Quantitative trait loci affecting clinical mastitis and somatic cell count
in dairy cattle
Hanne Gro Olsen,
* Dag Inge Våge,
Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 Ås, Norway
Department of Morphology, Genetics and Aquatic Biology, Norwegian College of Veterinary Medicine, P.O. Box 8146 Dep., N-0033 Oslo, Norway
Agricultural Research Centre MTT, Animal Production Research, Animal Breeding, FIN-31600 Jokioinen, Finland
Received: 9 May 2001 / Accepted: 6 July 2001
Abstract. Norway has a field recording system for dairy cattle
that includes recording of all veterinary treatments on an indi-
vidual animal basis from 1978 onwards. Application of these data
in a genome search for quantitative trait loci (QTL) verified ge-
nome-wise significant QTL affecting clinical mastitis on Chromo-
some (Chr) 6. Additional putative QTL for clinical mastitis were
localized to Chrs. 3, 4, 14, and 27. The comprehensive field re-
cording system includes information on somatic cell count as well.
This trait is often used in selection against mastitis when direct
information on clinical mastitis is not available. The absence of
common QTL positions for the two traits in our study indicates
that the use of somatic cell count data in QTL studies aimed for
reducing the incidence of mastitis should be carefully evaluated.
Mastitis is the most frequent and costly disease in dairy produc-
tion. In Norwegian cattle (NRF), several functional traits have
been included in the breeding goal, including disease resistance
and fertility traits (Heringstad et al. 2001; Karlsen et al. 2000; Lien
et al. 2000). Norway was the first country to establish a nation-
wide health recording system for dairy cattle, and it and Denmark,
Sweden, and Finland are the only countries with a health recording
system (Heringstad et al. 2000). Therefore, exceptional data for
genetic studies on disease resistance, among them clinical mastitis,
are available for NRF.
Clinical mastitis is inherited with an unfavorable genetic cor-
relation to milk production, and has to be included in the breeding
program in addition to milk production for avoiding an increased
frequency of mastitis (Heringstad et al. 1999; 2001). Clinical mas-
titis has been included in the Norwegian breeding program since
1978 (Solbu 1983). Since information on clinical mastitis is not
generally available, several breeding programs use indirect selec-
tion based on somatic cell count (SCC). Distinct from clinical
mastitis, the basic SCC level does not depend upon any inflam-
mation. Consequently, there is no direct connection between low
SCC levels and the probability for getting mastitis. In Norwegian
dairy herds, both mastitis and SCC are recorded. With these
unique data, this breed is a resource for comparing these two traits
in QTL studies, as well as in other genetic studies.
In Norway, the heritability of SCC has been estimated at 0.11
(Ødegård et al. 2001), and the genetic correlation between SCC
and clinical mastitis has been reported to range from 0.30 to 0.97
(Emanuelson et al. 1988; Lund et al. 1999; Po¨so¨ and Ma¨ntysaari
1996; Rupp and Boichard 1999; Shook and Schutz 1994; Weller et
al. 1992). Although some of these findings indicate a relatively
strong genetic correlation between SCC and mastitis, the low ge-
netic correlation in first lactation reported by Po¨so¨ and Ma¨ntysaari
(1996) indicates that clinical mastitis and SCC monitor different
characteristics of udder health. Therefore, a comparison of QTL
affecting clinical mastitis versus SCC should be of great interest.
Furthermore, QTL affecting mastitis in NRF have the potential of
being used also in populations lacking this information, through
On the basis of the design studies by Gomez-Raya et al.
(1998), it was shown that the power of detecting a QTL of a given
effect is higher for low heritable traits than for those with high
heritability, amounting to 0.92 for a trait with heritability of 0.10
and a QTL-effect of 0.3 phenotypic standard deviation. The main
objective of this study was to use the unique data for clinical
mastitis and SCC in the NRF population in a whole-genome search
Materials and methods
All animals were NRF, which is a heterogeneous population of
cattle based on local breeds and Ayrshire, Swedish Red-and-White, Frie-
sian/Holstein (Felius 1995). Animals from six half-sib families with a total
of 285 sons were used in the study (Table 1).
The Norwegian Cattle Map (NCM), available at http://
www.nlh.no/Institutt/IHF/Genkartstorfe/, was utilized in the study (Våge et
Correspondence to: H. Klungland, E-mail: firstname.lastname@example.org
*Present address: Centre UdL-IRTA, Area de Produccio Animal, Av.
Alcalde Rovira Roure, 177, 25198 Lleida, Spain.
**Present address: FAO, Animal Production and Health Division, Viale
delle Terme di Caracalla, 00100 Rome, Italy.
Table 1. Families of the Norwegian cattle breed used in the QTL study. Number of
sons and number of granddaughters with clinical mastitis and SCC records per sire
family are given. All sons were progeny tested based on at least 200 daughters
(average number of daughters are in brackets).
Sons Granddaughters Sons Granddaughters
Bull sire Clinical mastitis SCC
2005 Smidesang 71 62,534 (881) 71 65,437 (922)
2052 Mauland 32 40,302 (1259) 32 42,052 (1314)
2402 Thorset 54 51,058 (946) 54 48,789 (904)
2463 Jørgentvedt 39 45,439 (1165) 39 43,837 (1124)
2946 Bekkevold 42 17,597 (419) 42 15,772 (376)
3131 Okkelberg 47 19,957 (425) 46 13,220 (287)
Total 285 236,887 (831) 284 232,107 (817)
Mammalian Genome 12, 837–842 (2001).
© Springer-Verlag New York Inc. 2001