Nutritive and nonnutritive sucking and the temporal organization of the suckling behavior of domestic piglets

Parental Behaviour in Sows

Parental behaviour in sows begins with prepartum nest-building behaviour, which mainly consists of rooting, pawing, and foraging, to achieve a structure for farrowing and to nurse and protect the offspring. A hormonal background is linked to the onset and cessation of nest-building behaviour. The ambient farrowing environment that can adequately address the needs for nest-building behaviour thus plays an important role in good parental behaviour of the sows during and after farrowing. In addition to these environmental factors, here we also discuss other well-known intrinsic factors, such as heredity, parental experience, and litter size, affecting parental behaviour of the sows for successful farrowing and lactating performance.

Early milk ejection, prolonged parturition and periparturient oxytocin release in the pig

Plasma oxytocin was measured in 11 multiparous sows for 13 h after the start of parturition to confirm the existence of early milk ejections and determine whether they were associated with pulsatile oxytocin release. The relationship between oxytocin concentrations and duration of parturition was also analysed. Oxytocin was released in pulses during and after parturition and mean concentrations reached maximum 2 to 4 h after the first birth. Discrete milk ejections occurred during parturition but only 42% of these were associated with oxytocin peaks before 4 hpost partum. After this more than 80% of milk ejections occurred with oxytocin peaks. Sow grunting increased during milk ejections and peak grunt rate increased after parturition. Oxytocin peaks without milk ejections did not lead to an increased rate of grunting. Sows with prolonged parturition had lower basal and peak oxytocin concentrations. During the first 4 h only half of the piglets were born during an oxytocin peak. Discrete milk ejections with oxytocin peaks can occur before parturition is completed. However, during the first 4 hpost partum, basal oxytocin concentrations may be high enough for milk ejection to occur without further oxytocin secretion. Both milk ejection and oxytocin release are necessary for the sow to increase grunt rate. Low oxytocin concentration is associated with prolonged parturition.

Oral compression activity on a surrogate nipple in the newborn rat: Nutritive and nonnutritive sucking

Newborn rats, 3 hr after birth and before any experience in suckling, were exposed for 10 min to a surrogate nipple providing milk. One hour later, they were exposed to an empty nipple for another 10-min period. The basic characteristics of oral behavior (oral compression activity, OCA) were assessed by recording intranipple pressure during the pups' first attachment to a nipple. The peculiarities of milk-induced changes of OCA were examined with three modes of milk delivery (milk infusions, and intermittent and continuous milk deliveries). The pattern of OCA exerted by the newborn pups on a surrogate nipple consisted of rhythmic oscillations within a frequency range of 0.4 to 1.0 Hz superimposed on slow (frequency < 0.2 Hz), irregular intranipple pressure fluctuations. Oral behavior during the first minute after oral capture of the nipple differed significantly from that during any subsequent 1-min interval in terms of frequency content of OCA. The pattern of OCA changes induced by milk infusions or intermittent milk delivery included an abrupt rise in intranipple pressure, accompanied or followed by a burst of fast nipple compressions (bites). Our data suggest that newborn rats attached to a surrogate nipple demonstrate patterns of oral behavior that simulate, in terms of basic frequency characteristics, patterns of nutritive and nonnutritive suckling observed in more mature pups on the maternal nipple.

Begging for milk: evolution of teat massaging in suckling pigs

We present a model that simulates the evolution of teat massaging (begging) by suckling piglets (Sus scrofa) and milk distribution among teats (provisioning) by their mothers. Contrary to previous begging models, this one incorporates an ontogenetic dimension in that the inherited begging and provisioning rules are repeatedly allowed to interact, and their consequences for milk intake, growth and death probability are assessed, during each nursing. We test the model under three selection regimes differing in the relative importance of the between-litter selection component. We show that the selection regime with the strongest between-litter selection component leads to lowest begging levels and most effective milk utilization, thus supporting the hypothesis that selection based on whole litters may attenuate sibling competition.

Postpartum maternal oxytocin release by newborns: effects of infant hand massage and sucking

BACKGROUND

Newborns placed skin-to-skin with their mothers show an inborn sequence of behavior similar to that seen in other mammals. The purpose of this study was to make a detailed exploration of hand movements and sucking behavior in healthy term newborns who were placed skin-to-skin on their mothers' chests, and to study maternal oxytocin release in relation to these behaviors.

METHODS

Ten vaginally delivered infants whose mothers had not been exposed to maternal analgesia were video-recorded from birth until the first breastfeeding. Video protocols were developed based on observations of the videotapes. Each infant's hand, finger, mouth, and tongue movements, positions of the hand and body, and sucking behavior were assessed every 30 seconds. Maternal blood samples were collected every 15 minutes, and oxytocin levels were analyzed by radioimmunoassay. A statistical test for establishing the relationship between maternal oxytocin levels and infants' hand movements or sucking behavior was developed.

RESULTS

Infants used their hands to explore and stimulate their mother's breast in preparation for the first breastfeeding. A coordinated pattern of infant hand and sucking movements was also identified. When the infants were sucking, the massagelike hand movements stopped and started again when the infants made a sucking pause. Periods of increased massagelike hand movements or sucking of the mother's breast were followed by an increase in maternal oxytocin levels (p < 0.005).

CONCLUSIONS

The findings indicate that the newborns use their hands as well as their mouths to stimulate maternal oxytocin release after birth, which may have significance for uterine contraction, milk ejection, and mother-infant interaction.

Parity-related differences in suckling behavior and nipple preference among free-ranging Japanese macaques

Suckling behavior of primiparae in free-ranging Japanese macaques (Macaca fuscata) was compared with that of multiparae at Jigokudani Monkey Park, the Shiga Heights, Nagano Prefecture, Japan, from April 1984 to 1994. The estimated rates of milk secretion in a single preferred nipple among primiparae were lower than those among multiparae from birth to 5 months of age. Milk secretion capabilities of primiparous mothers, hence, appear to be inferior to those of multiparous mothers. In nutritive suckling, although Japanese macaque infants preferred one single nipple, nipple preferences in primiparae were weaker than those in multiparae. With supplementary two-nipple use during suckling, however, the infants of primiparae appear to overcome a suckling flaw of their primiparous mothers. After infants were 5 months of age and after a drop (from approximately 10% to approximately 5%) in the rates of milk secretion, however, milk secretion rates in a single preferred nipple among primiparae were similar to those in multiparae and the supplementary two-nipple use in primiparous mother-infant dyads disappeared.

Butting by calves, Bos taurus, and rate of milk flow

During nursing, the young of many ungulates butt at their dams' udder, which has been hypothesized to reflect difficulty obtaining milk. We investigated the effect of manipulating milk flow rate on the butting behaviour of domestic calves sucking milk from an artificial teat. The lowest rate of butting during nutritive sucking occurred with the fastest flow rate, and the highest rate of butting occurred with the slowest flow rate. When milk flow rate was changed during a meal, calves butted more following a decrease in flow rate than following an increase in flow rate. Butting rates were consistent and relatively low with a constant flow of milk. Regardless of flow rate, calves butted more at the beginning of their meal compared with the middle and end. Overall, the highest butting rate occurred when milk flow stopped, either at the end of the meal or when milk flow during the meal was stopped repeatedly for 30-s periods. We conclude that calves are sensitive to variations in milk flow rate and that butting rate changes accordingly. The occurrence of butting by young ungulates during nursing thus may indicate either a stoppage of milk flow or a decrease in milk flow rate, and thus may help identify periods of nonnutritive sucking during nursing. (c) 1998 The Association for the Study of Animal Behaviour.

Is suckling behaviour a useful predictor of milk intake? A review

In studies on mammalian parental investment, time spent suckling is often used as a predictor of the milk transferred from mother to infant. It is assumed that the rate of milk transfer is positively correlated with the time spent suckling. However, this assumption has not been tested and empirical studies show conflicting results. Nevertheless, in species in which suckling can readily be observed, time spent suckling is still used to measure milk transfer, although an increasing number of workers recognize that the measure is potentially inaccurate. A meta-analysis on studies that have correlated measures of time spent suckling with milk intake estimates based on weight gain revealed a weak positive relationship and significant heterogeneity between studies. Isotope-labelling techniques for the measurement of milk transfer independent of behaviour have been in use since the 1970s, particularly in studies of species in which suckling is difficult to observe. Only one study has attempted to correlate behavioural measures with independent isotope measures, and it found no relationship between the two measures. I suggest that researchers have avoided such a test as it is unlikely that a strong relationship will be found between milk transfer and suckling behaviour, and I discuss the various factors that confound the relationship and contribute to high heterogeneity between studies. Consequently, the assumption that milk transfer can be measured by time spent suckling has inadequate empirical foundation, and needs to be tested using isotope-labelling methods. Copyright 1998 The Association for the Study of Animal Behaviour

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.

Pathogenesis, prevention, and treatment of lactational insufficiency in sows

Lactational insufficiency is one of the major problems in swine production, and the consequences on the growth of the litter must be emphasized. Pathophysiology involves neuroendocrinologic interactions and the role of target organs such as the mammary glands, uterus, bladder, and gut. The complexity of these interactions and the fact that all interactions are not well understood leads to a broad approach. Some risk factors and their associations with lactational insufficiency are described to help the practitioner in the clinical approach to such a problem.