Singleton or twin male lambs: Effects on their reproductive development

Area of Science:

• Reproductive Biology
• Animal Science
• Developmental Physiology

Background:

• Intrauterine environments differ between singleton and twin pregnancies, potentially influencing fetal programming.
• Fetal programming in sheep can impact reproductive physiology and behavior post-sexual maturation.
• Understanding these effects is crucial for livestock management and reproductive studies.

Purpose of the Study:

• To compare sperm output and sexual behavior in developing singleton- and twin-born ram lambs of similar body weight.
• To investigate the long-term effects of birth type on reproductive characteristics in sheep.

Main Methods:

• Evaluated body weight, scrotal circumference, sexual behavior, and semen characteristics in singleton (n=12) and twin (n=9) ram lambs from 5.4 to 9.1 months of age.
• Sexual behavior was assessed every 14 days, and semen characteristics were evaluated every 28 days.
• Semen volume, sperm concentration, courtship initiation, and mounting behavior were key parameters.

Main Results:

• Singleton lambs ejaculated a larger semen volume in the third ejaculate (P=0.03).
• Twin lambs exhibited higher pooled sperm concentration across three ejaculates (P=0.015).
• Singleton lambs initiated courtship behavior earlier (P<0.0001), with interactions noted for courtship onset and mount attempts.

Conclusions:

• Slight differences in semen characteristics and sexual behavior exist between singleton and twin-born ram lambs of similar weight.
• Singleton-born lambs showed earlier courtship initiation and greater third ejaculate volume.
• Twin-born lambs had a higher overall sperm concentration, indicating potential differences in reproductive maturation influenced by birth status.