Why invest in cows if their return is negative?

In some developing economies, cattle are used as store of value. This is because there is no other good asset available as financial markets are not developed. Cattle has its drawbacks though, as it can die from disease or hunger, usually at the worst moment, can walk away or be stolen, and thus needs constant guard. This implies that their return could actually be negative.

Santosh Anagol, Alvin Etang and Dean Karlan find that cows and buffaloes in rural India have a negative return of a whooping 64% respectively 39%. If you take the extreme assumption that labor has no return, then their returns are minus 6% respectively plus 13%. How is that possible? The authors offer several potential explanations: measurement error, preference for home-made milk, the lack of other saving vehicles, in particular those that allow commitment to keeping those savings, improvement in social and religious standing, and preference for lotteries (small probability of striking it rich with female cattle). The one I like the most is that marginal return of labor is actually zero. Indeed, farms do not operate like firms. As they are typically family-operated, everyone "works" even if that means being idle most of the day. This idle person may have a productivity close to zero, and may thus be used to guard cattle.