@TeaLovingDave But there is a plenty of browse in the zoo, that can be given instead of hay from grass/lucerne, to protect the health of the black rhinos and to increase reproductive success.
@Nikola Chavkosk So, the zoo's rhinos need to improve their fecundity, do they? They seem to be popping out rhino calves like there's no tomorrow - and, unless I'm missing something, there's never been any issue with the well-being of their animals.
@Nikola Chavkosk This triggered a vague memory - and on checking I have been able to confirm that Chester have a nutrition officer whose PhD involved studying alternative foods for browsing ruminants: Dr Cathrine Sauer | Nutrition Officer | Chester Zoo
... so I think it's safe to say this is a conscious choice, not a lazy one.
EDIT: And yes, I know rhinos aren't ruminants, but the point stands!
Yes allright. Chester is holder of most numerous population in Europe. It just from what I have read, that captive black rhinos iron content of blood and internal organs is much greater than those in the wild, irrespectively whether they show sign of illness or not (the captive rhinos) or decreased survival of the newborns/increased stillbirths. Plus that Iron storage disease had never been observed in rhinos in the wilderness, and finaly because grass/lucerne and almost all green low plants contains 100 to 1000 times higher iron content than leaves from trees. It can be enforced some policy of not giving a lot of grass/lucerne like preventive measure or even more like from welfare point for the browser animal itself, loving more browse like more palatable food.
@ThylacineAlive Irrespectively that there is some branch with leaves. Given the fact that grass/lucerne (legume) contain 100 to 1,000 times more iron (Fe) than leaves from trees, even 1 kg of grass can deliver amount of iron otherwise delivered by 100 to 1,000 kg of browse! That means that even giving very small amounts of grass/lucerne (hay) can be detrimental to the health of certain browsers like black rhino (but seemingly not others like giraffes or browsing ruminants in general). Plus browser animals have brahidont teeth that wear fast due to silicates/soil in/on grass/low plants; leaves from trees don't have so much silicates and no soil.
