Opportunities and limits of commercial farm data to study the genetic determinism of feed efficiency throughout lactation in dairy sheep
Résumé
The collective economic and environmental interest of the whole dairy sheep sector is to reduce feed
costs and the negative impact of milk production on the environment. Thus, this study focused on the
characterisation and genetic selection potential of feed efficiency in the Lacaune breed. Estimates for feed
efficiency in dairy ewes are limited, mainly due to a lack of individual feed intake measurements in the
sheepfold or in the pasture. We estimated the genetic parameters for two approximated (not entirely
based on individual data) feed efficiency traits (lactation feed conversion ratio (LFCR) and residual energy
intake (REI)) and daily milk yield (DMY) at different stages of lactation and throughout lactation. The
accuracy of the efficiency traits was first evaluated on samples from Lacaune dairy ewes that were mon-
itored individually, especially for their feed intake. Then, feed efficiency estimation methods were applied
on eight commercial farms corresponding to 4 680 Lacaune dairy ewes over two milk lactations (30 854
records). Animals were collectively (for a large part of feed intake) or individually (for milk performance
and dynamics of body fat reserves) monitored at different lactation stages. The heritabilities of LFCR and
REI were estimated over lactations at 0.10 ± 0.01 and 0.11 ± 0.01, respectively. High genetic correlations
were observed between the two efficiency traits and milk production traits, with a genetic correlation
between LFCR and DMY of 0.74 ± 0.04 and between REI and DMY of 0.79 ± 0.04. A strong influence
of environmental factors such as farm, year of milk production and lactation stage affected the genetic
link between REI and milk production traits. Efficiency values observed in early lactation when animals
were bred in the sheepfold were less genetically correlated with values obtained later in lactation when
animals were grass-fed. However, individual characterisation of feed efficiency remains difficult due to
the collective feeding context in dairy ewe farms.
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