Volume 5: Animal Health, 1989-96
6. Breeding
Introduction

6.1 Uncertainty as to whether BSE could be transmitted from cow to calf during pregnancy or birthing ('maternal transmission' or 'vertical transmission') made it difficult for MAFF to formulate a breeding policy in relation to BSE. Despite being quick to implement maternal transmission studies and experiments (see vol. 2: Science and vol. 11: Scientists after Southwood) MAFF still needed to consider whether it should implement restrictive breeding policies before the results of the experiments became available.

6.2 A major factor that influenced action in this area was that should BSE prove to be maternally transmissible, this alone would not be sufficient to maintain the epidemic. For BSE to become endemic, each infected cow would need, on average, to be replaced by one infected offspring. However, of all calves born, only one in five was kept for breeding purposes. Further, it was calculated that on average a cow with BSE would produce 2.5 calves within its lifetime, whereas a healthy cow would produce more. Thus, less than one offspring per BSE cow would be retained for breeding. This meant that even if each offspring of a BSE-affected cow became infected, BSE would still be self-limiting if maternal transmission was the only means of transmission. ¹

6.3 MAFF officials treated the likelihood of maternal transmission occurring as a real possibility. Ministers asked for advice on what measures should be adopted in anticipation of the experiment results. They were advised that a first step should be an improvement in movement and breeding records that farmers were required to hold for each animal they owned. These recommendations were approved and resulted in legislative changes, which are described in Chapter 5 on cattle-tracking.

6.4 This chapter examines MAFF's deliberations on how the offspring of BSE-affected cattle should be treated. It describes the policy options considered by MAFF, and the conflict between Mr Meldrum's views and the advice of the Spongiform Encephalopathy Advisory Committee (SEAC), which prevailed. We also discuss the parallel issue of the use of semen from BSE-affected bulls for artificial insemination purposes and the formulation of MAFF's policy that restricted the use of semen from such animals. Transmission, or the lack thereof, of BSE by embryo transfer was also of interest to MAFF officials. We look briefly at this aspect to conclude this chapter.

6.5 See vol. 12: Livestock Farming for descriptions of the breeding industries and breeding techniques covered in this chapter.