Ž . Animal Reproduction Science 52 1998 63–69 Effect of vulvomucosal injection of PGF2 a at insemination on subsequent fertility and litter size in pigs under field conditions F.J. Pena ) , J.C. Domınguez, B. Alegre, J. Pelaez ˜ ´ ´ Department of Reproduction and Obstetrics, Faculty of Veterinary Medicine, UniÕersity of Leon, Campus de ´ Vegazana, 24071 Leon, Spain ´ Accepted 3 April 1998 Abstract The aim of this study was to determine the effects of injecting 5 mg of PGF2 a into the vulvar mucosa on the reproductive performance of sows maintained under field conditions. At an intensively managed piggery in northwest Spain, two experimental groups were formed randomly and observed throughout the year. The first group comprised sows receiving simultaneously, with every insemination, 5 mg of PGF2 a injected into the vulvar lips. Group 2 sows received 1 ml of saline solution injected into the vulvar lips at insemination and served as the controls. The farrowing rates for each group were 78.46 and 54.39, while the litter sizes were 10.72 "0.27 and Ž . 9.14 "0.47 during the low fertility season July–September . During the rest of the year Ž . October–June , the farrowing rates were 83.91 and 80.93, while the litter sizes were 11.16 "0.15 and 9.99 "0.15. We conclude that injection of 5 mg of PGF2 a into the vulvar lips at insemination is an effective method of compensating for the low fertility together with the decreased litter size of the summer months. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Pig; Reproductive performance; Fertility; Litter size; PGF2 a 1. Introduction The tendency among pigs towards reduced reproductive efficiency during the summer Ž . has been reported by several authors, with MacLean 1969 being one of the first. The summer infertility syndrome is characterised by a reduction in the number of sows Ž . farrowing Love, 1978; Love et al., 1993; Domınguez et al., 1996 and a decrease in ´ ) Corresponding author. Tel.: q34 87 291324; fax: q34 87 291322; e-mail: tel00183@globalnet.es 0378-4320r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0378-4320 98 00083-9