Sucking and allosucking duration in farmed red deer (Cervus elaphus)

Evidence suggesting that reindeer mothers allonurse according to the direct reciprocity and generalized reciprocity decision rules

Allonursing is the nursing of the offspring of other mothers. Cooperation is an emergent property of evolved decision rules. Cooperation can be explained by at least three evolved decision rules: 1) direct reciprocity, i.e. help someone who previously helped you, 2) kin discrimination, i.e. preferentially direct help to kin than to non-kin, and 3) generalized reciprocity, i.e. help anyone if helped by someone. We assessed if semi-domesticated reindeer, Rangifer tarandus, mothers allonursed according to the decision rules of direct reciprocity, generalized reciprocity and kin discrimination over 2 years. To assess if reindeer mothers allonursed according to the direct reciprocity decision rule, we predicted that mothers should give more help to those who previously helped them more often. To assess if reindeer mothers allonursed according to the kin discrimination decision rule, we predicted that help given should increase as pairwise genetic relatedness increased. To assess if reindeer mothers allonursed according to the generalized reciprocity decision rule, we predicted that the overall number of help given by reindeer mothers should increase as the overall number of help received by reindeer mothers increased. The number of help given i) increased as the number of help received from the same partner increased in the 2012 group but not in both 2013 groups, ii) was not influenced by relatedness, and iii) was not influenced by an interaction between the number of help received from the same partner and relatedness. iv) The overall number of help given increased as the overall number of help received increased. The results did not support the prediction that reindeer mothers allonursed according to the kin discrimination decision rule. The results suggest that reindeer mothers may allonurse according to the direct reciprocity and generalized reciprocity decision rules.

Allonursing in Wild and Farm Animals: Biological and Physiological Foundations and Explanatory Hypotheses

The dams of gregarious animals must develop a close bond with their newborns to provide them with maternal care, including protection against predators, immunological transference, and nutrition. Even though lactation demands high energy expenditures, behaviors known as allonursing (the nursing of non-descendant infants) and allosuckling (suckling from any female other than the mother) have been reported in various species of wild or domestic, and terrestrial or aquatic animals. These behaviors seem to be elements of a multifactorial strategy, since reports suggest that they depend on the following: species, living conditions, social stability, and kinship relations, among other group factors. Despite their potential benefits, allonursing and allosuckling can place the health and welfare of both non-filial dams and alien offspring at risk, as it augments the probability of pathogen transmission. This review aims to analyze the biological and physiological foundations and bioenergetic costs of these behaviors, analyzing the individual and collective advantages and disadvantages for the dams' own offspring(s) and alien neonate(s). We also include information on the animal species in which these behaviors occur and their implications on animal welfare.

Further behavioural parameters support reciprocity and milk theft as explanations for giraffe allonursing

Suckling of a non-filial calf, or allosuckling, is an extreme case of allomaternal care in mammals. There have been many hypotheses postulated in an attempt to explain this behaviour; however, the supporting evidence differs, together with the conclusions drawn from the investigated variables. Previously, suckling bout rejection was analysed, and the milk theft and reciprocity hypotheses were both determined as the most appropriate explanation of allosuckling in giraffe. In this study, seven hypotheses were tested using different behavioural parameters, namely suckling bout frequency, suckling bout duration, and time spent suckling. It is well-documented that these parameters are associated with various aspects in ungulate biology; for example, suckling rejection typically reflects milk intake and parent-offspring conflict, whereas the suckling bout duration and frequency is associated with social behaviours (affiliation, bonding, social stress). In total, 22 nursing females and 47 suckling calves were observed, in four Czech zoos during a five-year period. The correlation of the observed parameters between the reciprocal female-calf dyads was found to be in line with the reciprocity hypothesis. In addition, non-filial calves tried to steal the milk from non-maternal females, supporting the milk theft hypothesis. Thus, the results support both the reciprocity and milk-theft hypotheses as the most plausible explanation of allosuckling in giraffe, and illustrates the importance of using suckling bout duration and frequency, and the time spent suckling, as behavioural parameters that may aid in explaining the extremity of maternal investment, such as allosuckling.

Giraffe males have longer suckling bouts than females

In polygynous mammals, females are expected to bias maternal investment in favor of male calves. The mother should invest more in males to enhance their reproductive success in adulthood, or the males require greater investment as they are bigger and stronger than females. In this study, we used nursing duration to compare the difference in the amount of maternal investment provided by females. We compared differences according to sex of the offspring and the influence of calves’ identification by sniffing, using captive giraffes (Giraffa camelopardalis) as a model. Since a high intensity of allonursing (nursing of a nonfilial calf) was reported in giraffes, we also focused on the difference between filial and nonfilial calves. We observed 22 nursing females and 47 suckling calves in four zoological gardens in the Czech Republic from 2007 to 2011. Nursing duration was longer for male calves than for female calves and for calves sniffed by the nursing female regardless whether the calves were filial or nonfilial. We conclude that male calves are more demanding for the amount of investment received and they are more successful in this effort than female calves. Since females provided investment in the same way to filial and nonfilial calves, selection for higher demand for investment by male than by female offspring should be important for their future development. Our results also demonstrate the importance of sniffing for the identification of the suckling calf by the female.

Giraffe nursing behaviour reflects environmental conditions

Nursing behaviour is one component of mammalian life history strategy that demonstrates context-dependent flexibility within species. Wild giraffes live in groups and feed themselves over large area. In the zoo, giraffes are kept in enclosures with abundant food resources. We aimed to analyse whether the nursing behaviour of giraffes differs between the zoo and nature reserve and discuss which factor (food intake, presence of predators, population density) can explain the difference. We observed seven and four female–calf pairs in the Bandia reserve, Senegal, and in Prague Zoo, Czech Republic, respectively. Nursing bouts were less frequent and longer and calves were less successful in nursing solicitations in the reserve, as females there seemed to be more selective for nursing times and locations, likely due to presence of predators and differences in food intake. Allonursing occurred more frequently in the zoo which can be attributed to higher population density in captive conditions.

The Many Axes of Deer Lactation

In undomesticated animals information about the production and composition of milk over time is still scarce. In general, for most mammals it is known that milk composition changes across lactation, is different for male and female offspring, and even that marsupials, such as kangaroos, can simultaneously produce milk of different compositions for young of different ages. Such parallel milk production of differing compositions has not yet been studied in single-offspring placental mammals, but may help to explain behavioural processes like allosuckling (feeding the young of other adults) and lateralized suckling preferences. In this study we analysed the production and composition of milk in red deer throughout the lactation period and now confirm for the first time that there are axial differences present. The front teats, which are the favoured suckling positions of the deer's offspring, produce milk with a greater protein-to-fat ratio. Also, from the beginning of lactation the yield is greater on the left side, the side preferred by calves in all of the studied species, both at population and individual level. The links between milk production and calf behaviour in deer deserve further study.

Suckling behavior in goitered gazelle: do females invest more in twins or singletons?

The mother-offspring social unit is a universal feature in the social life of all mammals and nursing is the most direct and vital component of maternal investment in young. Living in diverse environments, various ungulate species have different strategies for rearing offspring, from bearing a single, relatively large newborn and supplying only limited amounts of milk, to bearing several relatively small newborns with intensive post-partum lactation. In this paper, we consider the rearing strategy of goitered gazelle with a focus on suckling behavior, which, until now, has never been a subject of special investigation. Adult females of this species in their reproductive prime typically bear twins when environmental conditions are favorable, but the proportion of singletons increases when conditions are unfavorable. We expected that in goitered gazelles suckling intensity would be maximal during the first weeks after birth, and then decrease with the growth of the young; we also expected that twins would demand more energy, but receive significantly less maternal investment per young than singletons. We found that, indeed, suckling behavior had similar dynamics as typical of all bovid species, but our expectation for less maternal investment in twins vs. singletons was wrong. In reality, female goitered gazelles suckled twins significantly more intensively and terminated suckling less often compared to singletons. We concluded that in favorable situations females of high quality have the ability to show significantly more maternal investment in each twin, while singletons are typically born to weaker females. This ability of females to produce mostly twins allows goitered gazelles to take advantage of any favorable opportunity to quickly increase their population in an environment with unpredictable and abrupt yearly changes typical of the arid regions of Central Asia.

Allosuckling in reindeer (Rangifer tarandus): milk-theft, mismothering or kin selection?

Allosuckling, the suckling of offspring from females other than their own mother, has been reported in a number of mammalian species, including reindeer. The causes and function of this behaviour are still being investigated. We monitored 25 doe-calf pairs of semi-domestic reindeer Rangifer tarandus over 10 weeks to test three allosuckling/allonursing hypotheses: (1) milk theft, calves opportunistically allosuckle; (2) mismothering, misdirected maternal care; and (3) kin-selected allonursing. A calf soliciting an allosuckling bout was categorized as non-filial (NF), and a calf soliciting a suckling bout from its mother was categorized as filial (F). We recorded 9757 solicitations, of which 5176 were successful F bouts and 1389 were successful NF bouts. The rejection rates were greater for NF than F calves. The proportions of antiparallel positions adopted were greater for F than NF calves. The odds of an allobout were lower for calves arriving 1st, 3rd, 4th, 5th or 6th than for those arriving 2nd, but the odds did not vary with position adopted and relatedness. Our results provided support to the milk-theft hypothesis, whereas limited support for the mismothering hypothesis was found. Our results did not support the hypothesized kin selection function of allosuckling in reindeer. This article is part of a Special Issue entitled: insert SI title.

Camel calves as opportunistic milk thefts? The first description of allosuckling in domestic bactrian camel (Camelus bactrianus)

Allosuckling is a situation when a female nurses a non-filial offspring. It was described in various ungulate species; however for camels this is the first description of this behaviour. The aim of the study was to assess the occurrence of allosuckling in captive camels (Camelus bactrianus) and to test whether it can be explained as a ‘milk-theft’ (opportunistic behaviour of calves) or alternatively as an altruistic behaviour of females. During 2005 and 2007, nine camel females and ten calves in four zoological gardens in the Czech Republic were observed. In total, 373 sucking bouts were recorded, from which 32 were non-filial (the calf sucked from the non-maternal female). Allosuckling regularly appeared in captive camel herds. As predicted for the milk-theft explanation, the non-filial calves sucked more often in the lateral position and even did not suck in the antiparallel position at all. The non-filial calves preferably joined the filial calf when sucking but in five cases (15.6% of non-filial sucking bouts) the calves sucked from non-maternal dam without the presence of filial calf. We then expected the differences in terminations of sucking bouts by females but did not find any difference in sucking terminations for filial and non-filial calves. As the calves were getting older, the incidence of allosucking increased. This was probably because skills of the calf to outwit the non-maternal dam increased and/or the older calves might be more motivated for allosucking due to the weaning process. Finally, duration of a sucking bout was shorter with non-filial than filial calves. The results of the study support the hypothesis of ‘milk theft’, being mostly performed by calves behaving as opportunistic parasites, but we cannot reject certain level of altruism from the allonursing females or their increased degree of tolerance to non-filial calves.