Investigation into the variation in follicular and endocrine responses of prepubertal gilts treated with exogenous gonadotropins

Long-acting injectable progesterone treatment prior to puberty induction in gilts

Progesterone (P4) has a pivotal role on female puberty attainment in most farm animals. However, there are no studies evaluating the effect of P4 treatment previously to boar exposure for puberty induction in gilts. Therefore, serum P4 concentration, estrus expression and reproductive performance after boar stimuli were evaluated in gilts intramuscularly treated with long-acting P4 before boar exposure. In Experiment I, prepubertal gilts received either 1 mL of saline (control) or intramuscular (I.M.) P4 treatment (150 mg, 300 mg or 600 mg; n = 6 per treatment). Serum P4 concentration for P4-treated gilts was greater than for control gilts for at least 8 d for P4300 and P4600 groups (P < 0.05), but greater until after 16 d only for those treated with 600 mg (P < 0.05). In Experiments II (prepubertal) and III (peripubertal), gilts received either saline (control) or 300 mg P4 I.M. and those showing estrus signs were artificially inseminated (AI), whereas gilts without estrus expression were culled. In prepubertal gilts (Exp. II), estrus expression rate did not differ (P < 0.05) for control (79.1%; n = 110) and P4-treated gilts (81.5%; n = 108). In peripubertal gilts (Exp. III), although estrus expression did not differ between control (77.6%; n = 106) and P4-treated (69.6%; n = 102) gilts (P > 0.05), P4-treated gilts presented longer (23.1 ± 1.4 days) interval from treatment to estrus expression than control gilts (17.1 ± 1.3 days; P < 0.05). In Experiments II and III, the proportion of culled gilts with ovarian structures consistent with normal estrous cycles, farrowing rate, and litter size did not differ between treatments (P > 0.05). In conclusion, I.M. treatment with 300 or 600 mg of long-acting P4 was efficient in maintaining high P4 concentrations in prepubertal gilts for at least 8 days. However, P4 treatment over this time interval did not benefit the reproductive performance of prepubertal and peripubertal gilts.

Effects of physical or fenceline boar exposure and exogenous gonadotropins on puberty induction and subsequent fertility in gilts

The present study was part of a larger experiment that evaluated litter of origin effects on gilt production. The objectives of this study were to determine the effect of physical or fenceline boar exposure and exogenous gonadotropins on puberty induction and subsequent fertility in a commercial farm environment. The experiment was performed in three replicates. Prepubertal gilts were assigned by pen (13/pen) to receive 15 min of daily Fenceline (FBE, n = 153) or Physical (PBE, n = 154) Boar Exposure (BE) for 3 weeks starting at 184 d of age in a purpose-designed Boar Exposure Area (BEAR). At the start of week 3, prepubertal gilts were randomly assigned to receive PG600 or none (Control). From weeks 4 to 6, estrus was checked using only FBE. During weeks 1 to 3, measures of reproductive status were obtained weekly or until expression of estrus. Upon detection of first estrus, gilts were relocated into stalls and inseminated at second estrus. PBE reduced age (P = 0.001) and days to puberty (P = 0.002), increased the proportion of gilts in estrus (P = 0.04) in week 1 (38.3 vs. 27.5%), and tended (P = 0.08) to improve estrus in week 2 (37.6 vs. 26.1%) compared to FBE, respectively. In week 3, more prepubertal gilts receiving PBE-PG600 exhibited estrus (P = 0.04; 81.8%) compared to PBE-Control (40.3%), FBE-PG600 (56.4%), and FBE-Control (47.8%). Overall, expression of estrus through week 6 tended (P = 0.08) to be greater for PBE than FBE (91.5 vs. 85.0%). PBE increased (P ≤ 0.05) or tended to increase (P > 0.05 and ≤0.10) service and farrowing rates in parities 1 through 4, but within parity, there were no effects (P > 0.10) on pig production or wean to service interval. Analyses also indicated that weeks from start of boar exposure to puberty, litter of origin traits, and follicle measures at puberty were related to the subsequent fertility. The results of this study confirm the advantages of using increased intensity of boar exposure, combined with PG600 treatment, for effective induction of pubertal estrus in a commercial setting.