Utilization of soybeans or corn milling byproducts in beef heifer development diets

¹ University of Nebraska, West Central Research and Extension Center, North Platte 69101
² Department of Animal Science, University of Nebraska-Lincoln 68583
³ USDA, ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301

^* To whom correspondence should be addressed. E-mail: rfunston2{at}unl.edu.

	Abstract

Whole raw soybeans (SB), wet corn gluten feed (WCGF) and corn dried distillers grains (DDG) are sources of protein in heifer development rations. Objectives of this study were to compare puberty status before synchronization of estrus, response to synchronization, and AI and final pregnancy rates in heifers developed on diets containing SB and either WCGF or DDG that were formulated to be similar in energy and CP. These ingredients vary substantially in fat content which may affect reproductive performance. Rate of gain during the feeding period and post-AI performance were also compared. In a preliminary experiment, 104 crossbred heifers were fed diets containing either 1.25 kg SB/d or 2.0 kg WCGF/d for 110 d (DM basis), beginning at 10 mo of age. In Exp. 1, 100 crossbred heifers received either 1.25 kg SB/d or 2.5 kg WCGF/d from approximately 7 to 10 mo of age (91 d; 4 pens/diet), then were fed 1.25 kg SB/d for an additional 114 d (4 pens/diet). In Exp. 2, 1.25 kg SB/d or 1.25 kg DDG/d was fed to 100 crossbred heifers for 226 d, beginning at 6 mo of age (4 pens/diet). At approximately 13 mo of age, heifers were fed melengestrol acetate (0.5 mg/d) for 14 d followed by an i.m. injection of PGF₂ (25 mg) 19 d later to synchronize estrus. Heifers (14 mo of age) were artificially inseminated for 5 d after PGF₂, at which time treatments were ended. Heifers were commingled while grazing on native pasture and exposed to bulls for approximately 60 d beginning 10 d after the last day of AI. Pregnancy to AI was determined by ultrasound 45 d after the last day of AI. Heifers fed SB in the preliminary experiment had a lower (P < 0.05) synchronization rate (81 vs. 96%) and longer interval (P = 0.05) from PGF₂ to estrus (76.6 vs. 69.2 h) compared to heifers fed WCGF. In Exp. 1, age heifers were started on SB diets did not alter (P > 0.10) synchronization rate (79%) or timing of estrus after PGF₂ (77.8 h). In Exp. 2, synchronization rate (86%) and timing of estrus after PGF₂ (69.3 h) did not differ (P > 0.10) due to diet. There were no differences (P > 0.10) due to diet for AI conception rates (overall mean for each experiment: 76.5, 60, and 68.5%), percent of all heifers becoming pregnant to AI (67, 46, and 59%), or final pregnancy rates (92, 90 and 90%) in the preliminary experiment, Exp. 1, or Exp. 2, respectively. In summary, SB, DDG, and WCGF can be used as sources of protein in heifer development diets at the inclusion rates used in these studies.

Key Words: fertility, heifer development, protein supplements