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See detailAccounting for heterogeneous variances in multi-trait evaluation of Jersey type traits
Gengler, Nicolas ULg; Wiggans, G. R.; Thornton, L. et al

in Journal of Dairy Science (2005), 88(Suppl. 1), 11-11

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See detailEffect of carprofen treatment following experimentally induced Escherichia coli mastitis in primiparous cows.
Vangroenweghe, F.; Duchateau, L.; Boutet, Philippe ULg et al

in Journal of Dairy Science (2005), 88(7), 2361-2376

Acute Escherichia coli mastitis is one of the major sources of economic loss in the dairy industry due to reduced milk production, treatment costs, discarded milk, and occasional fatal disease ... [more ▼]

Acute Escherichia coli mastitis is one of the major sources of economic loss in the dairy industry due to reduced milk production, treatment costs, discarded milk, and occasional fatal disease. Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used as adjunctive therapy to antibiotics. The objective of the current study was to evaluate the effect of carprofen treatment following infusion of Escherichia coli into the mammary glands of primiparous cows during the periparturient period. Severity of mastitis was scored based on the average milk production in the uninfected quarters on d +2 postinoculation and a clinical severity score. Carprofen was administered intravenously at 9 h postchallenge, when clinical signs of mastitis appeared. In previous work, efficacy of NSAIDs was mainly evaluated using clinical symptoms. In the present study, the effect of carprofen on innate immune response was also assessed by quantification of inflammatory mediators. All primiparous cows reacted as moderate responders throughout the experimental period. Primiparous cows were intramammarily inoculated with 1 x 10(4) cfu of E. coli P4:O32 in 2 left quarters. Analysis of blood and milk parameters, including IL-8, complement component C5a, lipopolysaccharide-binding protein (LBP), soluble CD14, prostaglandin E2, and thromboxane B2 was performed from d 0 to d +6 relative to intramammary inoculation. Rectal temperature in carprofen-treated animals was lower than in control animals at 3 and 6 h posttreatment. Treatment also restored the decreased reticulorumen motility that occurs during E. coli mastitis to preinfection levels faster than in control animals. Carprofen treatment resulted in an earlier normalization of the clinical severity score. Eicosanoid (prostaglandin E2 and thromboxane B2) production in milk tended to be inhibited by carprofen. No significant differences in the kinetic patterns of somatic cell count, IL-8, complement component C5a, LBP, and soluble CD14 were observed. In conclusion, carprofen treatment improved general clinical condition by effective antipyrexia and restoration of reticulorumen motility but did not significantly inhibit eicosanoid production. Carprofen treatment did not result in a significant decrease of chemotactic inflammatory mediators, IL-8 and C5a, and early innate immune molecules, sCD14 and LBP. Therefore, major modulatory effects from NSAID administration were not observed in this mastitis model, although a larger study might confirm some apparent trends obtained in the present results. [less ▲]

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See detailShort communication: Pasteurization of milk abolishes bovine herpesvirus 4 infectivity.
Bona, C.; Dewals, Benjamin G ULg; Wiggers, L. et al

in Journal of Dairy Science (2005), 88(9), 3079-83

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus highly prevalent in the cattle population that has been isolated from the milk and the serum of healthy infected cows. Several studies reported the ... [more ▼]

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus highly prevalent in the cattle population that has been isolated from the milk and the serum of healthy infected cows. Several studies reported the sensitivity and the permissiveness of some human cells to BoHV-4 infection. Moreover, our recent study demonstrated that some human cells sensitive but not permissive to BoHV-4 support a persistent infection protecting them from tumor necrosis factor-alpha-induced apoptosis. Together, these observations suggested that BoHV-4 could represent a danger for public health. To evaluate the risk of human infection by BoHV-4 through milk or serum derivatives, we investigated the resistance of BoHV-4 to the mildest thermal treatments usually applied to these products. The results demonstrated that milk pasteurization and thermal decomplementation of serum abolish BoHV-4 infectivity by inactivation of its property to enter permissive cells. Consequently, our results demonstrate that these treatments drastically reduce the risk of human infection by BoHV-4 through treated milk or serum derivatives. [less ▲]

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See detailEstimated heterogeneity of phenotypic variance of test-day yield with a structural variance model
Gengler, Nicolas ULg; Wiggans, George; Gillon, Alain ULg

in Journal of Dairy Science (2004), 87

First-lactation test-day milk, fat, and protein yields from New York, Wisconsin, and California herds from 1990 through 2000 were adjusted additively for age and lactation stage. A random regression model ... [more ▼]

First-lactation test-day milk, fat, and protein yields from New York, Wisconsin, and California herds from 1990 through 2000 were adjusted additively for age and lactation stage. A random regression model with thirdorder Legendre polynomials for permanent environmental and genetic effects was used. The model included a random effect with the same polynomial regressions for 2 yr of calvings within herd (herd-time effect) to provide herd-specific lactation curves that can change every 2 yr. (Co)variance components were estimated using expectation-maximization REML simultaneously with phenotypic variances that were modeled using a structural variance model. Maximum heritability for test-day milk yield was estimated to be ∼20% around 200 to 250 d in milk; heritabilities were slightly lower for test-day fat and protein yields. Herd-time effects explained 12 to 20% of phenotypic variance and had the greatest impact at start of lactation. Variances of test-day yields increased with time, subclass size, and milking frequency. Test month had limited influence on variance. Variance increased for cows in herds with low and high milk yields and for early and late lactation stages. Repeatabilities of variances observed for a given class of herd, test-day, and milking frequency were 14 to 17% across nested variance subclasses based on lactation stage. [less ▲]

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See detailDelayed neutrophil apoptosis in bovine subclinical mastitis.
Boutet, Philippe ULg; Boulanger, D.; Gillet, Laurent ULg et al

in Journal of Dairy Science (2004), 87(12), 4104-4114

Bovine subclinical mastitis can be defined as a moderated inflammatory disease characterized by a persistent accumulation of neutrophils in milk. As GMCSF-mediated delay of neutrophil apoptosis ... [more ▼]

Bovine subclinical mastitis can be defined as a moderated inflammatory disease characterized by a persistent accumulation of neutrophils in milk. As GMCSF-mediated delay of neutrophil apoptosis contributes to the accumulation of inflammatory cells at the site of inflammation in many human diseases, we sought to determine whether subclinical mastitis in cows is also associated with a GMCSF-dependent increase in milk-neutrophil survival. We first addressed the hypothesis that GMCSF delays bovine neutrophil apoptosis by activation of the signal transducer and activator of transcription (STAT) family members STAT3 and STAT5, which are critical regulators of the expression of various Bcl-2 family proteins. Granulocyte-macrophage colony-stimulating factor significantly delayed apoptosis of blood neutrophils obtained from healthy cows. In these cells, GMCSF activated STAT5, but not STAT3, and induced an increase in the mRNA of the antiapoptotic Bcl-2 member, Bcl-xL. Granulocyte-macrophage colony-stimulating factor-dependent STAT5 activation and up-regulation of Bcl-xL mRNA were blocked by the Jak inhibitor, AG-490. This inhibition was associated with abrogation of the prosurvival effect of GMCSF, demonstrating a key role for STAT5 in delayed neutrophil apoptosis. We further found that GMCSF expression was increased in milk cells from cows affected with subclinical mastitis. Neutrophils from these cows demonstrated a significant delay of apoptosis as compared with neutrophils obtained from healthy cows and were unresponsive to GMCSF. Active STAT5 complexes were detected in these neutrophils. Finally, in the presence of AG-490, apoptosis was induced and a time-dependent down-regulation of Bcl-xL mRNA was observed in milk neutrophils from mastitis-affected cows. These results indicate that neutrophil survival is enhanced in milk of subclinical mastitis-affected cows and suggest a role for a GMCSF-activated STAT5 signaling pathway in this phenomenon. This pathway could thus represent a target for the control of persistent accumulation of neutrophils in the bovine mammary gland [less ▲]

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See detailSomatic Cell (Neutrophil) Counts in the War Against Staphylococcus aureus: Predator-Prey Models at the Rescue
Detilleux, Johann ULg

in Journal of Dairy Science (2004), 87(11), 3716-3724

To address the question of whether a minimum concentration of blood neutrophils is necessary to decrease Staphylococcus aureus concentration in mastitic milk, literature was searched for studies in which ... [more ▼]

To address the question of whether a minimum concentration of blood neutrophils is necessary to decrease Staphylococcus aureus concentration in mastitic milk, literature was searched for studies in which neutrophils were incubated with Staph. aureus. Different mathematical models that describe the changes in Staph. aureus population as a function of neutrophilic concentrations were applied to the collected data. The best fitted model established (1) that the rate of bacterial killing depended on the ratio of neutrophils to bacteria with neutrophilic attack rate accelerating at first before decelerating as the ratio increases, and (2) that neutro-phil concentration should be within a limited range to trigger a decline in the bacterial population. Outcomes of this model are supported by what is known about neutrophilic functions and laboratory findings in bovine and human neutrophils. These results may be of assistance in setting selection goals for a better resilience to Staph. aureus mastitis in dairy cattle. Indeed, an optimal neutrophilic concentration appears to exist for successful clearance of Staph. aureus infection, which is neither the lowest nor the highest one. [less ▲]

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See detailType trait (co)variance components for five dairy breeds
Wiggans, G. R.; Gengler, Nicolas ULg; Wright, J. R.

in Journal of Dairy Science (2004), 87(7), 2324-2330

(Co)variance components were estimated for final score and 14 or 15 linear type traits for the Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn breeds. Appraisals from 1995 or later were ... [more ▼]

(Co)variance components were estimated for final score and 14 or 15 linear type traits for the Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn breeds. Appraisals from 1995 or later were used. New estimates were calculated to accommodate changes in scoring of traits and because of a change from multiplicative to additive adjustment for age and lactation stage. The adjustment method was changed for better support of the adjustment for heterogeneous variance within iteration, which was implemented in 2002. The largest changes in heritability were an increase of 0.10 for rump angle for Milking Shorthorns and a decrease of 0.11 for udder depth for Jerseys. The new estimates of (co)variance components should provide improved accuracy of type evaluations, particularly for traits that have had variance changes over time. [less ▲]

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See detailPrediction of daily milk, fat, and protein production by a random regression test-day model
Mayeres, P.; Stoll, J.; Bormann, J. et al

in Journal of Dairy Science (2004), 87(6), 1925-1933

Test-day genetic evaluation models have many advantages compared with those based on 305-d lactations; however, the possible use of test-day model (TDM) results for herd management purposes has not been ... [more ▼]

Test-day genetic evaluation models have many advantages compared with those based on 305-d lactations; however, the possible use of test-day model (TDM) results for herd management purposes has not been emphasized. The aim of this paper was to study the ability of a TDM to predict production for the next test day and for the entire lactation. Predictions of future production and detection of outliers are important factors for herd management (e. g., detection of health and management problems and compliance with quota). Because it is not possible to predict the herd-test-day (HTD) effect per se, the fixed HTD effect was split into 3 new effects: a fixed herd-test month-period effect, a fixed herd-year effect, and a random HTD effect. These new effects allow the prediction of future production for improvement of herd management. Predicted test-day yields were compared with observed yields, and the mean prediction error computed across herds was found to be close to zero. Predictions of performance records at the herd level were even more precise. Discarding herds enrolled in milk recording for <1 yr and animals with very few tests in the evaluation file improved correlations between predicted and observed yields at the next test day (correlation of 0.864 for milk in first-lactation cows as compared with a correlation of 0.821 with no records eliminated). Correlations with the observed 305-d production ranged from 0.575 to 1 for predictions based on 0 to 10 test-day records, respectively. Similar results were found for second and third lactation records for milk and milk components. These findings demonstrate the predictive ability of a TDM. [less ▲]

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See detailIncreased nuclear Factor kappa B activity in milk cells of mastitis-affected cows
Boulanger, D.; Bureau, Fabrice ULg; Melotte, D. et al

in Journal of Dairy Science (2003), 86(4), 1259-1267

Bacterial mastitis is accompanied by a drastic increase in milk somatic cell count (SCC), with neutrophils being the predominant cell type found in the infected quarters. Accumulation and activation of ... [more ▼]

Bacterial mastitis is accompanied by a drastic increase in milk somatic cell count (SCC), with neutrophils being the predominant cell type found in the infected quarters. Accumulation and activation of neutrophils at the site of infection require local expression of many inflammatory genes encoding adhesion molecules, chemokines and cytokines. Most of the inflammatory genes contain binding sites for the nuclear factor kappaB (NF-kappaB) within their promoter and therefore partly depend on NF-kappaB for their expression. We thus hypothesized that an increase in NF-kappaB activity in the mammary gland could contribute to development of the neutrophilic inflammation that characterizes mastitis. In an attempt to verify this hypothesis, we first assessed milk cells from healthy and acute and chronic mastitis-affected cows for NF-kappaB activity using electrophoretic mobility shift assays. We next studied the relationships between the intensity of NF-kappaB activity in these cells and the degree of udder inflammation. Active NF-kappaB complexes were undetectable in milk cells from healthy cows, whereas high levels of NF-kappaB activity were always found in cells from cows with acute mastitis. In milk cells obtained from chronic mastitis-affected cows, NF-kappaB activity varied from low to high. Finally, the level of NF-kappaB activity measured in milk cells from chronic mastitis-affected cows was not correlated to SCC or to the proportion of neutrophils present in milk samples, but was highly correlated with the expression level of interleukin-8 and granulocyte/macrophage colony-stimulating factor, two NF-kappaB-dependent cytokines crucially involved in initiation and perpetuation of neutrophilic inflammation. These results suggest that NF-kappaB might play a role in mastitis pathogenesis. [less ▲]

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See detailModeling lactation curves and estimation of genetic parameters for first lactation test-day records of French Holstein cows.
Druet, Tom ULg; Jaffrezic, F.; Boichard, D. et al

in Journal of Dairy Science (2003), 86(7), 2480-90

Several functions were used to model the fixed part of the lactation curve and genetic parameters of milk test-day records to estimate using French Holstein data. Parametric curves (Legendre polynomials ... [more ▼]

Several functions were used to model the fixed part of the lactation curve and genetic parameters of milk test-day records to estimate using French Holstein data. Parametric curves (Legendre polynomials, Ali-Schaeffer curve, Wilmink curve), fixed classes curves (5-d classes), and regression splines were tested. The latter were appealing because they adjusted the data well, were relatively insensitive to outliers, were flexible, and resulted in smooth curves without requiring the estimation of a large number of parameters. Genetic parameters were estimated with an Average Information REML algorithm where the average information matrix and the first derivatives of the likelihood functions were pooled over 10 samples. This approach made it possible to handle larger data sets. The residual variance was modeled as a quadratic function of days in milk. Quartic Legendre polynomials were used to estimate (co)variances of random effects. The estimates were within the range of most other studies. The greatest genetic variance was in the middle of the lactation while residual and permanent environmental variances mostly decreased during the lactation. The resulting heritability ranged from 0.15 to 0.40. The genetic correlation between the extreme parts of the lactation was 0.35 but genetic correlations were higher than 0.90 for a large part of the lactation. The use of the pooling approach resulted in smaller standard errors for the genetic parameters when compared to those obtained with a single sample. [less ▲]

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See detailImbalance between lipoxin A(4) and leukotriene B-4 in chronic mastitis-affected cows
Boutet, Philippe ULg; Bureau, Fabrice ULg; Degand, Guy ULg et al

in Journal of Dairy Science (2003), 86(11), 3430-3439

Persistent accumulation of inflammatory cells in the udder, with neutrophils being the predominant cell type, is a characteristic feature of chronic mastitis in dairy cows. Leukotriene (LT) B-4 is a ... [more ▼]

Persistent accumulation of inflammatory cells in the udder, with neutrophils being the predominant cell type, is a characteristic feature of chronic mastitis in dairy cows. Leukotriene (LT) B-4 is a potent chemotactic agent, known to induce recruitment and accumulation of neutrophils in the bovine mammary gland. The LTB4-stimulated neutrophil functional responses are closely opposed by lipoxin (LX) A(4), which promotes the resolution of inflammation. We thus hypothesized that the chronic inflammation of the udder could be associated with an unfavorable ratio between these two eicosanoids and that the persistence of neutrophil accumulation could be due to an increase in LTB4 synthesis and/or an impaired LXA(4) production. In an attempt to verify this hypothesis, we first measured LXA(4), LTB4, and their ratio in the milk of healthy and acute and chronic mastitis-affected quarters. Next, we studied the relationships between these variables and the degree of udder inflammation as assessed by somatic cell count measurement. The LTB4 concentration was low in healthy quarters, drastically increased in acute mastitis, and reached intermediate levels in chronic mastitis-affected quarters. However, whereas LXA(4) concentration was highly increased in acute mastitis, healthy and chronic quarters had similarly low values. The LXA(4):LTB4 ratio was thus significantly lower in chronic mastitis-affected cows. The LTB4 concentrations measured in chronic quarters were highly correlated to somatic cell count and to milk neutrophil and macrophage numbers. A weaker correlation was observed between LXA(4) and these variables. For both eicosanoids, the highest correlation was observed with the number of neutrophils. These results show the existence of an LXA(4):LTB4 imbalance in chronic mastitis-affected cows because of low LXA(4) concentrations. Further studies are needed to determine whether administration of LX or stable analogs could have therapeutic potential in the control of chronic bovine mastitis. [less ▲]

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See detailWithin-herd effects of age at test day and lactation stage on test-day yields
Bormann, J.; Wiggans, G. R.; Druet, Tom ULg et al

in Journal of Dairy Science (2003), 86(11), 3765-3774

Variance ratios were estimated for random within-herd effects of age at test day and lactation stage, on test-day yield and somatic cell score to determine whether including these effects would improve ... [more ▼]

Variance ratios were estimated for random within-herd effects of age at test day and lactation stage, on test-day yield and somatic cell score to determine whether including these effects would improve the accuracy of estimation. Test-day data starting with 1990 calvings for the entire US Jersey population and Holsteins from California, Pennsylvania, Wisconsin, and Texas were analyzed. Test-day yields were adjusted for across-herd effects using solutions from a regional analysis. Estimates of the relative variance ( fraction of total variance) due to within-herd age effects were small, indicating that regional adjustments for age were adequate. The relative variances for within-herd lactation stage were large enough to indicate that accuracy of genetic evaluations could be improved by including herd stage effects in the model for milk, fat, and protein, but not for somatic cell score. Because the within-herd lactation stage effect is assumed to be random, the effect is regressed toward the regional effects for small herds, but in large herds, lactation curves become herd specific. Model comparisons demonstrated the greater explanatory power of the model with a within-herd-stage effect as prediction error standard deviations were greater for the model without this effect. The benefit of the within-herd-stage effects was confirmed in a random regression model by comparing variance components from models with and without random within-herd regressions and through log-likelihood ratio tests. [less ▲]

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See detailEstimating effects of permanent environment, lactation stage, age, and pregnancy on test-day yield.
Bormann, J.; Wiggans, G. R.; Philpot, J. C. et al

in Journal of Dairy Science (2002), 85(1), 2631-26321

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See detailDeriving lactation yields from test-day yields adjusted for lactation stage, age, pregnancy, and herd test date
Wiggans, G. R.; VanRaden, P. M.; Bormann, J. et al

in Journal of Dairy Science (2002), 85

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See detailAdditive and dominance genetic variance of fertility by method R and preconditioned conjugate gradient
Druet, Tom ULg; Solkner, J.; Groen, A. F. et al

in Journal of Dairy Science (2001), 84(4), 9871-98716

The objectives of this study were threefold: 1) estimation of additive and dominance genetic variances for fertility traits for Austrian Simmental and Brown Swiss dairy cattle; 2) use of method R and the ... [more ▼]

The objectives of this study were threefold: 1) estimation of additive and dominance genetic variances for fertility traits for Austrian Simmental and Brown Swiss dairy cattle; 2) use of method R and the preconditioned conjugate gradient compared to solving for method R by second-order Jacobi iteration; and 3) study of the impact of inclusion of parental subclass effects on solutions for other random effects. Dominance variances were modeled for the inseminated cow and ranged from 0.32 to 1.36% of total variance. These values were similar to values for additive effects, which were approximately 1% of total variance. Convergence was clearly improved with preconditioned conjugate gradient and number of extrapolations reduced. Variance for permanent environment under a model without dominance could be split into a new estimate of permanent environmental variance and parental subclass variance. Solutions for parental subclass dominance effects were approximately proportional to permanent environment effects, but highly dependent on the number of animals contributing dominance relationships, especially full-sibs and three-quarter-sibs. For animals with a lot of dominance information (full-sibs, three-quarter-sibs, cousins), permanent environment and parental subclass dominance effects were nearly independent. Changes in additive effects were negligible, probably because both variances for parental subclass dominance effects and additive genetic effects were very small compared with residual variance. [less ▲]

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See detailHeterogeneity of (co)variance components for Jersey type traits
Gengler, Nicolas ULg; Dusseldorf, T.; Wiggans, G. R. et al

in Journal of Dairy Science (2001), 84

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See detailAssociations between casein haplotypes and first lactation milk production traits in Finnish Ayrshire cows
Ikonen, T.; Bovenhuis, H.; Ojala, M. et al

in Journal of Dairy Science (2001), 84(2), 507-514

The objective of this study was to estimate the effects of ß--casein (CN) haplotypes on first-lactation milk production traits. The ß--CN haplotypes were deduced using information on ß- and -CN genotypes ... [more ▼]

The objective of this study was to estimate the effects of ß--casein (CN) haplotypes on first-lactation milk production traits. The ß--CN haplotypes were deduced using information on ß- and -CN genotypes of cows and their sires for 16,973 Finnish Ayrshire cows that had at least nine paternal half sibs. Effects of CN haplotypes on milk production traits were estimated for one haplotype at a time using an animal model, which included the fixed effects for calving year and month, age at calving, days open, ß-lactoglobulin, and a ß--CN haplotype. Differences in milk production traits were also estimated between haplotype combinations A1A+A2B and A1B+A2A within ß--CN genotype A1A2AB and between combinations A1E+A2A and A1A+A2E within genotype A1A2AE. The ß--CN haplotypes A2A and A2B were associated with high milk and protein yields and low fat content, and those that included the ß-CN A1 allele were associated with low yields and high fat content. Protein content was affected by the -CN locus; haplotype A1B was associated with high protein content and A1E was with low protein content. The haplotype combination A1A+A2B was associated with 140 kg more milk yield (P = 0.045) and 0.03 percentage units less protein content (P = 0.055) than combination A1B+A2A, and combination A1A+A2E showed 0.02 percentage units greater protein content (P = 0.098) than A1E+A2A. These results indicate that genes linked to the CN loci contribute to the variation in milk yield and protein content. [less ▲]

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See detailEstimation of (co)variance functions for test-day yields during first and second lactations in the United States
Gengler, Nicolas ULg; Tijani, A.; Wiggans, G. R. et al

in Journal of Dairy Science (2001), 82

(Co)variance components for milk, fat, and protein yields during first and second lactations were estimated from test-day data from 23,029 Holstein cows from 37 herds in Pennsylvania and Wisconsin using a ... [more ▼]

(Co)variance components for milk, fat, and protein yields during first and second lactations were estimated from test-day data from 23,029 Holstein cows from 37 herds in Pennsylvania and Wisconsin using a multitrait test-day model. Canonical transformation was used with an expectation-maximization algorithm. To allow description of (co)variances within and across yield traits and parities, four lactation stages of 75 d were defined6 for each parity, and the test day nearest the center of each interval was used. Prior to analysis, data were adjusted for lactation curves within lactation stages using all records from all available cows. Data from cows with missing values were excluded to allow a canonical transformation to be used for estimation of (co)variance matrices. Data from 9110 cows were available for canonical analysis of lactations with test days in all lactation stages. (Co)variance functions were used to describe (co)variance structure within and across yield trait and parity. (Co)variance components of biological functions (305-d yield, persistency defined as difference between yields on d 280 and 60, and maturity rate defined as difference between second- and first-lactation yields) were developed from (co)variance functions. Heritabilities ranged from 0.09 to 0.22 for test-day yields, from 0.21 to 0.23 for 305-d yields, from 0.03 to 0.11 for persistencies, and from 0.05 to 0.07 for maturity rates. Phenotypic correlations between first- and second-lactation persistencies were low, but genetic correlations were high. Genetic correlations with maturity rate ranged from 0.11 to 0.61 for 305-d yields and persistencies. [less ▲]

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See detailApplication of a Mixed Normal Mixture Model for the Estimation of Mastitis-Related Parameters
Detilleux, Johann ULg; Leroy, P. L.

in Journal of Dairy Science (2000), 83(10), 2341-9

The current methodology for estimating genetic parameters for SCC (SCS) does not account for the difference in SCS between healthy cows and cows with an intramammary infection (IMI). We propose a two ... [more ▼]

The current methodology for estimating genetic parameters for SCC (SCS) does not account for the difference in SCS between healthy cows and cows with an intramammary infection (IMI). We propose a two-component finite mixed normal mixture model to estimate IMI prevalence, separate SCS subpopulation means, individual posterior probabilities of IMI, and SCS variance components. The theory is presented and the expectation-conditional maximization algorithm is utilized to compute maximum likelihood estimates. The methodology is illustrated on two simulated data sets based on the current knowledge of SCS parameters. Maximum likelihood estimates of IMI prevalence and SCS subpopulation means were close to simulated values, except for the estimate of IMI prevalence when both subpopulations were almost confounded. Individual posterior probabilities of IMI were always higher among infected than among healthy cows. Error and additive variance components obtained under the mixture model were closer to simulated values than restricted maximum likelihood estimates obtained assuming a homogeneous SCS distribution, especially when subpopulations were completely separated and when mixing proportion was highest. Convergence was linear and rapid when priors were chosen with caution. The advantages of the methodology are demonstrated, and its feasibility for large data sets is discussed. [less ▲]

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See detailA Homologous Radioimmunoassay For Quantification Of Insulin-Like Growth Factor-Binding Protein-2 In Blood From Cattle
Vleurick, Lieve; Renaville, Robert ULg; Vandehaar, M. et al

in Journal of Dairy Science (2000), 83(3), 452-458

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