Milk Urea Nitrogen Concentration Research Articles

Milk Urea Concentration to the Evaluation of Nitrogen Efficiency Transformation on Dairy Farms

Abstract The aim of this study was to evaluate the effects of nutrition on the milk urea nitrogen (MUN) concentration; on the transformation of N in the farm’s conditions; and there-by allow the milk urea nitrogen concentration to serve as a tool to maximize the protein nutrition and the metabolism of the cows. The relations evaluated by linear or multiple regression confirmed that the highest nutritional effects of the crude protein (CP) on the MUN concentration, which represented a 69.3 % variation in the MUN content. According to the CP content in the total mix ration (TMR) and MUN content (3150 milk samples) under farm conditions, a regression relationship was determined for the estimated of MUN (mg.dl–1) = –13.2 + 0.16 × CP (g.kg–1 dry matter). For multiple regression, the rate of variation expressed by this relationship increased to 72 for nutrient content and 78.3 % for nutrient intake in the TMR. The efficiency of nitrogen utilization (ENU) determined by calculations based on the MUN content according to the regression equations represented a negative correlation (P < 0.0001; R2 = 0.854) with respect to the CP content in the TMR and that the increased CP content by 1 % in the range of 14 to 18 % in the TMR decreased the ENU by 1.48 %. Validation of the models for prediction of nitrogen transformation (ENU) for practical application on the farms determined the best equation, which used the available data from the routine analysis of Breeding services of Slovakia. After taking into consideration of our breeding conditions, it was confirmed that the equation of ENU had taken into account the MUN, in addition to the amount of the milk produced.

Nitrogen Use Efficiency and Excretion in Grazing Cows with High and Low Milk Urea Nitrogen Breeding Values

Milk urea nitrogen content is moderately heritable and is phenotypically related to urine nitrogen (UN). Based on this relationship, it has been suggested that genetic selection for lower milk urea nitrogen in grazing dairy cows could decrease UN concentration thereby reducing nitrogen excretions into the ground. The objective of this study was to compare the nitrogen use efficiency (NUE) and excretion in grazing cows with high and low milk urea nitrogen breeding values (MUNBV) in two farms of contrasting farming intensity. On the high-intensity farm (HIF) 68 and 70 cows with low and high MUNBV, respectively, were fed higher levels of supplementation and milked twice-daily, while on the low-intensity farm (LIF) 82 and 86 cows with low and high MUNBV, respectively, were fed lower levels of supplementation milked once-daily. Nitrogen use efficiency (g/g) was calculated as the ratio of daily milk N to daily N intake. Daily N intake (g/day) was derived from feed intake estimates based on energy requirements. The UN (g/day) was estimated by back-calculation from dietary N and subtracting milk N, faecal N, and N retained in body tissues. Irrespective of farm, cows with low MUNBV had significantly lower MY and milk urea nitrogen (p < 0.001) but this was not linked to significantly less UN. In the LIF, cows with low MUNBV had lower NUE (p < 0.001) than cows with high MUNBV, and this was explained by the reduced protein yield (p < 0.001). Selecting cows for low MUNBV was not an effective tool to reduce N losses and to increase the NUE in two dairy farms of contrasting farming intensity.

Effects of a blend of live yeast and organic minerals or monensin on performance of dairy cows during the hot season

The objective of this study was to evaluate the effects of feed additives on intake and digestibility of nutrients, milk yield and composition, feeding behavior, and physiological parameters of dairy cows during the hot season. Forty Holstein cows were assigned to a randomized block design experiment with a 2 × 2 factorial treatment arrangement to evaluate (1) control diet without inclusion of additives; (2) monensin (MON), 20 mg/kg diet dry matter sodium monensin (Rumensin; Elanco); (3) Milk Sacc+ (MS+), inclusion of 40 g/cow per d of Milk Sacc+ (a blend of live yeast and organic minerals, Alltech); and (4) combination of MON and MS+. The average temperature-humidity index throughout the experimental period was 73 ± 2.84 (standard deviation). The experiment lasted 11 wk, including 2 preliminary weeks for covariate adjustments. Cows fed MS+ increased dry matter intake (% body weight), milk yield, 3.5% fat-corrected milk, and solids yield, and cows fed MON had greater milk urea nitrogen content in comparison with counterparts. Feeding MS+ increased the intake of feed particles with size between 8 and 19 mm and decreased the intake of particles shorter than 4 mm compared with other treatments. Rumination time (min/d) and chewing time (min/kg of neutral detergent fiber) were lower for cows fed MS+. Physiologic parameters (i.e., heart and respiratory rates, and body temperature) were not affected by the treatments. Overall, the use of monensin did not differ from control, and Milk Sacc+ improved performance of cows.

Performance evaluation of an enzymatic spectrophotometric method for milk urea nitrogen

Our objective was to determine the within and between laboratory performance of an enzymatic spectrophotometric method for milk urea nitrogen (MUN) determination. This method first uses urease to hydrolyze urea into ammonia and carbon dioxide. Next, ammonia (as ammonium ions) reacts with 2-oxoglutarate, in the presence of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) and the enzyme glutamate dehydrogenase (GlDH), to form l-glutamic acid, water, and NADP+. The change in light absorption at 340 nm due to the conversion of NADPH to NADP+ is stoichiometrically a function of the MUN content of a milk sample. The relative within (RSDr) and between (RSDR) laboratory method performance values for the MUN enzymatic spectrophotometric method were 0.57% and 0.85%, respectively, when testing individual farm milks. The spectrophotometric MUN method demonstrated better within and between laboratory performance than the International Dairy Federation differential pH MUN method with a much lower RSDr (0.57 vs. 1.40%) and RSDR (0.85 vs. 4.64%). The spectrophotometric MUN method also had similar method performance statistics as other AOAC International official validated chemical methods for primary milk component determinations, with the average of all RSDr and RSDR values being <1%. An official collaborative study of the enzymatic spectrophotometric MUN method is needed to achieve International Dairy Federation, AOAC International, and International Organization for Standardization official method status.

Preservation of sugarcane silage with urea and calcium oxide: performance and metabolic efficiency of dairy cows

Background: Inclusion of urea and calcium oxide (CaO) during sugarcane ensilage has been hypothesized to improve dairy cow performance. Objective: To evaluate the use of urea and calcium oxide as additives to preserve sugarcane silage quality and determine whether they improve dairy cow performance and metabolic efficiency. Methods: Four diets were used: sugarcane silage without additive (SS), sugarcane silage with 10 g/kg urea (SU), sugarcane silage with 5 g/kg urea + 5 g/kg CaO (SUC), and sugarcane silage with 10 g/kg CaO (SC). Eight crossbred cows at approximately 100 days of lactation were distributed in two 4x4 Latin squares, and their diets were formulated to reach an average milk production of 15 kg/day. Results: Dry matter, non-fibrous carbohydrates, organic matter, total carbohydrates, and total digestible nutrient intake were the highest (p&lt;0.05) for the cows fed SC. Urinary excretion of nitrogen was higher (p&lt;0.05) for cows fed diets based on SUC than those fed diets with SC. Milk urea nitrogen content was the highest (p&lt;0.05) in animals fed SU diets. Nitrogen balance was positive in all treatments; however, the microbial protein synthesis was low for all diets. Conclusions: The diet with SU showed the highest nitrogen loss through the milk. Among the evaluated silages, those with SC and SUC are recommended to promote a high intake of nutritional components.

Effect of dietary non-fiber carbohydrate source and inclusion of buffering on lactation performance, feeding behavior and milk stability of dairy cows

The present study hypothesized that partial replacement of ground corn (GC) by pelleted citrus pulp (PCP) and buffering (BF) inclusion in diets of lactating cows does not change lactation performance, but does reduce milk concentration of ionic calcium (iCa), increasing its stability at ethanol test and heating at 140 °C (heat coagulation time – HCT). We evaluated the effect of PCP and buffer inclusion on digestive metabolism, feeding behavior, milk yield, and milk stability of lactating cows. Sixteen Holstein cows (average milk yield of 28 ± 4.8 L/d and days in milk of 130 ± 81.0; mean ± SD) were distributed in a Latin square design with 4 replicated squares, 4 periods of 21 d (14 d for adaptation and 7 d for sampling) and 4 treatments in a 2 × 2 factorial arrangement. Treatment factor 1 was the partial replacement (134 g/kg) of GC by PCP and factor 2 was the inclusion of buffer (7.1 g/kg of Na bicarbonate plus 2.4 g/kg of Mg oxide; DM basis) in diets composed of 40:60 of forage: concentrate ratio. The partial replacement of GC with PCP reduced dry matter intake (DMI) by 1.35 kg/d, increased dry matter (DM) and neutral detergent fiber assayed with a heat stable amylase and expressed exclusive of residual ash (aNDFom) digestibility, and ruminal concentration of acetic and butyric acids, but no change was observed on milk yield, resulting in higher production efficiency. The partial replacement of GC with PCP also reduced the ruminal concentration of iso-butyric and iso-valeric acids, milk urea nitrogen concentration, and casein content and tended to reduce HCT. There was no isolated effect of GC replacement or buffer addition or their interaction on iCa concentration and milk stability at the ethanol test. For diets without the inclusion of PCP, cows increased drinking time by 8 min/d. When cows were fed diet with the inclusion of PCP, the rumination time decreased 57 min/kg physical effective aNDFom (peNDF) intake compared to when cows were fed diets without partial replacement of GC with PCP. The buffer inclusion increased milk fat content and urinary pH. However, milk stability at ethanol test did not change in response to treatments and HCT tended to be reduced when GC was replaced by PCP. The results of our study suggested that, although partial replacement of GC with PCP and BF inclusion altered DMI, short chain fatty acids (SCFA) concentration, and urinary pH, those factors did not change milk yield and milk stability.

Effects of lactic acid bacteria in a silage inoculant on ruminal nutrient digestibility, nitrogen metabolism, and lactation performance of high-producing dairy cows

Silage treated with lactic acid bacteria inoculants has been reported to increase ruminal microbial biomass when tested in vitro. Therefore, we tested if alfalfa silage inoculated with Lactobacillus plantarum MTD-1 would improve ruminal N metabolism and increase milk production in high-producing dairy cows. Twenty-eight early lactation Holstein cows (8 ruminally cannulated) were blocked by DIM and milk production; animals were used in a double crossover design consisting of four 28-d periods. Animals in each block were randomly assigned to 2 treatments: a diet containing uninoculated alfalfa silage (control) and a diet containing alfalfa silage inoculated with L. plantarum MTD-1 (LP). Diets were formulated to contain 50% of alfalfa silage, 16% crude protein, and 25% neutral detergent fiber (dry matter basis). Milk production and dry matter intake were recorded in the last 14 d of each period. Milk samples were collected twice at both daily milkings on d 20, 21, 27, and 28 of each period. On d 22, omasal samples were collected from the cannulated animals over a period of 3 d to quantify ruminal digestibility and nutrient flows. Data were analyzed using mixed models of SAS 9.4 (SAS Institute). Compared to the control, cows receiving the LP treatment had greater milk production (40.4 vs. 39.6 kg/d) and lower milk urea nitrogen concentration (11.6 vs. 12.7 mg/dL), despite minor changes in energy-corrected milk. Milk lactose concentration was greater in the milk produced by cows fed the LP treatment, which reflected a tendency for increased milk lactose yield. Although milk true protein concentration was lower for cows in the LP treatment, milk true protein yield was the same on both control and LP treatments. Improvements in milk production of animals under the LP treatment were associated with greater organic matter truly digested in the rumen, especially ruminal neutral detergent fiber digestion. Minor changes were observed in total omasal microbial nonammonia N flow in cows receiving the LP treatment. Therefore, alfalfa silage treated with L. plantarum MTD-1 may improve ruminal fermentation and milk production; however, because of a lack of response in ruminal N metabolism, these changes did not result in greater energy-corrected milk in high-producing dairy cows.

Infrared milk analyzers: Milk urea nitrogen calibration

Our first objective was to redesign a modified 14-sample milk calibration sample set to obtain a well-distributed range of milk urea nitrogen (MUN) concentrations while maintaining orthogonality with variation in fat, protein, and lactose concentration. Our second objective was to determine the within- and between-laboratory variation in the enzymatic spectrophotometric method on the modified milk calibration samples and degree of uncertainty in MUN reference values, and then use the modified milk calibration samples to evaluate and improve the performance of mid-infrared partial least squares (PLS) models for prediction of MUN concentration in milk. Changes in the modified milk calibration sample formulation and manufacturing procedure were made to achieve the desired range of MUN concentrations. A spectrophotometric enzymatic reference method was used to determine MUN reference values, and the modified milk calibration samples were used to calibrate 3 mid-infrared milk analyzers. The within- and between-laboratory variation in the reference values for MUN were 0.43 and 0.77%, respectively, and the average expanded analytical uncertainty for the mean MUN value of the 14-sample calibration set was (mean ± SD) 16.15 mg/100 g ± 0.09 of milk. After slope and intercept adjustment to achieve a mean difference of zero with the calibration samples, it could be seen that the standard deviation of the differences of predicted versus reference MUN values among 3 different instruments and their PLS models were quite different. The orthogonal sample set was used (1) to determine when a PLS model did not correctly model out the background variation in fat, true protein, or anhydrous lactose; (2) to calculate an intercorrection factor to eliminate that effect, and (3) to improve the model performance (i.e., 50% reduction in standard deviation of the difference between instrument predictions and reference chemistry values for MUN).

Milk urea nitrogen variation explained by differences in urea transport into the gastrointestinal tract in lactating dairy cows

Milk urea nitrogen (MUN) and blood urea nitrogen are correlated with nitrogen balance and nitrogen excretion; however, there is also a genetic component to MUN concentrations that could be associated with differences in urea transport. It was hypothesized that a portion of the variation in MUN concentrations among cows is caused by variation in gastrointestinal and kidney urea clearance rates. Eight lactating cows with varying MUN concentrations while fed a common diet were infused with [15N15N]urea to determine urea N entry rate (UER), gastrointestinal entry rate, returned to ornithine cycle, urea N used for anabolism, urea N excretion in feces and urine. Urea clearance rates by the kidneys and gastrointestinal tract were calculated from isotopic enrichment of urea excretion in urine and gut entry rate, respectively, and plasma urea N concentrations (PUN). Over the course of the experiment, animals weighed an average of 506 ± 62 kg and produced 26.3 ± 4.39 kg of milk/d, with MUN concentrations ranging from 11.6 to 17.3 mg/dL (average of 14.9 ± 2.1 mg/dL). Plasma urea N was positively correlated with UER, urea N excretion in urine, and urea N used for anabolism. Plasma urea N and MUN were negatively correlated with gut clearance rates and ratio of gastrointestinal entry rate to UER. This relationship supports the hypothesis that differences in gut urea transport activity among animals causes variation in PUN and MUN concentrations, and that cows with high PUN and MUN are less efficient at recycling PUN to the gastrointestinal tract and thus may be more susceptible to ruminal N deficiencies when fed low RDP diets. Such biological variation in urea metabolism necessitates an adequate safety margin when setting regulations for maximal MUN levels as an indicator of herd N efficiency.

Non-genetic effects on daily milk yield and components of Holstein cows in Morocco

The objectives of this study were to determine milk yield and constituents' levels of Holstein cows under Moroccan conditions and to assess the effects of environmental factors influencing them. Data including 93,815 test day records of 6343 Holstein cows in 162 herds were analyzed for milk yield, contents of fat, protein, lactose and solids-not-fat (SNF), milk urea nitrogen (MUN), and somatic cell score (SCS). Averages were 25.1 ± 7.33 kg/day, 3.54 ± 0.76%, 3.02 ± 0.34%, 4.89 ± 0.24%, 8.72 ± 0.36%, 17.6 ± 8.17 mg/dl, and 4.12 ± 2.06 units, respectively. The effects of herd and calving year were found to be significant on all the studied traits. Parity was determined to have significant effects on all analyzed traits, with the exception of MUN concentration. Milk yield, fat content, protein content, and SCS increased with parity, whereas lactose percentage decreased in later parities. Except fat and lactose contents, all the other studied variables were significantly influenced by calving season. Milk yield and MUN were highest for cows calving during humid season, whereas protein content, SNF content, and SCS tended to be higher in dry season. All the studied traits changed significantly according to stage of lactation. The peaks of milk yield and lactose content occurred between 35 and 65 days, whereas that of MUN between 95 and 125 days after parturition. Protein and SNF contents and SCS attained their lowest values between days 35 and 65, while fat content between days 65 and 95. It was concluded that these environmental factors should be taken into consideration if the milk yield and quality in Morocco is to be optimized.

Can Nitrogen Excretion of Dairy Cows Be Reduced by Genetic Selection for Low Milk Urea Nitrogen Concentration?

Simple SummaryNew Zealand dairy cows predominantly feed on pasture with protein to energy ratios well in excess of requirements and consequently their urine has a substantially greater concentration of nitrogen compared to cows fed indoors on total mixed rations. The nitrogen excreted directly onto land decompose into nitrous oxide and ammonium, causing global warming and freshwater pollution, respectively. One of the strategies to reduce the environmental contamination is genetic selection for reduced nitrogen excretion. The nitrogen excreted in urine is an expensive trait to measure in cows grazed outdoors. One possible approach to reduce the concentration of nitrogen excreted in urine is by selection for reduced urea nitrogen concentration in milk, which is readily measurable. The primary objective of this study was to quantify the likely correlated responses for milk production and liveweight traits in a selection index including breeding values for concentration of milk urea nitrogen with different relative emphasis in order to evaluate the usefulness of milk urea nitrogen for the purpose of reducing nitrogen excretion. Although a per cow reduction in urinary nitrogen excretion was predicted through selection in this study, the reduction of excretion is negligible at the whole farm level due to the influence of stocking rate, measured as the number of cows grazed per hectare, on the per hectare nitrogen excretion. Therefore, selection for low concentration of milk urea nitrogen is unlikely to be effective in reducing nitrogen excretion of dairy cows in New Zealand.The objectives of this study were two-fold. Firstly, to estimate the likely correlated responses in milk urea nitrogen (MUN) concentration, lactation yields of milk (MY), fat (FY) and crude protein (CPY) and mature cow liveweight (LWT) under three selection scenarios which varied in relative emphasis for MUN; 0% relative emphasis (MUN0%: equivalent to current New Zealand breeding worth index), and sign of the economic value; 20% relative emphasis positive selection (MUN+20%), and 20% relative emphasis negative selection (MUN−20%). Secondly, to estimate for these three scenarios the likely change in urinary nitrogen (UN) excretion under pasture based grazing conditions. The predicted genetic responses per cow per year for the current index were 16.4 kg MY, 2.0 kg FY, 1.4 kg CPY, −0.4 kg LWT and −0.05 mg/dL MUN. Positive selection on MUN in the index resulted in annual responses of 23.7 kg MY, 2.0 kg FY, 1.4 kg CPY, 0.6 kg LWT and 0.10 mg/dL MUN, while negative selection on MUN in the index resulted in annual responses of 5.4 kg MY, 1.6 kg FY, 1.0 kg CPY, −1.1 kg LWT and −0.17 mg/dL MUN. The MUN−20% reduced both MUN and cow productivity, whereas the MUN+20% increased MUN, milk production and LWT per cow. Per cow dry matter intake (DMI) was increased in all three scenarios as milk production increased compared to base year, therefore stocking rate (SR) was adjusted to control pasture cover. Paradoxically, ten years of selection with SR adjusted to maintain annual feed demand under the MUN+20% actually reduced per ha UN excretion by 3.54 kg, along with increases of 63 kg MY, 26 kg FY and 16 kg CPY compared to the base year. Ten years of selection on the MUN0% index generated a greater reductions of 10.45 kg UN and 30 kg MY, and increases of 32 kg FY and 21 kg CPY per ha, whereas the MUN−20% index reduced 14.06 kg UN and 136 kg MY with increases of 32 kg FY and 18 kg CPY compared to base year. All three scenarios increased partitioning of nitrogen excreted as feces. The selection index that excluded MUN was economically beneficial in the current economic circumstances over selection indices including MUN regardless of whether selection was either for or against MUN. There was no substantial benefit from an environmental point of view from including MUN in the Breeding Worth index, because N leaching is more a function of SR rather than of individual cow UN excretion. This study demonstrates that attention needs to be paid to the whole system consequences of selection for environmental outcomes in pastoral grazing circumstances.

The effects of rumen nitrogen balance on intake, nutrient digestibility, chewing activity, and milk yield and composition in dairy cows vary with dietary protein sources

The objective was to study the interaction effects of rumen nitrogen balance (RNB) and dietary protein source on feed intake, apparent total-tract digestibility (ATTD), eating and ruminating activity, milk yield (MY), and milk composition in lactating dairy cows. Twenty-four lactating Holstein cows were divided in 4 groups, which were randomly assigned to the dietary treatments included in a replicated 4 × 4 Latin square experimental design that consisted of four 20-d periods, each with 12 d of adaptation to the experimental diets and 8 d of sampling. The dietary treatments followed a 2 × 2 factorial arrangement with 2 main protein sources, faba bean grain (FB) and SoyPass (SP; Beweka Kraftfutterwerk GmbH), offered at 2 dietary RNB levels: RNB0 (RNB of 0 g/kg of dry matter) and RNB- (RNB of -3.2 g/kg of dry matter; i.e., 4 treatments). The composition of concentrate mixtures was adjusted to create diets with the desired RNB levels. Each of the protein sources supplied ≥35% of the total dietary crude protein (CP). Both diets within a protein source had similar forage sources and forage to concentrate ratios and were iso-energetic, but differed in CP concentrations. The main effects of RNB, protein source, and their interactions were tested by PROC MIXED in SAS 9.4 (SAS Institute Inc.). Interaction effects were observed for daily dry matter intake and energy-corrected MY, which were lower for RNB- than RNB0 in diets containing FB (23.5 vs. 24.4 kg dry matter/d; 28.6 vs. 30.6 kg milk/d), but similar in diets containing SP (24.2 vs. 24.3 kg dry matter/d; 31.3 vs. 31.7 kg milk/d). The ATTD of NDF was lower for RNB- compared with RNB0 in the FB (44.9 vs. 49.1 g/100 g) and SP (48.5 vs. 51.9 g/100 g) diets, and greater for the SP than for FB diets. There were interaction effects for ATTD of CP and concentrations of milk urea nitrogen, which were lower for RNB- compared with RNB0 in both, FB (55 vs. 63.1 g/100 g of CP; 5.65 vs. 11.3 mg/dL milk) and SP diets (60 vs. 64.4 g/100 g of CP; 8.74 vs. 13.4 mg/dL milk). However, differences between RNB levels were greater for FB than for SP diets. Furthermore, proportions of milk fatty acids followed the same pattern as that of dietary fatty acids, but biohydrogenation appeared to be greater for RNB- than RNB0 for both protein sources and in FB than in SP diets for both RNB levels. There was an interaction effect on total number of chews per unit of NDF intake, which was greater for RNB- compared with RNB0 for both protein sources. However, the differences between RNB levels were greater in FB than in SP diets. Overall, differences in the animal responses to negative RNB between FB and SP diets suggest a need to better understand the effect of negative RNB levels with different dietary ingredients at similar utilizable CP supply.

Genetic parameters of blood urea nitrogen and milk urea nitrogen concentration in dairy cattle managed in pasture-based production systems of New Zealand and Australia

Context Urinary nitrogen excretion by grazing cattle causes environmental pollution. Selecting for cows with a lower concentration of urinary nitrogen excretion may reduce the environmental impact. While urinary nitrogen excretion is difficult to measure, blood urea nitrogen (BUN), mid-infrared spectroscopy (MIR)-predicted BUN (MBUN), which is predicted from MIR spectra measured on milk samples, and milk urea nitrogen (MUN) are potential indicator traits. Australia and New Zealand have increasing datasets of cows with urea records, with 18 120 and 15 754 cows with urea records in Australia and New Zealand respectively. A collaboration between Australia and New Zealand could further increase the size of the dataset by sharing data. Aims Our aims were to estimate genetic parameters for urea traits within country, and genetic correlations between countries to gauge the benefit of having a joint reference population for genomic prediction of an indicator trait that is potentially suitable for selection to reduce urinary nitrogen excretion for both countries. Methods Genetic parameters were estimated within country (Australia and New Zealand) in Holstein, Jersey and a multibreed population, for BUN, MBUN and MUN in Australia and MUN in New Zealand, using high-density genotypes. Genetic correlations were also estimated between the urea traits recorded in Australia and MUN in New Zealand. Analyses used the first record available for each cow or within days-in-milk (DIM) intervals. Key results Heritabilities ranged from 0.08 to 0.32 for the various urea traits. Higher heritabilities were obtained for Jersey than for Holstein, and for the New Zealand cows than for the Australian cows. While urea traits were highly correlated within Australia (0.71–0.94), genetic correlations between Australia and New Zealand were small to moderate (0.08–0.58). Conclusions Our results showed that the heritability for urea traits differs among trait, breed, and country. While urea traits are highly correlated within country, genetic correlations between urea traits in Australia and MUN in New Zealand were only low to moderate. Implications Further study is required to identify the underlying causes of the difference in heritabilities observed, to compare the accuracies of different reference populations, and to estimate genetic correlations between urea traits and other traits such as fertility and feed intake. Larger datasets may help estimate genetic correlations more accurately between countries.

Influence of fiber degradability of corn silage in diets with lower and higher fiber content on lactational performance, nutrient digestibility, and ruminal characteristics in lactating Holstein cows

The effect of neutral detergent fiber (NDF) degradability of corn silage in diets containing lower and higher NDF concentrations on lactational performance, nutrient digestibility, and ruminal characteristics in lactating Holstein cows was measured. Eight ruminally cannulated Holstein cows averaging 91 ± 4 (standard error) days in milk were used in a replicated 4 × 4 Latin square design with 21-d periods (7-d collection periods). Dietary treatments were formulated to contain either conventional (CON; 48.6% 24-h NDF degradability; NDFD) or brown midrib-3 (BM3; 61.1% 24-h NDFD) corn silage and either lower NDF (LNDF) or higher NDF (HNDF) concentration (32.0 and 35.8% of ration dry matter, DM) by adjusting the dietary forage content (52 and 67% forage, DM basis). The dietary treatments were (1) CON-LNDF, (2) CON-HNDF, (3) BM3-LNDF, and (4) BM3-HNDF. Data were analyzed as a factorial arrangement of diets within a replicated Latin square design with the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) with fixed effects of NDFD, NDF, NDFD × NDF, period(square), and square. Cow within square was the random effect. Time and its interactions with NDFD and NDF were included in the model when appropriate. An interaction between NDFD and NDF content resulted in the HNDF diet decreasing dry matter intake (DMI) with CON corn silage but not with BM3 silage. Cows fed the BM3 corn silage had higher DMI than cows fed the CON corn silage, whereas cows fed the HNDF diet consumed less DM than cows fed the LNDF diet. Cows fed the BM3 diets had greater energy-corrected milk yield, higher milk true protein content, and lower milk urea nitrogen concentration than cows fed CON diets. Additionally, cows fed the BM3 diets had greater total-tract digestibility of organic matter and NDF than cows fed the CON diets. Compared with CON diets, the BMR diets accelerated ruminal NDF turnover. When incorporated into higher NDF diets, corn silage with greater in vitro 24-h NDFD and lower undegradable NDF at 240 h of in vitro fermentation (uNDF240) allowed for greater DMI intake than CON. In contrast, for lower NDF diets, NDFD of corn silage did not affect DMI, which suggests that a threshold level of inclusion of higher NDFD corn silage is necessary to observe enhanced lactational performance. Results suggest that there is a maximum gut fill of dietary uNDF240 and that higher NDFD corn silage can be fed at greater dietary concentrations.

Relationship between feed protein content and faeces nitrogen content in early lactation dairy cows

Relationship between feed protein content and faeces nitrogen content in early lactation dairy cows

165 Evaluation of Milk Urea Nitrogen Measurement Precision and Accuracy

Abstract High levels of urea in blood, milk and urine have been linked to poor nitrogen efficiency, increased feed costs, poor reproductive performance and increased environmental impacts of dairy farming. Milk urea nitrogen (MUN) is a commonly used metric to manage herd nitrogen efficiency, with current recommendations for MUN to be between 8–14 mg/dL to maintain milk production and reduce nitrogen losses. However, a previous work suggests commercial analysis of MUN with mid-infrared spectroscopy (MIR) may not be precise enough to determine if a milk sample is within the recommended range. Thus, the objective of this study was to evaluate the precision and accuracy of milk testing lab MUN measurements. Four sets of bulk tank samples were sent to 3 commercial labs and one research lab for analysis by MIR. Samples were sent to commercial labs in duplicate and MUN was also assessed through an enzymatic assay. The Euclidean distance (ED) was calculated as a combined metric of precision and accuracy. The ED was not different between labs and ranged from 0.81–1.27. Repeatability (sr) and reproducibility (sR) were estimated for commercial labs and ranged from (0.297–0.469) and (0.555–0.791) respectively. Differences between individual sample MIR and enzymatic MUN were regressed on the centered enzymatic MUN in a linear mixed model that included a random effect of lab and fixed effects for milk protein and milk fat. Regression results indicate MIR analysis over-predicts MUN at low MUN concentrations and under predicts MUN at high MUN concentrations. Results suggest MIR analysis of MUN is more accurate around milk MUN, protein, and fat concentrations of ~13 mg/dl, 3.4% protein, and 4.2% fat. Further, the combined residual error and random effect of lab suggest the standard error of an MUN MIR measurement is ±1.8.

Effect of active dry yeast on lactation performance, methane production, and ruminal fermentation patterns in early-lactating Holstein cows

This study was conducted to examine the effect of active dry yeast (ADY) supplementation on lactation performance, ruminal fermentation patterns, and CH4 emissions and to determine an optimal ADY dose. Sixty Holstein dairy cows in early lactation (52 ± 1.2 DIM) were used in a randomized complete design. Cows were blocked by parity (2.1 ± 0.2), milk production (35 ± 4.6 kg/d), and body weight (642 ± 53 kg) and assigned to 1 of 4 treatments. Cows were fed ADY at doses of 0, 10, 20, or 30 g/d per head for 91 d, with 84 d for adaptation and 7 d for sampling. Although dry matter intake was not affected by ADY supplementation, the yield of actual milk, 4% fat-corrected milk, milk fat yield, and feed efficiency increased quadratically with increasing ADY supplementation. Yields of milk protein and lactose increased linearly with increasing ADY doses, whereas milk urea nitrogen concentration and somatic cell count decreased quadratically. Ruminal pH and ammonia concentration were not affected by ADY supplementation, whereas ruminal concentration of total volatile fatty acid increased quadratically. Digestibility of dry matter, organic matter, neutral detergent fiber, acid detergent fiber, nonfiber carbohydrate, and crude protein increased quadratically with increasing ADY supplementation. Supplementation of ADY did not affect blood concentration of total protein, triglyceride, aspartate aminotransferase, and alanine aminotransferase, whereas blood urea nitrogen, cholesterol, and nonesterified fatty acid concentrations decreased quadratically with increasing ADY supplementation. Methane production was not affected by ADY supplementation when expressed as grams per day or per kilogram of actual milk yield, dry matter intake, digested organic matter, and digested nonfiber carbohydrate, whereas a trend of linear and quadratic decrease of CH4 production was observed when expressed as grams per kilogram of fat-corrected milk and digested neutral detergent fiber. In conclusion, feeding ADY to early-lactating cows improved lactation performance by increasing nutrient digestibility. The optimal ADY dose should be 20 g/d per head.

Effect of protein level and grain source on milk production, nutrient digestibility and ruminal fermentation in primiparous Holstein cows

AbstractThis study investigated whether the interaction of protein level and grain type can affect milk production, nutrient digestibility and rumen fermentation in primiparous Holstein cows. Four dietary treatments were used: high-protein with barley as the only grain source, HP-B; (2) high-protein with an equal mix of barley and maize, HP-BM; (3) low-protein with barley as the only grain source, LP-B and (4) low-protein with equal proportions of barley and maize, LP-BM. High-protein diets showed no improvement in milk or protein yield compared with low-protein, but barley and maize mix diets increased energy-corrected milk yield and fat yield compared with barley-only diets. The highest total apparent digestibility of dry matter, organic matter and neutral detergent fibre was observed for LP-BM whereas HP-BM showed the greatest crude protein digestibility. Treatment had no effect on total volatile fatty acid concentrations, molar proportion of acetate and propionate and acetate to propionate ratio. The lowest ruminal pH was observed for LP-B. High-protein diets resulted in greater concentrations of ammonia nitrogen (N), urinary N, blood and milk urea nitrogen compared with low-protein diets, whereas low-protein diets showed better nitrogen utilization efficiency. This study showed that primiparous lactating cows do not benefit from high-protein diets with different fermentation rates of grain sources, but barley and maize diets may improve milk production performance, ruminal fermentation and pH under the present dietary conditions. The current results on milk production performance should be interpreted with caution due to the small number of cows used (eight in each treatment).

Enteric methane emission, milk production, and composition of dairy cows fed 3-nitrooxypropanol

This study examined the effect of 3-nitrooxypropanol (3-NOP), an investigational substance, on enteric methane emission, milk production, and composition in Holstein dairy cows. Following a 3-wk covariate period, 48 multi- and primiparous cows averaging (± standard deviation) 118 ± 28 d in milk, 43.4 ± 8 kg/d milk yield, and 594 ± 57 kg of body weight were blocked based on days in milk, milk yield, and enteric methane emission and randomly assigned to 1 of 2 treatment groups: (1) control, no 3-NOP, and (2) 3-NOP applied at 60 mg/kg feed dry matter. Inclusion of 3-NOP was through the total mixed ration and fed for 15 consecutive weeks. Cows were housed in a freestall barn equipped with a Calan Broadbent Feeding System (American Calan Inc., Northwood, NH) for monitoring individual dry matter intake and fed ad libitum once daily. Enteric gaseous emissions (methane, carbon dioxide, and hydrogen) were measured using 3 GreenFeed (C-Lock Inc., Rapid City, SD) units. Dry matter intake, cow body weight, and body weight change were not affected by 3-NOP. Compared with the control group, 3-NOP applied at 60 mg/kg feed dry matter decreased daily methane emission, emission yield, and emission intensity by 26, 27, and 29%, respectively. Enteric emission of carbon dioxide was not affected, and hydrogen emission was increased 6-fold by 3-NOP. Administration of 3-NOP had no effect on milk and energy-corrected milk yields and feed efficiency, increased milk fat and milk urea nitrogen concentrations, and increased milk fat yield but had no other effects on milk components. Concentration of C6:0 and C8:0 and the sum of saturated fatty acids in milk fat were increased by 3-NOP. Total trans fatty acids and the sum of polyunsaturated fatty acids were decreased by 3-NOP. In this experiment, 3-NOP decreased enteric methane daily emission, yield, and intensity without affecting dry matter intake and milk yield, but increased milk fat in high-producing dairy cows.

Differences between Holstein dairy cows in renal clearance rate of urea affect milk urea concentration and the relationship between milk urea and urinary nitrogen excretion

Urine and fecal excretions from cattle contribute to global nitrogen (N) emissions. The milk urea nitrogen (MUN) concentration in dairy cows is positively correlated with urinary urea N (UUN) emissions, and both decline with the reduction in crude protein intake. However, MUN concentration may differ between individual cows despite feeding the same ration. Thus, we hypothesized that due to differences in endogenous N utilization cows with high MUN concentration excrete more UUN than cows with a low MUN concentration. The objective of the present study was to elucidate N partitioning and urea metabolism in dairy cows with divergent MUN concentrations fed two planes of crude protein. Twenty Holstein dairy cows with high (HMU; n = 10) and low (LMU; n = 10) milk urea concentrations were fed two isocaloric diets with a low (LP) and normal (NP) crude protein level. Methane and ammonia emissions were recorded in respiration chambers. Feed intake, feces and urine excretions and milk yield were recorded for four days and subsamples were analyzed for total N and N-metabolites. A carbon-13 labeled urea bolus was administered intravenously followed by a series of plasma samplings. Total N and UUN excretions and ammonia emissions from excreta were lower on the LP diet, however, methane emissions, urinary N excretions and ammonia emissions were comparable between groups. Although plasma and salivary urea concentrations, urea pool size and urea turnover were higher, HMU cows had lower renal urea clearance rates. Additionally, HMU cows had lower renal clearance rates for creatinine, uric acid and creatine and excreted less uric acid (on the LP diet only) and creatine with urine. In conclusion, contrary to our hypothesis, HMU cows did not excrete more UUN than LMU cows. The lower urinary creatine excretion of HMU cows suggests that these animals have a lower environmental nitrogen footprint.