Relationships between LH, FSH and prolactin secretion and reproductive activity in the weaned sow

Abstract

Blood samples were collected from primiparous sows via indwelling jugular cannulae at 15-min intervals for 12 h before and for 24 h (2 sows) or 48 h (10 sows) after weaning and then every 4 h until behavioural oestrus. Weaning to oestrus intervals ranged from 3 to 10 days and 2 sows showed no signs of oestrus and had not ovulated by Days 11 and 16 after weaning. Prolactin concentrations in plasma decreased significantly (P less than 0.001) and reached basal levels 1-2 h after weaning in all sows whilst plasma progesterone concentrations remained basal until approximately 30 h after the preovulatory LH surge in sows that ovulated. Elevated concentrations of prolactin or progesterone during the post-weaning period were, therefore, not responsible for delayed restoration of cyclicity. Overall, mean LH concentrations rose significantly (P less than 0.001) from 0.22 +/- 0.02 during the 12-h period before weaning to 0.38 +/- 0.03 ng/ml during the 12-h post-weaning period. After weaning, pulsatile and basal LH secretions were markedly increased for sows that showed an early return to oestrus (less than or equal to 4 days) compared with sows showing a longer weaning to oestrus interval but a correlation did not exist between either of these LH characteristics and the time taken to resume cyclicity. Mean LH concentrations before weaning were, however, inversely related (r = -0.649; P less than 0.05) to the weaning to oestrus interval. Overall, mean FSH concentrations rose significantly (P less than 0.001) from 151.1 +/- 6.2 (s.e.m.) ng/ml in the 12-h period immediately before weaning to 187.7 +/- 9.7 ng/ml in the subsequent 12-h period but there was no correlation between FSH concentrations, before or after weaning, and the interval from weaning to oestrus. However, a significant correlation was apparent between ovulation rate and peak concentrations of the rise in FSH after weaning (r = 0.746; P less than 0.05) and overall mean FSH values (r = 0.645; P less than 0.05). It is concluded that both LH and FSH concentrations in peripheral blood rose in response to removal of the suckling stimulus at weanling. The increase in LH pulse frequency associated with weaning was not directly related to the weaning to oestrus interval although a specific pattern of LH secretion was observed in sows showing an early return to oestrus (less than or equal to 4 days).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of naloxone or transient weaning on secretion of LH and prolactin in lactating sows

“…1; Table 1), which is consistent with results from other experiments (Shaw & Foxcroft, 1985;Cox & Britt, 1986) in which samples were collected frequently for several hours. For example, Shaw & Foxcroft (1985) obtained samples at 15-min intervals from 12 h before until 48 h after weaning and demonstrated that frequency of release and concentration of LH increased after weaning.…”

“…Hourly administration of gonadotrophin-releasing hormone (GnRH) stimulates follicular growth, oestrus and ovulation in lactating sows (Cox & Britt, 1982a). Weaning results in increased GnRH in the hypothalamus, increased LH in the anterior pituitary (Cox & Britt, 1982b), an increase in frequency of episodic release of LH and a decrease in prolactin (Shaw & Foxcroft, 1985;Cox & Britt, 1986). Suckling therefore limits follicular growth by reducing secretion of GnRH by the hypothalamus.…”

“…Both transient weaning and infusion of naloxone resulted in similar declines in serum prolactin values. Others reported that weaning of the litter (Stevenson et al, 1981;Shaw& Foxcroft, 1985) or administration of naloxone (Mattioli et al, 1986) resulted in a decline in prolactin in the sow. Agonists of opioids typically elevate prolactin values (Bruni et al, 1977;Meites et al, 1979;Shaar & Clemens, 1980;Seimanoff & Gregerson, 1986) and suckling caused an increase in serum prolactin and ß-endorphin concentrations in rats (Riskind et al, 1984) and sheep (Gordon et al, 1987).…”

Endocrine bases of lactational anoestrus in the sow

“…Mean concentrations of circulating LH are high during the 3 d following parturition and decrease thereafter (Tokach et al, 1992a;De Rensis et al, 1993a,b (Tokach et al, 1992a (Stevenson etal, 1981;Shaw and Foxcroft, 1985;De Rensis et al, 1993b). Weaning between 3 and 5 weeks pp results in an immediate and transient increase in LH mean levels and pulsatility (Parvizi etal, 1976; Van de Wiel etal, 1978;Shaw and Foxcroft, 1985;Armstrong et al, 1986b).…”

“…Weaning between 3 and 5 weeks pp results in an immediate and transient increase in LH mean levels and pulsatility (Parvizi etal, 1976; Van de Wiel etal, 1978;Shaw and Foxcroft, 1985;Armstrong et al, 1986b). From (Stevenson et al, 1981; Edwards and Foxcroft, 1983a;Foxcroft et al, 1987), whereas others have reported that FSH concentrations rise after weaning (Cox and Britt, 1982a;Shaw and Foxcroft, 1985).…”