IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Ration Phosphorus Management: Requirements and Excretion Dave Beede Department of Animal Science Michigan State Univeristy East Lansing 48824 Introduction Dairy farms must be environmentally sustainable businesses. Environmental sustainability means that the management objective of zero phosphorus (P) balance is realized. Zero P balance is achieved when the amount P imported into the farm equals the amount exported during some defined period of time. Attainment of zero P balance typically occurs in a whole-farm system composed of animals, crops, animal and manure handling facilities, plus access to cropland to recycle manure P, or other means to export manure P out of the system. Legislation in the U.S. aims to reduce soil P build-up and losses from livestock systems by controlling manure management (CAST, 2002; USDA- NRCS, 2001). Additionally, the Environmental Protection Agency‟s recent final rule (released December 15, 2002) for Concentrated Animal Feeding Operations (CAFOs) emphasizes the need for meticulous on-farm P balancing and management. This management starts with accurate input of P to cattle, largely from feed supplements (Sutton and Beede, 2003; CAST, 2002). Typically, imported feed P makes up the majority of imported P in dairy farms (Klausner, 1993); the other major input is P-containing fertilizer. Both sources should and must be managed effectively to achieve whole-farm P balance. The emphasis on P in nutrient management additionally is underscored by the fact that application of manure P to cropland generally is first limiting because recommended or allowable maximum application rates of P are reached before the maximum allowable application rates of nitrogen or potassium are met. This paper focuses on management of feed P inputs and the effects of ration P on excretion of P by dairy cattle. Phosphorus Balancing Surveys in several states indicate that in many dairy cattle operations P inputs often are greater than outputs. When inputs are greater than outputs, P builds-up in soils over time and the potential for P runoff increases when soil P builds up to excessive concentrations (CAST, 2002; NPMP, 2002). Phosphorus in runoff causes oxygen debt killing aquatic life and excessive algae growth reducing water quality of steams and lakes (CAST, 2002; NRC, 2001). This series of event is not sustainable --- environmentally or legally. Total P inputs (imports) must be less than or equal to total P outputs (exports) for a sustainable system. IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Phosphorus Nutrition The National Research Council (2001) publication for dairy cattle reviews and summarizes the fundamental biological roles of P for productive functions. Also, explanation is given on the approach to estimate the dietary requirements of cattle for various physiological functions --- growth, pregnancy, lactation, and maintenance. The factorial approach is used to estimate the total dietary P requirement. This is the summation of amounts of P needed for various physiological functions divided by the absorption coefficient of P in the ration. For dairy cattle, different absorption coefficients are specified for forages (0.64) and concentrates (0.70) (NRC, 2001). And, the P in inorganic mineral sources varies in absorbability [e.g., 0.75 for dicalcium phosphate; 0.80 for bone meal; and, 0.90 for monosodium phosphate (NRC, 2001)]. Based on the NRC (2001) model the absorption coefficient for P will vary from ration to ration depending upon what specific set of feed ingredients that make-up that particular ration. Optimizing Ration P How can dairy producers, nutritionists, or feed suppliers optimize ration P in herd rations? Who’s in charge? Firstly in my opinion, dairy producers must understand that they are the ultimate and supreme managers of their farm‟s P balance. They must be in charge of and responsible for the P concentrations of their rations. This responsibility can not and must not be “farmed-out” to nutritionists, feed sales persons, or employees. Nutrition consultants, veterinarians, employees, and other service-providers really only can help dairy producers manage P in rations and the whole farm system. Match ration P content to requirements. Secondly, matching ration P content (%) to the amount of milk produced by different management groups within the herd or the whole herd is absolutely critical. To do this effectively good knowledge about the rate of feed intake of the different management groups within the herd is paramount. As reference, use the National Research Council‟s (2001) feeding recommendations (examples are in Table 1). Note that the highest concentration of P recommended for high producing cows is only 0.38%, dry basis. Table 1. Phosphorus feeding recommendations for lactating dairy cows a. Milk yield (lb/cow/day) Ration P(%, dry basis) 55 0.32 77 0.35 99 0.36 120 0.38 a Assumes feed intake rates of the NRC (2001) model. Thirdly, analyze feeds for P content. This includes concentrates, especially byproduct feeds, as well as forages. Use a qualified laboratory to IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . determine P contents of feeds and adjust inputs and rations as necessary. “Book values” for P content of feeds will not give the needed management accuracy. Many feed ingredients, especially byproducts resulting from wet- or dry- processing or fermentation (e.g., distiller‟s grain), have variable P contents or values different from the book. Also, to have reliable information for P balancing, laboratory analysis must be done by the wet chemistry method, instead of NIRS (near infrared reflectance spectroscopy). Analysis by NIRS gives inaccurate estimates of actual P concentrations of most feeds. Re-analysis of different lots of a specific type of purchased feed through time as well as home- grown forages is highly recommended because of the variation associated with different sources and processes used to produce concentrates (e.g., byproduct feeds). Purchasing Byproducts and Supplements Typically feed byproducts are incorporated into dairy rations because of their relatively high protein or energy contents at cost-attractive market prices. But, some byproducts contain quite high concentrations of P. Table 2 gives „ballpark‟ P and crude protein concentrations of some common protein sources and byproduct feeds. Table 2. Phosphorus (P) and crude protein (CP) contents of common protein sources and byproduct feedsa. Crude Protein sources Phosphorus protein CP-to-P and byproduct feedsb content (%) content (%) ratio Blood meal 0.30 95.5 318 Corn gluten meal 0.60 65.0 108 Soybean meal (44%CP; expellers) 0.70 49.9 71 Brewer‟s grain (dried) 0.67 29.2 44 Cottonseed, whole 0.60 23.5 39 Distiller‟s grain, corn (with solubles, dried) 0.83 29.7 36 Canola meal (mechanically extracted) 1.10 37.8 34 Corn gluten feed 1.00 23.8 24 Wheat middlings 1.00 18.5 19 Corn steep liquors 1.70 33.0 19 Wheat bran 1.18 17.3 15 Whey 1.04 14.6 14 Porcine meat and bone meal 4.73 54.2 12 a Values from NRC (2001). b Refer to Sidebar comment at end of this paper for additional discussion of the real cost of byproduct feeds when whole-farm P balancing is an important consideration. Additionally, dairy producers and nutritionists must be vigilant to ensure that unneeded supplements are not used in rations --- even as a „safety factor‟? Rations should be carefully and routinely (e.g., monthly). It might be possible to reduce ration costs by eliminating unneeded supplements. Is a supplement IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . included that contributes to more total ration P than is necessary to meet animals' requirements? In many dairy rations (including lactation rations), very little if any, supplemental P is needed. In most cases, the primary objective of a supplement is to provide protein, not P. Therefore, using protein sources with higher crude protein-to-phosphorus ratios will provide more of the needed protein with less P (e.g., blood meal, corn gluten meal, and soybean meal; Table 2). Actually, using protein sources or byproduct feeds that supply more P than needed in the ration (those with lower crude protein-to-phosphorus ratios; Table 2) may be even more costly than one might think ---- especially in the long-term (see Sidebar comment following this main paper). Consequences of Fat-Feeding and Ca-to-P Ratio on Ration P Management When feeding supplemental fat, it is fairly routine practice to feed supplemental Ca in excess of that needed to meet the cow‟s Ca requirement. It is common to find 1.0 to 1.2% Ca (dry basis) in lactation rations. It apparently is suspected that supplemental fat forms insoluble soaps (salts) with Ca (and Mg) in the digestive tract rendering the Ca unavailable for absorption. Research results to support this idea are far from conclusive. In research with lactating dairy cows Palmquist and Conrad (1978) fed blended hydrolyzed fat at 5.9 and 10.8% of the TMR dry matter. No effects (negative or positive) of supplemental fat on Ca absorption were detected. Similarly, when supplemental yellow grease was fed to Holstein steers in digestion trials no effects on total tract absorption of Ca were detected (Zinn and Shen, 1996). When blended animal-vegetable fat (0, 2.5, and 5% of diet dry matter) was added to rations of lactating dairy cows total tract Ca absorption was not affected (Rahnema et al., 1994). However, when wethers were fed diets with high levels corn oil or soy oil (4 to 7.5% of diet dry matter) and feed intake was restricted (1.5 to 2.6% of body weight) Ca digestibility was reduced compared with wethers not fed the vegetable oils (Tillman and Brethour, 1958; Steele, 1983). Adequate study to determine optimal dietary concentrations of Ca and Mg with supplemental fat feeding has not been done. Thus, the general formulation strategy to increase dietary Ca when supplemental fat is included must be questioned because of the complication caused in P nutrition described below. Two points are especially important when considering excess Ca in rations for lactating dairy cows supplemented with fat. Firstly, the extra Ca is most likely not needed and even though it may not be exceedingly expensive to add, it is an expense and takes space in the ration. Secondly, and more importantly, if the routine ration formulation strategy is to set a particular Ca-to-P ratio, then with the increased Ca content of the ration the P concentration will increase too. For example, if one formulates to a 2-to-1 ratio of Ca-to-P and if the Ca content of the ration is increased to 1% then the P content will increase to 0.5%. This concentration of ration P is well in excess of that needed to meet the dairy cow‟s requirement, and the excess P will be excreted in manure. Furthermore, there is no evidence in the dairy nutrition research literature that there is some optimal ratio of Ca-to-P in rations of lactating dairy cows as long as the requirements IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . (grams/day) for each mineral element are met (NRC, 2001). Milk yield and persistency and reproduction were normal and not different among early lactation cows when Ca-to-P ratios ranged from 1-to-1 to 8-to-1 (Smith et al., 1966) or from 3-to-1 to 1.5-to-1 (Stevens et al., 1971). For reference, based on the Ca and P requirements of lactating cows yielding between 55 and 120 lb/day the Ca-to-P ratio is between 1.1-to-1 and 1.2-to-1 (NRC, 2001). Managing P Excretion through Management of P in Ration Lower Ration P, Lowers Manure P, Lowers Acres Required. There is little doubt that the first and foremost management strategy to control P excretion in dairy farms is to never allow imported (feed or fertilizer) P onto the farm if it is not needed to improve animal or crop performance, or to improve the margin of revenue over expenses. Because importation of P in feed supplements represents such a significant potential source of excess P, prudent management of ration P is paramount. The maximum ration P concentration needed for the highest producing cows in most dairy herds is 0.38%, dry basis. For many (most) herds and management groups of cows within herds, less than 0.38% ration P is necessary (Table 1). Lowering dietary P to recommended concentrations automatically will lower manure P (Table 3). This will result in the need for fewer acres of cropland on which to spread manure. Table 3. Example of relationships among ration P, manure P, and spreadable acres a. Spreadable Acres Relative to Ration P Manure P acres needed recommendations (%) (lb/cow/yr) (per cow/yr)b /100 cows Exceeds NRC (2) 0.55 78 2.9 290 recommendations 0.48 65 2.4 240 Within NRC (2) 0.38 47 1.8 180 recommendations 0.35 42 1.6 160 a Adapted from: Understanding soil phosphorus: An overview of phosphorus, water quality and agricultural management practices, 2002. (http://ipcm.wisc.edu), Nutrient and Pest Management Program, Univeristy of Wisconsin-Extension and USDA-ARS Dairy Forage Research Center. b Spreadable acres required depends upon local estimates of crop removal rates, soil types, etc. Without accurate management control of ration P concentrations, more acreage will be required. For example using the information in Table 3, for a 100-cow dairy farm, if ration P was lowered from 0.55% to 0.38%, the amount of land needed to spread manure would be reduced by 110 acres annually. If ration P concentrations are not lowered to NRC (2001) recommendations and the operation is subject to the new CAFO Final Rule, more acres will be needed to spread manure. Even if a particular dairy farm does not fall under the new CAFO IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Rule, the land needed to follow local states‟ guidelines based on P balancing will be much easier to achieve by feeding at NRC (2001) recommendations. Predicting P Excretion Various models (equations) have been developed and evaluated to predict the amount of P excreted by lactating dairy cows (Beede and Davidson, 1999). It would be valuable to have good estimates (predictions) of actual P excretion from dairy herds especially to help in nutrient management planning. We evaluated various published models using results from the dairy research literature. A simple relationship for predicting P excretion in manure is the difference between dietary P intake and P secreted in milk. Figure 1 shows the relationship between actual P excretion measured in research trials and the difference between actual P intake minus actual P secreted in milk. Not surprising, this difference calculation explained 86% of the variation in actual measured P excretion in manure (Beede and Davidson, 1999). 100 Excretion (g/d) 80 Measured P R2 = 0.86, P < 0.01 60 40 20 0 0 20 40 60 80 100 Measured Intake P - Milk P (g/d) Figure 1. Measured phosphorus excretion versus P intake minus milk P secretion from research results from the scientific literature (Beede and Davidson, 1999). Numeric values for the variables (pounds of ration dry matter intake and known [analyzed] P content of the rations, and the amount of milk produced and the average P content of milk [0.09%]) in this simple difference equation can be obtained relatively easily on farm to predict P excretion. We believe this approach gives dairy producers reasonable, useful information for nutrient management planning. Example: Excess Ration P, Impact on P Excretion, Need for More Cropland Rations balanced to meet P requirement. To emphasize the importance of management of P in dairy rations consider the following example IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . using the simple difference approach to compute the change in the amount of P excreted by a herd of dairy cows when: 1) ration P concentrations are formulated to just meet NRC (2001) requirements; or, 2) when higher (excess) ration P is included in rations. A herd of 300 Holstein cows are in management groups (high, medium, and low with average daily milk yield of 80, 70 and 60 lb/cow, respectively). There are 100 cows in each group. Three rations (high, medium and low) are balanced to meet the NRC (2001) energy and nutrient requirements (including P) of cows in each management group based on the expected rates of daily feed intake (NRC, 2001). The P contents of each group‟s ration (0.34, 0.33, 0.32% dry basis, for high, medium, and low groups, respectively), the actual amount of feed consumed by each group of cows, and the total P intake by each group is in Table 4. The total daily P intake for the entire herd of 300 cows is 49.7 lb. In the example, the average amount (lb) of milk produced by cows in each group is multiplied by 0.0009 (milk contains 0.09% P on average) to determine the amount of total P secreted daily. In the example, the total P secreted in milk daily is 18.9 lb. From this information, the amount of manure P excreted by the whole herd can be predicted by calculating the difference between total P intake and total P produced in milk. The total predicted P excretion is 30.8 lb/day for the whole herd fed ration P concentrations that are formulated to meet NRC (2001) P requirements (Table 4). Situation with excess ration P. Now consider the case in which this same herd of 300 cows produces the same amount of milk, but the concentrations of P in the rations are 0.44, 0.43, 0.42%, dry basis. That is, just 0.1 percentage unit higher P in each ration than is needed to meet the requirement. Having higher ration P concentrations than needed to meet requirements is common in many dairy herds. In this case, total daily P intake by the whole herd is 64.7 lb/day (Table 4). Phosphorus secreted in milk is still 18.9 lb per day; milk production or the concentration of P in the milk would not be expected to increase. No more P is needed to meet requirements for milk production. Therefore, the excess dietary P was consumed and simply excreted in manure. In this case, the amount of P excreted daily in manure is 45.8 lb. In this case of excess feeding of P, 15 lb/day excess P was excreted compared with the case when the herd was fed to requirements. Being just 0.1 percentage unit in excess of needed ration P content to meet requirements, resulted in a 49% increase in P in manure. This is equivalent to 12,443 lb of additional (excess) P2O5 that must be managed [(15 lb/day 0.44) x 365 days). If one was to apply this excess manure P to cropland with the expectation of 50 lb P2O5 annual crop removal rate, then the extra cropland needed to manage the extra manure P and still maintain whole-farm P balance would be about 249 acres or an additional 0.83 acre/cow per year in this example 300-cow Holstein herd! That is a very significant amount of excess manure P and cropland requirement from simply being 0.1 percentage unit of ration P concentration in excess of NRC (2001) requirements in milking herd rations. This is not sustainable ---- environmentally or economically. IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Table 4. Example: comparison of manure phosphorus excretion in a herd of 300 Holstein cows fed ration phosphorus to requirements (NRC, 2001) or fed rations with excess phosphorus. P Milk P Predicted Management DMI, Ration P, intake, Milk yield, yield, manure Group lb/d % lb/d lb/d lb/d a P, lb/d b 1. Herd fed to NRC (2001) phosphorus requirements: High (80 lb) 5610 0.34 19.1 8,000 7.2 11.9 Med (70 lb) 4884 0.33 16.1 7,000 6.3 9.8 Low (60 lb) 4532 0.32 14.5 6,000 5.4 9.1 Total 49.7 18.9 30.8 2. Herd fed in excess of NRC (2001) phosphorus requirements: High (80 lb) 5610 0.44 24.7 8,000 7.2 17.5 Med (70 lb) 4884 0.43 21.0 7,000 6.3 14.7 Low (60 lb) 4532 0.42 19.0 6,000 5.4 13.6 Total 64.7 18.9 45.8 Daily excess manure P (lb/day per 300 cows) from excess ration-P (2.) compared with ration-P fed to meet NRC requirements (1.) in 15.0 example. a Average P content of milk equals 0.09% (NRC, 2001). b Predicted as the difference between P intake minus milk P, lb/day. Summary Managing P inputs and outputs to achieve zero whole-farm P balance should be a primary goal of dairy operations to control costs, achieve environmental sustainability, and to be in compliance under the new CAFO rule and states‟ guidelines. Balancing for P is achievable when dairy producers effectively manage P inputs through accurate feeding and if sufficient land base is available to spread manure P. Ration P concentrations in excess of those needed to meet animals‟ needs result in excess manure P. Using imported feeds (supplements) with lower P concentrations will help reduce P in manure. Phosphorus balancing is achievable if feed P inputs are controlled and managed carefully, and if adequate cropland is accessible. References Beede, D. K., and J. A. Davidson. 1999. Phosphorus: Nutritional Management for Y2K and beyond. Proc. Tri-State Dairy Nutr. Conf. p. 51-99. IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Council for Agricultural Science and Technology (CAST). 2002. Animal diet modifications to decrease the potential for nitrogen and phosphorus pollution. Issue Paper 21:1-16. Klausner, S. D. 1993. Mass nutrient balances of dairy farms. Proc. Cornell Nutr. Conf. Ithaca, NY. p. 126. NRC (National Research Council). 2001. Nutrient Requirements for Dairy Cattle. 7th Revised Ed., National Academy Press, Washington, DC. NPMP (Nutrient and Pest Management Program), Univeristy of Wisconsin- Extension and USDA-ARS Dairy Forage Research Center. Understanding soil phosphorus: An overview of phosphorus, water quality and agricultural management practices, 2002. (http://ipcm.wisc.edu). Palmquist, D. L., and H. R. Conrad. 1978. High fat rations for dairy cows. Effects on feed intake, milk and fat production, and plasma metabolites. J. Dairy Sci. 61:890-901. Rahnema, S. Z., Wu, O. A. Ohajuruka, W. P. Weiss, and D. L. Palmquist. 1994. Site of mineral absorption in lactating cows fed high-fat diets. J. Anim. Sci. 72:229-235. Smith, A. M., G. L. Holck, and H. B. Spafford. 1966. Re-evaluation of nutrient allowances for high-producing cows. Calcium, phosphorus and vitamin D. J. Dairy Sci. 49:239-246. Steele, W. 1983. Intestinal absorption of fatty acids, and blood lipid composition in sheep. J. Dairy Sci. 66:520-527. Stevens, J. B., L. J. Bush, J. D. Stout, and E. I. Williams. 1971. Effects of varying amounts of calcium and phosphorus in rations for dairy cows. J. Dairy Sci. 54:655-661. Sutton, A., and D. K. Beede. 2003. Feeding strategies to lower nitrogen and phosphorus in manure. IN: Best Environmental Management Practices – Farm Animal Production. Extension Bulletins ID-304 (Purdue University) or E-2822 (Michigan State University Extension). Tillman, A. D., and J. R. Brethour. 1958. The effect of corn oil upon the metabolism of calcium and phosphorus by sheep. J. Anim. Sci. 17:782- 786. USDA-NRCS. 2001. USDA Natural Resource Conservation Service. Conservation Practice Standard, Nutrient Management. CODE 590, Part 402. NRCS, Washington, DC. IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Zinn, R. A., and Y. Shen. 1996. Interaction of dietary calcium and supplemental fat on digestive function and growth performance of feedlot steers. J. Anim. Sci. 74:2303-2309. IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . Sidebar Feed for Thought: Hidden Costs, Real Costs of Byproduct Feeds in Dairy Rations? by Dave Beede Department of Animal Science Michigan State University Dairy farmers have long been primary users of byproduct feeds resulting from wet- and dry-milling processes, corn syrup production, and distillery and brewery fermentations. Increased ethanol production from corn and other fermentable substrates in many states doubtless will make even more distiller‟s byproduct feed available. These byproduct feeds currently have few other uses except as livestock feed. Traditionally, we have considered byproduct feeds valuable sources for ration protein and energy --- especially in relation to their usual market prices. Ration formulation programs (least-cost or best-cost formulations) often call for byproducts to be used in rations. However, it is time to re-think how we use some byproduct feeds in cattle rations. There are hidden costs of feeding byproducts that must be considered and accounted for. As indicated in the preceding main article, many of these byproduct feeds contribute significant amounts of P to rations, sometimes in excess of dairy animals‟ requirements. Often dairy rations with significant amounts of byproduct feeds yet with no supplemental P from mineral premixes or other supplements, have P concentrations well in excess of the animals‟ requirements. Excess ration P results in excess manure P. There are costs associated with this excess manure P --- mGholamore land required to spread extra manure P at agronomic rates, more processing to sequester and remove excess manure P, or other costs associated with processing and exporting excess P from dairy farms. For sound economics and environmental management, these additional costs, which are real costs of extra (excess) manure P should be reflected in feed prices in ration formulation – the extra costs of handling and disposal associated with high-P byproduct feeds. Doing so would better reflect the real cost of byproduct feeds in rations, including the true cost of achieving whole-farm P balancing. What that real price should be in ration formulation is a difficult question to answer. Doubtless, the real extra cost of excess manure P likely is very different from farm to farm. For example, if more land has to be purchased to spread excess manure P associated with feeding byproducts, then the extra cost associated with the excess P somehow should be computed considering cost of that land to deal with the excess P. Another approach if land is not available might be to determine the actual costs associated with export (disposal) of excess manure P and appropriately increase the price of the byproduct feed in ration IN: Proc. Four-State Applied Nutrition and Management Conf. July 9-10, 2003. pp.145 - 151 . formulation. Then one would know when it is not cost-effective to include a particular byproduct feed in the ration; or, at least one would know and understand that there is extra cost associated with disposing of the excess manure P directly linked with use of that byproduct to maintain P balance in the whole farm system. For many years, dairy operations have been the “dumping ground” for excess P produced by the food, beverage, and fermentation industries through their byproducts. In effect, the dairy farmers have been given the responsibility (environmental and financial) of managing someone else‟s excess P. One way to help see that this is done equitably in the future is to put an appropriate price on each ton of high-P feed byproduct used in a farm‟s rations. When there are extra costs associated with managing the excess P, it should be reflected in the price of that feed ingredient in ration formulation. Ultimately, cattle producers should set the real demand for each particular high-P feed byproduct based on its real cost in their dairy operation. This is a shift in mindset for some --- from simply taking the best-value ingredients (lowest market price for a specified set of desired nutrients) to considering the real total cost of using those byproduct ingredients in a ration. If ration P is in excess of that absolutely needed to meet dairy animals‟ requirements, manure P increases and extra costs will be incurred. To use high- P byproducts in many cattle rations ultimately increases costs. The real costs of high-P byproducts are greater than we have considered traditionally. There are additional hidden costs beyond the market price of many “good value” feed byproducts. Sound economic and environmental management of byproduct feeds is essential for sustainability of dairy farm systems. Feed for thought and action?!
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