Animal Science, Department of

 

First Advisor

Kacie McCarthy

Committee Members

Travis Mulliniks, Robert Cushman

Date of this Version

5-2024

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Animal Science

Under the supervision of Professor Kacie McCarthy

Lincoln, Nebraska, May 2024

Comments

Copyright 2024, Josie Nicole Crouch. Used by permission

Abstract

Three experiments were conducted at the Gudmundsen Sandhills laboratory near Whitman, NE. Experiment 1, a retrospective regression analysis, evaluated the impact of heifer percentage of mature body weight (BW) at breeding on heifer performance, subsequent pregnancy rates, and calf production. Overall pregnancy rates were greater (P < 0.01) for heifers at 60 to 70% of mature BW than 50 to 55%, with no differences in pregnancy rates (P ³ 0.15) after 2-years of age. Heifers at 50 to 60% of mature BW had a greater (P =0.05) proportion give birth in the first 21-d. A higher percentage of mature BW at breeding resulted in greater (P < 0.01) BW at birth and weaning for offspring.

Experiments 2 and 3 were 3-year studies that evaluated the impact of supplementation strategy on heifer growth rates, reproductive performance, and economics. Experiment 2 investigated two overwinter rates of gain due to different levels of supplementation. March-born heifers (n = 182) were assigned to achieve a rate of gain of 0.34 kg/d (LO) or 0.68 kg/d (HI) from January to May. High gain heifers were heavier (P < 0.01) at breeding, though this advantage did not (P ³ 0.16) persist. Body condition score (BCS) was not different (P ³ 0.12) between treatments. Overwinter supplementation did not impact (P > 0.38) percent pubertal, pregnancy rates, or the proportion that gave birth in the first 21-d. Lower gain heifers had a greater net return of $31.26 per heifer developed compared to HI heifers.

Experiment 3 investigated the effect of providing a pre-breeding (July) and breeding (August) rumen undegradable protein supplementation on heifer and calf performance. May-born heifers (n = 191) either received 0.908 kg/d of supplementation (SUPP) or no supplementation (NoSupp). Heifer BW was not influenced (P ³ 0.17) by supplemental treatments. Average daily gain was greater (P = 0.02) for Supp heifers from breeding to pregnancy diagnosis. A treatment x year interaction (P = 0.05) was observed for BCS at pregnancy diagnosis; however, no BCS differences (P = 0.89) at pre-calving were detected. While Supp heifers had a greater (P < 0.01) proportion cycling before breeding, pregnancy rates and the percent that gave birth in the first 21-d (P ³ 0.34). Supplemented heifers had a lower net return of $17.38 per heifer developed compared to heifers not supplemented.

Advisor: Kacie McCarthy

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