Best practices in the lactating and weaned sow to optimize reproductive physiology and performance - The Gestating and Lactating Sow - page 380

important to make sure that the sow will show a second oestrus. Whether or not these
techniques should be applied is a matter of economic feasibility.

Use of progesterone analogues

To artificially extend the weaning-to-oestrus interval and allow recovery of follicle
quality, sows can be given an oral progesterone analogue, altrenogest, which is provided
at a dosage of 15-20 mg/day. Consequences for subsequent reproductive performance
depend on the treatment period. When treated for only 3-4 days after weaning, pregnancy
rate and litter size may remain similar (Van Leeuwen et al. , 2011) or increase (Boland,
1983; Martinat-Botté et al. , 1995). However, treatment periods of 6-8 days may decrease
subsequent performance (Van Leeuwen et al. , 2011; Werlang et al. , 2011), and longer
treatment periods of 14 days consistently increase performance by +1.8 fetuses on day
50 of pregnancy (Patterson et al. , 2008; Van Leeuwen et al. , 2011) and +2.5 piglets born
(van Leeuwen et al. , 2011). These consequences were linked to the growth pattern of
follicles during altrenogest treatment. Initial follicle growth, to approximately 5 mm on
days 6-8, is followed by a slight decrease and stabilisation of follicle size at 4.0-4.5 mm
(Van Leeuwen et al. , 2010). This pattern of follicle development is indicative of follicle
turnover on day 6-8 of altrenogest treatment. Therefore, ending the altrenogest treatment
at that stage may result in ovulation of aged follicles and explain the lower reproductive
performance of these sows (van Leeuwen, 2011). Optimized strategies for post-weaning
altrenogest treatment still need to be developed.

17.4.3 Conclusions

Although the weaning-to-oestrus interval is usually short (4-6 days) in most sows,
follicle development can still be optimized by providing appropriate boar contact,
feeding and housing conditions. In sows with an expected low fertility after weaning,
such as first litter sows with excessive weight loss, the weaning-to-oestrus/weaning-to-
insemination interval can be extended by either using the skip-a-heat strategy, which
results in 21 non-productive days (a cycle length), or by using a 10-14 day treatment
with a progesterone analogue.

17.5 Oestrus and insemination: ensure maximal fertilisation

To achieve maximal fertilisation, inseminations should be performed at the appropriate
time relative to ovulation, with good quality semen and sufficient sperm numbers, using
a hygienic, non-traumatizing, and low stress insemination procedure. The challenges for
maximal fertilisation are discussed in this section.

17.5.1 Timing of insemination

In sows, fertilisation results are very much dependent on the time of insemination
relative to ovulation (reviewed by Kemp and Soede, 1997). After insemination, uterine
contractions transport the sperm cells to the sperm reservoir in the utero-tubal junction