Great Lakes Dairy Sheep Symposium - the Department of Animal ...

that, whereas only half of the models include food factors, all models include animal factors
as independent variables, in that they influence nutritive requirements.
If body weight changes, then so does intake. This is connected to the basal
metabolism that affects requirements, and to rumen volume. One empirical method which is
very widely used to predict the intake capacity of ruminants is to calculate it as a percentage
of the body weight (for sheep about 4 to 5.5% of BW). The correlation between the body
weight of different genetic types and the intake of adult sheep is clear (Table 5). The same
tendency is not always observed, however, when the regression within each genetic type is
analysed. Indeed, one can say that in this case, because an increase in weight over the
normal mature weight is an index of fattening, intake tends to diminish (Forbes, 1995).
Table 5 - Dry matter intake and body weight in various sheep breeds (Avondo and Lutri, 2004).
Breed
Frisona orientale
Lacaune
Chios
Delle Langhe
Manchega
Massese
Comisana
Churra
Sarda
Body weight
kg
74.8
73.2
60.0
58.0
57.0
52.4
57.4
50.0
42.2
96
DM intake
kg/day head -1
2.49
2.67
2.24
1.83
2.24
1.98
1.99
1.83
1.55
When pasture conditions are favourable, intake is positively correlated with productive
level. However, literature highlights the great variability of this correlation coefficient, with
values ranging from 0.2 to 0.8 (Serra, 1998). This variability depends on the stage of lactation.
There is a phase when the ewes satisfy their increased nutritional requirements by mobilizing fat
reserves. Any attempt to estimate the intake capacity of lactating ewes should therefore take into
account their physiological tendency to mobilize body reserves in the early months of lactation
and then later to restore them. This means that the fall in intake in the phase after the lactation
peak may not always be as marked as expected. Various experiments (D’Urso et al., 1993;
Pauselli et al., 1993; Pulina et al., 1992; Trimarchi et al., 1981) on dairy sheep during lactation
have found falls in intake lower than 20% while the corresponding falls in milk production were
higher than 65% (Table 6).