The effect of different postweaning altrenogest treatments of primiparous sows on follicular development, pregnancy rates, and litter sizes1

Abstract

This study investigated follicular development during and after postweaning altrenogest treatment of primiparous sows in relation to subsequent reproductive performance. Primiparous sows (n = 259) were randomly assigned at weaning (d 0) to 1 of 4 groups: control (no altrenogest, n = 71), RU4 (20 mg of altrenogest from d -1 to 2, n = 62), RU8 (20 mg of altrenogest from d -1 to 6, n = 65), or RU15 (20 mg of altrenogest from d -1 to 13, n = 61). Average follicular size (measured by ultrasound) increased during altrenogest treatment and resulted in larger follicles at the start of the follicular phase for RU4, RU8, and RU15 compared with controls (5.3 ± 0.9, 5.5 ± 1.3, 5.1 ± 1.2, and 3.4 ± 0.6 mm, respectively; P < 0.0001). Farrowing rate was greater in RU15 (95%) than in RU8 (76%; P = 0.04). The RU15 group also had more piglets (2 to 3 more piglets total born and born alive; P < 0.05) than the other treatment groups. Follicular development at weaning clearly affected reproductive performance. At weaning, average follicular size: small (<3.5 mm), medium (3.5 to 4.5 mm), or large (≥ 4.5 mm), was associated with farrowing rates of 86, 78, and 48%, respectively (P < 0.001). Sows with large follicles at weaning had low farrowing rates (71%) in RU4, very low farrowing rates (22%) in RU8, but normal farrowing rates in RU15 (83%). In conclusion, this study showed that 15 d of postweaning altrenogest treatment of primiparous sows may allow follicle turnover in sows that had large follicles at weaning and that this was associated with an improved reproductive performance. It also showed that shorter treatment with altrenogest (4 or 8 d) is beneficial for sows with small follicles at weaning, but is not recommendable for sows with large follicles at weaning.

Effect of a GnRH analogue (Maprelin) on the reproductive performance of gilts and sows

“…Ovary scanning was conducted according to the procedures described earlier [23]. The ovaries of the sows were monitored using transabdominal ultrasound scans performed with a sectorial probe (5 MHz, MS Multiscan digital, MS Schippers, The Netherlands) to estimate the average follicle size.…”

Effect of dosage and duration of altrenogest treatmenton follicular development and ovulation in sows*

“…Even though previous studies revealed improved fertility of the sows that were treated with ALT was a consequence of better follicular development, especially increasing follicular size (11)(12)(13), the effect of ALT on the homogeneity of preovulatory follicles was not mentioned. Since follicular diversity is associated with the diversity of embryonic development and survival during early pregnancy (1,6), there is a need to investigate homogeneity of preovulatory follicles for better fertility in sows.…”

The effect of farrowing duration and parity on preovulatory follicular size and oxytocin release of sows at subsequent oestrus

“…After weaning, the production and release of OT are stimulated by estradiol produced from follicles (Carter, ; Gimpl & Fahrenholz, ; Wathes et al., ), which is supported by increasing gonadotrophin stimulation, particularly by FSH and LH (Kemp, Soede, & Langendijk, ; Van den Brand, Dieleman, Soede, & Kemp, ; Van Leeuwen et al., ). The positive relationship between follicular development and estradiol concentrations during the follicular phase was confirmed by several studies (Breuel et al., ; Nayudu & Osborn, ; Sheldon & Dobson, ).…”