Maturational changes in gonadotrophin secretion: the LH response to realimentation and a nocturnal increment in LH secretion of feed-restricted prepubertal gilts

Abstract

Potential maturational changes in patterns of LH secretion during feed restriction and the LH response to realimentation were examined.

Feeding lactating primiparous sows to establish three divergent metabolic states: I. Associated endocrine changes and postweaning reproductive performance.

“…At d 26 ± 1.3 of lactation, an indwelling jugular catheter was surgically implanted under general anesthesia via the cephalic vein (Cosgrove et al, 1993). On the day of blood sampling, feed was withheld during the first 2 h of sampling to allow for an estimate of preprandial insulin concentration.…”

Ovarian and hepatic insulin-like growth factor-I gene expression and associated metabolic responses in prepubertal gilts subjected to feed restriction and refeeding

“…Blood sampling An indwelling jugular cannula was surgically placed under general anaesthesia via the superficial cephalic vein (Cosgrove et al 1993) on day 9 of the study to facilitate stress-free, frequent blood sampling. On day 13, 10 ml heparinized blood samples were taken at 30-min intervals from 07.00 until 11.00 h and then hourly until 16.00 h. Plasma was obtained by centri¬ fugation of samples at 2000 g for 20 min immediately after collection and then stored in two aliquots per sample at -20°C until analysis for plasma insulin and IGF-I.…”

Effects of season and regulated photoperiod on the reproductive performance of sows

“…According to observations by Cosgrove et al (1993) the low farrowing rates indicate that pituitary support of the ovaries is at its weakest at the time when summer infertility is most frequent. Tast et al (2002) reported that the maternal factors that could be considered to cause the low farrowing rate are failure of sows to respond to embryonic signals, regression of the corpus luteum because of inappropriate luteinizing hormone (LH) secretion, or inadequate endometrial secretion interfering with normal development of embryos and their ability to produce the oestrogen signals when needed.…”

“…It is significant that a decrease in LH concentration occurred at the same time as the frequency of disrupted fertility increased. However, the seasonal decrease in LH is not considered to be of sufficient magnitude to directly cause regression of the CL (Cosgrove et al, 1993;Peltoniemi et al, 1997b;Tast et al, 2001b). Although the seasonally diminished LH cannot directly cause regression of CL, it may decrease the progesterone secretion of the CL after it has become dependent upon pituitary LH support (Tast et al, 2002).…”