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At least 991 records · Page 55Linked to original sources
PubMed1993

Fracture and loosening of Charnley femoral stems. Comparison between first-generation and subsequent designs.

We report the results of a 4- to 17-year clinical and radiological follow-up of 264 Charnley first-generation stems in comparison with those of 402 second- and subsequent-generation stems. The incidence of fracture was 4.1% in first-generation stems and 0.5% in second- and subsequent-generation stems. The incidence of stem loosening requiring or likely to require revision was 3.1% in first-generation and 11.4% in second-generation stems. We believe that the increased loosening rate in second- and subsequent-generation stems is due to their larger cross-sectional area, which produces an increase in flexural stiffness.

Adolescent↗
PubMed2005

Second-generation antipsychotic medications in the treatment of mood disorders: focus on aripiprazole.

Second-generation antipsychotic medications offer a broader range of therapeutic efficacies than first-generation agents. Consequently, our field has witnessed a rapid expansion of the use of second-generation antipsychotic drugs for several conditions beyond psychosis. The use of second-generation antipsychotic medications has been most pronounced in mood disorders, especially in bipolar disorders. Information about the agents clozapine, risperidone, olanzapine, quetiapine, ziprasidone and aripiprazole in terms of their efficacy and tolerability in bipolar disorder is now available. Aripiprazole, a new agent whose proposed mechanism(s) of action differs from that of other agents, has been shown in placebo-controlled comparative trials in bipolar patients to be an effective and well tolerated treatment option for this patient group. The role of second-generation antipsychotic medications in the therapeutic armamentarium for bipolar disorders will be determined by clinical experience, by additional phase IV studies and by trials that compare second-generation antipsychotics with each other and also with mood-stabilizing medications. There is also a pressing need for additional information on the long-term efficacy and safety of each second-generation antipsychotic agent during maintenance therapy for bipolar disorders.

Antipsychotic Agents↗
PubMed2002

Equivalence of cost generators for minimum cost flow phase unwrapping.

Phase unwrapping represents a crucial step in processing phase data obtained with techniques such as synthetic aperture radar interferometry, speckle interferometry, and magnetic resonance imaging. The so-called branch-cut approaches form an important class of phase unwrapping algorithms. In 1996, Costantini proposed to transform the problem of correctly placing branch cuts into a minimum cost flow problem [Proceedings of the Fringe '96 Workshop (European Space Agency, Munich, 1996), pp. 261-272]. The critical point of this new approach is to generate cost functions that have to represent all the a priori knowledge necessary for phase unwrapping. Any function transforming a priori knowledge into a cost function is called a cost generator. Several types of algorithms ranging from heuristic approaches to generators based on probability-theory interpretations were suggested. A problem arising from the growing diversity of algorithms is to find a criterion for the equivalence of different cost generators. Two cost generators are equivalent if they produce cost functions with the same minimal flow for every residue configuration on every image with all possible a priori knowledge. Comparing the results of different cost generators on test scenes can show only their non-equivalence. We solve this problem by proving the following mathematical classification theorem: Two cost generators are equivalent if and only if one can be transformed into the other by multiplication by a fixed constant.

Journal Article↗
PubMedDate not supplied

Does DNA methylation pattern mark generative development in winter rape?

In this paper we report on changes in DNA methylation pattern in rape apices and leaves during transition from vegetative to reproductive stage due to grafting and/or vernalization. Grafted plants of winter rape (Brassica napus L., var. "Górczański") (stock from vernalized, scion from non-vernalized plants) were used together with vernalized non-grafted plants. In addition, methylation status was determined also in spring rape (var. "Młochowski") grown under normal and low temperature. The methylation-sensitive amplification polymorphism (MSAP) method with EcoRI/MspI and EcoRII/HpaII restriction enzymes was employed. The majority (ca. 68%) of analyzed loci (566 in winter and 551 in spring rape) were monomorphic, i.e. did not undergo methylation. Both cultivars showed a similar degree of methylation. 188 loci in winter and 176 in spring cultivars expressed changes in the methylation pattern. All differentially amplified fragments resulted from either full methylation of an internal cytosine or from hemi-methylation of an external cytosine. A pair-wise comparison showed that a similar number of loci underwent development-related methylation changes in apices of the winter and spring rape. The majority (80%) of changes were demethylation events in generative (vernalized) apices of the winter cultivar. However, an increased number of demethylated loci was detected in vernalized apices in comparison with generative, non-vernalized ones. In apices of vegetative and generative grafted plants the same number of demethylation events was observed. Overall, 10 MSAP loci were detected that expressed methylation changes in vernalized apices only; among them 7 loci underwent demethylation after vernalization and remained methylated in both vegetative and generative non-vernalized stage. Only 1 locus was demethylated in generative non-vernalized apices. Thus, most of demethylation events can be ascribed to vernalization and not to the generative stage. In leaves of winter rape methylation and demethylation events occurred with similar frequency, while in the spring cultivar more demethylation events were detected. The results show that during vernalization and transition to the generative stage different sets of genes are activated.

Base Sequence↗
PubMed1994

Effect of P1-purinergic agonist on thyrotropin stimulation of H2O2 generation in FRTL-5 and porcine thyroid cells.

Our previous studies have shown that the generation of H2O2 in FRTL-5 thyroid cells is regulated via both the adenylate cyclase/cyclic adenosine monophosphate (cAMP) and Ca2+/phosphatidylinositol pathway: thyrotropin (TSH) stimulates H2O2 generation through both pathways, via the former at a low concentration and via the latter at a high concentration. In porcine thyrocytes in primary culture H2O2 generation is stimulated only via the Ca2+/phosphatidylinositol route. In the present study we explored the effect of a P1-purinergic agonist (phenylisopropyladenosine, PIA) on stimulations induced by TSH and by adenosine triphosphate (ATP), an activator of the Ca2+/phosphatidylinositol cascade via the P2-purinergic receptor. In FRTL-5 cells, PIA potentiated H2O2 generation stimulated by TSH at 10 U/l (but not at 1 U/l, Ca2+ mobilization induced by TSH and Ca2+ mobilization induced by ATP at 1 mumol/l (but not 10 mumol/l). Phenylisopropyladenosine strongly inhibited TSH-induced cAMP accumulation in FRTL-5 cells. In pig thyrocytes, PIA had no effect on H2O2 generation stimulated by TSH or ATP and no effect on ATP-stimulated Ca2+ mobilization. Also, PIA did not inhibit TSH-stimulated cAMP accumulation in pig thyrocytes, and by itself had no effect on H2O2 generation or Ca2+ mobilization. Thus, in FRTL-5 cells, but not in porcine thyrocytes, PIA modulates TSH-stimulated H2O2 generation by enhancing the Ca2+/phosphatidylinositol route and inhibiting the adenylate cyclase/cAMP route of the TSH signal. The net result of this modulation apparently depends on the balance between inhibition of the cAMP route and enhancement of the Ca2+ route. This may explain the lack of potentiation observed by 1 U/l TSH.

Adenosine Triphosphate↗
PubMed2001

Two inbred strains of mice with high and low mammary tumor potentials established from the same basal stock of Swiss albino (SHN and SLN): history of mammary tumorigenesis and reproduction after the 30th generation of full-sib mating.

We established SHN and SLN strains of mice with a high and a low mammary tumor potentials from the same basal stock of Swiss albino. The selection history of females (mothers) for subsequent generations, mammary tumorigenesis and reproduction up to recent generations are presented and compared with the results up to F30 published in 1979. The changes with generation of each parameter varied in both strains except the conditions of female (mother) selection for subsequent generations, which were generally constant. However, the fluctuations in parameters up to F30 became generally smaller with advancing generations. Based on the fluctuations from generation to generation of mammary tumorigenic and reproductive parameters, an interdependency between mammary tumor potential and reproductivity is suggested in SLN, but less so in SHN. The pup growth rate was increased and associated with selection for mammary tumorigenesis in SHN; this parameter is usually used as an indicator of mother lactational performance in mice. The significance of selection for mammary tumor potential in association with reproductivity was further discussed.

Aging↗
PubMed2002

Behavior and development of preschool children born to adolescent mothers: risk and 3-generation households.

OBJECTIVE: To investigate whether living in a 3-generation household (grandmother-mother-child) is associated with fewer behavior problems and better cognitive development among preschool children of mothers who gave birth during adolescence and whether it protects children from the behavior and developmental problems associated with maltreatment and maternal depression. DESIGN: Cohort study. SETTING: Participants included low-income families recruited from 4 sites: East, Northwest, Midwest, and South, who are part of LONGSCAN, a longitudinal study of children's health, development, and maltreatment. PARTICIPANTS: One hundred ninety-four mothers who were adolescents (less than age 19) at delivery. Data were gathered when children were 4 to 5 years of age. Twenty-six percent of the children lived in 3-generation households, 39% had a history of maltreatment, and 32% of the mothers had depression scores in the clinical range. MAIN OUTCOME MEASURES: Child behavioral problems were measured with the Child Behavior Checklist, completed by the mother, and child developmental status was assessed with the Battelle Developmental Inventory Screening Test, administered by research assistants. RESULTS: Multiple regression analyses revealed that children who had been reported for maltreatment and had mothers with depressive symptoms had more externalizing behavior problems, compared with children who experienced neither risk or only 1 risk. However, when residential status was considered, children with the greatest number of externalizing behavior problems were those who experienced both maltreatment and maternal depressive symptoms and lived in 3-generation households. Children who had been reported for maltreatment or had mothers with depressive symptoms were more likely to have internalizing problems, compared with children with neither risk. Residential status was not related to children's internalizing behavior problems or cognitive development. CONCLUSIONS: Living in a 3-generation household did not protect preschool children from the behavior problems associated with maltreatment and depression. In contrast, living in a 3-generation household was associated with more behavior problems among the highest risk group of children--those who had been maltreated and had mothers with symptoms of depression. Although 3-generation families may provide an important source of support and stability for adolescent mothers and their infants early in the parenting process, it may not be advisable to rely on 3-generation households as young mothers enter adulthood, particularly among those with a history of maltreatment or depression. Children with the fewest number of behavior problems were living with their mothers in their own household (often with the father), had not been maltreated, and had mothers with few symptoms of depression.

Adolescent↗
PubMed2004

Enforced activation of STAT5A facilitates the generation of embryonic stem-derived hematopoietic stem cells that contribute to hematopoiesis in vivo.

Little is known about the molecular mechanisms that direct the transition from primitive to definitive hematopoiesis. In this study, we cocultured murine embryonic stem (ES) cells on OP9 stroma to induce hematopoietic differentiation as a model to study factors involved in the generation of adult hematopoietic stem cells (HSCs). Overexpression of the constitutively activated mutant signal transducer and activator of transcription (STAT) 5A(1*6) in ES cells facilitated the generation of cells that expressed the endothelial-hemangioblast marker Flk-1 within 5 days of coculture on OP9. The first CD41+/ CD45+/c-Kit+/(Flk-1)- hematopoietic cells arose in our culture conditions between days 5 and 7. Persistent activation of STAT5A greatly enhanced the generation of hematopoietic progenitors compared with controls, as determined by colony assays in methylcellulose. Moreover, whereas controls generated only a short transient wave of hematopoiesis lasting less than 3 weeks, expression of STAT5A(1*6) resulted in the generation of hematopoietic cobblestone area-forming cells (CAFCs) on OP9 that could be serially passaged onto new OP9, giving rise to second and third CAFCs that generated hematopoietic progenitors for > or = 5 weeks, indicating a role for STAT5A in HSC self-renewal in vitro. Several definitive hematopoietic genes were upregulated by STAT5A (1*6), as well as Runx1/AML1, vascular endothelial growth factor, oncostatin M receptor, HoxB4, Wnt5A, Delta-like-1, and Bmi-1. Furthermore, ES-derived hematopoietic cells expressing STAT5A(1*6) contributed to myeloid-lymphoid hematopoiesis in primary and secondary nonobese diabetic-severe combined immunodeficiency recipients, although no donor-derived cells could be detected after 7 weeks in the secondary recipients. These data indicate that a persistent activation of STAT5A allows the generation of ES-derived HSCs that can, at least for an intermediate period, contribute to hematopoiesis in vivo.

Animals↗
PubMed1997

Important differences in clinical data from third, second, and first generation periodontal probes.

This study compared relative attachment levels (RAL) and probable crevice depths (PCD) from 6 periodontal probes (1 third, 4 second, and 1 first generation). A single clinician recorded RAL and PCD in 6 patients with chronic adult periodontitis (mean age 48.2 years) during two visits (interval: 1 week) using a Latin square examination order. Replicate measurements were recorded at the 4 interproximal sites of the Ramford index teeth to examine intra-probe differences. Additional single measurements were recorded at similar sites of units 11, 26, 31 and 46 to investigate interprobe differences. Intra-probe RAL and PCD reproducibility was < or = 1 mm at > 94% of the sites. All intra-probe Pearson correlation coefficients were > 0.85 (P = 0.00). Inter-probe RAL and PCD agreement was < or = 1 mm at > 49% of the sites for RAL and > 61% of the sites for PCD. All inter-probe Pearson correlation coefficients were > 0.42 (P = 0.00) for RAL and > 0.49 (P = 0.00) for PCD. Analyses of variance showed significant differences in RAL and PCD between the first generation probe and the second generation probes (P < 0.005); in RAL between the third generation probe and the first and second generation probes (P = 0.0354); and in PCD between the third generation probe and the first and second generation probes (P = 0.0475). Inter-probe differences were clinically significant in the recorded percentages of pockets > or = 4 mm and > or = 6 mm. Significant inter-probe differences were found in RAL and PCD which have clinical importance in data interpretation and comparison.

Adult↗
PubMed1990

Generational differences in perinatal health among the Mexican American population: findings from HHANES 1982-84.

Data from the Hispanic Health and Nutrition Examination Survey (HHANES) were used to examine a profile of social, medical, and behavioral characteristics associated with low birth-weight (LBW) and miscarriages in first and second generation Hispanics of Mexican descent. The percentage of LBW was 5.3 and of miscarriages was 12.7. LBW rates were higher for second generation primipara and multipara compared with first generation women. Using multivariate logistic regression techniques and adjusting for complex design effects, generation was found to be a significant predictor of LBW but not of miscarriages. The findings support existing evidence that a Mexican cultural orientation protects first generation. Mexico-born women against a risk for LBW. However, the findings do not show significant effects of generation on miscarriages, suggesting that cultural effects are not consistent for all pregnancy outcomes. Furthermore, we suggest that the higher rates of LBW in second generation women are not due to a higher rate of miscarriages as has been hypothesized.

Abortion, Spontaneous↗
PubMed1999

Comparative tolerability of second generation antihistamines.

Second generation histamine H1 receptor antagonists, the so-called 'nonsedating' antihistamines, have high potency and additional antiallergic properties as well as H1 antagonism and are associated with fewer adverse effects compared with the first generation antihistamines. A number of drugs in this class are approved for use: acrivastine, astemizole, azelastine, cetirizine, ebastine, fexofenadine, loratadine, mizolastine and terfenadine. All of them have a more favourable risk-benefit ratio with regard to the CNS adverse effects. Even those second generation antihistamines that are not actually 'nonsedating' are less impairing than their predecessors, but not one of them is entirely devoid of CNS activity. Under certain circumstances some antihistamines may affect cardiac repolarisation resulting in cardiovascular adverse effects. Serious cardiovascular effects have been reported with terfenadine and astemizole when they are used in high dosages or when they are given to 'at risk' patients. Animal models indicate that there might be a potential risk of cardiovascular adverse effects with other antihistamines as well. However, up to now there is no clinical evidence for this assumption, despite some confusing reports. Likewise there has been much discussion about a link between these agents and carcinogenicity. However, there is no evidence that any of the second generation antihistamines increase the risk of tumour growth in humans. Small children, elderly patients and persons with chronic renal or liver impairment are special groups in which the individual adverse effects of the second generation antihistamines must be kept in mind. The dosage for an individual has to be modified with respect to their metabolic situation. Despite the fact that some of the second generation antihistamines are listed in the US Food and Drug Administration pregnancy risk classification as class B, the use of second generation antihistamines should be avoided during pregnancy and they should never be administered to nursing mothers. Taking into account their negligible CNS activity, the low incidence of cardiovascular adverse effects, their lack of anticholinergic effects and other benefits, this class of antiallergic drugs represents a definite advance in therapy.

Age Factors↗
PubMedDate not supplied

Clinical pharmacokinetics of the third generation cephalosporins.

At the present time, the third generation cephalosporins that are already on the market or close to this point include cefsulodin, cefotaxime, cefoperazone, latamoxef, ceftriaxone, ceftazidime, ceftizoxime and cefotetan. Other newer compounds are also under development but have not been included in this review. None of the third generation compounds is suitable for oral administration and, accordingly, their pharmacokinetics have been studied only after intravenous and intramuscular administration. Microbiological assays and HPLC methods have been used for the measurement of plasma/serum, urine, bile and cerebrospinal fluid (CSF) concentrations. As found with cefotaxime, microbiological assays should only be used when the full metabolite spectrum of a particular drug is known, as otherwise, the presence of microbiologically active metabolites may lead to erroneous conclusions. Under normal conditions, the major route of elimination is via the kidneys for cefsulodin, latamoxef, ceftazidime, ceftizoxime and cefotetan. In contrast, cefoperazone is mainly eliminated in the bile, whereas cefotaxime and ceftriaxone depend both on the liver and the kidneys for their elimination. With the exception of ceftriaxone, which has a longer elimination half-life (i.e. around 8 hours), all the other third generation cephalosporins have a t1/2 ranging between 1.5 and 2.5 hours. Plasma protein binding is variable from one compound to another. However, the clinical relevance of this parameter is not clearly established since tissue penetration also depends on the relative affinity of the drug for tissue components. Third generation cephalosporins seem to penetrate adequately into the CSF and, thus pharmacokinetically appear to be appropriate agents for the treatment of meningitis. The degree of modification of pharmacokinetic parameters by renal insufficiency or hepatic diseases depends, as for other drugs, on the extent to which the compound is excreted via the kidneys or the liver. The third generation cephalosporins have been extensively studied under these conditions and recommendations for dosage modification in special circumstances are available for most of them. The pharmacokinetics of some third generation cephalosporins may be modified in neonates and elderly patients. Accordingly, their use at the extremes of age must be accompanied by a closer than usual clinical monitoring of the patient. From a clinical point of view, the third generation cephalosporins possess reliable pharmacokinetic properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

New insights into the second generation antihistamines.

Second generation antihistamines are recognised as being highly effective treatments for allergy-based disease and are among the most frequently prescribed and safest drugs in the world. However, consideration of the therapeutic index or the benefit/risk ratio of the H1 receptor antagonists is of paramount importance when prescribing this class of compounds as they are used to treat non-life threatening conditions. There are many second generation antihistamines available and at first examination these appear to be comparable in terms of safety and efficacy. However, the newer antihistamines in fact represent a heterogeneous group of compounds, having markedly differing chemical structures, adverse effects, half-life, tissue distribution and metabolism, spectrum of antihistaminic properties, and varying degrees of anti-inflammatory effects. With regard to the latter, there is growing awareness that some of these compounds might represent useful adjunct medications in asthma therapy. In terms of safety issues, the current second generation grouping includes compounds with proven cardiotoxic effects and others with the potential for adverse drug interactions. Moreover, some of the second generation H1 antagonists have given cause for concern regarding their potential to cause a degree of somnolence in some individuals. It can be argued, therefore, that the present second generation grouping is too large and indistinct since this was based primarily on the concept of separating the first generation sedating compounds from nonsedating H1 antagonists. Although it is too early to talk about a third generation grouping of antihistamines, future membership of such a classification could be based on a low volume of distribution coupled with a lack of sedating effects, drug interactions and cardiotoxicity.

Anti-Asthmatic Agents↗
PubMed2000

Effects on haemostasis variables by second and third generation combined oral contraceptives: a review of directly comparative studies.

Previous reports and reviews indicate differences in effects of second and third generation combined oral contraceptives (COCs) on haemostasis variables. This review analyses directly comparative studies on such effects. From the literature, 17 longitudinal comparative studies with parallel groups were retrieved, containing data on comparisons between COCs containing levonorgestrel (second generation COCs) and COCs containing desogestrel, gestodene or norgestimate (third generation COCs) with 30-35 ug ethinylestradiol. Six or more comparisons were available only for fibrinogen, platelet count, antithrombin III, factor VII, factor VIII and factor X. The comparisons reveal a consistently larger increase in factor VII with the third generation COCs compared to the second generation COCs. The effects on factor VII do not coincide in these comparative studies with effects on factor X and prothrombin, rendering a specific sensitivity of the vitamin K-dependent mechanisms for progestogens unlikely. Fibrinogen effects tend to be different for the different progestogens, suggesting a progestogen-specific dependence. Trends in antithrombin III are towards more reduction for the third generation COCs, but the effects are very minor. The effects on factor V suggest a possible progestogen specificity, which may be relevant to explain the difference in APC-resistance between second and third generation of COCs. In general, direct comparisons of effects of different types of COCs on haemostatic variables are available for only a very few factors, which hampers the drawing of general conclusions with respect to haemostatic consequences.

Animals↗
PubMed2003

Library design practices for success in lead generation with small molecule libraries.

The generation of novel structures amenable to rapid and efficient lead optimization comprises an emerging strategy for success in modern drug discovery. Small molecule libraries of sufficient size and diversity to increase the chances of discovery of novel structures make the high throughput synthesis approach the method of choice for lead generation. Despite an industry trend for smaller, more focused libraries, the need to generate novel lead structures makes larger libraries a necessary strategy. For libraries of a several thousand or more members, solid phase synthesis approaches are the most suitable. While the technology and chemistry necessary for small molecule library synthesis continue to advance, success in lead generation requires rigorous consideration in the library design process to ensure the synthesis of molecules possessing the proper characteristics for subsequent lead optimization. Without proper selection of library templates and building blocks, solid phase synthesis methods often generate molecules which are too heavy, too lipophilic and too complex to be useful for lead optimization. The appropriate filtering of virtual library designs with multiple computational tools allows the generation of information-rich libraries within a drug-like molecular property space. An understanding of the hit-to-lead process provides a practical guide to molecular design characteristics. Examples of leads generated from library approaches also provide a benchmarking of successes as well as aspects for continued development of library design practices.

Combinatorial Chemistry Techniques↗
PubMed1991

Streptozocin- and alloxan-induced H2O2 generation and DNA fragmentation in pancreatic islets. H2O2 as mediator for DNA fragmentation.

Streptozocin (STZ) and alloxan (ALX) exhibit the most potent diabetogenicity and are used for induction of experimental diabetes mellitus. An understanding of the mechanisms of action of the typical diabetogenic agents is important for elucidating the causes of diabetes. Okamoto proposed a model in which DNA fragmentation plays an important role in the development of diabetes. DNA fragmentation supposedly results from the accumulation of superoxide or hydroxyl radicals. However, direct evidence for this accumulation is lacking. With isolated rat pancreatic islets in vitro, we demonstrated that STZ and ALX stimulated H2O2 generation and caused DNA fragmentation. Addition of STZ or ALX resulted in an increase in H2O2 generation. On DNA analysis, when incubated without STZ or ALX, DNA sedimented as a single peak; when incubated with STZ or ALX, DNA sedimented slower as a broad peak and was fragmented. Graded doses of STZ and ALX stimulated H2O2 generation and induced DNA fragmentation; their effects on H2O2 generation and DNA fragmentation were evident at a concentration of 0.1 mM and were maximal at 1 mM. Administration of STX or ALX to rats in vivo stimulated H2O2 generation and caused DNA fragmentation in pancreatic islets. H2O2 itself also induced DNA fragmentation. These findings may support Okamoto's proposal that STZ and ALX induce diabetes through the following biochemical events: STZ and ALX----H2O2 generation----DNA fragmentation----beta-cell destruction. This study may constitute the first demonstration of STZ- and ALX-stimulated H2O2 generation, which probably acts as a mediator of STZ- and ALX-induced DNA fragmentation.

Alloxan↗
PubMed2002

Role of education in generativity differences of employed and unemployed women in Korea.

This study investigated generativity differences between employed and unemployed women in Korea and examined the effect of education on generativity. There were 472 participants in this study, 252 employed married women and 220 unemployed married women living in the Kwangju metropolitan area. A questionnaire requesting demographic information and responses to the translated Loyola Generativity Scale was administered individually. Analysis showed significant generativity differences between the two groups, who also differed in education and mother and spouse roles. However, employment status was not a significant predictor for generativity when a stepwise regression analysis was applied. The analysis showed that education was the strongest predictor for generativity, while mother/wife roles, socioeconomic status, health, and childcare stress were also significant predictors. It was concluded that for Korean married women, generativity is more strongly related to education than employment status.

Adult↗
PubMed1991

Breed effects and heterosis in advanced generations of composite populations for preweaning traits of beef cattle.

The effects of heterosis for gestation length, dystocia, calf survival, birth weight, 200-d weight, and ADG from birth to weaning were evaluated in F1, F2, and combined F3 and F4 generations in three composite populations. Breed effects were evaluated for the nine parental breeds (Red Poll, Hereford, Angus, Limousin, Braunvieh, Pinzgauer, Gelbvieh, Simmental, and Charolais) that contributed to the three composite populations. Breed effects were significant for all traits evaluated except survival at birth. The large differences among breeds in additive direct and additive maternal genetic effects offer a great opportunity to use the genetic differences among breeds to achieve and maintain optimum additive genetic (breed) composition to match genetic resources to a wide range of production-marketing ecosystems. There was no heterosis for gestation length. Mean heterosis for dystocia was significant estimated in F1 but not in F2 or in the combined F3 and F4 generations. Mean heterosis was not significant in any generation for survival at birth, to 72 h, and to weaning for the F1 generation; mean heterosis was significant for survival to weaning for the F2 generation and approached significance (P = .06) for the combined F3 and F4 generations. Mean heterosis over all composite populations and heterosis for each composite population were significant in all generations for weight at birth and at 200 d and for ADG from birth to weaning. Retained heterosis was not less than expected from retained heterozygosity in composite populations for the traits evaluated. These results suggest that heterosis for these traits likely is due to dominance effects and, thus, can be attributed to the recovery of accumulated inbreeding depression in the parental breeds.

Analysis of Variance↗