Degree Type

Thesis

Date of Award

2020

Degree Name

Master of Science

Department

Animal Science

Major

Animal Science

First Advisor

Daniel D Loy

Abstract

Two separate studies were conducted over a span of two years, combining the two-step weaning method with a short-term creep feed period. In a 2 x 2 factorial, 203 (year 1, n = 103; year 2, n = 100) purebred angus calves were ranked by gender, body weight (BW), age, dam parity, and sire group and then randomly assigned to one of four groups: 1) two-step weaned by inserting a nose flap 1 wk prior to weaning (NF), 2) traditionally weaned, separated from their dam on d 0 (TRAD), 3) traditionally weaned and creep fed, separated from their dam on d 0 and offered free choice creep feed 3 wk prior to weaning (TRADC), and 4) two-step weaned by inserting a nose flap 1 wk prior to weaning, offered free choice creep feed for 3 wk prior to weaning (NFC). The objective of this study was to analyze the effects of the two-step weaning method coupled with a short-term creep feed period on weaning stress and post-weaning calf performance, feed intake, and antibody titer response, as well as steer carcass quality and heifer fertility.

The preweaning period (d -28 to 0) was the same over both years. All pairs were brought in on d -28 and weekly BW were measured for both calves and cows. Starting on d -21 creep feeders were placed in TRADC and NFC pens, all calves received vaccinations against respiratory pathogens, and all calves were bled on a weekly basis (d -21, -14, -7, 0, 7, 14, 21, and 28) for the analysis of serum antibody titers. On d -7 nose flaps were inserted into NFC and NF calves. On d 0 all calves were administered a booster vaccine, nose flaps were removed, and all calves were weaned.

The post-weaning period for the two years differed. For year 1, on d 0 all calves were moved to new housing at the same location after separation from their dams. Also, on d 0 and 1 circulating cortisol concentrations were analyzed. At this point all steer calves were transported to a different farm to be fed out while heifer calves remained at the same farm and were housed with other heifers the farm was keeping in their replacement program. Steers were scanned for carcass characteristics on d 28 and were harvested on d 263. Heifers were developed and were given reproductive tract scores before they were deemed fit to be artificially inseminated (AI) at approximately 14 months of age.

For year 2, on d 0, all bull calves were transported for approximately 2.5 hours to a feedlot where they would remain until the conclusion of the trial on d 28 while heifers remained on farm and were managed with the other heifers being kept in the farm's replacement program. Bulls had blood collected on d 0, 1, 2, and 3 for analysis of circulating cortisol concentrations. They were also monitored for disease and treated if signs of sickness were detected.

During the preweaning period, there were no statistical differences for ADG between calves that were two-step weaned compared to those that were not for both year 1 and 2 (P = 0.75, 0.63, respectively). No difference was measured among groups for BW (P > 0.05), but BW was influenced by creep as calves in creep fed groups had a greater overall BW for the preweaning period and BW at d 0 (P < 0.01). The weaning method did not impact cow performance for either year (P > 0.05) but change in BW was greater in cows whose calves were creep fed for both years (P < 0.03). Calf antibody titer response to Bovine Viral Diarrhea (BVD) tended to be greater in NF calves on d 0 for year 1 compared to TRAD calves (P = 0.059). However, no differences were measured for BVD antibody titers for year 2.

During the post-weaning period, calf BW was greatly influenced by nutrition (P =0.005) where creep fed calves had increased BW values compared to non-creep fed calves for year 1. This same result was found for ADG in creep fed vs. non-creep fed calves (P =0.05). For year 2 no differences were found between groups. Initial carcass scans from steer calves were not influenced by creep feed or weaning method (P > 0.05). However, BF, REA, and YG at time of harvest were impacted (P = 0.02, P = 0.09, and P = 0.005, respectively). NF calves had the lowest BF measurement compared to all other groups. TRAD calves tended to have the lowest REA measurement compared to all other groups. NF calves had the lowest YG compared to TRAD and NFC groups. Heifers weaned using nose flaps had a greater BCS at the time they were checked for pregnancy (d 384) compared to traditionally weaned heifers (P = 0.02). They also tended to have higher AI conception rates (P = 0.09). NF calves tended to have the lowest level of circulating cortisol compared to all other groups (P = 0.05). There were no differences measured in morbidity rates between any of the groups (P = 0.97). For BVD antibody titers for year 1, the TRAD calves tended to have the lowest response on d 14 compared to all other calves (P = 0.08). However, for year 2, there was a tendency for NF calves to have the lowest response for BVD antibody titers (P = 0.08).

We conclude that preweaning calf and cow gains could be positively impacted by combining two-step weaning with a short-term creep feed period, and post-weaning performance would not be negatively impacted. Utilizing nose flaps in heifer calves could increase BCS and AI conception rate compared to heifers that are traditionally weaned. Final steer carcass traits can also be positively impacted by combining two-step weaning with short-term creep feeding.

DOI

https://doi.org/10.31274/etd-20200624-109

Copyright Owner

Kendi Elise Tjardes

Language

en

File Format

application/pdf

File Size

97 pages

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