Genetic and Phenotypic Relationships Among Milk Yield and Somatic Cell Count Before and After Clinical Mastitis

Abstract

This paper studies whether cows with originally lower somatic cell count (SCC) are more susceptible to clinical mastitis (CM) than cows with higher somatic cell count, and evaluates the correlations between CM, SCC, and milk yield. Data were extracted from the Finnish national milk-recording database and from the health recording system. First and second lactation records of 87,861 Ayrshire cows calving between January 1998 and December 2000 were included. Traits studied were incidence of CM, test-day SCC, and test-day milk yield before and following CM. Genetic parameters were estimated using multitrait REML with a sire model. Results did not indicate that cows with genetically low SCC would be more susceptible to CM. The genetic correlation between CM in the first and second lactation was reasonably high (0.73), suggesting that susceptibility to mastitis remains similar across lactations. The genetic correlation between CM and milk yield traits was positive (from 0.38 to 0.56), confirming the genetic antagonism between production and udder health traits. The genetic correlation between SCC and milk was positive in the first lactation, but negative, or near zero in the second lactation. This indicates that breeding for lower SCC might not affect milk production in later lactations. The results of this study support the use of SCC as an indicator of mastitis and a tool for selection for mastitis resistance.

An analysis of the genetic relationship between udder health and udder conformation traits in South African Jersey cows

“…The distribution of SCC is positively skewed and its variances among groups or herds are heterogeneous (Ali and Shook, 1980); hence, SCC is usually transformed logarithmically to somatic cell score (SCS). SCS and mastitis are however, not considered as expressions of the same trait, as shown by their genetic correlation of about 0.50 to 0.70 (Mrode and Swanson, 1996;Rupp and Boichard, 1999;Koivula et al, 2005).…”

“…Direct selection for resistance to mastitis is not widely practiced because of its low heritability (Amin et al, 2002;Zwald et al, 2004;Koivula et al, 2005) and the fact that mastitis incidences are difficult to measure. In view of its medium to high genetic correlation with and its higher heritability than mastitis, Mrode and Swanson (1996) considered somatic cell count (SCC) as the most suitable indicator of mastitis resistance.…”

Efeitos genéticos e de ambiente sobre a produção de leite e a contagem de células somáticas em vacas holandesas

“…Contudo, em estudos onde as correlações foram estimadas a partir de conjuntos de dados de primeiras, segundas e terceiras lactações separadamente, houve tendência de correlações positivas na primeira lactação e negativas ou próximas de zero nas lactações subseqüentes (Banos & Shook, 1990 ;Pösö & Mäntysaari, 1996;Koivula et al, 2005). Banos & Shook (1990) obtiveram resultados que variaram de 0,31 (primeira lactação) a -0,29 (terceira lactação), semelhantes aos obtidos neste trabalho.…”

“…Outros pesquisadores (Emanuelson et al, 1988;Boettcher et al, 1992;Welter & Freeman, 1992;Gadini et al, 1997;Rupp & Boichard, 1999;Carlen et al, 2004) encontraram valores baixos e positivos (0 a 0,22), que, apesar da baixa magnitude, podem indicar que vacas com altos valores genéticos para produção de leite tendem a ser mais suscetíveis à mastite e que a incidência de mastite pode aumentar como resposta à seleção para produção de leite. Na Finlândia, Koivula et al (2005) obtiveram correlação genética positiva entre CCS e produção de leite na primeira lactação, mas, apesar desses resultados, encontraram valores negativos ou pró-ximos de zero na segunda lactação, indicando que a seleção para redução da CCS na primeira lactação pode não afetar a produção de leite nas lactações subseqüentes. Resultados semelhantes foram obtidos por Pösö & Mäntysaari (1996), que verificaram correlações genéticas de -0,10 e 0 para a segunda e terceira lactações, respectivamente.…”

Simultaneous genetic evaluation of simulated mastitis susceptibility and recovery ability using a bivariate threshold sire model

“…In addition to its high incidence and economic importance (due to discarded milk, reduced milk production, culling cows, and treatments cost), dairy cows welfare and consumers' demand for antibiotics-free milk and milk products makes mastitis a concern both to the dairy farms and the community. The well-documented (Carlén et al, 2004;Koivula et al, 2005) genetic antagonism between milk production and clinical mastitis is an additional reason to include mastitis in a dairy cattle breeding goal. Developing better models for genetic evaluation of mastitis is among the top priorities for breeding dairy cows with improved mastitis resistance.…”