Yogurt Diet Gives Mice Big Balls

Scientific American:

First, the scientists noticed that the yogurt-eating mice were incredibly shiny. Using both traditional histology techniques and cosmetic rating scales, the researchers showed that these animals had 10 times the active follicle density of other mice, resulting in luxuriantly silky fur.
Then the researchers spotted some­thing particular about the males: they projected their testes outward, which endowed them with a certain “mouse swagger,” Erdman says. On measuring the males, they found that the testicles of the yogurt consumers were about 5 percent heavier than those of mice fed typical diets alone and around 15 percent heavier than those of junk-eating males. 
More important, that masculinity pays off. In mating experiments, yogurt-eating males inseminated their partners faster and produced more offspring than control mice. Conversely, females that ate the yogurt diets gave birth to larger litters and weaned those pups with greater success. Reflecting on their unpublished results, Erdman and Alm think that the probiotic microbes in the yogurt help to make the animals leaner and healthier, which indirectly improves sexual machismo.
The findings could have implications for human fertility.

If there wasn't the increase in fertility, the walking around funny doesn't sound like something to try to develop in the human population.  When we had sheep on the farm, I thought that it would be extremely uncomfortable to be a buck.  Man, their balls were huge.  If those things getting bumped is as uncomfortable for them as it is in guys, they would be miserable.