Can you rely on the veterinarian as an expert witness?

Veterinarians are commonly referred to as society's "animal health and welfare experts". So it comes as no surprise that veterinarians are often asked to provide reports to courts describing factual observations and providing their "expert" opinion on the presence or absence of unnecessary suffering in animals. 
But is there consistency among veterinarians regarding their assessment of what constitutes "unnecessary suffering"?
A recent report concludes that there is significant variation regarding what constitutes "suffering", and assessments of the reasonable actions of the owners. While lawyers are familiar with the concept of "opinion shopping", the variability of veterinary opinion demonstrated in the study raises questions about how much reliance the courts should be appropriately attributed to the "expert's" opinion.
That raises the question of how to improve the consistency and therefore the reliability of societies animal health and welfare experts? This study suggested that expert witness reports should include a systematic consideration of the animal’s mental and physical states, severity of harm, duration of harm and a commentary on the necessity of suffering as defined by legislation.
It's a constructive suggestion which supports the initiative taken by some veterinary schools and societies, toward ensuring that their animal welfare experts at least know how the law is defining key terms such as "animal welfare", "suffering", and what the law benchmarks as "necessary".