Theses and Dissertations at Montana State University (MSU)
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Item A study on some aspects of lifetime production in Targhee and Columbia sheep(Montana State University - Bozeman, College of Agriculture, 1970) Basuthakur, A. K.The relative lifetime lamb and wool production data for Targhee and Columbia sheep maintained by the Agricultural Experiment Station at Montana State University was analyzed for ewes born from 1950 to 1962. The productive traits concerned were analyzed by least square analysis of variance with interaction, phenotypic correlation and heritability was estimated. The total number of animals studied was 732 Targhees and 411 Columbias. In Targhees, it was observed that type of birth of the ewes sire affects the number of lambs born, whereas in Columbias the type of birth of ewe affects the trait. The interaction of type of birth was observed to be significant for number of lambs weaned in Targhees. The fleece production showed a significant effect of type of birth of ewe and her sire in Targhees but not in Columbias. Multiple births showed a positive significant correlation in Targhees with type of birth of the ewes sire whereas in Columbias type of birth of ewe was significant. Lamb and wool production showed variable significant correlations with yearling and weaning weights in both the breeds but were of low magnitude. The heritability for weaning and yearling weight were observed to be quite high in both the breeds in comparison tp other traits studied. The heritability of multiple births in Targhees was observed to be quite high compared to other breeds of sheep.Item Genetic analysis of growth and its relationship with lifetime production in Rambouillet, Targhee and Columbia ewes under range conditions of Montana(Montana State University - Bozeman, College of Letters & Science, 1986) Chavez, Juan FranciscoGrowth characteristics of sheep from birth to maturity and the evaluation of the genetic and phenotypic relationships between growth traits with lifetime lamb and wool production were studied using data from 302 Rambouillet, 338 Targhee and 175 Columbia ewes born between I960 and 1976. The Brody (1945) growth model was used for the derivation of growth parameters mature weight (A) and maturing rate (k). The Fitzhugh and Taylor (1971) equation-free model was used for the estimation of growth statistics; Absolute Growth Rate (AGR), Relative Growth Rate (RGR) and Absolute Maturing rate (AMR) for five intervals from birth to 18 mo. Genetic and phenotypic parameters were estimated by half-sib intraclass correlation using Harvey (1977) least-squares method for each breed and for the pooled data. Targhees were superior to Rambouillet and Columbias for weight of lamb at weaning (ATWW) and efficiency index (El). ATWW was the lifetime yearly average of kg of lamb weaned and El was ATWW per unit of ewes mature weight (A). Columbias were superior for yearly average grease wool produced (ATFP). Age at maturity was estimated on 39 mo, 38 mo and 41 mo for Rambouillets, Targhees and Columbias, respectively. Columbias had the highest A and the smallest k, Targhees matured the fastest. Ewes born twins had the highest El. From the pooled data, heritability estimates of average total of lambs born (ATLB), average total of lambs weaned (ATLW), average total weight of lambs weaned (ATWW), average total grease fleece produced (ATFP) and El were .43±.15, .33±..15, .11±>15, 68±..16 and .15±,15, respectively. Genetic correlation, between ATWW and A, indicated that ewes with high additive genetic potential for ATWW will have high genetic potential for larger A. The genetic correlation between ATWW and k was zero. For the three Fitzhugh and Taylor (1971) growth statistics, highest heritabilities were obtained for the weaning-12 mo interval: AGR2 (.80+.16), RGR2 (.76+.16) and AMR2 (.81+.16). RGR2 had the highest positive genetic correlations with ATWW (.95+.81), El (.77+.S2) and ATFP (.39+.19) among growth statistics. Inclusion of AGR2 and RGR2 in the construction of selection indexes would improve accuracy of selection for ATWW, ATFP and El. However, the contributions of A and k were inferior to AGR2 and RGR2. The use of any of the growth traits studied in selection indexes for improvement of ATFP and El simultaneously gave no advantage in improving efficiency of selection.