Effects of restricted feeding of beef heifers during the postweaning period on growth, efficiency, and ultrasound carcass characteristics

¹ USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301
² University of Wyoming, Laramie, WY 82071

^* To whom correspondence should be addressed. E-mail: andy.roberts{at}ars.usda.gov.

	Abstract

Traits used for identification of replacement beef heifers and feeding levels provided during postweaning development may have major financial implications due to effects on maintenance requirements and level of lifetime production. The present study evaluated effects of 2 levels of feeding during the postweaning period on growth, feed efficiency, and ultrasound carcass measurements of heifers, and associations among these traits. Heifers (composite: Red Angus, Charolais, Tarentaise) born in 3 different years were randomly assigned to either control (fed to appetite; n = 205) or restricted (fed at 80% of that consumed by controls adjusted to a common BW basis; n = 192) feeding during a 140-d postweaning period. Heifers were individually fed a diet of 68% corn silage, 18% alfalfa, and protein-mineral supplement (DM basis) in pens equipped with Calan gates. Ultrasound measurements of LM area, intramuscular fat (IMF), and subcutaneous fat thickness over the LM (FT) were made on d 140 (382 ± 0.8 d of age). Average daily DMI was 4.1 and 5.6 kg/d for restricted and control heifers, respectively (P < 0.001). Feed restriction decreased (P < 0.001) BW (291 vs. 314 kg), ADG (0.52 vs. 0.65 kg/d), LM area (55 vs. 59 cm²), IMF (3.2 vs. 3.5%) and FT (3.2 vs. 3.9 mm), but increased G:F (0.12 vs. 0.11) when compared to control at the end of the 140-d study, Magnitude of associations of DMI with ADG (r = 0.32 vs. 0.21), 140-d BW (r = 0.78 vs. 0.36), hip height (r = 0.57 vs. 0.17), LMA (r = 0.30 vs. 0.18) and BCS (r = 0.17 vs. 0.11) were greater in restricted than control-fed heifers. Variance of residual feed intake (RFI) calculated within each treatment, was greater (P < 0.01) in control (0.088) than restricted (0.004) heifers, and magnitude of association between RFI and average DMI was greater in control (r = 0.88) than restricted (r = 0.41) heifers. Pregnancy rate tended (P = 0.11) to be reduced in heifers that had been developed on restricted feed (86.3 ± 2.3 vs. 91.5 ± 2.3%). However, ADG was greater (P < 0.001) in restricted than control heifers (0.51 vs. 0.46 kg/d) while grazing native range in the 7 mo after restriction. In summary, restricted heifers consumed 22% less feed on a per pregnant heifer basis during the development period and had greater magnitude of association between DMI and several growth related traits at the end of the140-d post weaning feeding period which is indicative of improved efficiency.

Key Words: carcass, cattle, feed efficiency, feed level, growth, heifer development

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