Genetic correlations between milk production traits and somatic cell scores on test day within and across first and second lactations in Holstein cows

doi:10.1016/j.livsci.2012.12.015

Livestock Science

Volume 152, Issues 2–3, April 2013, Pages 120-126

https://doi.org/10.1016/j.livsci.2012.12.015 Get rights and content

Abstract

The genetic correlations between milk production traits (daily milk yield, 305-day milk yield, and lactation persistency as the difference between milk yields at days 240 and 60) and daily somatic cell score (SCS) within and across first and second lactations in Holstein cows were estimated by using a multiple trait test day (TD) animal model. The data set consisted of 200,095 TD milk and SCS records from 21,238 cows in their first lactations and 143,051 records from 15,281 cows in their second. Data were analyzed by using a two-trait, two-lactation random regression animal model. Genetic correlations between daily SCS and milk production traits were estimated from additive genetic variance component estimates of random regression coefficients. Genetic correlations between daily milk yield in first lactation and daily SCS in both lactations were positive and peaked in early lactation stage. In contrast, the genetic correlations between persistency and daily SCS in both lactations were negative, except in very early lactation stage. These correlations suggested that focusing selection on increasing milk yield early in the first lactation would likely increase SCS, whereas selecting for increased persistency would decrease SCS during both lactations. The genetic correlations between 305-day milk yield and persistency were positive within and across the first and second lactations. These results suggested that selection for lactation persistency could help to increase lactation yield overall in the first and second lactations without increasing SCS.

Introduction

Mastitis is the most common health disorder in dairy cows (Bigras-Poulin et al., 1990, Rajala-Schultz and Gröhn, 1999). Somatic cell counts (SCCs), generally log-transformed to somatic cell scores (SCSs), are used widely as indicators of clinical and subclinical mastitis (Detilleux et al., 1997, Schutz, 1994). SCSs increase with intramammary infection (Schepers et al., 1997, Schukken et al., 2003) and are highly correlated with the occurrence of clinical mastitis (reviewed by Mrode and Swanson, 1996). There have been many estimates of the genetic parameters of SCSs and their relationship to production traits (Haile-Mariam et al., 2001, Jamrozik et al., 2010, Jamrozik and Schaeffer, 2011, Jamrozik and Schaeffer, 2012, Koivula et al., 2005, Miura and Suzuki, 2005, Miura and Suzuki, 2006, Negussie et al., 2008, Samoré et al., 2008). In addition, several reports have addressed the relationships between average SCS and lactation persistency (Haile-Mariam et al., 2003, Weller et al., 2006). It has been suggested that lactation persistency is related to the lactation curve (Togashi and Lin, 2003) and that modifying the curve by improving persistency could increase total milk yield without increasing metabolic stress and disease susceptibility in early lactation (Dekkers et al., 1998).

Haile-Mariam et al. (2003) reported a negative genetic correlation between lactation persistency and average SCS in first lactation. Weller et al. (2006) reported that this correlation was quite low in the first lactation and negative in the second lactation. These results were estimated only by using a lactation model; however, a random regression test day (TD) model has not yet been used to assess the genetic correlations between daily SCS and lactation persistency. Applying the TD model in this context can be important, because the genetic correlations between daily milk yield and daily SCS may differ with lactation stage and parity (Haile-Mariam et al., 2001, Jamrozik et al., 2010). The results of such a study could reveal the genetic relationship between these traits at various lactation stages and might suggest the idea of modifying the lactation curve to increase milk yield without increasing SCS during the first and second lactations.

Therefore, the aims of this study were to investigate the genetic correlations between daily SCS and milk production traits (especially persistency) during first and second lactations by using a multiple trait random regression TD model.

Section snippets

Data

Monthly TD milk and SCS records for 305 days in milk (DIM) in first- and second-lactation Holstein cows in the Hokkaido region that had calved between 2004 and 2009 were obtained from the Hokkaido Dairy Milk Recording and Testing Association (Hokkaido, Japan). SCSs were calculated from SCCs as follows: SCS=log₂ (SCC/100,000)+3 (Ali and Shook, 1980). The data set consisted of 200,095 TD records from 21,238 cows in their first lactations and 143,051 records from 15,281 cows in their second

Results and discussion

Average lactation curves for TD milk and SCS within 305 DIM in the data set (Fig. 1) revealed that daily milk yield peaked at 36–95 DIM in first lactation and at 36 to 65 DIM in second lactation and gradually declined thereafter. The changes in SCS during the first and second lactations were inverted relative to those of milk yield within lactation. After reaching a nadir (first lactation, 2.00 at about 70 DIM; second lactation, 1.80 at about 40 DIM), mean SCS started to increase in both

Conclusions

The genetic correlations between daily milk yield in first lactation and SCS on the same DIM in first and second lactations were positive and peaked in early lactation. In contrast, the genetic correlations between persistency and daily SCS were negative for most of both the first and the second lactation, after an initial brief positive period. These correlations suggested that focusing selection on increasing milk yield early in the first lactation would likely increase SCS, whereas selecting

Conflictions of interest

There are no conflictions of interest for publishing this manuscript.

Acknowledgments

We thank Mrs. K. Yukawa for her support with the experiments.

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Pregnancy and calving are elements indispensable for dairy production, but the daily milk yield of cows decline as pregnancy progresses, especially during the late stages. Therefore, the effect of stage of pregnancy on daily milk yield must be clarified to accurately estimate the breeding values and lifetime productivity of cows. To improve the genetic evaluation model for daily milk yield and determine the effect of the timing of pregnancy on productivity, we used a test-day model to assess the effects of stage of pregnancy on variance component estimates, daily milk yields and 305-day milk yield during the first three lactations of Holstein cows. Data were 10 646 333 test-day records for the first lactation; 8 222 661 records for the second; and 5 513 039 records for the third. The data were analyzed within each lactation by using three single-trait random regression animal models: one model that did not account for the stage of pregnancy effect and two models that did. The effect of stage of pregnancy on test-day milk yield was included in the model by applying a regression on days pregnant or fitting a separate lactation curve for each days open (days from calving to pregnancy) class (eight levels). Stage of pregnancy did not affect the heritability estimates of daily milk yield, although the additive genetic and permanent environmental variances in late lactation were decreased by accounting for the stage of pregnancy effect. The effects of days pregnant on daily milk yield during late lactation were larger in the second and third lactations than in the first lactation. The rates of reduction of the 305-day milk yield of cows that conceived fewer than 90 days after the second or third calving were significantly (P<0.05) greater than that after the first calving. Therefore, we conclude that differences between the negative effects of early pregnancy in the first, compared with later, lactations should be included when determining the optimal number of days open to maximize lifetime productivity in dairy cows.

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Genetic correlations between milk production traits and somatic cell scores on test day within and across first and second lactations in Holstein cows

Abstract

Introduction

Section snippets

Data

Results and discussion

Conclusions

Conflictions of interest

Acknowledgments

J. Dairy. Sci.

Prev. Vet. Med.

Livest. Prod. Sci.

Livest. Sci.

J. Dairy Sci.

Livest. Prod. Sci.

Livest. Prod. Sci.

J. Dairy Sci.

J. Dairy Sci

J. Dairy Sci.

J. Daily Sci.

J. Dairy Sci.

Livest. Prod. Sci.

J. Dairy Sci.

J. Dairy Sci

Prev. Vet. Med.

J. Dairy Sci.

J. Dairy Sci.