Rather than a continuous relationship
between the two variables, a transition point
in the order of 6 g UNDFL kg^1 BW
appeared evident. This value is consistent
with the interpretation of data in Tables 16.2
and 16.3 suggesting a transition point no
greater than 9 g UF kg^1 BW in a data set
involving only four levels of ruminal load of
UF. Relationships between dietary UF con-
centrations, UF load and ruminal efflux rate
of UF are plotted in Fig. 16.7. Dietary levels
of UF in excess of approximately 0.25 g g^1
OMI (Fig. 16.7C) resulted in ruminal digesta
loads of UF >6 g kg^1 BW (Fig. 16.7A) and
what appeared to be minimal^2 UF–ein the
order of 0.35 day^1 (Fig. 16.7B). Conversely,
dietary levels <0.2 g UF g^1 OMI (Fig.
16.7C) resulted in digesta loads of UF <6 g
kg^1 BW (Fig. 16.7A) and were associated
with relatively large, >0.7 day^1 , and
variable^2 UF–e(Fig. 16.7B).
Thus when UNDFL was <6 g UNDFL
kg^1 of BW, ruminal flux of UF was
dominated by changes in^2 UF–e whereas
ruminal flux of UF was dominated by
changes in UNDFL when UNDFL exceeded
6 g UNDFL kg^1 BW. The data in Fig. 16.7
exclude data from animals receiving diets
containing <0.1 CP because variations in
these lower levels of CP were associated
with variations in UF flux and load as
indicated in Table 16.3. This relationship
suggested that variations in^2 UF–e and
ruminal efflux would respond to ruminal
efflux of MP, and this is examined in Fig.
16.8.
When UF load was >6 g kg^1 BW, flux
of MP kg^1 BW was positively related to
changes in UF load and unrelated to
changes in^2 UF–e. In contrast, when UF
load was <6 g kg^1 BW, increased flux of
MP kg^1 BW was positively related to
changes in^2 UF–eand unrelated to UF load.
Although UF load may be accomplished
via hypertrophy of the rumen in lactating
ruminants, differential responses byFeed Intake in Ruminants 349Fig. 16.6.Relationships between rumen load of undigested neutral detergent fibre (UF) and mean effective
escape rate from the sequence of lag-rumination and mass turnover pools,^2 UF–e, in lactating () and non-
lactating () cattle and sheep fed a variety of diets. Note that when UF load is less than approximately 6 g
of UF kg^1 BW UF, load is relatively constant at approximately 2–3 g kg^1 BW, in contrast to a positive
relationship when UF loads exceeded 6 g UF kg^1 BW.