Endocrine response of gilts to various common stressors: a comparison of indicators and methods of analysis.

The first aim of the present study was to determine whether various common events encountered by pigs in commercial farms or experimental units induce activation of the sympathetic and hypothalamo-pituitary-adrenal (HPA) axes. The second aim was to compare the efficiency of various indicators and methods of analysis to detect the occurrence of a stress reaction. Responses to two blood sampling methods, immobilization by snaring, brief electric shocks, loud noise, ear tagging, tattooing, biopsy, pen relocation or delayed feeding time have been evaluated. Series of blood and saliva samplings (from 10 min before to 120 min after stressor application) were collected for each stressor on a total of 8 catheterized sows. Plasma glucose, lactate, cortisol and ACTH levels as well as salivary cortisol were measured. Acute increases of cortisol or ACTH (at least at time points +5 or +15 min) were observed for intense noise, electric shocks, ear tagging, tattooing, biopsy, cava blood sampling, snaring and pen relocation. Snaring, relocation and vena cava blood sampling generated longer stress responses whereas delayed meal and tail blood sampling had no influence. Plasma lactate was also significantly increased in several time-points after stressor application contrarily to plasma glucose. Comparison of successive time points with the starting basal level and comparison with the control group were more sensitive methods to detect a stress response to moderate stressors like electric shocks and tattooing, than comparing the area under the curve. These data confirmed that salivary cortisol is a good indicator to measure the HPA response to a stressor, provided that post-treatment levels can be compared with pre-treatment levels.

Effects of castration, tooth resection, or tail docking on plasma metabolites and stress hormones in young pigs.

Changes in the activity of the sympathetic nervous system or in the hypothalamo-pituitary-adrenal axis have been extensively used to evaluate pain induced by castration or tail docking in numerous species. Such data are missing in pigs. Therefore, three experiments were conducted to determine the effects of castration, tail docking, or tooth resection on stress hormones. Glucose and lactate also were measured because catecholamines stimulate mobilization of glycogen, which results in glucose and lactate release. In Exp.1, 18 male pigs from seven litters (two or three pigs per litter) were catheterized surgically into one jugular vein, under general anesthesia, at 5 or 6 d of age. Two days later, they were submitted either to bilateral castration, control handling, or no handling (n = 6 per group). Blood samples were collected before (- 15 and -2 min) and after (5, 15, 30, 60, 90, 180 min) the experimental treatment. In Exp. 2, 27 female pigs from 12 litters (one to four pigs per litter) were submitted either to tooth clipping with pliers, tooth resection with a grinder apparatus, control handling, or no handling (n = 6 or 7 per group) at 1 d of age. In Exp. 3, 17 female pigs from nine litters (one to three pigs per litter) were submitted to one of the following treatments: 1) tail docking with an electric-heated scissor docking iron, 2) control handling, and 3) no handling (n = 5 or 6 per group) at 1 d of age. Castration induced significant (P < 0.05) increases in adrenocorticotropin hormone (ACTH; from 5 to 60 min), cortisol (from 15 to 90 min), and lactate (from 5 to 30 min). These variations are indicative of stress and tissue damage following castration. In contrast, neither tail docking nor tooth resection had marked effects on plasma cortisol, ACTH, glucose, and lactate. Measurements of plasma cortisol, lactate, and ACTH could be useful for validating treatments designed to relieve the distress reaction induced by castration in pigs.

Feed restriction in cyclic gilts: gonadotrophin-independent effects on follicular growth.

Our objective was to determine whether changes in metabolic hormones, induced by feed restriction, can alter follicle distribution in swine ovaries through effects independent of LH pulsatility. In a factorial arrangement, 24 gilts were fed a high or a low level of dietary energy (240 or 80% of maintenance requirements) and given an antagonist of GnRH or saline between days 3 and 12 of the oestrous cycle. Serial blood samples were collected on day 12 and ovaries on day 13. Antagonist treatment, that blocked LH pulsatility, decreased the number of follicles larger than 2 mm and increased the number of follicles smaller than 1 mm. The feed restriction did not alter gonadotrophin secretion, decreased the number of follicles smaller than 1 mm and increased the number of 1 - to 1.9-mm follicles. These findings indicate that feed restriction can alter the growth of small follicles independently of gonadotrophin levels.

Does feed restriction mimic the effects of increased ambient temperature in lactating sows?

We evaluated the effects of high ambient temperature and feed restriction in primiparous lactating sows. Females were exposed to either a constant thermoneutral (20 degrees C) or hot environment (30 degrees C). Lactating sows at 30 degrees C were given free access to feed (30AL; n = 12), and sows at 20 degrees C were restricted according to the feed intake recorded at 30 degrees C (20RF; n = 6) or were given free access to feed (20AL; n = 6). Jugular vein catheters were surgically inserted at 100 +/- 1 d postcoitum. During lactation, 30AL sows exhibited higher rectal temperatures (P < .05) than 20AL and 20RF sows. Feed intake was reduced by 43% for 30AL compared with 20AL sows. Daily body weight loss was lower (P < .05) in the 30AL than in the 20RF group, and mean litter daily gain over the whole lactation was 18% lower in 30AL than in 20AL sows (P < .05) and was intermediate in 20RF females. Plasma concentrations of thyroid hormones (triiodothyronine [T3] and thyroxine [T4]) were lower at 30 degrees C than at 20 degrees C at d 4 postpartum and d 8 after weaning for T4 (P < .001) and at d 4 postpartum (P < .001) and at d 1 and d 8 after weaning for T3 (P < .01) but were not influenced by feed restriction at 20 degrees C. Mean concentrations of cortisol measured on d 4 and 19 postpartum and on d 1 after weaning were lower in the 30AL than in the 20AL group (P < .05), and neither was different from that in 20RF sows. Ambient temperature and feed intake had no influence on prolactin concentrations on d 19 postpartum and d 1 after weaning. In the 30AL group, concentrations of T3, cortisol, and prolactin measured at d 19 postpartum were positively correlated with the litter gain observed during the 2nd and 3rd wk of lactation (P < .05). The return to estrus was slightly delayed in 20RF compared with 20AL sows (P < .05) and was quite variable in the 30AL group. These results demonstrate that high ambient temperature has negative consequences on litter growth and return to estrus and induces plasma hormonal variations, that cannot be fully mimicked by feed restriction in primiparous sows.

Influence of feed restriction in primiparous lactating sows on body condition and metabolic parameters.

Twenty-four primiparous sows were allocated at farrowing to a high (H: 5.5-6 kg feed/day) or a low (L: 2.5-3 kg/day) level of feeding. Litters (8-10 piglets) were weaned at 28+/-2 days. Serial blood samples were collected 1 day before weaning (W-1), in the hours following weaning (W) and 1 day after (W + 1). L sows lost significantly more weight (38 versus 15 kg) and backfat (5.3 versus 2.3 mm) during lactation than H sows. On day W-1, L sows had higher mean concentrations of NEFA (P < 0.01) and GH (P < 0.1 ) and lower concentrations of insulin and IGF-I (P < 0.05) than H sows. Mean concentrations of glucose and cortisol did not differ between groups of sows. On day W + 1, these parameters were not different between treatments, except IGF-I concentrations which remained lower in L than in H sows (P < 0.05). We conclude that lactating primiparous sows alter secretion of metabolic hormones to favour mobilization of body reserves to support milk production. Low insulin and IGF-I may be involved in reduced ovarian activity at and after weaning, through LH-dependent and independent pathways.

Influence of feed restriction during lactation on gonadotropic hormones and ovarian development in primiparous sows.

Effects of nutritional deficit during lactation on secretion of gonadotropic hormones and ovarian follicular populations around weaning were investigated in 24 primiparous crossbred sows. Sows were allocated to receive close to ad libitum intakes (H) or approximately 50% of this amount (L) during a 28-d lactation. Serial blood samples were collected 1 d before weaning (W-1), in the hours following weaning (W), and 1 d after (W+1). Their ovaries were removed on the day of weaning or 2 d later (W+2) and subjected to macroscopic and histological observations. Mean and basal LH concentrations were not influenced by the level of feeding. Frequency of LH pulses was reduced in L sows (.17, .5, and .5 vs 1.50, 1.17, and .83 pulses/6 h at d W-1, W, and W+1 respectively; P < .05). Mean and basal concentrations of LH were influenced by the day of sampling, being significantly increased within hours following weaning. Mean FSH concentrations were influenced neither by the level of feeding nor by the day of sampling. At weaning, the ovaries from L sows were lighter and had smaller follicles and fewer follicles > or = 4 mm (P < .05). Values of these macroscopic characteristics increased after weaning ( P < .05). At weaning, the percentage of healthy follicles was higher in the first class (< 1 mm) and lower in the second class (1 to 2.99 mm) in L compared to H sows (P < .05). Whatever the day of sampling, IGF-I concentrations in follicular fluid tended to be lower in L than in H sows. These results indicate that feed restriction during lactation inhibits LH pulsatility and ovarian activity.

Metabolic and endocrine changes associated with undernutrition in the peripubertal gilt.

The effect of feed restriction on circulating metabolites and metabolic and gonadotropic hormones was determined in Large White gilts. From 25 kg BW and 80 d of age, control gilts (CTRL, n = 10) were fed close to ad libitum intake, whereas restricted-fed gilts (REST, n = 10) were offered approximately 50% of the CTRL diet. Estrus was detected with a mature boar. Serial blood samples were collected at approximately 160 and 210 d of age from 0800 to 2000. A meal was supplied at 0900, and an i.v. injection of GnRH (80 ng/kg BW) was given at 1600. The gilts were slaughtered at 220 d of age. No REST and four CTRL gilts exhibited their first estrus between the two series of blood samplings. Feed intake, daily gain, and fat content of the carcass were reduced by 50% in REST gilts (P < .001). Preprandial concentrations of free fatty acids were significantly lower in CTRL gilts at 210 d of age than at 160 d and than in REST gilts at both ages. Within the CTRL group, concentrations were lower (P < .05) at both ages in gilts pubertal before 210 d than in others. After the meal, plasma insulin and urea increased in all gilts, whereas glucose increased and free fatty acids decreased in all except the 210-d CTRL gilts. The afternoon concentration of cortisol was slightly higher (P = .09) in REST than in CTRL gilts. The number of pulses and mean and interpulse concentrations of growth hormone did not show any clear variation with feed level and age.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of plasma LH, FSH, oestradiol and corticosteroids from birth to the first oestrous cycle in Meishan gilts.

Hormonal changes associated with pubertal development in a breed of pig exhibiting early puberty were determined. In Expt 1, blood from prepubertal Meishan gilts was collected at about 1 (n = 5), 10 (n = 5), 20 (n = 4), 30 (n = 5), 50 (n = 5), 70 (n = 10), 80 (n = 10) and 90 (n = 7) days of age. In Expt 2, females were sampled between 99 and 116 days of age before (n = 16) or during (n = 9) the first oestrous cycle. Serial blood samples were collected through a jugular catheter at 20 min intervals. In Expt 2, age at puberty was determined by daily examination for oestrus and weekly evaluation of plasma progesterone and found to occur at 111 days of age. Hormone profiles determined at least 19 days before the first oestrus were grouped to constitute a prepubertal stage. In Expt 1, mean concentration of LH was high at 1 day of age, significantly lower at 10 days and showed nonsignificant variations until 90 days. Frequency of LH pulses increased between 10 and 50 days (0.42 versus 0.85 pulse h-1, P < 0.05), decreased between 50 and 70 days (0.49 pulse h-1, P < 0.05) and remained low thereafter. Amplitude of LH pulses was high between 1 and 30 days and declined progressively until 80 days. Mean concentration of FSH was high between 1 and 20 days and decreased progressively until 80 days (7.2 and 2.3 ng ml-1, respectively, at 20 and 80 days, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the presence of a mature female on puberty attainment in gilts.

At 90 days of age, 40 Large White gilts were assigned to one of two treatments. At 155 days, a mature female which was left intact (Treatment I) or ovariectomized (Treatment O) was placed in each pen of five experimental gilts. From 180 days, estrus was checked daily with the back pressure test, and the occurrence of ovulation was detected by measuring the concentration of plasma progesterone at weekly intervals. From 240 days, a mature boar was introduced, for 5 minutes daily, into each pen during estrus detection. Gilts were slaughtered within 12 days after ovulation or at 270 days of age if they were not cyclic earlier. The percentage of gilts reaching puberty before 225 days of age was significantly higher in Treatment I (7 19 ) than in Treatment O (0 19 ) even though the average age at puberty was similar (I, 231 +/- 24 days; O, 243 +/- 12 days; mean +/- SD). Age at puberty and the number of days between mature female introduction and puberty differred significantly between the pens of gilts in Treatment O but not in Treatment I. Ovarian weights, ovulation rate and percentage of gilts with silent estrus were similar in the two treatments. Thus, the occurrence of pubertal estrus may be influenced by contact with an older, cyclic female or with other contemporary females raised in the same pen.