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Description:
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Objectives were to characterize residual feed intake (RFI ) and determine the
phenotypic correlation between performance , feed efficiency , and other biological
measurements in Brahman heifers , as well as the relationship between RFI determined in
confinement and measurements of grazing activity on pasture . Three separate 70 d
feeding trials were performed , and RFI was determined as the residual between actual
and predicted dry matter intake (DMI ) for a given level of production . Brahman heifers
(n = 103 ; 5 -to -9 mo of age ) were individually limit -fed a pelleted 12 % CP complete
ration daily in Calan gates . Weekly body weight (BW ) and DMI data were collected , and
predicted DMI was determined by linear regression of actual DMI on mid -test metabolic
BW . Ytterbium chloride was used to evaluate digestive kinetics , and fecal samples were
collected to determine fecal volatile fatty acids (VFA ) concentration and determine
apparent dry matter digestibility (DMD ) utilizing acid insoluble ash as an internal
marker . Measurements of temperament were evaluated on all heifers at weaning . High (n
= 6 ) and low (n = 6 ) RFI heifers (Exp . I ) grazed fescue and ryegrass to determine
variation in grazing behavior , DMI , and apparent DMD . Data from all three experiments were pooled , and RFI was not correlated with
average daily gain (ADG ) , DMI , BW , partial efficiency of gain , feed conversion ration ,
fecal VFA concentration , or any measures of temperament . There were no significant
differences in digestive kinetics between the RFI efficiency groups . Fecal samples taken
for acid detergent insoluble ash (ADIA ) determination were not collected at frequent
enough intervals to account for weekly variation in fecal ADIA concentration . Pasture
measurements were not different between the efficiency groups for heifers evaluated for
grazing behavior , as well as estimated intake as a proportion of BW , or apparent DMD .
Results of this study suggest that Bos indicus cattle appear to have similar efficiency
traits as Bos taurus and Bos indicus influenced cattle , making this measure of efficiency
equally as valid for use in both types of cattle . This indicates that selection based on RFI
can be made to increase feed efficiency without affecting ADG or BW in Brahman
cattle . |