Dairy Sheep Symposium - the Department of Animal Sciences ...

MILK STORAGE WITHIN THE UDDER OF EAST FRIESIAN
DAIRY EWES OVER A 24 HOUR PERIOD
Brett C. McKusick 1 , David L. Thomas 1 , and Pierre-Guy Marnet 2
1 Department of Animal Sciences, University of Wisconsin-Madison, Madison
2 Institut National de la Recherche Agronomique, UMR Production du Lait,
Rennes, France
Abstract
Accumulation and storage of milk within the cistern between milkings is advantageous for
dairy ruminants because feedback inhibition of lactation and over-distention of the alveoli,
factors that potentially limit milk secretion, can be reduced. While the distribution of milk and
udder filling rates in dairy cows and goats have been evaluated, there exist no reliable reports in
dairy ewes. Additionally, improved techniques for the study of milk distribution within the udder
with the aid of an oxytocin receptor antagonist have been recently developed. Cisternal and
alveolar milk fractions were measured in multiparous East Friesian-crossbred dairy ewes (n =
32) at 4, 8, 12, 16, 20, and 24 h in a 6 x 6 Latin square design by administration of Atosiban, an
oxytocin receptor antagonist, for the recuperation of cisternal milk, followed by injection of
oxytocin to remove the alveolar fraction. Less than half (38 to 47%) of the total milk yield is
stored within the cistern for the first 12h of udder filling, compared to up to 57% after 24 h.
Because subsequent milk yield was significantly reduced following the 16, 20, and 24-h treatments,
it is recommended that the milking interval in East Friesian dairy ewes should not exceed
16 h. Although the cistern of dairy ewes is capable of storing large quantities of milk, cisternal
milk is significantly inferior in fat content compared to alveolar milk (4.49 vs. 7.92%, respectively)
which highlights the importance for proper milk ejection during machine milking of dairy
ewes for recuperation of a milk that is rich in total solids. Milk protein percentage was not
different between cisternal and alveolar fractions for the majority of milking interval treatments,
indicating that casein micelles pass more freely from the alveoli to the cistern between milkings
compared to fat globules. Somatic cell count (SCC) decreased with increasing level of milking
frequency treatment; alveolar SCC was significantly higher than cisternal SCC at the 16, 20, and
24-hr treatments. At the 24-h treatment, significant increases in cisternal milk yield, fat and
protein content, and SCC were observed which implies that some milk transfer to the cistern had
occurred even prior to milking, possibly due to contraction of the overly distended alveoli and
small intramammary ducts. We conclude that dairy ewes are capable of supporting longer
milking intervals (up to 16 h) and that the main difference between milk fractions is the poor fat
content within cisternal milk.
Introduction
Milk within the udder of dairy ruminants can be divided into two fractions: the cisternal
fraction which has already been transferred from the alveoli to the cistern during the intermilking
interval, and is therefore immediately obtainable without milk ejection; and the alveolar fraction
which can only be removed from the udder if milk ejection occurs during machine milking.
Large differences between dairy species exist with respect to the proportion of total milk that can
be stored within the cistern. For example, the dairy ewe and goat can store up to 75% of the total
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