Intact Litters Research Articles

Stress responses in pigs postweaning: Effect of heavier hybrid and weaning intact litters

Early and abrupt weaning of pigs is a stressful event. In addition, the use of hyperprolific sows with increasing numbers of live born piglets has decreased the average pig’s birth weight, colostrum intake and weaning weight. The aim of this study was to investigate whether behavioural (tail posture, agonistic and abnormal behaviour), clinical (ear and tail lesions) and physiological (saliva cortisol) indicators of stress postweaning can be minimised by 1) using a pig hybrid that is heavier at birth and weaning, and 2) trough specific-stress-free housing where intact litters of pigs stay in the pen of birth after removing the sow at weaning. The study was a 2 × 2 factorial design, with pigs from Topigs Norsvin TN70 (TN) sows as a heavier alternative to the lighter pigs from DanBred LY sows (DB), and the specific-stress-free (SSF) weaning strategy as an alternative to the conventional weaning strategy (CON) where pigs are regrouped and moved to weaner pens. Fiftyseven litters, on average 26 days of age, were included. Behaviour recordings on the day (d) of weaning (d0), showed that the rate of fights and attacks were 23 and 42 times higher in CON compared to SSF, respectively. Furthermore, on d+1 pig in CON had a 9 (in DB) to 13 (in TN) times higher odds of having clinical ear lesions compared to SSF. Only on d+2, saliva cortisol was lower in TN-SSF than TN-CON, but not lower that DB-SSF. A higher rate of high tail posture was seen in CON d+1, which may reflect higher arousal due to mixing and moving. The rate of belly nosing was 5 times higher in the lighter hybrid (DB compared to TN), but increased from d+7 to d+14 in both hybrids. On d+7 the rate of ear directed behaviour tended to be higher in DB than TN, but the rate increased from d+7 to d+14 in TN to a similar rate as in DB. The rate of tail directed behaviour increased from d+7 to d+14 and tended to be higher in CON than SSF. In conclusion, specific-stress-free weaning reduced agonistic behaviour and ear lesions and tended to reduce tail directed behaviour postweaning. Using the heaver hybrid TN reduced belly nosing postweaning. However, since belly nosing and tail directed behaviour increased over time for both hybrids and weaning strategies additional measures are needed to reduce stress associated with early and abrupt weaning.

Postweaning growth and feeding behaviour in pigs: effect of heavier hybrid and weaning intact litters in farrowing pens for loose-housed sows

Abrupt weaning of four-week-old pigs is associated with multiple stressors. Housing pigs in intact litters is a way to reduce the stress associated with moving and mixing of unfamiliar pigs. Furthermore, higher weaning weight may improve pigs’ robustness against postweaning stressors. In the present study, it was investigated whether: (1) A heavier pig hybrid, and (2) weaning intact litters in the farrowing pen for loose-housed sows could increase postweaning feeding behaviour and growth. Two sow hybrids (DanBred LY (DB) and Topigs Norsvin TN70 (TN)) and two weaning strategies (the litter stayed intact in the farrowing pen after removing the sow (STAY), or two litters were moved and mixed in conventional weaner pens (MOVE)) were compared in a 2 × 2 factorial design. In total, 57 litters from four batches were included in the study. The TN hybrid sows gave birth to heavier piglets but smaller litter sizes and had more functional teats than DB sows. At weaning, TN pigs were heavier than DB. The number of feed trough (FT) visits on the day before weaning was low in both hybrids. On the day after weaning, the number of FT visits was higher in MOVE compared to STAY, and in TN-STAY compared to DB-STAY. The average daily gain the first two days postweaning was negative in both hybrids and weaning strategies but more pronounced in DB than TN, and STAY tended to lose more weight than MOVE. Over the entire 28-day postweaning period, there was an interaction between hybrid and weaning strategy in that TN-STAY (392 g/d) had higher growth than both TN-MOVE (251 g/d) and DB-MOVE (283 g/d), whereas growth of DB-STAY (316 g/d) was intermediate. In addition, higher weaning weight was associated with a lower number of FT visits and greater weight loss the first two days postweaning but higher growth over the 28-day postweaning period. The results show that abrupt weaning at four weeks of age causes weight loss the first days postweaning despite being housedas intact litters, most likely due to low feed consumption. However, the combination of a heavier pig hybrid and housing intact litters in the farrowing pen postweaning resulted in a higher growth performance over the 28-day postweaning period. In conclusion, pigs that are heavier at weaning reach better growth performance in the longer term, despite having the largest acute postweaning growth depression and fewest FT visits on the day before and after weaning.

Fetal growth restriction shortens cardiac telomere length, but this is attenuated by exercise in early life.

Fetal and postnatal growth restriction cause a predisposition to cardiovascular disease (CVD) in adulthood. Telomeres are repetitive DNA-protein structures that protect chromosome ends, and the loss of these repeats (a reduction in telomere length) is associated with CVD. As exercise preserves telomere length and cardiovascular health, the aim of this study was to determine the effects of growth restriction and exercise training on cardiac telomere length and telomeric genes. Pregnant Wistar Kyoto rats underwent bilateral uterine vessel ligation to induce uteroplacental insufficiency and fetal growth restriction ("Restricted"). Sham-operated rats had either intact litters ("Control") or their litters reduced to five pups with slowed postnatal growth ("Reduced"). Control, Restricted, and Reduced male rats were assigned to Sedentary, Early exercise (5-9 wk of age), or Late exercise (20-24 wk of age) groups. Hearts were excised at 24 wk of age for telomere length and gene expression measurements by quantitative PCR. Growth restriction shortened cardiac telomere length ( P < 0.001), but this was rescued by early exercise ( P < 0.001). Early and Late exercise increased cardiac weight index ( P < 0.001), but neither this nor telomere length was associated with expression of the telomeric genes Tert, Terc, Trf2, Pnuts, or Sirt1. Growth restriction shortens cardiac telomere length, reflecting the cardiac pathologies associated with low birth weight. Exercise in early life may offer long-term protective effects on cardiac telomere length, which could help prevent CVD in later life.

Is the rodent maternal separation model a valid and effective model for studies on the early-life impact on ethanol consumption?

RationaleEarly-life events can cause long-term neurobiological and behavioural changes with a resultant effect upon reward and addiction processes that enhance risk to develop alcohol use disorders. Maternal separation (MS) is used to study the mediating mechanisms of early-life influences in rodents. In MS studies, the pups are exposed to maternal absence during the first postnatal weeks. The outcome of MS experiments exhibits considerable variation and questions have been raised about the validity of MS models.ObjectivesThis short review aims to provide information about experimental conditions that are important to consider when assessing the impact of early-life environment on voluntary ethanol consumption.ResultsThe results from currently used MS protocols are not uniform. However, studies consistently show that longer separations of intact litters predispose for higher ethanol consumption and/or preference in adult male rats as compared to shorter periods of MS. Studies using individual pup MS paradigms, other controls, low ethanol concentrations, adult females or examining adolescent consumption reported no differences or inconsistent results.ConclusionsThere is no “a rodent MS model”, there are several models and they generate different results. The compiled literature shows that MS is a model of choice for analysis of early-life effects on voluntary ethanol consumption but there are examples of MS paradigms that are not suitable. These studies emphasize the importance to carefully designed MS experiments to supply the optimal conditions to definitely test the research hypothesis and to be particulate in the interpretation of the outcome.

Litter reductions reveal a trade-off between offspring size and number in brown bears

Experimental manipulations have revealed positive effects of litter reduction on offspring mass in small mammals, but little is known about this trade-off in large mammals. We examined the determinants of natural litter size variation and quantified the effects of litter size, maternal characteristics, and litter composition on yearling mass using 24 years of data on marked brown bears (Ursus arctos) in Sweden. Infanticide by adult males is a major cause of cub-of-the-year mortality, leading to litter size reductions. Litter size (n = 265) at den emergence ranged from one to four cubs (average, 2.7) and increased with maternal age. Litter size, however, appeared independent of maternal size, population density, interlitter interval, study area, or previous litter sex ratio. Yearling body mass increased with maternal body size but was independent of litter sex ratio. Litter size and yearling mass were negatively correlated, mostly because singletons were about 30 % heavier than yearlings from litters of two to four cubs. In reduced litters, survivors were on average 8 % heavier as yearlings than individuals from intact litters, suggesting that sibling competition reduces growth. Trade-offs between litter size and yearling mass in bears appear similar in magnitude to those found in small mammals.

The effects of zonation of the pen and grouping in intact litters on use of pen, immune competence and health of pigs

Abstract The effects of pen design and group composition were examined with respect to activity, use of pen, floor conditions, health condition and immune competence for groups of 60 pigs. The experiment was designed with the two factors with zones/without zones and divided litters/intact litters . The experiment included a total of 1440 pigs from weaning at the age of 4 weeks to the age of 18 weeks after weaning. In pens with zones, the selection of different areas for different activities was improved. Pens with zones were more dirty in the elimination and open areas than pens without zones. In pens with zones, the number of lymphocytes was decreased, the ability to respond to an additional challenge by a model infection was decreased and the number of neutrophils was increased in intact litters. In week 9, the health condition was better with a group composition consisting of intact litters compared to divided litters. The health condition of the pigs was unaffected by pen design, but non-infectious health condition was improved in pens with zones.

Behavioural uniformity or diversity? Effects on behaviour and performance following regrouping in pigs

Behavioural differences among pigs can be reliably determined using the human approach test. This study investigated the theory of ‘pre-forming’ a stable hierarchy based on behavioural composition. While in the nursery with littermates, 222 pigs were individually tested in two human approach tests and classified as either being slow, medium, or fast to approach a novel person. Pigs were then regrouped at eight weeks of age. Groups of 12 pigs, consisting of either all slow (uniform slow), all fast (uniform fast), or slow, medium, and fast (diverse) were formed. Intact litters were used as a control treatment. Subsequent aggression, average daily gain, and approach times were assessed. Regrouped pigs took longer to approach than pigs in intact litters (28.6 versus 9.25 ± 3.03 s; P = 0.02) during the final human approach test. There was less fighting per pig in the intact litters (0.45) compared with regrouped pigs (greater than 3.61 ± 0.45 s; P < 0.01). Pigs in the intact litters tended to grow faster than pigs in the uniform fast treatment (863 versus 805 ± 21.6 g/day; P = 0.09). The slow pigs in the intact litters, diverse and uniform-slow treatments all became faster to approach over time ( P < 0.05), and did not differ in average daily gain. Whereas, fast pigs in the intact litters became slower to approach than fast pigs in the diverse treatment (49.4 ± 8.61 versus 13.4 ± 7.04 s; P = 0.02) and tended to take longer than the uniform-fast pigs (49.4 ± 8.61 versus 26.7 ± 7.04 s; P = 0.09). There were no differences in average daily gain among fast pigs in any of the treatments ( P > 0.1). The human approach test is useful for distinguishing among individuals. Regrouping affects the ability to habituate over time. Furthermore, the type of regrouping strategy influences the ease of habituation. Pigs that are initially classified as slow, medium, or fast may habituate differently to the test. The pigs also have different growth patterns depending on whether they have experienced regrouping. Behavioural uniformity tended to result in more aggression and less weight gain, when compared to intact litters.

Effects of regrouping on the individual behavioural characteristics of pigs

The behaviour of an animal is a combination of that which is inherited and that which is influenced by the environment. This study was conducted to determine a means for assessing and distinguishing individuals based on behavioural characteristics and to better understand the environmental impact on behavioural trait changes in pigs. Eighty-nine pigs (nine litters) were followed from birth until the end of the grow–finish period. All litters remained intact until four were mixed when they entered the grow–finish phase. Data on general activity, social behaviour, average daily gain and injury scores were collected throughout the entire experimental period. When the pigs were still with the sow, we also collected data on teat order consistency, suckling and suckling bouts. The pigs were subjected to a series of behavioural tests when in the nursery and grow–finish phases. The data were subjected to a factor analysis to determine individual behavioural traits. The effect of regrouping was determined by using an analysis of variance, comparing scoring coefficients of pigs that either remained intact or were regrouped. Three primary factors were identified and interpreted as indicating levels of approachability, exploration, and aggression. Regrouped and intact treatments only differed in level of approachability. The intact litters followed a typical habituation response to repeated exposures of a novel arena test. However, the pigs in the regrouped litters consistently took longer to approach a human and novel object. This suggests that the trauma caused by regrouping resulted in a generalisation of fear associated with an environmental change.

Uniform or heterogeneous weight groups as factors in mixing weanling pigs

A series of trials evaluated the behavior and performance of pigs grouped into three main categories at weaning: (1) unmixed litters, (2) mixed into uniform body weight groups (light, medium and heavy) and (3) mixed into heterogeneous weight groups. The effects of grouping on performance criteria were conflicting among trials and with time after weaning. In trial 1, heterogeneous groups had lower (P = 0.09) average daily gain to 5 d after weaning than intact litters. The reverse was observed in trial 2. In trial 3, uniform weight groups grew more rapidly (P &lt; 0.01) than heterogenous groups. These treatment differences persisted through 19 d post-weaning for pigs in trials 1 and 2 but were no longer evident in trial 3. Play/fight behavior was highest (P &lt; 0.01) among uniform weight groups resulting in an increased wounding score for head and shoulders of pigs in medium and heavy weight groups. In trial 1, structures which allowed individuals to hide their heads were available for the first 5 d but did not affect behavior or wounding. In trial 2, pigs from the three main groupings were mixed again on day 19 into three new groupings (unmixed, uniform weight or heterogenous weight). There were no performance differences among the nine grouping combinations 40 d after weaning. We conclude that if litter groups cannot be maintained after weaning, it may be advantageous to mix newly weaned pigs into uniform weight groups although the benefit is not consistently present. If space is limited, the greatest benefit would be to group light weight pigs together. Key words: Pigs, weanlings, behavior, lesions, head hides, mixing

A comparison of methods for testing homogeneity of proportions in teratologic studies

We consider teratologic studies in which the aim is to compare the survival rate of animals in a treatment group to the corresponding rate in a control group. The design of such studies often involves the allocation of intact litters of animals to treatment, invalidating the application of standard statistical methods. We review the strengths and weaknesses of several approaches for dealing with this problem including methodology recently developed for the analysis of clustered binary data. A simulation study is conducted in which litter sizes are generated from a distribution having specified mean and degree of imbalance. It is recommended on the basis of this study and on theoretical considerations that the choice of method should depend on whether the comparison of interest is experimental or observational. For experimental comparisons, involving the random assignment of litters to different treatment groups, methods based on the adjustment of standard chi-square statistics are recommended unless the number of litters in each group is very large.

Thermal preference behavior in preweaning genetically obese ( ob/ob) and lean (+/?, +/+) mice

Impaired nonshivering thermogenesis and lowered rectal temperatures (T re) are hallmarks that appear early in the postnatal ontogeny of the genetically obese ( ob/ob) mouse. Adult obese mice compensate behaviorally for these impairments and do not defend their low T res. We predicted that, because young mice primarily rely on behavior to ensure thermal homeostasis during preweaning development, the appearance of the obese mouse's thermoregulatory impairment should promote their continued reliance on behavioral thermoregulation compared to lean pups. Accordingly, intact litters of pups from heterozygous lean (C57BL/6J, ob/+) and from homozygous lean (+/+) matings were tested at 6, 12, and 18 days postpartum on a thermal gradient (14–44°C). Obese pups had lower pretest T res than lean (+/?) littermates at 6 days and lower pretest T res than both lean littermates and homozygous (+/+) lean control pups at 12 and 18 days. Exposure to the gradient ameliorated these differences (i.e., no posttest T re differences among phenotypes). Correspondingly, obese pups preferred warmer gradient locations than +/+ pups but similar locations to their phenotypically lean (+/?) littermates until 18 days, when both lean groups preferred similar thermal locations compared to warmer-seeking obese pups. These data support our hypothesis and emphasize the age-dependent impact of the ob gene on altering mouse pups' thermal preferences.

Milk intakes of genetically obese ( ob/ob) and lean mouse pups differ with enhanced milk supply

Although obese (C57Bl/6J, ob/ob) pups have greater avidity for nonnutritive suckling than leans as early as 15 days postpartum (25), previous research has not found differences in milk intake between ob/ob and lean mice during the preweaning period (5, 21, 22). Because ob/ob pups suckle longer than leans, their perseveration should enhance their opportunity to ingest milk if (a) maternal milk supply is not limited and (b) longer sucking durations reflect increased pup willingness to ingest milk. Accordingly, the present study was designed to evaluate the milk intake of ob/of and lean pups when they had access to an enhanced supply of maternal milk. Intact litters of pups, from heterozygous lean ( ob/+) parents, were randomly assigned to be tested at either 6, 12, or 18 days. Pups were neither dam- nor milk-deprived before being cross-fostered successively to milk-replete surrogate dams for 60 min each. Obese pups showed a greater percentage body weight gain (the index of milk intake) than leans did, with younger pups showing larger increments than 18-day-olds. Although early adiposity in ob/ob pups may not rely on increased intake in the single-dam, nest situation, these data emphasize an early predisposition to overeating in this mutant.

Early exposures to intermale aggression increases the adult aggression of male rats

Intact litters of rats were exposed to three brief episodes of intense paternal aggression against an unfamiliar adult conspecific prior to weaning on day 31. Control litters were not exposed to paternal conflict. Male offspring of both groups were given a long-term test of their aggression against an unfamiliar intruder when the subjects were 103–114 days old. During the initial 10-minute observational phase of the aggression test, few animals in either group attacked the intruder, but intruders lost more bodyweight during the 22 1 2 -hour test when placed into the cages with the aggression-exposed subjects. Thus, early exposure to aggressive exchanges between adult animals increases the use of an aggressive strategy during subsequent confrontations with unfamiliar conspecifics. Two mechanisms possibly underlying this phenomenon are discussed.

Delta-9-tetrahydrocannabinol during pregnancy in the rat: II. Effects on ontogeny of locomotor activity and nipple attachment in the offspring

Either 15 or 50 mg/kg delta-9-tetrahydrocannabinol (THC) in sesame oil was administered by gastric intubation to gravid rats during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 50 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Intact litters from the two THC treated and the two control groups were tested at 3-day intervals from birth to 32 days of age for differences in locomotor activity. In addition, pups were tested for nipple attachment on days 2, 5, 8, 11, and 14 of age. There were no differences in locomotor activity among any of the groups although activity level varied during development. Pups from dams exposed to 50 mg/kg of THC, as well as the pair-fed controls, displayed significantly longer latencies to attach to a nipple. These results suggest that the impaired nipple attachment observed among the high-dose offspring was not a primary effect of THC, but rather was secondary to the significant reduction of food and water intake among the dams. The behavioral findings are discussed with respect to other animal and clinical reports of prenatal cannabinoid exposure.

Discrimination between full-sibling spiny mice ( Acomys cahirinus) by olfactory signatures

Discrimination between individual full siblings was tested in spiny mice ( Acomys cahirinus). At weaning, intact litters were separated into two pairs so that animals only had social contact with one of their full siblings. Following 10 days of being housed in pairs, the four weanlings from a given litter were reunited in an observation terrarium. Pairings by familiar siblings were more frequent than unfamiliar-sibling pairings, indicating that interactions among close kin are mediated by the recognition of individual signatures rather than general phenotypic traits shared by all members of a kin class. Animals rendered anosmic by intranasal injections of zinc sulphate displayed no evidence of discriminating between familiar and unfamiliar siblings. Olfactory cues therefore appear to function as the signatures by which individual siblings are recognized. Since all animals were fed identical diets and otherwise maintained in similar environments, the differences in olfactory signatures between full siblings are most likely a function of genetic variability within this class of kin.

Comparative ontogeny of social behaviour in three South American canids, the maned wolf, crab-eating fox and bush dog: Implications for sociality

Aspects of behavioural development were investigated to determine how a relatively social canid like the bush dog Speothos venaticus differs from the moderately social crab-eating fox Cerdocyon thous or the relatively solitary maned wolf Chrysocyon brachyurus. Differences emerged that were surprising in light of conventional ideas about sociality. The behavioural repertoire of Speothos was more limited than those of the other two species and Speothos' interaction sequences were simpler, comprised fewer different elements, and were more rigidly determinate. Submissive behaviours, biting, vocalizing, and object play were prominent in Speothos. Cerdocyon and Chrysocyon interaction sequences were more like the play behaviour described for Canis species, being characterized by vigorous wrestling, frequent switching between behavioural categories, and manoeuvring to upset the partner. Although Speothos pups spent a greater percentage of their time interacting, there were no interspecific differences in the length of interaction sequences. In contrast to what has been seen in some polygamous mammals, no sex differences in behaviour were found here, indicating that in monogamous, monomorphic species with little adult social role differentiation, the young are behaviourally alike as well. Dominance hierarchies among pups were only very weakly indicated and unstable in these intact litters raised by both parents.

Development of the renal response to blood volume expansion in normal and fast-growing rats

Male rats from reduced (fast-growing) litters between 14 and 50 days of age were studied. Standard renal clearnce techniques were employed. After a 60-min control period, the animals were infused (2.3% body wt) with heparinized donor blood obtained from lillermates of the same age. Renal function was followed for an additional 60 min. The efficiency of the diuretic response, the percent infused volume excreted above control levels, and the sodium efficiency, the percent infused Na excreted, were calculated. Results indicate that both efficiencies develop in a discontinuous pattern and that they are comparable. This pattern of development, as well as the magnitude of the mature response, is comparable to that previously reported for rats from intact (normally growing) litters. The onset and attainment of the mature response is, however, shifted in time, such that reduced-litter animals achieve the mature response 10-15 days earlier than intact-litter rats. Results exclude chronological age or body weight alone as principal determinant of the mature response and suggest that some function of growth rate is responsible for the maturation of this regulatory function.

Absolute Rates of Sodium and Potassium Reabsorption by Proximal Tubule of Immature Rats

Using micropuncture procedures, the rate of proximal tubular sodium and potassium transport in mannitol-infused rats has been studied. Tubular diameter and length increase with animal size, but the rates of change are greater in small animals than in larger animals. SNGFR increases with body weight in a linear fashion. Animals from reduced litters have larger SNGFR than do animals from intact litters and males have higher SNGFR than do females. Absolute transport rates for sodium and potassium increase with age and parallel the increases in SNGFR. These results indicate that the predominant factor maintaining proximal glomerular tubular balance as animals grow is an increase in absolute proximal transport rates. With a 50-fold change in SNGFR, change in transport rate accounts for about a 10-fold change, and the rest of the increase in overall proximal absorption is accounted for by an increase in surface area.

Maximal gradients of na and k across proximal tubules of kidneys of immature rats.

The magnitude of proximal transtubular ionic gradients produced by mannitol loading has been measured in developing and mature rats using micropuncture techniques. Immature rats were able to establish the same sodium and potassium gradients as did adult animals, providing proximal tubular length is greater than 1,500 μm. No differences in establishment of the gradient determined as a function of tubular length was found between animals obtained from litters left intact or reduced. Animals from reduced litters weighing less than 125 g body weight had higher GFR than did animals from intact litters weighing the same. Although urinary concentrations of sodium and potassium are the same for both populations of immature rats at comparable weights, volume excretion as well as excretion of sodium and potassium is greater in animals from reduced litters.

Growth rates and organ weights of rats.

Previous studies from this laboratory have indicated that changing food availability of neonatal rats results in differences in functional development of the kidney. Results here show that during early development only, kidney to body weight ratios were lower for animals from reduced litters in comparison to those from Heart intact litters. In contrast, heart to body weight ratios were lower in animals from intact litters. In adult animals, no differences in organ weight to body weight ratios could be established between animals from different litters. It is suggested that these relationships are not determined by a common body weight factor like the amount of fat or change in muscle or skeletal mass which may however, account for the observations that animals from reduced litters are heavier than those from intact litters at a given age. It is argued that every organ studied reaches a maximum organ to body weight ratio sometime during development.