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QTL for mastitis resistance and udder morphology in the Churra population

For mastitis resistance somatic cell scores are measured routinarely in Churra selection flocks.

REgarding udder shape we have scored four basic udder traits and a fifth trait that globally defines udder morphology, on a nine-point linear scale. The five traits are associated with aptitude for machine milking.

- Udder depth is defined by the distance between rear attachment and the udder floor, using as a reference the hock. Udders with excessive depth (below the hock) usually reflect deficiencies in the suspensory ligament.

- Udder attachment is determined by the perimeter of the insertion to the abdominal wall of the ewe. The maximum insertion base (9 points) is considered optimum.

- Teat placement is defined by teat angle. The optimum is completely vertical teats (9 points), directed toward the ground, that coincide with minimum cistern height.

- Teat size is determined by length. Extreme sizes impede adaptation to standard teat cups, manual milking and suckling. In the Churra breed, the average teat length corresponding to 5 points on the scale.

- Udder shape measures the morphology of the udder relative to the optimum for machine milking (9 points), and corresponds to the udder machine.

- Udder shape is scored by its symmetry, depth, attachment, teat position and size. Although udder shape includes several udder traits, it is also considered in the method in order to have a general parameter of the udder, similar to the dairy form in cattle.

For mastitis resistance, a QTL on chromosome 20 was found for SCC (logarithm transformation of somatic cell counts), in the interval flanked by BM1905 and TFPA2 markers.

Regarding udder morphological traits we have evidenced four regions showing a significant effect (chromosome-wise P value <0.05) on Teat placement (chromosome OAR7), Udder attachment (chromosome OAR26) and Udder depth (chromosomes OAR14 and OAR20). Furthermore six genomic regions have evidenced an influence on udder traits with a suggestive signification level (P<0.1, chromosome-wise): on chromosome OAR4 for udder shape, on chromosome OAR22 for udder depth and on chromosomes OAR6, OAR8, OAR15 and OAR23 for udder depth.

These results are detected in our commercial population and should be verified in an independent experiment before a possible use in selection.

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Contacto

Juan Jose ARRANZ, (Official University Lecturer)
Tel.: +34-987-291470
Fax: +34-987-241311
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