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

Results
Treatment milk yield increased (P < 0.01) with increasing level of treatment (Table 1). Cisternal
and alveolar fractional yields were different (P < 0.05) at 4, 8, and 24 h, with cisternal milk
accounting for approximately 35% of the total milk yield prior to 12 h, and 57% of the total yield
at 24 h (Table 1 and Figure 1). Alveolar milk yield increased (P < 0.05) with increasing level of
treatment until 20 h (0.26 to 0.89 kg, respectively), whereas cisternal milk yield increased (P <
0.05) until 24 h (0.12 to 1.26 kg, respectively) (Figure 1). Milk yield during the first complete
12-h interval following treatment was similar compared to pre-treatment values for the 4, 8, and
12-h treatments, yet reduced by 15% (P < 0.01) for the 16, 20, and 24-h treatments (Table 1).
Total milk yield during a 3-d treatment period was lowest (P < 0.01) for the 20- and 24-h treatments
(6.87 kg) compared to all other treatments (7.24 kg) (Table 1).
With respect to increasing milking interval treatment, percentage of milk fat (9.20 to 5.72%)
decreased (P < 0.01), while percentage of milk protein (4.13 to 4.65%), and milk fat (36.3 to
127.5 g) and protein yield (15.2 to 104.8 g) increased (P < 0.01) (Table 1). Alveolar percentage
of milk fat was higher (P < 0.05) than cisternal percentage of milk fat for all treatments except 4
h (Figure 2A). Alveolar percentage of fat tended to increase from the 8-h to the 24-h treatment
(7.5 to 8.9%, respectively), whereas cisternal percentage of milk fat decreased from the 4- to 20h
treatment (9.1 to 3.4%, respectively) (Figure 2A). Alveolar milk fat yield increased with
increasing level of treatment (25.0 to 85.0 g), and was consistently higher (P < 0.05) than cisternal
milk fat yield for all treatments (Figure 2B). Cisternal milk fat yield increased (P < 0.05)
during the 4, 8, and 12-h treatments (11.4 to 29.0 g), was constant during the 16- and 20-h
treatments (31.5 g), and then increased (P < 0.05) again for the 24-h treatment (42.5 g) (Figure
2B). Milk protein percentage did not differ between cisternal and alveolar milk fractions for all
treatments except 24 h (P < 0.05) (Figure 3A). Alveolar milk protein yield increased (P < 0.05)
with increasing level of treatment until 20 h (10.9 to 40.5 g, respectively), whereas cisternal milk
protein yield increased (P < 0.05) until 24 h (13.3 to 62.6 g, respectively) (Figure 3B).
Somatic cell count decreased (P < 0.05) from the 4-h to the 20-h treatment (5.29 to 4.94 log
units, respectively), and then increased slightly at 24 h (5.02 log units) (Table 1). Alveolar and
cisternal SCC were not different during the 4, 8, or 12-h treatments (5.16 log units), however
during the 16, 20, and 24-h treatment cisternal SCC (4.85 log units) was lower (P < 0.05) than
alveolar SCC (5.08 log units) (Figure 4).
Discussion
During the first 12 h of milk secretion, our experimental East Friesian dairy ewes stored the
majority of their total milk volume in the alveolar compartment, which is consistent with reports
in dairy cattle (Knight et al., 1994a). However, in contrast, the cisternal compartment began
filling as early as 4 h indicating that there was at least passive transfer of milk from the alveoli to
the cistern much earlier than one report in dairy cows (Knight et al., 1994a) yet similar to a
second report in dairy cows (Stelwagen et al., 1996) and one report in dairy goats (Peaker and
Blatchford, 1988). When the milking interval exceeded 12 h, the cisternal compartment became
more important in accommodating milk storage, which possibly helped reduce alveolar milk
stasis, alveolar pressure, and concentrations of feedback inhibitors of lactation, allowing milk
secretion to continue (Labussière, 1993; Wilde et al., 1995). In contrast to one report in dairy
goats (Peaker and Blatchford, 1988), which stated that alveolar milk volume remained constant