I've given up trying to scan the pages of the Harlan Uk report in, and have just typed the following paragraphs for you on intracardiac injection.

The point is that, although 'speed is of the essence', why should farm animals be treated any differently to domestic animals?

APC report of Harlan Uk 1999
p 21 point 2.10.9

The BUAV report cites a European Commission report 'Euthenasia of experimental animals' on humane killing. The commission document favours intravenous injection, and describes intra-pulmonary and intra-cardiac administration as 'very painful'. The 1997 edition of the Home Office Code of Practice on Humane Killing similarly advises 'Direct Injection into the heart through the chest wall in the conscious animal can be painful and should not be used.'
Recommendations P32 point 14
Young puppies, where venous access was not easily secured were killed by intra-cardiac injection although the Home Office code of practice advises this method is painful and should be avoided. Intra-abdominal injection is now used.