153 The effects of parity and oxytocin or prostaglandin F_2α added to insemination doses on reproductive performance of pigs bred in summer

Abstract

Summer is the least favourable season for swine reproduction, mainly due to long photoperiods and heat stress. Such conditions negatively impinge on the reproductive system of sows and boars, manifesting in debilitated uterine and gonadal function. This situation is exacerbated by the dilution of ejaculates in semen extender before AI. Consequently, there is a noticeable decline in piglet productivity of summer-breeding gilts and sows. The main goal of this study was to determine the effect of oxytocin (OX) or prostaglandin F_2α analogue (PG) added to boar semen extender on the duration of insemination and reproductive performance of pigs bred in July and August. A total of 144 females (80 gilts and second-parity sows (G+SP) and 64 multiparous sows (M)) were divided into three groups (n = 48 per group). The OX (11 G+SP and 37 M) and PG (20 G+SP and 28 M) groups were inseminated twice (at the onset of behavioural oestrus and 22-24 h later) using semen supplemented with 20 IU of OX or 5 mg of PG, respectively; the controls (33 G+SP and 15 M) were artificially inseminated with non-supplemented inseminate doses. Pregnancy was detected ultrasonographically on gestational day 42, and the number and viability of piglets were recorded at farrowing. Proportions were analysed using chi-square test (Brandt and Snedecor formula), and other numerical data were analysed using two-way analysis of variance and least significant difference test to determine the differences between individual mean values (SigmaPlot, Systat Software Inc.). The mean duration of first insemination was shorter (P < 0.05) in M females (80 ± 22 s) compared with G+SP females (191 ± 26 s) inseminated with PG-supplemented semen, whereas the second insemination was shorter (P < 0.05) in M females than in G+SP females artificially inseminated with OX-supplemented semen (93 ± 15 s compared with 192 ± 28 s). The mean pregnancy rate was lower (P < 0.05) in control G+SP females (26/33; 85%) than in OX G+SP females (11/11; 100%). The farrowing rate was less (P < 0.05) in control females (36/48; 75%) than in OX females (44/48; 92%), and it was less (P < 0.05) in PG G+SP females (14/20; 70%) compared with PG M females (26/28; 93%). The M females in the OX group had more (P < 0.05) stillborn piglets per litter compared with their G+SP counterparts (0.6 ± 0.1 vs. 0.1 ± 0.1). Overall, PG females had more (P < 0.05) weak piglets per litter (1.2 ± 0.2) compared with the control (0.5 ± 0.2) and OX (0.6 ± 0.2) groups. The present results reveal the occurrence of both beneficial and undesirable effects of PG and OX added to boar semen extender on reproductive performance of breeding pigs in summer. Addition of PG was associated with shorter first-insemination times in older sows compared with G+SP animals but also with lower farrowing rates in younger animals and an overall increase in the number of weak piglets at farrowing. Supplementation of OX was in turn associated with a shorter second insemination and higher pregnancy rates in young females but more stillborn piglets per litter in multiparous sows. The specific causative mechanisms of these associations remain to be elucidated.