Computer simulation of beef cattle production systems in the Llanos of Columbia Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/st74cv26x

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  • A simulation model capable of execution on a programmable calculator was developed to study voluntary intake, liveweight change, and fertility of grade Zebu cows in the Llanos of Colombia. Organic nitrogen in the diet and meta bolic weight were used to predict intake; age, liveweight, and energy concentration were the driving variables for the maintenance prediction equation. Energy concentration was calculated as a function of crude protein and digestible organic matter, and liveweight change was predicted as a function of intake, maintenance, liveweight, and energy concentration. Multiplicative correction factors were fitted from data obtained from cow-calf experiments to adjust intake and maintenance for the effects of burning the native savanna, compensatory gain, mineral deficiency, and lactation and gestation. The correction factors were .89 for intake after burning the native savanna, 1.05 and .95 for intake and maintenance during compensatory gain, and .90 for reduced intake due to mineral deficiency. Correction factors for physiological status were 1.20 for intake during early and late lactation, and 1.40, 1.32, and 1.05 for maintenance during early lactation, late lactation, and late gestation, respectively. The correction factors for burning and compensatory gain were fitted against data from dry cows of Herds 4-5 of the Herd Systems Experiment (HSE) and yielded a Pearsonian correlation coefficient of .95 (p<.001) between observed and simulated average daily gains. between March 1975 and June 1976. Correction factors for early lactation, late lactation, and late gestation were fitted with data from early lactation, late lactation, and late gestation cows from Herds 4-5, and correlation coefficients for observed vs. predicted daily gains computed. Results were .89, .83, and .84 (p<.01) for each physiological state, respectively. The correction factor for mineral deficiency was fitted against dry cows of Herds 2-3 and yielded a correlation coefficient of .90(p<.01). The first validation of the model performed against lactating and late gestating cows of Herds 2-3 and all cows from Herds 6-9 of the HSE yielded correlation coefficients between observed and predicted average daily gains for early lactating, late lactating, and late gestation cows from Herds 2-3 of .77 (p<.05), .75 (p<.05), and .62 (p<.10). Results obtained for Herds 6-7 were .93 (p .001), .73 (p<.05), .94 (p<.01), and .87 (p<.01) for dry, early lactation, late lactation, and late gestation cows, respectively. Results for the same categories of cows in Herds 8-9 were .90 (p<.01) .87 (p<.01), .88 (p<.01), and .93 (p<.001), respectively. Two cows selected at random from each herd of the HSE were simulated. Correlation coefficients between observed and predicted liveweights were calculated in each case. Results for Herds 2-3, 4-5, 6-7, and 8-9 were .89 (p<.01), .92 (p<.001), .20, and .12, respectively. Validations were performed against steer grazing data collected at Carimagua at the same time as the HSE. A distribution relating liveweight at breeding to probability of calving was developed. Results showed that less than 10% of conceptions occurred at breeding weights below 260 kg, 10% or more of conceptions occurred within each 20 kg weight interval from 260-380 kg and calving rates decreased at cow breeding weights greater than 380 kg. Results obtained for predicting the calving rate of each cow herd of the HSE were good. A validation of the calving rate predictions was conducted with independent data. Observed conceptions were 56 and 76% for two herds. Predicted calving rates were 53 and 68%, respectively. In an experiment with the model it was concluded that a maximum of 80% calving could be reached with an optimal combination of the inputs of the Herd Systems Experiment.
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