> They eat grass, distress the soil and leave their fertilizer behind. The grass regrows, which captures carbon via photosynthesis.

I think the equation is a lot more complicated than that. For instance, did you know that the vast majority of weight that your body regularly sheds is due to the carbon you breathe out? The average human breathes out around 2.3 lbs of C02 per day. That increases a lot when you're engaging in physical exertion.

I'm guessing that the same holds true for cows, but the poundage is going to be a lot higher because their body mass is a lot larger. Cows (and people) have to eat as much they shed in order to avoid wasting away, and most of that is carbon.

I would expect that a fully grown cow is essentially carbon neutral, not carbon-absorbing, if you're just looking at the dietary cycle.