Impacts of postweaning dry matter intake classification on beef heifer performance, prebreeding intake, and reproduction

Duncan, Hattie Inza

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https://hdl.handle.net/2142/120140 Copy

Description

Title

Impacts of postweaning dry matter intake classification on beef heifer performance, prebreeding intake, and reproduction

Author(s)

Duncan, Hattie Inza

Issue Date

2023-05-03

Director of Research (if dissertation) or Advisor (if thesis)

Shike, Daniel W

Committee Member(s)

• McCann, Joshua C
• Braz, Camila U

Department of Study

Animal Sciences

Discipline

Animal Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• heifer development
• intake
• grazing
• repeatability
• reproduction

Abstract

The objective was to evaluate the relationship of postweaning dry matter intake (DMI) classification on grazing performance, prebreeding DMI, and reproduction in fall-born beef heifers. One hundred and forty-two heifers, either Angus or Hereford sired by commercial dams, were utilized. Heifers were weaned at 82 ± 7 days of age. After weaning, heifers were managed in drylot pens and fed a moderate-roughage, growing diet. Heifer postweaning DMI was determined over 56 days using the GrowSafe system (Vytelle, Lenexa, KS). At postweaning DMI evaluation initiation (day 1), heifers were 170 ± 22 kg and 156 ± 7 days of age. Heifers were classified on postweaning DMI as low (LoDMI; < - 0.5 SD from mean), average (AveDMI; ± 0.5 SD from mean), or high (HiDMI; > + 0.5 SD from mean). Following the postweaning evaluation, heifers rotationally grazed endophyte-infected tall fescue. Heifers returned to the drylot on day 223 for a prebreeding DMI evaluation of a high-forage diet. Percent cycling prior to synchronization, synchronization rate, AI conception rate, and overall pregnancy rate were determined for reproductive performance. By design, postweaning DMI differed (P < 0.01) between treatments (5.4, 6.2, and 6.9 kg/d for LoDMI, AveDMI, and HiDMI, respectively). Treatment × time effects were detected (P < 0.01) for body weight (BW); LoDMI were lightest, AveDMI were intermediate, and HiDMI were the heaviest for the duration of the trial. Average daily gain (ADG) differed (P < 0.01) during the postweaning evaluation, with LoDMI being least, AveDMI intermediate, and HiDMI greatest. Gain to feed (G:F) during the postweaning evaluation was different (P = 0.01); LoDMI were greater than AveDMI and HiDMI. During the grazing phase, ADG tended (P = 0.06) to be greater for LoDMI than AveDMI and HiDMI. Hair shedding score was less desirable (P ≤ 0.04) for LoDMI than HiDMI on days 56, 84, and 113; however, there were no differences (P ≥ 0.17) on days 168 and 196. At prebreeding evaluation, DMI was correlated to postweaning DMI (r = 0.47; P < 0.01), with HiDMI having the greatest (P = 0.01) DMI. During the prebreeding evaluation, ADG and G:F were not different (P ≥ 0.30). LoDMI tended (P = 0.11) to have a lesser AI conception rate than AveDMI and HiDMI. However, there were no differences (P = 0.40) for overall pregnancy rate. In summary, DMI was moderately repeatable between postweaning and prebreeding diets. Ultimately, AveDMI had similar reproductive performance to HiDMI at lighter BW and lesser DMI.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Hattie Duncan

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