The Impact of Maternal Chronic Inflammatory Conditions on Breast Milk Composition: Possible Influence on Offspring Metabolic Programming

Breastfeeding is the best way to provide newborns with crucial nutrients and produce a unique bond between mother and child. Breast milk is rich in nutritious and non-nutritive bioactive components, such as immune cells, cytokines, chemokines, immunoglobulins, hormones, fatty acids, and other constituents. Maternal effects during gestation and lactation can alter these components, influencing offspring outcomes. Chronic inflammatory maternal conditions, such as obesity, diabetes, and hypertension, impact breast milk composition. Breast milk from obese mothers exhibits changes in fat content, cytokine levels, and hormonal concentrations, potentially affecting infant growth and health. Similarly, diabetes alters the composition of breast milk, impacting immune factors and metabolic markers. Other pro-inflammatory conditions, such as dyslipidemia and metabolic syndrome, have been barely studied. Thus, maternal obesity, diabetes, and altered tension parameters have been described as modifying the composition of breast milk in its macronutrients and other important biomolecules, likely affecting the offspring's weight. This review emphasizes the impact of chronic inflammatory conditions on breast milk composition and its potential implications for offspring development through the revision of full-access original articles.

Chronic Stress Decreases Lactation Performance

The ability to provision offspring with milk is a significant adaptive feature of mammals that allows for considerable maternal regulation of offspring beyond gestation, as milk provides complete nutrition for developing neonates. For mothers, lactation is a period of marked increases in energetic and nutritive demands to support milk synthesis; because of this considerable increase in demand imposed on multiple physiological systems, lactation is particularly susceptible to the effects of chronic stress. Here, we present work that explores the impact of chronic stress during lactation on maternal lactation performance (i.e., milk quality and quantity) and the expression of key milk synthesis genes in mammary tissue using a Sprague-Dawley rat model. We induced chronic stress using a well-established, ethologically relevant novel male intruder paradigm for 10 consecutive days during the postpartum period. We hypothesized that the increased energetic burden of mounting a chronic stress response during lactation would decrease lactation performance. Specifically, we predicted that chronic exposure to this social stressor would decrease either milk quality (i.e., composition of proximate components and energy density) or quantity. We also predicted that changes in proximate composition (i.e., lipid, lactose, and protein concentrations) would be associated with changes in gene expression levels of milk synthesis genes. Our results supported our hypothesis that chronic stress impairs lactation performance. Relative to the controls, chronically stressed rats had lower milk yields. We also found that milk quality was decreased; milk from chronically stressed mothers had lower lipid concentration and lower energy density, though protein and lactose concentrations were not different between treatment groups. Although there was a change in proximate composition, chronic stress did not impact mammary gland expression of key milk synthesis genes. Together, this work demonstrates that exposure to a chronic stressor impacts lactation performance, which in turn has the potential to impact offspring development via maternal effects.

Non-nutritive bioactive components in maternal milk and offspring development: a scoping review

Lactation is a critical time in mammalian development, where maternal factors shape offspring outcomes. In this scoping review, we discuss current literature concerning maternal factors that influence lactation biology and highlight important associations between changes in milk composition and offspring outcomes. Specifically, we explore maternal nutritional, psychosocial, and environmental exposures that influence non-nutritive bioactive components in milk and their links to offspring growth, development, metabolic, and behavioral outcomes. A comprehensive literature search was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews (PRISMA-ScR) guidelines. Predetermined eligibility criteria were used to analyze 3,275 papers, and the final review included 40 primary research articles. Outcomes of this review identify maternal obesity to be a leading maternal factor influencing the non-nutritive bioactive composition of milk with notable links to offspring outcomes. Offspring growth and development are the most common modes of programming associated with changes in non-nutritive milk composition due to maternal factors in early life. In addition to discussing studies investigating these key associations, we also identify knowledge gaps in the current literature and suggest opportunities and considerations for future studies.

Maternal effects shape offspring physiological condition but do not senesce in a wild mammal

In vertebrates, offspring survival often decreases with increasing maternal age. While many studies have reported a decline in fitness-related traits of offspring with increasing maternal age, the study of senescence in maternal effect through age-specific changes in offspring physiological condition is still at its infancy. We assessed the influence of maternal age and body mass on offspring physiological condition in two populations of roe deer (Capreolus capreolus) subjected to markedly different environmental conditions. We measured seven markers to index body condition and characterize the immune profile in 86 fawns which became recently independent of their known-aged mothers. We did not find striking effects of maternal age on offspring physiological condition measured at 8 months of age. This absence of evidence for senescence in maternal effects is likely due to the strong viability selection observed in the very first months of life in this species. Offspring physiological condition was, on the other hand, positively influenced by maternal body mass. Between-population differences in environmental conditions experienced by fawns also influenced their average body condition and immune phenotype. Fawns facing food limitation displayed lower values in some markers of body condition (body mass and haemoglobin levels) than those living in good quality habitat. They also allocated preferentially to humoral immunity, contrary to those living in good conditions, which allocated more to cellular response. These results shed a new light on the eco-physiological pathways mediating the relationship between mother's mass and offspring condition.

Milk composition in a wild mammal: a physiological signature of phenological changes

Understanding how spring phenology influences early life can provide important insights into drivers of future development and survival. We combined unique, long-term data from a bighorn sheep population and satellite-derived phenology indices to quantify the relative importance of maternal and environmental influences on milk composition and lamb overwinter survival. Based on 216 milk samples from 34 females monitored over 6 years, we found that longer snow-free and vegetation growing seasons increased milk fatty acid, iron and lactose concentrations. Structural equation modelling revealed no causality between milk energy content, lamb weaning mass and lamb overwinter survival. Our results suggest that spring conditions can affect milk energy content, but we did not detect any effect on lamb overwinter survival either directly or indirectly through lamb weaning mass. The effect of green-up date on milk composition and energy content suggests that herbivores living in seasonal environments, such as the bighorn sheep, might rely on a strategy intermediate between 'capital' and 'income' breeding when energy demands are high.

Sons accelerate maternal aging in a wild mammal

Aging, or senescence, is a progressive deterioration of physiological function with age. It leads to age-related declines in reproduction (reproductive senescence) and survival (actuarial senescence) in most organisms. However, senescence patterns can be highly variable across species, populations, and individuals, and the reasons for such variations remain poorly understood. Evolutionary theories predict that increases in reproductive effort in early life should be associated with accelerated senescence, but empirical tests have yielded mixed results. Although in sexually size-dimorphic species offspring of the larger sex (typically males) commonly require more parental resources, these sex differences are not currently incorporated into evolutionary theories of aging. Here, we show that female reproductive senescence varies with both the number and sex ratio of offspring weaned during early life, using data from a long-term study of bighorn sheep. For a given number of offspring, females that weaned more sons than daughters when aged between 2 and 7 y experienced faster senescence in offspring survival in old age. By contrast, analyses of actuarial senescence showed no cost of early-life reproduction. Our results unite two important topics in evolutionary biology: life history and sex allocation. Offspring sex ratio may help explain among-individual variation in senescence rates in other species, including humans.

Linking genetic merit to sparse behavioral data: behavior and genetic effects on lamb growth in Soay sheep

Wild quantitative genetic studies have focused on a subset of traits (largely morphological and life history), with others, such as behaviors, receiving much less attention. This is because it is challenging to obtain sufficient data, particularly for behaviors involving interactions between individuals. Here, we explore an indirect approach for pilot investigations of the role of genetic differences in generating variation in parental care. Variation in parental genetic effects for offspring performance is expected to arise from among-parent genetic variation in parental care. Therefore, we used the animal model to predict maternal breeding values for lamb growth and used these predictions to select females for field observation, where maternal and lamb behaviors were recorded. Higher predicted maternal breeding value for lamb growth was associated with greater suckling success, but not with any other measures of suckling behavior. Though our work cannot explicitly estimate the genetic basis of the specific traits involved, it does provide a strategy for hypothesis generation and refinement that we hope could be used to justify data collection costs needed for confirmatory studies. Here, results suggest that behavioral genetic variation is involved in generating maternal genetic effects on lamb growth in Soay sheep. Though important caveats and cautions apply, our approach may extend the ability to initiate more genetic investigations of difficult-to-study behaviors and social interactions in natural populations.

Reproductive senescence: new perspectives in the wild

According to recent empirical studies, reproductive senescence, the decline in reproductive success with increasing age, seems to be nearly ubiquitous in the wild. However, a clear understanding of the evolutionary causes and consequences of reproductive senescence is still lacking and requires new and integrative approaches. After identifying the sequential and complex nature of female reproductive senescence, we show that the relative contributions of physiological decline and alterations in the efficiency of parental care to reproductive senescence remain unknown and need to be assessed in the light of current evolutionary theories of ageing. We demonstrate that, although reproductive senescence is generally studied only from the female viewpoint, age-specific female reproductive success strongly depends on male-female interactions. Thus, a reduction in male fertilization efficiency with increasing age has detrimental consequences for female fitness. Lastly, we call for investigations of the role of environmental conditions on reproductive senescence, which could provide salient insights into the underlying sex-specific mechanisms of reproductive success. We suggest that embracing such directions should allow building new bridges between reproductive senescence and the study of sperm competition, parental care, mate choice and environmental conditions.

Diets derived from maize monoculture cause maternal infanticides in the endangered European hamster due to a vitamin B3 deficiency

From 1735 to 1940, maize-based diets led to the death of hundreds of thousands of people from pellagra, a complex disease caused by tryptophan and vitamin B3 deficiencies. The current cereal monoculture trend restricts farmland animals to similarly monotonous diets. However, few studies have distinguished the effects of crop nutritional properties on the reproduction of these species from those of other detrimental factors such as pesticide toxicity or agricultural ploughing. This study shows that maize-based diets cause high rates of maternal infanticides in the European hamster, a farmland species on the verge of extinction in Western Europe. Vitamin B3 supplementation is shown to effectively restore reproductive success in maize-fed females. This study pinpoints how nutritional deficiencies caused by maize monoculture could affect farmland animal reproduction and hence their fitness.

Immunoglobulin A and nutrients in milk from great apes throughout lactation

Differences in macronutrients between human and ape milks appear relatively small, but variation in other components such as immunoglobulins (Ig) may be greater. This study characterized the macronutrient and secretory (sIgA) profiles in milk from gorillas and orangutans throughout lactation. Fifty-three milk samples from four gorillas and three orangutans were collected throughout 48 and 22 months postpartum (MPP), respectively. Samples were grouped in five stages of lactation (0 to 6 months, more than 6 months to 12 months, more than 12 months to 18 months, more than 18 months to 36 months, and more than 36 months to 48 months). Data were analyzed as a complete randomized design. Concentration of sIgA did not change due to species or its interaction with MPP. Crude protein, regardless of MPP, was greater for gorillas compared with orangutans (1.27 vs. 0.85%). Fat, sugar, and gross energy were affected by the interaction of species × MPP. For gorilla milk, concentrations of sIgA were 43 mg/L at 6 MPP increasing to 79 mg/L at 48 MPP. Protein was highest at 48 MPP. Sugar was lowest at 48 MPP. Values for fat and gross energy were the highest 36 MPP. For orangutan milk, concentrations of sIgA were highest at 6 MPP. Sugar decreased with MPP. Protein, dry matter, or fat were unaffected by MPP. Gross energy content was steady during the first 18 MPP but it tended to decrease by 36 MPP. The results indicate that macronutrients are similar between human, published data, and great ape milk, though gorilla milk has higher protein and human milk higher fat (published data). Concentrations of sIgA in ape milk were about 10-fold lower than human values from the literature. Differences between human and ape milk may lie more in bioactive/immune molecules than nutrients.

RESEARCH HIGHLIGHTS

Milk macronutrients from great apes differed throughout lactation. Milk macronutrients but not IgA from non-human great apes and humans were quite similar. Milk protein was greater in Gorilla compared with Orangutan.