Influence of Rearing Environment on Longitudinal Brain Development, Object Recognition Memory, and Exploratory Behaviors in the Domestic Pig (Sus scrofa)

Introduction

Over the last 40 years, the domestic pig has emerged as a prominent preclinical model as this species shares similarities with humans with regard to immunity, gastrointestinal physiology, and neurodevelopment. Artificial rearing of pigs provides a number of advantages over conventional rearing (i.e., true maternal care), including careful control of nutrient intake and environment conditions. Yet there remains a gap in knowledge when comparing brain development between sow-reared and artificially reared domestic pigs. Thus, our research sought to model brain development and assess recognition memory in a longitudinal manner by directly comparing rearing environments.

Methods

Forty-four intact (i.e., not castrated) male pigs were artificially reared or sow-reared from postnatal day 2 until postnatal week 4. After postnatal week 4, all pigs were housed in a group setting within the same environment until postnatal week 24. Magnetic resonance imaging was conducted on pigs at 8 longitudinal time-points to model developmental trajectories of brain macrostructural and microstructural outcomes. Additionally, pigs behavior were tested using the novel object recognition task at postnatal weeks 4 and 8.

Results

Throughout the 24-week study, no differences between rearing groups were noted in weekly body weights, average growth and feed intake patterns, or feed efficiency. Whole brain, gray matter, white matter, and cerebrospinal fluid growth patterns also did not differ between pigs assigned to different early-life rearing environments. Moreover, minimal differences in regional absolute volumes and fractional anisotropy developmental trajectories were identified, though artificially reared pigs exhibited higher initial rates of myelination in multiple brain regions compared with sow-reared pigs. Furthermore, behavioral assessment at both PNW 4 and 8 suggested little influence of rearing environment on recognition memory, however, an age-dependent increase in object recognition memory was observed in the sow-reared group.

Conclusion

Our findings suggest that early-life rearing environment influences the rate of development in some brain regions but has little influence on overall brain growth and object recognition memory and exploratory behaviors in the domestic pig. Artificial rearing may promote maturation in certain brain areas but does not appear to elicit long-term effects in outcomes including brain structure or object recognition memory.

The newborn rat gastric emptying rate is volume and not developmentally dependent

BACKGROUND

Gastric residuals are a common finding in enterally fed preterm neonates and traditionally thought to reflect immaturity-related delayed gastric emptying. Adult human data suggest that the meal volume regulate the gastric emptying rate, but early in life, this has not been adequately evaluated. The goal of this study was to study the rat postnatal changes in gastric emptying rate and the strain-induced effect on muscle contraction. We hypothesized that the stomach content volume and not developmental factors determines the newborn gastric emptying rate, via the Rho-kinase 2 (ROCK-2) pathway.

METHODS

Gastric volume and emptying rate measurements were obtained by ultrasound at different postprandial times and the wall strain-dependent changes in muscle contraction were evaluated ex vivo.

KEY RESULTS

The newborn rat gastric emptying rate was unrelated to postnatal age, maximal 30 min postprandial, and directly proportional to content volume. In vitro measurements showed that the agonist-induced gastric muscle contraction was directly proportional to the stomach wall strain. These changes were mediated via upregulation of ROCK-2 activity.

CONCLUSIONS & INFERENCES

The newborn rat gastric emptying rate is not developmentally regulated, but dependent on the content volume via wall strain-induced ROCK-2 activation. Further clinical studies addressing the content volume effect on the rate of gastric emptying are warranted, to enhance feeding tolerance in preterm neonates.

Survival implications of the development of behavioural responsiveness and awareness in different groups of mammalian young

This paper focuses on the development of behaviours that are critical for the survival of newborn and juvenile mammals of veterinary and wider biological interest. It provides an updated, integrated and comparative analysis of how postnatal maturation of sensory, motor and perceptual capacities support and constrain behavioural interactions between mammalian young and the mother, any littermates and the environment. Young that are neurologically exceptionally immature, moderately immature and mature at birth are compared, and include, for example, marsupial joeys, rodent pups and ruminant offspring. Mothers in these three groups exhibit distinctive patterns of birthing and postnatal care behaviours. To secure survival of the young, maternal care must compensate for behavioural inadequacies imposed by the limited sensory capacities the young possess at each stage. These sensory capacities develop in a predictable sequence in most mammals such that before birth the sequence progresses to an extent that parallels the degree of neurological maturity reached at birth. The extent of neurological maturity is likewise reflected in how long it takes after birth for the necessary brain circuit connectivity to develop sufficiently to support cortically based cognitive modulation of behaviour. This takes several months, days-to-weeks or minutes-to-hours in young that are, respectively, neurologically exceptionally immature, moderately immature, or mature at birth. Once achieved, cognitive awareness confers a high degree of behavioural flexibility that allows the young to respond more effectively to the unpredictability of their postnatal environments. It is shown that the onset of this cognitively based flexibility in the young of each group coincides with their first exposure to a variable environment that requires such behavioural flexibility.

Maternal separation and gastrointestinal transit time in neonate rats

Gastrointestinal transit times (GItts) were compared in separate litters of 10- and 15-day-old Sprague Dawley rats using barium sulphate. By tracking the leading front of the bolus on radiographs, the gastrocaecal transit times in pups were estimated. To measure the total GItt, the duration from orogastric gavage until an observable defecation of barium sulphate was recorded. The gastrocaecal times for 10-day-old pups maintained with their dam (n = 5) ranged from 4-5 h and those removed from the dam ranged from 2.5-5 h. For 15-day-old pups with their dam (n = 6) and without dam (n = 5), gastrocaecal times ranged from 4-6 h and 3.5-5 h, respectively. Ten-day-old pups that remained with the dam had a GItt of 13.8 ± 0.9 h and those kept in the absence of the dam had a time of 9.3 ± 0.7 h. This decrease (P < 0.05) in GItt in the absence of the dam was age-dependent in 10-day-old pups, and was not observed (P > 0.05) in 15-day-old pups. The results provide a basis, for the design of future studies involving neonate rat metabolism, to include maternal presence.

Galloping colts, fetal feelings, and reassuring regulations: putting animal-welfare science into practice

About a decade ago, concern was expressed that fetuses might suffer while dying in utero after the death of their dams. However, reference to already published literature provided compelling evidence that fetuses cannot consciously experience negative sensations or feelings, such as breathlessness and pain, and showed that, provided certain precautions are taken, they cannot suffer--their welfare is assured. In this article, I outline the major features of fetal and neonatal physiology that underlie this conclusion as it relates to fetuses that are neurologically exceptionally immature, moderately immature, or mature at birth. As an example of the practical application of this knowledge, I also show how the results of detailed studies reported in the biomedical literature, together with evolving understanding of the capacity of animals to experience negative sensations reported in the animal-welfare science literature, led to the development of international guidelines for the humane management of livestock fetuses when their dams are slaughtered commercially. I also highlight the notion that significant progress in the scientific understanding of animal welfare, and its applications, can be made by remaining open to knowledge developed in disciplines at the margins of or beyond those in the animal-welfare science, ethology, and veterinary sciences arenas.

Electroencephalographic responses to tail clamping in anaesthetized rat pups

We investigated electroencephalographic (EEG) responses to tail clamping in lightly anaesthetized rat pups (5–22 days) in order to determine the ontogeny of EEG activity and at what age they may be capable of experiencing pain. Median frequency (F50) and spectral edge frequency (F95) of the power spectrum in the range of 1–30 Hz were determined before and after the application of a noxious stimulus and power spectra were compared by multivariate analysis. There was a postnatal increase in EEG power as, before clamping, pups aged 5–7 days exhibited isoelectric traces, whereas those aged 12–14 days and 21–22 days had intermittent EEG activity where the power in all frequencies was significantly lower at the former than at the latter age. Pups aged 5–7 days exhibited no EEG response to clamping in view of their isoelectric traces. Pups aged 12–14 days showed a significant decrease in F95 ( P = 0.002), whereas those aged 21–22 days showed highly significant reduction in F50 and F95 ( P = 0.028 and P < 0.001, respectively) as well as changes in EEG power of specific frequencies after clamping. The results and related literature suggest that rat pups aged 5–7 days and younger are not likely to perceive pain and that the ability to perceive pain develops gradually between postnatal ages 12–14 days and 21–22 days.