Population analysis of a commercial beef cattle herd Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/mc87pt69h

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  • Twenty-four years of records (1958-1981) from a commercial Angus ranch were utilized in a population analysis to characterize the herd as a biological unit. The herd averaged 632±129 cows and 123±6 replacement heifers with all replacement heifers and many bulls from within the herd. Life tables were calculated for seven full cohorts (1958-1964) and for 15 partial cohorts (1965-1979) with data corrected for a large herd reduction sale in 1967. The model used was female only, for seasonal breeders with overlapping generations, and a time reference of immediately postpartum. Leaving the herd for any reason was equated with mortality. Nine statistics are reported: probability, at birth, of surviving to age x (Lx); age-specific survival and mortality rates (Px and Qx); expected herd life (Ex); age-specific birth rate (Mx); reproductive value (Vx); net reproductive rate (Ro); generation interval (T), and instantaneous rate of population increase (r). Average life table statistics were calculated to characterize the herd. The Lx curve was a quadratic curve (R² =.91); Px and Qx reflected culling for replacements and increased mortality after age 11; the highest Ex was 5.73±.31 at one year of age (replacement heifers); Mx ranged from .33 to .47 with no age-specific pattern; Ro, T and r equaled 1.261.18, 5.62±.13 and .03±.03, respectively. Comparisons were made with two other studies of demographic analysis of beef cattle populations. Descriptive statistics were calculated, overall and by cohort, for productive years in the herd (YIH), total offspring per cow (TOC) and replacement daughters per cow (ROC). The YIH, TOC and RDC statistics averaged 4.49±.09, 3.78±.09 and 1.10±.03, respectively. Descriptive statistics and maximum possible values were calculated for three measures of genetic contribution by the summation of additive genetic relationships between a foundation animal from the 1959 cohort replacement heifers to the 1981 cohort replacement heifers (coefficient of cohort descent, CCD), to the 1981 herd (coefficient of herd descent, CHD), or to all their female descendants (coefficient of gene replication, CGR). The CCD, CHD and CGR statistics had means (and maxima) of .007±.003 (17.2), .06±.021 (102) and .486±.086 (> 400), respectively.
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