Milking characteristics of dairy goats

Abstract

The objectives of this study were to define and to describe sources of variation and relationships among milking traits of goats. Two data sets collected at the INRA Experimental Station of Bourges (France) were studied: 51 milkings of 30 goats were measured using an experimental automated milk jar which records the volume of milk at each second (data set 1), and 1596 milkings of 133 goats were measured routinely using an automated milk recording system (12 milk jars working simultaneously), recording milk volume every 15 s (data set 2). The analysis of data set 1 indicated that traits associated with milk flow were closely correlated. In particular, the milk collected during the first minute of milking (MF1), traditionally used for characterizing milking ability, was highly correlated with the maximum milk flow (MAMF), the average flow during milking (AMF) and during milk emission (AMFE) (0.92, 0.85 and 0.85, respectively), these last two traits representing the entire milking (milking time and milk emission). MF1 includes a `latency interval or reaction interval' between the setting-up of teat cups and the beginning of milk emission. By using the experimental automated milk jar, three candidate traits were measured and the `latency interval' was estimated: the time at the arrival of milk at the milk claw (TMC), at the test jar (TTJ) and at the recording of the first quantity of milk in the test jar (TR1). These traits were highly correlated with each other, and partially correlated with those traits associated with milk flow and milking time (total milking time (TMT) and milking emission time (MET)). TR1, easily and routinely measured via automated milk recording, can be used to classify animals according to their `latency interval'. Concerning the data set 2, the correlations between the total milking time (TMT) and the other milking characteristics were low due to overmilking which may have occurred in routine milkings. MF1 was highly correlated with MAMF (0.80) while TR1 was negatively correlated with MF1 and MAMF (−0.79 and −0.58, respectively). The age of female, the lactation stage, the milking time and the random effect of female within year of production had a highly significant effect on all characteristics of milking, while litter size had no significant effect. Within lactation, repeatabilities of milking traits were high, in particular for MF1 and TR1.