Development of a new grading system to assess the foster performance of lactating sows

Increasing litter size has created the need for more sophisticated, accurate, and welfare-oriented systems for assessing the foster performance of lactating sows. The estimation of milk yield alone is not sufficient for meeting these requirements. Therefore, the aim of the current study was to develop a grading system for assessing the foster performance of lactating sows that can be easily applied in commercial farm practice. Data were collected in two German conventional farrow-to-feeder farms with a total sample size of 639 sows (4.05 ± 2.86 parities) and 1 728 litters. Besides general performance data, the piglets were weighed individually within the first 24 hours after birth and at the peak of lactation (day 18.22 ± 2.48). Based on these data, we proposed a new score referring to the milk score (MS). This score was compared with the commonly used formula for estimating milk yield (est. MY), which solely involves litter weight gain and litter size. The improvement of the developed MS allowed us to distinguish between the birth and foster performances of the lactating sows through considering cross-fostering, litter size, individual piglet weights, and piglet mortality during lactation. Both scores showed a similar progression across parities. It was found that litter size had a significant impact on the performance of lactating sows. A high est. MY was found to be associated with a significantly higher number of piglets per litter (15.79 ± 2.20), lower weight gain per piglet, and increased piglet mortality during lactation compared with sows with high MS, which showed a smaller litter size (13.51 ± 2.18) (P < 0.05). The focus on smaller litter size indicates a performance limitation, which seems to be related to the average teat number of 13–15 teats per sow. We recommend the consideration of the number of functional teats, because a litter size above it will not result in a sow having higher foster performance. In conclusion, as an extension of the common est. MY calculation, the MS considers cross-fostering as current farm-management practice when dealing with larger litters. Our recommendations emphasise the importance of an MS which indicates smaller litter size, higher piglet weight gain, and lower piglet mortality during lactation; these factors are related to an improvement in animal welfare for sows and piglets. Moreover, the presented MS could be used to develop a management tool for farmers to assess the foster performance of lactating sows, considering individual farm-management practices.     

Pre-laying nutrition mediates maternal effects on offspring immune capacity and growth in the pied flycatcher

We have aimed at detecting prelaying maternal effects on nestling antibody defences and growth through experimental food supplementation of female pied flycatchers Ficedula hypoleuca and subsequent exchange of whole clutches with control nests. The levels of immunoglobulins and the mass and size of chicks at 12 days of age were ascertained. This is the first study controlling for maternal incubation effects by exchanging eggs rather than nestlings. Our prediction is that the females' availability of pre-laying nutritional resources affects offspring immune capacity and growth through maternal effects in the eggs when conditions during incubation and rearing are controlled for. Nestling immunoglobulin Y (IgY) levels and tarsus length were indeed positively associated with maternal food supplementation at laying. The only rearing environmental effect detected was that of mite infestation which affected both IgY levels and growth of nestlings. Nestlings that recruited to the population in the subsequent 2 years had higher IgY levels than those that did not. Maternal adaptations for allocating resources to eggs play an important role in moulding offspring phenotypes and may affect their survival prospects.     

Variation in heritability of immune function in the tree swallow

Heritability is an important component of the ability of a trait to respond to natural selection; variation in heritability can lead to differences in how a trait responds to selection pressures. Here we test whether an important physiological trait, immune function, varies by comparing heritability estimates through cross-fostering brood manipulation at three wide-spread sites in the tree swallow (Tachycineta bicolor): Alaska, New York and Tennessee. In two of three sites, there was no additive genetic component to nestling immune response to the mitogen phytohaemagglutinin, while immune response had a heritable component in Tennessee. Bootstrapping revealed significant differences in estimated heritability. This conclusion was supported by mother–offspring regressions; in Tennessee breeding females mounting strong immune responses tended to have offspring with strong immune responses, while in New York and Alaska, there was no relationship between the immune responses of mothers and offspring. These results suggest that studies investigating the roles of common origin and rearing environment should consider yearly or spatial variation within a species.     

Egg size and offspring performance in the collared flycatcher (<Emphasis Type="Italic">Ficedula albicollis</Emphasis>): a within-clutch approach

Adaptive within-clutch allocation of resources by laying females is an important focus of evolutionary studies. However, the critical assumption of these studies, namely that within-clutch egg-size deviations affect offspring performance, has been properly tested only rarely. In this study, we investigated effects of within-clutch deviations in egg size on nestling survival, weight, fledgling condition, structural size and offspring recruitment to the breeding population in the collared flycatcher (Ficedula albicollis). Besides egg-size effects, we also followed effects of hatching asynchrony, laying sequence, offspring sex and paternity. There was no influence of egg size on nestling survival, tarsus length, condition or recruitment. Initially significant effect on nestling mass disappeared as nestlings approached fledging. Thus, there seems to be limited potential for a laying female to exploit within-clutch egg-size variation adaptively in the collared flycatcher, which agrees with the majority of earlier studies on other bird species. Instead, we suggest that within-clutch egg-size variation originates from the effects of proximate constraints on laying females. If true, adaptive explanations for within-clutch patterns in egg size should be invoked with caution.     

Environmental and genetic components of oxidative stress in wild kestrel nestlings (Falco tinnunculus)

In this study, we estimated the environmental and genetic components of two variables related to avian oxidative stress using wild nestlings of the Eurasian kestrel (Falco tinnunculus). The study was carried out during two breeding seasons. In the first season, we assessed the between- and within-nest resemblance in serum reactive oxygen metabolites (ROMs) and total serum antioxidant barrier (OXY). In the second season, we carried out a cross-fostering experiment to determine the importance of environmental and genetic factors on ROMs and OXY. The 23.5% of ROMs variance was explained by the nest of origin, indicating a main genetic component. In contrast, the 52.8% of OXY variance was explained by the nest of rearing, indicating that this variable was more influenced by environmental components. These findings suggest that variations in ROMs and OXY could reflect, respectively, the expression of different genetic polymorphisms and differences in dietary uptake of antioxidants.     

Phenotypic, genetic, and environmental causes of variation in yellow skin pigmentation and serum carotenoids in Eurasian kestrel nestlings

In the context of sexual selection and parent-offspring communication, carotenoid-based coloration operates as a dynamic condition-dependent signal, as pigments stored in the skin and in the bill can be reallocated to other tissues in accordance with physiological needs. We studied the proximate factors affecting the carotenoid-dependent coloration of the Eurasian kestrel (Falco tinnunculus). Kestrel nestlings show carotenoid-based coloration at the integument level. Adult males and females share similar characteristics, but to a different extent. By cross-fostering nestlings, we evaluated the importance of the “nest of rearing” and the “nest of origin” to determine variation in skin color and blood carotenoids. The nest of rearing accounted for most of the observed variance in skin color, as well as serum carotenoids, while the nest of origin was not causal to the variability of carotenoids in young kestrels. The study indirectly shows that carotenoid-based color expressed by young kestrels is not affected by pre-laying conditions. Furthermore, we found that carotenoid coloration and blood carotenoid concentration were correlated at phenotypic and environmental levels, while the hereditary component of the carotenoid traits was too low to estimate their correlation at the genetic level.     

Cross-fostering reveals an effect of spleen size and nest temperatures on immune responses in nestling European starlings

Immunocompetence may be a good measure of offspring quality, however, factors affecting variation in immune responses are not clear. Research suggests that immune function can vary due to differences in genetics, development conditions and individual quality. Here, I examined factors affecting variation in immune response among nestling European starlings through a split-nest cross-fostering brood manipulation that included two important covariates: spleen size and nest temperatures. Immunocompetence was assessed via a cell-mediated immune response to phytohaemagglutinin (PHA). This paper provides the first direct evidence that individuals with large spleens also mount strong immune responses. Exposure to PHA did not cause splenomegaly, as there was no difference in spleen size between control birds and those injected with PHA. Offspring immune function was affected by common origin and by rearing environment, though rearing environment appeared to exert its influence only through nest temperatures. A comparison of the immune performance of siblings reared in their home nest versus those reared in other nests revealed a strong effect of maternal quality. As the difference in natal clutch size increased, the magnitude of the difference in immune performance between home-reared nestlings versus out-reared nestlings increased. Overall, nestling immune function appears to be determined by the combination of genetic, maternal and environmental effects.     

Environmental and genetic variation in T-cell-mediated immune response of fledgling American kestrels

We investigated genetic and environmental components of variance in avian T-cell-mediated immune response (CMI) through a cross-fostering experiment conducted on wild American kestrels (Falco sparverius). CMI was evaluated in vivo by an experimental challenge with phytohaemagglutinin, a T-cell mitogen, injected intradermally in fledglings. Additionally, we assessed two measures of nutritional condition (body mass and circulating plasma proteins) which could influence the variance components of CMI. A two-way nested ANOVA indicated that CMI of fledgling kestrels was explained more by the nest where the bird was reared (33% of the explained variance) than by the nest of origin (12%). Body mass was explained equally by familial and environmental components, while plasma proteins were only related to the rearing environment. CMI of fledglings was not related to their circulating plasma proteins, but was positively correlated with their body mass. Fledgling body mass seemed to be influenced by pre-hatching or post-hatching maternal effects prior to manipulation since resemblance in body mass of sibships at the age of manipulation was high (h ²≤0.58), and body mass at this age predicted body mass at fledging. Therefore, pre-manipulation parental effects on body mass, such as investment in egg size, could have inflated the familial effects on body mass of fledglings and then on its correlated CMI. When controlling for body mass, most of the variation in CMI of fledglings was explained by the nest where the bird was reared (36.6%), while the variance explained by the nest of origin (4%) was not significant. This means that environmental influences are major determinants of offspring CMI. The low proportion of variance explained by the familial component may have been due to the high correlation of CMI to fitness. Received: 19 October 1999 / Accepted: 23 December 1999     

Mothers influence offspring body size through post-oviposition maternal effects in the redbacked salamander, Plethodon cinereus

In the terrestrial salamander (Plethodon cinereus), previous work has shown that mothers body size is positively correlated to offspring size at the time of hatching even after controlling for the effects of egg size. This study was designed to determine whether maternal body size affects offspring size via pre-oviposition factors (e.g., yolk quality, jelly coat composition, or maternal genes) or post-oviposition factors (e.g., parental care behaviors, parental modification of environment). Gravid females were captured and induced to lay eggs in experimental chambers in which the environment was standardized. Fifteen clutches were exchanged, or cross-fostered, between female pairs differing in body size. Ten females whose eggs were taken away and then returned served as controls for the crossing treatment. Foster mothers did not significantly differ from control mothers in the time spent with eggs, body position, or number of egg movements during brooding. Average egg mass measured midway through development was not significantly correlated to the body size of either the genetic or foster mother, but was correlated to pre-oviposition oocyte size. At hatching, offspring body length was positively correlated to egg size and the foster mothers body size. This correlation suggests that in P. cinereus post-oviposition maternal effects have a greater impact on offspring size than other maternal factors incorporated into the egg prior to oviposition. While our study showed that larger mothers moved their eggs less often and tended to spend more time in contact with their eggs, further work needs to be done to identify the specific mechanisms through which larger mothers influence the body size of their offspring. This is the first experimental demonstration of post-oviposition maternal effects for any amphibian with parental care.     

Effects of Common Origin and Common Rearing Environment on Variance in Ectoparasite Load and Phenotype of Nestling Alpine Swifts

Knowledge of the quantitative genetics of resistance to parasitism is key to appraise host evolutionary responses to parasite selection. Here, we studied effects of common origin (i.e. genetic and pre-hatching parental effects) and common rearing environment (i.e. post-hatching parental effects and other environment effects) on variance in ectoparasite load in nestling Alpine swifts (Apus melba). This colonial bird is intensely parasitized by blood sucking louse-flies that impair nestling development and survival. By cross-fostering half of the hatchlings between pairs of nests, we show strong significant effect of common rearing environment on variance (90.7% in 2002 and 90.9% in 2003) in the number of louse-flies per nestling and no significant effect of common origin on variance in the number of louse-flies per nestling. In contrast, significant effects of common origin were found for all the nestling morphological traits (i.e. body mass, wing length, tail length, fork length and sternum length) under investigation. Hence, our study suggests that genetic and pre-hatching parental effects play little role in the distribution of parasites among nestling Alpine swifts, and thus that nestlings have only limited scope for evolutionary responses against parasites. Our results highlight the need to take into consideration environmental factors, including the evolution of post-hatching parental effects such as nest sanitation, in our understanding of host-parasite relationships.