Relationships Between Milk Urea and Production, Nutrition, and Fertility Traits in Israeli Dairy Herds

Single-step genome-wide association analyses for milk urea concentration in Walloon Holstein cows

The aims of this study were to conduct a single-step genome-wide association to identify genomic regions associated with milk urea (MU) and to estimate genetic correlations between MU and milk yield (MY), milk composition (calcium content [CC], fat percentage [FP], protein percentage [PP], and casein percentage [CNP]), and cheese-making properties (CMP; coagulation time [CT], curd firmness after 30 min from rennet addition [a30], and titratable acidity [TA]). The used data have been collected from 2015 to 2020 on 78,073 first-parity (485,218 test-day records) and 48,766 second-parity (284,942 test-day records) Holstein cows distributed in 671 herds in the Walloon Region of Belgium. Data of 565,533 SNP located on 29 BTA of 6,617 animals (1,712 males) were used. Random regression test-day models were used to estimate genetic parameters through the Bayesian Gibbs sampling method. The SNP solutions were estimated using a single-step genomic BLUP approach. The proportion of the total additive genetic variance explained by windows of 50 consecutive SNPs (with an average size of ∼216 kb) was calculated, and the top-3 genomic regions explaining the largest rate of the genetic variance were considered promising regions and used to identify potential candidate genes. Mean (SD) MU was 25.38 (8.02) mg/dL and 25.03 (8.06) mg/dL in the first and second lactation, respectively. Mean heritability estimates for daily MU were 0.21 and 0.23 for the first and second lactation, respectively. The genetic correlations estimated between MU and MY, milk composition, and CMP were quite low (ranged from -0.10 [CC] to 0.10 [TA] and -0.05 [CT] to 0.13 [TA] for the first and second lactations, respectively). The top-3 regions associated with MU were located from 80.61 to 80.74 Mb on BTA6, 103.26 to 103.41 Mb on BTA11, and 1.59 to 2.15 Mb on BTA14. Genes including KCNT1, MROH1, SHARPIN, TSSK5, CPSF1, HSF1, TONSL, DGAT1, SCX, and MAF1 were identified as positional candidate genes for MU. The findings of this study can be used for a better understanding of the genomic architecture underlying MU in Holstein cattle.

Observational study on the associations between milk yield, composition, and coagulation properties with blood biomarkers of health in Holstein cows

The considerable increase in the production capacity of individual cows owing to both selective breeding and innovations in the dairy sector has posed challenges to management practices in terms of maintaining the nutritional and metabolic health status of dairy cows. In this observational study, we investigated the associations between milk yield, composition, and technological traits and a set of 21 blood biomarkers related to energy metabolism, liver function or hepatic damage, oxidative stress, and inflammation or innate immunity in a population of 1,369 high-yielding Holstein-Friesian dairy cows. The milk traits investigated in this study included 4 production traits (milk yield, fat yield, protein yield, daily milk energy output), 5 traits related to milk composition (fat, protein, casein, and lactose percentages and urea), 11 milk technological traits (5 milk coagulation properties and 6 curd-firming traits). All milk traits (i.e., production, composition, and technological traits) were analyzed according to a linear mixed model that included the days in milk, the parity order, and the blood metabolites (tested one at a time) as fixed effects and the herd and date of sampling as random effects. Our findings revealed that milk yield and daily milk energy output were positively and linearly associated with total cholesterol, nonesterified fatty acids, urea, aspartate aminotransferase, γ-glutamyl transferase, total bilirubin, albumin, and ferric-reducing antioxidant power, whereas they were negatively associated with glucose, creatinine, alkaline phosphatase, total reactive oxygen metabolites, and proinflammatory proteins (ceruloplasmin, haptoglobin, and myeloperoxidase). Regarding composition traits, the protein percentage was negatively associated with nonesterified fatty acids and β-hydroxybutyrate (BHB), while the fat percentage was positively associated with BHB, and negatively associated with paraoxonase. Moreover, we found that the lactose percentage increased with increasing cholesterol and albumin and decreased with increasing ceruloplasmin, haptoglobin, and myeloperoxidase. Milk urea increased with an increase in cholesterol, blood urea, nonesterified fatty acids, and BHB, and decreased with an increase in proinflammatory proteins. Finally, no association was found between the blood metabolites and milk coagulation properties and curd-firming traits. In conclusion, this study showed that variations in blood metabolites had strong associations with milk productivity traits, the lactose percentage, and milk urea, but no relationships with technological traits of milk. Specifically, increasing levels of proinflammatory and oxidative stress metabolites, such as ceruloplasmin, haptoglobin, myeloperoxidase, and total reactive oxygen metabolites, were shown to be associated with reductions in milk yield, daily milk energy output, lactose percentage, and milk urea. These results highlight the close connection between the metabolic and innate immunity status and production performance. This connection is not limited to specific clinical diseases or to the transition phase but manifests throughout the entire lactation. These outcomes emphasize the importance of identifying cows with subacute inflammatory and oxidative stress as a means of reducing metabolic impairments and avoiding milk fluctuations.

Effect of Parity and Days in Milk on Milk Urea Concentration and Milk Components in Holstein Dairy Cows

The objective of this study was to assess the effects of parity and of days in milk (DIM) on milk urea (MU) and other milk components in Holstein dairy cows. Milk yield was lower (P < 0.05) in primiparous cows compared with multiparous cows and tended to increase until the third parity and then decrease. The MU concentration was lower (P < 0.05) at the first lactation than at the other lactations. Milk fat and protein contents were higher (P < 0.05) in the primiparous cows than that in multiparous cows and were reduced until the third parity and then increased. Lower (P < 0.05) milk lactose content was found in primiparous cows and tended to increase until the third parity and then decreased. Primiparous cows had lower (P < 0.05) daily protein and fat yields compared with multiparous cows. The lowest value of milk yield was recorded during the first lactation with a peak of lactation between 61—90 DIM and a persistence of lactation of 3 %. The highest milk yield was confirmed at the third and fourth lactations with a peak of lactation between 61—90 DIM and a persistence of lactation of 7 % and 6 %. The effect of DIM on MU confirmed a significant (P < 0.01) positive relationships in primiparous and multiparous cows. The lowest level of MU concentration was found between 0—30 DIM. The content of MU increased and the maximum was achieved between 271—305 DIM. It is suggested that although MU for nutritional management and measures of production or reproduction are used, non-nutritional factors should be considered.

Effects of Milk Urea Nitrogen (MUN) and Climatological Factors on Reproduction Efficiency of Holstein Friesian and Jersey Cows in the Subtropics

This study investigated the effects of MUN and climatological factors on the inter calving period (ICP), reproductive performance (RP%), and reproductive index (RI) in Holstein Friesian (n = 1177) and Jersey cows (n = 3305) in different seasons in the subtropics. Threshold values for MUN on the reproduction of dairy cows in the subtropics remain controversial due to complex environmental interactions, especially with high environmental temperatures. A retrospective analysis was conducted of data obtained from the National Milk Recording scheme of the Agricultural Research Council (ARC) in South Africa. The results confirm that MUN influences the reproduction of dairy cows in the subtropics. MUN concentrations exceeding 18.1 ± 4.28 mg/dL in Holstein Friesian cows and 13.0 ± 4.70 mg/dL in Jersey cows extended the inter calving period (ICP), and decreased RP% and RI. Jersey cows have a lower threshold MUN concentration compared to Holstein Friesian cows, but they are not adversely affected by high humidity or temperatures, while Holstein Friesian cows are.

Factors associated with estrous expression and subsequent fertility in lactating dairy cows using automated activity monitoring

The objective of this observational study was to identify factors associated with estrous duration (DU) and intensity measured as the peak of activity (PA) change and subsequent fertility in lactating Holstein cows using a neck-mounted automated activity monitor (Heatime Pro, SCR Engineers Ltd., Netanya, Israel). Ambient temperature and relative humidity were recorded hourly to calculate the temperature-humidity index (THI). A total of 5,933 estrus events from 3,132 cows located on 8 commercial dairy farms in Germany were used for this study. Farms participated in monthly DHIA testing. Pregnancy diagnosis was performed either by transrectal palpation [farm 1: 42 ± 3 d; farm 3: 40 ± 3 d; farms 4 and 8: 38 ± 3 d; farm 5: 43 ± 3 d after artificial insemination (AI)] or transrectal ultrasonography (farms 2, 6, and 7: 30 ± 3 d after AI). Estrous intensity was categorized based on peak activity of estrus into low (35-89 index value), and high (90-100 index value) PA. Overall, 73.5% of estrus events were of high PA. The mean (± standard error of the mean) DU was 14.94 ± 0.06 h. There was a strong correlation between DU and PA (r = 0.67). In the final statistical model, only PA was associated with pregnancy per artificial insemination (P/AI), with 1.35 greater odds of pregnancy for cows with high PA compared with cows with low PA. Increased THI 1 wk before AI was associated with shorter DU, lower PA, and decreased P/AI. A small percentage of cows (4.7%) showed short interestrus intervals (i.e., more than 1 activity peak within 7 d close to the event of estrus), resulting in reduced DU, PA, and P/AI. The change of weighted rumination was associated with DU and PA, as a lower nadir was associated with a greater risk for high PA and long DU. There was no association, however, between the nadir of change of weighted rumination and P/AI. Whereas milk yield and somatic cell count from the DHIA test date before AI were negatively associated with estrous expression, neither milk yield nor somatic cell count was associated with P/AI. Surprisingly, multiparous cows expressed estrus with longer DU (13.15 ± 0.31 h) compared with primiparous cows (12.52 ± 0.32 h), whereas PA did not differ among parities. Pregnancy per AI was greater for primiparous (29.4%) than for multiparous (22.1%) cows. An estrus event with long DU or high PA was more likely later in lactation. Milk fat, milk protein, milk urea nitrogen, and lactose from the DHIA test date closest to AI had no association with estrous expression or P/AI. In conclusion, DU and PA were highly correlated, and cows with high PA were particularly associated with greater odds for pregnancy. A negative association between estrous expression and P/AI was identified for increased THI 1 wk before AI and cows with short interestrus intervals using automated activity monitor.

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.

Relationship between milk constituents from milk testing and health, feeding, and metabolic data of dairy cows

A new evaluation scheme to assess the nutritional status of dairy cows on the basis of milk constituents was derived from 7.37 million German records of milk testing. The aim of this work was to validate this new scheme. Two data sets with fertility and health information (data set A) and with measured energy and nutrient intake and metabolic characteristics (data set B) were analyzed. Data set A included 32 commercial dairy farms in northeast Germany, with 72,982 records of 43,863 German Holstein cows; data set B included 12 German experimental farms, with 49,275 records of 1,650 German Holstein, Simmental, and Brown Swiss cows. Milk traits were linked to health disorders and metabolic and feeding characteristics. Frequently used limits of milk constituents were compared with ranges of the new "Dummerstorf feeding evaluation." To distinguish an optimal from a deficient energy supply, a milk protein content ≥3.20% (previously used) and a milk fat:protein ratio (FPR) ≤1.4 (new scheme) were chosen and compared with feed energy intake in relation to demand. Energy status was more often correctly assigned by FPR than by milk protein content (80.7 and 68.7%, respectively). Over all data, the new optimum range of milk urea between 150 and 250 mg/L was better suited to dietary crude protein intake in relation to demand than the previously used range of 150 to 300 mg/L (42.4 and 38.0%, respectively). Ketosis or blood values associated with ketosis such as β-hydroxybutyrate >1.2 mmol/L or nonesterified fatty acids >1,000 µmol/L, as well as strong mobilization of body weight ≥1.5 kg/d, loss of back fat thickness ≥10 mm, and loss of body condition score ≥1 unit in first 60 days in milk were compared with different milk trait thresholds. For the updated scheme FPR >1.4 was used in combination with either milk protein content below the individual statistical lower limit of milk protein content, or milk fat content greater than the individual statistical upper limit of milk fat content; FPR >1.5 was taken as a frequently used threshold. For these ketosis indicators, the new scheme had higher sensitivities. Energy oversupply or the risk of overconditioning could not be identified by milk constituents alone. Urinary acid-base content was not related to milk content. Similarly, milk testing data did not allow a clear distinction to be made between the diagnoses of acidosis and, for example, ketosis. Essential requirements for good herd management are the continuous observation of milk testing data in combination with other established instruments of feeding and animal monitoring.

Milk urea nitrogen concentration is higher in Brown Swiss than in Holstein dairy cows despite identical feeding

Milk urea nitrogen (MUN) content is closely related to blood urea nitrogen (BUN) concentration and reflects the balance of dietary crude protein and energy supply for ruminal microbial metabolism. The present study investigated whether the higher MUN content in Brown Swiss (BSW) compared with Holstein (HOL) cows is related to milk production and feeding conditions. Therefore, we evaluated test-day records of three consecutive official milk recordings from 86 BSW and 200 HOL cows kept on the same farm under identical feeding and management conditions. In addition, the relationships between BUN and MUN assessed either by an enzymatic method or by mid-infrared spectroscopy were analysed. For the second objective, milk and blood samples (1,112 samples each) were collected in parallel from day 5 until day 150 of lactation from 141 dairy cows housed at different farms. Concentrations of MUN determined either enzymatically (MUN_ENZ ) or by Fourier transform infrared spectroscopy (FTIR; MUN_IR ) were regressed on the BUN concentrations of the concomitantly obtained blood samples. Both MUN_IR and MUN_ENZ were well correlated with BUN (r = .93 and .89 respectively). Concentration of MUN was higher in BSW compared with HOL independently of lactational stage or parity number (p < .0001). Protein and fat content were higher in BSW than in HOL (p < .05). Primiparous cows had lower milk yield and ECM (p < .001 for BSW, p < .0001 for HOL) than multiparous in both breeds. Multiparous BSW had a similar milk production than primiparous HOL (p = .13). In conclusion, BSW cows have higher MUN than HOL when kept under identical feeding and management conditions. The higher MUN in BSW compared with HOL cows is not related to milk production and therefore rather genetically determined.

The Assessment of Housing Conditions, Management, Animal-Based Measure of Dairy Goats’ Welfare and Its Association with Productive and Reproductive Traits

Simple Summary

Small ruminant production systems are generally perceived by consumers to be associated with a high standard of welfare, notably in relation to aspects of traditional breeding. However, their performances have reached the same levels of the dairy cow sector, with similar negative externalities. We aimed to evaluate the welfare of dairy goats of 32 farms located in Northwestern Italy by the application of an on-farm assessment protocol. The farms were classified as ‘intensive’ or ‘semi-intensive’ according to the access to pasture. Overall, we observed an adequate level of animal wellbeing both in intensive and semi-intensive farming systems. This is possible thanks to the increased knowledge on goat breeding characteristics, and to the fact that veterinarians and farmers understood the importance of welfare protection to achieve a better health, although some challenges remain, such as the farmers’ approach toward animals. The importance of the farmer’s role is highlighted by the positive association between the milk yield and the presence of the owner on the farm.

Abstract

The aim of the study was to evaluate the welfare of dairy goats of 32 farms located in Northwestern Italy, applying an on-farm assessment protocol, centered on animal-, resources- and management-based measures. The farms were classified as ‘intensive’ or ‘semi-intensive’ according to access to pasture. During each on-farm visit, a checklist was compiled, based on specific scores for housing and management conditions, and animals’ nutritional status, health, and behavior. Finally, the possible association between welfare measures and productive and reproductive traits was assessed. Overall, we observed an adequate level of animal wellbeing both in intensive and semi-intensive farming systems. This is possible thanks to the increased knowledge on goat breeding characteristics, and to the fact that veterinarians and farmers understood the importance of welfare protection to achieve a better health. Higher milk production was associated to some management practices (presence of the owner on the farm, high frequency of bedding change), and to seasonal breeding (which was mainly performed in the intensive farming). Moreover, it was associated to a quantity of urea in the milk comprised between 33 and 44 mg/dL. In intensive farms, the prevalence of caseous lymphadenitis was significantly higher compared to non-intensive farms. The semi-intensive breeding system positively influences the animals’ behavior.

Factors affecting the milk urea nitrogen concentration in Chinese Holstein cows

In order to investigate the factors affecting milk urea nitrogen in Chinese Holstein cows, a large commercial dairy farm participated in a 30-month study. In this study, the mean milk urea nitrogen concentration was 11.75 mg/dl. The milk urea nitrogen reached its maximum value on day 90 of lactation for the first parity and the third or higher parities, but it peaked at the end of lactation for the second parity. The milk urea nitrogen of the first parity was lower than that of other parities. The milk urea nitrogen showed its minimum level in January, and reached its maximum in July. The milk urea nitrogen at the first month of lactation in cows calving in summer was higher than other seasons, while at the fourth month of lactation, the milk urea nitrogen of cows calving in autumn was significantly lower than in cows calving in other seasons. Positive correlations were observed between daily milk yield, net energy for lactation, crude protein and milk urea nitrogen for the first and third parities, but negative correlations were observed in the second parity. The milk urea nitrogen showed significantly positive correlations with fat content, total solid content and daily matter intake for all parities. A negative correlation was observed between milk urea nitrogen and protein content, with the exception of the second parity. For all data, as milk urea nitrogen concentration increased, milk protein content decreased. It has been recommended that milk urea nitrogen concentration should be evaluated in combination with parity, days in milk, season (or month), daily matter intake and dietary nutritional components, in order to improve the management and economic benefits of dairy farm.

Evaluation of heat stress on Tarentaise and Holstein cow performance in the Mediterranean climate

This study was undertaken to first quantify the effect of heat stress on milk yield and components of Tarentaise in comparison to Holstein cows. A dataset of 16,143 monthly individual records of production traits was collected for 435 Tarentaise and 543 Holstein cows from 21 farms in Tunisia (2009 to 2014). This dataset was merged with meteorological data from 5 public stations relative to the 21 farms. The temperature-humidity index (THI), calculated as a combination of ambient temperature and relative humidity, was used to characterize heat stress. When the THI increased from an average value of 53.7 in winter to 75.4 in summer, the Holstein and Tarentaise cows decreased their milk production by 0.93 and 0.15 kg/day, respectively. Milk fat, protein, and urea content decreased similarly in both breeds (-2.20 g/kg, -1.40 g/kg, and -14 mg/L, respectively), and the milk somatic cell count increased for Holstein cows (+352,000/mL) while decreased for Tarentaise cows (-160,000/mL). The second aim of this study was to describe the relationship between the variations of the milk yields between the summer and the winter (Δ milk yields) and some barn characteristics during the hot season. A survey carried out on 19 of the 21 previous farms permitted to conclude that the closed buildings led to a higher decrease in milk yield between the summer and winter than the open buildings (-1.13 vs. -0.27 kg/day). A metallic roof had a more negative impact on Δ milk yields than the other roof types (-1.04 vs. -0.15 kg/day).

The eff ect of selected factors on urea concentration in the milk of Polish Holstein-Friesian cows

The objective of the study was to determine the relationships between milk urea concentration and factors such as lactation number, stage of lactation, month and season of the test day, age at calving, milk yield and protein percentage. Data for the calculations consisted of 7,731 test-day records from 1,078 Polish Holstein-Friesian cows. Test-day milking was performed for first, second and third lactations during the period from December 2010 to December 2011. Calculations were performed using the MIXED procedure in SAS/STAT. A mixed linear model using was applied in which parameters were estimated by the restricted maximum likelihood (REML) method. Least squares means for fixed eff ects in the model were compared by the Tukey-Kramer test. The first lactation diff ered significantly (p<0.05) from the second and third in terms of mean urea concentration, but there were no significant diff erences between the second and third lactations. For primiparous cows the milk urea concentration increased throughout lactation, but for older cows it increased only up to 7–8 months of lactation. Urea concentrations did not diff er significantly in the same stages of consecutive lactations, i.e. the first and second or second and third. Statistically significant diff erences were noted between the first and third lactations only in months 9 and 10 of lactation. Seasonal changes in milk urea content varied depending on the lactation number. In the first lactation the milk urea concentration was lowest in spring and highest in autumn. This tendency was not observed in the second and third lactation. Milk urea concentration was positively associated with both milk yield and protein percentage

Genetic and environmental determinants of the urea level in cow's milk

Abstract. This study was conducted on a sample of 2237 Polish Holstein-Friesian cows. The aim was to estimate the effect of selected environmental factors on the level of urea in cow's milk and on its genetic parameters, i.e. the heritability coefficients, and genetic correlation with other selected traits of milk production. The present study has revealed the existence of a highly significant influence of herd, year of calving, parity, lactation phase, and milk performance level on the urea content in cow's milk. A high urea level in milk was detected in samples collected from older animals, both during the winter season and the middle phase of lactation (101–200 days). The heritability estimates were generally at a low level, particularly in terms of milk yield (0.183) and urea content (0.152–0.159), which may indicate the dominant role of the environment in shaping them. Relatively low values of genetic correlation (−0.097–0.140) between the urea content and other traits suggest that improvement of milk yield and its composition modify the urea level in milk only to a small degree.

A field study to unravel factors that are significantly associated with the secretory activity of the corpus luteum during the first three postpartum cycles in high yielding dairy cows, based on the amount of steroidogenic and endothelial cells present in the luteal tissue

Fourteen multi- and eight primiparous high-yielding dairy cows were followed from the first till the fourth ovulation postpartum. Cows were randomly divided into two groups and supplemented with soybean (group I; n = 11) or rapeseed meal (group II; n = 11). Both groups were subjected to a biopsy sampling of the corpus luteum (CL) at cycle day 9. The luteal capillary network (visualized by Bandeiraea simplicifolia) was denser in cycles 2 and 3 (p = 0.0005). The same was seen for the surface occupied by steroidogenic cells (visualized by 3β-hydroxysteroiddehydrogenase) (p = 0.0001). The peripheral blood progesterone concentration showed an increasing trend with increasing cycle number and was higher in primiparous cows (p = 0.013), which had also larger glands on cycle day 9. The area occupied by endothelial cells was positively correlated with the area occupied by steroidogenic cells (r = 0.59; p < 0.0001). Both the areas occupied by endothelial and by steroidogenic cells were negatively correlated with the blood concentration of nonesterified fatty acids (NEFAs) (respectively, r = -0.377; p = 0.004 and r = -0.355; p = 0.007). We can conclude that primiparous cows generally have higher peripheral progesterone levels during the first three cycles after calving which is associated with a larger CL. In comparison with those of the first post-partum cycle, corpora lutea of cycles 2 and 3 have a denser capillary network and a larger area of steroidogenic cells, while these are only associated with a trend of higher peripheral progesterone concentrations.

Nitrogen metabolism and microbial production of dairy cows fed sugarcane and nitrogen compounds

The aim of this study was to evaluate the effect of dairy cow diets containing two different sources of urea on nitrogen metabolism and microbial synthesis. Eight crossbred cows were confined and distributed in two 4x4 Latin: FS - soybean meal (control), conventional urea (UC) 100%; ULL 44 UC = 56% / 44% ULL, ULL 88 UC = 12% / 88% ULL. Diets were offered to animals during 21 days with 14 days of adaptation. The N intake, retained nitrogen balance, nitrogen excretion in milk, urine, feces and total N excretion were similar and presented averages of 340.27g/day, 136.73g/day, 43.25g/day, 53.17g/day, 103.54g/day, and 199.96g/day, respectively. The percentages of urine and total nitrogen excretion were 16.24 and 60.71 (%), respectively. Ureic nitrogen in milk, urine and blood were 3.95mg/dL, 4.32mg/dl and 23.73mg/dL, respectively. The results found for the excretion of purine derivatives, allantoin, absorbable purines, microbial nitrogen, microbial protein and the relationship between microbial protein and digestible nutrients were 321.68mmol/day, 296.35mmol/day, 334.61mmol/day, 210.6g/day, 1316.27g/day, and 127.36g/kg, respectively. The partial replacement of soybean meal by conventional urea and / or urea encapsulated in feeding lactating cows yielded similar results in nitrogenous compounds, the concentrations of nitrogen from urine and milk and microbial protein synthesis.

Genetic parameters for milk urea concentration and milk traits in Polish Holstein-Friesian cows

Milk urea concentration (MU) used by dairy producers for management purposes can be affected by selection for milk traits. To assess this problem, genetic parameters for MU in Polish Holstein-Friesian cattle were estimated for the first three lactations. The genetic correlation of MU with milk production traits, lactose percentage, fat to protein ratio (FPR) and somatic cell score (SCS) were computed with two 5-trait random regression test-day models, separately for each lactation. Data used for estimation (159,044 daily observations) came from 50 randomly sampled herds. (Co)variance components were estimated with the Bayesian Gibbs sampling method. The coefficient of variation for MU in all three parities was high (40-41 %). Average daily heritabilities of MU were 0.22 for the first parity and 0.21 for the second and third lactations. Average genetic correlations for different days in milk in the first three lactations between MU and other traits varied. They were small and negative for protein percentage (from -0.24 to -0.11) and for SCS (from -0.14 to -0.09). The weakest genetic correlation between MU and fat percentage, and between MU and lactose percentage were observed (from -0.10 to 0.10). Negative average genetic correlation with the fat to protein ratio was observed only in the first lactation (-0.14). Genetic correlations with yield traits were positive and ranged from low to moderate for protein (from 0.09 to 0.33), fat (from 0.16 to 0.35) and milk yield (from 0.20 to 0.42). These results suggest that the selection on yield traits and SCS tends to increase MU slightly.

A comparative study at two different altitudes with two dietary nutrition levels on rumen fermentation and energy metabolism in Chinese Holstein cows

The object of this study was to investigate the effect of two altitudes (1600 vs. 3600 m) with two nutritional levels [5.88 MJ/kg dry matter (DM) vs. 7.56 MJ/kg DM] on apparent total tract digestibility, rumen fermentation, energy metabolism, milk yield and milk composition in Chinese Holstein cows. Sixteen Chinese Holstein cows in their third lactation with close body weights, days in milk and milk yield were randomly divided into four groups, of which two were directly transferred from Lanzhou (altitude of 1600 m) to Lhasa (altitude of 3600 m). Four treatments (high plateau and high nutrition level, HA-HN; high plateau and low nutrition level, HA-LN; low plateau and high nutrition level, LA-HN; and low plateau and low nutrition level, LA-LN) were randomly arranged in a 2 × 2 factorial experimental design. Results indicated that the apparent total tract digestibility of a diet's DM, organic matter, crude protein, neutral detergent fibre and acid detergent fibre and DM intake were not affected by either altitude or nutrition level (p > 0.05). Milk protein percentage was higher for the diet with the high level of nutrition than for the diet with low nutrition level irrespective of altitude (p < 0.05). Percentages of milk fat and milk lactose were not affected by either altitude or nutrition level (p > 0.05). The metabolizable energy used for milk energy output was decreased by high altitude in comparison with that at low altitude (p < 0.05). No differences were observed in the live body weight or body condition score (BCS) of Chinese Holstein cows among all of the four treatments (p > 0.05).

Genetic relationship between milk urea nitrogen and reproductive performance in Holstein dairy cows

The objective of this study was to describe the genetic and phenotypic relationship between milk urea nitrogen (MUN) and reproductive traits in Iranian Holstein dairy cows. Test-day MUN data obtained from 57 301 dairy cows on 20 large dairy herds in Iran between January 2005 and June 2009. Genetic parameters for MUN and reproductive traits were estimated with a five-trait model using ASREML program. Random regression test-day models were used to estimate heritabilities separately for MUN from first, second and third lactations. Regression curves were modeled using Legendre polynomials of order 3. Herd-year-season along with age at calving was included as fixed effects in all models for reproductive traits. Heritabilities for MUN and reproductive traits were estimated separately for first lactation, second lactation and third lactation. The estimated heritabilities for MUN varied from 0.18 to 0.22. The heritability estimate was low for reproductive traits, which ranged from 0.02 to 0.06 for different traits and across parities. Except for days open, phenotypic and genetic correlations of MUN with reproductive performance traits were close to zero. Genetic correlations between MUN and days open were 0.23, 0.35 and 0.45 in first, second and third lactation, respectively. However, the phenotypic correlation between MUN at different parities was moderate (0.28 to 0.35), but the genetic correlation between MUN at different parities was high and ranged from 0.84 to 0.97. This study shows a limited application of MUN for use in selection programs to improve reproductive performance.

Genetic and phenotypic relationships among milk urea nitrogen, fertility, and milk yield in holstein cows

The aims of the study were to evaluate the relationships among milk urea nitrogen and nonreturn rates at the phenotypic scale, and to estimate genetic parameters among milk urea nitrogen, milk yield, and fertility traits in the early period of lactation. Milk yield, protein percentage, the interval from calving to first service, and 56- and 90-d nonreturn rates were available from 73,344 Holstein cows from 2,178 different herds located in a region in northwestern Germany. Generalized linear models with a logit link function were applied to assess the phenotypic relationships. Bivariate threshold-threshold, linear-threshold, and linear-linear models, fitted in a Bayesian framework, were used to estimate genetic correlations among traits. Milk yield, protein percentage, and milk urea nitrogen were means from test-day 1 (on average 20.8 d in milk) and test-day 2 (on average 53.1 d in milk) after calving. An increase in milk urea nitrogen was associated with decreasing 56-d nonreturn rates on the phenotypic scale. At fixed levels of milk urea nitrogen, greater values of protein percentage, indicating a surplus of energy in the feed, were positively associated with nonreturn rates. Heritabilities were 0.03 for 56- and 90-d nonreturn rates, 0.07 for interval from calving to first service, 0.13 for milk urea nitrogen, and 0.19 for milk yield. Service sire explained a negligible part (below 0.15%) of the total variance for nonreturn rates. Genetic correlations between the interval from calving to first service and nonreturn rates were close to zero. The genetic correlation between nonreturn rates was 0.94, suggesting that a change from nonreturn after 90 d to nonreturn after 56 d in the national genetic evaluation would not result in any loss of information. The genetic correlation between milk yield and nonreturn after 56 d was -0.31, and between milk yield and calving to first service was 0.14, both indicating an antagonistic relationship between production and reproduction. The genetic correlation between milk yield and milk urea nitrogen was 0.44, reflecting an energy deficiency in early lactation. The genetic correlations between milk urea nitrogen and nonreturn rates were too weak (-0.19 for 56-d nonreturn rate, and -0.23 for 90-d nonreturn rate) to justify the use of milk urea nitrogen as an additional trait in genetic selection for fertility, as demonstrated by selection index calculations.

The analysis of milk components and pathogenic bacteria isolated from bovine raw milk in Korea

Bovine mastitis can be diagnosed by abnormalities in milk components and somatic cell count (SCC), as well as by clinical signs. We examined raw milk in Korea by analyzing SCC, milk urea nitrogen (MUN), and the percentages of milk components (milk fat, protein, and lactose). The associations between SCC or MUN and other milk components were investigated, as well as the relationships between the bacterial species isolated from milk. Somatic cell counts, MUN, and the percentages of milk fat, protein, and lactose were analyzed in 30,019 raw milk samples collected from 2003 to 2006. The regression coefficients of natural logarithmic-transformed SCC (SCCt) on milk fat (-0.0149), lactose (-0.8910), and MUN (-0.0096), and those of MUN on milk fat (-0.3125), protein (-0.8012), and SCCt (-0.0671) were negative, whereas the regression coefficient of SCCt on protein was positive (0.3023). When the data were categorized by the presence or absence of bacterial infection in raw milk, SCCt was negatively associated with milk fat (-0.0172), protein (-0.2693), and lactose (-0.4108). The SCCt values were significantly affected by bacterial species. In particular, 104 milk samples infected with Staphylococcus aureus had the highest SCCt (1.67) compared with milk containing other mastitis-causing bacteria: coagulase-negative staphylococci (n = 755, 1.50), coagulase-positive staphylococci (except Staphylococcus aureus; n = 77, 1.59), Streptococcus spp. (Streptococcus dysgalactiae, n = 37; Streptococcus uberis, n = 12, 0.83), Enterococcus spp. (n = 46, 1.04), Escherichia coli (n = 705, 1.56), Pseudomonas spp. (n = 456, 1.59), and yeast (n = 189, 1.52). These results show that high SCC and MUN negatively affect milk components and that a statistical approach associating SCC, MUN, and milk components by bacterial infection can explain the patterns among them. Bacterial species present in raw milk are an important influence on SCC in Korea.

Influence of estrus of dairy goats on somatic cell count, milk traits, and sex steroid receptors in the mammary gland

Two experiments were conducted to study the effect of the stage of a spontaneous estrus cycle on milk yield and constituents [somatic cell count (SCC), fat, protein, caseins, lactose, and urea content] and on estrogen receptor-alpha (ERalpha ) and progesterone receptor (PR) immunostaining in the mammary gland. In experiment I, the major components of milk and SCC were monitored weekly in 80 lactating Saanen goats for 6 wk, whereas detection of estrus was daily. In experiment II, milk samples were collected daily for SCC determination during 1 spontaneous estrus (d 0) until the second spontaneous estrus in 14 Saanen goats. The day of the estrous cycle was confirmed by plasma progesterone and 17beta-estradiol levels. Immunoreactivity of ERalpha and PR was analyzed in mammary gland samples of 8 Saanen goats (d 0, n = 4; d 10, n = 4) and the number of positive nuclei and intensity of the staining were evaluated in 1,000 cells. In experiment I, milk casein and protein percentages were significantly affected by the stage of estrous cycle; during proestrus and estrus, these variables were higher (3.32 +/- 0.06 and 4.44 +/- 0.08) than during metestrus (3.03 +/- 0.07 and 4.07 +/- 0.10), but not higher than during diestrus (3.23 +/- 0.06 and 4.35 +/- 0.09, respectively). In experiment II, daily measurement of SCC revealed higher levels at estrus (7,195 +/- 672 x 10(3) cells/mL) and a decline toward the luteal phase (1,694 +/- 672 +/- 10(3) cells/mL). Estrogen receptor-alpha and PR immunostaining were exclusively detected on epithelial cells. The percentage of positive nuclei to ERalpha was higher on d 0 than on d 10 (75.4 +/- 8.8 vs. 68.3 +/- 8.8%), but no change was observed for PR (4.0 +/- 0.3 vs. 3.5 +/- 0.4%). The average immunostaining intensity for both receptors was greater on d 0 than on d 10 (ERalpha : 1.44 +/- 0.02 vs. 1.35 +/- 0.02; PR: 0.079 +/- 0.008 vs. 0.057 +/- 0.008). The high SCC at estrus in experiment II was associated with high plasma estradiol and low progesterone, suggesting that the increased SCC could be brought about by the estrogen-induced proliferation and exfoliation of epithelial cells. In addition, this action may be supported by the higher sensitivity to estrogens (ERalpha content) found at d 0.

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 (gMP/kg fermented organic matter) was the same, g MP/d and g MP/MJ ME were significantly lower with RNB = -0.6g/MJ ME as compared to RNB = 0. The group with thelowest RNB showed the highest level of feedprotein degradation as well as the lowest organic matter, NDF and ADF fermentation. An effect on cholesterol, total bilirubin and gammaGT 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 t he degradation and synthesis capacity of the rumen micro-organisms as compared to RNB = 0.

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 15.3 mg/dL (SD = 3.8) and 593 kg (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.