摘要:

Design of control populations to be used in the simulation studies of assortative mating is discussed. In order to be useful for 25 generations a control population should satisfy the following requirements: (i) phenotypic correlation of mates,rP, close to zero; (ii) negligible amount of random drift; and (iii) large number of loci controlling the trait under consideration. It was concluded that under the assumptions of the design used in the present study the number of animals to produce a negligible amount of random drift (200 mating pairs) is much smaller than the number of animals necessary forrpto be sufficiently close to zero to exclude unconscious assortative mating (400 mating pairs). The minimum number of loci required allowing the trait to show a sufficiently large amount of genetic variation even in long‐term selection studies depends, among other things, on the selection intensity and the number of generations involved. In more intensely selected populations more loci are required. In long‐term selection experiments with 25 generations and 25% selected, the number of loci required, each with a very small equal effect, was 2500. An unselected control population fulfilling these requirements behaves similarly to the predictions of both the Hardy‐Weinberg model and the infinitesimal model.

ISSN:0906-4702    

DOI:10.1080/09064709709362372

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Effects of 25 generations of positive and negative phenotypic assortative mating were compared with that of random mating in unselected (all individuals reproducing) and randomly chosen (25% of individuals reproducing) populations of various size. The trait under assortation was controlled by either 100 or 2500 loci. Twenty‐five generations of positive assortative mating in large unselected populations (effective population size equal to 1600) caused an accumulating increase in additive genetic variance(VA)causingVAto become 440% of the base population'sVA.Negative assortative mating had a small asymptotic effect in the opposite direction, causingVAto become 72% of the base population'sVA.Changes inVAwere due almost exclusively to gametic phase (linkage) disequilibrium. Positive and negative assortative mating were able to slightly increase or decrease the inbreeding coefficient and the degree of homozygosity. Number of loci, population size and structure had either negligible effects in combination with negative assortative mating or worked in the direction of accentuating the effects of positive assortative mating.

ISSN:0906-4702    

DOI:10.1080/09064709709362373

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Growth performance was studied in 2918 standard black mink kits. The kits originated from a divergent selection experiment for body growth between two and four weeks. Growth was influenced by sex, litter size, age of dam, and production year. Sex dimorphism was found already at birth. Litter size had a negative effect on body weight and body length from birth to pelting. The age of the dam (yearlings vs. adults) had a positive influence on body weight, especially during the suckling period, and after weaning until September (age about 4.5 months) and even longer in female kits. The effect on body length was significant for female kits until July (age about 3 months).

ISSN:0906-4702    

DOI:10.1080/09064709709362374

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The effects on milk yield and health of feeding dairy cows at calving with diets containing different ratios of concentrate/forage (5/95, 30/70, 40/60 or 60/40 on a dry matter basis) at a similar nutritional level was studied in two experiments with a total of 105 multiparous cows. In experiment 2, two groups were fed additional vegetable fat to provide 3 or 6% crude fat in the total diet throughout the experiment. The feed intakes were increased and the ratios of concentrate/forage were changed gradually from 4 weeks before calving to achieve these ratios 3 days before calving. In early lactation the ratios were changed gradually to 35/65, 50/50 or 65/35 by 3 weeks after calving. These diets were fed for 14 weeks after calving.

ISSN:0906-4702    

DOI:10.1080/09064709709362375

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Peas, dried or toasted, were fed to growing pigs. Peas harvested in 1990 were used in Expt. 1 and peas harvested in 1993 in Expt. 2. In pea cotyledons, 49–55% of the non‐starch polysaccharides (NSP) monomers were insoluble. Arabinose and uronic acids and cellulose were the main constituents. In the hulls, 83–84% of the NSP residues were insoluble, with cellulose, xylose and uronic acids as the dominating sugars. The caecum and proximal colon were the sites of highest fermentation. In the caecum, NSP digestibility was 40–48% in Expt. 1 and 29–45% in Expt 2. NSP digestibility values of 84–87% (Expt. 1) and 85–90% (Expt. 2) were observed in the distal colon. Arabinose and uronic acids and galactose were fermented to a high extent in the proximal large intestine. Xylose and glucose disappeared at a lower extent and to a lower rate, and were fermented more distally in the colon. In spite of the different rate of fermentation of the sugars, no marked changes in the pattern of SCFA were detected along the large intestine. Toasting did not significantly affect the parameters measured.

ISSN:0906-4702    

DOI:10.1080/09064709709362376

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Housing and management were described in 114 randomly selected farrowing units. Associations between housing/management factors, enzootic pneumonia, erysipelas and disease signs of importance for feeder pig quality were investigated. Diarrhea, coughing, sneezing, joint infection and mange signs were scored and summed to create a total sign score. Factors increasing the risk of unfavorable outcomes included slatted pen floors, liquid manure management, restricted water, free access of cats and dogs into the piggery, pigs’ admission to dung alley, low relative humidity, creep feed serving on floor, existence of boar(s) in the herd and large herd size. Solid, concrete pen floors, straw bedding, solid manure management, nipple water and quarantine for replacement pigs decreased the risk of unfavorable outcomes.

ISSN:0906-4702    

DOI:10.1080/09064709709362377

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0906-4702    

DOI:10.1080/09064709709362371

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor