Vitamin C (Ascorbic Acid)
Cats synthesize sufficient vitamin C (ascorbic acid) from glucose in their small intestine, and the cat's natural prey diet is devoid of a pure source of this vitamin. Additional supplementation can be harmful, because excessive ascorbic acid is excreted in the urine as oxalates. A high concentration of oxalate in the urine can contribute to the formation of calcium oxalate stones in the urinary tract, including the kidneys. A controlled study has also shown that large doses of injectable ascorbic acid has no beneficial effects for preventing or reducing the severity of feline respiratory disease. In addition, an overdose on vitamin C can enhance iron absorption and cause a resulting overdose of this mineral. The cat's resistance to disease is much less dependant on vitamin C, as is the case for humans. Instead, it is much more vital that sufficient amounts of vitamin A are available to the cat through her diet, which promotes disease resistance and proper immune function.

"Cats normally synthesize vitamin C (ascorbic acid) from glucose, so there is no need to supplement the diet unless there is a high metabolic need or inadequate synthesis. Excessive supplementation may actually be harmful, because excessive ascorbic acid is excreted in the urine as oxalate. A high concentration of oxalate in the urine has the potential to contribute to the formation of calcium oxalate stones in the urinary tract."
The Cornell Book of Cats, 2nd. edition, page 82

There are many molecular substances in foods that offer no nutritional benefit, and must be processed and excreted. Oxalic acid, for example, is excreted in the urine, and its crystals are commonly found in microscopic urinalysis. Too much oxalic acid in the urine will result in kidney or bladder stones. Calcium combines with oxalic acid to form the less soluble salt, calcium oxalate, which is also found in kidney stones. Plant leaves, especially rhubarb, cabbage, spinach, and beet tops, contain oxalic acid. Oxalic acid is also found in potatoes and peas. Vitamin C is metabolized to oxalic acid; it contributes to over-saturation of the urine with crystals and possibly to stone formation."
Excerpt from: Food Chemistry: Chemical Stressors and Toxins in Plant Foods and Herbs.
Stephen Gislason, M.D. Helping you find solutions for common medical problems.

And theres more where that came from to support my comment

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An old man walking on the beach at dawn noticed a boy picking up a starfish and throwing it into the sea. When asked why, the boy explained that the stranded starfish would die if left to lie in the morning sun. ‘But there are millions of starfish on this beach' said the old man. ‘How can your efforts make a difference?’The boy picked up another starfish and placed it in the waves. ‘It makes a difference to this one.' he said

Okay, so what's an excessive level of ascorbic acid?

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Feline Nutrition

VITAMIN C (ASCORBIC ACID)

Ascorbic acid, commonly known as vitamin C, has a chemical structure that is closely related to the monosaccharide sugars. It is synthesized by plants and most animal species, including dogs and cats. Ascorbic acid is produced in the liver from either glucose or galactose through the glucuronate pathway. With the exception of humans and a few other animal species, all animals, including cats, are capable of producing adequate levels of endogenous vitamin C and therefore do not have a dietary requirement for this vitamin. Therefore, unless there is a high metabolic need or inadequate amounts are being synthesized by the body, a dietary source of ascorbic acid is unnecessary in cats. In addition to being unwarranted, ascorbic acid supplementation in cats may be detrimental. Excess ascorbic acid is excreted in the urine as oxalate, and high concentrations of oxalate have the potential to contribute to the formation of calcium oxalate uroliths in the urinary tract.

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An old man walking on the beach at dawn noticed a boy picking up a starfish and throwing it into the sea. When asked why, the boy explained that the stranded starfish would die if left to lie in the morning sun. ‘But there are millions of starfish on this beach' said the old man. ‘How can your efforts make a difference?’The boy picked up another starfish and placed it in the waves. ‘It makes a difference to this one.' he said

Well I didn't know that before!

I can't see 60mg/kg having too much of an effect on a cat though. Considering they only eat about 50grams of food a day thats only about 3mg a day.

I agree it's unnecessary but Orijen is certainly far better than any other commercial cat food available, it does not manage to even come close to feeding a natural diet though.

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Yes i agree thats why i am going to feed Betz it!

I dont give her much dry food, she is 3 years old and is used to eating felix and royal canin!! So least i have got her onto natures menu and abit of orijen now

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An old man walking on the beach at dawn noticed a boy picking up a starfish and throwing it into the sea. When asked why, the boy explained that the stranded starfish would die if left to lie in the morning sun. ‘But there are millions of starfish on this beach' said the old man. ‘How can your efforts make a difference?’The boy picked up another starfish and placed it in the waves. ‘It makes a difference to this one.' he said