Relationship between pre-pubertal biometrical measures and sperm parameters for the selection of high genetic merit pure and crossbred boars

The determination of specific reproductive parameters, which allow the early selection of high genetic merit boars from different lines, is critical as it may avoid the high maintenance costs of keeping unfertile males in the production system. The aim of this work was to evaluate body and testicular measurements during the pre-pubertal phase, and associate them with reproductive characteristics, such as precocity and libido, and seminal characteristics during puberty in two different lines. Two pure breeds used in the crossing of female lines (FL) and two crossbred terminal lines (TL) were evaluated through body and testicular biometrical measures and seminal characteristics. Terminal line boars presented greater body weights and testicular measures (P < 0.01) compared to FL animals throughout the pre-pubertal period. TL males had their first collection at 24.0 ± 0.3 weeks, while their FL counterparts started about one week later (25.0 ± 0.3 weeks, P < 0.05) and age of selection presented a two-week delay in FL males (29.0 ± 0.7 versus 27.0 ± 0.6 weeks). Overall, 57% of FL boars were selected up to 31 weeks of age, while 90% of TL males were selected during the same period (P < 0.05). It was observed that genotype did not affect the seminal characteristics evaluated: volume, concentration, number of total spermatozoa, number of viable spermatozoa or sperm motility and kinetics. However, TL crossbred males showed higher percentage of normal spermatozoa and lower percentage of tail and head defects (P < 0.05). Sperm concentration in the 28th week was positively correlated with body weight in the 1st (r = 0.58, P < 0.001) and 15th (r = 0.39, P < 0.05) weeks of age. Moreover, sperm concentration in the 28th week was also correlated with right testicle length (RTL) in the 3rd week (r = 0.40, P < 0.05), and right testicle width (RTW) at week 15 (r = 0.36, P < 0.05). There was a negative correlation between RTW at week 15 and age of selection (r = −0.32, P < 0.05). Therefore, body and testicular measurements in the pre-pubertal period may predict semen concentration and can be used as early classification criteria for the selection of boars from different lines, without the risk of culling high value boars.