Milk Urea Concentration Research Articles

Effects of extruded linseed dietary supplementation on milk yield, milk quality and lipid metabolism of dairy cows

Twenty Italian Friesian dairy cows were used in an experimental trial to study the effects of extruded linseed dietary supplementation on milk production, milk quality and fatty acid (FA) percentages of milk fat and total plasma lipids and plasma phospholipids. Control cows were fed a corn silage based total mixed ration (TMR) while treated animals also received 700g/head/d of extruded linseed supplementation. Feed intake was similar between groups. Milk yields was tendentially greater for cows fed extruded linseed. Milk urea content (P<0.05) were reduced by treatment. Results showed a significant increase n-3 FA concentration (particularly alpha linolenic acid) and a significant reduction of n-6/n-3 FA ratio in milk fat, total plasma lipids and plasma phospholipids (P<0.001); moreover a reduction trend (P<0.1) of arachidonic acid concentrations was observed in milk fat, total plasma lipids and plasma phospholipids. At last, treatment enhanced milk fat conjugated linoleic acid (CLA) percentage (P<0.05).

Effect of herd, parity, stage of lactation and milk yield on urea concentration in milk

The objective of this study was to determine how non-nutritional factors such as herd, parity, days in milk, milk production, and milk components affect the concentration of milk urea. A retrospective, observational study comprising analyses of individual cow records from monthly dairy herd improvement milk tests including milk urea tests was conducted. Six commercial Holstein dairy herds were involved in the investigation from October 2000 to September 2003. The data were evaluated using the mixed linear model with repeated measures, and parameters were estimated by the REML method. Significant differences in milk urea concentrations were observed between herds (P &amp;lt; 0.0001), with a significant variability between test dates within herds. Significant effects of parity (P = 0.0003), days in milk (P &amp;lt; 0.0001), and their interaction were also found. Higher concentrations of milk urea were determined in the cows on the first and second parity (5.63 and 5.62 mmol/l, respectively) compared to the groups of cows on the third and fourth parity (5.47 mmol/l). It was found that milk urea concentration increased with the square of milk yield (P &amp;lt; 0.0001), while a negative quadratic relationship was found between milk urea concentration and milk fat % (P &amp;lt; 0.0001). It was concluded that milk urea concentration should be evaluated in association with days in milk, milk yield, milk fat %, and milk protein %. &amp;nbsp;

Studies on the tryptophan requirement of lactating sows. Part 2: Estimation of the tryptophan requirement by physiological criteria

Mature sows were fed for a total of 72 lactations with diets which provided an adequate supply of energy and nutrients except for tryptophan (Trp). By supplementing a basal diet [native 1.2 g Trp/kg, equivalent to 0.8 g apparent ileal digestible (AID) Trp or 0.9 g true ileal digestible (TID) Trp] with L-Trp, five further diets (2-6) containing 1.5-4.2 g Trp/kg were formulated. The dietary Trp content had no effect on amino acid contents in milk on days 20 and 21 of lactation, but Trp in blood plasma on day 28 of lactation reflected the alimentary Trp supply with an increase from 2.74 +/- 1.14 mg/l (diet 1) to 23.91 +/- 7.53 mg/l (diet 6; p < 0.001). There were no directional differences between the diets with regard to the other amino acids. Concentrations of urea in milk and blood were higher with diet 1 (211 and 272 mg/l, respectively) than with diets 3-6 (183 and 227 mg/l, respectively). Serotonin levels in the blood serum were lower with diet 1 (304 ng/ml) than the average of diets 4-6 (540 ng/ml). This study confirms previously given recommendations for the Trp content in the diet of lactating sows, estimated by means of performance, of 1.9 g AID Trp (equivalent to 2.0 g TID Trp; approximately 2.6 g gross Trp) per kg diet.

Monitoring Feeding Adequacy in Dairy Cows Using Milk Urea and Milk Protein Contents under Farm Condition

The experiment was conducted on 264 crossbred Karan-Fries (Holstein FriesianxTharparkar) cows, over one year to explore the possibility of using milk urea (MU) concentration and milk protein content to monitor feeding adequacy under farm condition and to investigate the effects of different animal factors and season on MU concentration. Individual noon (1200 to 1300 h) milk samples were collected once in every month and analysed for urea and protein contents. Representative feed samples were also collected on the same day of milk collection and were analysed for CP content. A significant positive association (p 60 mg/dl. MU concentration was found to be associated significantly (p<0.05) with CP content of forages rather than concentrate. A close positive association (p<0.01) between MU level and daily milk protein (DMP) yield was observed during the investigation. The regression equation, DMP yield (g) = -24.6+33.5 daily milk yield (kg) +0.9 MU (mg/dl) was developed to establish the reference level of DMP yield. The result indicates that the effect of parity and stage of lactation may be ignored while interpreting MU values. However, reference MU values may be standardised separately for high milk yielders as level of milk yield contributes significantly to the variation of MU. The study revealed that the MU values together with DMP yield and milk protein content could be used as a potential non-invasive pointer to monitor feeding adequacy in dairy cows under farm conditions.

Concentrate supplementation responses of the pasture-fed dairy cow

The aim of this study was to investigate the effects of increasing amounts of cereal-based concentrate on milk production. The study consisted of a series of three separate experiments in which cows were grazed in intensive rotation on timothy-meadow fescue pasture. In Experiment 1, 28 multiparous Holstein–Friesian cows received 0, 3, 6 and 9 kg concentrate in a cross-over designed trial with a fixed daily herbage allowance of 21 kg DM/cow. The energy-corrected milk yield increased linearly 0.84 kg/kg DM (P < 0.001), up to the 9 kg concentrate level. The milk fat (P < 0.001) and urea (P < 0.001) content decreased linearly (0.41 g/kg DM and 0.15 mmol/kg DM, respectively). The milk protein content tended (P = 0.08) to increase 0.10 g/kg DM with increasing supplementation. In Experiment 2, 17 primiparous cows and 28 multiparous cows were used in a randomized-block designed trial with 3, 6 and 9 kg concentrate supplementation and a fixed 25 kg DM herbage allowance. The energy corrected milk yield increased linearly (P < 0.01) 0.67 kg/kg DM, whereas the milk urea content decreased linearly (P < 0.001) 0.27 mmol/kg DM. The milk protein content increased and the fat content decreased, but these differences were not significant. In Experiment 3, a cross-over design was used to assess the response to concentrate supplementation of 24 multiparous cows (treatments: 6, 9 and 12 kg; fixed herbage allowance 25 kg DM) and 12 primiparous cows (treatments: 4, 7 and 10 kg; herbage allowance > 25 kg DM). The energy-corrected milk yield of the multiparous cows varied quadratically (Pquad < 0.001; 30.0, 32.5 and 32.2 kg for 6, 9 and 12 kg supplementation, respectively). Supplementation linearly decreased the urea (P < 0.001) 0.13 mmol/kg DM and fat (P < 0.001) 0.46 g/kg DM contents. The milk fat content also varied quadratically, showing the lowest content with the 12 kg level (Pquad < 0.05; 37.3, 37.3 and 34.9 g/kg for 6, 9 and 12 kg supplementation, respectively). The energy-corrected milk yield of the primiparous cows increased linearly (P < 0.001) 0.54 kg/kg DM up to 10 kg supplementation, whereas the milk urea (P < 0.001) and fat contents decreased linearly (P < 0.01) by 0.19 mmol/kg DM and 0.61 g/kg DM, respectively. The results showed that the milk response remained linear up to the 9 kg supplementation level, but the highest level of supplementation resulted in only a marginal increase in milk yield. There was no interaction between season and milk or milk protein yield, which indicates that it is possible to maintain stable grazing conditions during the main grazing season in Nordic latitudes. The results support to some extent the hypothesis that the marginal milk response to supplementation increases with increasing milk production.

Milk urea concentration as affected by the roughage type offered to dairy cattle

Milk urea content (MUC) is used to manage protein nutrition and predict nitrogen excretion of dairy cows. However, MUC might depend on the roughage type offered and hence, for comparable MUC values, different N-excretions might be found. To evaluate this, three diets were compared in a feeding trial with 18 lactating Holstein cows in a Latin square design with as roughages 100% maize silage (treatment 100 MS), 50%/50% maize silage/prewilted grass silage (treatment 50 MS) and 100% prewilted grass silage (treatment 100 PGS). For all treatments, cows were fed to supply 105% of their net energy and digestible protein requirements and to have a daily rumen degraded protein balance (RDPB) intake of 100 g. This was only possible by feeding soybean meal as a protein corrector to 100 MS and 50 MS and by feeding citruspulp as an energy corrector in 100 PGS. The same balanced concentrate was fed to all groups. In a separate trial, N-balance was determined for both 100% rations. In the feeding trial, the MUC of 100 MS (230 mg/l) and 50 MS treatment (214 mg/l) were significantly ( P < 0.001) different from that of 100 PGS (171 mg/l). Cows on treatments 50 MS and 100 PGS ingested the same amount of RDPB (71 and 73 g/day), but when fed 100 MS cows ingested −16 g/day. After correction for differences in energy and protein supply, MUC of the 100 MS was 71 mg/l higher than that of 100 PGS. N-balances indicated that total N-excretion (faecal, urinary and milk) was almost identical for both treatments: 392 for 100 MS versus 389 g/day for 100 PGS, as was environmental N-excretion (faecal and urinary): 259 for 100 MS versus 272 g/day for 100 PGS. However, the MUC content for 100 MS was significantly higher: 248 mg/l versus 180 mg/l for 100 PGS. From a correction for differences in energy and protein supply, this difference increased up to 84 mg/l between 100 MS and 100 PGS. These results suggest that MUC is roughage dependent and that a system to predict N-excretion should account for these differences. Therefore the exact mechanism behind the determined roughage influence should be investigated further.

Investigations on the effect of the ruminal N-balance on rumen metabolism, urea content in blood serum and milk as well as some liver parameters of lactating cows

Seven dairy cows fitted with ruminal and duodenal cannulae were used to investigate the influence of the amount of ruminally available N (Ruminal N-Balance, RNB) on the rumen metabolism and to answer the question on the lowest N-amount in the rumen, without negative effects on the fermentation. Animals were fed a ration on the basis of 7.9 kg corn silage and 7.2 kg concentrates related to dry matter, intended to meet the animals mean NEL and protein requirements. RNB amounted to −0.6 g/MJ ME in the basis ration. The other 3 rations were adjusted to RNB-values of −0.3, 0 and +0.3 g/MJ ME by urea supplements in the concentrates. The increase in RNB resulted in higher NH3-N concentrations in the rumen fluid and in the duodenal digesta and higher urea concentrations in the blood and milk. The significantly highest amount of protein at the duodenum was detected when RNB showed an equilibrium (RNB = 0). The efficiency of microbial protein (MP) synthesis (g MP/kg fermented organic matter) was the same, g MP/d and g MP/MJ ME were significantly lower with RNB = −0.6 g/MJ ME as compared to RNB = 0. The group with the lowest RNB showed the highest level of feed protein degradation as well as the lowest organic matter, NDF and ADF fermentation. An effect on cholesterol, total bilirubin and γGT due to different RNB was not detected. The activities of GLDH and AST were highest when the RNB was −0.6 g/MJ ME. From the results, it can be concluded that significantly negative effects on rumen fermentation occur when RNB-values are below −0.3 g/MJ ME. However, a positive RNB did not increase the degradation and synthesis capacity of the rumen micro-organisms as compared to RNB = 0.

Effects of dietary protein level on ewe milk yield and nitrogen utilization, and on air quality under different ventilation rates

The experiment, which lasted 53 d, was conducted during the winter (February and March) of 2004 and used 48 Comisana ewes in mid lactation. A 2 x 2 factorial design was used, with ewes receiving two levels of dietary crude protein (CP) (moderate, 16% CP v. low, 13% CP) in the dry matter (DM) and being exposed to two ventilation rates (moderate, 47 m3/h v. low, 23.5 m3/h per ewe) for each dietary treatment. Air concentrations of NH3 and of microorganisms were measured twice weekly. Milk yield was recorded daily. Individual milk samples were analysed weekly for composition and fortnightly for bacteriological characteristics. After the last milk sampling (day 49 of the study period), four animals from each group were placed in a metabolism box and their individual faeces and urine were collected for three consecutive days. Amounts of urine and faeces excreted, and urinary and faecal N outputs were measured. The 16% CP diet resulted in a lower milk casein content and a higher milk urea concentration than the 13% CP diet, as well as in a reduced gross efficiency of utilization of dietary N, a greater amount of N excreted and a higher total coliform concentration in milk. The moderate ventilation rate resulted in higher yields of milk, irrespective of CP content. Significant interactions of CP level x ventilation rate were found for the amounts of urine, of total water and of faecal N, and for mesophilic concentration in milk, the highest values being displayed by the ewes fed the 16% CP diet and exposed to the low ventilation rate. The moderate dietary CP level and low ventilation rate had a deleterious effect on air concentrations of microorganisms and ammonia. Results suggested that a reduction of dietary CP level from 16 to 13% of DM had no detrimental effect on ewe milk yield in mid lactation and could even improve some of its nutritional and hygienic characteristics. Our findings also indicate that the choice of a proper ventilation rate is critical for high efficiency of production in the lactating ewe, especially in intensively managed flocks receiving diets high in CP.

Balanço de nitrogênio e estimativas de perdas endógenas em vacas lactantes alimentadas com dietas contendo palma forrageira e teores crescentes de uréia e mandioca

The effects of the soybean when replaced by a mixture of urea and cassava, in rations composed of forage cactus, sorghum silage and concentrate, were assessed on: (i) urea concentration; (ii) nitrogen (N) balance; and (iii) total endogenous loss estimate. Eight lactating Holstein/Zebu cows were distributed in two 4x4 simultaneous latin squares. Urea and N-urea concentration in plasma and milk (mg dL-1), and milk N-urea (g day-1) were not affected by the increase of urea levels in the ration; their means were 31.37, 14.62, 37.43, 17.44, and 5.37, respectively. Also, urea and N-urea urinary excretion were not affected by the increase of urea levels in the ration, and the mean values of those parameters were 249.45 and 116.24 mg kg-1 LW, respectively. The treatments did not influence N levels, with average values of 87.75, 87.63, 62.91, and 60.97 g day-1 to 0, 1.06, 2.12 e 3.20 % of urea addition in the ration, respectively. The endogenous loss estimate varied according to the nutritional demand system used.

Energy status of dairy cows determined by biochemical analysis of organic components of milk

Valid indicators of the energy status of cows are the body condition, parameters of the metabolic profile, hormonal status, and organic components of milk. The energy status of cows of the Holstein-Friesian breed from four farms was estimated on the grounds of urea, protein and fat concentration in milk. Investigations covered 62 samples of milk (11 from farm A, 16 from farm B, 15 from farm C, and 20 from farm D). All cows were in the first stage of lactation and fed rations recommended for that category of animal. The average fat concentration in all milk samples was 23?13 g/l, the average protein concentration was 29?3 g/l, while the average urea concentration was 4.6?1.3 mmol/l. It could be concluded on the basis of the value for the milk fat concentration alone that a decreased milk fat syndrome was present. In addition, graphic presentations are given for the relation between urea concentration and protein concentration, as well as protein and fat concentrations in the individual milk samples. Such an analysis provided a more detailed picture of the energy status of the examined cows. It was established that cows on farm A had a deficiency of energy and protein, and cows on farms B and C a deficiency of energy with a relative surplus of proteins. It was established that cows from farm D had a deficiency of energy, and there was an equal number of cows with a deficiency and with a relative surplus of proteins. The obtained results provide grounds for making recommendations for correcting the feed rations and improving the health of the cows. It stems from the obtained results that the determination of urea, fat and protein concentrations in milk is a reliable indicator of the energy status of cows, that it is rational and financially acceptable for every producer, regardless of whether it is implemented in small or large cattle farms. The diagnostic procedures used so far have been implemented in a limited form in daily practice because of insufficient reliability (evaluation of body condition) or lack of economic feasibility (metabolic profile and hormonal status of cows).

Usefulness of Milk Urea Concentration to Monitor the Herd Reproductive Performances in Crossbred Karan-fries Cowsp

The study was undertaken to investigate the validity of milk urea concentration as an index of the reproductive performances in crossbred Karan-Fries (Holstein FriesianxTharparkar) cows under farm condition. Milk urea wasanalysed in noon milk samples (1200 to 1300 h) to interrelate with the interval from parturition to first service, number of insemination per conception, first service conception rate and service period. Milk progesterone (P4) was analysed in noon milk samples on the day 1, 10, 20 and 30 post insemination to study the effect of milk urea concentration on early embryonic mortality. The interval from parturition to first service was found significantly (p<0.01) higher (77.2′5.5 days) when milk urea concentration was ≥63.4 mg/dl. The average milk urea concentrations (mg/dl) were found 42.1′2.5, 47.9′1.5 and 50.3′3.1, respectively in cows that conceived at 1 s t , 2 n d and 3 r d insemination. However, the variation was not statistically significant. The first insemination conception rate was found significantly (p<0.05) higher (68.8%) when milk urea level was ≤32.4 mg/dl. The service period was found significantly (p<0.05) higher (125.4′8.8 days) when milk urea concentration was ≥45.1 mg/dl. The milk P4 level indicated that the cows, those were detected as non-pregnant on day 60 post insemination were initially pregnant but the pregnancy was terminated sometime during the day 30 to 60 post insemination. The study indicates that the milk urea values may be used as an index of reproductive performances in dairy herd when individual animals are not being monitored for nutritional status. The altered milk urea values may be utilised by the farmers as ready reference to rectify the protein and energy nutrition in cows to achieve the better reproductive performances in herd.

Effect of Dietary Feeding Regimens on Urea and Protein Concentration of Milk in Murrah Buffaloes

The present study was planned to examine the effect of different feeding regimens on milk urea concentration and milk protein concentration. The objectives are to describe the diurnal variations of milk urea (MU) concentration and to predict plasma urea (PU) concentration from MU concentration. Six lactating Murrah buffaloes were distributed in two groups and were fed two different diets in a crossover design. The diets consisted of leguminous crops as diet 1 (berseem (Trifolium alexandrinum)+concentrate mixture 1+wheat straw)) and non-leguminous crops as diet 2 (oats (Avana sativa)+concentrate mixture 2+wheat straw). All the diets were isocaloric and isonitrogenous. Each diet was fed to the animals for a period of 28 days, followed by a 10 day gap to obviate the carry over effect of the previous diet and then a switch over to the other diet. Digestibility trials were conducted on the last 7 days of each feeding period. Milk samples were collected on day 3, 7, 10, 14, 17, 21, 24 and 28 of the feeding period and blood samples were collected on the same day at morning within 30 minutes after morning milking. The average milk urea (MU) values (mg/dl) differed significantly (p<0.01) and were 44.83±0.62 and 42.53±0.73, respectively, for diets 1 and 2. Milk urea concentrations (mg/dl) also varied (p 0.01) among the days of feeding period, but were stabilized after 10th day of feeding period. In contrast, diets and days of feeding period had no significant effect on percent milk protein. Plasma urea concentration showed a significant (p<0.01) positive correlation (r = 0.93) with MU concentration. To predict the from MU the following equation was developed PU = 10.67±0.76×MU (mg/dl) with R 2 = 0.87. A clear diurnal variation of MU was found with lowered morning value (42.04±0.68 mg/dl) than the evening value (45.32±0.66 mg/dl). Present findings suggested that MU or concentration could be used as an indicator to monitor the feeding strategy. Plasma urea can be predicted from MU, whenever interpretation of milk urea data required consideration of diurnal variation. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 7 : 973-979)

Machine Learning as an aid to management decisions on high somatic cell counts in dairy farms

Abstract. High somatic cell counts (SCC) is associated with mastitis infection, in dairy herds, worldwide. This work describes Machine Learning (ML) techniques designed to improve the information offered to farmers on animals producing high SCCs according to particular herd profiles. The analysed population included 71 dairy farms in Asturias (Northern Spain) and a total of 2,407 lactating cows. Four sources of information were available: a) a questionnaire survey describing facilities, milking routines and management practices of the farms studied; b) dairy recording information; c) classification of the cows suspected of being healthy or subclinical mastitic according to farmers’ expertise; and d) positive or negative scores with respect to the California Mastitis Test (CMT). The decimal logarithm of the SCC (linear score), lactation number, herd size, lactating cows per milker, milk urea concentration, number of clusters per milker and actual SCC are shown to be the most informative attributes for mimicking both farmers’ expertise or CMT performance in order to identify animals producing persistently high SCCs in dairy herds. However, to improve the identification of cows suspected of being non-healthy, the system uses other information related to management and milking routines. Decision rules to predict CMT performance can provide useful, additional information to farmers to improve the management of dairy herds included in milk recording programs.

Performance of Dairy Cows on Swiss Farms with Organic and Integrated Production

Milk production of cows on farms in which milk was organically produced (OP) tends to be less than that on farms with conventional or integrated production (IP), but causes for the difference have not been thoroughly evaluated. We performed a study to investigate management, nutritional, metabolic, and endocrine risk factors that may be associated with lower milk production on OP farms. Fertility traits were also compared. In 60 OP and 60 IP farms, matched in size, location, and agricultural zone (altitude), 970 cows were selected. Body condition scores (BCS) and body weights (BW) were determined at approximately 29 d prepartum (visit 1) and at 31 (visit 2) and 102 d postpartum (visit 3). Blood was sampled at visit 2 to determine plasma concentrations of glucose, nonesterified fatty acids, β-hydroxybutyrate, albumin, urea, insulin-like growth factor-1 (IGF-I), and 3,5,3′-triiodothyronine. Metabolic and endocrine traits as well as milk yield, fertility, and feeding factors were compared among cows in the 2 production systems. A univariable and stepwise multivariable logistic regression model was used to identify risk factors for poor milk yield. Energy-corrected milk yield medians and milk urea concentrations were less in OP than in IP cows at visits 2 and 3. Organic farms provided less concentrates, and OP cows at all visits had lower BW than IP cows. Plasma albumin and urea concentrations were lower in OP than IP cows. The following factors were positively associated with low milk yield (below median): Simmental breed, greater BCS, positive California mastitis test in hindquarters, and sampling during summer. Factors associated with an elevated (above median) milk yield were: Holstein breed, greater BW and lactation number (age), weak udder suspension, greater blood albumin, milk fat and milk protein, more lactation persistency, longer calving intervals, routine teat dipping, and more outdoor access during winter. In conclusion, significant differences including milk yield were detected between Swiss OP and IP cows. Lower milk yields were due to a range of individual animal and farm-level factors such as breed, nutrition, management, and udder health.

Effects of feeding perennial ryegrass with an elevated concentration of water-soluble carbohydrates on intake, rumen function and performance of dairy cows

This study investigated effects of feeding perennial ryegrass with an elevated concentration of water-soluble carbohydrates (WSC) on dry matter intake (DMI), rumen function, milk production and composition of dairy cows. Twelve Holstein–Friesian dairy cows in mid lactation were stall-fed with fresh herbage of six varieties of perennial ryegrass during three 2-week periods, using a double 3 × 3 Latin square design. In each Latin square, three varieties were fed, one of which was characterised by a higher level of WSC (HSV) of 24 and 31 g/kg DM, respectively, than the lower WSC varieties (LSV). Other chemical components were similar or differed marginally and digestibility was similar. The results prove that it is possible to select for grass varieties with an elevated level of WSC. The DMI was not positively influenced by the increased WSC content, as cows fed HSV had similar DMI to cows fed the LSV (16.2 kg/day versus 16.6 kg/day). Rumen pH, neutral detergent fibre fractional clearance (Kcl NDF) and fractional degradation (kd NDF) rates were not reduced as a result of feeding HSV. Total VFA concentrations were not changed, nor were the proportions of acetate:propionate:butyrate. Milk urea concentration was reduced ( P < 0.05) as a result of feeding HSV. Milk yield and concentrations of milk fat, crude protein and lactose were not influenced. At the level of difference in WSC between grasses in this experiment, feeding HSV was not beneficial in improving DMI and milk production, or in altering the composition of milk. The hypothesis that feeding high WSC grasses increases DMI and milk production was, therefore not confirmed.

Effect of Rumen-Degradable Protein Balance and Forage Type on Bulk Milk Urea Concentration and Emission of Ammonia from Dairy Cow Houses

As the Dutch government and dairy farming sector have given priority to reducing ammonia emission, the effect of diet on the ammonia emission from dairy cow barns was studied. In addition, the usefulness of milk urea content as an indicator of emission reduction was evaluated. An experiment was carried out with a herd of 55 to 57 Holstein-Friesian dairy cows housed in a naturally ventilated barn with cubicles and a slatted floor. The experiment was designed as a 3×3 factorial trial and repeated 3 times. During the experiment, cows were confined to the barn (no grazing) and were fed ensiled forages and additional concentrates. The default forage was grass silage. The nutritional experimental factors were: (1) rumen-degradable protein balance of the ration for lactating cows with 3 levels (0, 500, and 1000 g/cow per d), and (2) proportion of corn silage in the forage ration for lactating cows with 3 levels (0, 50, and 100%) of forage dry matter intake. Several series of dynamic regression models were fitted. One of these models explained emission of ammonia by the nutritional factors and the temperature; another model explained ammonia emission by the bulk milk urea content and the temperature. The ammonia emission from the barn increased when levels of rumen-degradable protein balance increased. Furthermore, at a given level of rumen-degradable protein balance, the emission of ammonia correlated positively with the corn silage content in the forage ration. However, this correlation was not causal, but was the result of interaction between corn silage proportion and intake of ileal digestible protein. The bulk milk urea content and the temperature correlated strongly with the ammonia emission from the barn; the selected model accounted for 76% of the variance in emission. It was concluded that the emission of ammonia from naturally ventilated dairy cow barns was strongly influenced by diet. The emission can be reduced approximately 50% by reducing the rumen-degradable protein balance of the ration from 1000 to 0 g/cow per d. The milk urea content is a good indicator of emission reduction.

Association Between Live Body Weight and Milk Urea Concentration in Holstein Cows

Use of milk urea (MU) concentration as a parameter for detection of nutritional imbalances requires identification and quantification of nutritional and nonnutritional factors that influence it. The objective of this study was to assess the relationship between live body weight (BW) and MU concentration in Holstein cows. Results for the test-day measurements at 7 dairy farms were obtained from the Israeli Dairy Herd Improvement Center and concomitant cow weights were registered in local computerized weighing systems. A total of 1996 cows and 25,485 records were studied. The overall unadjusted per-cow mean MU nitrogen concentration and BW were 15.3mg/dL (SD=3.8) and 593kg (SD=84), respectively. The linear association between BW and MU was negative and highly significant and the quadratic component of BW had a highly significant positive association with MU. There was a significant interaction between the association of MU and BW with lactation number. Sampling month, milk yield, milk fat percentage, and somatic cell count accounted for significant variation in MU. Predicted MU concentrations at different BW values were calculated for each parity group, by setting equations that included the estimates of the variables associated with MU and constant values (lactation averages) for the independent variables, with the exception of BW. Plotting of results showed exponential characteristics for the relationship between BW and predicted MU concentrations. At any of the considered BW, predicted MU concentrations were lower for first-parity cows. The trends and interactions found in the present study may contribute to improving accuracy of models designed to calculate urinary nitrogen excretion rates and normative milk urea concentrations.

Effect of carbohydrate source on ammonia utilization in lactating dairy cows1

This study was conducted to investigate the effect of dextrose, starch, NDF, and a carbohydrate (CHO) mix on utilization of ruminal ammonia in dairy cows. Four ruminally and duodenally cannulated Holstein cows (BW = 788 +/- 31 kg; 217 +/- 35 d in milk) were allocated to four treatments in a 4 x 4 Latin square design trial. Cows were fed an all alfalfa diet at 12-h intervals (DMI = 22.2 +/- 0.25 kg/d). Treatments were control, white oat fiber (NDF); corn dextrose (GLU); cornstarch (STA); and a CHO mix (25% of each): apple pectin, GLU, STA, and NDF (MIX). Carbohydrates were introduced intraruminally during feeding at 20% of dietary DMI. Ruminal ammonia was labeled with (15)N. Ruminal pH was the highest for NDF followed by STA and MIX and GLU (P < 0.001). Ruminal ammonia concentration and pool size were decreased by GLU and STA compared with NDF (P < 0.001 and P = 0.03, respectively). Acetate, isobutyrate, isovalerate, and total VFA concentration in the rumen were decreased (P = 0.009 to 0.001), and butyrate was increased (P < 0.001) by GLU compared with the other CHO. Microbial N flow to the duodenum was decreased (P < 0.05) by NDF compared with the other CHO, and the flow of microbial N formed from ammonia was greater for STA compared with GLU and NDF (P = 0.04 and 0.03, respectively). Urinary N loss was decreased (P = 0.05) by GLU and STA, but overall (feces plus urine) N losses were not affected (P = 0.73) by treatment. Milk urea concentration was lowered by GLU and STA compared with NDF and MIX (P = 0.002). The proportion of bacterial N synthesized from ammonia in the rumen was greater with STA than with NDF and MIX and was least for GLU (P = 0.02). Irreversible ammonia loss and flux were lower (P = 0.09 and 0.02, respectively) for GLU than for STA and NDF. As a percentage of the dose given, cumulative secretion of (15)N ammonia in milk protein was greater for STA than for GLU or NDF (P = 0.01 and 0.001, respectively). This experiment demonstrated that provision of readily fermentable energy can decrease ammonia concentrations in the rumen through decreased ammonia production (GLU), or through enhanced uptake of ammonia for microbial protein synthesis (STA). Rapidly fermentable energy in the rumen decreased ammonia production and flux, but the overall efficiency of ammonia utilization for milk protein synthesis was only increased by enhancing ruminal microbial ammonia uptake.

Effect of urea supplemented and urea treated straw based diet on milk urea concentration in crossbred Karan-Fries cows

The study was undertaken to evaluate the effect of urea supplemented and urea treated straw based diet on milk urea concentration. Six multiparous crossbred Karan-Fries (Holstein Friesian × Tharparkar) cows were blocked into three groups of nearly equal body weight, DIM, milk yield and milk fat content and were randomized into a 3 × 3 Latin square design with 3-week period. Three experimental diets were fed to the animals. Composition of these diets were: Diet 1) green maize, wheat straw and concentrate mixture; Diet 2) green maize, wheat straw, concentrate mixture (urea supplemented) and molasses; Diet 3) green maize (4 % of total DM), 4 % urea treated wheat straw and concentrate mixture. Intake of DM and CP did not vary across the diets. Intake of digestible crude protein (DCP) was found significantly higher in diet 2, while ME and NEl intakes were found significantly lower in diet 3 but did not differ between diets 1 and 2. Average milk and plasma urea concentrations (mg dl-1) were found 29.2 ± 2.6, 45.3 ± 0.9, 34.5 ± 2.3 and 28.9 ± 2.4, 36.6 ± 1.4, 33.9 ± 2.2, respectively in diet 1, diet 2 and diet 3. Urea concentrations in morning milk samples were found significantly lower than noon or evening samples in all the three diets. Concentrations of urea in milk and plasma were found closely correlated (r = 0.94) and the regression equation developed was, plasma urea = 8.90 (.89) + .79 (.02) milk urea. Intake (g) of DCP than CP, per unit (MCal) of ME was found more closely associated with milk urea concentration. The study revealed that urea supplementation and urea treated straw based diet increased urea concentration significantly in milk and plasma. Morning milk urea values that estimated at a time gap of 15 hr since last major feeding may be considered as the lowest level and can be used for interpretation to monitor feeding adequacy or reproductive performances in dairy cows.

Evaluation of nutritional status of dairy cows based on milk analysis results

Milk composition data, milk fat percentage (g/100ml), milk protein percentage (g/100g) and milk urea content (mg urea/dl) of 50,000 individual milk samples of cows under milk recording were used to evaluate nutritional status of dairy cows on Croatian farms. Analysis of average values of milk components indicates that most of the animals (60%) had a ration well balanced in energy and fibre, but ration protein deficiency could be a major characteristic of nutrition of considerable number (61.5%) of cows. Using milk analysis results it is possible to estimate major problems in dairy cow nutrition, predict and prevent possible metabolic and reproductive disturbances.