Selection for Age at Puberty in Swine: Correlated Boar Response

The objective of the study was to examine correlated boar characteristics from genetic lines (GL) selected for female age at puberty. Composite Landrace × Large White females were divergently selected for age at puberty, defined as first observed standing reflex in the presence of a boar. Selection resulted in two GL, young age at puberty (AP) and old age at puberty (OLD). Data consisted of boars from generations 3 (n=35) and 4 (n=113) reared at the North Carolina Department of Agriculture Tidewater Research Station. In generation 4, AP and OLD gilts obtained puberty at 162 and 177 d of age, respectively, and 85 and 50%, respectively, exhibited puberty. Boars were group housed on partial slatted floors in environmentally controlled buildings. Sprinklers were manually activated when temperature reached 27^oC. Production traits included: birth weight (BWT), weaning weight (WWT), ADG, backfat depth (BF) and loin eye area (LEA). Reproductive traits included: testis width (TW), testis length (TL), testis volume (VOL), testosterone (TEST), progressive sperm motility (MOTILITY), total sperm cells per ejaculate (TOT_CELL), projected semen doses per boar (DOSE) and libido score (LIBIDO). In generation 3 and 4, reproductive traits were measured when animals were on average 293 and 214 d old, respectively. Semen collection was performed on cull sows. Statistical analysis was performed in SAS using PROC GLM. Fixed effects of generation, boar age (used as a covariate) and generation nested within boar age were added in models when (P<0.05). Genetic line did not influence (P>0.05) WWT, ADG, BF or LEA. Yet AP boars had greater (P<0.05) BWT when compared to OLD (1.24 vs. 1.15 kg). Least squared means for reproductive traits are shown in Table 1. Boars from the AP line had increased (P<0.05) TW, TL, VOL, TEST and LIBIDO when compared to OLD. Yet AP and OLD lines did not differ (P>0.05) for MOTILITY, CELL or DOSE. Results suggest divergent selection for early puberty in females impacted piglet birth weight, testicular development and testosterone in boars.

Table 1. Least squared means for boar reproductive traits by genetic line.

Trait	No.	AP	OLD	SE
Testis width, cm*	147	4.35	4.02	0.13
Testis length, cm*	147	11.77	11.11	0.23
Testis volume, cm2*	147	392	324	19.6
Testosterone, log(np/ml)*	30	3.89	2.56	0.36
MOTILITY, %	29	72.6	82.1	5.7
TOT_CELL, billions	29	21.2	19.6	3.3
DOSE	29	7.6	8.7	2.0
LIBIDO*	35	5.9	4.6	0.5

*Genetic line differed (P<0.05).