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QTL for milk production traits in the Sarda x Lacaune population

Milk yield and milk composition were bimonthly recorded in the back-cross Sarda x Lacaune population in order to detected QTL wich affect this trait, which , at present, still represent the major selection criteria for dairy ewes. On a lactation basis, 5 traits were considered: milk yield (MY), fat and protein yields (FY, PY), fat and protein contents (FC, PC). Two kinds of traits were analyzed: either the first lactation (first parity) only, or the 4 first lactations considered as a repeated measurement trait for a given trait (for instance, milk yield). MY, FY and PY were pre-adjusted for length of milking period and parity using multiplicative factors. The fixed effects considered were year x group of management (during the milking period), year x age at lambing, and year x number of suckled lambs.

Phenotypes for QTL analysis were, in first lactation the residuals of the fixed model for single measurements of each trait (given the fixed effects described above), in all lactations the individual solutions of the linear mixed model for repeated measurements. At the genome wise significance threshold (p=0.0038), a total of 14 QTLs were found (table 32). This number reached 27 at the genome wise significance threshold with a suggestive linkage (p=0.038).

QTL for milk, fat or protein yields with the best confidence level were found on OAR 3, OAR 4 and OAR 20, while the level was only suggestive on OAR 16. For one of the given chromosomes OAR3, OAR 16, and OAR 20, the QTLs affect simultaneously milk, fat and protein yields, in first and all lactations, with estimates effects of the same sign, more or less for the same families and comparable LRT profiles: it suggests that it is the same QTL for milk, fat and protein yield. On the other hand, QTLs at the genome wise significance threshold (p=0.0038), were detected for protein content (PC) on OAR 1, for fat content (FC) on OAR 7 and OAR 20. Other consistent results at the suggestive level were obtained for FC on OAR 3 and OAR 16, and for PC on OAR 7.

At present those findings are being verified on the experimental population derived by crossing the the backcross ewes with 22 Sardinian rams. As far as milk yield is concerned, the availability of estimated breeding values for the commercial population and of DNA bank of all animals of the herd-book born in the last 4 years, will allows us to verify whether this QTL are also segregating the pure bred population and to better define their location, thus opening the possibility of the direct utilisation of our results for selection.

Related information

Reported by

Istituto zootecnico e caserio per la Sardegna
S.S. Sassari Fertilia km 18.6
07040 Olmedo
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