[quote name='FredOrJoeBloggs' timestamp='1343206959' post='4962860']
Especially the redundant nulling of the pointers, its good practice, but might have performance issues in games.

Oh in what sense is that a bad thing, as this is definitely games coding!
[/quote]

It depends on what your compiler does.
If it compiles the code as is, then it will waste a few instructions.
If the compiler optimises the code, it might well remove the code.
If you want speed remove redundent code before you compile.

[quote name='FredOrJoeBloggs' timestamp='1343206959' post='4962860']
However, I can't see why you are using dynamic memory for this data, why not just let the class members be a string and an int? I apreciate you may have simplified it for the question, in which case ignore this comment.

So if i want to store floating point numbers and strings they can just be basic type def calls and that will save on CPU power will it?, what would I need to use the dynamic memory for? just the initial instantiation of the class (or Animal) into a vector (as in larspensjo's example), and then delete it if the object dies in game for instance.
[/quote]
Dynamic memory is useful if you don't know who many of the objects you are going to have. If you know how many objects of a certain type you will have at maximum AND the amount of memory that uses doesn't hinder the running of the program then use stack memory. However since you are using a std::vector you are already using dynamically allocated memory (al be it managed in a library for you). The objects that you are placing into the vector can have dynamic memory, but they could also be 'non-dynamic'.
If performance is an issue then write your code such that you can replace the way the data is stored without affecting the rest of the code and then bench mark the two options by performing so many thousand operations that will excersize the code.
[source lang="cpp"]#include <afx.h>
#include <string>
#include <vector>

class CAnimalsD
{ // Animal class using dynamic memory
public:
typedef std::vector<CAnimalsD> VECTOR;
public:
CAnimalsD(const std::string& name = "", const int& health = 2)
: m_pName(new std::string(name))
, m_pHealth(new int(health))
{}
CAnimalsD(const CAnimalsD& other)
: m_pName(new std::string(*other.m_pName))
, m_pHealth(new int(*other.m_pHealth))
{}
~CAnimalsD()
{
if (m_pName)
delete m_pName;
if (m_pHealth)
delete m_pHealth;
}

private:
std::string* m_pName;
int* m_pHealth;
};

class CAnimalsS
{ // Animal class using static memory
public:
typedef std::vector<CAnimalsS> VECTOR;
public:
CAnimalsS(const std::string& name = "", const int& health = 2)
: m_Name(name)
, m_Health(health)
{}
CAnimalsS(const CAnimalsS& other)
: m_Name(other.m_Name)
, m_Health(other.m_Health)
{}
~CAnimalsS(){}
private:
std::string m_Name;
int m_Health;
};

// Gash test program.
int main (void)
{
static const int constTestCycles = 10000;
CAnimalsD::VECTOR animalsD;
CAnimalsS::VECTOR animalsS;

const DWORD startTime = GetTickCount();
for (int i = 0; i < constTestCycles; ++i)
{
animalsS.push_back(CAnimalsS("FRED", i));
}
animalsS.clear();
const DWORD midTime = GetTickCount();
for (int i = 0; i < constTestCycles; ++i)
{
animalsD.push_back(CAnimalsD("FRED", i));
}
animalsD.clear();
const DWORD endTime = GetTickCount();

printf("dynamic test = %d\n", midTime - startTime);
printf("static test = %d\n", endTime - midTime);
printf("press enter to exit\n");
return fgetc(stdin);
}[/source]

[source lang="cpp"]void AttackAnimals(int dam)
{
for(int i = 0; i < myCritters.size(); i++)
{
myAnimals.SetHealth(dam);
};[/source]

The funtion is called AttackAnimals, but your iterator ranges from 0 to the size of myCritters, shouldn't that be myAnimals( this is dangerous because you might go out of bounds if myCritters.size() > myAnimals.size() )? Also, your SetHealth() method isn't very descriptive of what it does, it doesn't actually set the health to a value, but subtracts that value from it, consider renaming it to takeDamage() or something like that.

bool Animal::Check4Death()
{
if(*m_pHealth <= 0)
return true;
else
return false;
}; [/quote]

You can reduce this to:

bool Animal::Check4Death()
{
return *m_pHealth <= 0;
}; [/quote]

Looks a lot cleaner.

Now as to your problem, your m_pHealth member is a pointer, I think that could be it. Why is this a pointer? Are you sure your animals aren't sharing this pointer?

* used quotes for code because source tags don't seem to function very well