Lactation Cell Count Research Articles

The association between high milk somatic cell counts in the first lactation and somatic cell counts in the second lactation

With the advent of web-based recording and analysis systems, individual cow composite somatic cell count (SCC) data are being increasingly used for decision support in mastitis control at both the individual cow and herd level. SCC data from first and second lactation dairy cows (n=1912) from 12 farms were analysed using multinomial logistic regression to investigate possible associations between high SCC patterns in the first lactation and the subsequent lactation. Animals with three non-consecutive counts >200,000 cells/mL in their first lactation were significantly more likely to have three non-consecutive counts >200,000 cells/mL (OR 3.11; 95% CI 1.72-5.62) or three consecutive counts >200,000 cells/mL (OR 2.00; 95% CI 1.09-3.68) in their second lactation. Similarly animals with three consecutive counts >200,000 cells/mL in their first lactation were significantly more likely to have three non-consecutive counts >200,000 cells/mL (OR 1.90; 95% CI 1.13-3.19) or three consecutive counts >200,000 cells/mL (OR 4.14; 95% CI 2.81-6.08) in their second lactation. These findings suggest that patterns established in the first lactation may have an impact on udder health in the subsequent lactation. However, simulation modelling of positive predictive values for the first lactation cell count patterns as predictors of second lactation patterns demonstrated that, at prevalences likely to be encountered on UK dairy farms, the associations were not a sufficient basis for major management decisions such as culling.

Genetic parameters of lactation cell counts and milk and protein yields in dairy ewes.

A total of 3231 lactation records of somatic cell counts (SCC), milk yield, and protein percentage for 2379 Spanish Churra ewes from 10 flocks were used to estimate genetic and environmental parameters. Genetic parameters were estimated by REML with a multitrait repeatability animal model. A lactation measure of SCC was obtained as the mean of test day log SCC adjusted for stage of lactation. Heritabilities for SCC, milk yield, and protein percentage were 0.12, 0.24, and 0.17, respectively. The corresponding repeatabilities were 0.35, 0.49, and 0.38. Heritability and repeatability estimates of SCC obtained from this study fell within the range frequently reported for dairy cows. Therefore, as practiced for dairy cattle, future possibilities for sire evaluation to improve udder health status using lactation measures of SCC for dairy sheep are not rejected, although hygienic practices are regarded as more important. Genetic correlations of SCC with milk yield and protein percentage were -0.15 and -0.03, respectively. The genetic correlation between milk yield and protein percentage was -0.47. The low genetic correlations of SCC with milk yield and protein percentage may indicate that breeding decisions to improve milk and protein yields of Churra ewes are not expected to have an effective correlated response in SCC.

Effect of Bull Selection for Somatic Cell Count in First Lactation on Cell Counts and Pathogens in Later Lactations

Somatic cell counts were measured one time on Meuse-Rhine-Ijssel cattle in The Netherlands. Experiment 1 involved 1,741 first lactation daughters of 31 bulls. Eleven bulls with daughters with either high or low average cell count were selected for further study of their daughters in third and fourth lactation. Cell counts and bacteriological tests were performed on 684 of the older daughters. A second experiment was conducted to measure daughters in second lactation and to obtain additional daughters in first lactation. This experiment recorded cell counts of 1,071 daughters of 10 of the bulls selected in Experiment 1. Heritability of the natural logarithm of cell count in first lactation was .081 based on daughters of 31 bulls in Experiment 1. Geometric daughter averages ranged from 206 to 700×103 cells/ml. Transmitting ability of bulls was estimated by the regressed least squares method. Ranking of bulls on first lactation cell count was different between the two experiments. Management factors and stage of lactation effects could be responsible for these differences. Within Experiment 2, the ranking of bulls on cell counts was nearly identical between first and second lactation. Daughter groups with low average cell count in first lactation in Experiment 2 had low averages in third and fourth lactation although some changes in ranking did occur. These results are consistent with a low to moderate genetic correlation between lactations for cell count. In general, daughter groups with higher average cell count had higher percentage of quarters with mastitis pathogens.

Genetic and Phenotypic Statistics of Lactation Cell Counts in Different Lactations of Holstein Cows

Between February 1977 and February 1982, 680,246 monthly test-day observations of somatic cell count were taken for Holstein cows having completed 79,124 lactations in 941 herds on the Quebec Dairy Herd Analysis Service. Data were transformed to natural log scale, and analyses were separate within five parity groups. Two lactational measures of cell count, geometric mean, and weighted (by test-day milk yield) mean of the log of monthly cell counts were calculated for each lactation. Maximum likelihood, iterative Minimum Norm Quadratic Unbiased Estimation, and multivariate Restricted Maximum Likelihood procedures were used for estimation of genetic and phenotypic parameters.Repeatabilities of log test-day cell counts and log of test-day cell counts corrected for milk yield were the same at each parity, .36, .41, .42, .42, and .42 in first, second, third, fourth, and fifth and later parities. Repeatabilities of lactational measures of cell count were .33 between first and second parities, .40 between second and third parities, .13 between first and third parities, and .27 between first, second, and third parities.Heritabilities of measures of lactational cell count were small from .06 to .14 in the five parities. Genetic correlations between measures of lactational cell count in different parities were close to unity, .90 to .97.

Genetic and Phenotypic Relationships Between Lactation Cell Counts and Milk Yield and Composition of Holstein Cows

Monthly somatic cell count data were collected between February 1977 and February 1982 for Holstein cows in 928 herds enrolled on the Quebec Dairy Herd Analysis Service. The geometric mean of the log monthly cell counts was calculated for each lactation. Official lactation records for 305-day milk, fat, and protein yields, and fat and protein percents were obtained for same cows. There were 18,189 cows in first lactation representing 257 sires, 13,225 in second lactation representing 206 sires, and 8,683 in third lactation representing 151 sires. Heritabilities of yield traits and protein percent increased across three lactations. Heritability of fat percent was similar in first and third lactations but decreased slightly in second lactations. Heritability of lactation cell count was small, being least in second lactations. Genetic correlations between lactation cell count and yield traits were positive in first lactations, small and negative in second lactations, and small and positive in third lactations. Genetic correlations between lactation cell count and fat and protein contents were small in the three lactations. Phenotypic correlations between lactation cell count and production traits were small in each of the three lactations. Genetic correlations between yield traits in early lactation and lactation cell count in a subsequent lactation were positive. The genetic correlation between protein percent in an early lactation and cell count in a later lactation was large between first and second lactations, decreased between second and third lactation, and small between first and third lactations. Genetic correlations were small and negative for fat percent.

Heritability of Lactation Cell Count Measures and Their Relationships with Milk Yield and Composition in Ayrshire Cows

Lactation measures of somatic cell count were calculated from monthly test-day observations (transformed to a log scale) taken between February 1977 and February 1981 in Ayrshire cows in 115 herds enrolled in the Quebec Dairy Herd Analysis Service. Analyses were separate within three groups: 1137 first lactations, representing 37 sires; 1728second and later lactations, representing 57 sires; and 2510 all lactations, representing 74 sires. Heritabilities of lactation measures were estimated from sire and error variances obtained by iterative minimum norm quadratic unbiased estimation. Heritabilities ranged from .09 to .16 in first lactations and averaged .09 for the group of second and later lactations and .07 for all lactations. Genetic correlations of lactation measures of cell count with milk, fat, protein yield, fat percent, and protein percent averaged .36, .68, .74, .38, and .45, in first lactations; −.97, −.27, −.56, .52, and .03 in second and later lactations; and −.50, −.54, −.73, .43, and .19 in all lactations. Respective average phenotypic correlations were low and negative for milk, fat, protein yield, and fat percent and low and positive for protein percent.

Relationship Between Lactation Measures of Somatic Cell Concentration and Milk Yield

Data were from herds on Dairy Herd Improvement in Wisconsin which were regularly tested for somatic cells. Lactation cell counts were taken as the average of either actual or natural log of individual tests during the lactation. Lactation milk yield was regressed on somatic cell concentration, among other concomitant variables, for each of the first four lactations. The amount of data ranged from 4,912 cows in 346 herds for lactation 1 to 1,759 cows in 202 herds for lactation 4. Yield loss per unit increase in average loge cell count was 135±20kg in first lactation and 270±30kg for all other lactations. These relationships were linear, indicating that loss per unit increase in actual cell count is greatest when cell count is low. Linearity of the regression of yield on average log cell count makes this more desirable than actual cell count as a potential trait for indirect selection for genetic resistance to mastitis. The effect on yield in a given lactation of increased average log cell concentration in the previous lactation was not statistically significant. However, the magnitude of estimates for carry-over effects were as much as 50% of concurrent effects. This suggests the possibility of an important amount of carry-over.