Mortality in neonates has always represented significant economic wastage and slow progress has been made in the understanding of the factors influencing the probability of survival or death. There is also increasing pressure in the animal agriculture sphere to pursue improved welfare and in the situation where neonatal deaths are a high proportion of the liveborn offspring, then this becomes not only an economic concern but also a welfare issue. This paper highlights principal problems within the neonatal area in order to introduce the ensuing text dealing with specific technical challenges.

The magnitude of loss for different species including humans is given and the factors affecting mortalities are discussed. The major components include: human factors, pathogenic agents, immunological factors, temperature and thermoregulation, nutrition, behaviour and physical factors.

Although single factors are often ascribed as the cause of death, the reality is that there are usually multifactorial components involved which interact and contribute to the final mortality of the individual.

The approach to the practical management of neonates varies widely between the different animal industries and the techniques deployed depend on relative economic values. In human health care every available resource is used to ensure very high survival rates because of the incalculable value of each individual delivered. With farm animals the use of resources is at a much lower level and survival rates are lower. It ought to be possible in animal agriculture to adopt some of the methods used in the medical profession to assess high risk situations and to divert resources appropriately.

The epitheliochorial placenta of the pig does not allow the passage of immunoglobulin to the foetus and thus the young piglet is born without passive immune protection. During the first 36 h of life there is a massive transmission of macromolecules across the intestine, virtually all that are present in the gut may be effectively endocytosed and transmitted into the blood stream. The postnatal transmission of antibody from colostrum during this period provides the young animal with a spectrum of serum antibodies indistinguishable from that of its mother. It is established that even in utero the piglet is capable of mounting some response to antigenic challenge. Despite this, the ability of the young animal to respond may be influenced profoundly by the absorption of macromolecules (antibodies and antigens in colostrum and in sow's milk as well as antigens in the farrowing house) during the first hours after birth. These effects range from passive protection from infectious agents during the neonatal period to determining the precise nature of the immune response to antigens during later periods (e.g. at weaning).

At birth all cellular components of the immune system are represented but during the first few weeks of life dramatic changes occur in the number and distribution of these cells. Our histological studies have shown that shortly after birth the predominant T lymphocytes in the small intestine are T2+, T4− and T8−; whilst in other organs there are large numbers of conventional T4+ and T8+ cells. By 1 week of age there is a dramatic increase in the numbers of T4+ cells, whilst T8+ cells remain low, and only start to increase by week 7. Thus, changes in lymphocyte populations are occurring concurrent with increasing exposure to environmental antigens. The functional capacity of these cells also changes during this period and this process may be particularly affected by early weaning.

During the neonatal period an animal is presented with a vast array of antigenic material for the first time. How and when these antigens are presented may profoundly influence the capacity of the immune system to respond to them.

This review is directed to thermoregulation in ruminants relative to weather and husbandry conditions of the United Kingdom in which the principal ruminant species are cattle and sheep. The main thermoregulatory demands for neonates, but not necessarily for older animals, are posed by cold rather than heat. Thermoregulation is critical to the survival of neonatal ruminants. On many farms, neonatal deaths are, for example, 20% of lambs born. Neonatal ruminants are precocial compared with many altrical neonatal mammals and have well developed thermoregulation which allows them to maintain homeothermy in many environments. However, at birth the neonatal ruminant moves from a very stable thermal environment, of similar temperature to its core body temperature, to a variable thermal environment which is 10 to 50°C colder than its core temperature. At birth the coat is wet and energy losses can be very high. To maintain homeothermy, heat production can usually be increased 3- to 5-fold above resting heat production. However, there are only limited quantities of tissue substrates available for this and the early intake of sufficient colostrum by the newborn is essential to continued heat production and survival. Nutrition in early and late pregnancy also affects the viability of, at least, young lambs: placental insufficiency may cause chronic prenatal hypoglycaemia and hypoxaemia which, postnatally, inhibits spontaneous respiration and restricts heat production. In calves, dystocia may cause acidosis and decreased heat production.

The principal thermoregulatory mechanisms and some factors which affect their efficiency in newborn calves and lambs are presented, with consideration of the limitations of lower critical temperatures.

At birth the neonate switches from a dependent to a totally independent extra-uterine environment. It must begin to regulate its own body temperature to survive. This paper considers thermoregulation in the newborn piglet and those factors which influence survival.

The first few days are important for the development of thermoregulation. Metabolic heat production and rectal temperature both increase and the development of adequate thermal insulation helps to withstand the effects of a cold environment. The body reserves play an important rôle and are needed to ensure that the piglet survives within the first hours of life. It is the glycogen and fat reserves that are readily utilized as major energy substrates for heat production within the first 12 to 24 h; the contribution from protein is minimal. However, not all reserves are available for mobilization. Attempts to improve the body reserves of piglets have been unsuccessful but the quality and composition of colostrum, especially its fat content, can be manipulated by maternal nutrition. Coldness impairs the development of thermostability and induces hypothermia. This diminishes the vigour of the piglet and reduces colostrum intake and hence immunoglobulins. The incidence of disease, especially scouring, may therefore be increased. The maintenance of an adequate environment also ensures a good immunological status. The development of housing, husbandry and management practices must take these various phenomena into account.

The postnatal period is the most dangerous phase of life and survival depends on the neonate behaving appropriately from birth. Consequently, many aspects of neonate behaviour are often near to being fully formed at birth. However, experience will often be required to shape the expression of the behaviour and improve its effectiveness. The immediate problems facing the neonate will be related to the overall reproductive strategy of the species. In pigs, sibling rivalry will be critical in establishing and maintaining fidelity to a teat, and this early conflict is probably most important for survival. The teat order that succeeds this early rivalry is probably not, however, the result of competition over the most productive teats but because of certain intrinsic advantages of teat fidelity that maximize growth. In sheep the need to quickly follow and solicit sucking only from the dam makes learning to recognise the mother a priority. Recent results suggest that the ability of the neonate lamb to recognize its mother has been under-estimated and that failure of lambs to recognise their mothers can make a significant contribution to mortality rates. Survival in any species is, however, not simply a matter of appropriate neonate behaviour but may depend critically on the quality of the interaction between the mother and offspring. It is difficult to determine the end of the neonate period given the often protracted nature of weaning. As weaning progresses there is a shift to bonding with siblings and peers and to an extent these relationships take over some of the social functions of the mother-infant relationship such as avoidance of predators. Lastly, experiences gained during the neonate period can have long-term effects on behaviour such as diet selection, social preferences and responses to fear with important implications for farmed livestock.

Recent advances in molecular biology have begun to identify many of the molecular mechanisms involved in the control of cellular differentiation and subsequent growth. However, while this information may ultimately permit manipulation of animal growth it is important to remember that the most essential factor for growth remains adequate nutrition. The high correlation of growth rate with milk intake in neonates reminds us that growth is highly dependent on the rapid establishment of enteral nutrition after birth. The endocrine changes consequent on this, as well as the supply of nutrients to support metabolic homeostasis, play important rôles in determining survival.

Birth is associated with dramatic changes in the secretion and plasma concentrations of many hormones (including insulin, glucagon, growth hormone (GH), triiodothyronine (T3), adrenaline and cortisol among others). However, while changes in secretion at this time may be of great significance for survival and adaptation during the perinatal period, after this it is only changes in the secretion of insulin and GH which appear closely related to neonatal growth. Sixty percent or more of variation in live-weight gain among lambs during the 1st month of life is positively associated with variation in plasma insulin levels, while associations with GH are strongly negative, despite the evidence for essentiality of GH as a promoter of insulin-like growth factor-1 (IGF-1) production. Observations on other species are consistent with those in lambs.

Investigations in foetal lambs have established that insulin's crucial rôle as a primary regulator of anabolic metabolism and growth begins well before birth. However, while birth does not alter this important rôle, the establishment of enteral nutrition changes the way in which its secretion is modulated and increases its rôle as the principal endocrine regulator of glucose homeostasis. Secretion of gastrointestinal hormones in response to the first food plays an important rôle in this, modulating the secretion of insulin and promoting gut development through trophic actions on the mucosa. Insulin itself, also appears to have trophic effects on the liver and is probably an important determinant of nutritionally mediated alterations in hepatic IGF-1 production. Plasma IGF-1 concentrations, like those of insulin, are highly correlated with the rate of postnatal growth, but unlike insulin, the status of plasma IGF-1 as a direct regulator of cellular growth remains controversial. IGF-1 and the large molecular weight proteins to which it is bound in plasma are synthesized by many peripheral tissues as well as the liver and it seems likely that IGF-1, in association with other specific growth factors, acts principally in the extravascular compartment, as a local paracrine/autocrine regulator of cellular differentiation and growth. Whatever the status of the plasma IGF-1 pool its concentration appears to act as a useful index of the rate of tissue growth. While GH is essential for normal postnatal growth and the production of IGF-1, it does not appear rate-limiting in relation to nutritionally determined variations in growth rate. This contrasts strikingly with its rôle in growth manipulation.

Early postnatal intestinal development involves the preparation of the intestinal epithelium for extrauterine life when maternal secretions provide the sole nutrient source. A further shift in the digestive capability of the epithelium occurs later in development with the introduction of complex solid foods. Ontogenesis involves extensive epithelial cell proliferation and cytodifferentiation including changes in the expression of enzymes, receptors and transport systems and is regulated through the interaction of endogenous and exogenous factors. The mucosal epithelium plays a key rôle in the reception and transmisson of these trophic signals. In particular, the interplay between dietary constituents and microvillar membranes exerts profound influence on intestinal development and adaptation during the postnatal period.

Strategies to reduce the relatively high incidence of death and disease in young animals must be based on an understanding of the particular metabolic requirements in the period from birth to weaning. In this period, substrate availability and the pathways of substrate utilization differ from those of the foetus and of the adult. Metabolic requirements must be met from the energy stores laid down before birth and from the nutrients present in colostrum and milk. The young animal has a large glucose demand and after exhaustion of hepatic glycogen reserves this must be met by gluconeogenesis. Initiation of gluconeogenesis requires concomitant oxidation of fatty acids, either derived from adipose tissue or from the diet. The young animal is particularly susceptible to hypothermia. Non-shivering thermogenesis in brown adipose tissue uses fatty acids to uncouple oxidation from phosphorylation and also as the major oxidative substrate. In addition, non-shivering thermogenesis is dependent on a minimum concentration of circulating glucose. Shivering thermogenesis is initially fuelled by oxidation of intra-muscular glycogen and then primarily by dietary fat. Growth of white adipose tissue by deposition of dietary fatty acids is an important feature of the metabolism of many species before weaning and this may have several survival advantages.

Refinements in the techniques used for incorporation of fat and spray drying have improved the nutritional value of milk substitutes. The significance of these developments in protein separation and evaporation/spray drying technology are demonstrated in the new range of substitutes for colostrum which not only have a high nutritional value but also contain active immunoglobulins.

Whilst milk replacers still remain a necessary outlet for excess skim milk powder production, progress has been made in the quality of novel ingredients available. The effect of European Community policy on the formulations used has been to divide milk replacers into two groups, those which do, and those which do not, contain at least 500 g/kg skim milk powder.

A whole range of products based on high protein whey powders has been developed in order to replace skim milk protein in milk replacers. Differences in these whey products reflect the method of manufacture and this has repercussions on their nutritional value. The benefits of ultrafiltration technology, developed for the human food industry, have recently become available to the whey-based milk replacer market.

Although the majority of milk substitutes are used for feeding calves, specific products have been developed for other species. Milk substitutes for lambs were introduced in the 1970s but there has been little commercial incentive for the use of alternatives to skim milk protein in the United Kingdom. Sow milk replacers are a more recent innovation and have taken advantage of developments in whey processing technology.

In the United Kingdom, the majority of pigs are weaned at 3 to 4 weeks of age. Prior to weaning the main source of nutrients is milk produced by the sow. After weaning, suitable complete diets need to be given that are compatible with the physiological state of the digestive system and supply adequate nutrient inputs to achieve maximal growth with minimum digestive upset. The weaning process, however, imposes considerable stress on the piglet which frequently results in a retardation of growth, often accompanied by problems associated with diarrhoea.

The challenge to the commercial nutritionist and the pig producer is to achieve sufficiently high nutrient intakes to reach the maximum growth potential. Improved understanding of the digestive physiology of the weaned pig and better estimations of the nutrient requirements of genetically improved stock has led to the development of appropriate diet specifications. There is a perpetual need to reconsider the most suitable food ingredients to use in diet formulations to meet these nutrient specifications, due to economic circumstances. The food ingredients need to be highly digestible, extremely palatable and to contain no anti-nutritive factor or antagonist to the digestive process. The food form and method of feeding can greatly influence food intake post weaning. The piglet weaning weight to age relationship can also affect the subsequent food intake, growth rate and incidence of problems associated with diarrhoea.

There are continual changes and developments within the animal food and pig production industries that affect nutrition of the young pig. These include genetic selection for prolificacy, development of outdoor pig breeding systems, ‘green issues’ including welfare and use of food additives, use of enzymes and probiotics and improvements in food production technology. In the development of diets for young pigs all these aspects need to be considered in achieving an optimal solution in terms of nutrition, management and economics.

Young calves and lambs are weaned early to reduce the amount of milk products consumed and potentially improve the profitability of rearing enterprises. At weaning the pre-ruminant must make a number of adjustments to cope with the change in dietary substrate. The microbial population in the rumen must develop and metabolic changes are required in order for the young ruminant to metabolize the end products of microbial digestion. It is recognized that early weaning poses a stress to the calf but it is generally considered that the calf rapidly adjusts to the change in diet composition. A number of factors indicate that considerable advantage would be gained from delaying the weaning of calves and indeed that the calf is not physiologically capable of adapting to an early-weaning regime. Work has indicated that a diverse anaerobic microbial population can be identified in the developing rumen of the calf. More recent results show that the presence of a faculative anaerobic population, which exists for a considerable period of time, has an adverse effect on the development of a mature anaerobic population. Low rumen pH is a problem in the young calf. The level of rumen pH verges on that which would be described as acidosis in the adult ruminant. The young calf is unable to stabilize rumen pH and increasing the level of dry food intake at weaning may further depress rumen pH if the salivary buffering capacity of the calf is not adequately developed. Results indicate that the ability to utilize volatile fatty acids is not fully developed in the young calf and that early weaning can result in high levels of VFAs in the circulation.

The composition of the dry diet has a major effect on the response of the calf to weaning. Choice of the ingredients can affect the buffering capacity of the rumen and the physiological development of the digestive tract. Strategies to limit the nutrient intake from dry food to levels commensurate with the developing physiology of the calf may result in a more uniform transition to full ruminant status with consequent benefits in growth rate and health.

There are many agents which can assist in ensuring neonatal survival and growth. The most important is still colostrum and although there are many substitutes available, the best of which will be prepared from colostrum of the same species (cattle, sheep and goats), or where this is impracticable, from plasma or serum (horses, pigs). Other agents which can enhance viability include antibiotics, probiotics, vitamins, minerals, the lactoperoxidase system, lactoferrin, lysozyme, hyperimmune sera, vaccines, acidifiers, enzymes and oligosaccharides. Many probiotic products are available containing different organisms which may be live or dead. Probiotics have been available for many years as nutritional supplements. However, results obtained with them have been variable and often of dubious validity. There is at present a trend to suggest such products have therapeutic or prophylactic activity. Thus it would appear that they are developing along the reverse route to that of antibiotics which initially were used for therapy or prevention, only later to be used as food additives and growth promoters. It is likely that any successful probiotic will need to meet criteria laid down by proponents of their use in human beings 50 years ago. These include that they contain live organisms capable of multiplication in the alimentary tract and of a strain indigenous to the species. A large number of organisms will be required daily and the diet of the animal will need to be defined. It would appear that treatment should commence as soon as possible after birth.

As therapeutic claims are often directly or indirectly implied it would seem justified that probiotics should be registered and criteria for their evaluation discussed. Results of recent trials with oral colostrum substitute and injection of hyperimmune serum are used to illustrate the type of trials likely to be required for probiotics.

Other methods of enhancing survival are discussed.

Management information can be used as a substitute for other business resources. Sheep farmers may find such substitution provides a means to maintain incomes as the price of information falls relative to other scarce resources during the severe cost price squeeze they are currently experiencing.

To illustrate how management information may be obtained and used, a multivariate regression technique is described. This is applied to data on the physiological responses of newborn lambs to cold exposure. It shows that an increase of one standard deviation in total body insulation provides a significantly greater direct response in cold resistance in lambs bred for high cold resistance (HCR) compared with lambs bred for low cold resistance (LCR). The countervailing correlated drop in peak metabolic response to cold exposure did not show a significant between-line difference. This information suggests that HCR lambs give a metabolically more efficient response to cold exposure than LCR lambs. Subsequent research has provided physiological evidence to corroborate these findings.

The cold resistance of lambs has been shown to be related to lamb survival in the field. Information obtained about the response of individuals or groups of lambs to cold exposure by methods such as those described here may suggest more cost-effective steps that managers should take in order to exploit to the full the varying abilities to resist cold. This in turn should improve enterprise gross output by reducing lamb mortality. It should also reduce costs by ensuring that steps to control cold exposure or alleviate its symptoms are provided only when necessary.

A system of high-care calf rearing which was developed and demonstrated at the National Agricultural Centre Beef and Calf Unit is described. The unit reared around 600 calves per year which were purchased at 2 to 3 weeks of age, reared and then transferred to one of several finishing systems on the unit. The system depends on good calf nutrition, airy buildings which were rested regularly, careful disinfection of equipment and buildings and a programme of health management.

The calves were purchased mostly in batches of about 40 from a farmers' co-operative and reared on milk replacer which was restricted and given twice daily to force a discipline for inspection of calves. They were also fed through teats which gave more efficient food conversion than buckets. They were penned in pairs because it had been found they were less stressed in pairs than penned singly. Detail of management and health routines are described. Target live-weight gains on the system were 0.5kg per day up to weaning and 1.0 kg per day thereafter. For simplicity the commercial names of foods, drugs and vaccines are given.

In the pig industry the mortality of piglets both during the birth process and in the subsequent 3 to 5 weeks is unacceptably high. This review attempts to summarize the major causes of these losses and to suggest means whereby such losses may be minimized in the commercial situation. Stillbirth rate is discussed in relation to various management regimes and it is concluded that anoxia (the primary cause of intra-partum piglet deaths) may be minimized by the provision of careful assistance during the birth process. Pre-weaning mortality is presented as a complex interaction of factors predominant amongst which are overlying by the sow, chilling, starvation and infection. Each of these areas is discussed in detail and recommendations are made to reduce their negative influence on the survival rate of piglets. Finally, the rōle of piglet activity level/vigour is considered in relation to pre-weaning survival rate. Various factors are discussed in relation to piglet vigour and it is concluded that the two major contributors to low activity level/vigour are intra-partum hypoxia and the endocrine status of the sow and piglet at birth. To reduce hypoxia, careful intervention is again suggested. The rôle of endocrine status is yet to be fully established but promising results are presented on the use of oestradiol treatment of piglets at birth to raise activity level and reduce pre-weaning mortality rate.

The newborn lamb lacks circulating antibodies and relies on an early and adequate intake of colostrum for passive protection against disease and for energy (Black, Francis and Nicholls, 1985; Mellor, 1990). However, lambs may receive less colostrum than they require because of sibling competition, maternal undernutrition or udder disease. Colostrum insufficiency accounts for about 25% of perinatal lamb deaths world wide (Khalaf, Doxey and Baxter, 1979).

Powdered colostrum substitutes may be used to supplement ‘at risk’ lambs but, because the products are manufactured outside the United Kingdom (UK), mainly from bovine sources, their relevance to UK sheep enterprises is uncertain. Further, their available energy content is low because the main constituent, protein, is not catabolized by newborn lambs (Mellor and Cockburn, 1986). The present work measured the ability of one substitute derived from bovine whey (based on ProLAM, Fisons Animal Health Ltd), with or without supplementary glucose; to prevent disease and promote growth to 3 months in lambs reared in typical UK farm conditions.

The prolific ewe can be regarded as a valuable asset only if she produces viable lambs and, at the same time, sufficient colostrum to meet their needs for energy (MJ) and immunoglobulin (Ig) in the first days of life.

The energy requirements of the lamb will depend on its weight and the climatic conditions of its surroundings. Mellor and Murray (1986) recommend 180 ml colostrum per kg body weight during the first 18 h of life for lambs born indoors and 210 ml/kg body weight for lambs born in field conditions. The Ig requirement of the lamb will depend on its size and the disease challenge of the environment into which it is born.

Although lower immunoglobulin G (IgG) levels have been recorded in dead lambs compared with live lambs (Halliday, 1968 and 1978; Khalaf, Doxey, Baxter, Black, FitzSimons and Ferguson, 1979), it has been shown that many lambs having low serum IgG levels do survive (Halliday, 1974) and some with high levels die (Halliday, 1978).

The minimum intake of colostrum required for passive immunity is not known, but it is probably considerably less than that needed to meet the energy requirements (Mellor and Murray, 1986). Spedding, Treacher and Penning (1970) showed that as little as 8 g colostrum per kg lamb birth weight can provide protection from disease. Under poor conditions of hygiene this would probably not be sufficient. It thus seems likely that provided that the energy requirement of the lamb is met by feeding it colostrum, the Ig requirement will also be met.

It has been suggested (Mills, 1981) that there was a lack of research on the effects of cobalt (Co) deficiency on the reproductive performance of sheep. Duncan, Morrison and Garton (1981) reported that clinically Co-deficient ewes produced fewer lambs with a higher incidence of stillbirths and neonatal mortalities than Co-sufficient animals. Garton, Duncan and Fell (1981) related these findings to the vitamin B12 and methylmalonic acid status of dams. However, their investigations used few animals and were therefore inconclusive. The objectives of this work were to investigate the effects of subclinical Co deficiency in pregnant hill sheep on reproductive performance and neonatal lamb viability.

Experiment 1 (1985/86) comprised 60 Scottish Blackface × Swaledale ewes, while experiment 2 (1986/87) included 30 of these animals plus 30 pure Scottish Blackface sheep. In both experiments the ewes were housed and bedded on sawdust and a Co-deficient diet of timothy hay, micronized maize, maize gluten, dibasic calcium phosphate and sodium chloride was offered. Skimmed milk powder was introduced to the diet during lactation. The Co content of the diet was 0.06 mg Co per kg dry matter.

A major financial and welfare problem is the loss of 1 to 4 million lambs annually in the United Kingdom (Slee, 1979) with many of these deaths being caused by failure of the lamb to maintain normal thermoregulatory responses in the cold. This may be associated with a change in the response to cold exposure from non-shivering thermogenesis (NST) to shivering thermogenesis (ST) as brown adipose tissue (BAT) is replaced by white adipose tissue over the first 2 weeks of life in the lamb (Symonds, Andrews and Johnson, 1989).

It has been shown that environmental temperature can affect BAT development in the lamb (Gemmel, Bell and Alexander, 1972) and calf (Casteilla, Champigny, Bouilland, Robelin and Riquier, 1989) but it is not known what effect this has on the thermogenic capacity of BAT or how it may alter the ability of the lamb to thermoregulate.

This study investigated the effect of artificially rearing lambs at warm or cold ambient temperatures on the thermogenic capacity of BAT and the extent to which metabolic rate and the ability to respond to warm and cold challenges was altered by these treatments over the first 9 days of life.

In the ovine foetus brown adipose tissue (BAT) is mainly found in the perirenal region and grows rapidly relative to body weight between 70 to 120 days of gestation (Alexander, 1978). After this stage only a small amount of BAT growth occurs in comparison with that of the whole foetus, and in the case of undernutrition may decline (Alexander, 1978). Maternal cold stress, induced by winter shearing twin-bearing pregnant ewes 8 weeks before parturition improves lamb birth weight and lamb growth rate independently of effects on maternal food intake (Symonds, Bryant and Lomax, 1986 and 1990). At the same time this can stimulate the in vivo capacity for non-shivering thermogenesis in newborn lambs (Stott and Slee, 1985). The following study extends these findings by investigating the extent to which changing the maternal metabolic environment influences BAT development over the final month of gestation.

Thirty-two Bluefaced Leicester × Swaledale ewes were housed individually at ambient temperature (−6 to 19°C) 6 weeks prior to lambing and 2 weeks later 15 ewes were shorn. Ewes were offered daily a diet comprising 200 g barley concentrate and 1 kg chopped hay. Between 116 and 145 days of gestation and within 2 h of birth ewes were humanely slaughtered with an overdose of barbiturate and foetal or neonatal perirenal BAT sampled, born from shorn or unshorn ewes. The thermogenic capacity of BAT was assessed by guanosine-5′-diphosphate (GDP) binding to uncoupling protein in mitochondrial preparations (Cooper, Dascombe, Rothwell and Vale, 1989) and the amount of mitochondrial protein measured from cytochrome Coxidase activity.