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PubMed2003

Overwintering in Drosophila melanogaster: outdoor field cage experiments on clinal and laboratory selected populations help to elucidate traits under selection.

Insects can adapt to temperate environments by increasing levels of resistance to cold conditions over winter and/or altering reproductive patterns to focus reproduction in favourable conditions. In temperate areas, Drosophila melanogaster persists over winter at the adult stage. A previous experiment, conducted with flies kept in outdoor population cages in the temperate winter, indicated that temperate populations produced more eggs than did tropical populations following an abrupt increase in reproduction in late winter. In contrast, the tropical populations produced more eggs prior to the increase. Both patterns resulted in a higher net number of surviving offspring for temperate populations. Here we again examine the clinal pattern in reproduction using outdoor cages, this time held under tropical winter conditions. In this environment, surprisingly, egg production was higher and on average earlier in populations originating from temperate areas. However, mortality rates also increased with latitude of origin, and the relationship of lifetime egg production to latitude should therefore be measured. To test the role of altered pattern of egg production per se in the reproductive advantage of temperate populations in the temperate winter, we tested the performance of laboratory lines selected for altered reproductive patterns, under temperate winter conditions. Lines selected for high early fecundity exhibited this characteristic in the field cages and lines selected for late reproduction exhibited a relatively high fecundity in spring. The timing of the abrupt increase in egg production was identical in these sets of lines and occurred at the same time in recently collected populations, suggesting evolutionary conservation of the switch. These findings suggest that changes in early and late reproduction per se determine adaptation to temperate winter conditions, and illustrate how laboratory selection lines can be used to understand traits underlying adaptive shifts in field performance.

Adaptation, Physiological↗
PubMed2000

A stochastic model simulating the feeding-health-production complex in a dairy herd.

A dynamic, stochastic, and mechanistic Monte Carlo model, simulating a dairy herd with focus on the feeding-health-production complex is presented. By specifying biological parameters at cow level and a management strategy at herd level, the model can simulate the technical and economic consequences of scenarios at herd level. The representation of the feeding-health-production complex is aimed to be sufficiently detailed, to include relationships likely to cause significant herd effects, and to be sufficiently simple to enable a feasible parameterization of the model and interpretation of the results from the model. Consequently, diseases are defined as four disease types: two metabolic disease types, an udder disease type, and a reproductive disease type. Risk factors for the diseases were defined as parity, yield capacity, disease recurrence, disease interrelationships, lactation stage, and season. Direct effects of the diseases were defined according to milk yield, feed intake, feed utilization, conception, culling, involuntary removal, and death. Scenarios differing in base risks of milk fever and ketosis, heat detection rate, and culling strategy were simulated for describing the model behavior. Annual milk yield per cow was decreased by increased risk of ketosis and by increased risk of milk fever, even though no direct effect of milk fever on milk yield was modeled at the cow level. The indirect effect from milk fever is a consequence of increased replacement rate (relatively lower milk yield from younger cows). By ignoring the history of milk fever in insemination and replacement decisions, a significantly reduced net income per cow was found in some herds. We concluded that important benefits from using such a herd model are the capability of accounting for herd management factors and the advantage of avoiding to double count the indirect effects from disease, such as increased risk of other diseases, poorer reproduction results, and increased risk of culling and death.

Animals↗
PubMed1999

[Reproductive performance and milk production of Israeli-Holstein cows with different supplementation during the dry period].

In three field trials comprising 602 Israeli-Holstein dairy cows, the effect of the dry period ration on reproductive performance, culling rate and milk production was investigated. The cows were fed in groups. The basic dry period rations consisted for two herds of medium quality cereal hay and for one herd of corn straw, which were fed ad libitum. In each herd dry cows were assigned to an experimental and control group. Cows of the experimental group were supplemented with 1.5 to 3 kg of lactating cows mixed ration (LMR), whereas in the control group the amount of supplement was increased by the factor two or 3.3. In the experimental group the amount of the supplement was calculated to achieve levels of net energy and of crude protein close to NRC requirements; in the control group the level of net energy and protein was 12 to 18% higher as compared to the experimental group. The amount of LMR supplement in the experimental group of herds A, B, C were 1.5 kg, 1.9 kg, and 3 kg, respectively. In the control groups these amounts were 5 kg, 3.8 kg, and 6 kg, respectively. The groups fed moderate amounts of LMR supplement had a higher conception rate at first insemination, a higher percentage of cows conceiving and fewer cows culled in the consecutive lactation than cows fed increased amounts of LMR supplement. The lactational incidence of reproductive disorders and the milk production were not affected by the differences in feeding during the dry period. Reproductive performance and culling rate appeared to be more favorable for cows fed moderate amounts of supplement during the entire dry period or during the last 3 to 4 weeks of the dry period.

Animal Feed↗
PubMed2006

Further evaluation of alternative air-filtration systems for reducing the transmission of Porcine reproductive and respiratory syndrome virus by aerosol.

The purpose of this study was to compare 4 methods for the reduction of aerosol transmission of Porcine reproductive and respiratory syndrome virus (PRRSV): high-efficiency particulate air (HEPA) filtration, 2x-low-cost filtration, bag filtration, and use of a filter tested against particles derived from dioctylphthalate (DOP). The HEPA-filtration system used a prefilter screen, a bag filter (Eurovent [EU] 8 rating), and a HEPA filter (EU13 rating). The low-cost-filtration system contained mosquito netting (prefilter), 2 fiberglass furnace filters, and 2 electrostatic furnace filters. Bag filtration involved the use of a filter rated EU8 and a minimum efficiency reporting value (MERV) of 14. The 95%-DOP, 0.3-microm-filtration system involved a pleat-in-pleat V-bank disposable filter with a 95% efficiency rating for particles 0.3 microm or greater in diameter and ratings of EU9 and MERV 15. No form of intervention was used in the control group. The experimental facilities consisted of 2 chambers connected by a 1.3-m-long duct containing the treatments. Recipient pigs, housed in chamber 2, were exposed to artificial aerosols created by a mechanically operated mister containing modified live PRRSV vaccine located in chamber 1. Aerosol transmission of PRRSV occurred in 0 of the 10 HEPA-filtration replicates, 2 of the 10 bag-filtration replicates, 4 of the 10 low-cost-filtration replicates, 0 of the 10 95%-DOP, 0.3-microm-filtration replicates, and all 10 of the control replicates. Using a similar approach, we further evaluated the HEPA- and 95%-DOP, 0.3-microm-filtration systems. Infection was not observed in any of the 76 HEPA-filtration replicates but was observed in 2 of the 76 95%-DOP, 0.3-microm replicates and 42 of the 50 control replicates. Although the difference between the 95%-DOP, 0.3-microm and control replicates was significant (P < 0.0005), so was the level of failure of the 95%-DOP, 0.3-microm system (P = 0.02). In conclusion, under the conditions of this study, some methods of air filtration were significantly better than others in reducing aerosol transmission of PRRSV, and HEPA filtration was the only system that completely prevented transmission.

Aerosols↗
PubMed2006

Ageing and the evolution of female resistance to remating in seed beetles.

Female remating behaviour is a key mating system parameter that is predicted to evolve according to the net effect of remating on female fitness. In many taxa, females commonly resist male remating attempts because of the costs of mating. Here, we use replicated populations of the seed beetle Acanthoscelides obtectus selected for either early or late life reproduction and show that 'Early' and 'Late' females evolved different age-specific rates of remating. Early females were more likely to remate with control males as they aged, while Late females were more resistant to remating later in life. Thus, female remating rate decreases with age when direct selection on late-life fitness is operating and increases when such selection is relaxed. Our findings not only demonstrate that female resistance to remating can evolve rapidly, but also that such evolution is in accordance with the genetic interests of females.

Aging↗
PubMed1995

The use of progestins for programming assisted reproductive cycles and gonadotropin-releasing hormone agonist flare-up protocols in older patients.

OBJECTIVES: To determine if the use of norethisterone acetate (NET) in the previous cycle affects the ovarian response to GnRH agonist (GnRH-a) in flare-up protocols and controlled ovarian hyperstimulation in older patients. DESIGN: Retrospective analysis of the outcome of the assisted reproductive technology (ART) cycle. PATIENTS: Eighty women > 37 years old undergoing controlled ovarian hyperstimulation (COH) for a ART cycle (GIFT, IVF, zygote intrafallopian transfer). Forty received NET during the luteal phase of the previous cycle for programming the procedure and 40 did not receive NET (control group). Gonadotropin-releasing hormone agonist in follicular phase (flare-up) protocols were administered to all the patients. MAIN OUTCOME MEASURES: Cycle outcome: amount of gonadotropins used, oocyte production and quality, fertilization, and pregnancy rates. Estradiol, FSH, and LH levels the first 3 days of COH in eight patients. RESULTS: There were no differences between both groups in the cycle outcome. Estradiol levels during the first 3 days of COH were higher in the patients that did not receive NET in the previous cycle. Follicle-stimulating hormone and LH levels were similar in both groups. CONCLUSIONS: The administration of NET in the previous cycle in patients > 37 years old does not affect the ovarian response to the combination of follicular phase GnRH-a and gonadotropins for COH.

Adult↗
PubMed1994

Long-term benefits and risks of alternative methods of fertility control in the United States.

A risk-benefit analysis of five alternative approaches to fertility control among US women over the age of 30 was performed: tubal ligation, vasectomy, intrauterine device, barrier method (condom), and combined oral contraceptives. Taken into account were age-specific probabilities of contraceptive failure, fecundability, spontaneous abortion, reproductive mortality (ectopic pregnancy, delivery, or induced abortion), life table mortality, and mortality from specific cancer sites (ovarian, endometrial, breast, and prostate) and cardiovascular disease. Relative to women using no contraceptive precautions, the use of any method of contraception between the ages of 30 and 50 was associated with net benefit in terms of averted deaths. However, when duration of observation was extended up to age 80, we predicted an excess of about 880 deaths from prostate cancer per 100,000 users of vasectomy. Other methods continued to be associated with net benefit, ranging from 130 to 360 deaths averted per 100,000 users. It was concluded that the non-reproductive risks and benefits of contraceptive methods continue to be relevant long after the reproductive years. The balance of risks and benefits may differ in other countries with different cause-specific and life table mortality rates.

Adult↗
PubMed1982

WHO special programme of research, development and research training in human reproduction. Task force on long-acting agents for the regulation of fertility.

A multicentre phase III clinical trial has been undertaken to compare norethisterone enantate (NET-EN) given by two different treatment regimens and depot-medroxyprogesterone acetate (DMPA). After 18 months of observation, preliminary findings are reported for 1,589 women who received DMPA 150mg every 90 days; 790 women who received NET-EN 200mg every 60 days; and 796 women who received NET-EN, 200mg every 60 days for 6 months, then 200mg every 84 days. The overall discontinuation rates per 100 women were similar for all three treatment groups over the 18 months observation (61.8 - 63.5 per 100 women). The discontinuation rates for bleeding problems and for personal reasons were also similar for all three treatment groups. However, terminations due to amenorrhoea were significantly higher among DMPA users (12.1 and 17.4 per 100 women at 12 and 18 months) as compared with both NET-EN groups (6.8 - 8.2 per 100 women at 12 months and 10.4 - 10.9 per 100 women at 18 months). The only significant difference in pregnancy rates observed between the three groups was a higher rate at 18 months among NET-EN (84 days) users (1.6 per 100 women), as compared with DMPA users (0.2 per 100 women). There was no overall significant difference between the two NET-EN groups, although between the 6 and 18 month's follow-up when the two NET-EN regimens diverged, the NET-EN (84 days) users' pregnancy rate rose significantly, whereas in the NET-EN (60 days) group the pregnancy rate did not change. There was a significantly higher weight gain in those subjects using NET-EN at 60-day intervals compared with those using it at 84-day intervals.

Amenorrhea↗
PubMed1994

Glucose and L-lactate metabolism in pregnant and in lactating ewes fed barley- or ground maize-based diets.

The contribution of glucose absorbed from the small intestine to whole-body glucose metabolism was examined in ewes during late pregnancy and early lactation, using diets based on ground barley or ground maize. Glucose and L-lactate turnover in the whole body and the mesenteric-drained viscera were investigated in these ewes using isotope dilution techniques. The net absorption of glucose by the mesenteric-drained viscera and whole-body glucose turnover were unaffected by diet or reproductive status. Arterial and mesenteric venous blood glucose concentrations, arterial and mesenteric venous L-lactate concentrations and whole-body lactate turnover were all significantly higher in lactation than in pregnancy. The whole-body rates of lactate conversion to glucose and to other products were significantly higher in lactation than in pregnancy. Using a two-pool model of whole-body glucose and lactate metabolism, a relatively high percentage of glucose was converted to lactate (64-84%), accounting for 60-80% of whole-body lactate turnover. A model of glucose and lactate metabolism by the mesenteric-drained viscera was constructed. Both the calculated endogenous glucose production and the visceral conversion of glucose to lactate were greater in lactation than in pregnancy when barley was fed. Calculated total glucose absorption was relatively constant, contributing between 26 and 59% of whole-body glucose turnover. Diet had little effect on glucose and lactate metabolism in either the mesenteric-drained viscera or the whole-body of breeding ewes.

Animals↗
PubMed1991

Animal choice behavior and the evolution of cognitive architecture.

Animals process sensory information according to specific computational rules and, subsequently, form representations of their environments that form the basis for decisions and choices. The specific computational rules used by organisms will often be evolutionarily adaptive by generating higher probabilities of survival, reproduction, and resource acquisition. Experiments with enclosed colonies of bumblebees constrained to foraging on artificial flowers suggest that the bumblebee's cognitive architecture is designed to efficiently exploit floral resources from spatially structured environments given limits on memory and the neuronal processing of information. A non-linear relationship between the biomechanics of nectar extraction and rates of net energetic gain by individual bees may account for sensitivities to both the arithmetic mean and variance in reward distributions in flowers. Heuristic rules that lead to efficient resource exploitation may also lead to subjective misperception of likelihoods. Subjective probability formation may then be viewed as a problem in pattern recognition subject to specific sampling schemes and memory constraints.

Animals↗
PubMed2001

What affects the costs of raising replacement dairy heifers: a multiple-component analysis.

A DP model of a dairy replacement herd was developed to analyze the impact of different dairy and replacement herd variables on the cost of rearing replacements for a representative dairy herd of 100 cows. A model was developed with Pennsylvania and US average information as the basis for the parameters. We used age at first calving of 25 mo, calving interval of 13 mo, herd-culling rate of 25%, and preweaned calf death of 10% as the base for comparison. We examined the impact of factors including age at first calving, calving interval, PDR, and the number of replacements required. From the base model, the total cost of rearing sufficient replacements for a 100-cow herd was $32,344. A reduction in culling rate to 20%, holding all other factors fixed, caused the net costs of raising replacements for the dairy herd to fall by $7968 or 24.6%. Increasing the culling rate above 25% led to a deficit in replacements for maintaining constant herd size, assuming a closed herd. The average age at first calving also affected the net costs of raising replacement heifers; reducing the age at first calving by 1 mo lowered the cost of a replacement program by $1400 or 4.3%. Changes in the length of the calving interval or in the PDR had marginal impacts on the net costs of replacement programs when compared with either herd-culling rate or average age at first calving.

Age Factors↗
PubMed1975

Growth and Development of Soybean (Glycine max [L.] Merr.) Pods: CO(2) Exchange and Enzyme Studies.

The rates of CO(2) exchange and (14)CO(2) incorporation in the light and dark and the activities of several photosynthetic, photorespiratory, and respiratory enzymes of soybean (Glycine max [L.] Merr. cv. Wye) reproductive structures were determined at weekly intervals from anthesis to pod maturity. At all stages of pod development soybean reproductive structures were found to be incapable of net photosynthesis under the experimental conditions employed, but capable of gross photosynthesis and light-induced (14)CO(2) uptake. Consistent with the lack of net photosynthesis throughout the development of the reproductive structure, the maximum in vitro activity of ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) in pod tissue was only 3% of that in leaf extracts when expressed on a fresh weight basis. We concluded that the major role of the reproductive structure of the soybean with respect to photosynthetic carbon metabolism is the reassimilation of its respiratory CO(2).

Journal Article↗
PubMed1990

Influence of variations in biological and economical parameters on beef production net returns.

Net returns were defined as a function of the monetary returns (revenue) generated by the outputs less the monetary costs generated by the variable inputs. Outputs included total weaning weights of steers and heifers, weight of cull cows and weight of open heifers. Inputs included both feed and nonfeed costs. The net returns equation was incorporated as the objective function in a linear programming model. By maximizing the objective function, the breeding system that generated the highest net returns could be identified considering certain resource constraints. Breeding systems included purebred Herefords; small rotational dual purpose (SR), utilizing the breeds Angus, Pinzgauer, Gelbvieh and Tarentaise; large rotational (LR), a three-way rotational cross with the breeds Charolais, Simmental and Maine-Anjou; and Angus-sired terminal (AL) utilizing Angus as the sire breed and LR heifers as the maternal breed. Large rotational generally produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size), calving rates, management systems, environment, beef to feed price ratios and purchased or farm-produced (inexpensive) feed utilized. Only under the conditions of a herd size constraint and farm-produced feed did AL exceed SR in net returns. Hereford had larger net returns than LR only when the two breeding systems were evaluated in an environment assumed to be reproductively stressful to LR. Ranking of breeding systems were dependent on specific conditions and indicated that one must consider each resource constraint and environment in which cattle are expected to produce before making breeding system recommendations.

Animal Feed↗
PubMed1999

Keep the chicks moving: how Sandwich terns can minimize kleptoparasitism by black-headed gulls.

Sandwich terns, Sterna sandvicensis, often nest in association with black-headed gulls, Larus ridibundus. The gulls provide protection against predators, but can also adversely affect the terns' reproductive success through predation and piracy of fish. To test whether leading the chicks away from the nest site is an evasive strategy used by the parents to reduce the incidence of robbery by the gulls, we kept one group of Sandwich tern chicks at their original breeding site, while, with a wire-netting enclosure, we moved another group away from the gulls. The rate of kleptoparasitism was greatly reduced when the tern chicks were moved away from the original nest site, resulting in faster growth and earlier fledging. The rate of food parasitism and chick condition were affected only during the first 5 days of the experiment. After that, the rate of kleptoparasitism no longer differed between chicks that we moved away and those remaining in the colony. A second shift of the chicks again led to less kleptoparasitism and better chick condition. In line with these findings, the condition of free-living chicks that were lured away from their nesting site by their parents also improved. In particular, chicks initially in poor condition, which apparently suffered from high rates of kleptoparasitism, left the colony site. Free-living chicks are often lured away from the robbing gulls. However, not all subcolonies provided suitable escape routes and subsequently chicks in such subcolonies suffered from high mortality rates. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1993

Integrated systems analysis of sow replacement rates in a hierarchical swine breeding structure.

Sow replacement rates in a three-tiered breeding structure were investigated for a 10-yr planning horizon using a stochastic life-cycle swine production model. Market hogs were produced in a three-breed static crossing program and marketed on a liveweight basis. Growth and reproductive traits of individual pigs were simulated using genetic, environmental, and economic parameters. Sows were culled after a maximum of 1, 5, or 10 parities. Systems were defined by maximum sow age at culling and included combinations of 1- and 5-parity nucleus and 1-, 5-, and 10-parity multiplier and commercial tiers. Economic response to index selection was considerable for all culling alternatives with yearly increases in system profits ranging from $1.06 to 1.44 for each commercial hog marketed. When sows were culled after one parity in nucleus, multiplier, and commercial tiers, respectively (1,1,1), annual changes in net returns and all cost measures were 40 to 50% larger than responses in systems with lower sow replacement rates. Based on 10-yr averages for net returns, systems with low multiplier- and commercial-level replacement rates were more profitable than systems with higher replacement rates. The most profitable system (5,10,10) differed from the least profitable system (1,1,1) by more than $10 per pig, but when the (1,1,1) system was excluded, the range was only $3 per pig. The system with lowest replacement rates supported 3,388 more multiplier and 34,151 more commercial sows from a 750-sow nucleus level than the (1,1,1) system. Output from the two extremes differed by > 664,000 commercial market hogs sold.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Simulated economic effects of improving the sensitivity of a diagnostic test in paratuberculosis control.

Low sensitivity (Se) of diagnostic tools is often mentioned as a major problem in the control of paratuberculosis (PTB) and much effort is put into the improvement of these tests. The hypothetical perspectives of improving the Se of a milk-antibody ELISA (hereafter: milk-ELISA) used in test-&-cull strategies against PTB in dairy cattle were investigated by simulations. The current Se varies between 10 and 80%, increasing with increasing lactation stage, parity and infection stage. We simulated the effects on a dairy herd's production of improving this Se to 80% (independent of these factors) and assumed no concomitant decrease in specificity. By using a PTB model called PTB-Simherd, 12 scenarios were simulated to study three test-&-cull strategies in each of four herds with 200 dairy cows. To show the maximal effect of using test-&-cull with such an improved test we simulated three strategies: (1) no testing, (2) testing with milk-ELISA test with the current Se and culling of positive cows immediately and (3) testing with milk-ELISA test with a Se improved to 80% and culling positive cows immediately. The four herds were defined by a moderate (25%) or high (80%) initial true within-herd prevalence (including young stock), and a poor or good heat-detection success of 40 or 60%. We assumed that these factors influenced the effects of improving the Se of the milk-ELISA. Management both concerning calf management and in general was specified to represent a typical Danish herd. Using an improved milk-ELISA was predicted to reduce the prevalence of PTB more effectively than the current ELISA, and over 10 years bring the production of a herd with moderate initial prevalence up to a production level comparable to a non-infected herd (unlike if the current ELISA had been used). In a herd with high initial prevalence (80%) milk production was increased more by using the improved milk-ELISA, but after 10 years the replacement rate was still very high causing problems with having enough recruitment animals-especially in high-prevalence herds with poor reproductive performance. Economically important measurements in all four herds benefited from the improvement of the test over a 10-year period. However, in the first 3-5 years the improved test would be more expensive to use than the current test, due to increased replacement (reduced net annual revenue per cow euro15 on average) but after that, net annual revenue increased continuously; after 10 years it was euro70-90 higher, than if the current milk-ELISA was used. Also, the milk-ELISA test with its current Se seemed to be profitable already after 2 years in high-prevalence herds using a test-&-cull strategy based on the milk-ELISA alone.

Animals↗
PubMed2004

Adaptive changes in harvested populations: plasticity and evolution of age and size at maturation.

We investigate harvest-induced adaptive changes in age and size at maturation by modelling both plastic variation and evolutionary trajectories. Harvesting mature individuals displaces the reaction norm for age and size at maturation toward older ages and larger sizes and rotates it clockwise, whereas harvesting immature individuals has the reverse qualitative effect. If both immature and mature individuals are harvested, the net effect has approximately the same trend as when harvesting immature individuals only. This stems from the sensitivity of the evolutionary response, which depends on the maturity state of harvested individuals, but also on the type of harvest mortality (negatively or positively density dependent, density independent) and the value of three life-history parameters (natural mortality, growth rate and the trade-off between growth and reproduction). Evolutionary changes in the maturation reaction norm have strong repercussions for the mean size and the density of harvested individuals that, in most cases, result in the reduction of biomass--a response that population dynamical models would overlook. These results highlight the importance of accounting for evolutionary trends in the long-term management of exploited living resources and give qualitative insights into how to minimize the detrimental consequences of harvest-induced evolutionary changes in maturation reaction norms.

Adaptation, Biological↗
PubMed1997

Weight-length relationships and reproduction of bream (Abramis brama L.) in Keszthely Bay of Lake Balaton.

The weight-length relationships of bream (Abramis brama L. 1758, family Cyprinidae) were studied in Lake Balaton, Hungary, Fish were randomly collected with a gill net from Keszthely bay between March and November 1995. The condition of bream was investigated monthly, using morphometric parameters of the body, fecundity estimations, and gonadosomatic indices (GSI). The weight-length relationships show that the body weight of bream increased at an approximately 3.4 times higher rate than its length (b = 3.41). The GSI of females were always higher than those of the males. The GSI values of females reached their maximum (14.76-22.22) from March to May. Egg diameter is positively correlated with the spawning months, as demonstrated by the relationship found between egg diameter and GSI (r = 0.94; P < 0.001) Fecundity estimates exhibited a linear relationship to length and weight.

Animals↗