New Zealand Journal of Agricultural Research abstracts
Effects of maize silage supplementation before lucerne grazing
on the occurrence of bloat in cattle
G. BRETSCHNEIDER*
XII Curso de Posgrado en Producción Animal
Facultad de Ciencias Agrarias
Universidad Nacional de Mar del Plata
Balcarce, Provincia de Buenos Aires
Argentina
F. J. SANTINI
J. P. FAY
Area de Producción Animal
Estación Experimental Agropecuaria Balcarce
Instituto Nacional de Tecnología Agropecuaria (INTA) and
Universidad Nacional de Mar del Plata
Balcarce, Provincia de Buenos Aires
Argentina
C. FAVERIN
Facultad de Ciencias Exactas y Naturales
Universidad Nacional de Mar del Plata
Mar del Plata, Provincia de Buenos Aires
Argentina
*Present address: Area de Producción Animal. Instituto Nacional de
Tecnología Agropecuaria. Ruta 226 Km 73.5 Casilla de correo 276, (7620)
Balcarce, Provincia de Buenos Aires, Argentina. email:
animbalc@balcarce.inta.gov.ar
Abstract The effects of maize silage supplementation, before
lucerne grazing, on the occurrence of pasture bloat were studied under the
hypothesis that this treatment could reduce the severity of this digestive
disorder. The experiment was divided into two trials. Six ruminally fistulated
heifers were used for the study of ruminal parameters, and in vitro
measurements and 36 heifers were used for the study of bloat score. Treatments
were: T1, no supplement; T2, 0.5% body weight of maize silage dry matter
animal-1 day-1; and T3, 1.0% of the same supplement.
Lucerne was grazed ad libitum in the vegetative to pre-bloom stage using
a daily rotational grazing system. Visual bloat score in non-supplemented
animals was higher (P < 0.01) than in the treated groups but it did
not differ (P > 0.01) between the different supplementation levels.
When lucerne leaflets were mixed in vitro with inoculum from T1, T2, and
T3 animals, differences in microbial gas production were detected (P
< 0.01) between T1 and T3 from the fourth hour of incubation, and between T1
and T2 from the twelfth hour of incubation. Soluble protein concentrations in
the liquid phase of these in vitro incubates were lower (P <
0.05) for T1 than for T2 and T3, but soluble carbohydrate concentrations did
not differ. In the ruminal fluid from the fistulated heifers, proteolytic
activity, pH, and total N-NH3 and N-NH4+ concentrations did not
differ (P > 0.05) among treatments. When sampled at the first (0800
h) and second (1200 h) sampling times, N-NH3 concentrations were higher
(P < 0.05) for T1 at both sampling times. Thus, maize silage
supplementation at 0.5% and 1.0% of body weight before lucerne grazing reduced
bloat occurrence and severity. Although the mechanisms involved in the control
of this digestive disorder could not be clearly demonstrated, it is suggested
that the lower fermentative capacity of the ruminal fluid from supplemented
animals would reflect a reduction of the rumen-free microbial population, which
is the one available to attack bloating legumes immediately after the legumes
reach the rumen. A reduced free rumen microbial population would lead to a
slower release of soluble nutrients from lucerne leaflets and, consequently, to
a reduction in bloat development.
Keywords bloat; bovine; lucerne; maize silage
New Zealand Journal of Agricultural Research, 2001, Vol. 44: 241-251
0028-8233/01/4404-0241 $7.00/0 (c) The Royal Society of New Zealand
2001
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