<p> Two evaluations were conducted to evaluate the biological and economic production efficiency of retaining replacement females in a straight-bred Angus herd (HR) as opposed to purchasing crossbred replacements for a terminal sire production system (PR) where maximum maternal and individual heterosis is achieved. The first study was a comparison of the HR system versus PR system. It was modeled after a 100 hd, straight-bred Angus cowherd that raises their own replacement females. The (NASEM, 2016) model was used to determine the required metabolizable energy (ME)/animal for each stage of production. Stages were broken into segments including weaning – d 28, d 29 – breeding, breeding – mid-gestation. It was determined, that on the same ME resources, an operator can run 117 cows and produce 7,833 more kilograms in the PR system compared to the 100 cows in the HR system. Economically, the PR system produced $10,949 more dollars of net income than the HR system. In the second study, 25 Angus and 29 SimAngus heifers were placed in the South Dakota State University Cow Calf Education and Research Facility Insentec feeding system, where they were evaluated for dry matter intake, average daily gain, gain:feed, metabolizable energy intake, predicted dry matter intake, and residual feed intake based on NRC prediction equations. At the start of the trial there was no difference in initial BW. The first period (d 1 - 98) featured no difference in BW, DMI, G:F, ME intake, predicted DMI or RFI<sub>NRC</sub>. However, Angus heifers exhibited a greater ADG (<i>P</i> ≤ 0.02) than SimAngus heifers. During period 2 (d 99 - 167), heifer BW, G:F, and RFI<sub>NRC</sub> were not different between breeds; however, Angus heifers had a greater ADG (<i> P</i> ≤ 0.02), DMI (<i>P</i> < 0.01), ME intake (<i> P</i> <0.01) and predicted DMI (<i>P</i> ≤ 0.04). Cumulatively (d 1 - 167) Angus heifers had greater ADG (<i>P</i> < 0.01), DMI (<i>P</i> ≤ 0.03), G:F (<i>P</i> ≤ 0.05), ME intake (<i>P</i> ≤ 0.03), and tended to have greater predicted DMI (<i>P</i> ≤ 0.06) than SimAngus heifers, but no difference was observed in RFINRC. Contrary to our initial assumptions, these results show that in this herd, Angus heifers have the advantage in performance, feed intake and efficiency over SimAngus heifers. These results warrant further research with a larger sample size and greater genetic diversity, in order to draw compelling conclusions that explain these biological differences. </p><p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:13419267 |
| Date | 20 December 2018 |
| Creators | Ruble, Grady D. |
| Publisher | South Dakota State University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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