PS3-3. Characterization of Physical and Physiological Traits of Testicular Growth Affecting Sexual Maturity in Katahdin Ram Lambs.

Abstract Ram fertility and reproductive efficiency are critically important factors of productivity in the sheep industry. Reproductive seasonality, regulated by the photoperiod cycle, gestation length, and litter size, limits the flock's annual output capacity. Therefore, early sexual maturity and breeding capability of rams are particularly advantageous. The objective of this study is to evaluate possible correlations between body weight, weight gain, and testicular growth parameters associated with sexual maturity and early breeding potential in Katahdin ram lambs. Forty-two ram lambs from Lincoln University's agriculture station were monitored from birth to post-weaning at monthly intervals. Data collected included animal ID, birth weight (BW), weaning weight (WW), post-weaning weight (PW), and testicular traits including diameter, length, circumference, and estimated volume. These testicular measurements were conducted using ultrasound scanning, denoted as TDU (mm), TCU (mm), and TVU (cm³), and a caliper ruler denoted as TDC (mm), TLC (mm), and TCC (mm). Data were analyzed using ANOVA statistics and compared in a t-test. Correction and regression analysis were conducted for pooled data by traits. There was no significant difference between selection flocks; however, birth rearing rank ultimately influenced testicular development. Monthly averages measured at five-point intervals showed progressive growth as TCC was 91, 92, 109, 110, 115 mm; TVC was 35.8, 37.4, 63.9. 64.9, 99.8 cm³; TDC was 28.7, 29.3, 35.2, 35.0, 36.8 mm; TLC was 47.6, 48.1, 56.3, 59.0, 89.8 mm, respectively. There were strong correlations (r = 0.8 to 0.9, P < 0.001) among testicular traits (TVC, TLC, TWC, TCC). However, TDU, TCU, and TVU were corrected with TDC, TCC, and TVC moderately (r = 0.5 to 0.6, P < 0.01). Major testicular measures, such as TLC, TCC, and TVC, were highly correlated with WW and PW (P < 0.001). These findings showed there were significant relationships among these testicular development traits with live weight, weight gain, and sexual maturity, highlighting the potential of phenotypic indicators to predict breeding readiness of Katahdin ram lambs.