Abstract :
Accurate estimates of milk production or milk intake are difficult, as all methods interfere
to some degree with the natural behaviour of the dam and her young, and potentially alter
milk yield itself. The present study compared milk yield obtained by the “oxytocin” method,
udder dimensions (UD), the isotope dilution method, and live weight change of the lamb, in
an attempt to select the most accurate and convenient way of measuring milk production
in non-dairy sheep. In addition, the study investigated which of the three milk-estimation
techniques was an accurate predictor of growth rates of lambs. Thirty-seven singletonbearing
and rearing ewes were milked once a week, for seven consecutive weeks, using
the “oxytocin” method. Prior to each afternoon milking, the external dimensions of the
ewe’s udder were measured. Lambs were weighed weekly for the first seven weeks of
life and live weight change was calculated. The deuterium oxide (D2O) dilution technique
was used to estimate milk intake of the lambs and performed at approximately 7 days
post-partum and finishing on approximately day 14. Pearson’s correlation coefficients and
multiple regression coefficients among techniques were calculated. The UD-models at d7
(R2 = 0.35), d35 (R2 = 0.36) and d42 (R2 = 0.34), were the best models explaining variation
in milk yield (concordance correlation coefficient (CCC) = 0.49; 0.53; 0.51; for d7, d35 and
d42, respectively). The lamb live weight-change model explained the variation in milk
yield best at d28 (R2 = 0.32; CCC = 0.49), at d35 (R2 = 0.22; CCC = 0.36) and at d42 (R2 = 0.28;
CCC = 0.44). At d14, the intake of milk by lambs as measured by the D2O technique, did
not explain the variation in milk yield. In conclusion, udder dimensions, lamb live weight
change and lamb milk intake are relatively poor estimators of the milk yield of singletonrearing
ewes obtained by the “oxytocin” method. Additionally, udder dimensions, milk yield
and lamb milk intake do not give an accurate prediction of growth rates of singleton lambs.
These results emphasize that there is a difference between ewe milk production potential
and lamb milk intake, which need to be considered when estimating milk production in
non-dairy animals.
