RESUMEN
The use of hormonal protocols in puberty induction and synchronization of oestrus has lead to an increase in the efficiency of replacement gilts. The aim of this study was to evaluate different doses of porcine LH in precocious puberty induction and oestrus synchronization in a homogeneous group of gilts. Sixty-seven homogeneous prepubertal gilts (Camborough 22) at 137 +/- 4 days of age and 87 +/- 7 kg were treated with three different hormonal protocols: T1--600 UI of equine chorionic gonadotrophin (eCG; Novormon) and after a 72-h period 5 mg of LH (Lutropin); T2--600 UI of eCG and a 72-h period 2.5 mg of LH; T3--600 UI of eCG and a 72-h period 1.25 mg of LH. The ovaries were examined at slaughter, on day 6 after the hormonal treatment. There were no statistical differences (p > 0.05) between the different LH doses in the percentage of the detected oestrus (T1 = 42.85%; T2 = 60.87%, T3 = 52.18%), oestrus duration (T1 = 41.44 +/- 16.30 h; T2 = 48.57 +/- 16.29 h, T3 = 39.33 +/- 11.42 h), number of corpora lutea (T1 = 9.61 +/- 5.43; T2 = 9.86 +/- 3.32, T3 = 8.13 +/- 5.52) and percentage of animals presenting ovarian cystic degeneration (T1 = 33.33%; T2 = 39.13%, T3 = 39.13%). The T2 (2.5 mg of LH) presented the lowest dispersion (p < 0.05) of the LH-ovulation interval (T1 = 37.17 +/- 4.07 h; T2 = 38.26 +/- 2.84 h; T3 = 36.25 +/- 5.69 h). The LH dose reduction to 2.50 and 1.25 mg presented equal results with the recommended dose of 5.0 mg, and could be used in the precocious induction of oestrus in gilts. The 2.5-mg LH dose showed the lowest dispersion of ovulation and it can be used in fixed-time artificial insemination programmes.