Boar effects and their relations to fertility and litter size in sows

Abstract

Twenty Large White boars and 60 sows were used in two experiments for this study. In experiment 1, 20 sows were assigned per group to each of three treatments, twice daily for a 30-min period during a 4-wk  observation, involving: (1) NBE, a control in which sows were not exposed to boars during oestrus detection; (2) FBE, in which sows were exposed to fence-line boars during oestrus detection and (3) PBE, in which sows received physical contact with the boar during oestrus detection. In experiment 2, semen were collected at 24- or 96-h intervals from each boar and used (3.5 x 10⁹ sperm/100 mL/sow) to artificially inseminate three oestrus-synchronised sows, 24 h after the onset of oestrus, for four weeks. Boar exposure for 4 d before oestrus induction (PG600) increased the proportion of sows expressing oestrus within 7 d by 44% with 88.3 ± 5.5% farrowing rate in the PBE group with the shortest interval from PG600 to oestrus (3.5 ± 0.2 d), number of returns to oestrus (0.01 ± 0.02) and farrowing-farrowing interval (136 ± 0.01 d). On average, 45.8 ± 2.5% of the control NBE group of the sows showed spontaneous oestrus compared to 56.3 ± 1.9 vs. 88.5 ± 0.7% of FBE and PBE groups, respectively. Ejaculates collected on the 96-h intervals had larger volumes (288 ± 9.3 vs. 124.9 ± 5.7 mL), sperm motility (87.1 ± 3.3 vs. 55.2 ± 0.9%) and type of movement (8.7 ± 0.5 vs. 3.0 ± 0.1), live sperm (78.3 ± 9.6 vs. 57.9 ± 12.6.), sperm/mL (132.6 ± 8.1 vs. 90. 4 ± 12.1 x10⁶), total  sperm/ejaculate (83.2 ± 7.7 vs. 52.5 ± 4.6 x10⁹) and normal acrosome (92.5 ± 18.4 vs. 55.5 ± 15.6%) than ejaculates collected on the 24-h intervals. Semen collected at 96-h had gave higher non-return rate (93.5 ± 2.9 vs. 76.8 ± 5.2 %), farrowing rate (85.5 ± 14.3 vs. 56.8 ± 9.1%,), litter size (12 ± 0.03 vs. 8 ± 0.02) and live piglets were 30% higher compared with those from sows inseminated with semen collected at 24-h intervals, respectively. Results suggest that direct exposure of boars to sows prior to semen collection enhances oestrus expressions and farrowing rates. Secondly, ejaculating boars at 96-h intervals enhances semen quality and quantity leading to significant improvement in the fertility and litter size of artificially inseminated sows.

Keywords: Boar exposure, ejaculation frequency, semen viability, fertility, litter size