Undesirable side effects of selection for high production efficiency in farm animals: a review

Milk yield per cow has more than doubled in the previous 40 years and many cows now produce more than 20,000 kg of milk per lactation. The increase in production should be viewed with concern because: i) the increase in milk yield has been accompanied by declining fertility, increasing leg and metabolic problems and declining longevity; ii) there are unfavourable genetic correlations between milk yield and fertility, mastitis and other production diseases, indicating that deterioration in fertility and health is largely a consequence of selection for increased milk yield; and iii) high disease incidence, reduced fertility, decreased longevity and modification of normal behaviour are indicative of substantial decline in cow welfare. Improving welfare is important as good welfare is regarded by the public as indicative of sustainable systems and good product quality and may also be economically beneficial. Expansion of the Profitable Lifetime Index used in the UK to include mastitis resistance and fertility could increase economic response to selection by up to 80%, compared with selection for milk production alone. In the last 10 years, several breeding organisations in Europe and North America followed the example of Nordic Countries and have included improving fertility and reducing incidence of mastitis in their breeding objectives, but these efforts are still timid. A multi-trait selection programme in which improving health, fertility and other welfare traits are included in the breeding objective, and appropriately weighted relative to production traits, should be adopted by all breeding organisations motivated in their goal of improving welfare.

The impact of genetic selection for increased milk yield on the welfare of dairy cows.

Fish aquaculture for commodity production, fisheries enhancement and conservation is expanding rapidly, with many cultured species undergoing inadvertent or controlled domestication. Cultured fish are frequently released, accidentally and deliberately, into natural environments where they may survive well and impact on wild fish populations through ecological, genetic, and technical interactions. Impacts of fish released accidentally or for fisheries enhancement tend to be negative for the wild populations involved, particularly where wild populations are small, and/or highly adapted to local conditions, and/or declining. Captive breeding and supplementation can play a positive role in restoring threatened populations, but the biology of threatened populations and the potential of culture approaches for conserving them remain poorly understood. Approaches to the management of domestication and cultured-wild fish interactions are often ad hoc, fragmented and poorly informed by current science. We develop an integrative biological framework for understanding and managing domestication and cultured-wild fish interactions. The framework sets out how management practices in culture and for cultured fish in natural environments affect domestication processes, interactions between cultured and wild fish, and outcomes in terms of commodity production, fisheries yield, and conservation. We also develop a typology of management systems (specific combinations of management practices in culture and in natural environments) that are likely to provide positive outcomes for particular management objectives and situations. We close by setting out avenues for further research that will simultaneously improve fish domestication and management of cultured-wild fish interactions and provide key insights into fundamental biology.

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Cultured fish: integrative biology and management of domestication and interactions with wild fish

This text synthesizes existing knowledge of the process of domestication and how domestication has affected the behaviour of captive wild and domesticated animals, including both farm, zoo and companion animals. Three broad themes are addressed: genetic contributions to the process of domestication; experimental contributions to the process of domestication; the process of feraliztion (i.e. the adaptation of domesticated animals when returned to their natural habitat.

Animal Domestication and Behavior

The immune system is a life history trait that can be expected to trade off against other life history traits. Whether or not a trait is considered to be a life history trait has consequences for the expectation on how it responds to natural selection and evolution; in addition, it may have consequences for the outcome of artificial selection when it is included in the breeding objective. The immune system involved in pathogen resistance comprises multiple mechanisms that define a host's defensive capacity. Immune resistance involves employing mechanisms that either prevent pathogens from invading or eliminate the pathogens when they do invade. On the other hand, tolerance involves limiting the damage that is caused by the infection. Both tolerance and resistance traits require (re)allocation of resources and carry physiological costs. Examples of trade-offs between immune function and growth, reproduction and stress response are provided in this review, in addition to consequences of selection for increased production on immune function and vice versa. Reaction norms are used to deal with questions of immune resistance vs. tolerance to pathogens that relate host health to infection intensity. In essence, selection for immune tolerance in livestock is a particular case of selection for animal robustness. Since breeding goals that include robustness traits are required in the implementation of more sustainable agricultural production systems, it is of interest to investigate whether immune tolerance is a robustness trait that is positively correlated with overall animal robustness. Considerably more research is needed to estimate the shapes of the cost functions of different immune strategies, and investigate trade-offs and cross-over benefits of selection for disease resistance and/or disease tolerance in livestock production.

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Immune response from a resource allocation perspective

ummary
We have provided a bridge between geneticists, who tend to concentrate on genes and their frequencies, and other biologists, who are much more aware of how severely the environment constrains and limits life. This bridge is the recognition that

a. fitness is a product of important component traits,
b. these and most other traits consume environmental resources and these resources are additively related and can sum to no more than the total resources an animal can obtain from the environment,
c. allele frequencies can alter only to the degree that the phenotypes that carry the alleles reproduce themselves successfully, i. e. are fit,
d. fitness must rise, because it is never free from natural selection upwards, to the point where it can rise no further, because all environmental resources available to an animal are being used most efficiently,
e. in this state of adaptation, fitness is completely limited by the environment and all other traits important to the animal are constrained to a greater or lesser degree at intermediate, “optimal” values, and
f. traits or molecules unimportant to animals, so that they are completely neutral with respect to fitness, are free to drift genetically and hence gene substitutions can occur at rates related to their mutation rates.


This bridge between genetics and other parts of biology shows that the various theories apparently causing concern for the modern synthetic theory of evolution are entirely compatible with it. Bursts of rapid evolutionary change between long periods of evolutionary stasis are the necessary consequences of strong natural selection acting on fitness, in ecosystems that are stable until external forces cause them to change. Neutral (random) evolution describes the fate of genetic material that is unimportant for organisms, i. e. material that is truly neutral with respect to fitness.

Zusammenfassung
Quantitative Genetik und Evolution. Genugt unser genetisches Verstandnis um Evolution zu erklaren?

Wir bauten eine Brucke zwischen Genetikern, die mit Genen und ihren Frequenzen arbeiten, und anderen Biologen, die wissen wie stark die Umwelt Lebewesen hemmend beeinflust. Diese Brucke besteht aus den folgenden Erkenntnissen:

a. Fitness ist ein Produkt der wichtigsten Komponenten.
b. Diese und die meisten anderen Merkmale verbrauchen Nahrung. Die Nahrung, die ein Lebewesen nur aus der Umwelt erhalten kann, enthalt die maximale Summe der metabolischen Ressourcen, die das Wesen dann in additiver Weise in einzelne Merkmale investiert.
c. Allelfrequenzen konnen sich nur erhohen, wenn der Phanotyp, der die Allele tragt, sich erfolgreich fortpflanzt.
d. Weil Fitness immer unter naturlicher Selektion nach oben steht, mus der Fitnesswert steigen bis alle Umweltressourcen so effizient wie moglich genutzt werden.
e. In solchem Stadium der volligen Anpassung an die Umwelt, ist Fitness ganz durch die Umwelt limitiert und alle anderen wichtigen Merkmale in groserem oder kleinerem Mase in Optimalwerte gezwangt.
f. Unwichtige Merkmale oder genetische Molekule, die keine Wirkung im Lebewesen haben, so das sie wirklich neutral sind gegenuber Fitness, durfen ungehemmt driften und zeigen deshalb Substitutionsraten, die ihren Mutationsraten entsprechen.


Diese Brucke zwischen Genetik und der ubrigen Biologie zeigt, das die Evolutionstheorien, die angeblich die moderne Evolutionssynthese storen, vollkommen mit ihr im Einklang sind. Sprungartige Evolution zwischen langen, stabilen Zeitraumen sind die Zwangsfolgen starker naturlicher Selektion auf Fitness in Okosystemen, die sich nicht andern bis ein Druck auserhalb des Systems das bewirkt. Neutrale Evolution beschreibt, was mit dem Material passiert, das unwichtig fur Lebewesen ist.

Quantitative genetics and evolution: Is our understanding of genetics sufficient to explain evolution?

Summary

Interest in molecular biology and cloning of animals is high. It is widely predicted that biotechnological improvements will revolutionize animal production on farms. The environment, as a constraint, is usually ignored. Yet, as organisms need environmental resources to live, there must come a point above which the genetically improved animals are no longer economically sustainable in farm environments. This recognition may be more important than ethical questions about biotechnology. This paper presents a fundamental theorem about natural selection and ‘improvement’ of organisms. This shows that, in evolution and on farms, the environment usually limits organisms and that, as a direct consequence, ‘improvement of genotypes’ beyond this limit is pointless, and does not occur in evolution.



Zusammenfassung

Umwelt als limitierende Grenze der genetischen Verbesserung. Ein alternatives Theorem der Naturlichen Selektion



Grosses Interesse an Biotechnologie fuhrt zu der Erwartung das Tierproduktion sich revolutionar verandern wird. Die Umwelt, als Hemmfaktor, wird generell ubersehen. Trotzdem brauchen Tiere Ressourcen aus der Umwelt um zu leben. Andauernde genetische Verbesserung bringt Tiere unausweichlich zu dem Niveau uber welchem sie nicht mehr wirtschaftlich haltbar sein werden in der kommerziellen Tierproducktion. Diese Erkenntnis ist wahrscheinlich wichtiger als ethische Fragen uber Anwendung der Biotechnologie an Tieren. Diese Arbeit bringt ein fundamentales Theorem uber naturliche Selektion und “Verbesserung” von Organismen. Dieses zeigt das, in der Evolution und in landwirtschaftlichen Betrieben, die Umwelt normalerweise Grenzen setzt fur Organismen. Als direkte Folge ist die “Verbesserung der Genotypen”uber solche Grenzen hinaus zwecklos, und kommt auch in der Evolution nicht vor.

Environmental limit to genetic change. An alternative theorem of natural selection

Summary

It is known that performance in Thoroughbred racing is not a single character. This study analysed horses' performances for a number of parameters which may prove useful to Thoroughbred breeders. Each horse, and subsequently each sire and dam, were given an estimate for their speed, stamina, best distance, and best track condition, and several different measures of peak performance, as well as average performance. Most of these parameters proved highly heritable, with the exception of best track condition. The most startling result was the almost 100% heritability calculated for best racing distance.



If accurate estimates of values for highly heritable parameters such as these were available for all horses in a population, then breeders would be in a much better position to plan matings to obtain a horse which will compete well in a particular type of event. Given the large range of conditions in which Thoroughbreds compete, it would seem more sensible to aim at producing a horse with a specialty ability, rather than hoping to produce one which will excel in all conditions.

The inheritance of speed, stamina and other racing performance characters in the Australian Thoroughbred

Summary

An analysis is described using heritability estimates for racing performance in the Australian Thoroughbred, calculated using the complete race results of two recent years. A number of methods, some new, for assessing racing performance were used. The results confirm that heritability for racing performance is high, with the estimates ranging to above 0.6. This value is somewhat higher than that obtained in overseas studies, although when the same measures are analysed, the estimates found are comparable.



Rather than just dismissing these estimates as too high, a number of factors which may affect their size, both upwards and downwards, are discussed. The conclusions reached are that high estimates are probably real and are compatible with a constantly selected population if the selection practised is not accurate. Furthermore, the danger (or folly) of striving to lower the estimates obtained by the utilization of more sophisticated statistical processes, without proper consideration for the biological nature of the characters being studied, nor indeed their precise definition, is highlighted.



Zusammenfassung

Hentabilitat von Rennerfolg in Vollblutern: Eine Analyse australischer Daten



Anhand von den gesammten Daten uber Ergebnisse von Galopprennen in ganz Australien in zwei der letzten Jahren wurde Heritabilitat von Rennerfolg geschatzt. Verschiedene Methoden den Rennerfolg zu messen wurden benutzt, darunter auch neue. Die Analyse bestatigt das Heritabilitat von Rennerfolg hoch ist, einige Schatzwerte liegen uber 0.6. Diese Werte sind etwas hoher als ubliche Werte in der Literatur, aber wo die gleichen Messmethoden benutzt wurden sind unsere Werte mit denen der Literatur vergleichbar.



Ohne diese Schatzwerte als zu hoch abzuwerten, diskutieren wir Faktoren welche Schatzwerte in ihrer Grose beeinflussen konnen, nach oben wie nach unten. Wir ziehen den Schlus, das hohe Schatzwerte fur Heritabilitat von Rennerfolg wahrscheinlich den richtigen Sachverhalt darstellen. Dieser ist mit einer Population unter standigem Selektionsdruck vereinbar wenn die Selektion nicht akkurat ist. Weiterhin wird die Gefahr beleuchtet, die in Versuchen besteht, Schatzwerte der Heritabitat durch sophistische statistische Methoden zu mindern, wenn man die eigentlichen biologischen Sachverhalte der analysierten Merkmale nur ungenau kennt.

Heritabilities of racing performance in Thoroughbreds: a study of Australian data

Summary

In general, the environment limits the fitness of individual animals, and environmental limitation leads to selection for “optimal”, intermediate values for all traits that matter, whether imposed by natural or artificial selection. We compared the reproduction of laboratory mice in a normal and a hot, humid environment to test this claim. Thirty males and 150 females from a non-inbred line adapted to normal conditions were mated twice (the second time after rerandomisation) to produce the experimental animals. Individual experimental mice from each litter were allocated from weaning (3 weeks) either to the normal or hot environment. At 9 to 12 weeks of age these mice were paired, 1 male with 1 female, until the female had a chance to have 2 litters. 354 pairs in the normal and 362 pairs in the hot environment were mated. All living progeny were weaned at 3 weeks. Average values of reproductive traits, phenotypic correlations between traits, and heritability estimates for many traits were found in each environment.



Negative correlations (trade-offs) between litter number and weight of individual progeny in both environments demonstrated clearly that fitness was limited even in the normal laboratory situation. All quantitative measures of reproduction were lower in the hot room showing that it was more stressful. Yet size of individual young and their survival was not reduced. This may be an adaptive mechanism restricted to housemice.



Lower heritability estimates in first than in second parities for quantitative measures of litter size show that while the mouse is still growing she has fewer resources available for reproduction, making her more susceptible to environmental stress. This challenges accepted wisdom that animal breeders should select their animals when they are young. They are least likely to respond then.



We believe that natural selection causes animals always to push their fitness (reproduction and survival of the progeny) against a limit set by their particular environment. Each environment selects animals that optimally allocate environmental resources there. Problems arise when inappropriate genetic settings cause phenotypes to misallocate metabolic resources. In relatively difficult environments productive animals, including successful transgenics, allocate insufficient resources to fitness.



Zusammenfassung

Begrenzung der Fitnes durch die Umwelt: Reproduktion von Labormausen in gunstigen und schwierigen („tropischen”) Bedingungen



Im Normalfall soll die Umwelt der Fitnes eine obere Grenze setzen. Diese Begrenzung fuhrt zu Selektion auf mittlere „Optimalwerte” bei alien wichtigen Merkmalen. Wir untersuchten die Fortpflanzung von Labormausen in entweder normaler oder heiser Umwelt. Aus einer an erstere angepasten, nichtingezuchteten Linie wurden 30 Mannchen mit 150 Weibchen zweimal verpaart (beim zweiten Mal neu randomisiert) um die Versuchstiere zu erzeugen. Individuen aus jedem Wurf wurden zufallsmasig an die zwei Umwelten verteilt, worin sie ab 3 Wochen aufgezogen wurden. Im Alter zwischen 9 und 12 Wochen wurden sie zufallsmasig 1:1 verpaart bis die Paare Zeit fur zwei Wurfe gehabt hatten. An 354 und 362 Paaren im normalen und heisen Zimmer wurden Daten ihrer Reproduktion erhoben. Alle lebendgeborenen Jungen wurden bis 3 Wochen alt verfolgt. In beiden Umwelten wurden Durchschnittswerte der einzelnen Merkmale, phanotypische Korrelationen wichtiger Merkmale, und Heritabilitatswerte der Merkmale errechnet.



Starke negative Korrelationen zwischen Anzahl der Jungen im Wurf und Gewicht der einzelnen Jungen im Wurf, in beiden Umwelten, zeigen das Fitnes auch in normalen Laborverhaltnissen begrenzt war. Alle quantitativen Mase der Wurfe waren betrachtlich niedriger im heisen Raum, was zeigt, das diese Umwelt mehr Stres bot. Jedoch die Grose und Uberlebensrate der einzelnen Jungen im heisen Raum wurden nicht beeintrachtigt. Diese adaptive Anpassung an schwierige Bedingungen konnte einmalig bei Mus musculus sein.



Niedere Heritabilitaten von quantitativen Masen der Wurfgrose im ersten gegenuber dem zweiten Wurf zeigen, das noch selbst wachsende Weibchen nur wenig Ressourcen fur Fortpflanzung einsetzen konnen und deshalb mehr von Umweltdruck abhangen. Paradoxerweise versuchen Tierzuchter meistens so Jung wie moglich Tiere zu selektieren, die solcher Selektion auf Reproduktion am wenigsten folgen konnen. Diese Situation sollte erneut durchdacht werden.



Uns scheint, das Tiere, weil naturliche Selektion andauernd fortwirkt, jederzeit ihre Fitnes bis an eine obere Grenze, von der Umwelt gesetzt, schieben. Jede Umwelt selektiert Tiere, die ihre metabolischen Ressourcen darin optimal einsetzen. Probleme entstehen, wenn genetische Information Phanotype erzeugt, die Ressourcen fehl einsetzen. In relativ schwieriger Umwelt haben Leistungstiere, und auch erfolgreiche transgenische Tiere, ungenugend Ressourcen ubrig fur Fortpflanzung.

R. G. Beilharz

Papers

Quantitative genetics and evolution: Is our understanding of genetics sufficient to explain evolution?

Environmental limit to genetic change. An alternative theorem of natural selection

The inheritance of speed, stamina and other racing performance characters in the Australian Thoroughbred

Heritabilities of racing performance in Thoroughbreds: a study of Australian data

Environmental limitation on fitness: Reproduction of laboratory mice in benign and stressful ("tropical") conditions.