Effect of gonadotropin administration on reproductive performance in relation to the age at first conception, time of application, and body condition of weaned sow

Abstract. The administration of hormone preparations to synchronize the onset of oestrus in gilts and sows is a good way of achieving breeding objectives economically on large-scale farms. Therefore, the objective of this study was to analyse the effects of the timing of administration of gonadotropins (400 IU (international unit) eCG – equine chorionic gonadotropin – and 200 IU hCG – human chorionic gonadotropin; Intervet International B.V.), the age of gilts at first conception, and their backfat thickness (BFT) at weaning on the length of weaning to oestrus interval (WEI) and litter size in the following four parities. A total of 578 crossbred sows (Landrace×Large White) from a commercial farm were divided into three groups: the control PG0 (without gonadotropins, n=192), PG72 (gonadotropin administration 72 h before weaning, n=192), and PG24 (gonadotropin administration 24 h after weaning, n=194). Within each group, gilts were also divided into two classes according to their age at first conception: 240–260 d and >260 d. Body condition of sows was determined based on BFT, measured on the 110th day of gestation and at weaning on the 28th day of lactation, which were classified into four classes of body condition within each reproduction cycle. Primiparous sows that were younger at first conception (240–260 d and BFT >14.3 mm at weaning) had a significantly shorter WEI but only at first weaning. At the subsequent farrows, age at first conception had no significant effect on WEI length. With subsequent farrows, increasing BFT along with gonadotropin administration (72 h before and 24 h after weaning) had a significant effect on reducing WEI. Age at first conception (240–260 d) of the primiparous sow with both gonadotropin administrations significantly increased the number of live-born piglets in all parities studied in comparison to the older group (>260 d). In conclusion, the study showed that it is necessary to adjust the selective timing of gonadotropin administration at weaning to the age of primiparous sows and their body condition.