Effects of feeding level during lactation on FSH and LH secretion patterns, and follicular development in primiparous...

In the primiparous lactating sow undernutrition affects LH, but the effect on FSH is less clear. This study was conducted to investigate the effect of ad libitum (AL; n = 5) and restricted (RE; 70% of the AL feed; n = 5) feeding on the secretion patterns of FSH and LH, and on follicular development in primiparous lactating sows. Body side fat thickness (BSFT) was measured prior to farrowing and at weaning on day 21 postpartum (pp). Sows had an intravenous catheter fitted on day 6 or 7 pp. Blood samples were taken on days 12, 15 and 18 pp, every 15 min starting at 0700 h for 11 h, and plasma analysed for FSH and LH by radioimmunoassay (RIA). Daily transcutaneous ultrasonography of the ovaries was performed between days 10 and 20 pp to monitor follicular growth. Reduction in BSFT was higher in RE than in AL sows (p < 0.05). Mean and basal LH were significantly higher in AL than in RE sows on days 12 and 15 pp. (p < 0.05), and LH pulse frequency tended to be higher (p < 0.1). Mean FSH was higher in AL than in RE sows on days 15 and 18 (p < 0.05), and had a tendency to be higher on day 12 (p = 0.1). Follicle size increased in AL sows between days 10 and 20 of lactation (p < 0.05; r = 0.71), but remained unaffected in RE sows. In conclusion, the study demonstrates that feed restriction of primiparous sows during lactation affects not only LH, but also FSH, as well as lactational follicular growth. An association between those events is suggested.