Changes in milk urea around insemination are negatively associated with conception success in dairy cows

Dietary protein levels are a risk factor for poor reproductive performance. Conception is particularly impaired in cases of high blood or milk urea. The objective of this study was to investigate the association between conception and low milk urea or changes in milk urea around artificial insemination (AI). Data were obtained from the French Milk Control Program for a 4-yr period (2009–2012). Milk urea values between 250 and 450 mg/kg (4.3 and 7.7 mM) were considered intermediate (I), and values ≤150 mg/kg (2.6 mM) were considered low (L). Milk urea values before and after each AI were allocated into 4 classes representing the dynamics of milk urea (before-after; I-I, I-L, L-I, and L-L). Subclinical ketosis was defined using milk fat and protein contents before AI as proxies. A logistic regression with a Poisson correction and herd as a random variable was then performed on data from Holstein or all breeds of cows. The success of conception was decreased [relative risk (95% confidence interval) = 0.96 (0.94–0.99)] in low-urea cows compared with intermediate-urea cows after AI; no significant association was found for urea levels before AI. When combining data on urea before and after AI, I-L urea cows exhibited a 5 to 9% decrease in conception compared with I-I urea cows, and L-I urea cows showed no difference in conception success compared with I-I urea cows. A decreased conception success for L-L urea cows compared with I-I urea cows was observed for the analysis with cows of all breeds. This work revealed that a decrease in urea from intermediate (before AI) to low (after AI) is a risk factor for conception failure. Surveys of variation in milk urea in dairy cows close to breeding are highly recommended.     

Modeling milk urea of Walloon dairy cows in management perspectives

The aim of this study was to develop an adapted random regression test-day model for milk urea (MU) and to study the possibility of using predictions and solutions given by the model for management purposes. Data included 607,416 MU test-day records of first-lactation cows from 632 dairy herds in the Walloon Region of Belgium. Several advanced features were used. First, to detect the herd influence, the classical herd × test-day effect was split into 3 new effects: a fixed herd × year effect, a fixed herd × month-period effect, and a random herd test-day effect. A fixed time period regression was added in the model to take into account the yearly oscillations of MU on a population scale. Moreover, first autoregressive processes were introduced and allowed us to consider the link between successive test-day records. The variance component estimation indicated that large variance was associated with the random herd × test-day effect (48% of the total variance), suggesting the strong influence of herd management on the MU level. The heritability estimate was 0.13. By comparing observed and predicted MU levels at both the individual and herd levels, target ranges for MU concentrations were defined to take into account features of each cow and each herd. At the cow level, an MU record was considered as deviant if it was <200 or >400 mg/L (target range used in the field) and if the prediction error was >50 mg/L (indicating a significant deviation from the expected level). Approximately 7.5% of the MU records collected between June 2007 and May 2008 were beyond these thresholds. This combination allowed for the detection of potentially suspicious cows. At the herd level, the expected MU level was considered as the sum of the solutions for specific herd effects. A herd was considered as deviant from its target range when the prediction error was greater than the standard deviation of MU averaged by herd test day. Results showed that 6.7% of the herd test-day MU levels between June 2007 and May 2008 were considered deviant. These deviations seemed to occur more often during the grazing period. Although theoretical considerations developed in this study should be validated in the field, this research showed the potential use of a test-day model for analyzing functional traits to advise dairy farmers.     

Factors associated with milking characteristics in dairy cows

Milking characteristics, and in particular milking duration, are a known contributor to costs in dairy production systems. Results from previous studies suggest that higher-yielding animals, on average, milk for a longer duration. Culling or selection for reduced milking duration alone may, therefore, reduce milk yield. Here, we propose 2 new traits, residual milking duration (RMD) and residual milking duration including somatic cell score (RMDS). Residual milking duration is represented by the residuals from a least squares regression of milking duration on milk yield; RMDS is represented by the residuals from a least squares regression of milking duration on both milk yield and somatic cell score [i.e., logarithm (base 10) of somatic cell count]. The mathematical properties of least squares regression ensure than the residual traits are independent from the regressor variables, or, in other words, RMDS is not correlated with either milk yield or somatic cell score. Both RMD and RMDS were defined using electronically measured individual cow milking duration from 235,036 part-day milking events from 74,607 cows from 1,075 Irish dairy herds. Twenty-four percent of the variation in milking duration was explained by the multiple regression model containing both milk yield and somatic cell score. The phenotypic standard deviation of RMD and RMDS was 102.2 and 98.2 s, respectively, suggesting large variation in milking duration independent of milk yield (and somatic cell score). The correlation of RMD and RMDS with average milk flow rate, which may also be considered a measure of milking efficiency, was −0.74 and −0.75, respectively. Neither RMD nor RMDS was correlated with somatic cell score. However, average milk flow rate was correlated with milk yield (0.57) and milking duration (−0.38). Both RMD and RMDS are useful traits, which exhibit considerable variation and, therefore, can be used by farmers to identify phenotypically slower milking animals irrespective of milk yield (and somatic cell score). However, because of the lack of a correlation between RMD and somatic cell score in the sample population used in the present study, RMD and RMDS values per milking were almost identical.     

Association between milk urea nitrogen and fertility in Ohio dairy cows

The purpose of this study was to evaluate the association between milk urea nitrogen (MUN) and fertility of dairy cows using field data. The data came from 24 dairy herds belonging to Ohio Dairy Herd Improvement Cooperative Inc. Reproductive data and MUN measurements from cows that calved between June 1998 and May 1999 and that had been bred at least once were included in the study. Survival analysis, using the Cox proportional hazards model, was performed and days from calving to conception or to the end of the study was used as the outcome. Cows that had not been reported pregnant during the study were considered censored. The mean of monthly MUN values of cows before conception (or the end of the study for censored cows) was used to reflect the MUN status of a cow. Animals were categorized into quartiles based on MUN values in these data. Parity, calving season, peak milk yield, number of services, and herd were included in the models as fixed effects. Cows with MUN levels below 10.0 were 2.4 times more likely and cows with MUN levels between 10.0 and 12.7 mg/dl were 1.4 times more likely to be confirmed pregnant than cows with MUN values above 15.4 mg/dl. Our results indicate that increasing MUN levels appear to be negatively related to dairy cow fertility and are associated with a lower risk of detectable pregnancy at herd checks. They also suggest that the levels of MUN that are adversely associated with fertility might be lower than reported earlier.     

Relationships between milk urea concentrations and nutritional management, production, and economic variables in Ontario dairy herds

The objectives of this study were to describe the relationships between milk urea concentrations and nutritional management, production, and economic variables in commercial dairy herds. Dairy Herd Improvement (DHI) test-day milk urea data, production data, and information on ration nutrient composition and feeding management programs were collected over a 13-mo period from 53 commercial Ontario dairy herds. Economic variables included gross milk revenue, feed costs, and income over feed costs. Herd mean milk urea concentrations had a positive relationship with dietary levels of crude protein (CP), rumen degradable protein (RDP), and rumen undegradable protein (RUP) and a negative relationship with dietary levels of nonfiber carbohydrates (NFC), forage:concentrate (F:C) ratio, NFC:CP ratio, and NFC:RDP ratio. These findings are consistent with experimental studies that used chemical methods of milk urea analysis. Herd mean milk urea concentration was not associated with feeding management (e.g., total mixed rations, component feeding, feeding frequency, or synchrony of forage and concentrate feeding). Herd mean milk urea was not associated with either mean milk yield or linear score. Herd mean milk urea had a positive relationship with feed costs per cow per day but was not associated with gross milk revenue per cow per day. Herds with a high mean milk urea concentration tended to have lower income over feed costs per cow per day. High herd mean milk urea concentrations were associated with higher feed costs per kilogram of milk fat but lower gross milk revenue and lower income over feed costs per kilogram of milk fat. The results of this study demonstrate that DHI milk urea measurements produced by an infrared test method offer a useful tool for monitoring the efficiency of nitrogen utilization in commercial dairy herds. The results also suggest that diets may be balanced to achieve greater efficiency of nitrogen utilization, lower milk urea concentrations, and lower feed costs, while still achieving high milk production. This may lead to improved income over feed costs.     

Factors associated with colostral specific gravity in dairy cows

The objectives of this study were to identify factors associated with colostral specific gravity in dairy cows, as measured by a commercially available hydrometer (Colostrometer). Colostral specific gravity was measured in 1085 first-milking colostrum samples from 608 dairy cows of four breeds on a single farm during a 5-yr period. Effects of breed, lactation number, and month and year of calving on colostral specific gravity were determined, as were correlations between colostral specific gravity, nonlactating period length, and 305-d yields of milk, protein, and fat. For 75 multiparous Holstein cows, relationships between colostral specific gravity, colostral IgG1, protein, and fat concentrations, and season of calving were determined. Colostral specific gravity values were lower for Brown Swiss and Ayrshire cows than for Jersey and Holstein cows, and lower for cows entering first or second lactation than third or later lactations. Month of calving markedly affected colostral specific gravity values, with highest values occurring in autumn and lowest values in summer. In multiparous Holstein cows, colostral specific gravity was more strongly correlated with colostral protein concentration (r = 0.76) than IgG1 concentration (r = 0.53), and colostral protein concentration varied seasonally (higher in autumn than summer). Our results demonstrate that colostral specific gravity more closely reflects colostral protein concentration than IgG1 concentration and is markedly influenced by month of calving. These results highlight potential limitations of using colostral specific gravity as an indicator of IgG1 concentration.     

Effect of mastitis on milk perchlorate concentrations in dairy cows

Recent surveys have identified the presence of perchlorate, a natural compound and environmental contaminant, in forages and dairy milk. The ingestion of perchlorate is of concern because of its ability to competitively inhibit iodide uptake by the thyroid and to impair synthesis of thyroid hormones. A recent study established that milk perchlorate concentrations in cattle highly correlate with perchlorate intake. However, there is evidence that up to 80% of dietary perchlorate is metabolized in clinically healthy cows, thereby restricting the available transfer of ingested perchlorate into milk. The influence of mastitis on milk perchlorate levels, where there is an increase in mammary vascular permeability and an influx of blood-derived components into milk, remains unknown. The present study examined the effect of experimentally induced mastitis on milk perchlorate levels in cows receiving normal and perchlorate-supplemented diets. Over a 12-d period, cows were ruminally infused with 1 L/d of water or water containing 8 mg of perchlorate. Five days after the initiation of ruminal infusions, experimental mastitis was induced by the intramammary infusion of 100 μg of bacterial lipopolysaccharide (LPS). Contralateral quarters infused with phosphate-buffered saline served as controls. A significant reduction in milk perchlorate concentration was observed in the LPS-challenged glands of animals ruminally infused with either water or perchlorate. In control glands, milk perchlorate concentrations remained constant throughout the study. A strong negative correlation was identified between mammary vascular permeability and milk perchlorate concentrations in LPS-infused glands. These findings, in the context of a recently published study, suggest that an active transport process is operative in the establishment of a perchlorate concentration gradient across the blood-mammary gland interface, and that increases in mammary epithelial and vascular endothelial permeability lead to a net outflow of milk perchlorate. The overall finding that mastitis results in lower milk perchlorate concentrations suggests that changes in udder health do not necessitate increased screening of milk for perchlorate.     

Genetic and nongenetic factors associated with milk color in dairy cows

Milk color is one of the sensory properties that can influence consumer choice of one product over another and it influences the quality of processed dairy products. This study aims to quantify the cow-level genetic and nongenetic factors associated with bovine milk color traits. A total of 136,807 spectra from Irish commercial and research herds (with multiple breeds and crosses) were used. Milk lightness $\left(\stackrel{?}{\text{L}}*\right)$, red-green index $\left(\stackrel{?}{\text{a}}*\right)$ and yellow-blue index $\left(\stackrel{?}{\text{b}}*\right)$ were predicted for individual milk samples using only the mid-infrared spectrum of the milk sample. Factors associated with milk color were breed, stage of lactation, parity, milking-time, udder health status, pasture grazing, and seasonal calving. (Co)variance components for $\stackrel{?}{\text{L}}*,\stackrel{?}{\text{a}}*$, and $\stackrel{?}{\text{b}}*$ were estimated using random regressions on the additive genetic and within-lactation permanent environmental effects. Greater $\stackrel{?}{\text{b}}*$ value (i.e., more yellow color) was evident in milk from Jersey cows. Milk $\stackrel{?}{\text{L}}*$ increased consistently with stage of lactation, whereas $\stackrel{?}{\text{a}}*$ increased until mid lactation to subsequently plateau. Milk $\stackrel{?}{\text{b}}*$ deteriorated until 31 to 60 DIM, but then improved thereafter until the end of lactation. Relative to multiparous cows, milk yielded by primiparae was, on average, lighter (i.e., greater $\stackrel{?}{\text{L}}*$), more red (i.e., greater $\stackrel{?}{\text{a}}*$), and less yellow (i.e., lower $\stackrel{?}{\text{b}}*$). Milk from the morning milk session had lower $\stackrel{?}{\text{L}}*,\stackrel{?}{\text{a}}*,$ and $\stackrel{?}{\text{b}}*$ Heritability estimates (±SE) for milk color varied between 0.15 ± 0.02 (30 DIM) and 0.46 ± 0.02 (210 DIM) for $\stackrel{?}{\text{L}}*$, between 0.09 ± 0.01 (30 DIM) and 0.15 ± 0.02 (305 DIM) for $\stackrel{?}{\text{a}}*$, and between 0.18 ± 0.02 (21 DIM) and 0.56 ± 0.03 (305 DIM) for $\stackrel{?}{\text{b}}*$ For all the 3 milk color features, the within-trait genetic correlations approached unity as the time intervals compared shortened and were generally <0.40 between the peripheries of the lactation. Strong positive genetic correlations existed between $\stackrel{?}{\text{b}}*$ value and milk fat concentration, ranging from 0.82 ± 0.19 at 5 DIM to 0.96 ± 0.01 at 305 DIM and confirming the observed phenotypic correlation (0.64, SE = 0.01). Results of the present study suggest that breeding strategies for the enhancement of milk color traits could be implemented for dairy cattle populations. Such strategies, coupled with the knowledge of milk color traits variation due to nongenetic factors, may represent a tool for the dairy processors to reduce, if not eliminate, the use of artificial pigments during milk manufacturing.     

Factors associated with body temperature of healthy Holstein dairy cows during the first 10 days in milk

In this prospective observational study rectal and vaginal temperature of 82 (26 primiparous, 56 multiparous) early post-partum healthy dairy cows that calved without intervention within 3 months and did not show clinical signs of infectious and metabolic diseases were continuously measured and evaluated for associations with plausible factors during the first 10 days in milk (DIM). During May, June and July mean (±SD) temperature humidity index (THI) was 60·1±5; 66·8±5·6 and 74·2±4·3, respectively. Environmental conditions had a negligible effect on body temperature (BT) during May (P<0·05). During June and July, however, the ambient temperature and THI influenced BT (P<0·05). Furthermore, plausible factors like parity, DIM, months and time of day had an effect on BT (P<0·05). Overall, primiparous cows demonstrated 0·2°C greater BT during the first 10 DIM than multiparous cows. The effect of parity, however, on BT varied between DIM according to month (P<0·001). During this 3-month study period all cows demonstrated BT rhythms; however, the amplitude of BT increased from May to July (0·3 to 0·7°C). A greater proportion of the vaginal temperature measurements exceeded a threshold tested (≥39·5°C) during July (46·8%) than in June (33·9%) and May (19·3%). Overall the percentage of BT values above a threshold of ≥39·5°C was lower during the period 6.00-10.00 compared with the remaining 20 h (P<0·05). Therefore this study concluded that the BT of healthy post-partum dairy cows during the period 1-10 DIM post partum is greater compared with the reference range of 38·6 to 39·5°C reported by others and is influenced by parity, DIM, time of day and THI. When the association between BT and THI increased the reliability of threshold levels of BT (≥39·5°C) decreased.     

Factors associated with milk processing characteristics predicted by mid-infrared spectroscopy in a large database of dairy cows

Despite milk processing characteristics being important quality traits, little is known about the factors underlying their variability, due primarily to the resources required to measure these characteristics in a sufficiently large population. Cow milk coagulation properties (rennet coagulation time, curd-firming time, curd firmness 30 and 60 min after rennet addition), heat coagulation time, casein micelle size, and pH were generated from available mid-infrared spectroscopy prediction models. The prediction models were applied to 136,807 spectra collected from 9,824 Irish dairy cows from research and commercial herds. Sources of variation were investigated using linear mixed models that included the fixed effects of calendar month of test; milking time in the day; linear regressions on the proportion of Friesian, Jersey, Montbéliarde, Norwegian Red, and “other” breeds in the cow; coefficients of heterosis and of recombination loss; parity; stage of lactation; and the 2-way interaction parity × stage of lactation. Within- and across-parity cow effects, contemporary group, and a residual term were also included as random effects in the model. Supplementary analyses considered the inclusion of either test-day milk yield or milk protein concentration as fixed-effects covariates in the multiple regression models. Milk coagulation properties were most favorable (i.e., short rennet coagulation time and strong curd firmness) for cheese manufacturing in early lactation, concurrent with the lowest values of both pH and casein micelle size. Milk coagulation properties and pH deteriorated in mid lactation but improved toward the end of lactation. In direct contrast, heat coagulation time was more favorable in mid lactation and less suitable (i.e., shorter) for high temperature treatments in both early and late lactation. Relative to multiparous cows, primiparous cows, on average, yielded milk with shorter rennet coagulation time and longer heat coagulation time. Milk from the evening milking session had shorter rennet coagulation time and greater curd firmness, as well as lower heat coagulation time and lower pH compared with milk from the morning session. Jersey cows, on average, yielded milk more suitable for cheese production rather than for milk powder production. When protein concentration was included in the model, the improvement of milk coagulation properties toward the end of lactation was no longer apparent. Results from the present study may aid in decision-making for milk manufacturing, especially in countries characterized by a seasonal supply of fresh milk.     

Factors associated with concentrations of select cytokine and acute phase proteins in dairy cows with naturally occurring clinical mastitis

The objective of the current observational study was to determine the potential associations between cow factors, clinical mastitis (CM) etiology, and concentrations of select acute phase proteins and cytokines in milk from affected quarters of cows with CM. Cows with CM (n = 197) were grouped based on systemic disease severity, milk culture result, parity, days in milk (DIM), previous CM occurrence, and season of the year when CM occurred. Concentrations of lipopolysaccharide-binding protein (LBP), haptoglobin (Hp), BSA, IFN-γ, tumor necrosis factor-α (TNF-α), IL-1β, IL-8, IL-10, IL-12, transforming growth factor (TGF)-α, and TGF-β and activity of lactate dehydrogenase (LDH) were evaluated. Differences in the least squares means log₁₀ transformed concentrations of these proteins were compared using multiple linear regression mixed models. The milk concentrations of LBP, Hp, IL-1β, IL-10, and IL-12, and activity of LDH in milk were higher in cows with moderate to severe versus mild systemic disease. The concentrations of Hp, BSA, IL-1β, and IL-10 in milk were higher in cows with a gram-negative versus gram-positive milk culture result. Season of the year when CM occurred was associated with the concentration of all proteins evaluated except for IL-1β and IL-12. Concentrations were higher in the winter versus summer except for Hp and TGF-β, for which the opposite was true. Concentrations of LBP, IL-10, and IL-12, and LDH activity in milk were associated with DIM group. Except for LBP, these proteins were lower in cows with CM during the first 60 DIM versus those in mid or later lactation. Interferon-γ, TNF-α, and IL-8 were undetectable in 67, 31, and 20% of samples, respectively. Detection of IFN-γ and IL-8 was associated with season, and detection of TNF-α and IL-8 was associated with systemic disease severity. The current study provides the most comprehensive report of milk concentrations of innate immune response proteins in cows with naturally occurring CM and identifies factors that potentially influence those concentrations. Further investigation into the seasonal variation of cytokine production and its potential effect on the outcome of CM is warranted. Furthermore, the results of this study provide useful data for planning future studies examining the role of the innate immune response in CM.     

Effects of supplementing dairy cows with chromium propionate on milk and tissue chromium concentrations

Eight primiparous and 8 multiparous Holstein cows were used to determine the effects of Cr supplementation, in the form of Cr propionate (Cr Prop), on milk and tissue Cr concentrations. Cows were randomly assigned by parity to one of 2 diets: 1) control diet or 2) 2 mg of supplemental Cr/kg of DM. The level of Cr Prop supplemented exceeded by 4-fold the concentration of 0.5 mg of Cr/kg permitted by the FDA. Experimental diets were fed from approximately 30 d prepartum until at least 91 d postpartum, resulting in a minimum of 121 d of exposure to supplemental Cr. The control prepartum and postpartum diets analyzed 0.48 and 0.38 mg of Cr/kg of DM, respectively. Milk samples were obtained from the a.m. milking on d 0 (colostrum), 7, 14, 21, 28, 42, 56, 77, and 90 and on the final day of the study for Cr analysis. Cows were harvested after lactating for a minimum of 91 d and samples of liver, kidney, semitendinosus muscle, and fat were obtained for Cr analysis. Chromium was measured using electrothermal atomic absorption spectrophotometry. Milk Cr concentration averaged 1.7 ng/mL and was affected by day of lactation but not by Cr or a Cr × day interaction. Supplementation of 2 mg of Cr/kg of DM increased kidney Cr by approximately 3-fold and liver Cr concentrations by approximately 2-fold. Chromium concentrations in muscle and fat were not affected by Cr supplementation. In summary, supplementation of Cr Prop at a level of 2 mg of Cr/kg of DM did not affect Cr concentration in milk, muscle, or fat, the major bovine products consumed by humans.     

Correlations of milk and serum element concentrations with production and management traits in dairy cows

The present study investigated the potential consequences, positive or negative, that selection for favorable production-related traits may have on concentrations of vitamin B₁₂ and key chemical elements in dairy cow milk and serum and the possible impact on milk healthiness, and associated benefits, for the dairy product consumer. Milk and serum samples (950 and 755, respectively) were collected from Holstein-Friesian dairy cows (n = 479) on 19 occasions over a 59-mo period, generating 34,258 individual records, and analyzed for concentrations of key trace and quantity elements, heavy metals, and milk vitamin B₁₂. These data were then matched to economically important production data (milk, fat, and protein yield) and management data (dry matter intake, liveweight, and body condition score). Multivariate animal models, including full pedigree information, were used to analyze data and investigate relationships between traits of interest. Results highlighted negative genetic correlations between many quantity and trace elements in both milk and serum with production and management traits. Milk yield was strongly negatively correlated with the milk quantity elements Mg and Ca (genetic correlation between traits, r_a = ?0.58 and ?0.63, respectively) as well as the trace elements Mn, Fe, Ni, Cu, Zn, and Mo (r_a = ?0.32, ?0.58, ?0.52, ?0.40, ?0.34, and ?0.96, respectively); and in serum, Mg, Ca, Co, Fe, and Zn (r_a = ?0.50, ?0.36, ?0.68, ?0.54, and ?0.90, respectively). Strong genetic correlations were noted between dry matter intake with V (r_a = 0.97), Fe (r_a = ?0.69), Ni (r_a = ?0.81), and Zn (r_a = ?0.75), and in serum, strong negative genetic correlations were observed between dry matter intake with Ca and Se (r_a = ?0.95 and ?0.88, respectively). Body condition score was negatively correlated with serum P, Cu, Se, and Pb (r_a = ?0.45, ?0.35, ?0.51, and ?0.64, respectively) and positively correlated with Mn, Fe, and Zn (r_a = 0.40, 0.71, and 0.55, respectively). Our results suggest that breeding strategies aimed at improving economically important production-related traits would most likely result in a negative impact on levels of beneficial nutrients within milk for human consumption (such as Mg, Ca, Fe, Zn, and Se).     

Phenotypic and genetic analysis of milk and serum element concentrations in dairy cows

Enhancing micronutrient (i.e., mineral and vitamin) concentrations within milk and serum from dairy cows is important for both the health of the cow and the nutritive value of the milk for human consumption. However, a good understanding of the genetics underlying the micronutrient content in dairy cattle is needed to facilitate such enhancements through feeding or breeding practices. In this study, milk (n = 950) and serum (n = 766) samples were collected from Holstein-Friesian dairy cows (n = 479) on 19 occasions over a 59-mo period and analyzed for concentrations of important elements. Additionally, a subset of 256 milk samples was analyzed for concentrations of vitamin B₁₂. Cows belonged to 2 genetic lines (average and highest genetic merit for milk fat plus protein yield) and were assigned to 1 of 2 diets based on either a by-product or homegrown ration. Univariate models accounting for repeated records were used to analyze element and vitamin B₁₂ data and investigate the effect of genotype and feeding system as well as derive estimates of variance components and genetic parameters. Bivariate models were used to study correlations both within and between milk and serum. Only concentrations of Hg in milk were seen to be affected by genotype, with higher concentrations in cows with high genetic merit. In contrast, element concentrations were influenced by feeding system such that cows fed the homegrown diet had increased milk concentrations of Ca, Cu, I, Mn, Mo, P, and K and increased serum concentrations of Cd, Cu, Fe, Mo, and V. Cows on the by-product diet had increased milk concentrations of Mg, Se, and Na and increased serum concentrations of P and Se. Heritability (h²) estimates were obtained for 6 milk and 4 serum elements, including Mg (h²_milk = 0.30), K (h²_serum = 0.18), Ca (h²_milk = 0.20; h²_serum = 0.12), Mn (h²_milk = 0.14), Cu (h²_serum = 0.22), Zn (h²_milk = 0.24), Se (h²_milk = 0.15; h²_serum = 0.10), and Mo (h²_milk = 0.19). Significant estimates of repeatability were observed in all milk and serum quantity elements (Na, Mg, P, K, and Ca) as well as 5 milk and 7 serum trace elements. Only K in milk and serum was found to have a significant positive genetic and phenotypic correlation (0.52 and 0.22, respectively). Significant phenotypic associations were noted between milk and serum Ca (0.17), Mo (0.19), and Na (−0.79). Additional multivariate analyses between measures within sample type (i.e., milk or serum) revealed significant positive associations, both phenotypic and genetic, between some of the elements. In milk, Se was genetically correlated with Ca (0.63), Mg (0.59), Mn (0.40), P (0.53), and Zn (0.52), whereas in serum, V showed strong genetic associations with Cd (0.71), Ca (0.53), Mn (0.63), Mo (0.57), P (0.42), K (0.45), and Hg (−0.44). These results provide evidence that element concentrations in milk and blood of dairy cows are significantly influenced by both diet and genetics and demonstrate the potential for genetic selection and dietary manipulation to alter nutrient concentration to improve both cow health and the healthfulness of milk for human consumption.     

Genetic analysis of milk urea concentration and its genetic relationship with selected traits of interest in dairy cows

The aim of this study was to estimate genetic parameters of milk urea concentration (MU) and its genetic correlations with milk production traits, longevity, and functional traits in the first 3 parities in dairy cows. The edited data set consisted in 9,107,349 MU test-day records from the first 3 parities of 560,739 cows in 2,356 herds collected during the years 1994 to 2020. To estimate the genetic parameters of MU, data of 109 randomly selected herds, with a total of 770,016 MU test-day records, were used. Genetic parameters and estimated breeding values were estimated using a multiple-trait (parity) random regression model. Herd-test-day, age-year-season of calving, and days in milk classes (every 5 d as a class) were used as fixed effects, whereas effects of herd-year of calving, permanent environment, and animal were modeled using random regressions and Legendre polynomials of order 2. The average daily heritability and repeatability of MU during days in milk 5 to 365 in the first 3 parities were 0.19, 0.22, 0.20, and 0.48, 0.48, 0.47, respectively. The mean genetic correlation estimated among MU in the first 3 parities ranged from 0.96 to 0.97. The average daily estimated breeding values for MU of the selected bulls (n = 1,900) ranged from −9.09 to 7.37 mg/dL. In the last 10 yr, the genetic trend of MU has gradually increased. The genetic correlation between MU and 11 traits of interest ranged from –0.28 (milk yield) to 0.28 (somatic cell score). The findings of this study can be used as the first step for development of a routine genetic evaluation for MU and its inclusion into the genetic selection program in the Walloon Region of Belgium.     

Effects of iodine intake and teat-dipping practices on milk iodine concentrations in dairy cows

Two studies were conducted to determine the effects of dietary iodine and teat-dipping practices on iodine concentrations in milk. In the first study, 63 cows in mid lactation were assigned to a 3×3 factorial design in which the main effects were dietary iodine levels (0.3, 0.6, and 0.9 mg of dietary I/kg of dry matter) and 3 different postdip managements (chlorhexidine with dip cup, 1% iodine dip cup, and 1% iodine by manual spray). During the 13-d pre-experimental period and the 15-d experimental period, noniodized sanitizers were used in premilking management. During the pre-experimental period, the levels of milk iodine averaged 241.2±5.8 μg/kg, and no relationship was found with lactation number, days in milk, or milk production. Milk iodine concentrations increased linearly with iodine intake. Although teat dipping with 1% iodine had no effect on milk iodine concentration, the same solution applied by spraying greatly increased milk iodine levels. The second study was conducted to determine the effects of udder preparation before milking on milk iodine concentrations. Thirty-two lactating cows were assigned to 4 treatments: no predip (Con); predip with a predip solution containing 0.5% iodine+complete cleaning (Comp); predip with a postdip solution containing 1% iodine+complete cleaning (Post); and predip with a predip solution containing 0.5% iodine+incomplete cleaning (Inc). During the 14-d pre-experimental period and the 19-d experimental period, cows were fed the same diet, and noniodized sanitizers were used for postmilking dipping. During the last week of treatment, milk iodine averaged 164, 189, 218, and 252±9.8 μg/kg for Con, Comp, Post, and Inc, respectively. Preplanned orthogonal contrasts indicated that predipping with a 0.5% iodine predip solution completely wiped off (Comp) tended to increase milk iodine content above that of the control and that the iodine content of Post and Inc were higher than that of the Comp treatment. The results of the first experiment confirm that, to preserve milk safety, iodine should not be fed above requirements. Spraying iodine-based teat-dipping solutions results in large increases in milk iodine content and should be avoided. Predipping teats with an iodine-based sanitizer is an acceptable practice, but must be performed with the appropriate product and completely wiped off before milking.     

Effects of milk urea nitrogen and other factors on probability of conception of dairy cows

The objective of this study was to evaluate the relationships between milk urea nitrogen (MUN) and other factors and the probability of conception in dairy cows. Data were retrieved from the Lancaster Dairy Herd Improvement Association (DHIA). A total of 713 dairy herds and 10,271 dairy cows were included in the study. Logistic regression was used to determine the within-herd effects of MUN, milk production, lactation number, and breeding season on the probability of conception for each of 3 services. Within herds, MUN displayed a slight negative association with probability of conception at first service. For example, there was a 2- to 4-percentage unit decrease in conception rate at first service with a 10-mg/dL increase in MUN. In among-herd regression analysis, there was no effect of MUN on probability of conception. These results suggest that MUN may be related to conditions affecting reproduction of individual cows within a herd. Diet formulation usually would affect MUN equally among all cows at a similar stage of lactation in a herd. Because there was no effect of MUN among herds, diet formulation did not appear to affect conception rate.     

Factors associated with occurrence and recovery of nonambulatory dairy cows in the United States

The primary objective of this study was to compare characteristics of US dairy operations that had one or more nonambulatory cows (unable to rise for any period of time) (cases) with operations that had no nonambulatory cows (controls) during 2004. A secondary objective was to describe factors associated with recovery of the last nonambulatory cow on the operation during 2004. Case dairy operations (n = 1,822) more often fed a total mixed ration [odds ratio (OR) = 2.0; confidence interval (CI): 1.1-3.4], produced more than 9,090 kg of milk (OR = 2.8; CI: 1.8-4.5), and were more likely to be of medium to large herd size (100 or more head of adult cows, O  = 3.7; CI: 2.2-6.2) compared with control dairies (n = 151). Compared with operations where the predominant flooring surface on which lactating cows stood or walked in winter was pasture, operations where pasture was not the predominant surface were at increased risk of having nonambulatory cows (OR = 4.7; CI: 2.2-10.2). Cows nonambulatory for less than 24 h were more likely to recover compared with cows nonambulatory for 24 h or more (OR = 3.0; CI: 2.0-4.4). Cows that received calcium, phosphorus, or potassium while non-ambulatory were more likely to recover (OR = 3.6; CI: 2.1-6.1) than cattle that did not receive these treatments. Cattle that were not repositioned periodically were more likely to recover (OR = 2.1; CI: 1.4-3.1), as were cattle that were not treated by a veterinarian before becoming nonambulatory (OR = 1.9; CI: 1.1-3.3). These findings are consistent with prolonged recumbency and prior history of health issues, respectively. Nonambulatory cattle with hypocalcemia were more likely to recover (OR = 6.0; CI: 3.4-10.7) compared with nonambulatory cows with all other causes of a nonambulatory condition (analyzed collectively as a single variable but including cancer, clinical mastitis, digestive conditions, metabolic imbalances, neurological problems, respiratory disease, other, unknown). The results of this study reveal that the majority of US dairy operations have at least one nonambulatory dairy cow over the course of a year. Additionally, individual animal factors associated with being nonambulatory may lead to improved identification and treatment of animals that are nonambulatory for a prolonged period. From the perspective of recovery, considering euthanasia is appropriate for cows that have been nonambulatory for more than 24 h.