Determining biological sources of variation in residual feed intake in Brahman heifers during confinement feeding and on pasture

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Title: Determining biological sources of variation in residual feed intake in Brahman heifers during confinement feeding and on pasture
Author: Dittmar (III), Robert Otto
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2115
Date: 2009-05-15

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Determining biological sources of variation in residual feed intake in Brahman heifers during confinement feeding and on pasture. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2115 .

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