Reproductive efficiency is imperative for the maintenance of profitability in both dairy and cow-calf enterprises. Bovine viral diarrhea virus is an important infectious disease agent of cattle that can potentially have a negative effect on all phases of reproduction. Reduced conception rates,early embryonic deaths, abortions, congenital defects, and weak calves have all been associated BVDV infection of susceptible females. In addition, the birth of calves PI with BVDV as a result of in utero fetal exposure is extremely important in the perpetuation of the virus in an infected herd or spread to other susceptible herds. Bulls acutely or PI with BVDV may bea source of viral spread through either natural service or semen used in artificial insemination. Management practices including elimination of PI cattle, biosecurity measures and strategic use of vaccination can be implemented to reduce the risk of BVDV related reproductive losses. Development of vaccines and vaccine strategies capable of providing better protection against fetal infection would be of benefit.

https://www.vetfood.theclinics.com/article/S0749-0720(03)00078-1/pdf

Reproductive consequences of infection with bovine viral diarrhea virus

EFSA and EMA have jointly reviewed measures taken in the EU to reduce the need for and use of antimicrobials in food-producing animals, and the resultant impacts on antimicrobial resistance (AMR). Reduction strategies have been implemented successfully in some Member States. Such strategies include national reduction targets, benchmarking of antimicrobial use, controls on prescribing and restrictions on use of specific critically important antimicrobials, together with improvements to animal husbandry and disease prevention and control measures. Due to the multiplicity of factors contributing to AMR, the impact of any single measure is difficult to quantify, although there is evidence of an association between reduction in antimicrobial use and reduced AMR. To minimise antimicrobial use, a multifaceted integrated approach should be implemented, adapted to local circumstances. Recommended options (non-prioritised) include: development of national strategies; harmonised systems for monitoring antimicrobial use and AMR development; establishing national targets for antimicrobial use reduction; use of on-farm health plans; increasing the responsibility of veterinarians for antimicrobial prescribing; training, education and raising public awareness; increasing the availability of rapid and reliable diagnostics; improving husbandry and management procedures for disease prevention and control; rethinking livestock production systems to reduce inherent disease risk. A limited number of studies provide robust evidence of alternatives to antimicrobials that positively influence health parameters. Possible alternatives include probiotics and prebiotics, competitive exclusion, bacteriophages, immunomodulators, organic acids and teat sealants. Development of a legislative framework that permits the use of specific products as alternatives should be considered. Further research to evaluate the potential of alternative farming systems on reducing AMR is also recommended. Animals suffering from bacterial infections should only be treated with antimicrobials based on veterinary diagnosis and prescription. Options should be reviewed to phase out most preventive use of antimicrobials and to reduce and refine metaphylaxis by applying recognised alternative measures.

https://hal-anses.archives-ouvertes.fr/anses-01634046/document

EMA and EFSA Joint Scientific Opinion on measures to reduce the need to use antimicrobial agents in animal husbandry in the European Union, and the resulting impacts on food safety (RONAFA)

Bovine leukaemia virus (BLV) is the aetiological agent of a chronic lymphatic leukaemia/lymphoma in cows, sheep and goats. Infection without neoplastic transformation has also been demonstrated in pigs, rhesus monkeys, chimpanzees and rabbits and observed in capybaras and water buffaloes. Structurally and functionally, BLV is a relative of human T lymphotropic viruses 1 and 2 (HTLV-I and HTLV-II) since all three viruses show clear-cut sequence homologies. The pathology of the BLV-induced disease, most notably the absence of chronic viraemia, a long latency period and lack of preferred proviral integration sites in tumours, is similar to that of adult T-cell leukaemia/lymphoma induced by HTLV-I. The most striking feature of the three naturally transmitted leukaemia viruses is the X region located between the env gene and the long terminal repeat (LTR) sequence. The X region contains several overlapping long open reading frames, one of which, designated XBL-1, encodes a trans-activator function capable of increasing the level of gene expression directed by BLV-LTR and is most probably involved in genetic instability of BLV-infected cells of the B-cell lineage. The 'genetic instability' may put the cell into a state of fragility, ready to move along a number of stages towards full malignancy. Little is known about these events and their causes and we present some theoretical possibilities. BLV infection has a worldwide distribution. In temperate climates the virus spreads mostly through iatrogenic transfer of infected lymphocytes. In warm climates and in areas heavily populated by haematophagous insects, there are indications of insect-borne propagation of the virus.

Bovine leukaemia: facts and hypotheses derived from the study of an infectious cancer.

https://link.springer.com/content/pdf/10.1007%2F978-94-009-1243-4_4.pdf

Bovine leukaemia: Facts and hypotheses derived from the study of an infectious cancer

About 17,000 bovine pregnancies were produced by superovulation and embryo transfer in North America in 1979. The major use of these techniques is to increase the reproductive rate of valuable cows. Other applications include circumventing infertility, exporting embryos, and testing potential carriers for Mendelian recessive alleles. Cryopreservation of embryos is beginning to be used commercially, and sexing embryos before transfer may soon become routine.

https://science.sciencemag.org/content/sci/211/4480/351.full.pdf

Superovulation and embryo transfer in cattle

The disease control potential of embryos

Embryo transfer as a means of controlling the transmission of viral infections. I. The in vitro exposure of preimplantation bovine embryos to akabane, bluetongue and bovine viral diarrhea viruses

Embryo transfer as a means of controlling the transmission of viral infections. II. The in vitro exposure of preimplantation bovine embryos to infectious bovine rhinotracheitis virus.

Embryo transfer as a means of controlling the transmission of viral infections

Studies on laboratory animals have shown that viruses vary as to whether or not they are transmissible by the gametes or are capable of passing through the zona pellucida and infecting the embryo.

Methods of studying early embryos for the presence of infectious agents include electron microscopy, immunocytochemistry and cell cultivation.

Determination that early bovine embryos do not become infected by certain agents might allow for easing of restrictions in the current import and export regulations for cattle embryos.

Embryo transfer could be used as a means of controlling or eliminating disease in a herd or flock if the causal agent does not infect the early embryo via the gametes or by penetrating the zona pellucida.

Embryo transfer: a discussion on its potential for infectious disease control based on a review of studies on infection of gametes and early embryos by various agents.

Elizabeth L. Singh

Papers

The disease control potential of embryos

Embryo transfer as a means of controlling the transmission of viral infections. I. The in vitro exposure of preimplantation bovine embryos to akabane, bluetongue and bovine viral diarrhea viruses

Embryo transfer as a means of controlling the transmission of viral infections. II. The in vitro exposure of preimplantation bovine embryos to infectious bovine rhinotracheitis virus.

Embryo transfer as a means of controlling the transmission of viral infections

Embryo transfer: a discussion on its potential for infectious disease control based on a review of studies on infection of gametes and early embryos by various agents.