Emissions of ammonia,nitrous oxide,methane, and carbon dioxide during storage of dairy cow manure as affected by dietary forage-to-concentrate ratio and crust formation

Sixteen 200-L barrels were used to determine the effects of dietary forage-to-concentrate (F:C) ratio on the rate of NH₃-N, N₂O, CH₄, and CO₂ emissions from dairy manure during a 77-d storage period. Manure was obtained from a companion study where cows were assigned to total mixed rations that included the following F:C ratio: 47:53, 54:46, 61:39, and 68:32 (diet dry matter basis) and housed in air-flow-controlled chambers constructed in a modified tiestall barn. On d 0 of this study, deposited manure and bedding from each emission chamber was thoroughly mixed, diluted with water (1.9 to 1 manure-to-water ratio) and loaded in barrels. In addition, on d 0, 7, 14, 28, 35, 49, 56, 63, 70, and 77 of storage, the rate of NH₃-N, N₂O, CH₄, and CO₂ emissions from each barrel were measured with a dynamic chamber and gas concentration measured with a photo-acoustic multi-gas monitor. Data were analyzed as a randomized complete block with 4 replications. Dietary F:C ratio had no effect on manure dry matter, total N and total ammoniacal-N (NH₃-N + NH₄⁺-N), or pH at the time of storage (mean ± SD: 10.6 ± 0.6%, 3.0 ± 0.2%, 93.1 ± 18.1 mg/dL, and 7.8 ± 0.5, respectively). No treatment differences were observed in the overall rate of manure NH₃-N, N₂O, CH₄, and CO₂ emissions (mean ± SD over the 77-d storage period; 117 ± 25, 30 ± 7, 299 ± 62, and 15,396 ± 753 mg/hr per m², respectively). The presence of straw bedding in manure promoted the formation of a surface crust that became air dried after about 1 mo of storage, and was associated with an altered pattern in NH₃-N and N₂O emissions in particular. Whereas NH₃-N emission rate was highest on d 0 and gradually decreased until reaching negligible levels on d 35, N₂O emission rate was almost zero the first 2 wk of storage, increased sharply to peak on d 35, and decreased subsequently. The emission rate of CH₄ and CO₂ peaked simultaneously on d 7, but decreased subsequently until the end of the storage period. In this study, C:N ratio of gaseous losses was 32:1, reflecting higher volatile C loss than volatile N loss during storage. On a CO₂-equivalent basis, the most important source of non-CO₂ greenhouse gas emitted was CH₄ until formation of an air-dried crust, but N₂O thereafter. Taken together, these results suggested that the formation of an air-dried crust resulting from the straw bedding present in the manure reduced drastically NH₃-N, and CH₄ emissions, but was conducive of N₂O production and emission.     

Prediction of ammonia emission from dairy cattle manure based on milk urea nitrogen: Relation of milk urea nitrogen to ammonia emissions

The main objectives of this study were to assess the relationship between ammonia emissions from dairy cattle manure and milk urea N (MUN; mg/dL) and to test whether the relationship was affected by stage of lactation and the dietary crude protein (CP) concentration. Twelve lactating multiparous Holstein cows were randomly selected and blocked into 3 groups of 4 cows intended to represent early [123 ± 26 d in milk (DIM)], mid (175 ± 3 DIM), and late (221 ± 12 DIM) lactation stages. Cows within each stage of lactation were randomly assigned to a treatment sequence within a split-plot Latin square design balanced for carryover effects. Stage of lactation formed the main plots (squares) and dietary CP levels (15, 17, 19, and 21% of diet dry matter) formed the subplots. The experimental periods lasted 7 d, with d 1 to 6 used for adjustment to diets and d 7 used for total collection of feces and urine as well as milk sample collection. The feces and urine from each cow were mixed in the proportions in which they were excreted to make slurry that was used to measure ammonia emissions at 22.5°C over 24 h using flux chambers. Samples of manure slurry were taken before and after ammonia emission measurements. The amount of slurry increased by 22% as dietary CP concentration increased from 15 to 21%, largely because of a greater urine volume (25.3 to 37.1 kg/d). Initial urea N concentration increased linearly with dietary CP from 153.5 to 465.2 mg/dL in manure slurries from cows fed 15 to 21% CP diets. Despite the large initial differences, the final concentration of urea N in manure slurries was less than 10.86 mg/dL for all dietary treatments. The final total ammoniacal N concentration in manure slurries increased linearly from 228.2 to 508.7 mg/dL as dietary CP content increased from 15 to 21%. Ammonia emissions from manure slurries ranged between 57 and 149 g of N/d per cow and increased linearly with dietary CP content, but were unaffected by stage of lactation. Ammonia emission expressed as a proportion of N intake increased with percentage CP in the diet from about 12 to 20%, whereas ammonia emission as a proportion of urinary urea N excretion decreased from 67 to 47%. There was a strong relationship between ammonia emission and MUN [ammonia emission (g/d per cow) = 25.0 (±6.72) + 5.03 (±0.373) × MUN (mg/dL); R² = 0.85], which was not different among lactation stages. Milk urea N concentration is one of several factors that allows prediction of ammonia emissions from dairy cattle manure.     

The effect of steam flaked or dry ground corn and supplemental phytic acid on nitrogen partitioning in lactating cows and ammonia emission from manure

The effect of starch source and supplemental phytic acid (PA) on N partitioning and excretion and ammonia volatilization from dairy manure was evaluated with 8 midlactation cows. Cows were randomly assigned to treatments in replicated 4 x 4 Latin squares with four 18-d periods. Diets were 61% forage, 25% starch, 17.2% crude protein, and 31% neutral detergent fiber and included dry ground corn (DG) or steam flaked corn (SF) with no supplemental P (L; 0.34% P) or supplemental purified PA (0.45% P) to provide additional P from a non-mineral source. Total collection of milk, urine, and feces was conducted on d 16 to 18 of each period. Cows fed SF had lower dry matter (DM) intakes than those fed DG, which, in addition to increased starch digestibility and ruminal fermentation, contributed to higher DM digestibility. Cows fed SF had reduced feces and urine excretion compared with cows fed DG. Also, N intake for cows fed SF was lower, and N digestibility was higher, compared with cows fed DG; therefore, N excretion in both feces and urine was reduced in these cows. Despite the differences in DM intake, lactation performance was not affected by starch sources. Therefore, the efficiency of N utilization increased with SF. Addition of PA did not affect N intake or utilization. Feces and urine were subsampled from each cow, and wet feces and urine were mixed in sealed chambers in the proportions excreted. Ammonia volatilization was measured for 36 h using acid traps sampled on a planned time course. Nitrogen at time zero (A0), rate of ammonia emission (k), and residual N (R) were calculated using the exponential decay model At = A0 e(-kt) + R. Rate of ammonia loss from mixed feces and urine was lower from cows fed SF than from those fed DG. Altering dietary starch source to improve nutrient digestibility and to reduce N excretion by lactating cows may provide opportunity to reduce ammonia losses from manure.     

Prediction of ammonia emission from dairy cattle manure based on milk urea nitrogen: relation of milk urea nitrogen to urine urea nitrogen excretion

The objectives of this study were to assess the relationship between urinary urea N (UUN) excretion (g/d) and milk urea N (MUN; mg/dL) and to test whether the relationship was affected by stage of lactation and the dietary crude protein (CP) content. Twelve lactating multiparous Holstein cows were randomly selected and blocked into 3 groups of 4 cows intended to represent early [123 ± 26 d in milk (DIM); mean ± standard deviation], mid (175 ± 3 DIM), and late (221 ± 12 DIM) lactation stages. Cows within each stage of lactation were randomly assigned to a treatment sequence within a split-plot Latin square balanced for carryover effects. Stage of lactation formed the main plots (squares) and dietary CP levels (15, 17, 19, and 21% of diet dry matter) formed the subplots. Graded amounts of urea were added to the basal total mixed ration to linearly increase dietary CP content while maintaining similar concentrations of all other nutrients among treatments. The experimental periods lasted 7 d, with d 1 to 6 used for adjustment to diets and d 7 used for total collection of urine as well as milk and blood sample collection. Dry matter intake and yields of milk, fat, protein, and lactose declined progressively with lactation stage and were unaffected by dietary CP content. Milk and plasma urea-N as well as UUN concentration and excretion increased in response to dietary CP content. Milk and urine urea-N concentration rose at increasing and decreasing rates, respectively, as a function of plasma urea-N. The renal urea-N clearance rate differed among lactation stages and dietary CP contents. The relationship between UUN excretion and MUN differed among lactation stages and diverged from linearity for cows in early and late lactation. However, these differences were restricted to very high MUN concentrations. Milk urea N may be a useful tool to predict the UUN excretion and ultimately NH₃ emission from dairy cattle manure.     

Effect of dietary crude protein modification on ammonia and nitrous oxide concentration on a tie-stall dairy barn floor

Dietary crude protein (CP) reduction is considered a useful strategy to minimize cow N excretion and NH₃ and N₂O emissions. The aim of the current work was to relate dietary CP modification to whole-animal N balance and subsequent NH₃ and N₂O concentrations on a tie-stall barn floor. The effect of temperature on NH₃ and N₂O concentration was also studied. Three Holstein mid to late lactating cows were confined in separate tie-stalls and randomly assigned to 3 diets with varying CP content [low CP (LCP): 14.1%; moderate CP (MCP): 15.9%; high CP (HCP): 16.9%]. Increasing N intake (from 438.6 to 522.8 g of N/d) improved milk yield (from 22.1 to 24.2 kg/d). However, N use efficiency tended to decrease with increasing dietary CP, as shown by milk N use efficiency (from 23.9 to 22.6%), milk urea N (from 15.4 to 18.7 mg/dL), and excreted N per milk yield unit (from 14.7 to 16.4 g of N/kg of milk). Because of higher N excretion, NH₃ concentration on the dairy barn floor increased (LCP: 7.1 mg of NH₃/m³; MCP: 10.4 mg of NH₃/m³; HCP: 10.8 mg of NH₃/m³). In contrast, N₂O concentration did not respond to dietary manipulation (mean 1.1 mg of N₂O/m³). Temperature, which ranged between 12.6 and 18.0°C, did not affect NH₃ and N₂O concentrations at the stall level. However, when fecal and urinary samples were incubated at 4, 19, and 29°C in the laboratory, ammonia concentration increased for all diets, especially for the MCP and HCP diets, as the temperature increased. In contrast, N2O concentration was negatively related to increasing temperature. In conclusion, data from the current trial demonstrate that lowering dietary CP minimizes NH₃ concentration on dairy stall floors although temperature controls the rate of NH₃ volatilization. On the other hand, N₂O concentration is not affected by dietary treatments on tie-stall floors.     

Enteric and manure emissions from Holstein-Friesian dairy cattle fed grass silage–based or corn silage–based diets

This study aimed to evaluate trade-offs between enteric and manure CH₄ emissions, and the size of synergistic effects for CH₄ and nitrogenous emissions (NH₃ and N₂O). Sixty-four Holstein-Friesian cows were blocked in groups of 4 based on parity, lactation stage, and milk yield. Cows within a block were randomly allocated to a dietary sequence in a crossover design with a grass silage-based diet (GS) and a corn silage-based diet (CS). The GS diet consisted of 50% grass silage and 50% concentrate, and CS consisted of 10% grass silage, 40% corn silage, and 50% concentrate (dry matter basis). The composition of the concentrate was identical for both diets. Cows were housed in groups of 16 animals, in 4 mechanically ventilated barn units for independent emission measurement. Treatment periods were composed of a 2-wk adaptation period followed by a 5-wk measurement period, 1 wk of which was without cows to allow separation of enteric and manure emissions. In each barn unit, ventilation rates and concentrations of CH₄, CO₂, NH₃, and N₂O in incoming and outgoing air were measured. Cow excretion of organic matter was higher for CS compared with GS. Enteric CH₄ and cow-associated NH₃ and N₂O emissions (i.e., manure emissions excluded) were lower for CS compared with GS (−11, −40, and −45%, respectively). The CH₄ and N₂O emissions from stored manure (i.e., in absence of cows) were not affected by diet, whereas that of NH₃ emission tended to be lower for CS compared with GS. In conclusion, there was no trade-off between enteric and manure CH₄ emissions, and there were synergistic effects for CH₄ and nitrogenous emissions when grass silage was exchanged for corn silage, without balancing the diets for crude protein content, in this short-term study.     

Nitrogen and phosphorus retention and excretion in late-gestation dairy heifers

The objectives of this study were to evaluate the effects of limit feeding diets containing concentrates or by-products in place of forages on manure and nutrient excretion in growing, gravid heifers. Eighteen Holstein heifers confirmed pregnant were grouped by due date and fed 1 of 3 diets (n = 6 per treatment) for the last 14 wk of pregnancy. Diets were high forage, fed ad libitum (HF); by-product based (BP), fed at the same rate as HF-fed heifers; or low forage (LF), fed at 86% of the HF diet. Diets were designed to supply equal quantities of P, N, and metabolizable energy. Total collection of feces and urine was conducted in wk 14, 10, 6, and 2 prepartum. The HF ration was 90.7% forage, 13.7% crude protein (CP), and contained orchardgrass hay, corn silage, corn grain, soybean meal 44%, and a vitamin-mineral premix. The BP diet was 46.2% forage and 14.0% CP, with 70% of the grain mix space replaced with soybean hulls and cottonseed hulls in a 1:1 ratio, with intake limited to 93% of the dry matter intake (DMI) of HF. The LF ration was 45.3% forage and 17.8% CP, with intake limited to 86% of the DMI of HF. The effect of diet was analyzed with repeated measures, using preplanned contrasts to compare HF with BP and LF with HF and BP. As designed, heifers fed HF and BP had greater DMI than the heifers limit-fed LF, and there was no effect of diet on average daily gain or BW. Intake and digestibility of N were lower, and fecal N excretion was higher, in heifers fed HF and BP than heifers fed LF. Mean feces excretion on both a wet and dry basis was greater for HF heifers compared with BP heifers and less for LF heifers than for HF and BP heifers. Despite differences in urinary output, diet had no effect on urea N excretion, but there was a trend for heifers fed HF and BP rations to excrete less urinary N compared with those fed LF. Compared with HF and BP heifers, LF heifers tended to have lower fecal P excretion and had higher urinary P excretion. Measured manure and urine excretion from heifers fed LF was greater than current American Society of Agricultural and Biological Engineers values, whereas heifers fed HF excreted less manure and urine than predicted. Heifers achieving similar rates of gain from diets differing in forage, grain, and by-product content excreted widely varying quantities of manure.     

Updating analysis of nitrogen balance experiments in dairy cows

Nitrogen balance (NB) experiments allow calculation of N retention in the body by subtracting N excreted in feces (NF), urine (NU) and milk (NM) from N intake (NI). In a previous study, we found that NB data from experiments with lactating dairy cows were generally high and, in the current meta-analysis, we update our earlier study with experiments from the last 2 decades and investigate probable causes of error. A total of 83 publications, with 86 experiments and 307 dietary treatments, were selected from top-ranked scientific journals that reported all NB components. The NB and NB components were analyzed by linear regression with a model that used NI as an independent variable and experiment as a random effect. The NF, NU and NM each represented 27 to 34% of NI, and the remaining N accumulated in the body was equal to 38.5 g/d (overall SD = 43.2 g/d). Retained N (as g/d or % of NI) increased linearly with NI, and this led to unlikely high N retentions, especially at high NI. Both NF and NU (g/d) increased with increasing NI, and we assume that some N in feces and urine were unaccounted. Only ~22% of experiments measured N in wet feces samples and, when analysis used dry samples, no mention of corrections due to potential volatile N losses during drying were reported. No experimentalists preserved feces immediately to prevent volatilization during collection. Moreover, ~27% of experiments estimated urine volumes by concentration of creatinine in spot samples, and in these experiments, NU was ~12% lower than those where total urine was collected (168 vs. 191 g/d). Only 40 experiments reported the volume and concentration of acids used for urine preservation, 33 furnished incomplete information, and the remainder did not describe the urine preservation method. In conclusion, the results of NB experiments using lactating dairy cows overestimate N retention, and the losses of N from feces and urine are the most probable reason.     

Effect of a direct-fed fibrolytic enzyme formulation on nutrient intake,partitioning, and excretion in early and late lactation Holstein cows

The effect of a fibrolytic enzyme formulation on N and P intake, partitioning, and excretion was evaluated in dairy cows in early and late lactation. Twelve lactating Holstein cows (6 early lactation, 6 late lactation) were fed diets with or without the enzyme formulation in a switchback design with three, 4-wk periods. Diets for the early lactation group contained 45% forage, and late lactation diets contained 61% forage. Cows fed diets containing the enzyme formulation gained more weight than those on the control diet; this weight gain with enzyme addition was greater in early lactation cows than in late lactation cows. The main effect of enzyme treatment did not significantly affect apparent digestibility or excretion of N and P, or retention of these nutrients in body tissue. Interactions observed between the effects of group (stage of lactation) and treatment indicated differences in the nature of the milk yield and manure excretion responses to enzyme treatment between early and late lactation cows. These interactions were due to numerical increases in milk yield, feces excretion, and N excretion in early lactation cows fed diets containing the enzyme formulation compared to control, and slight decreases in these measures in late lactation cows with enzyme addition. Cows fed diets containing a direct-fed fibrolytic enzyme formulation had increased body weight gain, but the effect of addition of the enzyme formulation on milk yield and manure nutrient excretion differed for early and late lactation cows.     

Effects of a polymer-coated urea product on nitrogen metabolism in lactating Holstein dairy cattle

The purpose of this study was to evaluate the impact of polymer-coated urea on nitrogen retention, rumen microbial growth, and milk production and composition. Coated urea (CU) that is more slowly hydrolyzed to ammonia than unprotected urea could potentially be used more efficiently by rumen microorganisms. Eight cows were offered each of three diets in a randomized crossover design. Each treatment period consisted of a 14-d adjustment period and a 5-d collection period. Diets were formulated to maintain milk production while reducing plasma urea nitrogen concentrations and urinary nitrogen excretion. Diets consisted of corn silage, mixed grass/legume haylage, chopped alfalfa hay, corn meal, protein, vitamin and mineral supplements, in a total mixed ration and fed ad libitum. The diets contained 17.9%, 18.1%, and 16.4% CP and 0, 0.77%, and 0.77% CU (dry matter basis) and are denoted as CP18-CU, CP18+CU, and CP16+CU, respectively. Individual feed intakes were measured, and total fecal, and urine collections were conducted. Cows were milked twice daily at 0500 and 1700 h, and the milk sampled for composition and milk urea N analysis. Dry matter intake averaged 23.5 +/- 0.2 kg/d and was not altered by diet. Also, milk fat and true protein were not altered by diet and averaged 3.72 and 3.07%, respectively. Milk yield was highest for diets CP18-CU and CP18+CU. Significant differences were observed in N intake and excretion in urine, feces, and milk between dietary treatments. Cows fed CP16+CU consumed 11% less N than in CP18-CU. Cows fed CP18+CU showed the highest excretion of N in urine, and together with CP16+CU, the lowest N excretion in feces. Nitrogen excretion in milk was lower for cows fed CP16+CU. Calculated N balance was not significantly different between diets nor was it significantly different from zero. Efficiency of N capture in milk protein as a function of N intake was higher for animals on CP16+CU. Urinary excretion of purine derivatives was not different between diets, and estimated microbial CP was also similar. Coated urea was not effective at reducing nitrogen excretion by dairy cattle.     

Seasonal diet affects ammonia emissions from tie-stall dairy barns

Federal and state regulations are being promulgated under the Clean Air Act to reduce hazardous air emissions from livestock operations. Although much is known about air emissions from livestock operations in Europe, few data are available on emissions from livestock facilities in the United States and the management practices that may minimize these emissions. The objective of this study was to measure seasonal and diet effects on ammonia emissions from experimental tie-stall dairy barns located in central Wisconsin. Four experimental chambers each housed 4 lactating Holstein dairy cows for three 28-d trial periods corresponding to spring, early fall, and winter. A 4 × 4 Latin square statistical design was used to evaluate 4 diets [corn silage (CS)- or alfalfa silage (AS)-based diets at low or high crude protein] in each chamber for a 4-d ammonia monitoring period. Partially due to higher crude protein levels, average ammonia-N emissions during spring (18.8 g/cow per d) were approximately twice the emissions recorded during early fall (8.4 g/cow per d) and 3 times greater than emissions during winter (6.7 g/cow per d). Ammonia-N emissions accounted for approximately 1 to 3% of consumed feed N, 2 to 5% of excreted manure N, and 4 to 11% of manure ammonical N. Nighttime ammonia emissions were on average 30% lower than daytime emissions. Forage type did not affect ammonia emissions during winter or early fall. Only during early spring were ammonia emissions lower from chambers containing cows fed low-CP diets than from cows fed high-CP diets. Of the total chamber N inputs (feed and bedding), 93, 91, and 95% were recovered in N outputs (milk, manure, body weight change, and ammonia N) during spring, early fall, and winter trials, respectively. Confidence in the accuracy of ammonia emission results was gained by the relatively high chamber N balances and favorable comparisons of study data with published relationships among the variables of feed N intake, milk urea N, manure N, and urine N excretion, and ammonia emissions.     

烤烟施用畜禽粪便商品有机肥的效应

为探索畜禽粪便商品有机肥在烤烟生产中的效果,通过大田试验研究了该肥料对烤烟生长发育及产质量的影响。结果表明,施用该有机肥大部分处理烟株的团棵期推迟,各处理烟株的腰叶、顶叶成熟期基本相同;施用有机肥处理的株高高于烟草专用肥处理;大部分施用有机肥处理的平均有效叶数比烟草专用肥处理多1~2.7片/株;施用猪粪和牛粪的有效叶数比鸡粪的多;处理间的产量差异未达显著水平;猪粪1、猪粪2处理的产值比饼肥处理和专用肥处理的略高,但差异未达显著水平,牛粪和鸡粪3处理的产值最低;施用畜禽粪便有机肥烟叶的香吃味与施用饼肥的烟叶无实质性区别,烤烟生产可大面积应用畜禽粪便商品有机肥。     

Varying forage type, metabolizable protein concentration, and carbohydrate source affects manure excretion, manure ammonia, and nitrogen metabolism of dairy cows

Effects of forage source, concentration of metabolizable protein (MP), and type of carbohydrate on manure excretion by dairy cows and production of ammonia from that manure were evaluated using a central composite experimental design. All diets (dry basis) contained 50% forage that ranged from 25:75 to 75:25 alfalfa silage:corn silage. Diets contained 10.7% rumendegradable protein with variable concentrations of undegradable protein so that dietary MP ranged from 8.8 to 12%. Starch concentration ranged from 22 to 30% with a concomitant decrease in neutral detergent fiber. A total of 15 diets were fed to 36 Holstein cows grouped in 6 blocks. Each block was a replicated 3 × 3 Latin square resulting in 108 observations. Manure output (urine and feces) was measured using total collection, and fresh feces and urine were combined into slurries and incubated for 48 h to measure NH₃-N production. Feces, urine, and manure output averaged 50.5, 29.5, and 80.1 kg/d, respectively. Manure output increased with increasing dry matter intake (∼3.5 kg of manure/kg of dry matter intake), increased concentrations of alfalfa (mostly via changes in urine output), and decreased concentrations of starch (mostly via changes in fecal output). The amount of NH₃-N produced per gram of manure decreased with increasing alfalfa because excreted N shifted from urine to feces. Increasing MP increased NH₃-N produced per gram of manure mainly because of increased urinary N, but increased fecal N also contributed to the manure NH₃. Manure NH₃-N production per cow (accounts for effects on manure production and NH₃-N produced per unit of manure) was least and milk protein yields were maximal for diets with high alfalfa (75% of the forage), moderate MP (11% of diet dry matter), and high starch (30% of diet dry matter).     

Partition of nitrogen excretion in urine and the feces of holstein replacement heifers

Increasing public concern has been focused on animal production systems as a major nonpoint source of pollution. These studies were conducted to further our understanding of whole-animal N metabolism, N excretion, and its partition between feces and urine in growing dairy heifers. Isocaloric diets [2.31 Mcal of metabolizable energy (ME)/kg of dry matter (DM)], ranging from 12.4 to 34.2 g of N/kg of DM, were fed to Holstein heifers in 2 experiments at approximately 1.8 times maintenance. Diets were formulated to provide 54 to 143% of the ruminal ammonia requirements as predicted by the Cornell Net Carbohydrate and Protein System. Increasing the N content of the diet increased urinary N excretion and N balance, but did not affect fecal N excretion. Holstein heifers fed low N diets were able to maintain growth rates consistent with current recommendations while at the same time reducing N excretion, in particular nitrogenous compounds that are readily converted to ammonia. However, more research is needed before this type of diet is recommended for growing heifers because of possible changes in body composition that may affect future milk production and performance.     

Effects of amounts and degradability of dietary protein on lactation,nitrogen utilization,and excretion in early lactation Holstein cows

Five treatment diets varying in crude protein (CP) and rumen undegradable protein (RUP) were calculated to supply a postruminal lysine to methionine ratio of about 3:1. Diets were fed as a total mixed ration to 65 Holstein cows that were either primiparous (n = 28) or multiparous (n = 37) from 21 to 120 d in milk to determine effects on lactation and nitrogen utilization. Crude protein % and calculated RUP (% of CP) of diets [on a dry matter (DM) basis] were: 1) 19.4, 40 (HPMU), 2) 16.5, 34 (LPLU), 3) 16.8, 40 (LPMU), 4) 16.8, 46 (LPHU), 5) 17.2, 43 (LPHU + UREA), which is the result of adding 0.4% of the diet DM as urea to LPHU. The corn silage-based treatment diets contained an average of 24% acid detergent fiber and 1.6 Mcal/kg net energy of lactation. Milk urea nitrogen (MUN) concentrations and body weights (BW) were used to calculate predicted amounts of urinary nitrogen (N) using the relationship: urinary N (g/d) = 0.0259 x BW (kg) x MUN (mg/dl). Cows fed HPMU had greater CP and RUP intakes, which resulted in higher concentrations of plasma urea nitrogen, rumen ammonia, MUN, and predicted urinary N. Milk yield, fat yield, fat percent, protein yield, and protein percent were not significantly different among treatments. Parity primarily affected parameters that were related to body size and not measurements of N utilization. The interaction of treatment and parity was not significant for any measurements taken. In this study, cows fed LPHU had significantly lower MUN and predicted urinary N without limiting production. These results demonstrate the potential to optimize milk production while minimizing N excretion in lactating dairy cattle.     

Effect of amount and ruminal degradability of soybean meal protein on performance of lactating dairy cows

Twenty-eight Holstein cows (4 with ruminal cannulas) were blocked by days in milk into 7 groups and then randomly assigned to 1 of 7 balanced 4 × 4 Latin square diet sequences. The diets contained [dry matter (DM) basis] 20% alfalfa silage, 35% corn silage, and 45% concentrate mainly from high-moisture corn and soybean meal. Diets differed in crude protein (CP) content and source of protein supplement: diet A) 15.6% CP, 3.7% solvent-extracted soybean meal (SSBM), 4.5% expeller soybean meal (ESBM); diet B) 16.6% CP, 9.6% SSBM, 0% ESBM; diet C) 16.6% CP, 4.6% SSBM, 5.9% ESBM; and diet D) 17.6% CP, 11.7% SSBM, 0% ESBM. Each experimental period consisted of 14 d for adaptation plus 14 d for collection of production data. Sampling of ruminal digesta and spot sampling of blood, feces, and urine was done on d 26 and 27 of each period. Planned contrasts compared included diet A vs. diet B, diet B vs. diet C, and diet B vs. diet D. There were no effects of diet on most of the production traits measured. However, milk yield tended to be higher for diet B vs. A. Trends were also detected for higher DM intake and weight gain and lower milk yield/DM intake in cows fed diet D vs. diet B. Milk lactose content was higher on diets A and C than on B. Ruminal NH₃ was higher on diet D vs. B, but other ruminal metabolites, apparent nutrient digestibility, and estimated bacterial CP synthesis did not differ across diets. Blood and milk urea-N were higher on diets C and D than on B; milk urea-N was higher on diet B than on A. Increasing dietary CP from 16.6% (diet B) to 17.6% (diet D) increased urinary N excretion by 54 g/d and reduced apparent N efficiency (milk N/N intake) by 2.5 percentage units, without altering yield. Under the conditions of this trial, milk production was not improved by feeding rumen-undegraded protein from ESBM or greater amounts of rumen-degraded protein from SSBM. Feeding more than 16.6% CP depressed N efficiency.