All animals do indeed need Vitamin C to live. But, dogs and cats, mice and rats, most birds and fish, horses and donkeys, oxen and cattle, sheep and goats, hogs and hippos, rabbits and hares, hamsters and gerbils, elephants and rhinos, gators and crocs, lizards and llamas, coyotes and foxes, the buffalo that roam, the deer and the antelope that play, lions, tigers, and bears (oh my!), among many, many others, all get along just fine without having to eat Vitamin C. Why not, if they need it to live?
Because, all of those other animals make their own Vitamin C! But how? We know how. We know exactly how they do it. We know every step involved. They make it within their livers. Tiny factories located deep within certain liver cells produce enzymes, under the control of DNA.
Four different enzymes are produced. The first one takes ordinary, everyday water (an extremely simple inorganic molecule necessary for life, and partly for this very reason) and glucose (a slightly more complex organic molecule found in all living things and obtained from nearly all foods) and turns it into a more complex intermediate organic molecule. The second enzyme takes the resulting intermediate molecules formed by the first and assembles it with others to form an even more complex intermediate molecules. The third does likewise with the results of the second, producing a chemical called "D-glucuronolactone" aka "L-gulono-1,4-lactone".
The fourth enzyme takes that D-glucuronolactone aka "L-gulono-1,4-lactone" produced by the third, and combines it with oxygen (with flavin adenine dinucleotide [FAD] as a co-factor) to form "L-xylo-hex-3-gulonolactone" aka "2-keto-gulono-γ-lactone" (that's a Greek lowercase gamma [uppercase: "Γ"], not an English/Latin lowercase "Y" or "y") which then, without enzymatic action, spontaneously converts to hexuronic acid aka ascorbic acid, aka Vitamin C!
Think of it as like a modern factory robotic assembly line with four stages, and each cellular factory is a factory robot, with the enzymes being materials that the robots make and use to do their tasks. Just as factory robots are programmed, each of these cellular "factory robots" is programmed by a DNA enzyme-encoding gene sequence to perform a specific task in a specific way. The first "robot" starts with common raw materials found in all living things (water and glucose), and the remaining "robots" each take the output of the preceding "robot" and further build onto it.
The fourth and final enzyme in this process is called "L-gulonolactone oxidase" (aka "L-gulono-γ-lactone oxidase"). Like the other three enzymes, it's produced by a cellular factory programmed by a specific DNA sequence, or gene. In this case, the gene is called "GULO." We know exactly where it is on the genomes of animals that we've mapped so far (for instance, in various species of hogs, it's on either Chromosome #4 or #14). We also know where it is on the genomes of haplorrhini primates, including tarsiers and simians (the latter including apes, and thus us). For us, it's on the shorter arm of Chromosome #8 (8p), at location 8p21.
Or, at least, that's where the erroneous version is for humans! We have an error in our DNA at that spot! We have everything we need to make our own Vitamin C, just like all those other animals! We have livers, just like they do. Our livers have cells, just as theirs do. Those cells have microscopic enzyme factories, just like theirs. Ours produce the first three enzymes just fine, just like theirs do!
We have everything we need, but it all fails at the final stage because our GULO gene is faulty and prevents the final enzyme of the four from being produced correctly! The erroneous version is called a "pseudogene" ("GULOP" in this case − the "P" suffix appended to "GULO" stands for "pseudogene") since it doesn't actually work. It doesn't program the production of L-gulonolactone oxidase. And without that, the D-glucuronolactone produced by the third enzyme in the process never gets converted into L-xylo-hex-3-gulonolactone and thus into hexuronic/ascorbic acid, aka Vitamin C.
Do you realize what this means? It means that our so-called "Creator" or "Intelligent" Designer would've had to've gone to all the extra work to give us everything we need to make our own Vitamin C, just like all those other animals have: the same sorts of liver cells, the same complex tiny enzyme factories within those liver cells, producing the same first three enzymes, which take the water and glucose and use it to produce the same intermediate-stage complex organic molecules, only to have the whole thing fail at the very last stage because of this error in the GULO gene (making it a GULOP psuedogene instead), aborting the Vitamin C-making process at the very last stage! Gee, that's not such an "Intelligent Design," now, is it?
But wait, it gets even better! Did you notice a whole class of animals was missing from my list of Vitamin C-making animals above? Not just us humans. What else?
Apes & monkeys! Collectively, they (and us − we are apes) are the Class of simian primates. And not just them, but the tarsiers, too. The tarsiers and simian primates together form the Sub-Order of haplorhinni ("dry-nosed") primates. None of them can make their own Vitamin C, either, and for the same reason!
How very interesting! Not only do the Creationists / IDers have to explain why their Creator / Designer made such a mistake with us, they also have to explain why He made the exact same mistake in almost the exact same way in all of the other animals, but only those other animals, that science places in the same Sub-Order as us! (There are some other animals that cannot make Vitamin C [prairie dogs, all bats, and some birds, among a few others], but mostly for differing reasons, and for those that are due to a GULOP, theirs are faulty in a different way than the GULOP of the haplorhinni primates.)
But what if, oh, about 63 million years ago (give or take), some common ancestor of all the haplorrhini primates, itself a primate, had its GULO gene mutated into a GULOP pseudogene, and passed that on to all of its descendants, all the way down to and including us? Why, that would explain it quite nicely, thenkyewverramuch! This common ancestor would've been related to, but not descended from, the common ancestors of another sub-order of primates, namely, the strepsirrhini ("wet-nosed") primates (lorises, galagos, pottos, and lemurs) who do have a functioning GULO gene and thus can and do make their own Vitamin C.
Evolution by descent from common ancestors through mutation selected by natural selection, aka Darwinism. That explains it. Neither Creationism nor "Intelligent" Design can, unless the Creator / "Intelligent Designer" were utterly incompetent, or else willfully, maliciously, and very deliberately deceptive.
Now, you may be saying, "B-b-but, the Fall of Adam and Eve! They were perfect when God made them, but when they fell, all manner of imperfections crept in! Couldn't this explain it?" In the immortal words of Bill Cosby's "Noah" character from his very first comedy album, "RIIIIIIiiiight!!" We're supposed to believe that, without any plan from God (who didn't want them to eat the Fruit, remember?), the moment that Eve bit into that fruit (or maybe when Adam bit into the one Eve brought him), every GULO gene (two each in the trillions of cells) in the human bodies of Adam and Eve, and in the bodies of all of the other haplorrhini primates, but only in the bodies of the haplorrhini primates (including Adam and Eve), got turned into a non-functioning, broken GULOP pseudogene, broken in that same way, causing the whole process to fail in the final stage! Didn't all of those other non-primate animals fall, too, when Adam and Eve did? The lions and tigers and bears and the deer and the antelope at play and all the rest? So why do they get to keep their functioning GULO genes? Why only the ones that Darwinian evolution says that we humans are related to!?
But wait, it gets even better! You see, there are in fact some slight differences in the GULOP pseudogenes of the various haplorrhini primate species (that have nothing to do with how they're broken). The extent of those differences differs exactly according to how closely or distantly related they are. For instance, using ours as the base for comparison, the GULOP of a bonobo (so-called pygmy chimpanzee, our closest surviving relative) is very slightly different. Those of the other chimpanzee species are a bit more different. Those of other Great Ape species (e.g. gorillas, orangutans, etc.) are a bit more different still, while those of lesser apes and monkeys (both simians) are even more different, and those of the tarsiers are the most different of all from ours among the haplorrhini primates. The same thing happens when you compare any other haplorrhini species's GULOP as the base of comparison against the others.
Not only does the mere presence of those differences utterly demolish the "Same Designer re-using Common DNA Building Blocks" excuse, do you have any idea what the odds of this would be for them to work out that way if it happened any other way than by evolution through common descent from a common ancestor!?