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The present pilot study was undertaken to examine whether split weaning would enhance the ovulatory response of lactating sows to gonadotrophin treatment.
During lactation, 42 mixed-parity Yorkshire sows were fed to appetite a standard lactation corn-soybean meal diet (3300 kcal metabolizable energy [ME] per kg). At 18 days of lactation, sows were assigned on the basis of parity and litter size suckled to have their largest piglets weaned, leaving either five (n = 16) or six (n = 5) piglets to suckle (Split-weaned; n = 21). Piglet selection for split weaning was subjective, based on a visual assessment of size and the manager’s preference to leave six pigs in larger litters. Numbers of piglets suckled were maintained in the litters of control sows (Control; n = 21). Also at day 18 of lactation, all sows received an injection (IM) of 400 IU eCG plus 200 IU hCG. Full weaning of all remaining piglets was performed at 26 days of lactation. A single blood sample obtained from each sow 2 days after full weaning was assayed for progesterone content. Sampling at 10 days after PG600 injection would be approximately 3 to 5 days after ovulation, at which time progesterone concentrations would be relatively low but increasing. A serum progesterone concentration of > 5 ng per mL was subjectively considered high and so was deemed indicative of ovulation. For the purpose of this study (ovulation; yes or no), a value of 10 ng per mL was recorded for progesterone concentrations ≥ 10 ng per mL. Estrus detection involved fence-line exposure to a mature boar for 2 minutes daily on days 1 to 14 after full weaning of all sows, as per routine farm protocol. Data for incidence of ovulation was examined by parity (1 versus > 1) and treatment (Split-weaned versus Control) and comparisons of data for parity and litter size suckled before and after split weaning were made.
There was no difference between treatments for average sow parity or number of piglets suckled prior to split weaning on day 18 of lactation, but litter size suckled was different after split weaning. Split weaning resulted in more (P < .05) sows ovulating in response to gonadotrophins injection, with all ovulating sows exceeding the cut-off serum progesterone limit of 5 ng per mL and having serum progesterone concentrations of ≥ 10 ng per mL. More split-weaned than control sows had elevated serum progesterone 2 days post weaning (47.6% versus 9.5%; P < .05). There was no difference in day 18 litter size (mean ± SE) between sows that did or did not subsequently ovulate (9.1 ± 0.3 versus 9.2 ± 0.2, respectively). In the non-ovulating Control sows, one had a serum progesterone concentration of 3 ng per mL and three remained anestrous at day 14 after full weaning. In non-ovulating Split-weaned sows, one had a serum progesterone concentration of 3 ng per mL, and all were detected as estrous by 14 days after full weaning.
The present data support that:
- Hormonal induction of ovulation at 18 days of lactation in sows is possible.
- Predictability of the ovulatory response must be improved if hormonal induction of ovulation during lactation is to become an accepted management option.
Kirkwood RN, Turner KC, Rutley DL. Effect of split weaning on sow ovulatory responses to injection of gonadotrophins during lactation. J Swine Health Prod. 2013;21(1):42–44.