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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/85879 |
| Date | 10 October 2008 |
| Creators | Dittmar (III), Robert Otto |
| Contributors | Forbe, David A., Randel, Ronald D. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, born digital |
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