Selection differentials and selection indices in retrospect were calculated to determine the relative emphasis placed on production and type traits through bull selection. Indices in retrospect including only production traits indicated that, for Holsteins, fat yield was the trait most heavily selected for between 1978 and 1987, followed by protein percent and then milk yield. Fat percent and protein yield had negative index weights throughout the nine year period. In Ayrshires, similar weights were observed except that milk yield index weights were negative throughout the nine year period. It was found that the relative weight placed on type was small and did not affect the relative weights place on production traits. Within Holsteins, differences in bull selection when multiple services were required to successfully service a cow indicated that selection for overall size was reduced in later services. Within Ayrshires, there were no differences in any production or type trait within multiple services.

No description available.

The objective of this study was to derive new selection indices for swine production in Quebec. First economic values were derived as change in profit per market pig for a one unit change in a trait while all other traits remain unchanged. Production figures and prices used were taken from Quebec figures. Comparing with the currently used economic values, the responses showed the same range for the sire line with a higher emphasis on age to 100 kg for the new values. The same trait, response in age to 100 kg was much smaller in the maternal line for the newly derived economic values but showed higher responses for backfat and litter size. Lean yield was found to have higher responses if used directly as a selection criterion for carcass composition instead of backfat. Feed intake was found to have unfavourable responses in the maternal line but did not change the responses for the paternal line. Including farrowing interval in the maternal line resulted in favourable responses for lean yield and litter size. Regulating the backfat level using a restricted index in the dam line had no effect on the other traits in the index.

Thesis (Ph. D.)--Oregon State University, 1993. / Typescript (photocopy). Includes bibliographical references (leaves 68-75). Also available on the World Wide Web.

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Three milk, fat yield and final score type records were simulated for each cow in 20 herds of 200 cows over 13 years. At completion of the simulation, cows were ranked by different selection methods and the top 2% were chosen to be bull dams. Preferential treatment was simulated by increasing milk and fat yields by 8, 16, 32, and 48% in separate copies of the simulation. Preferential treatment was given to a limited number of cows in copies of the original herds based on 8 strategies. Cows were chosen to receive preferential treatment for 2nd and 3rd records based on phenotypic records and ETA’s alone and in combination with a phenotypic minimum for final score type. Cows were also chosen to be biased in all records based on phenotypic records of dam, parent average ETA, maternal line and final score type. Bull dam selection methods compared used 2:2:1 milk:fat:type indexes of cow Predicted Transmitting Abilities (PTA), first lactation PTA, (PTA-F), PTA after requiring phenotypic minimums, (PTA-P), 3-generation Pedigree Index (PI-3) and PTA after preselection on 3-generation Pedigree Index (PI-3/PTA). Comparison criterion was average merit on a 2:.2:.1 weighting of true transmitting abilities for milk, fat and type for cows selected in each of 3 replicates of the cow population that were started with different random number seeds. Selection methods PTA and PTA-F gave the highest average true breeding values when no bias was present, and both methods were robust to bias levels of 8 and 16% mean response, and continued to give the best results at these levels for all bias patterns studied. In general, selection on PI-3 and PTA-P gave poor results and should not be considered viable selection methods. Selection ability of PTA was greatly decreased at the 32 and 48% bias levels. Selection on PTA-F continued to be effective when bias did not occur in the first lactation or when bias was based on type score, while selection on PI-3PTA was unaffected by bias at any level. Requiring a high level of 3-generation Pedigree Index before selection on PTA appears useful for selecting bull dams when very high levels of bias are present. / Master of Science

The objective of this study was to compute economic values of traits for dairy cattle improvement using an empirical approach. Field recorded data were obtained from the Programme d'Analyse des Troupeaux Laitiers du Quebec (PATLQ) and genetic evaluation data were obtained from the Canadian Dairy Network (CDN). After the editing procedure, the data set consisted of 195,001 lifetime records of Holstein, Ayrshire, Jersey, Brown Swiss and Canadienne cows which calved for the first time between January 1980 and December 1994. / Different profitability measurements were computed and used as the dependent variables in covariance model to compute different sets of economic values. Since the majority of cows produced 5 lactations or less, results obtained by using lifetime profits and profits until the end of the fifth lactation are similar. A kilogram genetic increase in fat production had higher economic values than the same increase in milk production in all breeds. A unit genetic increase in conformation had the highest positive impact on profit while a same increase in capacity had a negative impact on profit. Results obtained by using lifetime profit adjusted for the opportunity cost of postponed replacement showed that this adjustement reduced the influence of type traits on profit. Finally, profits of first lactations were used to study consequences of changes in pricing systems occurred in Quebec in August 1992. Economic values attached to protein production changed drastically. A kilogram genetic increase in protein production had negative economic values in the 80's and positive economic values after August 1992.

The most successful method used for improving the growth rate of broilers is genetic selection. Improvements in nutrition, housing and disease resistance have been impressive, yet genetic selection is purported to have contributed the majority of the tremendous increase in growth rate that has taken place over the past 50 years (McKay, 2008). Many selection strategies are available, but not all are suitable, as the choice is dependent on the objective of the breeder. Selection strategies are bound to change over time as different traits become more important, and this has been the case in the broiler industry: focus was initially placed predominantly on growth rate, but the negative genetic correlation that exists between growth rate and reproductive and liveability traits has forced breeders to change their position, especially as growth rate has almost reached its upper limit and reproductive traits lag behind. This has resulted in a change from single trait to multiple trait selection. In the exercise reported here, four selection strategies commonly used for single trait selection, namely individual, between family, within family and family-index selection, were applied to a simulated broiler population using the Monte Carlo method of simulation, and constructed with the use of genetic parameters obtained from the literature. Theoretical and simulated methods of the four selection strategies were compared. A fifth selection strategy, index selection, was applied to represent multiple trait selection. The relative merit of each selection procedure was then compared, as well as the results obtained from the theoretical and simulated methods. Construction of the selection index was complex in comparison to single trait selection, as each trait included in the index had to be assigned an economic value. This value is representative of the relative importance of that trait to the overall profitability, or ability to save costs in the operation. Therefore traits favourable to profitability, or having the ability to reduce production costs, are given a heavier weighting and will consequently achieve a relatively larger improvement when applied to the selection index. A model was constructed using production rates, income and costs to represent the current overall economic situation in the industry. This was then used to determine cost economic values, which represent the saving in cost per unit improvement in each of the economically important traits, and revenue economic values, calculated as the value of each unit improvement attained in each of the economically important traits. Body weight remains the most profitable trait in a broiler enterprise; however breeder egg production is equally important as the industry would fail without sufficient day-old broilers. Therefore, it would be beneficial to determine whether current egg production levels could be maintained, or even improved, whilst improvement is made to the growth rate of the progeny. The above statement was found to be possible with the use of index selection. This multiple trait selection strategy proved capable of defying the negative genetic correlation that exists between body weight and egg production by improving egg production to 60 weeks by eight eggs, and body weight at 35 days by 259 grams. Furthermore, in some cases index selection was able to achieve improvements in some traits greater than those attained with single trait selection, whilst simultaneously improving certain negatively correlated traits. Index selection has illustrated its superiority over single trait selection strategies and its relative value to the poultry industry. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

No description available.

Poultry have many behavioural, structural and biological features that are ideal for domestication and for meat and egg production (Appleby et al., 1992). Because of the importance of poultry meat and eggs to the human population, breeders and farmers are always looking for ways of improving these traits. Artificial selection is the primary method of trait improvement, and involves selecting individuals with the highest breeding values as parents in each generation. There are a number of different methods of artificial selection, including: individual selection, between family selection, within family selection, family-index selection and index selection. In order to maintain a good response to selection breeders are constantly striving to improve the effectiveness and accuracy of the different methods of artificial selection for traits of economic importance. One method of achieving this goal is the use of computer models. Computer models can be used to simulate selection strategies and to predict what strategy will be the most appropriate for the improvement of a particular trait. This is important as all traits are influenced by many different genetic and environmental factors (Falconer and Mackay, 1996). This investigation was designed to compare the effectiveness of five different artificial selection strategies, namely individual selection, between family selection, within family selection, family index selection and index selection. Five computer models were developed using Microsoft Excel 2000 and these models were then used to compare the efficiencies of the five selection strategies for four different traits. The selection techniques were applied to an artificially, randomly generated population of 500 chickens. The four traits were egg weight with a heritability of 0.51, egg production with a heritability of 0.22, age at first egg with a heritability of 0.41 and body weight with a heritability of 0.55. Firstly, each of these traits were selected for independently using the first four selection methods and secondly the traits were selected for two at a time using index selection. The most significant results obtained from the single trait simulations were that for all traits family-index selection produced the best response to selection in the initial generations and between family selection produced the best response in the later generations. The traits with a higher heritability (egg weight and body weight) responded better to individual selection than they did to within family selection and between family selection in the initial generations. However, within family selection and between family selection proved to be more effective for traits with a low heritability such as egg production. Individual selection and family-index selection resulted in a very rapid decline in the standard deviation of all the traits. Between family selection resulted in the slowest drop in the standard deviation of all the traits, which is why this technique produced the best responses to selection in the later generations. The impact of the correlations between the economically important traits were evident from the results of index selection. For example, egg production is negatively correlated with egg weight making it difficult to gain a correlated response in both these traits simultaneously. Furthermore, egg production is negatively correlated with age at first egg implying that early maturing birds will lay more eggs, however, these eggs will be lighter. The majority of the results obtained were to be expected. Family-index selection takes all the information about an individual's breeding value into account resulting in this method of selection consistently identifying the most desirable individuals being selected. It is therefore the preferred method of selection under all circumstances. It is, however, often not economically and practically efficient to incorporate this technique and the use of another method of selection usually proves to be more beneficial. Individual selection proved to be most effective when applied to traits with high heritabilities, due to the fact that this method selects individuals based on their own phenotypic values. For traits with a high heritability, an individual with a good phenotypic value will have a good breeding value. Between family selection and within family selection proved better for traits with lower heritabilities. For traits with a low heritability the phenotypic value of an individual is a poor indicator of its breeding value. Information from a number of relatives may thus improve the accuracy of prediction of the breeding value by accounting for the influence of environmental effects. The use of computer models to simulate the selection techniques proved very successful in illustrating the effectiveness of the different selection techniques under various genetic and environmental conditions. The models may also prove to be very effective from an educational perspective. / Thesis (M.Sc.)-University of Natal, Pietemaritzburg, 2003.