The traditional practice on beef cow-calf ranches in the high desert region of Eastern Oregon has been to breed the cows to calve in the Spring months. Interest has been growing recently in the practice of Fall-calving; that is, breeding cows to calve in the months of October and November. The Squaw Butte Experiment Station at Burns, Oregon, began a Fall-calving program with part of their range beef herd several years ago. They found that climatic conditions are generally more favorable for calving in the Fall, resulting in higher weaned-calf percentages. Calves from both Spring and Fall-calving herds were weaned in late Summer, with Fall calves averaging around 500 pounds compared with 330 pounds for the Spring calves. There was little doubt about the biological feasibility of the Fall-calving practice in that area, but its economic feasibility was somewhat in question. The purpose of this research was to analyze the economic aspects of Fall-calving and determine what are the most important factors in deciding its economic feasibility. A linear programming model was developed for comparing Fall and Spring-calving systems under different conditions. The model was designed to maximize net returns to labor, management and fixed resources in the beef enterprise. This model took account of range forage utilization patterns. Solutions from the model indicated that Spring-calving systems may have slightly higher net returns than Fall-calving because of two main differences: (1) the lighter Spring-born calves bring a higher average price per cwt. , and (2) the Fall-calving herd requires about 1500 pounds more Winter hay than cows in the Spring-calving herd. An algebraic relationship was found between calf price differentials and the price of meadow hay, which would equate the net return values for Spring and Fall-calving systems. With an expected differential of $2. 95, between the average prices of calves sold from the Spring and Fall-calving herds, it was found that a price as low as $14.12 per ton of meadow hay would be needed to equate the net returns of a Fall-calving system with those of a Spring-calving system (with calf sales on September 1). Labor costs were not included in the model, but the ranch operator's labor situation may well be the most important element in his decision to go with Fall rather than Spring calving. The main difference is in the times of the year that labor is needed. The Fall-calving system needs more labor in the Fall, and the Spring-calving system needs even more in the Spring. / Graduation date: 1972

The use of molecular markers to identify quantitative trait loci ( QTL ) affecting economically important traits has become a key approach in animal genetics, both for understanding the genetic basis of these traits and to help design novel breeding programs. The general goal of the present work was to map QTL for economically important traits in beef cattle. Because of the practical limitations of phenotypic selection for meat quality, these traits are ideal candidates for the use of marker - assisted selection. Thus, the thesis specifically focused on carcass and beef quality traits. Six half - sib families were generated by mating six Limousin x Jersey crossbred sires to purebred Jersey or Limousin cows, producing 784 backcross progeny ( 366 and 418 progeny in Australia and New Zealand, respectively ). The six crossbred sires and all the backcross progeny were genotyped for 285 microsatellite markers ( on average 189 informative loci per sire family ) spread across the 29 bovine autosomes. A large number of traits were recorded on backcross progeny. In the first phase of the research, a single - QTL model based on regression interval mapping was used to map QTL for a wide range of economically important traits in the beef industry. Chromosome - wise significant evidence for linkage was found on BTA12 ( P < 0.01 ) and BTA16 ( P < 0.05 ) for age at puberty. Thirteen QTL were found to affect calving ease related traits ( birth weight, pelvic area and gestation length ). BTA11, 14 and 22 were most significant linkage groups affecting calving ease traits. Several genomic regions were linked to the carcass and beef quality traits. The results revealed a major QTL on BTA2 close to the map position of myostatin gene, affecting yield, carcass fatness and beef quality traits. In the second phase, the pleiotropic effects of a myostatin functional SNP on beef traits were studied. There was no association between this myostatin variant and birth weight and growth traits. However, the variant decreased overall fatness, increased muscle mass and improved meat tenderness, thus providing an intermediate and more useful phenotype than the more severe double - muscling phenotype caused by a major deletion in the myostatin gene described by others. In the third phase, a multiple marker analysis approach in the framework of the mixed - effects model was developed, allowing all markers of the entire genome to be included in the analysis simultaneously. Further, exploiting a factor analytic covariance structure for modeling trait by marker or family by marker interaction terms, the approach was extended to the multi - trait and multiple family situations. The simulation study showed that modeling multiple phenotypes and multiple families in a single linkage analysis simultaneously can markedly increase the power to detect QTL, compared to modeling each phenotype or family separately. Finally, the multi - trait multiple QTL approach developed herein was applied to map QTL influencing carcass and meat quality traits. Several pleoitropic QTL and also traitspecific QTL affecting beef traits were mapped, resulting in a useful resource from which fine mapping can be launched for subsequent gene discovery and marker - assisted selection. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?DB=local&Search_Arg=koshkoih+thesis+adelaide&Search_Code=GKEY%5E*&SL=None&CNT=50 / Thesis (Ph.D.)--University of Adelaide, School of Agriculture, Food and Wine, 2007.

The use of molecular markers to identify quantitative trait loci ( QTL ) affecting economically important traits has become a key approach in animal genetics, both for understanding the genetic basis of these traits and to help design novel breeding programs. The general goal of the present work was to map QTL for economically important traits in beef cattle. Because of the practical limitations of phenotypic selection for meat quality, these traits are ideal candidates for the use of marker - assisted selection. Thus, the thesis specifically focused on carcass and beef quality traits. Six half - sib families were generated by mating six Limousin x Jersey crossbred sires to purebred Jersey or Limousin cows, producing 784 backcross progeny ( 366 and 418 progeny in Australia and New Zealand, respectively ). The six crossbred sires and all the backcross progeny were genotyped for 285 microsatellite markers ( on average 189 informative loci per sire family ) spread across the 29 bovine autosomes. A large number of traits were recorded on backcross progeny. In the first phase of the research, a single - QTL model based on regression interval mapping was used to map QTL for a wide range of economically important traits in the beef industry. Chromosome - wise significant evidence for linkage was found on BTA12 ( P < 0.01 ) and BTA16 ( P < 0.05 ) for age at puberty. Thirteen QTL were found to affect calving ease related traits ( birth weight, pelvic area and gestation length ). BTA11, 14 and 22 were most significant linkage groups affecting calving ease traits. Several genomic regions were linked to the carcass and beef quality traits. The results revealed a major QTL on BTA2 close to the map position of myostatin gene, affecting yield, carcass fatness and beef quality traits. In the second phase, the pleiotropic effects of a myostatin functional SNP on beef traits were studied. There was no association between this myostatin variant and birth weight and growth traits. However, the variant decreased overall fatness, increased muscle mass and improved meat tenderness, thus providing an intermediate and more useful phenotype than the more severe double - muscling phenotype caused by a major deletion in the myostatin gene described by others. In the third phase, a multiple marker analysis approach in the framework of the mixed - effects model was developed, allowing all markers of the entire genome to be included in the analysis simultaneously. Further, exploiting a factor analytic covariance structure for modeling trait by marker or family by marker interaction terms, the approach was extended to the multi - trait and multiple family situations. The simulation study showed that modeling multiple phenotypes and multiple families in a single linkage analysis simultaneously can markedly increase the power to detect QTL, compared to modeling each phenotype or family separately. Finally, the multi - trait multiple QTL approach developed herein was applied to map QTL influencing carcass and meat quality traits. Several pleoitropic QTL and also traitspecific QTL affecting beef traits were mapped, resulting in a useful resource from which fine mapping can be launched for subsequent gene discovery and marker - assisted selection. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?DB=local&Search_Arg=koshkoih+thesis+adelaide&Search_Code=GKEY%5E*&SL=None&CNT=50 / Thesis (Ph.D.)--University of Adelaide, School of Agriculture, Food and Wine, 2007.