Whole-Farm Nitrogen Balance on Western Dairy Farms

Estimating Excreted Nutrients to Improve Nutrient Management for Grazing System Dairy Farms

Improving nutrient management in grazing system dairy farms requires determining nutrient flows through animals, the placement of cows within farms and potential for collection, and the re-use and loss of nutrients. We applied a model incorporating data collected at a range of temporal and spatial scales to quantify nutrient excretion in all locations that lactating herds visited on five days over a year on 43 conventional and organic grazing system dairy farms. The calculated nutrient loads excreted by cows in different places were highly skewed; while N, P and K deposited loads were consistent across the year, S, Ca and Mg loads varied between sampling times and seasons. The greatest mean and range in nutrient loads were deposited in paddocks, with the smallest amounts deposited in dairy sheds. All excreted nutrient loads increased with farm and herd sizes and milk production. Mean daily loads of 112, 15, 85, 11, 22 and 13 kg of N, P, K, S, Ca and Mg were deposited by the herds which, when standardised to a 305-day lactation, amounted to 24, 4, 20, 3, 5 and 3 t excreted annually, respectively. In addition to routine manure collection in dairy sheds, ensuring collection and recycling of nutrients excreted on feed pads and holding areas would decrease potential nutrient losses by 29% on average. Non-collected, recycled nutrients were disproportionately returned to paddocks in which cows spent time overnight, and except for S and Ca, nutrient loading rates were greater than rates applied as fertilisers. These data demonstrate the extent of excreted nutrients in grazing dairy systems and indicate the need to account for these nutrients in nutrient management plans for Australian dairy farms. We propose incorporating excretion data in current budgeting tools using data currently collected on most Australian grazing system dairy farms.

Key nitrogen and phosphorus performance indicators derived from farm-gate mass balances on dairies

Efficient management of N and P on dairy farms is critical for farm profitability and environmental stewardship. Annual farm-gate nutrient mass balance (NMB) assessments can be used to determine the nutrient-use efficiency of farms, set efficiency targets, and monitor the effect of management changes with minimal inputs required. In New York, feasible N and P balances have been developed as benchmarks for dairy farm NMB, alongside key performance indicators (KPI) that serve as predictors for high NMB. Here, 3 yr of NMB data from 47 farms were used to evaluate the main drivers of N and P balances and identify additional KPI. From the 141 farm records, 26% met both the feasible N balances per hectare and per megagram of milk produced. For P, 53% of the records met both benchmarks. Imports, rather than exports, drove NMB primarily by feed and fertilizer purchases, consistent with earlier findings. Linear regression analysis showed that a selection of KPI currently used, particularly animal density, nutrient-use efficiency, and the amount of home-grown feed, explained a large portion of variation in NMB. Heifer-to-cow ratio and the relative proportion of various forage crops may provide further insight into the drivers of feed and fertilizer imports and ultimately farm-gate NMB. This study provides avenues toward a better assessment of whole-farm nutrient management and means for farms to communicate progress to stakeholders and consumers.

Annual Nitrogen Balance from Dairy Barns, Comparison between Cubicle and Compost-Bedded Pack Housing Systems in the Northeast of Spain

Simple Summary

Environmental concerns related to livestock production have driven the importance of developing manure-management alternatives to mitigate N emissions. Hence, we carried out measurements of N loss in two different dairy housing systems (compost-bedded pack vs. cubicles), each system with a very distinct manure-management procedure. Since each system performs different manure-management practices, it may be important to compare their efficiency in terms of N recovery from manure in both systems. In contemplation of annual temperature variation, measurements of N recovery after manure management were carried out during warm and cold seasons of the year. Significantly higher volatilization rates were found in compost-bedded pack system with respect to cubicles system, therefore, N left in manure was lower in compost-bedded pack barns.

Abstract

The aim of this study was to determine N recovery and irreversible losses (i.e., through NH₃-N volatilization) from manure in two different housing systems throughout a year using an N mass balance approach. Dietary, milk, and manure N were monitored together with outside temperatures in six dairy barns during six months, comprising two different seasons. Three barns were designed as conventional free stalls (cubicle, CUB) and the other three barns as compost-bedded packs (CB). All the barns were located in the Ebro’s valley, in the northeast of Spain. Mass N balance was performed simultaneously in the six barns, during two three-month periods (Season I and II) and sampling at a 15-day interval. Results of ANOVA analysis showed that annual N retained in manure (kg/head per year) from cows housed in CUB barns was significantly higher than in manure from cows housed in CB (133.5 vs. 70.9, p < 0.001), while the opposite was observed for N losses (26.9 vs. 84.8, for CUB and CB barn, respectively; p < 0.005). The annual mean proportion of irreversible N loss from manure in relation to N intake was much lower in barns using conventional free-stall cubicles than the mean ratio registered in bedded pack systems barns.

Economic and environmental effects of revised metabolizable protein and amino acid recommendations on Canadian dairy farms

The objective of this research was to evaluate the potential economic and environmental effects of the formulation model used to balance dairy rations for metabolizable protein (MP) or 3 essential AA (EAA: His, Lys, and Met) in 3 regions of Canada with different farming systems. The Maritimes, Central Canada, and the Prairies reference dairy farms averaged 63, 71, 144 mature cows per herd and 135, 95, 255 ha of land, respectively. Using N-CyCLES, a whole-farm linear program model, dairy rations were balanced for (1) MP, based on National Research Council (NRC) requirements (MP_2001); (2) MP plus Lys and Met, based on NRC (AA_2001); (3) MP (MP_Rev); or (4) for His, Lys, and Met (AA_Rev), both based on a revised factorial approach revisiting both supply and requirements of MP and EAA. Energy was balanced to meet requirements based on NRC (2001). Assuming the requirements were met within each approach, it was considered that milk yield and composition were not affected by the type of formulation. Given the assumptions of the study, when compared with MP_2001 formulation, balancing dairy rations using the AA_Rev approach reduced calculated farm N balance by 3.8%, on average from 12.71 to 12.24 g/kg of fat- and protein-corrected milk; it also enhanced farm net income by 4.5%, from 19.00 to 19.70 $CAN/100 kg of fat- and protein-corrected milk, by reducing inclusion of protein concentrate in dairy rations. Calculated animal N efficiency was on average 4.3% higher with AA_Rev than with MP_2001 for mid-lactation cows. This gain in N efficiency would result in a reduction in N₂O emission by manure, contributing to a partial decrease of total greenhouse gas emission by 1.7%, through a reduction of N excreted in manure. With the AA_2001 formulation, farm N balance was 1% higher than with MP_2001 formulation while reducing farm net income by 6.4%, due to the need to purchase rumen-protected AA, with no effect on total greenhouse gas emission. Both MP formulations lead to fairly similar outputs. The AA_Rev formulation also indicated that His might be a co-limiting AA with Met in dairy rations balanced with ingredients usually included in Canadian dairy rations. Given the assumptions of the study, balancing dairy rations for 3 EAA (His, Lys, and Met) rather than MP, has some potential positive effects on Canadian dairy farms by increasing net incomes through a reduction of crude protein supply, leading to a decreased environmental effect.

The state of phosphorus balance on 58 Virginia dairy farms

Managing a sustainable dairy farm requires balancing phosphorus (P) imports and exports that enter and leave through the farm gate. Over the long term, P surpluses will elevate soil-test P concentrations above crop requirements through routine land applications of manure. The objectives of this study were aimed at Virginia dairy farms (a) to determine P mass balances, (b) to define potential guidelines for a sustainable and feasible zone of operation based on P balance and P use efficiency, and (c) to assess risk factors driving P surplus and P use inefficiencies. Data on farm-gate P imports and exports via feed, manure, crops, fertilizers, bedding, animals, and milk were collected for 58 dairy farms in Virginia. There was no relationship between farm P balance and milk production, indicating that a P surplus was not necessary for good milk productivity. A feasible P balance limit was calculated below which 75% of farms could operate, and this was 18.7 kg P ha^-1 . Two risk factors were identified for farms having a P balance above this limit: (a) land application of poultry litter and (b) excessive import of P through feed. Combined dairy and beef operations generally had more land and a lower P balance, whereas having combined dairy and poultry did not raise the P balance as long as poultry litter was exported. Dairy farms in Virginia can operate with a sustainable P balance as long as they avoid using excessive poultry litter and pay attention to P imported through purchased feed.

Nutrient Intake, Excretion and Use Efficiency of Grazing Lactating Herds on Commercial Dairy Farms

Simple Summary

Excess nutrients on dairy farms can affect soil and animal health and have negative impacts on the environment. More nutrients are usually brought onto farms in animal feed than in fertilizer and, as dairy cows do not efficiently use feed nutrients to produce milk, most consumed nutrients are excreted in dung and urine. Estimating nutrients excreted by cows relies on measuring feed and nutrient intake. However, measuring pasture nutrients consumed by cows that graze on commercial farms is complicated. We modified the ‘Feeding Standards’ approach to estimate daily pasture dry matter and nutrient intake and nutrients excreted using data and samples readily available on commercial dairy farms. These data were collected on five visits in different seasons from 43 grazing system farms located in diverse climatic zones. Although these herds graze daily, the lactating cows only obtained slightly more than half their dry matter intake from pasture. Each day, on average, we estimated that a grazing cow excretes 433 g nitrogen, 61 g phosphorus, 341 g potassium, 44 g sulphur, 92 g calcium and 52 g magnesium on these farms. Using this approach to estimate nutrients excreted by grazing animals on dairy farms can assist farmers improve nutrient distribution and fertilizer requirements.

Abstract

Estimating excreted nutrients is important for farm nutrient management, but seldom occurs on commercial grazing system farms due to difficulties in quantifying pasture intake. Nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) intake, excretion and use efficiency of 43 commercial dairy herds grazing pasture were calculated to understand the range in nutrient intake and excretion in these systems. Milk production, feed (grazed and supplement), as well as farm and herd management data were collected quarterly on representative farms located in temperate, arid, subtropical and tropical regions of Australia. Lactating herd sizes on these farms averaged 267 (30 to 1350) cows, with an average daily milk yield of 22 (9 to 36) kg/cow per day and the herds walked from <0.01 to 4 km/day on a variety of terrains. The mean total metabolizable energy (ME) required by cows in the herds was estimated to be 195 (116 to 289) MJ/cow per day. Although these farms are considered grazing systems, feeding strategies ranged from total dependence on pasture to total mixed rations (TMRTMR) and consisted of a wide variety of nutrient and energy contents. Mean pasture dry matter intake (DMI) (9 kg/cow per day, from 0.1 to 22 kg/cow per day) was just over half of total DMI. Dietary concentration of crude protein, P, K, S, Ca and Mg concentrations were, on average, 19%, 0.45%, 2.1%, 0.29%, 0.65%, and 0.3%, respectively, for all herds and, except for N, supplement nutrient concentrations were always more variable than pasture. Approximately 72% and 88% of diets provided greater than recommended P and N intakes, respectively. Calculated mean N, P, K, S, Ca and Mg excretions were 433, 61, 341, 44, 92 and 52 g/cow per day, respectively. Of the farm characteristics examined, residual maximum likelihood (REML) analysis indicated that daily excreted N, P and S were significantly related to per ha milk production, and excreted P, K and Mg were related to percentage of herd DMI provided as supplement. Mean use efficiencies by cows of N, P, K, S, Ca and Mg were 21%, 25%, 9%, 16%, 23% and 4%, respectively. These estimates of nutrient excretion and feed nutrient use efficiencies can be used to improve nutrient management on grazing system commercial dairy farms.

Effects of rumen-protected methionine and other essential amino acid supplementation on milk and milk component yields in lactating Holstein cows

Objectives of this study were to investigate the effects of supplementing rumen-protected methionine (RP-Met), threonine (RP-Thr), isoleucine (RP-Ile), and leucine (RP-Leu) individually or jointly to a low-protein diet, on the performance of lactating dairy cows, as well as to determine the effects of these amino acids (AA) on the mammalian target of rapamycin (mTOR) in vivo. Ten lactating Holstein cows were randomly allocated to a repeated 5 × 5 Latin square experiment with five 19-d periods. Treatments were high-protein diet (16% crude protein, positive control; HP), low-protein diet (12% crude protein, negative control; LP), LP plus RP-Met (LPM), LP plus RP-Met and RP-Thr (LPMT), and LP plus RP-Met, RP-Thr, RP-Ile, and RP-Leu (LPMTIL). The dry matter intakes (DMI) of the LP, LPM, and LPMT diets were lower than that of the HP diet, whereas the DMI of the LPMTIL diet was intermediate between the HP diet and the other LP diets. Supplementing RP-Met to the LP diet increased the yields of milk and milk protein, increased the content of milk urea N, and tended to increase milk N efficiency. Co-supplementation of RP-Thr with RP-Met resulted in no further milk production increase. Co-supplementation of all 4 rumen-protected amino acids (RP-AA) increased milk and lactose yields to the level of the HP diet and tended to increase milk protein yield compared with the LPMT diet. We found no significant differences in the contents and yields of milk components between the LPMTIL and HP diets except for a lower milk urea N content in the LPMTIL diet. Venous concentrations of the measured AA were similar across the LP and LP diets supplemented with RP-AA. Relative to levels of the HP diet, LP diets had higher venous concentrations of Met and Gly and tended to have higher Phe concentration and lower concentrations of Val and BCAA. The LPMTIL diet had higher venous concentrations of Arg, Lys, Met, Phe, and Glu, and a lower Val concentration. Phosphorylation status of the measured mTOR components in LPM and LPMT treatments were similar to those in the LP treatment but phosphorylation status of mTOR and eIF4E-binding protein 1 (4eBP1) in LPMTIL treatment were higher. The phosphorylation rates of eukaryotic elongation factor 2 (eEF2) in the 4 LP and LP plus RP-AA diets were higher than that of the HP diet. Overall, results of the present study supported the concept that under the relatively short time of this experiment, supplementing RP-AA, which are believed to stimulate the mTOR signal pathway, can lead to increased milk protein yield. This increase appears to be due to increased DMI, greater mTOR signaling, and greater eEF2 activity.

Mass balance analyses of nutrients on California dairies to evaluate data quality for regulatory review

Effective regulations may help reduce nitrate contamination of groundwater from agriculture. Dairy farmers in California must maintain a ratio below 1.4 of total nitrogen (N) applied to total N-removed (N-Ratio) on cropland receiving manure application. In annual reports to the regulatory agency, farmers detail nutrients applied to cropland, removed in harvests, and exported off farm. Data were extracted from all available annual reports for 62 dairies from 2011, 2012, and 2013. Excretions of N, phosphorus (P), and potassium (K) were calculated using reported herd demographics and standard excretion equations from the American Society of Agricultural and Biological Engineers. Calculated nutrient excretion values were compared to the reported values of manure nutrients applied to cropland and exported off farm. Reported N-Ratios were compared to mass balance simulations exploring variable crop yields and alfalfa management. In the nutrient excretion balance, the distribution of the percent of N and P recovered in manures applied or exported peaked at 24% (median=31%) and 26% (median=53%) of excreted, respectively. The distribution of recovered K was fairly uniform from 0% to 300% (median=146%) of excreted K. In N-ratio simulations, 62% and 66% of all reported N-ratios were lower than their respective simulated N-ratio, assuming alfalfa crops received no N fertilization and minimal fertilization (26% of N-removed in harvest) respectively. When simulated crop yields were normally (sd=0.25) or Student's t distributed (df=154) around expected crop yields, 28% and 57% of all reported ratios fell within the 95% confidence interval of the simulations, respectively. Low and erratic recovery rates of excreted P and K existed. Additionally, reported N-Ratios were generally lower and more varied than necessary for farmers to maintain crop yields while complying with regulations. Greater understanding of low recovery rates is needed before data are used to assess the impact of regulations.

Assessing agro-environmental performance of dairy farms in northwest Italy based on aggregated results from indicators

Dairy farms control an important share of the agricultural area of Northern Italy. Zero grazing, large maize-cropped areas, high stocking densities, and high milk production make them intensive and prone to impact the environment. Currently, few published studies have proposed indicator sets able to describe the entire dairy farm system and their internal components. This work had four aims: i) to propose a list of agro-environmental indicators to assess dairy farms; ii) to understand which indicators classify farms best; iii) to evaluate the dairy farms based on the proposed indicator list; iv) to link farmer decisions to the consequent environmental pressures. Forty agro-environmental indicators selected for this study are described. Northern Italy dairy systems were analysed considering both farmer decision indicators (farm management) and the resulting pressure indicators that demonstrate environmental stress on the entire farming system, and its components: cropping system, livestock system, and milk production. The correlations among single indicators identified redundant indicators. Principal Components Analysis distinguished which indicators provided meaningful information about each pressure indicator group. Analysis of the communalities and the correlations among indicators identified those that best represented farm variability: Farm Gate N Balance, Greenhouse Gas Emission, and Net Energy of the farm system; Net Energy and Gross P Balance of the cropping system component; Energy Use Efficiency and Purchased Feed N Input of the livestock system component; N Eco-Efficiency of the milk production component. Farm evaluation, based on the complete list of selected indicators demonstrated organic farming resulted in uniformly high values, while farms with low milk-producing herds resulted in uniformly low values. Yet on other farms, the environmental quality varied greatly when different groups of pressure indicators were considered, which highlighted the importance of expanding environmental analysis to effects within the farm. Statistical analysis demonstrated positive correlations between all farmer decision and pressure group indicators. Consumption of mineral fertiliser and pesticide negatively influenced the cropping system. Furthermore, stocking rate was found to correlate positively with the milk production component and negatively with the farm system. This study provides baseline references for ex ante policy evaluation, and monitoring tools for analysis both in itinere and ex post environment policy implementation.

Agriculture's Contribution to Nitrate Contamination of Californian Groundwater (1945-2005)

Nitrogen (N) use in intensive agriculture can degrade groundwater resources. However, considerable time lags between groundwater recharge and extraction complicate source attribution and remedial responses. We construct a historic N mass balance of two agricultural regions of California to understand trends and drivers of past and present N loading to groundwater (1945-2005). Changes in groundwater N loading result from historic changes in three factors: the extent of agriculture (cropland area and livestock herd increased 120 and 800%, respectively), the intensity of agriculture (synthetic and manure waste effluent N input rates increased by 525 and 1500%, respectively), and the efficiency of agriculture (crop and milk production per unit of N input increased by 25 and 19%, respectively). The net consequence has been a greater-than-order-of-magnitude increase in nitrate (NO) loading over the time period, with 163 Gg N yr now being leached to groundwater from approximately 1.3 million ha of farmland (not including alfalfa [ L.]). Meeting safe drinking water standards would require NO leaching reductions of over 70% from current levels through reductions in excess manure applications, which accounts for nearly half of all groundwater N loading, and through synthetic N management improvements. This represents a broad challenge given current economic and technical conditions of California farming if farm productivity is to be maintained. The findings illustrate the growing tension-characteristic of agricultural regions globally-between intensifying food, feed, fiber, and biofuel production and preserving clean water.

Whole-farm budgets of phosphorus and potassium on dairy farms in Manitoba

Plaizier, J. C., Legesse, G., Ominski, K. H. and Flaten, D. 2014. Whole-farm budgets of phosphorus and potassium on dairy farms in Manitoba. Can. J. Anim. Sci. 94: 119–128. Whole-farm budgets of phosphorus (P) and potassium (K) were determined on 10 dairy farms in Manitoba between October 2010 and October 2011. These budgets were determined as the difference between total exports, including milk, animals, feed, and manure, and total imports, including feed, manure, animals, and inorganic fertilizer, for each farm. Farms differed in their feeding and manure management strategies. Two farms imported all their feed and exported all their manure. Other farms produced some of their feed and spread most of their manure on their farm. Whole-farm P and K budgets varied from −0.42 to 3.35 and from −1.31 to 11.27 g kg−1 milk sold among farms, respectively. Efficiencies of P and K utilization were calculated as the exports as a percentage of imports. The P efficiency averaged 48%, and ranged from 22.1 to 109% among farms. The K efficiency averaged 37%, and ranged from 10 to 98% among farms. In the fall of 2010 and 2011, 94 and 98%, of fields sampled had soil test P concentrations lower than the concentration above which further accumulation of P would be regulated (60 ppm). Of the farms that spread their own manure, the highest P and K efficiency were on a farm that exported a proportion of the produced forages and did not import any inorganic fertilizer. The lowest P and K efficiencies were on a farm that imported concentrate feeds, bedding straw and most forages, and had the smallest land base per milking cow to spread manure. Variations in P and K efficiencies demonstrate opportunities to enhance these efficiencies.

Substantial Differences between Organ and Muscle Specific Tracer Incorporation Rates in a Lactating Dairy Cow

We aimed to produce intrinsically L-[1-(13)C]phenylalanine labeled milk and beef for subsequent use in human nutrition research. The collection of the various organ tissues after slaughter allowed for us to gain insight into the dynamics of tissue protein turnover in vivo in a lactating dairy cow. One lactating dairy cow received a constant infusion of L-[1-(13)C]phenylalanine (450 µmol/min) for 96 h. Plasma and milk were collected prior to, during, and after the stable isotope infusion. Twenty-four hours after cessation of the infusion the cow was slaughtered. The meat and samples of the various organ tissues (liver, heart, lung, udder, kidney, rumen, small intestine, and colon) were collected and stored. Approximately 210 kg of intrinsically labeled beef (bone and fat free) with an average L-[1-(13)C]phenylalanine enrichment of 1.8±0.1 mole percent excess (MPE) was obtained. The various organ tissues differed substantially in L-[1-(13)C]phenylalanine enrichments in the tissue protein bound pool, the highest enrichment levels were achieved in the kidney (11.7 MPE) and the lowest enrichment levels in the skeletal muscle tissue protein of the cow (between 1.5-2.4 MPE). The estimated protein synthesis rates of the various organ tissues should be regarded as underestimates, particularly for the organs with the higher turnover rates and high secretory activity, due to the lengthened (96 h) measurement period necessary for the production of the intrinsically labeled beef. Our data demonstrates that there are relatively small differences in L-[1-(13)C]phenylalanine enrichments between the various meat cuts, but substantial higher enrichment values are observed in the various organ tissues. We conclude that protein turnover rates of various organs are much higher when compared to skeletal muscle protein turnover rates in large lactating ruminants.

Nutritional and management strategies on nitrogen and phosphorus use efficiency of lactating dairy cattle on commercial farms: an environmental perspective

Dairy farm activities contribute to environmental pollution through the surplus N and P that they produce. Optimization of animal feeding and management has been described as a key strategy for decreasing N and P excretion in manure. Sixty-four commercial dairy farms were studied to assess the efficiency of N and P use in lactating herds and to identify dietary and management factors that may contribute to improving the efficiency of nutrient use for milk production, and decrease N and P excretion. The average ration was formulated to 50:50 forage:concentrate ratio with grass silage and corn silage as the main forage sources. Mean N and P intakes were 562 g/d [16.4% crude protein (CP)] and 84.8 g/d (0.40% P), respectively. Milk yield averaged 29.7 kg/d and contributed to 25.8% (standard deviation +/- 2.9) of N utilization efficiency (NUE) and 31.9% (standard deviation +/- 4.5) of P utilization efficiency (PUE). Dietary N manipulation through fitting the intake of CP to animal requirements showed a better response in terms of decreasing N excretion (R(2) = 0.70) than that estimated for P nutrition and excretion (R(2) = 0.30). Improvement in NUE helped increase PUE, despite the widespread use of feedstuffs with a high P content. Management strategies for lactating herds, such as the use of different feeding groups, periodical ration reformulation, and selection of feeding system did not show any consistent response in terms of improved NUE and PUE. The optimization of NUE and PUE contributed to decreasing the N and P excretion per unit of milk produced, and therefore, reductions in N and P excretion of between 17 and 35%, respectively, were estimated. Nevertheless, nutritional and herd management strategies were limited when N and P excretion were considered in relation to the whole lactating herd and farmland availability. Dietary CP manipulation was estimated to decrease herd N excretion by 11% per hectare, whereas dietary P manipulation would be decreased by no more than 17%. We conclude that the correct match between the ingested and required N and P, together with an increase in milk productivity, may be feasible strategies for decreasing N and P excretion by lactating herds on commercial farms.

Efficiency of Use of Imported Magnesium, Sulfur, Copper, and Zinc on Idaho Dairy Farms

Six commercial dairies from south central Idaho were surveyed to estimate the whole-farm surpluses of magnesium (Mg), sulfur (S), copper (Cu), and zinc (Zn). Mineral imports and exports were monitored in a 12-mo period and samples from the diets, feeds, feces, urine, and manure were collected at regular farm visits. Soils from manure-amended fields were sampled in the spring and fall. In all cases, the largest import of Mg, S, Cu, and Zn to the dairy was with purchased feeds, from 91 (S) to 97% (Zn) of all imports. The major mineral export item was manure [from 60% (S) to 89% (Cu) of all exports] and forages, in the case of a dairy with a large land base. Export with milk represented on average only 8.6, 25, 2.1, and 11% (Mg, S, Cu, and Zn, respectively) of all exports. Thus, the conversion of the imported feed Mg, S, Cu, and Zn into milk was rather low (on a whole-farm scale): 5.6, 11, 1.4, and 5.2%, respectively. Concentrations of Mg, Cu, and Zn in the lactating cow diets from the participating dairies exceeded National Research Council (2001) recommendations on average by 85, 34, and 73%, respectively, which contributed to the inefficient use of imported minerals. Whole-farm Mg surplus varied from 4 to 54 t/yr (3 to 19 kg/cow per year). The efficiency of use of imported Mg varied from 27 to 88%. Sulfur surpluses were from 9 to 52 t/yr (12 to 40 kg/cow per year). Copper and Zn surpluses were also significant (average of 59 and 585 kg/yr and 0.05 and 0.4 kg/cow per year, respectively). The average efficiency of use of imported S, Cu, and Mg was 44, 62, and 56%, respectively and, as with Mg, varied significantly among the dairies. The results from this study suggest that reduction in the concentration of dietary Mg, Cu, and Zn is potentially the most efficient way of reducing overall excretions and whole-farm surpluses of these minerals.

Efficiency of Use of Imported Nitrogen, Phosphorus, and Potassium and Potential for Reducing Phosphorus Imports on Idaho Dairy Farms

Eight commercial dairies from south central Idaho were surveyed to estimate the whole-farm surpluses of N, P, and K and to investigate the possibility of reducing P excretions through dietary manipulation. Nitrogen, P, and K imports and exports were monitored in a 12-mo period, and samples from the diets, feeds, feces, urine, and manure were collected at regular farm visits. Soils from manure-amended fields were sampled in the spring and fall. In all cases, the largest import of N, P, and K to the dairy was with purchased feeds. Major nutrient export items were milk and manure and forages, in the case of a dairy with a large land base (dairy F). Whole-farm N surplus varied from 90 to 599 t/yr (91 to 222 kg/yr per cow). The efficiency of use of imported N varied from 25 to 64%, with dairy F having the greatest efficiency of imported N use. Phosphorus and K surpluses were also significant (average of 29 and 182 t/yr and 12 and 76 kg per cow per year, respectively). During the study period, dairy F was a net exporter of K. The average efficiency of use of imported P and K was 66 and 58%, respectively. Soil P levels in the 30-cm layer were above state threshold standards, most likely from overapplication of manure. Soil nitrate-N concentrations were also high, but K concentrations were within the accepted range. Average P content of the lactating cow diets at the start of the study was 0.49% and was reduced to 0.38%. The estimated reduction in imported P due to the reduced dietary P levels was from 5.7 to 61.4 t/yr per farm, or on average 12 kg per cow per year. This study demonstrated that in addition to exports with milk and manure, export of nutrients with forages produced on the farm (dairy F) is a major factor in reducing whole-farm N, P, and K surpluses.

Effect of Corn Silage Hybrid and Metabolizable Protein Supply on Nitrogen Metabolism of Lactating Dairy Cows

This experiment was conducted to determine the effects of corn silage hybrid and supply of metabolizable protein (MP) on manure excretion and N metabolism by lactating dairy cows. Eight Holstein cows in midlactation (replicated 4 x 4 Latin square with 21-d periods) were fed 1 of 4 treatments, arranged factorially. Diets contained 55% corn silage made from a dual-purpose hybrid or a brown midrib (BMR) hybrid, and 45% concentrate that contained either a low or high concentration of rumen undegradable protein (altered by the addition of fish meal and treated soybean meal). Crude protein averaged 14.0 and 17.5% and supply of MP averaged 2,360 and 2,990 g/d for the low and high MP treatments (not affected by hybrid). Increasing supply of MP greatly increased urine output and tended to increase total manure output, whereas diets with BMR silage tended to reduce manure output. Increased MP supply increased daily excretion of manure N by 25% (465 vs. 374 g/d), fecal N by 27 g, and urinary N by 64 g. When the effect of N intake was removed, cows fed BMR silage excreted about 15 g/d less N via manure than cows fed the other silage. Rumen ammonia, volatile fatty acid concentrations, and pH were not affected by treatment. Dry matter intake (overall mean = 24.9 kg/d) tended to be increased with increased MP but was not affected by hybrid. Milk production for cows fed BMR was higher than for cows fed the dual-purpose hybrid (36.9 vs. 35.3 kg/d), but because of changes in fat concentration, yield of energy-corrected milk was not affected by treatment. The only interaction observed was increased yield of milk protein when BMR silage was combined with increased supply of MP.

Varying protein and starch in the diet of dairy cows. II. Effects on performance and nitrogen utilization for milk production

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on the lactational performance and use of N for milk production. Sixty multiparous Holstein cows were used in a 210-d lactational trial with a completely randomized design with a 2 x 3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary CP (means = 14.8, 16.8, and 18.7%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25.0% corn silage, 20.0% alfalfa silage, 10.0% cottonseed, 26.7 to 37.0% corn grain, and 4.8 to 13.5% protein supplement, plus minerals and vitamins. Across the 210 d of lactation, the productive response of dairy cows to the source of supplemental CP depended on the concentration of CP in the diet. At 18.7% CP, cows fed SBM consumed more DM and produced more milk, 3.5% fat-corrected milk, fat, and true protein, but had lower efficiency of feed use and body condition score than cows fed AMB. At 16.8% CP, cows fed AMB produced more 3.5% fat-corrected milk, fat, and true protein than cows fed SBM. At 14.8% CP, cows fed SBM consumed more DM but produced less true protein and had lower feed efficiency than cows fed AMB. Across CP sources, cows fed 14.8% CP produced less fat-corrected milk and true protein than cows fed 16.8 and 18.7% CP. Across CP percentages, cows fed AMB produced more fat-corrected milk per kilogram of DM consumed than cows fed SBM. Despite these interactions, improvements in the gross efficiency of N use for milk production were achieved through reductions in the intake of N independently of the source of CP. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650 g daily if the source of RDP and RUP are properly matched with the source and amount of carbohydrate in the diet.