Domestic Livestock Species Research Articles

Relative risks and approaches to biosecurity in the use of embryo technologies in livestock

Embryo technologies have been integrated into production systems for a variety of livestock species. As relates to transmission of infectious diseases, our working hypothesis has been that use of embryo transfer for distribution of germ plasm within and between herds and flocks is likely safer than the movement of postnatal animals. Indeed, research and experience generally have been supportive of this hypothesis. However, the relative risks of transmitting infectious agents via embryo transfer vary among donor species. Further, different methods of producing embryos appear to present different risks. This paper provides a comparative overview of the risks of transmitting infectious diseases via transfer of both in vivo- and in vitro-derived embryos in common domesticated livestock species. Also discussed are universal approaches to biosecurity in embryo production and transfer.

Avian Semen Cryopreservation: What Are the Biological Challenges?

The value of the ability to cryopreserve and store germplasm has long been recognized for indefinite preservation of genetic material, especially for at-risk populations. In contrast to domestic livestock species, cryogenic storage of poultry semen is not reliable enough for germplasm preservation. The relatively low fertilizing ability of frozen/thawed poultry sperm most likely results from physiological sensitivity to the cryogenic process coupled with the requirement for prolonged sperm functionality in the hen reproductive tract; however, the concept of defining these physiological challenges has been underemphasized. For example, alterations in membrane carbohydrate content and diminished energy production in frozen/thawed sperm have important implications for successful gamete interaction. Recent data suggests that both glycoconjugate content and adenosine triphosphate (ATP) generation are affected by cryopreservation. Moreover, susceptibility to the cryogenic process seems to vary among lines and strains of birds, as illustrated by line-specific differences in ATP concentrations of frozen/thawed sperm from pedigreed commercial layers. Research based on biochemical and molecular comparisons of sperm among lines may lead to identification of factors that influence the freezability of poultry semen.

Cathepsin B Homologue at the Interface between a Parasitic Nematode and Its Intermediate Host

Parelaphostrongylus tenuis is a parasitic nematode that causes a debilitating neurologic disease in many North American cervids and domestic livestock species. We produced a PCR-based cDNA library from infective larvae (L3) in order to identify molecules that mediate parasitism. A dominant 1,250-bp amplicon encoded a homologue of cathepsin B cysteine proteases. The sequence incorporated a C29G substitution in the putative active site. Antibodies generated against a recombinant form detected the native protein (PtCPR-1) in Western blot assays of L3, but not adult worm, extracts. Immunohistochemical methods revealed that PtCPR-1 synthesis was restricted to larval stages within the snail intermediate host (Triodopsis sp.), beginning as early as 2 days postinfection (dpi) of snails. The protein was present in the intestine and luminal contents and was lost from larvae over time. Concurrent studies showed that larvae induced an immune response in snails beginning at 1 dpi. Layers of hemocytes encapsulated larvae immediately after infection, and granuloma-like structures formed around parasites in chronic infections. Loss of PtCPR-1 from L3 and its accumulation in host tissues coincided with degeneration of granuloma architecture 90 to 105 dpi. Fully developed L3 emerged from the snail at this time. Our data implicate PtCPR-1 in larval development and possibly in the emergence of P. tenuis from the intermediate host. Emerged L3 survived desiccation and cold stress, suggesting that they could remain infectious in the environment. Molecules promoting emergence would facilitate dispersal of L3 and increase the likelihood of transmission to definitive hosts.

Application of bovine microsatellite markers for genetic diversity analysis of Swiss yak (Poephagus grunniens)

In order to assess the applicability of bovine microsatellite markers for population genetic studies in Swiss yak, 131 bovine microsatellite markers were tested on a panel of 10 animals. Efficient amplification was observed for 124 markers (94.6%) with a total of 476 alleles, of which 117 markers (94.3%) were polymorphic. The number of alleles per locus among the polymorphic markers ranged from two to nine. Seven loci (ILSTS005, BMS424B, BMS1825, BMS672, BM1314, ETH123 and BM6017) failed to amplify yak genomic DNA. Two cattle Y-chromosome specific microsatellite markers (INRA126 and BM861) amplified genomic DNA from both male and female yaks. However, two additional markers on cattle Y-chromosome (INRA124 and INRA189) amplified DNA from only males. Of the polymorphic markers, 24 microsatellites proposed by CaDBase for within- and cross-species comparisons and two additional highly polymorphic markers (MHCII and TGLA73) were used to investigate the genetic variability and the population structure of a Swiss yak herd that included 51 additional animals. The polymorphic information content ranged from 0.355 to 0.752, while observed heterozygosity (HO) ranged from 0.348 to 0.823. Furthermore, a set of 13 markers, organized into three multiplex polymerase chain reactions, was evaluated for routine parentage testing. This set provided an exclusion probability in a family of four yaks (both parents and two offspring) of 0.995. These microsatellites serve as useful tools for genetic characterization of the yak, which continues to be an important domestic livestock species.

Chronic Wasting Disease and Animal Agriculture

Chronic wasting disease (CWD), a member of the transmissible spongiform encephalopathies (TSEs), is only known to naturally affect mule deer (Odocoileus hemionus), white-tailed deer (O. uirginianus), and Rocky Mountain elk (Ceruus elaphus nelsoni). It has been recognized in an endemic focus along the front range of the Rocky Mountains in northern Colorado and in the hills of southeastern Wyoming for more than 30 years. Since 1996, CWD has been identified in free-ranging and farmed cervids in 15 western and midwestern states and Canadian provinces and elk imported to Korea from Canada. Surveillance for a TSE in cattle sympatric with deer and elk with CWD began in the early 1990s and has been ongoing since then. Experiments to determine host range of CWD in livestock began in the 1980s. Since that time cattle, domestic sheep and domestic goats have been exposed to the CWD agent by various means. All of these species are susceptible to CWD by intracerebral inoculation but, to date, CWD has not been found to affect traditional domestic livestock species when exposed by natural routes. Chronic wasting disease is of concern in farmed elk and white-tailed deer. Control of this disease in the cervid industries is based in state, provincial, and federal regulations. Surveillance of domestic livestock for TSEs in parallel with surveillance for CWD in farmed and free-ranging cervids will need to be continued into the foreseeable future.

The effect of oocyte quality on development.

Oocyte quality affects early embryonic survival, the establishment and maintenance of pregnancy, fetal development, and even adult disease. Quality, or developmental competence, is acquired during folliculogenesis as the oocyte grows, and during the period of oocyte maturation. Assisted reproductive technologies involving ovarian hyperstimulation, or collection of immature oocytes followed by maturation in vitro, perturb this process and result in oocytes with reduced quality. In domestic livestock species, offspring have been produced using in vitro oocyte maturation, although only a small percentage of the original pool of immature oocytes is capable of developing to the blastocyst stage and subsequently resulting in pregnancy. In vitro maturation, as it is currently undertaken, does not support the correct development of oocyte competence. Follicle size affects oocyte quality, potentially implicating messenger RNA or protein stores as factors involved in oocyte competence. Oocytes from preantral follicles grown in vitro are competent to resume meiosis, although development to the blastocyst stage is decreased. An offspring from oocytes produced using this technique was normal at birth but experienced delayed onset health issues, highlighting the importance of oocyte quality long after embryogenesis. Metabolism may play a critical role in oocyte quality because glycolytic activity in mature oocytes is correlated with increased embryonic development. Communication between the oocyte and its surrounding cumulus cells is also important for the development of a competent oocyte. Ovarian stimulation causes delayed embryonic development, increased abnormal blastocyst formation, fetal growth retardation, and increased fetal loss. Thus, although meiosis and even early development may be completed successfully, there are a variety of other processes occurring within the cytoplasm of the oocyte that are required for complete developmental competence. However, the cellular mechanisms that impart oocyte quality are unclear. Until the mechanisms involved in oocyte quality are elucidated, any effort to use assisted reproductive technologies in animals for production or biomedical purposes will be inefficient at best.

Derivation of steady state herd productivity using stage-structured population models and mathematical programming

Assessing production efficiency in livestock herds requires the consideration of the effects of herd structure and dynamics on the calculation of efficiency measures. Steady state herd growth models can accommodate for these effects by considering sustained self-recruiting herds, in which herd size and structure are maintained in an equilibrium state over time. Previously published approaches to steady state herd productivity assessment share a number of limitations, e.g., individual animals are classified by their age only; vital parameters such as fecundity, litter size, milk yield, liveweight and liveweight gain are assumed to remain constant throughout the productive lifespan; and the corresponding computer programs lack the capability of choosing the optimal combination of offtake rates across animal classes that leads to a steady state in herd size and structure. In order to refine the concept of steady state herd productivity assessment and improve its flexibility and applicability, a new method of modelling herd dynamics over time and of deriving optimal steady state herd structure and offtake is presented. Herd dynamics are described through a deterministic, stage-structured matrix population model. Stage-structured matrix population models can be generalized to complex life cycles in which individual animals can be classified by several factors other than age. Translating the population dynamics model into a standard non-linear programming problem allows to derive the optimum offtake policy in each stage class. The proposed approach is very general and can easily be applied to a wide range of domestic livestock species and production systems. Combining stage-structured matrix population models with non-linear programming for the determination of optimal steady state herd structure and culling policy removes most limitations of previously published procedures for steady state herd productivity assessment. It is emphasized that the derivation of an optimal culling regime is crucial in comparative studies, in order to obtain a common basis on which alternatives can be compared in terms of a defined production efficiency measure. Biased comparisons may be obtained when using observed or estimated offtake rates for a given management alternative or production system. The reason is that the actual level of productivity achievable under a given management practice is not necessarily identical with the potential productivity achieved when optimal offtake decisions are taken. The choice of culling policy has a great impact on herd dynamics and structure, and needs to be controlled for in comparative assessments.

Neurological disorders produced by Clostridium perfringens type D epsilon toxin

Although the epsilon toxin of Clostridium perfringens type D produces disease in many species of domestic livestock, neurological disturbance is more common and better studied in sheep. High levels of circulating toxin, especially in lambs, cause cerebral microvascular endothelial damage with disruption of the blood–brain barrier leading to a severe, diffuse vasogenic oedema and an acute or peracute clinical course to death. With lower toxin levels, or in partially immune sheep, a focal, bilaterally symmetrical encephalomalacia sometimes occurs in selectively vulnerable brain regions after a more protracted clinical course, but the pathogenesis is uncertain.

Educational preparedness of veterinarians for foreign animal diseases.

Veterinary medical education in FADs has been and will continue to be critically important if veterinarians are expected to fulfill the profession's primary obligations to society--those of protecting our animals' health, conserving our animal resources, and promoting public health. It is imperative that curricula and instruction in veterinary schools and colleges provide the depth and breadth of knowledge and understanding necessary to prepare all veterinarians, including those in private practice, for their key role in defending against FADs. Development and implementation of governmental and military programs to diagnose, prevent, control, and eradicate FADs will require a dedicated cadre of public sector veterinarians who have a solid educational foundation in FADs and understand the contemporary issues and global challenges we face. Animal-related industries, associations, and organizations will increasingly rely on well-educated veterinarians to help guide them in ways that will protect animals, clientele, consumers, and trading partners from effects of FADs. Agencies and organizations concerned with conservation of animal resources will require veterinary expertise necessary to prevent FADs in a multitude of animal species, including marine animals, wildlife, endangered species, zoologic specimens, and important genetic lines as well as our domestic companion and livestock species. Species affected by FADs also include human beings for those disease agents with zoonotic potential; thus, veterinary education also plays a key role in public health.

Mucosal memory—maintenance and recruitment

The maintenance of IgA antibody responses at mucosal surfaces is the outcome of influences on IgA precursor cell dissemination from the mucosal inductive sites, such as the intestinal Peyer’s patches, their selective extravasation at mucosal effector sites and the retention and local proliferation of these cell populations under local influences. Examination of these local post-extravasational effects has implicated cytokines as major regulatory elements in this process. This paper will address the role of cytokines in induction and expression of IgA responses and the differential requirements for cytokine signals among IgA-committed B cell subsets in both rodent and domestic livestock species. The way in which cytokines influence local immunity in the gut with respect to microbial and parasitic challenge and comparative cytokine effects in extra-intestinal sites, particularly the eye, will be presented, and opportunities for therapeutic interventions to modify cytokine expression will be discussed.

Spatial and temporal patterns of exotic shrub invasion in an Australian tropical grassland

We used aerial photography from 1960, 1974 and 1994 to quantify meso-scale spatial and temporal invasion patterns of an exotic, leguminous shrub, Acacia nilotica, in a northern Australia grassland. The invasion was episodic, the population remained relatively stable from 1960 to 1974, then exhibited a large increase from 1974 to 1994. This episodic increase did not appear to be regulated by climate or changes in landscape attributes, but rather, paralleled a shift to cattle (a more effective dispersal vector) as the dominant domestic livestock species, implicating more effective dispersal as the proximate cause. We also measured much greater A. nilotica densities adjacent to water courses than in upland areas, suggesting either better quality habitat or greater numbers of seeds deposited there by cattle. We infer that habitat quality rather than seed availability regulates shrub density as density remained constant from 1974 to 1994 in areas that were occupied in the 1960 to 1974 period. There was a significant effect of landscape position on population dynamics of the invasion. A. nilotica increased in both extent and density in riparian areas but remained static in upland areas during 1960–1974. There were significant increases in extent and density in both riparian and upland areas in 1974–1994. Thus, it is likely that landscapes with fewer or smaller riparian areas would be less susceptable to the invasion of A. nilotica. However, the ability of domestic stock to transport seeds across distances that exceed the distance between riparian areas renders this argument less relevant. The transition from open grassland to shrubland may be irreversible in a practical sense, so control programs should emphasize containment of the invasion to existing levels as well as restoration of invaded areas. This will require strategies, tactics and operations to 1) control cattle movement, 2) exclude cattle from seed producing A. nilotica populations, 3) detect new populations early in the life cycle and implement broadscale, low-cost control techniques and 4) prioritize eradication efforts on populations that act as a seed source to uninfested areas.

Cytokines in the hypophysis: a comparative look at interleukin-6 in the porcine anterior pituitary gland.

Interleukin-6 (IL-6) is a multifunctional cytokine produced by a variety of cell types in tissues of both the immune and endocrine systems. Among the major functions described for IL-6 are its role in the maturation of B cells to high-output antibody-producing cells and its contribution to the acute physiological responses to infection and inflammation, notably production of hepatic acute phase proteins and activation of the hypothalamic-pituitary-adrenal axis. In addition to these better known functions, IL-6 recently has been found within the pituitary of laboratory rats and also in the human pituitary. In rats, pituitary IL-6 mRNA is upregulated by peripheral exposure to bacterial endotoxin. However, the role of anterior pituitary IL-6 in host responses to infection and inflammation remains uncertain, although it may regulate pituitary hormone secretion. The following brief review summarizes the information available concerning cytokine production within the anterior pituitary of species of domestic livestock. To our knowledge, experiments conducted in our laboratory evaluating regulation of IL-6 mRNA expression and secretion from the porcine anterior pituitary provide most of the data in domestic species confirming the presence of IL-6 in the pituitary. Our data indicate that IL-6 mRNA is present in cultured porcine anterior pituitary cells and that the pituitary directly responds to stimulation with bacterial endotoxin by increasing secretion of IL-6. Furthermore, endotoxin-induced upregulation of IL-6 mRNA expression and secretion appears to be dependent upon production of cyclooxygenase products of arachidonic acid metabolism.

Management practices to minimise infectious and parasitic diseases of farmed and ranched cervids and bison.

The game farming and ranching industries have evolved in the late 20th century from earlier domestication efforts in many parts of the world. Preventing transmissions of infectious diseases to, between and from farmed and ranched cervids and bison involves management components similar to those used for other species of domestic livestock. Fencing, handling systems, individual identification, knowledge of the biology of the species and potential pathogens, disease testing, quarantine and vaccination all serve to control the possible negative effects of disease on the commercial success of an operation.

Validity of using serological tests for diagnosis of diseases in wild animals.

Transposition of diagnostic tests used in domestic livestock species to free-ranging and captive wildlife species has two problems. First, most existing tests have not been adequately validated in domestic livestock. Second, assumptions that a serological test will perform identically in wildlife and livestock species may not be correct, due to differences in pathogenic strains and serovars, host serological responses, and exposure to organisms of similar antigenic structure which produce cross-reacting antibodies. Some assays require species-specific reagents/test components which might not be commercially available, and most assays have not been standardized. The authors outline the principles involved in the evaluation of a serological diagnostic test, and provide examples of how knowledge of test sensitivity and specificity can be used to estimate true prevalence, to determine whether a population is infected, and to facilitate management decisions with regard to animal translocations.

Control of blood flow to the gravid uterus of domestic livestock species.

Uterine blood flow during pregnancy is controlled by two distinct phenomena: phasic contractility and tone. Phasic contractility, which mediates short-term contractions, functions through catecholamine activation of alpha 1-adrenergic receptors (AR), leading to hydrolysis of phosphatidylinositol 4, 5-bisphosphate (PIP2) to inositol triphosphate (IP3) and diacylglycerol (DAG). The phasic contractions proceed as IP3 stimulates the release of intracellular calcium stores that activate the calmodulin pathway, causing myosin filaments to slide past actin filaments; however, the contraction is quickly terminated via a reduction in free cytosolic calcium. A tonic contraction is initiated when the DAG generated during PIP2 hydrolysis binds to and activates protein kinase C (PKC) in the presence of increased cytosolic calcium, leading to shortening of the actin filaments. Concomitantly, stimulation of alpha 2-AR increases extracellular calcium uptake via the potential-sensitive channels (PSC), which potentiates activity of the membrane-bound PKC-DAG complexes, thus maintaining the degree of tonic contractility. Progesterone maintains the phasic contractility of uterine arterial smooth muscle throughout pregnancy by increasing alpha 1-AR numbers. Estrogens decrease uterine arterial tone (i.e., increase arterial diameter and flow) via their conversion to catechol estrogens by peroxidase in uterine lymphatic fluid. Catechol estrogens directly inhibit calcium uptake through PSC, resulting in a reduced activity of membrane-bound PKC-DAG complexes.

LIVESTOCK PRODUCTION AND ANIMAL GENETIC RESOURCES IN CROATIA

SUMMARYThis paper describes the organization of livestock production in Croatia and briefly outlines the contribution of the various species of domestic livestock to the national economy. In the final part, the animal genetic resources of Croatia are described and the status of domestic animal diversity described.

Embryo importation and cryobanking strategies for laboratory animals and wildlife species

The transportation of embryos obtained from animal models, endangered species and nondomestic farmed animals (e.g., deer) can reduce/eliminate the need for shipping postnatal animals and thus has gained the interest of the biomedical and conservation fields. Efficient movement of germ plasm worldwide requires established cryobanks. Embryo cryopreservation has become a routinely successful technology for many species and efforts to develop usable cryobanks for many target species are ongoing. Recommended regulations for the movement of embryos from nontraditional (i.e. other than domestic livestock) species are nonexistent. Efforts are underway to establish domestic and international handling guidelines and to recommend suitable quarantine conditions to facilitate embryo importation. Further basic research on specific zona pellucida-pathogen interactions is encouraged to support embryo movement efforts.

Ophthalmology

Review of the limited literature on camelid eyes suggests they are anatomically similar to those of domestic livestock species, except they lack meibomian glands and have iridial folds (rather than corpora nigra). The microbial flora of the healthy camelid conjunctival sac also appears to be similar to those of domestic livestock and pets, except that no Mycoplasma have been isolated from camelids. Ocular diseases for which camelids are presented to veterinarians are numerous and varied. The most frequently presented conditions are ocular trauma and congenital abnormalities. Trauma to cornea, conjunctiva, eyelids, and sclera has been reported. Therapies for these injuries are the same as for other animals. Most congenital abnormalities are cataracts and optic nerve colobomas, but congenital eyelid defects, conjunctival cysts, and multiple ocular defects have been reported. Although these conditions are not demonstrably hereditary, breeding of animals with congenital ocular defects is strongly discouraged. Intraocular inflammatory diseases are seen commonly in camelids. Uveitis and chorioretinitis may cause permanent visual loss, usually with no indication of cause. Equine herpesvirus 1 has been isolated from camelids with severe ocular inflammation and is a known cause of chorioretinitis and neurologic abnormalities. Systemic aspergillosis causes severe chorioretinitis in alpacas. More research is needed to improve our understanding of ocular physiology and pathology in camelids. Genetic studies also are needed to establish hereditary patterns of ocular maldevelopment. Additional information from researchers and practitioners should improve our ability to recognize and treat ocular disease in camelids.

Co-culture conditions and partial zona dissection affect hatching rates of thawed bovine blastocysts produced In vitro: A preliminary report

Pregnancy rates after cryopreservation of large equine blastocyst stage embryos have remained lower than other domesticated livestock species. It is generally accepted that the embryonic capsule is the primary barrier to cryoprotectant entry into the embryo proper and techniques need to be developed to circumvent this obstacle. Therefore, the objective of this study was to develop an efficient Day 8 equine embryo cryopreservation protocol through blastocyst micromanipulation and vitrification. Grade 1 and 2 embryos recovered from mares (n = 15) 8 days after ovulation were used in these experiments. In experiment 1, the effect of either one- or two-puncture treatments before aspiration of blastocoel fluid and exposure to vitrification solutions was evaluated. No difference was detected in mean embryo volume across treatment groups after exposure to vitrification solutions or after 1, 24, 48, and 72 hours of culture. Percent of embryos re-expanding at 24 hours and percent of embryos showing diameter increase at 48 and 72 hours during in vitro culture were 100%, 83%, and 75% compared with 93%, 67%, and 50% for one- and two-puncture treatment groups, respectively. Capsule loss was 25% for one-puncture and 50% for two-puncture treatment groups. In experiment 2, no difference was detected in mean embryo volume for indirect introduction (aspiration of blastocoel fluid + equilibration) and direct introduction (injection of cryoprotectant into blastocoel cavity) treatment groups, after exposure to dilution solution or to culture medium. There was no difference in mean embryo volume for the indirect and direct introduction treatment groups after 1, 24, 48, and 72 hours of culture. Percent of embryos re-expanding at 24 hours and percent of embryos showing diameter increases at 48 and 72 hours during in vitro culture were 100%, 76.9%, and 69.2%, respectively, for both treatment groups. Those embryos subjected to the direct introduction treatment had a higher (P = 0.05) percent capsule loss (70%) compared with the indirect introduction treatment group (31%). The pregnancy rate after transfer of vitrified expanded Grade 1 blastocysts using the indirect introduction method was 83% (5/6). Three pregnancies were allowed to continue to term and resulted in the birth of three healthy foals. The vitrification protocol used in this study has the potential to become a key tool for the successful cryopreservation of equine expanded blastocysts.

Isolation and use of embryonic stem cells from livestock species

Abstract Embryonic stem (ES) cells are pluripotent cells isolated from early embryos. They proliferate in culture and retain the capacity to differentiate both in vitro and In vivo, including contributing to chimeric tissues after injection into normal blastocysts. Over the past decade ES cells have been used extensively as a model for embryogenesis. More recently they have been shown to be capable of stable integration of exogenous DNA and used for numerous studies involving genomic manipulation. ES cells provide many opportunities for genetic engineering of domestic livestock species, but to date their isolation from embryos has been documented only for the mouse and perhaps the hamster. Efforts to isolate pluripotent ES cells from embryos of domestic livestock species are described, including some of the problems encountered.