Quantitative relationships between suckling-induced teat stimulation and the release of prolactin, gastrin, somatostatin, insulin, glucagon and vasoactive intestinal polypeptide in sows

The role of hormones in the regulation of lactogenic immunity in porcine and bovine species

Colostrum and milk offer a complete diet and vital immune protection for newborn mammals with developing immune systems. High immunoglobulin levels in colostrum serve as the primary antibody source for newborn piglets and calves. Subsequent milk feeding support continued local antibody protection against enteric pathogens, as well as maturation of the developing immune system and provide nutrients for newborn growth. Mammals have evolved hormonal strategies that modulate the levels of immunoglobulins in colostrum and milk to facilitate effective lactational immunity. In addition, hormones regulate the gut-mammary gland-secretory immunoglobulin A (sIgA) axis in pregnant mammals, controlling the levels of sIgA in milk, which serves as the primary source of IgA for piglets and helps them resist pathogens such as PEDV and TGEV. In the present study, we review the existing studies on the interactions between hormones and the gut-mammary-sIgA axis/lactogenic immunity in mammals and explore the potential mechanisms of hormonal regulation that have not been studied in detail, to draw attention to the role of hormones in influencing the immune response of pregnant and lactating mammals and their offspring, and highlight the effect of hormones in regulating sIgA-mediated anti-infection processes in colostrum and milk. Discussion of the relationship between hormones and lactogenic immunity may lead to a better way of improving lactogenic immunity by determining a better injection time and developing new vaccines.

Validation of hand-held refractometers for assessing Merino ewe colostrum and neonatal lamb serum

ContextThe high incidence of lamb mortality in Merino sheep is a persistent issue for the industry. Poor-quality colostrum or inadequate colostrum consumption increases the risk of low energy intake and failed passive immunity transfer, resulting in lamb mortality. The rapid assessment of colostrum quality and intake would be a valuable tool for producers which house ewes for lambing.AimsThis experiment determined the relationship and accuracy of analysis techniques to measure immunoglobulin G (IgG) and total protein (TP) concentrations within ewe colostrum and lamb serum and compared those results against digital hand-held refractometers.MethodsMerino ewe colostrum and lamb blood were sampled at 4 and 24 h post-partum during autumn (n=93 ewes) and spring (n=79 ewes) in 2018. Colostrum was analysed for total milk solids (%) and lamb serum was analysed for total blood serum protein (%), and both colostrum and lamb serum were analysed for IgG and TP using in-house laboratory analysis techniques. Correlation coefficients were performed to identify the relationship between the different assessment methods.Key resultsThere was a significant Pearson’s correlation (P<0.05) between 4 h total milk solids and TP (R=0.19), between total milk solids and IgG (R=0.19), and TP and IgG (R=0.38). For 24 h colostrum samples, the significant correlations (P<0.001) between TP and IgG (R=0.54) and total milk solids and IgG (R=0.56) were higher than the correlation between total milk solids and TP (R=0.24; P=0.006). Further, 4 h serum IgG (R=–0.14; P=0.026) and 24 h total blood serum protein (R=0.21; P=0.009) were correlated with lamb survival to 72 h.ConclusionsWhile the refractometer provided a crude measure of colostrum IgG and TP and was valuable in identifying lambs with low IgG transfer at 24 h, further research is required regarding analysis techniques to allow for reliable measures need to be refined.ImplicationsThe use of refractometers to assess colostrum quality and intake could benefit researchers or producers who practice indoor lambing.

Epidural Analgesia With or Without Oxytocin, but Not Oxytocin Alone, Administered During Birth Disturbs Infant Pre-feeding and Sucking Behaviors and Maternal Oxytocin Levels in Connection With a Breastfeed Two Days Later

Aims This work aimed to study consequences of medical interventions in connection with birth on infant pre-feeding and feeding behaviors and on maternal oxytocin levels in connection with a breastfeed 2 days later.

Materials and Methods Mothers and their full-term newborns (n = 41) were videotaped during a breastfeed 2 days after birth. Duration and quality of rooting [Infant Breastfeeding Assessment Tool (IBFAT)] were assessed. Maternal blood samples were collected, oxytocin levels were analyzed, and mean oxytocin level and variance were calculated. Data on medical interventions during birth, number of breastfeedings, and infant weight loss since birth were recorded. Data were analyzed using logistic regression models.

Results The duration of infant rooting was significantly shorter when the mother had received epidural analgesia. The shorter the duration of infant rooting, the more often infants had breastfed and the greater was the infant weight loss since birth. Mothers with epidural analgesia with oxytocin had the lowest oxytocin mean levels in connection with a breastfeed. Oxytocin variance correlated positively with quality of rooting and correlated negatively with infant weight loss. In the control group alone, we found similar patterns of associations with oxytocin levels.

Conclusion Epidural analgesia and epidural analgesia with oxytocin infusion in connection with birth negatively influenced infant rooting behavior and maternal mean oxytocin levels, respectively. Oxytocin infusion alone was without effect. The data also suggest that infants who suck well stimulate oxytocin release more efficiently, as expressed by a high oxytocin variance, leading to a better stimulation of milk production and consequently to a reduced infant weight loss 2 days after birth.

Effect of Different Cross-Fostering Strategies on Growth Performance, Stress Status and Immunoglobulin of Piglets

The effect of different cross-fostering strategies on the growth performance, stress and immunity of piglets was investigated in this study. In the first experiment, a total of 20 litters (i.e., 20 sows) and 120 piglets were classified into one of six treatments in a 2 × 3 factorial arrangement. The treatments consisted of piglets without or with cross-fostering and different birth weights (low birth weight, LBW; intermediate birth weight, IBW; high birth weight, HBW). The weaning weight (WW) and average daily gain (ADG) of LBW piglets and IBW piglets were not significantly different between the not cross-fostered (NC-F) group and the cross-fostered (C-F) group. There was a higher (p < 0.05) ADG in the control piglets compared with the cross-fostered piglets. This effect on ADG was only seen in the HBW piglets. In the second experiment, six sows with a similar body condition and farrowed on the same day were selected. Three female piglets with a birth weight of 0.6-0.85 kg were selected from each litter as experimental piglets. Eighteen piglets were grouped into three treatments: (1) not cross-fostered (NC-F1), (2) cross-fostered at 36-48 h after birth (C-F1), (3) cross-fostered at day 7 after birth (C-F2). The growth performance of NC-F1 and C-F1 piglets was higher than C-F2 piglets (p < 0.05), and the suckling positions of NC-F1 and C-F1 piglets on days 8, 12, 16 and 20 were more forward than the C-F2 piglets (p < 0.05). Plasma cortisol (COR) concentrations of NC-F1 and C-F1 piglets were lower than C-F2 piglets (p < 0.05). A significant negative correlation was observed between BW at day 21 and plasma COR concentration. In conclusion, cross-fostering within 24 h of birth has adverse influences on the ADG of HBW piglets, while it has no negative effect on the ADG of LBW and IBW piglets. Moreover, for IBW piglets, late cross-fostering (i.e., on day 7 after farrowing) has negative impacts on the growth performance and teat order of piglets, and it increases the cortisol level of piglets.

Pharmacologic inhibition of mTORC1 mimics dietary protein restriction in a mouse model of lactation

Background

Understanding the mechanisms of N utilization for lactation can lead to improved requirement estimates and increased efficiency, which modern dairy diets currently fail to maximize. The mechanistic target of rapamycin complex 1 (mTORC1) is a central hub of translation regulation, processing extra- and intra-cellular signals of nutrient availability and physiological state, such as amino acids and energy. We hypothesized that dietary amino acids regulate lactation through mTORC1, such that inhibition of mTORC1 will lead to decreased lactation performance when amino acids are not limiting. Our objectives were to assess lactation performance in lactating mice undergoing dietary and pharmacologic interventions designed to alter mTORC1 activity.

Methods

First lactation mice (N = 18; n = 6/treatment) were fed an adequate protein diet (18% crude protein), or an isocaloric protein-restricted diet (9% crude protein) from the day after parturition until lactation day 13. A third group of mice was fed an adequate protein diet and treated with the mTORC1 inhibitor rapamycin (4 mg/kg every other day) intraperitoneally, with the first two groups treated with vehicle as control. Dams and pups were weighed daily, and feed intake was recorded every other day. Milk production was measured every other day beginning on lactation day 4 by the weigh-suckle-weigh method. Tissues were collected after fasting and refeeding.

Results

Milk production and pup weight were similarly decreased by both protein restriction and rapamycin treatment, with final production at 50% of control (P = 0.008) and final pup weight at 85% of control (P < 0.001). Mammary phosphorylation of mTORC1’s downstream targets were decreased by protein restriction and rapamycin treatment (P < 0.05), while very little effect was observed in the liver of rapamycin treated mice, and none by protein restriction.

Conclusions

Overall, sufficient supply of dietary amino acids was unable to maintain lactation performance status in mice with pharmacologically reduced mammary mTORC1 activity, as evidenced by diminished pup growth and milk production, supporting the concept that mTORC1 activation rather than substrate supply is the primary route by which amino acids regulate synthesis of milk components.

The effect of maize starch or soya-bean oil as energy sources in lactation on sow and piglet performance in association with sow metabolic state around peak lactation

The effects of different energy sources in the lactation diet on sow and piglet performance were assessed in association with effects on the metabolic state of the sow around peak lactation. Either maize starch (S) or soya-bean oil (F) was added to a basal diet to provide 0·34 of total digestible energy (DE) intake, such that the experimental diets provided the same daily intakes of DE and crude protein. Twenty-four multiparous sows were allocated between two groups at farrowing, each given one of the two dietary treatments for a lactation period of 28 days. Sow weight and backfat (P2) as well as individual piglet weights were measured on a weekly basis. Litter sizes were standardized to 10 piglets. Milk samples were collected from sows on days 8, 12, 17, 21 and 25 of lactation to measure milk composition and prolactin concentrations. Blood samples were taken via an ear vein catheter from a subsample (7 S, 6 F) of sows on day 14 of lactation; two pre- and seven post-feeding samples were taken at 60-min intervals to measure plasma prolactin, insulin, glycerol, triglyceride, non-esterified fatty acid, urea, b-hydroxybutyrate and glucose concentrations. There was no effect of energy source on sow weight or P2 loss or on subsequent weaning-to-oestrus interval. Sows offered starch weaned more piglets than sows offered soya-bean oil (9·4 v. 8·4, P < 0·05). Litter weight gains were higher for S than F sows in week 3 of lactation (2·2 v. 1·7 kg/day, P < 0·05), irrespective of litter size. Significantly increased plasma urea and b-hydroxybutyrate concentrations and lower post-prandial increases in plasma glucose and insulin concentrations were observed in F sows around peak lactation. Neither milk nor plasma prolactin concentrations were significantly affected by dietary treatments. The metabolic indices indicated that the F diet was more limiting in dietary glucose availability, which was associated with impaired milk yield as indicated by poorer litter performance. In conclusion, this study suggests that starch is superior to fat as an energy source in sow lactation diets, particularly in the later stages of lactation.

Altering prolactin concentrations in sows

Prolactin has a multiplicity of actions, but it is of particular importance in gestating and lactating animals. In sows, it is involved in the control of mammary development and also holds essential roles in the lactogenic and galactopoietic processes. Furthermore, low circulating concentrations of prolactin are associated with the agalactia syndrome. The crucial role of prolactin makes it important to understand the various factors that can alter its secretion. Regulation of prolactin secretion is largely under the negative control of dopamine, and dopamine agonists consistently decrease prolactin concentrations in sows. On the other hand, injections of dopamine antagonists can enhance circulating prolactin concentrations. Besides pharmacologic agents, many other factors can also alter prolactin concentrations in sows. The use of Chinese-derived breeds, for instance, leads to increased prolactin concentrations in lactating sows compared with standard European white breeds. Numerous husbandry and feeding practices also have a potential impact on prolactin concentrations in sows. Factors, such as provision of nest-building material prepartum, housing at farrowing, high ambient temperature, stress, transient weaning, exogenous thyrotropin-releasing factor, exogenous growth hormone-releasing factor, nursing frequency, prolonged photoperiod, fasting, increased protein and/or energy intake, altered energy sources, feeding high-fiber diets, sorghum ergot or plant extracts, were all studied with respect to their prolactinemic properties. Although some of these practices do indeed affect circulating prolactin concentrations, none leads to changes as drastic as those brought about by dopamine agonists or antagonists. It appears that the numerous factors regulating prolactin concentrations in sows are still not fully elucidated, and that studies to develop novel applicable ways of increasing prolactin concentrations in sows are warranted.

Behaviour and growth performance of low-birth-weight piglets cross-fostered in multiparous sows with piglets of higher birth weights

The aim of the study was to evaluate the behaviour, pre-weaning survival rate and growth performance of low birth weight (BW) piglets cross-fostered with piglets of higher weights. Piglets were transferred to 60 foster sows, and divided in three groups (G; n=20): G1- 12 low BW piglets (0.80 - 1.25kg); G2- six low BW piglets and six intermediate BW piglets (1.40 - 1.60kg), and G3- six low BW piglets and six high BW piglets (>1.70kg). For the analysis, groups G2 and G3 were subdivided in LG2 (six G2 light piglets); IG2 (six G2 intermediate piglets), LG3 (six G3 light piglets), and HG3 (six G3 heavy piglets). Behavioural observations were carried out on days 1, 2, 4 and 6 (visual direct observation) and on days 3 and 5 (video recording) after birth. The percentage of missed nursings was higher in LG3 piglets than in LG1, IG2 and HG3 piglets, on days 1 and 2. On day 4, light piglets (LG1, LG2 and LG3) missed more nursings than IG2 and HG3 piglets. On day 3, video recording showed a higher percentage of missed nursings in LG1, LG2, and LG3 piglets as compared to HG3 piglets. On day 1, the number of fights during nursing was higher in IG2 than in LG1 and LG3 piglets. Also on day 1, number of fights and percentage of piglets engaged in fights, during 15min after nursing, were higher in LG1, LG3 and HG3 than in LG2 piglets. More playful behaviours were observed on day 2 in IG2 and HG3 piglets compared to LG1, LG2 and LG3 piglets. Light piglets (LG1, LG2, and LG3) presented similar body weight on days 4, 8, 12 and 16 after birth, regardless of being mixed with piglets of higher weights or not; however, the survival rate until day 16 was most compromised in LG3 piglets compared to the other groups. Despite the lack of influence of littermates' weight on the growth of low BW piglets, their survival rate indicates that they should not be mixed with high BW piglets.

Presence of pituitary adenylate cyclase-activating polypeptide (PACAP) in the plasma and milk of ruminant animals

Milk contains a variety of proteins and peptides that possess biological activity. Growth factors, such as growth hormone, insulin-like, epidermal and nerve growth factors are important milk components which may regulate growth and differentiation in various neonatal tissues and also those of the mammary gland itself. We have recently shown that pituitary adenylate cyclase-activating polypeptide (PACAP), an important neuropeptide with neurotrophic actions, is present in the human milk in much higher concentration than in the plasma of lactating women. Investigation of growth factors in the milk of domestic animals is of utmost importance for their nutritional values and agricultural significance. Therefore, the aim of the present study was to determine the presence and concentration of PACAP in the plasma and milk of three ruminant animal species. Furthermore, the presence of PACAP and its specific PAC1 receptor were investigated in the mammary glands. Radioimmunoassay measurements revealed that PACAP was present in the plasma and the milk of the sheep, goat and the cow in a similar concentration to that measured previously in humans. PACAP38-like immunoreactivity (PACAP38-LI) was 5-20-fold higher in the milk than in the plasma samples of the respective animals, a similar serum/milk ratio was found in all the three species. The levels did not show significant changes within the examined 3-month-period of lactation after delivery. Similar PACAP38-LI was measured in the homogenates of the sheep mammary gland samples taken 7 and 30 days after delivery. PAC1 receptor expression was detected in these udder biopsies by fluorescent immunohistochemistry suggesting that this peptide might have an effect on the mammary glands themselves. These data show that PACAP is present in the milk of various ruminant domestic animal species at high concentrations, the physiological implications of which awaits further investigation.

Secretion pattern of growth hormone, prolactin, insulin and insulin-like growth factor-1 in the periparturient sow depending on the metabolic state during lactation

The aim of the study was to investigate the influence of different energy levels during a 4-week lactation on the regulation of the metabolic hormones somatotropin (GH), prolactin, insulin and insulin-like growth factor-1 (IGF-1). A total of 21 crossbred sows (German Landrace × Duroc) were cannulated for daily blood collection from 3 weeks before parturition until 2 weeks after weaning and for weekly window sampling (every 20 min for 10 h). Nineteen sows were given 2·8 kg food during late gestation, 5·0 kg food during lactation and 2·8 kg food per day after weaning and two sows were given food at a restricted level (3·0 kg) during lactation. In the 19 sows, the different energy balance was induced by allocation of different numbers of sucking piglets to the respective sows. One group of sows suckled seven piglets and served as a control (C; no. = 7) and another group suckled 10 to 12 piglets and was energy deficient (D). After the study, the sows of the deficient group were, based on their litter weight gain from parturition until weaning, divided into low (D-L; no. = 6) or high (D-H; no. = 6) litter weight gain. The D-H sows lost more body weight during lactation than C and had lower glucose and higher nonesterified fatty acids levels before morning feeding. GH and prolactin increased around parturition and their secretory profiles during lactation were altered by the frequent sucking stimulus, whereby the access of the piglets to their dams was not controlled. During lactation, GH and prolactin were highest in D-H sows. The results suggest a possible role of not only GH but also of prolactin in nutrient partitioning to the mammary gland just before the start of lactation and for minimizing the adverse effects of a negative energy balance. Furthermore, insulin and IGF-1 increased around parturition in all sows. Insulin was higher before and after feeding and the highest levels were found in C and D-L sows. The regulation patterns of insulin and IGF-1 indicate that the lactating sow is able to mobilize enough energy from body reserves to prevent metabolic disorders, even during a period with deficient energy supply. This is contrary to the regulation in the dairy cow, where the negative energy balance is coupled with a severe glucose deficit during phases of high milk yield, which causes decreased levels of insulin and IGF-1. In the sow, the glucose intake with the food meets the glucose requirement for metabolic pathways also during a deficient lactational energy intake. Therefore, in sows IGF-1 can be stimulated by increased GH levels via the GH receptor in the liver during a state of nutritional energy deficiency and the fact that sows can compensate a deficient metabolic state much better than cows is also reflected in the respective endocrinology.

Stress, behaviour and reproductive performance in female cattle and pigs

Female farm animals are exposed to a great variety of environmental and management related stressors. As a consequence, their reproductive and maternal abilities may be compromised through mechanisms acting on the hypothalamic, pituitary, ovarian and uterine function. Responses to short- and long-term stressors may differ as short-term stressors often fail to affect reproduction or even may have stimulatory effects. Thus, the stress response induces diverse neuroendocrine reactions that can either increase or decrease the probability of an animal reproducing depending on the specific situation. The aim of the present review is to summarise the current knowledge on the stress concept and its implications on behaviour and reproductive performance in cows and female pigs as phenomena reported in laboratory animals are unable to explain all effects encountered in domesticated farm animals.

Maternal behavior in pigs

When sows kept under commercial conditions were put into crates in the early 1960s, the neuro-endocrine regulation of the maternal behavior in these domestic animals was disputed. Thus, the study of sow maternal behavior intensified and today a significant body of knowledge has accumulated to support the hormonal regulation of sow maternal behavior. The onset of nest building is associated with a periparturient decline in progesterone, an increase in prolactin and a major rise in plasma concentrations of PGF2alpha the day before parturition. Some nest building behaviors, such as pawing and gathering straw, have been found to correlate with changes in the levels of progesterone, prolactin and somatostatin. The duration of the birth process correlates negatively with peripheral oxytocin levels. During lactation, the stimuli from the piglets affect the release of several hormones which not only regulate the let down of milk but also sow metabolism and mammary milk production. The sow's nursing behavior ensures an even distribution of milk to her piglets. The piglets suckling behavior, in turn, is mainly a way to communicate their individual nutritional needs.

Influence of litter size on metabolic status and reproductive axis in primiparous sows1

This study on primiparous sows was designed to 1) determine the impact of nursing a large litter on LH secretion and follicular development, and 2) investigate the metabolic adaptations by which milk yield increases with litter size. At farrowing, crossbred, primiparous sows were assigned to 1 of 3 experimental groups differing in litter size and feed allowance. Sows with 13 or 14 piglets (13AL, n = 7) were fed ad libitum. Sows with 7 piglets were fed ad libitum (7AL, n = 6) or were feed-restricted (7R, n = 8). The restriction was based on the estimated energy deficiency for the 13AL sows. On d 9 +/- 1 of lactation, a jugular catheter was surgically implanted. Serial blood samplings and glucose tolerance tests were performed in mid- and late lactation. Sows were slaughtered 3 d after weaning, and ovarian characteristics were recorded. During lactation, the 7AL sows lost no or little body reserves, and their estimated energy balance was near zero. The 13AL and 7R sows exhibited similar negative energy balances and similar losses of backfat and estimated lipid content. Litter growth rate was greater (P < 0.05) in the 13AL than in the 7AL and 7R groups. After weaning, the volume of the largest 14 follicles was smaller (P < 0.05) in sows nursing 13 or 14 piglets than in sows with 7 piglets. Plasma concentrations of LH and LH pulse frequency did not differ between groups (P > 0.1). The longer glucose half-life on d 16 than on d 27 of lactation (22.5 vs. 18.8 min; P < 0.05) indicated a lower glucose tolerance in mid- than in late lactation. The area under the insulin curve was greater in the 7AL than in the 13AL sows (P = 0.08) and intermediate in the 7R group, with no differences in glucose profiles. This led to the suggestion that the 7AL sows were more resistant to insulin than the 13AL sows. In all groups of sows, follicular development after weaning was correlated with LH secretion in midlactation. Active follicular development was associated with prolonged secretion of insulin in response to glucose challenge. Our results show that besides litter size, a sow's metabolic status in lactation influences follicular maturation after weaning and also indicate that the metabolic adaptations by which primiparous sows nursing large litters increase litter growth rate and body reserve mobilization do not involve an accentuated peripheral insulin resistance.

Massage-like stroking influences plasma levels of gastrointestinal hormones, including insulin, and increases weight gain in male rats

The aim of the present study was to investigate the effects of repeated massage-like stroking on plasma levels of some gastrointestinal hormones, insulin included, glucose and weight gain. For this purpose, male rats were exposed to stroking on the ventral side of the abdomen for 3 or 14 times. The treatments were given every second day. Control rats were picked up at the same time but received no stroking. Body weight was measured regularly. Rats were decapitated 10 min after the last treatment. Hormone levels were radioimmunoassayed and glucose was measured by spectrophotometry. In rats exposed to 3 sessions of massage-like stroking plasma levels of insulin (p<0.05) and somatostatin (p<0.01) were significantly decreased 10 min after the last treatment. After 14 treatments of massage-like stroking, decreased plasma levels of insulin (p<0.01) and gastrin (p<0.01) as well as increased glucose levels (p<0.01) were observed 10 min after the last treatment. In addition, weight gain was significantly increased (ANOVA p<0.0001) in rats exposed to 14 treatments. In conclusion, repeated massage-like stroking decreased plasma levels of gastrin, insulin and somatostatin, increased plasma levels of glucose and promoted weight gain. The effects were influenced by the number of treatments.

Neonatal-piglet weight variation and its relation to pre-weaning mortality and weight gain on commercial farms

To determine the effect of within-litter neonatal-weight variation on pre-weaning mortality and weight gain, we analyzed piglet survival and weight gain within 400 litters from 10 commercial farms. Neonatal-weight variation (independent of mean neonatal weight, litter size and sow parity) was associated with pre-weaning survival and weaning-weight variation-but not with mean weaning weight. Neonatal piglets with weights well below the range of most of the litter (low-birth-weight piglets) had an increased risk of dying and were unable to obtain normal weight gains by weaning if they survived. These piglets experienced lower survival and poorer weight gain in larger litters. These piglets also tended to have lower survival but normal (albeit low) weaning weights if they survived in litters from middle-aged and old sows. High neonatal-weight variation resulted in lower survival and more variable weaning weights. Small piglets had a greater risk for poor survival and weight gain compared to their heavier litter-mates (a disadvantage that was exacerbated in large litters).

Lactational estrus induction in the Mexican hairless sow

The purpose of this study was to determine the effects on the reproductive performance of the Mexican hairless pig (MHP) while inducing fertile lactational estrus. Lactational estrus was induced on day 8, postpartum, in 20 primiparous sows during two consecutive reproductive cycles. Boar presence and temporary litter withdrawal were used as stimuli. Group I did not receive stimuli (control, C); group II had a 15 min boar stimulus (B); group III had litter withdrawal for 4 h (LW), and group IV received both stimuli (B + LW). Fertile estrus was detected by sow behavior, exfoliative vaginal cytology, and 17 beta-estradiol and progesterone samples. Individual stimuli did not induce fertile lactational estrus; nevertheless, when used together, both stimuli induced 100% of females into estrus, and 80% of them got pregnant while lactating. The partial withdrawal of the litter had a significant and positive effect on the number of live born piglets. Sows pregnant during lactation had shorter reproductive cycles, by not having non-productive days and litter size was greater. Pregnancy induction during lactation allowed the Mexican hairless sow to reduce the period between parturition's without diminishing the lactation length and litter performance.

Birth weight variation in the domestic pig: effects on offspring survival, weight gain and suckling behaviour

In domestic pigs, litter-mates often vary considerably in birth weight. To examine whether this size variation influences piglet survival, weight gain and suckling behaviour, we experimentally manipulated the number and size distribution of litter-mates in 51 litters. Litters were small (eight or nine piglets) or large (11 or 12 piglets) compared to the herd mean of 10 piglets, and were made more or less variable in weight by using the largest and smallest quartiles of two combined litters (variable) or the middle two quartiles (uniform). Weights were measured on days 0, 3 and 21. Behavioural measures (percent of nursings missed, mean teat consistency score, per capita number of teat disputes before milk ejection, and percent time spent in teat disputes in the 20min after milk ejection) were recorded on days 1, 4, 10 and 17. Piglet weight variation (percent of coefficient of variation, CV) almost doubled over the 21 days in uniform litters and actually decreased in variable litters, but still remained higher in the variable litters. Overall, survival, percent of nursings missed, consistency in piglets' use of teats, number of teat disputes, percent time a piglet spent in teat disputes after milk ejection, and weight gain were unaffected by birth weight variation although there was a tendency (P=0.09) for more piglet deaths in variable litters. Behavioural measures of sibling competition were higher in large litters. The data provide little support for the hypotheses that high birth weight variation results in decreased survival, or that it permits rapid establishment of dominance, thereby reducing wasteful competitive behaviour in surviving piglets.

Prolactin and insulin levels in lactating sows in relation to nursing frequency

It has been established that sows up- or down-regulate their milk production as the frequency of nursings is changed. The amount of udder massage by piglets might also influence milk production. To investigate whether these effects are associated with changes in prolactin or insulin levels, we enforced five sows each to nurse either every 35 min (MIN35) or every 70 min (MIN70) over a 26- to 28-hr period. Milk production was measured during the first 24 hr of this period. During the last three to four nursings, blood was collected every 5 min. Plasma prolactin levels increased after milk ejection (P < 0.05), whereas insulin levels increased only briefly in MIN70 sows. Sows nursing every 35 min had lower basal (P < 0.001) and maximal (P < 0.05) concentrations of insulin than MIN70 sows. There were no differences between the two groups in prolactin levels. Nursings with a postejection udder massage longer than 90 s tended to induce a higher increase in prolactin (P < 0.1) than nursings with a shorter massage. When the effects of imposed nursing frequency were removed, there was an across-sows positive residual correlation between average prolactin levels (P < 0.05) and the duration of post-ejection udder massage during the preceding 24 hr. We conclude that when milk production of a sow is changed by altering the nursing frequency within natural limits, the necessary alteration in catabolic state of energy metabolism may be associated with altered insulin levels. The duration of udder massage in a single nursing might have only a slight immediate impact on prolactin levels, but may influence prolactin levels more substantially if increased for a period of 24 hr.

Effects of low feed intake and hot environment on plasma profiles of glucose, nonesterified fatty acids, insulin, glucagon, and IGF-I in lactating sows

This experiment was designed to compare the effects of high ambient temperature and of feed restriction on plasma hormones and metabolites in primiparous lactating sows. Females were exposed to a constant thermoneutral (20 degrees C) or hot environment (30 degrees C) during lactation. Sows housed at 30 degrees C were given free access to feed (30AL: n = 12), whereas those housed at 20 degrees C were either pair-fed with those at 30 degrees C (20RF: n = 6) or were fed ad libitum (20AL: n = 6). A jugular vein catheter was surgically inserted in all sows at 100 d of gestation. Absorption of nutrients during the meal induced significant increases in plasma glucose, insulin, and glucagon, and a decrease in nonesterified fatty acids on Day 19 of lactation and Day 1 postweaning (P < 0.05). On Day 19, feed restriction at 20 degrees C was associated with higher plasma glucagon before the meal, lower plasma insulin after the meal and a lower insulin-to-glucagon ratio (I/GA) before and after the meal (P < 0.05). On Day 19, mean plasma concentrations measured in 30AL females were between those measured in 20AL and 20RF sows for nonesterified fatty acids and glucagon before feeding, and for glucose, nonesterified fatty acids, insulin, and glucagon after feeding. None of the differences between the 30AL and the 20RF groups was significant (P < 0.1). On Day 19, the only significant differences between the 30AL and 20AL groups were observed after the meal for plasma insulin and I/GA. Plasma insulin-like growth factor-I increased after farrowing in 20AL and 30AL sows only (P < 0.05). It was higher in 20AL than in 20RF and 30AL sows on Days 4 and 19 of lactation (P < 0.05). Overall, underfeeding at 20 degrees C induced changes in plasma insulin, glucagon, I/GA, and insulin-like growth factor-I, which would favor gluconeogenesis and body-reserve mobilization during lactation. Differences in glucagon and I/GA before the meal between well-fed sows at 20 degrees C and heat-exposed sows were attenuated, which could have detrimental consequences on glucose availability to the mammary gland and hence on milk production at 30 degrees C.

Breastfeeding: physiological, endocrine and behavioural adaptations caused by oxytocin and local neurogenic activity in the nipple and mammary gland

It is now well established that oxytocin, as well as stimulating uterine contractions and milk ejection, promotes the development of maternal behaviour and also bonding between mother and offspring. In addition, oxytocin exerts by way of peripheral, circulating as well as by central, neurogenic mechanisms multiple physiological, endocrine and behavioural effects in connection with milk ejection and lactation. Some effects of oxytocin in the nipple and mammary gland appear to be exerted in close collaboration with peptides released from axon collaterals of somatosensory nerves originating in this region. The distribution of peptides localized to the somatosensory afferents in the nipple and mammary gland as well as possible effects by oxytocin and/or local neurogenic peptides in connection with milk ejection and lactation are reviewed in this paper.

Patterns of release of oxytocin, prolactin, insulin and LH in lactating sows, studied using continuous blood collection technique

To describe the patterns of release of oxytocin, prolactin, insulin and LH in relation to suckling and to investigate relationships between them, blood was collected continuously from four sows at a rate of 1 ml per min for 12 h (0900-2100 h) on day 10 (D10) and day 20 (D20) of lactation. The 12-h period was divided into four smaller periods: P1 (0900-1200 h), P2 (1200-1500 h), P3 (1500-1800 h) and P4 (1800-2100 h). The number of nursings occurring during a 12-h period tended to decrease between D10 (17.3 +/- 0.3) and D20 (16.0 +/- 0.3). About 40-50% of all sucklings induced a significant rise in plasma oxytocin, while prolactin gradually increased following each suckling. Decrease in the levels of oxytocin (14.1 +/- 0.4 vs 7.1 +/- 0.4 pmol/l, P < 0.001), prolactin (12.9 +/- 0.3 vs 7.9 +/- 0.1 micrograms/l, P < 0.001) and insulin (24.8 +/- 1.7 vs 14.4 +/- 1.7 mU/l, P < 0.001) were observed between D10 and D20. Average and basal levels of LH and the number of LH pulses increased (P < 0.01) between D10 and D20. A negative correlation between number of sucklings and number of LH pulses was demonstrated on D20 (r = -0.59, P = 0.07). There was a positive correlation between levels of LH and oxytocin on D10 (r = 0.54, P = 0.001) and between prolactin and insulin levels on D20 (r = 0.34, P = 0.05).

Plasma oxytocin, prolactin, insulin and LH after 24 h of fasting and after refeeding in lactating sows

The effects of 24 h of fasting and refeeding on the release of oxytocin, prolactin, insulin and LH in three lactating sows were investigated. The sows were starved, but supplied with water ad libitum, from 09.00 h on day 27 of lactation until 15.00 h on day 28 of lactation, when they were refed. Blood samples were collected continuously, using an automatic collection system, at a rate of 1 ml min-1 from 09.00 to 21.00 h on day 28 (P1 = 6 h period after the 24 h fast, P2 = 6 h period after refeeding). For both P1 and P2 the mean number of nursings was 7.0 +/- 1.0. Plasma insulin and glucose decreased to very low levels during fasting and increased (P < 0.001) after refeeding (insulin, 2.5 +/- 0.7 vs. 28.9 +/- 0.7 mU l-1; glucose, 2.6 +/- 0.3 vs. 6.4 +/- 0.3 mmol l-1). Following fasting, levels of prolactin were low (2.8 +/- 0.1 micrograms l-1), and sucking did not induce significant release of prolactin. However, prolactin increased rapidly after refeeding (5.4 +/- 0.1 micrograms l-1, P < 0.001). Neither the 24 h fast nor refeeding had a marked effect on basal levels of oxytocin, the percentage of sucklings with an oxytocin peak or the size of oxytocin peak. LH release (average and basal levels and number of pulses/6 h) during fasting was similar to that measured after refeeding. Plasma CCK increased significantly after feeding. The results indicate that the release of prolactin is also regulated by feed intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Nursing-induced changes in pain sensitivity, prolactin, and somatotropin in the pig

Suckling by piglets led to increases in prolactin and somatotropin in the sow. Failed nursing attempts, which did not result in milk ejection, also led to elevations of prolactin and somatotropin, suggesting that massage of the udder is sufficient and milk ejection is not necessary for these hormonal changes to occur. Prior treatment with the opioid antagonist, naloxone, blocked the nursing-induced increases in prolactin and somatotropin. Tail-flick latencies of the sows were significantly elevated after a nursing, suggesting reduced pain sensitivity. This was blocked by naloxone, suggesting that nursing directly increases endogenous opioid activity. Removing piglets for 2 h led to a drop in prolactin and somatotropin. When the piglets were returned, the nursing-induced increase in prolactin and somatotropin tended to be higher than following a normal nursing interval (1 h). However, prolactin concentrations remained at a significantly lower level following the extended nursing interval. A reduction in nursing frequency seems likely to lead to reduced prolactin levels and altered patterns of somatotropin secretion.

Relationship between lactation-associated body weight loss, levels of metabolic and reproductive hormones and weaning-to-oestrous interval in primiparous sows

Twelve conventionally fed primiparous sows with a similar number of piglets were divided into 3 groups (n = 4) according to their body weight loss after a 5-week lactation as follows: H-gr (loss greater than 25 kg), M-gr (loss 11-25 kg) and L-gr (loss less than or equal to 10 kg). Blood samples were collected at 9, 12, 15, 18 and 21 h, from 4 days before weaning until 3 days afterwards, and every 15 min for 6 h on the day before and the day after weaning. The group of sows with higher weight loss during lactation tended to have a higher farrowing weight and higher pre-weaning plasma prolactin levels. At weaning, the L-gr sows had higher plasma insulin and lower plasma cortisol concentrations, especially when compared with H-gr sows. Among the ten sows that showed oestrus within 10 days of weaning, no between-group differences were found in the length of the interval from weaning to oestrus. No significant differences between groups were observed in levels of oestradiol-17 beta and LH. The higher level of insulin in L-gr sows might relate to the higher number of corpora lutea observed in this group.

Endocrine responses in cows milked by hand and machine

Plasma concentrations of oxytocin, prolactin, and cortisol were compared in five Swedish Red and White cows milked by hand versus machine. Cows were divided into two groups. One group was hand-milked; the other group was machine-milked. Treatments were switched every other day. The experiment was carried out for 6 d. Blood samples were taken prior to, during, and after milking and were assayed for hormones. More oxytocin and prolactin were released in hand-milked cows. There were no significant diurnal differences between the total amount of oxytocin released for the different treatments, but prolactin tended to be higher during hand-milking in the evening than in the morning milking. Cortisol concentrations were greater during hand-milking than during machine-milking. There were no significant treatment differences with regard to the total amount of cortisol released. During morning milking, cortisol concentrations were higher during hand-milking than during machine-milking. Our data show that hand-milking results in a pronounced and prolonged release of oxytocin and prolactin.