Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Genetic parameters of milk traits, udder health and udder morphology in the Lacaune population

Nine traits were considered in the analysis: milk yield (MY), fat yield (FY), protein yield (PY), fat content (FC), protein content (PC), lactation SCS (LSCS), teat angle (TA), udder cleft (UC), and udder depth (UD).

Genetic parameters for milk production traits, LSCS and udder-type traits were estimated using a REML method applied to a sire model on 121,283 Lacaune first lactations and 86,975 udder appraisals recorded between 2001 and 2004 (table 6): all sampling sires born after 1997 and had at least 15 daughters, while proven sires were required to have at least 150 daughters and were considered as fixed effects.

The other fixed effects corresponded to those applied in the official BVE for each given trait.

Milk yield corresponded to milk at milking period only after a 25 days suckling period. Fat and protein contents, and LSCS came from the part-sampling design and data for these traits were from 2.9 test days on average per lactation at the morning milking versus 5.0 for milk yield.Individual test-day somatic cell count (SCC) were transformed to test-day somatic cell score (SCS) through the classical logarithmic transformation (SCS=log2(SCC/100,000)+3). Then Lactation somatic cell score(LSCS) was computed as the arithmetic mean of SCS adjusted for days in milk.

The three udder traits (teat angle, udder cleft, udder depth) were scored by 12 trained classifiers according to a linear scale from 1 to 9, and the results were presented such as 9 is the best appraisal whatever the trait to facilitate the interpretation of genetic correlations between production and functional traits.

Genetic parameters followed the well known patterns both for milk production traits and LSCS accounting for the part lactation sampling both for FC, PC and LSCS. It confirmed also that udder traits (TA, UC and UD) had moderate heritabilities (0.26 to 0.35).

The new results corresponded to the estimates of genetic correlations between all milk production traits (MY, FY, PY, FC and PC) and not only MY (as previously) and the functional traits (LSCS, udder traits) to be included at the moment in the global selection criteria of the dairy Lacaune breed. Except the correlations between FC or PC and UD, all the genetic correlations between milk traits and LSCS or udder traits were null to antagonistic with a range between 0.00 to -0.39: it was specially the case between the 2 main dairy traits (FY and PY) and LSCS (0.21 and 0.22 respectively, meaning genetic opposition a little higher than with MY 0.15); between FY or PY and TA (-0.11 and -0.07 respectively); between FY or PY and UD (-0.34 and -0.39 respectively).

Conversely all the genetic correlations between LSCS and udder traits were slightly favourable with an absolute range of 0.12 to 0.32. In other words selection for one of these functional trait will produce a genetic gain both for udder health and udder conformation related to milking ease as now expected by Lacaune breeders.

Finally, there is evidence that selection on milk traits only would lead in the long term to baggy udders more difficult to milk by machine and more susceptible to mastitis. Thus it is demonstrated that the inclusion of udder health and udder morphology is mandatory in an efficient breeding programme carried out on milk traits only for several decades.

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Reported by

Research
INRA - SAGA - BP 526267
31326 Castanet-Tolosan
France
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