forage decreases. Such a response supports previous discussion that cows want to ruminate if we provide them adequate fiber sources to stimulate that rumination. Harvatine et al. (2002) also reasoned that WCS are an active, rather than passive, participant in this stimulation of rumination. Clearly, WCS are nearly as good as forage NDF in low-forage diets so long as NFC concentrations are moderated (Slater et al., 2000).
Because of the difficulty in handling or storing WCS, various processing methods have been developed for increased flowability. Starch-coated WCS appear to be nearly as effective as conventional WCS (Table 3). Pima cottonseeds had been shown in previous studies to escape digestion more than linted WCS, so cracking was more beneficial in Pima than linted WCS (Arieli, 1998). Cracked Pima seeds worked well to partially replace linted WCS in another study (Preito et al., 2003). Extrusion of linted WCS decreased milk fat percentage (Bernard and Calhoun, 1997), but this response could have resulted from decreasing physical effectiveness and (or) from the rapid release of oil by extrusion. Based on unpublished results from Ohio State showing minimal change in chewing activity of various WCS sources (Table 4), I consider it more likely that the increase of fatty acid intermediates from biohydrogenation will depress milk fat. This milk fat depression would be more likely with low-forage diets (Pereira and Armentano, 2000).
|Wet brewers grains||Cottonseeds|
|NDF, % of DM||32.00||34.40||38.7||40.9||40.0||36.9|
|NDICP2, % of DM||2.30||2.42||3.17||3.83||2.65||1.89|
|NFC3, % of DM||40.3||38.8||35.1||33.8||33.1||36.0|
|NEL4, Mcal/lb of DM||0.83||0.81||0.79||0.77||0.77||0.78|
|NEL5, Mcal/lb of DM||0.77||0.76||0.75||0.74||0.74||0.75|
|Milk fat, %a||3.45||3.49||3.50||3.43||3.53||3.20|
|Milk energy/NEL intake||0.723||0.707||0.733||0.723||0.713||0.721|
|NEL balance, Mcal/day||0.9||1.3||0.3||0.5||1.3||0.6|
1Data are from Firkins et al. (2002). WCS = whole linted cottonseeds, DMI = dry matter intake, and Easiflo™ = WCS coated with 2.5% cornstarch to mat the linters.
2NDICP = Nitrogen insoluble in neutral detergent solution x 6.25.
3NFC = nonfiber carbohydrates; 100% – NDF – protein – fat – ash.
4NEL = net energy of lactation estimated for cows at three multiples of maintenance.
5NEL = net energy of lactation based on actual data using NRC (2001) software. These NEL data were used for subsequent energy efficiency and NEL balance calculations.
aMilk fat was higher for WCS than Easiflo cottonseeds.
|------------------------- Chewing, min/lb NDF intake-------------------------------|
1Data are from Moreira et al. (unpublished data from Ohio State University).
2LFD = Low forage diet (16% NDF from forage); WCS = Whole linted cottonseed diet (16% NDF from forage + 5% NDF from whole cottonseed); EAS = Easiflo™ cottonseed diet (16% NDF from forage + 5% NDF from Easiflo™ cottonseed; Easiflo™ = WCS coated with 2.5% cornstarch to mat the linters); DEL = delinted cottonseed diet (16% NDF from forage + 5% NDF from Delinted cottonseed); PEL = Pelleted cottonseed diet (16% NDF from forage + 5% NDF from pelleted cottonseed); HFD = High forage diet (21% NDF from forage).
a,b,c,dMeans with different superscripts are likely to be different with 95% confidence.
Cottonseed hulls have a lower fat concentration than WCS (Table 5), but cottonseed hulls still can be useful in dairy rations. Kononoff and Heinrichs (2003a) reported that chewing time per unit of NDF intake decreased when cottonseed hulls replaced corn silage. Although many would infer from these data that physical effectiveness of cottonseed hull NDF is inferior to silage NDF, total chewing time (minutes per day) was not affected. Cows often increase DMI when cottonseed hulls replace forage (Hall and Akinyode, 2000), as occurred in the previously mentioned study (Kononoff and Heinrichs, 2003a). Ruminal pH even increased when cottonseed hulls replaced corn silage. Therefore, the decreased chewing activity (minutes per unit of NDF intake) was really an indirect result of the increased NDF intake and probably did not accurately reflect the true effectiveness of cottonseed hulls, which probably is similar to that of WCS. Although much lower in NEL concentration than WCS (Table 5), the much higher NDF concentration means that more ration space can be occupied by other energy sources, making up much of the difference.
|Feedstuff||NDF, % of DM||NDICP, % of DM||Fat, % of DM||NEL, Mcal/lb||CP, % of DM||RUP, % of CP|
|Beet pulp||45.8 (6.6)||5.5 (1.3)||1.1 (0.4)||0.67||10.0 (1.1)||76.3|
|Brewers grains, wet||47.1 (6.8)||9.3 (3.9)||5.2 (NA)||0.78||28.4 (4.0)||35.4 (56.6 for dry)|
|Citrus pulp, dried||24.2 (3.5)||0.4 (0.3)||4.9 (1.3)||0.80||6.9 (0.6)||31.7|
|Corn distillers grains, dried||38.8 (7.8)||8.6 (3.4)||10.0 (3.4)||0.90||29.7 (3.3)||50.8|
|Corn gluten feed, dried||35.5 (6.8)||3.6 (1.5)||3.5 (1.)||0.79||23.8 (5.7)||30.0|
|Cottonseed, whole linted||50.5 (5.8)||2.4 (1.2)||19.3 (1.4)||0.88||23.5 (2.6)||22.9|
|Cottonseed hulls||85.0 (5.9)||3.0 (0.3)||2.5 (1.3)||0.22||6.2 (3.6)||55.7|
|Soybean hulls||60.3 (7.4)||3.5 (0.5)||2.7 (1.4)||0.66||13.9 (4.6)||44.6|
|Wheat middlings||36.7 (7.5)||2.8 (0.4)||4.5 (1.3)||0.76||18.5 (2.1)||23.7|
|1Data are from the NRC (2001). The values in parentheses are the standard deviation (NA = not available). As the standard deviation exceeds 10% of its respective mean value, the variation among sources becomes increasingly important to account for in dairy rations. The NEL is at 3x maintenance (Table 15-1 in the NRC), which overestimates its true value for high-producing cows. The rumen undegraded protein (RUP) is at 4x maintenance (Table 15-2a in the NRC); RUP is higher for dry than wet brewers grains. NDF = neutral detergent fiber, NDICP = neutral detergent insoluble crude protein, DM = dry matter, and CP = crude protein.|
When alfalfa silage was replaced with WCS, both the rates of ruminal digestion and passage of potentially digestible fiber were decreased (Harvatine et al., 2002). We proposed that these slower rates retained WCS longer in the rumen, maintained ruminal mat consistency, and kept the weight of ruminal contents similar to the high forage control. As weight of the rumen increases, distension receptors in the rumen could promote rumination activity. We suggested that this maintenance of ruminal weight could be an important mechanism behind the high effectiveness of WCS in low forage diets. Other FBP would probably be digested in, or pass faster from, the rumen. Based on unpublished data from Ohio State University (Table 4), we think that the form or even presence of linters have a minor role in their physical effectiveness.
Brewers grains can provide effective NDF for dairy rations. Brewers grains appear to have a low physical effectiveness factor when based on particle size (Mertens, 1997), contrasting with a moderate factor based on chewing data (Table 2). The fiber is degraded at a moderate rate (0.045 to 0.060/h compared with 0.08 to 0.09/h for alfalfa silage), so we calculated that brewers grains could have a lower ruminal NDF digestibility than alfalfa silage (Younker et al., 1998). Brewers grains therefore provide good chemical effectiveness (ability to dilute starch). In fact, we found that dried brewers grains decreased DMI when replacing concentrate but not when replacing forage. Subsequent research at Ohio State (Firkins et al., 2002) showed that when wet brewers grains were balanced to replace part of the forage NDF while reducing NFC, DMI and lactation performance data were similar to the control (Table 3). As will be discussed later, FBP often are optimized when they replace both forage and grain. When balancing rations using NDF, I caution all readers to account for the significant amount of protein contamination in NDF, which is particularly problematic for brewers grains and distillers grains (Table 5).
Brewers grains are a FBP that contribute multiple aspects to a dairy ration, including rumen undegraded protein, physically and chemically effective fiber, and even up to 10% fat for some batches. Use of SESAME might increase their inclusion in dairy rations because of their broad nutritional qualities. Although the high amount of moisture from wet brewers grains has been suggested to depress DMI, I find little evidence for this conclusion. In fact, it seems much more likely that brewers grains could promote bulk fill limitation of DMI when replacing exclusively concentrate, as discussed by Younker et al. (1998). Moreover, although not clearly documented based on research, wet brewers grains could help hold together TMR, especially those with hay, that are susceptible to sorting behavior by cows.
Fill can be estimated based on digestion kinetics (Jung and Allen, 1995): Fill = [intake of potentially digestible NDF / (kd + kp)] + [intake of indigestible NDF / kp], where kd = rate of digestion of the potentially digestible NDF, and kp is the rate of passage from the rumen.
When researched directly, this concept has not necessarily been related to production (Miller et al., 1990). Despite this apparent lack of support for the concept that FBP contribute to fill, several studies with FBP replacing grain did, or tended to, decrease DMI. Perhaps we have focused so much on the indigestible fraction of forages (which is important!) that we might unintentionally ignore the other part of the fill equation: digestion and passage of the potentially digestible fraction. Many FBP have digestion rates that are similar to, or slower than, those of forages. They generally have much lower indigestible fractions and a finer physical structure than most forages. If the FBP are retained in the rumen (slower passage rate), they should contribute to ruminal fill; if they are not retained because of low NDF concentration or particle size of forages, then the FBP will have reduced digestibility (Firkins, 1997; Grant, 1997).
When wet corn distillers grains replaced grain in 22% forage NDF diets, the total NDF increased from 28 to 43% of the total dietary DM in one recent study (Schingoethe et al., 1999), potentially explaining the 5.3 lb/day depression in DMI. However, dietary fat was also increased, compared with the control diet, such that NEL intakes were similar. In our study with wet brewers grains (Table 3), the higher fat concentration was accounted for by adding more fat to the control, so the brewers grains diets had decreasing NEL concentrations (opposite of the wet distillers trial). Even though NEL concentration decreased progressively, DMI was maintained. The efficiency of NEL usage was comparable for the brewers treatments. This example shows an important point in energy usage. Older NEL values ignored negative associative effects in digestibility, and, as discussed previously, FBP should provide highly digestible fiber that has moderate rates of degradation compared with starch. Therefore, negative associative effects would be expected to be decreased when grain is diluted. The 2001 NRC more aptly accounted for these associative effects and assigns a NEL concentration to the total diet, not to individual feed ingredients (Table 3). However, we need to remember that a fairly large change (for lactation rations) in NEL from 0.78 to 0.73 is about equivalent to a 4 lb/ day depression in DMI (i.e., from 60 to 56 lb/day), so the maintenance of high DMI compensated enough to prevent any detectable depressions in lactation performance in that study.
Corn gluten feed (CGF) can provide a good energy source for lactating cattle. When wet CGF replaced both forage and grain, lactation performance was equal or actually increased (VanBaale et al., 2001; Schroeder, 2003). Dry CGF appears to have similar value to the wet form (Bernard et al., 1991). Combining dry CGF with sodium bicarbonate was beneficial in another study (Firkins et al., 1991). Although there is no direct evidence, I think that it is likely that replacement of concentrate with dry CGF might be less likely to depress DMI than replacement with wet CGF because of its reduced particle size (not moisture level). Replacement of grain tended to increase DMI for dry CGF (Ohajuruka and Palmquist, 1989) but tended to decrease DMI for wet CGF (Staples et al., 1984).
Allen and Grant (2000) designed a comprehensive study to evaluate how wet CGF affects ruminal characteristics (Table 6). They used alfalfa silage in high and low forage controls and added 24% wet CGF to low forage diets with or without replacing half of the alfalfa silage with coarsely chopped alfalfa hay. They estimated that NDF from wet CGF was only 11 or 13% as effective at stimulation of chewing or maintaining ruminal pH (physical effectiveness factors of 0.11 or 0.13, respectively), compared with the alfalfa silage. However, the NDF from wet CGF was 74% as effective as alfalfa silage NDF when milk fat percentage was used as the response criterion (i.e., chemical effectiveness factor of 0.74). Therefore, the ruminal digestion kinetics would be very important to optimize the efficiency of usage of wet CGF fiber. Provision of the hay helped compact the ruminal mat, slowing passage rate, which should help retain more small particles, contribute to ruminal distension, and stimulate rumination. Total chewing time was increased but not to the level of the high forage control. Hay tended to increase ruminal pH but did not affect milk fat percentage. As explained previously, milk fat percentage is generally related to rumen function but also is affected by other variables. However, I would expect a lower response to hay added to CGF diets compared with the other Nebraska studies with other FBP. Although about 32% of the DM in wet CGF was retained on a 1.18-mm screen, which can be used to calculate the physical effectiveness factor (Mertens, 1997), over half of it passed through a 0.05-mm screen (0.2% of an inch) in the study of Allen and Grant (2000). Corn gluten feed has a large amount of steep liquor and other DM components that would not likely be retained longer by a firmer ruminal mat and would probably pass with the ruminal fluid.
|Forage, 66%||Forage, 40%|
½ Hay, ½ Silage
|Forage NDF, %||28.5||17.3||17.5||17.4|
|Rate of passage, %/h||4.20b||6.40a||4.20b||5.20ab|
|Total chewing, min/day||740a||531c||667b||529c|
|Mat consistency2, % of control||200a||107a||147b||100c|
|Milk fat, %||3.25b||3.15ab||3.14ab||2.90b|
1Data from Allen and Grant (2000).
2Data were transformed by taking the reciprocal of the data for 2-min ascension rates and standardizing them relative to the low forage control (100%). Increasing values represent a firmer, more compacted ruminal mat.
a,b,cMeans in a row with different superscripts are different with 95% confidence.
The steep liquor in CGF has a very high N degradability. Boddugari et al. (2001) pointed out that erroneous conclusions could be drawn from previous research in which CGF was evaluated as a main energy component, whereas the response could actually have been influenced by lower metabolizable protein. These researchers evaluated a new corn wet milling by-product, similar to CGF, in which metabolizable protein received more consideration in the experimental design. As the new wet milling by-product replaced concentrate, passage rate from the rumen was not affected, but ruminating and total chewing time increased. Milk yield increased, but milk fat percentage decreased, so fat-corrected milk production was not changed. In a second trial, when the new product replaced forage, rumination time and ruminal pH only decreased marginally. However, passage rate increased considerably, and the ruminal mat become less densely packed. Milk production increased, but milk fat percentage decreased. In their third experiment, the new product replaced both forage and grain. Milk production increased from 85 to 97 lb/day, and milk fat percentage was unchanged. Ruminal and chewing measurements were not taken in this trial, but, based on the first two trials, it appears that they optimized the feeding benefits of the new product as follows: 1) prevented rapid passage of the highly digestible fiber, 2) maintained adequate pH through chemical effectiveness of the NDF, 3) balanced the need for physically effective fiber from the forage with the rate of acid production from the nonforage sources (as in Table 1), and 4) provided enough metabolizable protein (microbial protein plus rumen undegraded protein) to support nearly 100 lb/day of milk production. The authors suggested that 50% replacement of the concentrate and 30% replacement of the forage was an optimal usage rate for this FBP.
Standard practice is to balance forage NDF and NFC, as described previously, but special consideration is needed when including beet and citrus pulps in dairy rations. These sources have a lot of pectin and soluble fiber that is not recovered by NDF and yet can be very rapidly degraded by ruminal microbes. Replacement of beet pulp for grain depressed DMI without affecting milk production in one study (Mansfield et al., 1994). Milk fat percentage increased while protein percentage decreased, perhaps because of the filling effects of beet pulp. When it replaced forage (Clark and Armentano, 1997), DMI was not affected. In that study, beet pulp was moderately effective at maintaining milk fat percentage but appeared to not be very physically effective. Citrus pulp was evaluated in three experiments in a Florida report (Leiva et al., 2000). Milk production tended to decrease and decreased significantly when citrus pulp replaced hominy and corn grain, respectively. The authors suggested that the response could have been a result of more microbial growth and protein reaching the duodenum when more cornstarch was fermented, compared with the pectins in citrus pulp. Starch can provide a good substrate for microbial protein synthesis, but high starch availability in the rumen does not always necessarily promote more flow of microbial protein to the duodenum (Firkins et al., 2001). I recommend that users pay close attention to metabolizable protein in commodity-based rations for high-producing cows because the available computer software might not model microbial growth in these cases as accurately as in more traditional rations.
Wheat middlings probably have lower fiber digestibility than other FBP (Bernard and McNeill, 1991), which is probably reflected by this FBP’s predicted lower fiber degradability in the rumen (Miron et al., 2001). Combined with its relatively low effectiveness (small particle size), wheat middlings would be expected to be primarily a chemically effective NDF source that can be used effectively in dairy rations (Stern and Ziemer, 1995) when priced competitively.
Ruminal kinetics greatly affect the efficiency of usage of soyhulls. In a nice review, Ipharraguerre and Clark (2003) reported an average rate of degradation of 5.6%/hour, but they noted studies in which the rate or extent of NDF digestibility could be depressed in an acidic rumen. Soyhulls can provide nearly as much digestible energy as corn, but they can have rapid passage rates when the ruminal mat is less consistent (Grant, 1997). As described previously, replacement of both grain and forage helps optimize the digestibility characteristics of FBP, potentially increasing milk production, as in a recent trial using soyhulls (DeFrain et al., 2002). However, most of the research has been done with soyhulls replacing grain or forage separately (not both).
Soybean hull NDF can replace forage NDF satisfactorily so long as the forage is coarse (Ipharraguerre and Clark, 2003). Ruminal mat consistency, rumination activity, and ruminal passage rates were discussed as reasons justifying this recommendation. I would stress another stipulation that NFC must be decreased concomitantly. They also discussed the loss of potentially digestible NDF from the total tract when soyhulls replaced forage in such circumstances. Nutritional advisors need to remember that the computer doesn’t necessarily adjust NEL for poor digestive function, but the cows certainly do. Despite greater excretion of potentially digestible NDF compared with their potential responses in some studies (if grain was also replaced by soyhulls), these authors reported average increases of 0.7, 1.5, and 0.9 lb/day for DMI, milk yield, and fat-corrected milk yield, respectively.
In studies in which soyhulls replaced grain, there were few differences in the overall average lactation performance (Ipharraguerre and Clark, 2003). Milk fat tended to increase (0.11 percentage unit). Despite few responses in the treatment means, they noted that some authors reported decreased milk protein yields. Metabolizable protein (less microbial protein) and(or) metabolizable methionine could have explained the decreased milk protein response. They suggested limits of 25% soyhulls in the diet when replacing forage (if adequate effective fiber) and 30% when replacing grain.
In my review, I have focused on dairy studies, but there are some analogous data from beef studies that support the dairy research.
Effective fiber can help maintain or increase DMI (Galyean and Defoor, 2003). Negative associative effects would be important in mixed diets (roughage plus grain) in which the forage is expected to provide energy rather than primarily for use to keep cattle on feed. A negative associative effect is when a response in digestibility, DMI, or growth is expected to be the average of the responses from two different feeds (such as a forage and a grain when fed separately), but the actual response is lower than the predicted average. Several beef reports have documented the benefits of FBP to lower negative associative effects. For example, when based on resultant performance, corn fiber might have more NEg than corn grain (Oliveros et al., 1989).
The differences between wet and dry FBP might be more pronounced in beef rations than dairy rations, and dairy nutritional advisors might gain perspective from such cases. Cattle had better performance when fed wet than dry distillers grains (Lodge et al., 1997), and wet CGF was predicted to have more NEg than dry CGF (Ham et al., 1995), perhaps by decreasing negative associative effects. In either wet or dry forms, sorghum distillers grains were inferior to corn distillers grains (Lodge et al., 1997). A modified corn FBP had poorer digestibility and lower cattle performance than dry CGF or dry corn distillers grains (Peter et al., 2000).
Titgemeyer (2000) reviewed the literature for soybean hulls. In addition to comments described previously, he assessed the potential to use soyhulls as the main ingredient in beef rations. Passage rate is rapid, as expected, but performance still was satisfactory. This underscores the economical considerations in such rations. Excretion of potentially digestible fiber in soyhulls might be acceptable if its price is competitive relative to forages and grains used in growing rations. Limit feeding was beneficial in diets with high amounts of wet CGF (Hussein and Berger, 1995), and perhaps such a case might be helpful for high soyhull diets. As discussed previously, the high intake rates of high-producing dairy cows would promote passage without adequate coarse forage. However, addition of 30% alfalfa hay to soyhull-based beef rations actually might have promoted positive associative effects (the response was greater than predicted) in a recent study (Trater et al., 2001), independent of passage rate effects. The passage rate from the rumen actually increased when alfalfa hay was added. They suggested that the benefit was due to increased ruminal pH. Even soyhulls can produce enough acids during fermentation to depress ruminal pH when saliva flow is lowered because of insufficient physically effective NDF. Finally, Titgemeyer (2000) concluded that soybean hulls make a very good energy supplement for forage-based diets because they should be highly digestible but should not decrease forage NDF digestibility as would some grain sources.
Fibrous by-products are becoming staples in many dairy rations. The FBP help meet the needs for physically effective fiber (especially WCS), particularly after the dairy cow has transitioned into lactation such that the feed intake pattern is stable and the rumen is adjusted to higher energy rations. However, most FBP probably have a more important role in slowing the rate of ruminal degradability compared with grain-based concentrates (high chemical effectiveness). As DMI continues to increase for high-producing dairy cows, digestion and passage rates become increasingly important. Besides affecting ruminal digestibility, these rates probably affect the ruminal mat and possibly even rumination activity. Nutritional advisors need to be more aware of these interactions to be able to use FBP on farms with different availabilities of forages or with different particle sizes of those forages. Unfortunately, the complexity of these interactions is difficult to assess for specific recommendations at this time, so decision analyses will need to be made on a case-by-case basis (as illustrated in Figures 1 and 2). Even so, our knowledge has increased such that decisions can be made either better or with less trial-and-error feeding. Various FBP should continue to provide increased flexibility and cost effectiveness in ruminant rations in the future.
Jeffrey L. Firkins
Department of Animal Sciences
The Ohio State University
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