text: Yo, let me break it down for you,
  Checkin' out them hens, seein' what they do.
  Three White Leghorn strains, two-way crosses too,
  Studyin' their fertility and hatchability, that's true.
  
  In the first layin' cycle, age was the game,
  Lookin' at mean heterosis, it ain't the same.
  Reciprocal effects, they didn't show a trend,
  But mean heterosis increased, my friend.
  
  Fertility and hatchability, we did assess,
  At 37, 47, and 70 weeks, no less.
  One hen per cage, block design in place,
  Seein' how they perform, ace to ace.
  
  As time went on, mean heterosis did rise,
  Them traits gettin' better, no surprise.
  Reciprocal effects didn't have much to say,
  No consistent trend, they went astray.
  
  Now let's talk 'bout A, Z, and H effects,
  Them strains responded different, that's correct.
  Age got 'em actin' in various ways,
  Genotypic differences, a factor that plays.
  
  Additive, heterotic, environmental too,
  Them variances increased, that's what they'd do.
  Except for hatchability's additive variance,
  It went up 'til 47 weeks, then took a chance.
  
  Heritability for fertility, it grew with age,
  But hatchability didn't follow a set stage.
  Genetic variance, it rose at the cycle's end,
  Pickin' older animals, performance to mend.
  
  So there you have it, the study and its findings,
  Age impacts them hens, their traits rewinding.
  Fertility and hatchability, they got potential,
  Selectin' older ones can be quite influential.