Lactational oestrus in sows : follicle growth, hormone profiles and early pregnancy in sows subjected to Intermittent Suckling

Keywords: sow; Intermittent Suckling; oestrus; lactation; oestradiol; LH; progesterone, embryo survival, embryo development, cystic ovaries. Weaning of piglets at a relatively young age (3 to 4 weeks) can compromise health and welfare. A possible way to increase piglet welfare is to extend lactation length, but this is economically undesirable due to lactational anoestrus of the sow. Thus, an extension of lactation would reduce the number of litters per sow per year. Intermittent Suckling (IS), a management system in which the lactating sow is separated from her litter for a fixed period of the day, is proposed as method to extend lactation length without compromising sow reproductive performance. The aims of this thesis were to study if by application of IS, lactational oestrus and ovulation could be induced in a large proportion of the sows and to examine the quality of such a lactational oestrus by studying hormone levels and pregnancy parameters. Within a first study, sows were separated from their piglets for either 12h continuously or at 6h intervals from d14 of lactation onwards. In a control group, weaning occurred at d21 of lactation. Lactational oestrus was induced in more than 80% of the sows. The pre-ovulatory LH surge, progesterone (P4) levels and the number of ovulating sows were negatively affected by IS and embryo development was negatively affected by the regimen of IS (6h). Low P4 levels have been related to a low embryo survival and one factor known to affect P4 levels was feeding level. Therefore, the aim of a second study was to examine the effect of the high lactational feeding level of IS sows on P4 levels. Multiparous sows, subjected to IS daily for 12h continuously, were fed at a high (±6.5kg/day) or low (±4kg/day) feeding level from ovulation to 6 days after ovulation. Results of this study indicated that P4 levels were not affected by high lactational feeding levels and that P4 levels were comparable to levels found in the first study. In a third study two other factors, possibly involved in the low P4 levels, were studied: timing of start of IS and continuance of IS during early pregnancy. Multiparous sows were subjected to IS for 12h continuously per day from d14 or d21 of lactation onwards. Weaning occurred either at ovulation or day 20 after ovulation. An early start of IS (d14) did not significantly affect the pre-ovulatory LH surge, but resulted in lower P4 levels at d7 after ovulation. Continuance of IS after ovulation resulted in lower P4 levels after ovulation and also negatively affected embryo development. Thus, lactational factors such as suckling related hormones or the metabolic state of the sow may caused the low P4 levels in IS sows. In general, a high proportion of IS sows developed cystic ovaries. In a final study, reproductive parameters were examined in sows developing cysts. Sows developing cysts lacked an LH surge. A dysfunction in oestradiol feedback seems the underlying mechanism responsible for the lack of the LH surge and may be related with stress or the metabolic state of IS sows. In conclusion, it is possible by means of IS to induce lactational oestrus and ovulation. The rate of success, however, is dependent on several factors such as the breed of the sow and the timing of start of IS. The quality of lactational oestrus (hormone levels, embryo survival) seems comparable to weaned sows when start of IS is not too early after farrowing and IS is not continued during early pregnancy.