Pup Mortality Research Articles

EFFECT OF DIETARY FIBRE AND FAT CONTENT ON THE REPRODUCTIVE PERFORMANCE OF RABBIT DOES BRED AT TWO REMATING TIMES DURING TWO SEASONS

One hundred and forty one rabbit does were used to study the effect of four diets differing in energy concentration (8.92 to 11.86 MJ DE/kg), fibre and fat content, two parturition-remating intervals (1 or 9 d), and two seasons (hot season and rest of the year) on productiva performance throughout a 18 months period. Addition of a 3.5 % of pork lard to a diet containing 18 % ADF implied an increase of energy digestibility (by 8 %, P<0.05), DE content (by 15 %, P<0.001), feed intake (by 6 %, P<0.1), and DE intake (by 22.5 %, P<0.05). Fat addition did not affect average weight of does, prolificacy, or replacement rate, but improved fertility (by 7%, P<0.1), weaning weight per pyp (by 3%, P<0.1), and numerical proauct1víty per cage and year (by 12 %, P<0.05). An increase of dietary fibre content (from 18.0 to 23.8 % ADF) decreased linearly (P<0.001) energy digestibility, and DE content, but increased (P<0.05) feed intake, so that neither DE intake (2.56 MJ/d as average) or does productivity were significantly affected. lntensification of reproduction system elicited a shorter parturition interval (- 3.2 days, P<0.05), but also a decrease of average does weight (- 0.14 kg, P<0.05), a lower conception rate (P<0.05), and a higher pup mortality, so that numerical productivity per cage and year was not significantly affected by treatment. The increase of temperatura during the hot season decreased feed intake (by 21 %, P<0.001), average weight of does (- 0.15 kg, P<0.05), fertility (- 16 %, P<0.001), numerical productivity (- 23 %, P<0.001), and weaning weight (- 7 %, P<0.01). No significant effects of the interactions diet x remating interval or diet x season were found on any of the variables studied.

Allo-suckling in the South American fur seal (Arctocephalus australis) in Isla de Lobos, Uruguay: cost or benefit of living in a group?

In some social mammals females feed alien offspring (allo-sucking, AS), a phenomenon rarely observed in otariids, possibly due to the existence of strict mother–pup recognition mechanisms. We studied the frequency of AS during the reproductive season in the largest South American fur seal rockery (in Uruguay). We recorded 57 AS attempts in 342 hr of observations, 26 of which were successful. Successful AS attempts represented 3.37% of all suckling events. In January most attempts were successful, while in February most attempts failed, probably reflecting a more active defence of milk by females and filial pups as a consequence of the increase in energy requirements. Females interrupted 72% of all AS attempts. We propose that allo-suckling is a benefit of living in a group that increases survival of offspring during the earliest months of life, the period of highest pup mortality.

CAUSES OF MORTALITY IN NORTHERN FUR SEALS (CALLORHINUS URSINUS), ST. PAUL ISLAND, PRIBILOF ISLANDS, ALASKA, 1986–2006

To determine whether infectious diseases might have contributed to the present-day decline of northern fur seals (Callorhinus ursinus), preweaned pups (n=2,735), subadult males (n=98), and adults (n=179) were examined postmortem from 1986 to 2006 on St. Paul Island, Alaska. Gross necropsy findings and histologic lesions were used to determine causes of death. Five general categories of mortality were identified for pups: emaciation (1,454 pups, 53%), trauma (497 pups, 18%), perinatal mortality (516 pups, 19%), infectious diseases (82 pups, 3%), and miscellaneous causes (186 pups, 7%). A condition of unknown etiology characterized by multifocal necrotizing myopathy and cardiomyopathy was found in 92 pups. Thirty-three congenital anomalies were identified in 49 pups, including a rare multicentric ganglioneuroblastoma. General linear models were used to examine change in pup mortality and condition (i.e., pup mass) over time. The prevalence of perinatal mortality appeared to increase during the study and relative to past reports. Trauma and infectious conditions appeared to decrease slightly from 1986 to 2006. Although relatively stable during this investigation, emaciation was greater than that reported for past studies. Emaciated pups weighed less than expected during 1988, 1996, and 2004 and more than expected during 1987, 1989, 1990, and 1994 (P</=0.003). Average annual weights for all other categories of mortality did not change significantly from 1986 to 2006. Fatal conditions for subadult males included hyperthermia, blunt trauma, entanglement, and bite wounds; nonfatal conditions included seizures, orange discoloration of the blubber, neoplasia, and parasitism. Causes of mortality for most adults included bite wounds with cellulitis and secondary infections, pulmonary edema, dystocia, blunt trauma, and neoplasia. We found no evidence to implicate infectious diseases as a cause in the recent decline of northern fur seals.

Combined exposure to endocrine disrupting pesticides impairs parturition, causes pup mortality and affects sexual differentiation in rats

Risk assessment is currently based on the no observed adverse effect levels (NOAELs) for single compounds. Humans are exposed to a mixture of chemicals and recent studies in our laboratory have shown that combined exposure to endocrine disrupters can cause adverse effects on male sexual development, even though the doses of the single compounds are below their individual NOAELs for anti-androgenic effects. Consequently, we have initiated a large project where the purpose is to study mixture effects of endocrine disrupting pesticides at low doses. In the initial range-finding mixture studies, rats were gavaged during gestation and lactation with five doses of a mixture of the fungicides procymidone, mancozeb, epoxyconazole, tebuconazole and prochloraz. The mixture ratio was chosen according to the doses of each individual pesticide that produced no observable effects on pregnancy length and pup survival in our laboratory and the dose levels used ranged from 25 to 100% of this mixture. All dose levels caused increased gestation length and dose levels above 25% caused impaired parturition leading to markedly decreased number of live born offspring and high pup perinatal mortality. The sexual differentiation of the pups was affected at 25% and higher as anogenital distance was affected in both male and female offspring at birth and the male offspring exhibited malformations of the genital tubercle, increased nipple retention, and decreased prostate and epididymis weights at pup day 13. The results show that doses of endocrine disrupting pesticides, which appear to induce no effects on gestation length, parturition and pup mortality when judged on their own, induced marked adverse effects on these endpoints in concert with other pesticides. In addition, the sexual differentiation of the offspring was affected. This as well as the predictability of the combination effects based on dose-additivity modelling will be studied further in a large dose-response study.

Pelage insulation, litter size, and ambient temperature impact maternal energy intake and offspring development during lactation

Energy balance during lactation critically influences survival and growth of a mother's offspring, and hence, her reproductive success. Most experiments have investigated the influence of a single factor (e.g., ambient temperature [T a] or litter size) on the energetics of lactation. Here, we determined the impact of multiple interventions, including increased conductive heat loss consequent to dorsal fur removal, cold exposure (T a of 5 °C versus 23 °C), and differential lactational load from litters of different sizes (2 or 4 pups), on maternal energy balance and offspring development of Siberian hamsters ( Phodopus sungorus). Lower T a, fur removal, and larger litters were associated with increased maternal food consumption. Females exposed to multiple challenges (e.g., both fur loss and lower T a) ate substantially more food than those exposed to a single challenge, with no apparent ceiling to elevated food intake (increases up to 538%). Thus, energy intake of dams under these conditions does not appear to be limited by feeding behavior or the size of the digestive tract. Housing at 5 °C attenuated pup weight gain and increased pup mortality to more than 5 times that of litters housed at 23 °C. Increases in the dam's conductive heat loss induced by fur removal did not affect pup weight gain or survival, suggesting that effects of low T a on pup weight gain and survival reflect limitations in the pups’ ability to ingest or incorporate energy.

Normal maternal behavior, but increased pup mortality, in conditional oxytocin receptor knockout females.

Oxytocin (Oxt) and the Oxt receptor (Oxtr) are implicated in the onset of maternal behavior in a variety of species. Recently, we developed two Oxtr knockout lines: a total body knockout (Oxtr-/-) and a conditional Oxtr knockout (OxtrFB/FB) in which the Oxtr is lacking only in regions of the forebrain, allowing knockout females to potentially nurse and care for their biological offspring. In the current study, we assessed maternal behavior of postpartum OxtrFB/FB females toward their own pups and maternal behavior of virgin Oxtr-/- females toward foster pups and compared knockouts of both lines to wildtype (Oxtr+/+) littermates. We found that both Oxtr-/- and OxtrFB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the OxtrFB/FB knockout dams experienced high pup mortality, compared to fewer than 10% of the Oxtr+/+ dams. We then went on to test whether or not this phenotype occurred in subsequent litters or when the dams were exposed to an environmental disturbance. We found that regardless of the degree of external disturbance, OxtrFB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in OxtrFB/FB females are discussed.

The influence of husbandry and pack management on Dhole Cuon alpinus reproduction

Dhole Cuon alpinus numbers are declining rapidly in the wild. Therefore, it is very important to have vital captive populations. European zoos have the largest collection of captive Dholes in the world but breeding success varies greatly between zoos. One of the biggest problems is high pup mortality owing to inexperience of adults and inadequate housing. Within the context of a dissertation about Dholes in captivity, the effects of different husbandry parameters on reproduction in the species have been studied over 4 years. As a result of information reported in the dissertation a European Endangered Species Programme for Dholes was launched in 2006 by the European Association of Zoos and Aquaria. Since then, all new packs that have been formed and housed according to the latest scientific results have started to reproduce without any problems.

Influence of litter size on the postnatal growth of rat pups: Is there a rationale for litter-size standardization in toxicity studies?

The standardization of rodent litter sizes (or culling) in reproductive toxicity studies has become a common practice because it is believed that litter size affects pup postnatal growth and development. A claim has also been made that culling on postnatal day 4 or earlier reduces litter-size-induced variability in the pup growth thereby making statistical detection of toxic effects more sensitive. Although these statements remain controversial, culling has been either recommended or considered optional in current proposals for new OECD guidelines for reproductive/developmental toxicity testing. This study was undertaken to provide data useful for a discussion on the need for culling in reproductive toxicity testing. Along this line, we investigated the effects of rat litter size on maternal body weight gain during pregnancy and lactation as well as on pup growth, somatic maturation and survival to weaning (PND 21). Two-hundred-forty-one untreated pregnant rats (Wistar, Bor:spf, TOR) delivered litters with 1-13 pups, being 10 the most frequent (24%) litter size. Pup mortality was 5.4%, 3.0% and 0.4% in the first, second and third postnatal weeks, respectively. Maternal and pup body weight gains, and the day of appearance of milestones of somatic maturation (fur development, incisor eruption and eye opening) were examined in a subset of litters/mothers (N=180) in which all pups survived to PND 21. An inverse relationship between litter size and pup body weight was found on day of birth (PND 1) and thereafter until PND 21. Delays in the attainment of maturational milestones as litter size increases were also found. These observations indicated that the rate of growth and development of rat pups during suckling period is dependent on the litter size. The consequences of litter-size standardization in toxicity studies are discussed in the light of these findings. Alternative procedures to attenuating litter-size-induced variability in pup growth or its impact on toxicity data evaluation are presented as well.

Reproduction and Mortality of Invasive Raccoon Dogs (Nyctereutes procyonoides) in the Białowieża Primeval Forest (Eastern Poland)

We investigated reproduction and mortality of raccoon dogs (Nyctereutes procyonoides) in the Białowieża Primeval Forest (eastern Poland). The species invaded the forest in 1955 and is more common than native species of medium-sized carnivores. The mean litter size of raccoon dogs, based on placental scars and foetuses was 8.4 (SD = 2.0). Mortality of pups was 61% during the first three months following parturition. Of 82 cases of raccoon dog deaths recorded from 1996 to 2006, 55% were caused by natural factors (predation and diseases), 40% were human-related (vehicle collisions, harvest, poaching), and 5% were indeterminable. Rabies was the most important disease. The main predators of raccoon dogs were wolves (Canis lupus) and domestic dogs (Canis familiaris). Almost all raccoon dogs killed by cars were dispersing juveniles. We did not find differences in causes of mortality between collared and uncollared individuals. The annual survival rate of radio-tracked raccoon dogs (n = 18, 1997–2000) was 0.38 (SD = 0.05), and did not differ between males and females. Survival of raccoon dogs varied seasonally. It was highest in winter (0.82) when raccoon dogs settle in burrows, which may protect them against predation. The life table constructed based on the age at death indicates that mortality was highest in the first year of the raccoon dog life (0.82), and lower in the following years (0.58–0.68). Most raccoon dogs (98%) died during the first three years of their life and the maximum life span was 7 years. Life expectancy at birth was 0.8 years.

Combined exposure to endocrine disrupting pesticides impairs parturition and causes pup mortality in rats

Combined exposure to endocrine disrupting pesticides impairs parturition and causes pup mortality in rats

A live guinea pig cytomegalovirus vaccine deleted of three putative immune evasion genes is highly attenuated but remains immunogenic in a vaccine/challenge model of congenital cytomegalovirus infection

Live attenuated vaccines for prevention of congenital cytomegalovirus infections encode numerous immune evasion genes. Their removal could potentially improve vaccine safety and efficacy. To test this hypothesis, three genes encoding MHC class I homologs (presumed NK evasins) were deleted from the guinea pig cytomegalovirus genome and the resulting virus, 3DX, was evaluated as a live attenuated vaccine in the guinea pig congenital infection model. 3DX was attenuated in vivo but not in vitro. Vaccination with 3DX produced elevated cytokine levels and higher antibody titers than wild type (WT) virus while avidity and neutralizing titers were similar. Protection, assessed by maternal viral loads and pup mortality following pathogenic viral challenge during pregnancy, was comparable between 3DX and WT and significant compared to naïve animals. These results suggest that the safety and perhaps efficacy of live attenuated human cytomegalovirus vaccines could be enhanced by deletion of viral immunomodulatory genes.

Role of ghrelin in regulating rabbit ovarian function and the response to LH and IGF-I

The aim of these in vivo and in vitro studies was to examine the role of ghrelin in the control of plasma hormone concentrations, the proliferation, apoptosis and secretory activity of ovarian granulosa cells and the response of these cells to hormonal treatments. Female rabbits were injected with ghrelin (10 μg/animal/day for one week before ovulation induced by 25 IU PMSG and 0.25 IU LHRH). On the day of ovulation, blood samples were collected and analyzed for concentrations of progesterone (P 4), testosterone (T), estradiol (E 2), estrone-sulphate (ES), insulin-like growth factor I (IGF-I) and leptin (L) by RIA. Some control and ghrelin-treated animals were killed in the periovulatory period, their ovaries were weighed and granulosa cells were isolated and cultured for 2 d. Cell proliferation (expression of PCNA) and apoptosis (expression of TdT) were evaluated by immunocytochemistry and TUNEL respectively. Secretion of P 4, T, E 2, IGF-I, and prostaglandin F (PGF) by granulosa cells cultured with and without LH or IGF-I (1, 10 or 100 ng/ml medium) was assessed by RIA. The remaining control and treated animals were kept until parturition, while the number, viability and body weight of pups were recorded. Ghrelin treatment increased rabbit plasma T and decreased ES concentrations but did not influence P 4, E 2, IGF-I or L. Granulosa cells from ghrelin-treated animals showed higher expression of PCNA and lower expression of TdT, than those from control animals. They also secreted less P 4, T, E 2, IGF-I and PGF than granulosa cells from untreated animals. Treatment of cultured granulosa cells with ghrelin (1, 10 or 100 ng/ml medium) either increased (at 1 ng/ml) or decreased (at 10 ng/ml) P 4 secretion, increased (at 100 ng/ml) or decreased (at 10 ng/ml) IGF-I secretion, decreased T (at 1 and 10 ng/ml) and OT (at 1 ng/ml) secretion, and increased (at 100 ng/ml) PGF secretion. LH treatment of cells from control animals stimulated P 4 (at 1 and 10 ng/ml), E 2, and IGF-I (both at 10 and 100 ng/ml), but not T secretion. IGF-I stimulated P 4 (all concentrations) and PGF (at 100 ng/ml) but suppressed T (all concentrations) and E 2 (at 1 and 10 ng/ml) secretion. Pre-treatment of animals with ghrelin stimulated, suppressed or even reversed subsequent LH and IGF-I effects on hormone secretion by cultured granulosa cells. Ghrelin injections did not affect ovarian weight or the number and body mass of pups born, although pup mortality was significantly lower in ghrelin-treated than in control mothers. These observations suggest that ghrelin is involved in the control of ovarian cell proliferation, apoptosis and secretion of hormones, as well as in the response of these cells to physiological stimulators such as LH and IGF-I.

Quality of rearing guides expression of behavioral and neural seizure phenotypes in EL mice

The present studies employed behavioral and neural markers of seizure-related plasticity to examine the relative contributions of genetic predisposition versus rearing environment in generating adult phenotypes in EL mice, a stress-induced animal model of epilepsy. Early environment was manipulated by cross-fostering pups of the EL strain to a seizure-resistant CD-1 control strain of mouse. The impact of changes in rearing quality on growth, exploratory and stress-reactivity phenotypes were examined, with a focus on the role of maternal care in shaping seizure susceptibility and neural cFos activation. Improvement in maternal care imposed by replacing biological EL dams with foster CD-1 mothers was sufficient to decrease pup mortality, to increase body weight gain (+ 0.1 g/day) and to delay the onset of seizure susceptibility in EL offspring beyond post-natal day 80–90. Moreover, hypoactivity in hippocampus and cortex among EL offspring cross-fostered to EL, but not CD-1 control, dams suggests that changes in rearing environment were accompanied by enduring changes in brain plasticity. Thus, neural and behavioral phenotypes of EL mice are dependent upon post-partum maternal care which if systematically enhanced can postpone seizure expression.

Normal mammary gland growth and lactation capacity in pregnant relaxin-deficient mice

Pups born to mice with a targeted deletion of relaxin or its receptor (Rxfp1) die within 24 h postpartum. This has been attributed, in part, to abnormal mammary gland development in relaxin-mutant mice (Rln-/-). However, mammary development is normal in relaxin receptor-mutant (Rxfp1-/-) mice. The present study aimed to verify the mammary phenotypes in late pregnant and early lactating Rln-/- mice and to test the hypothesis that relaxin is involved in milk protein synthesis. Comparisons between late pregnant and early lactating wildtype (Rln+/+) and Rln-/- mice showed no differences in lobuloalveolar structure or ductal branching in the mammary gland. Mammary explants from Rln-/- mice also expressed beta-casein and alpha-lactalbumin in response to lactogenic hormones at a similar level to Rln+/+ mice, implying normal milk protein synthesis. Pregnant Rln-/- mice infused with relaxin for 6 days gave birth to live pups without difficulty, and 96% of pups survived beyond 7 days. This is in contrast with the 100% pup mortality in saline-treated Rln-/- mice or 3-day relaxin-treated Rln-/- mice. Pups born to relaxin-treated Rln-/- dams weighed significantly less than Rln+/+ pups but had similar growth rates as their wildtype counterparts. In summary, relaxin is not critical for mammary gland development or beta-casein and alpha-lactalbumin expression in late pregnant mice. In addition, Rln-/- dams did not need to be treated with relaxin postpartum for the pups to survive, suggesting that relaxin has no role in the maintenance of lactation in mice.

Analysis and Integration of Developmental Neurotoxicity and Ancillary Data into Risk Assessment: A Case Study of Dimethoate

Dimethoate is an organophosphate (OP) pesticide used to control a wide variety of insects on agricultural crops and ornamentals. To ensure that dimethoate is used safely, it is important to determine exposure levels that protect against adverse effects at all life stages, including the developing fetus, infant, and child. Based on an analysis of a developmental neurotoxicity (DNT) study, a cholinesterase (ChE) sensitivity study, a cross-fostering study, and several single- and multigenerational reproductive toxicity studies, two potential critical endpoints for dimethoate were identified: brain ChE inhibition (ChEI) in adult females, and pup mortality. An initial evaluation concluded that pup mortality was a preferable endpoint, based on an increased number of pup deaths born to dams dosed with ≥3 mg/kg dimethoate via oral gavage. Closer examination, however, revealed that the pup deaths were clustered in a small number of litters in which the dams providing postnatal care exhibited maternal care deficits. When the data were analyzed using the dam as the unit of statistical significance, a significant increase in the average litter proportion of pup deaths was observed only when the dams were dosed postnatally with 6 mg/kg dimethoate while they were raising the pups. Gestational exposure (i.e., during pregnancy only) to 6 mg/kg dimethoate exerted no effect on pup survival. This leads to the conclusion that it is postnatal exposure of the nursing dams that is associated with pup mortality. Furthermore, a previous benchmark dose (BMD) meta-analysis approach revealed that BMDL10 for adult females (the lower 95% bound of the dose resulting in a 10% reduction in the parameter of interest) for ChEI was > 3-fold lower than the BMDL10 for pup mortality (0.19 and 0.68 mg/kg, respectively). Overall, this study underscores the importance of using the dam as the unit of statistical significance when assessing data collected in the perinatal period, and it is concluded that adult brain ChEI is the correct critical endpoint for assessing risk of dimethoate toxicity.

Testis Development, Fertility, and Survival in Ethanolamine Kinase 2-Deficient Mice

Ethanolamine kinase 2 (Eki2) was previously isolated from a differential expression screen designed to identify candidate genes involved in testis development and differentiation. In mouse, Eki2 is specifically up-regulated in Sertoli cells of the developing testis at the time of sex determination. Based on this expression profile, Eki2 was considered a good candidate testis-determining gene. To investigate a possible role of Eki2 in testis development, we have generated a mouse with targeted disruption of the Eki2 gene by using an EGFP replacement strategy. No abnormalities were detected in the Eki2-deficient mice with regard to embryonic and adult testis morphology, differentiation, function, or fertility. Furthermore, no significant differences were observed in litter sizes, pup mortality rates, or distribution of the sexes among the offspring. Ethanolamine kinases are involved in the biosynthesis of phosphatidylethanolamine, a major membrane phospholipid. Expression analysis indicates that the absence of an apparent phenotype in the Eki2-deficient mice may be due to compensation by Eki2-family members or the activation of an alternative pathway to generate phosphatidylethanolamine. Expression of EGFP in this mouse model enabled the isolation of gonad cell populations, providing a useful resource from which to obtain relatively pure early steroidogenic cells for further studies.

Causes and predictors of nest mortality in a European rabbit population

We conducted a study on nest mortality of an individually marked population of European rabbits ( Oryctolagus cuniculus L., 1758) living in a field enclosure. Over 4 years, we determined maternities and quantified pup mortality during the nest period of 703 pups born in subterranean breeding burrows. Overall, pup mortality occurred in 42.7% of the litters, whereas 32.4% of all born pups were affected. Mortality was highest during the first few postnatal days. In about 50% of the cases, we managed to quantify different causes of mortality such as malnutrition, flooding, cooling of the pups, infanticide, or predation. The pups’ body mass on postnatal day 1, the thermal environment and the number of litter mates were the most important predictors of nest mortality. Litter mortality risk decreased with increasing soil temperature around the subterranean nests. A comparatively higher average pup body mass lowered the nest mortality risk of a litter, whereas this effect was more pronounced when soil temperatures were low. Furthermore, mortality was lowest in medium-sized litters, most probably due to the balance between the thermal benefits of huddling with litter siblings and the costs of having them due to the lower share of milk obtained by the individual pups in larger litters. In addition, nest mortality depended on characteristics of the mother; mortality was increased in litters of low-ranking females and of mothers with lower body mass. In conclusion, our study highlights multiple causes and the effects of different environmental and social factors on nest mortality of this small mammal.

Direct Estimation of Early Survival and Movements in Eastern Wolf Pups

Abstract:Determining juvenile survival and recruitment rates is essential to assess status and viability of animal populations. Currently, the demographic attributes of juvenile carnivores, specifically wolves (Canis lycaon), are poorly known but of considerable conservation interest. We measured survival and dispersal rates for 51 juvenile (age 3.5–31 weeks) wolves in Algonquin Provincial Park, Canada, from 2004 to 2005, using implantable very high frequency transmitters. Monthly pup survival was high (0.970, 95% CI = 0.951–0.990) and constant from June to November, and most pup mortality was from natural causes. Pups dispersed as early as age 15 weeks, and monthly dispersal rates were high for young pups (min. = 0.008, 95% CI = 0.000–0.019; max. = 0.030, 95% CI = 0.010–0.050). We failed to detect any influence of pack or litter size on pup survival or probability of dispersal. Radiotelemetry offers an individual‐based monitoring technique capable of providing direct assessment of wolf pup survival and movements, with rigorous estimation of survival and dispersal rates and quantification of cause‐specific mortality.

Effects of cage-cleaning frequency on laboratory rat reproduction, cannibalism, and welfare

Regular cage-cleaning is important for health, but for breeding rats it disrupts the nest and removes olfactory signals important for parental care. To investigate how different cage-cleaning frequencies affect breeding rats’ health and welfare, we monitored reproductive output, pup mortality, pup sex ratios, parental chromodacryorrhoea and in-cage ammonia levels for rats in a commercial breeding facility. Cages were cleaned twice-weekly, once-weekly or every 2 weeks (18 cages/group), replicated in two buildings, for the entire 36-week reproductive period. Frequent cage-cleaning had no clear benefits or major negative effects, showing no significant reductions in ammonia levels, or affects on health or overall pup mortality. However, frequent cage-cleaning slightly but significantly increased cannibalistic behaviour. This was because: (i) vulnerable 0–2-day-old pups were more likely to be exposed to a cage-cleaning event in the more frequent cage-cleaning regimes, physically disturbing them, and disrupting the nest and scent marks; and (ii) in the twice-weekly and weekly cleaned groups, pups under 2 days old at their first cage-cleaning were more likely to be cannibalised. Possible mechanisms behind these effects are discussed, including that cleaning might induce premature births, or stress the parents through noise or olfactory and physical disturbance. Finally, the cage-cleaning frequency producing most pups differed between the two buildings—an interactive effect corroborating previous findings that same-strain rodents’ phenotypes can differ with environment. Overall, we suggest that for breeding rats, cage-cleaning regimes should minimise noise, dissemination of unfamiliar conspecific odours, and physical disturbance during very late pregnancy and the first few days following birth.

Maternal Effort is State Dependent: Energetic Limitation or Regulation?

AbstractMany small altricial rodents have a postpartum oestrus and are often simultaneously pregnant and lactating. Negative influences of concurrent pregnancy and lactation on both lactational performance and the litter in utero are commonly observed and have been interpreted as resulting from high simultaneous energetic demands of gestation and lactation. We studied these effects in the precocial guinea‐pig (Cavia aperea f. porcellus) that, like many altricial rodents, has a postpartum oestrus, but in which the peaks of energy expenditure on lactation and gestation are widely separated. This life history allowed to investigate whether physiological regulation other than by energetic limitations may be responsible for allocation conflicts arising when lactation and gestation overlap. By comparing simultaneously pregnant and lactating females with lactating non‐pregnant females, we show that females in the former group nurse less and wean earlier than females of the latter group. In a comparison of litter size, litter mass, and pup mortality of females that had not been lactating during pregnancy with females that had been simultaneously pregnant and lactating, we show that the latter do not reduce investment in the following litter. In our study, energetic constraints on ad libitum fed females are unlikely and we therefore suggest that the results must be explained by regulatory constraints on lactational effort. We point out that this explanation has not been excluded for the effects observed in altricial small mammals.