model.py

class Animal(models.Model):
    id_animal = models.PositiveIntegerField()
    nom_animal = models.CharField(max_length=50)
    edad_animal = models.PositiveIntegerField()
    condi_animal = models.TextField()
    id_especie = models.ForeignKey('Especie','id_especie')



class Especie (models.Model):
    id_especie = models.PositiveIntegerField(primary_key=True)
    des_especie = models.CharField(max_length=30)

form.py

 class AgregarAnimal(forms.ModelForm):

    especie = forms.ModelChoiceField(queryset=Especie.objects.all())

    class Meta:
        model = Animal
        fields = ['id_animal',"nom_animal", "edad_animal","condi_animal","especie"]

views.py

def Agregar_missperris(request):
    if request.method == "POST":
        form = AgregarAnimal(request.POST or None, request.FILES or None)
        if form.is_valid():
            nuevo_animal = form.save(commit=False)
            nuevo_animal.save()
            return render(request, 'WebMissPerris/listar_missperris.html', {'form': form})
    else:
        form = AgregarAnimal()

    return render(request, 'WebMissPerris/Agregar_missperris.html', {'form': form})