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1 Cornell Cooperative Extension of Delaware County, Hamden, NY 13782
2 Department of Animal Science, Cornell University, Ithaca, NY 14853
Corresponding author: P. E. Cerosaletti; e-mail: pec6{at}cornell.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: phosphorus • precision feeding • nutrient management
Abbreviation key: ADICP = acid detergent insoluble crude protein, CNCPS = Cornell Net Carbohydrate and Protein System, NDICP = neutral detergent insoluble crude protein
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Recent research indicates that dietary P management will be a key strategy in reducing P imports and accumulation on dairy farms (Kuipers et al., 1999; Valk et al., 2000; Powell et al., 2001). The Phosphorus Reduction Through Precision Animal Feeding Program was developed and implemented in the Cannonsville Reservoir Basin in Delaware County with the objectives of investigating and implementing strategies to reduce P accumulation on dairy farms. The objective of this study was to determine the excess P being fed on a sample of dairy farms in the Cannonsville Basin and to identify and evaluate dietary strategies that will reduce purchased feed P imports and P in manure.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Production test day data were collected, sorted, and summarized using Dairy Comp 305 (Valley Agricultural Software, Tulare, CA). Herd data were sorted for each month into 4 production groups within the herds: <23, 23 to 32, 32 to 41, and >41 kg/d per cow. Lactating cow diets were modeled and P intakes and excretions were predicted using the Cornell Net Carbohydrate and Protein System (CNCPS) version 4.0 (Fox et al., 2000) for each production group. Once rations were modeled across production groups, strategies were developed for herds A and B to reduce P intakes as close to requirement as possible by manipulating purchased feed P sources. Herds A and B were selected for dietary intervention based primarily on their willingness and capability to implement dietary changes. Their selection for implementation was made prior to determining baseline P intakes. Had there been no overfeeding of P in herd A or B baseline diets (which was not the case), another herd would have been selected. Forage intake levels in these herds were not controlled; the intent was to examine strategies that could be implemented through the purchased feed portion of the diet. Dietary strategies were developed by the project specialist in close cooperation with the farm owners and their feed industry representatives. Intervention strategies were implemented from November 2000 through January 2001, and changes in nutrient intakes and excretions, feed costs, milk production, and reproductive performance were monitored. Milk production was monitored short-term before and after implementation of dietary changes on the basis of daily milk sold per cow. Long-term milk production trends were monitored as monthly herd average milk production per cow, with the data standardized to 150 DIM and 4% FCM to control for stage of lactation and energy content variability. In herds C and D, monthly monitoring continued for the duration of the study without dietary intervention.
Whole-farm nutrient import and export data were collected for herds A and B for the years 2000 (preimplementation) and 2001 (postimplementation) to compute whole-farm mass nutrient balances for N, P, and K. These data were summarized for the pre- and postimplementation periods using the procedure of Klausner et al. (1997) to calculate whole-farm mass nutrient balances, where the whole-farm mass balance is equal to the difference between farm nutrient imports (concentrates, crops, bedding, animals, fertilizer, and, in the case of N, symbiotic fixation by legumes) and farm nutrient exports (milk, animals, and crops). Nutrient import and export amounts were determined from farm records. In the case of crops and bedding, nutrient content values were determined via analysis. Nutrient content values suggested by Klausner et al. (1997) were used for animals (mature cows, percentage of live weight, 2.53% N, 0.72% P, 0.19% K; calves and heifers, percentage of live weight, 2.88% N, 0.83% P, 0.22% K) and milk (as-sampled basis, 0.56% N, 0.10% P, 0.15% K). Nitrogen fixation was determined using the equation of Klausner et al. (1997):
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where fixation factor was a constant set equal to 0.60, and legume factor was set equal to 1.0 for crop acres of 
90% legume and 0.60 for crop acres of <90% legume. Crop yields were determined from farm records and percentage of CP was determined from forage analysis. An adjusted whole-farm mass balance was calculated for both herds for the postimplementation year, primarily to account for atypical crop purchases on both farms in the postimplementation year due to pest-induced crop loss, but also to remove variation in mass balance between years within herd from other sources, except for purchased concentrate feed. The adjusted mass balance was calculated by setting all nutrient imports and exports in the postimplementation year equal to those in the preimplementation year, except for purchased concentrate amounts and N, P, and K densities, which were adjusted to actual postimplementation purchased concentrate feeding rates per cow and N, P, and K densities.
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STATISTICAL ANALYSIS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). This excess is greater than the mean of 21% overfeeding reported by Bertrand et al. (1999) for 27 commercial dairy farms in South Carolina, but nearly identical to the average 30% overfeeding reported by Sansinena et al. (1999) in a survey of dairy nutritionists working in the midsouthern United States. Bertrand et al. (1999) reported a range of 76 to 213% P in intakes as a percentage of requirement, far larger than the range seen on the four farms in this study. Within herds B, C, and D, P intakes as a percentage of requirement, while still in excess, declined with increasing milk production level. This trend agrees with the dietary modeling of Chase (1998) and is due to higher-producing cows having a greater P requirement relative to DMI compared with lower producing cows. In herd A, no consistent trend in P intake across production level was detected.
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) and from by-product feeds used in the grain mix, in particular wheat middlings (Table 3). This feed was used heavily in this pelleted grain mixture not only to reduce feed cost, but also to obtain a good-quality pellet. Herd B, like herd A, had high forage P levels (Table 2). Additionally, this herd was fed a greater level of mineral P in the purchased concentrate (Table 3), as well as high-P concentrate feeds (distillers’ grains, whole roasted soybeans). The lower P intakes in herd C may be attributable to the use of a low P (8.73% P) liquid mineral source included in the TMR at a low rate (1.2 dl/d per cow; data not shown). Use of a mineral supplement of this type is not common on most northeastern US dairy farms. Lower P intakes in herd D may be attributable to the use of a low-P mineral mixture (4.6% P) included in the diet at a low rate (318 g/d per cow). Furthermore, this herd had the highest inclusion rate of corn silage of any of the herds in this study (data not shown), a strategy that has been shown to reduce ration P content (Alocilja, 1998). Across all herds in the study, corn silage had the lowest mean P content of all forages fed (Table 2).
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represent 2 growing seasons. The DairyOne averages included in this table are largely from northeastern US dairy farms, predominantly those in New York. Higher mean forage P levels for forages analyzed in this project compared with the DairyOne data may be attributable to higher soil P levels on the project farms or a difference in soil mineralogy, resulting in plants containing a higher P level. Forage P levels for forages in this study may also differ from those analyzed at DairyOne due to plant maturity. In general, mineral content decreases as forage maturity increases as a result of changing leaf:stem ratios, varying mineral content of plant organs, and increased fiber content (Fleming, 1973; Little, 1982). Variation in P content in project herds is similar to that reported for the DairyOne forages. The higher forage P levels observed in the project herds are of biological importance in balancing diets from a nutrient management perspective. These results point to the importance of analyzing forages accurately for nutrient content in balancing dairy rations. In this study, relying on average tabular values for forage P content would have resulted in an underestimation of forage P content and an oversupplementation of ration P. Higher forage P content provides an opportunity to reduce supplemental (imported) ration P. In some instances, as is presently the case in herds A and B, P supplied by forages and grains alone (with no mineral P) may meet or exceed animal P requirements. In these cases, further reductions in P imports will need to come from reductions in the amount of purchased concentrate fed.
From an agronomic perspective, higher forage P content represents an opportunity to remove more soil P in herbage biomass, which is important in P-based nutrient management planning, where manure spreading rates may be limited to crop P removal. Higher forage P removal rates could, over a long time period, result in a slower rate of soil P accumulation, or even a decline in soil P. Additionally, homegrown forage P represents a recycling of P within the farm and the opportunity to export P in the form of milk every time the P cycle is turned.
Composition, cost, and CP and P densities of the grain mixtures fed in herds A and B before and after dietary adjustments appear in Table 3 and indicate the changes needed in both herds to lower P intakes. To reduce P intake in herd A, an unpelleted grain mixture was developed that allowed for a reduced level of wheat middlings. To compensate for increased feed costs as a result of replacing wheat middlings with more expensive ingredients, a 2-feed system was implemented in this herd, with nearly equal amounts of a higher protein concentrate and cornmeal being fed as separate feeds. This reduced feed mixing costs and took advantage of economic benefits of concentrating nutrients in the higher protein feed. Additionally, total concentrate levels were reduced to bring the diets into protein and energy balance (Table 4). These changes resulted in a slightly decreased energy intake as well as decreased purchased feed costs of approximately $0.20/d or $6.00/mo per cow.
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), due largely to high P levels in the forages fed to this herd (Table 2). Many of the forages in herd A contained P levels that were higher than the NRC (2001) recommended total dietary P levels for cows at similar levels of milk production and DMI. Additional P reductions might have been achieved by replacing more wheat middlings in the protein mixture with a lower P feed, such as corn meal or citrus pulp. This was not done for cost and palatability reasons.
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). One of these mineral sources was a mineral premix, which, when removed, had to be replaced with another mineral premix and several individual mineral ingredients to maintain levels for all other minerals and vitamins. Due to the pricing structure of the mineral premixes and other mineral ingredients, there was only a slight decrease in purchased feed cost ($3.00/t of mixed grain; $0.02/d per cow). Level of concentrate fed in the diet was not changed. These changes alone were enough to lower P intake to required levels (100% of requirement; Table 5). As with herd A, herd B diets had large P contributions from homegrown forage, with mean forage P density exceeding NRC (2001) recommended minimum total dietary P density for cows at similar levels of milk production and DMI. With no corn silage fed to herd B, there were limited amounts of low-P forage to dilute the higher-P forages. Similar challenges have been reported regarding P content of the grass forages in the Netherlands (Valk et al., 2000).
By implementing P-reducing strategies in the diets of herds A and B, predicted P intakes and excretions were reduced by an average of 25 and 33%, respectively, across both herds (Table 5). Absolute P reductions averaged 40 and 25 g/d per cow (14.6 and 9.1 kg/yr per cow) for herds A and B, respectively. Within herds, these reductions increased with increasing production level, a result of the greater total daily P intake of higher-producing cattle. When P reductions are expressed as a percentage of P intakes and excretions, a similar trend holds for herd A, but is less consistent for herd B. Measured fecal P concentration decreased significantly (1.32% of DM before implementation vs. 0.88% after implementation, P < 0.001, n = 90), by an average 33% across herds A and B, whereas mean fecal P content of the nonimplementation herds did not decrease during the same period (0.96 vs. 0.92% of DM, P = 0.22, n = 90). These reductions in P intake are somewhat greater than those reported by Valk et al. (2000) when P-reduced diets were fed on Dutch dairies (3 to 6 kg/yr per cow); however, these dairies started with lower concentrate P levels than those in the present study.
Short- and long-term milk production data for both herds A and B before and after dietary adjustments (Table 6) suggest that no dramatic short-term drops in milk production have occurred as a result of reducing P in dairy diets. Herd A experienced a milk production increase immediately after implementing dietary changes, which may be attributable to increased intake of rumen-fermentable carbohydrate and/or metabolizable protein, although diets were not balanced to support such increases. Recent studies assessing long-term lactation performance have reported no reduction in milk yield with lactating dairy cattle fed at required or slightly lower than required P levels (Kuipers et al., 1999; Valk et al., 1999; Wu and Satter, 2000; Wu et al., 2000).
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) need to be interpreted with caution, as this study was not controlled for the many variables that can influence reproductive performance. Herd A experienced a slight decrease in BCS after implementation, which could be attributable to reduced metabolizable energy values in reduced-P diets (106 vs. 103% of requirement; Table 4). Heat detection, conception, and pregnancy rates were all lower (worse) after implementation for this herd, although the percentage of cows open (not pregnant) greater than 150 DIM improved (decreased). These changes in reproductive performance are small and may be due to normal variation. If reproductive performance was decreased in this herd postimplementation, it may have been due to reduced energy intake and greater BCS loss (greater negative energy balance), as evidenced by lower BCS in the postimplementation period. Although negative energy balance, especially in early lactation, has been reported to adversely affect fertility (Butler and Smith, 1989; Swanson, 1989), reported relationships between BCS and reproductive performance have not been consistent. Pryce et al. (2001) demonstrated that reproductive performance is negatively correlated with BCS loss in lactating dairy cows, whereas Waltner et al. (1993) and Ruegg and Milton (1995) found no such relationships. Herd B experienced an increase in BCS and all reproductive measurements showed improvement postimplementation. Changes in BCS in both herds were not large. With regard to the effect of P intake on reproductive performance, the data in herd B of this study are consistent with those of other studies (Wu and Satter, 2000; Wu et al., 2000, 2001), which indicate no improvement in reproductive performance when feeding P above NRC (2001) recommended levels. Several studies (Valk and Sebek, 1999; Wu and Satter, 2000; Wu et al., 2000) found no impairment in reproductive performance when feeding P below NRC requirement, even at levels as low as 0.30% of diet DM.
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). Initial nutrient balances are consistent with those reported for typical northeastern US commercial dairy farms (Tylutki and Fox, 1997; Cerosaletti et al., 1998; Klausner et al., 1998), as well as for dairy farms in The Netherlands (Valk et al., 2000). Through dietary manipulation of concentrate P sources alone, the amount of P remaining on the farms was reduced to 49% in the adjusted balances, with reductions of 65 and 32% in the amount of P remaining on the farms for herds A and B, respectively. The percentage of P remaining on both farms was reduced to less than 45%. These results are less than the 78% reduction in P remaining/ha predicted in the modeling study of Rotz et al. (2001) for a 100-cow New York dairy farm implementing reduced dietary P supplementation, where initial dietary P level was described as "somewhat higher than NRC (1989) requirements" and dietary P was reduced to NRC (2001) requirements. A smaller reduction in mass farm P balance (16%) was obtained on a UK research farm, where feed P imports were reduced 32% (Peel et al., 1997).
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In both herds, N mass balances remained unchanged after dietary adjustments; however, dietary adjustments in herd A did result in a 15% reduction in N feed imports on a per-cow basis (data not shown), reflecting the reduced dietary CP levels in the adjusted diet (Table 4). Whereas both herds imported substantial amounts of N for application to grass hay crops, thus raising N balances, herd A had a greater percentage of cropland in grass and was more aggressive in N applications to grass hay crops. Potassium balances were reduced in herd A after implementation as a result of reduced imports of the mixed feed and increased imports of cornmeal, which had a lower K level. Herd B had a higher K balance than herd A as a result of application of K fertilizer to alfalfa hay crops, a practice not used in herd A. Feed K imports in herd B were reduced after implementation due to reduced mineral K sources in the concentrate mixture.
The reductions in P intakes and manure P excretions obtained in this study have major implications for farm management. Reductions in manure P excretions can result in less crop acreage needed to recycle manure P under a P-based nutrient management plan (manure P application restricted to crop P removal). Powell et al. (2001) estimated that reducing dietary P density from 0.48 to 0.38% of DM would reduce manure P excretion enough to lower crop acreage required to recycle manure P by 44%. Crop fields that have a very high soil test P level resulting from excessive fertilizer and manure P application may also be restricted from further application of manure when nutrient management plans are designed according to USDA-NRCS (1999) guidelines. Reducing manure P content via dietary manipulation can significantly slow the rate of soil P accumulation, and in some cases, even bring it to equilibrium (Powell et al., 2001).
On a basin-wide scale, the P reductions obtained in this study have major implications. There are presently between 7000 and 8000 mature dairy cows in the Cannonsville Reservoir Basin. Should an average reduction in P intake and manure P excretion of 25 g/d per cow be achieved across all lactating cows in the basin, then the total feed P imports into the basin and P excreted in the dairy manure produced in the basin would be reduced by 64,000 to 73,000 kg/yr. This reduction is similar to the 50,000-kg average annual total phosphorus load to the Cannonsville Reservoir (Longabucco and Rafferty, 1998; Longabucco, 2001). Reductions of this magnitude represent a substantial reduction in P loading on agricultural soils via manure application. Phosphorus loading (both dissolved and total P) of watercourses has been shown to be highly correlated to dairy manure production and application (McFarland and Hauck, 1999). Delaware County, as part of their comprehensive strategy to manage P in the water bodies of the county, has set a 10,000-kg/yr goal for reducing total P loading to the Cannonsville Reservoir (Delaware County Watershed Affairs, 2002). Even if only a proportion of the manure P applied to the land makes it to reservoir, P reductions from dietary manipulation could make a substantial contribution toward that goal.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Received for publication August 8, 2003. Accepted for publication January 19, 2004.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSSTATISTICAL ANALYSISRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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