Abstract :
Breeders have always been interested in improving the ewes’ milkability, since the milking is the most time-consuming task of
dairy sheep farmers. This work was aimed at studying the evolution during the productive life and the individual variability of milk
emission traits at machine milking in sheep. Data were recorded in an experimental flock of 889 Sardinian×Lacaune back-cross
ewes, by using an automatic device developed by INRA. The analyzed variables (59,615 records) were total milk yield (TMY, ml),
machine milk yield (MMY, ml), stripped milk yield (SMY, ml), machine milking time (MMT, s), latency time (LT, s), maximum
(MMF) and average (AMF) milk flow (ml/s), collected fortnightly at a.m. and p.m. milking for 4 years. Univariate mixed models
were used for estimating the evolution of traits with lactation stage and parity number and the relative weights of sire and individual
variances within date and lactation and across lactations.
As general trend, MMY and SMY decreased with lactation stage. SMY and its ratio with TMY increased from first to fourth
parity. TL increased and MMF and AMF decreased with lactation stage and parity number. Machine milking time decreased with
lactation stage and increased in adult ewes less than proportionally to the variation in machine milk yield. Most of milkability
traits were highly repeatable within date. Within lactation repeatability was high for MMY, MMF and LT and moderate for TMY,
SMY and AMF. Similar within date, within lactation and across lactations repeatability estimates for MMF and LT suggest that
these traits are affected by random sources of variation, both environmental and genetic, which are constant in time. The proportion
of the sire variance respect to the overall phenotypic variance ranged from 4% for MMT to 27% for MMF. These proportions
were particularly high for MMY, LT, AMF and MMF and low for SMY and MMT. All the milk emission traits were favorably
correlated between them and with milk yield. Only SMY showed low individual correlation with the other traits. Results suggest
that milk emission traits are genetically determined and can be improved through selection. LT and MMF are the most relevant
measurements to characterize the ewes’ machine milking speed due to the high repeatability and the favorable correlation with
MMT.
© 2007 Elsevier B.V. All rights reserved.
