Objectives of this research were to characterize residual feed intake (RFI) in
growing and finishing steers and examine phenotypic correlations between performance,
feed efficiency, carcass, digestib ility, and physiological indicator traits. The research
included two growing studies and one finishing study. Braunvieh-sired crossbred steers
(n = 169) and Santa Gertrudis steers (n = 120) were individually fed a roughage-based
diet for 77 d during the growing phase. Santa Gertrudis steers (n = 120) were
individually fed a grain-based diet for 80 d during the finishing phase. Individual body
weight (BW) and feed intake data were recorded. Residual feed intake was calculated as
the difference between actual dry matter intake (DMI) and DMI predicted from linear
regression of DMI on mid-test metabolic BW. During the growing phase, initial
ultrasound measures of 12th rib fat thickness (FT) and final ultrasound measures of
Longissimus muscle area (LMA), FT, and intramuscular fat (IMF) were obtained.
During the finishing phase, initial and final LMA, FT, and IMF ultrasound
measurements were obtained. Finishing steers were slaughtered at 1.0 cm of FT and carcass cooler traits measured. Blood samples were collected at the start and end of each
feeding period and analyzed for physiological indicators. Temperament traits were also
measured at the start and end of each feeding period.
Growing and finishing steers with low RFI consumed 19-22% less feed than
growing and finishing steers with high RFI, but did not differ in average daily gain
(ADG). Consequently, steers with low RFI were also more efficient as measured by feed
conversion ratio and partial efficiency of growth. Steers with low RFI had less FT
compared to steers with high RFI. Initial serum IGF-I was correlated with RFI in
growing steers indicating that IGF-I could be a potential indicator trait for RFI in
growing cattle. Additionally, RFI was correlated with digestibility to indicate more
efficient cattle had higher dry matter digestibility. Results indicate that RFI has potential
to allow producers to select more efficient animals without increasing growth rate.
Moreover, serum IGF-I may facilitate early detection and more accurate selection of
animals that are superior for growing RFI.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3207 |
| Date | 12 April 2006 |
| Creators | Brown, Erin Gwen |
| Contributors | Carstens, Gordon E. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 439211 bytes, electronic, application/pdf, born digital |
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