The average height of a hippo is 1.5m to the shoulder, and the distance to the moon 384,400,000m. this mean that a tower of hippos simply standing on top of each other would require over 256 million hippos.
Luckily, we can be more efficient. The length of a hippo is, on average, 4.25m, needing only 90.5 million hippos. Better.
However, either of these options would be critically unstable. A single slip by any hippo would result in a significant splat, at least before the Lagrange point is reached.
A more stable result might be given by a minced hippo. A hippo has a mass of 1550kg on average, And
assuming an average density of 1400 kg/m^3 (ie. flesh), this gives us ~1.12 m^3 of minced hippo. even with a base size of 1 m^2, we now need almost 350 million hippos.
Now, it’s time to get realistic. A 384,400,000:1 height to width ratio would never get planning permission.
Here (You want page 76) is a table giving Height:base width ratios for radio towers.
Clearly, minced hippo flesh is not as strong as concrete, with significantly more sway. Whether or not it matches a steel lattice is debatacle, as construction grade steel has a density of around 7000 kg/m^3. The lattice takes up less space however, and I would take a convenient guess that this would give it a similar density to our own building material. Allowing for the fact that a tower of hippo flesh is solid, and thus has a higher surface area with which to catch the force of the wind, a mediocre value of 7:1 is chosen. Such a value would cause numerous protests from PETA, and pretty much any group interested in animal welfare, ever - without their interest, a lower ratio would be used for safety.
This gives us a required base width of around 55,000,000 m, to a tower volume of ~1.2x10^24 m^3 - or in other words, 1.1*10^24 hippos. This vastly exceeds the
world hippo population of ~130,000. Even if the moon itself was made entirely of minced hippo flesh (providing ~6.56x10^22 hippos worth), we still wouldn’t have enough. And the entire tower would be even more pointless than it already is.
It would also take over 3.2x10^19 years to mince the hippos, even using
kolbe’s biggest mincer. You’d need 6.4 billion such mincers to complete the tower before the world is engulfed by the sun - thankfully, given the world population, you’d have workers to spare for the necessary mass hippo cloning program.
Oh, and I should probably point out you’d need a bigger planet. The base alone is almost a million times the surface area of Earth. Oops.