Plasma Leptin Is Regulated Predominantly by Nutrition in Preruminant Lambs

Effects of birth weight and dietary fat on intake, body composition, and plasma thyroxine in neonatal lambs

Intrauterine growth restriction (IUGR) is often observed in one of the fetuses carried by well-fed prolific ewes. This condition is the result of an insufficient placental size to cover the nutritional needs of the fetus during the near exponential growth phase of the last trimester. After birth, these IUGR offspring have an elevated appetite and lower maintenance energy requirements, suggesting dysregulation of homeostatic systems governing energy metabolism. It is also unknown whether the consequent increase in fatness occurs similarly in both visceral and carcass fractions. To address these questions, lambs differing in birth size (BS, IUGR vs. Normal, 2.6 ± 0.05 vs. 4.2 ± 0.07 kg, P < 0.001) were offered unlimited amounts of a low fat [LF; 22% of dry matter (DM)] or a high fat (HF; 38% of DM) milk replacer and slaughtered on day 14 of postnatal age (n = 7 to 8 for each BS × Diet); a second group of IUGR lambs (n = 3 for each diet) was slaughtered when they reached 8.5 kg, corresponding to the weight of Normal lambs on day 14. When normalized to body weight (BW), the DM and energy intake of IUGR lambs were higher than those of Normal lambs over the first 14 d of life (BS, P < 0.01), but contrary to expectations, the HF diet did not exacerbate these effects of the IUGR condition. Intrauterine growth restricted lambs had increased viscera fat with both diets (BS and Diet, P < 0.05) but increased carcass fat only with the LF diet (BS × Diet, P = 0.08); the fatness promoting effect of the IUGR condition was increased in both body fractions when lamb groups were compared at the fixed BW of 8.5 kg. A subset of metabolic hormones was analyzed, including the metabolic rate-setting hormone thyroxine (T4) and its possible positive regulator leptin. Plasma T4 was lower in IUGR than in Normal lambs at birth (P < 0.05) but then disappeared by day 7 of postnatal life (BS × Day, P < 0.01). On the other hand, the HF diet had no effect on plasma T4 over the first 3 d but caused an increase, irrespective of BS by day 11 (Diet × Day, P < 0.001). Plasma leptin increased with dietary fat and time (P < 0.06) but bore no relation to the effects of BS or Diet on plasma T4. These data show that IUGR and Normal lambs are similarly unable to adjust caloric intake in early life and that the fatness promoting effects of the IUGR condition are more pronounced in the viscera than in the carcass. These data also reveal dynamic regulation of plasma T4 by BS and Diet in neonatal lambs.

Associations of feed efficiency with circulating IGF-1 and leptin, carcass traits and meat quality of lambs

The aim of this study was to investigate the effects of feed efficiency classifications on live animal measurements, circulating IGF-1 and leptin concentrations, and carcass, non-carcass and meat quality traits of lambs. One-hundred and two lambs approximately 70 days-old with initial live weight of 24.6 ± 3.71 kg (mean ± SD) were individually fed for 56 days to determine residual feed intake (RFI) and residual feed intake and gain (RIG). Lambs were then classified as phenotypically Low-, Medium- or High-RFI and Low-, Medium- or High-RIG phenotypes. Circulating leptin and IGF-1 concentrations were higher in more efficient lambs (Low-RFI or High-RIG). Variation in RFI and RIG did not affect meat redness or tenderness, but High-RIG lambs had darker meat. These findings show that the phenotypically more efficient Low-RFI and High-RIG lambs produced carcasses with similar characteristics and meat quality as the less efficient High-RFI and Low-RIG lambs but have a strategic advantage of lower feed intake to achieve similar production outcomes.

Technical note: Effects of pegylation and route of administration on leptin kinetics in newborn lambs1

Chronic energy insufficiency resulting from inadequate feed intake or increased nutrient demand reduces plasma leptin in ruminants. Treatment of energy-deficient ruminants with exogenous leptin has identified some physiological consequences of reduced plasma leptin, but their full complement remains unknown. Additional leptin-dependent responses could be identified by using strategies that interfere with leptin signaling such as administration of leptin mutants that act as competitive antagonists. The effectiveness of these antagonists depends on their fold excess over endogenous leptin, and this condition can be achieved under in vivo conditions by extending the half-life (t1/2) of the antagonist by addition of a polyethylene glycol (PEG) molecule (pegylation). Use of this approach in ruminants, however, is limited by the lack of information on the t1/2 of native and pegylated leptin and on the most effective route of administration. To answer these questions, newborn lambs (n = 3) were injected with an intravenous (i.v.) bolus of 150 µg of human leptin followed by blood sampling over the next 12 h. Analysis of the semilog plasma leptin concentration over time yielded a t1/2 of 43 ± 4.9 min; an i.v. bolus of 276 µg of bovine leptin yielded a comparable t1/2 (P > 0.05). Next, newborn lambs (n = 4) received a single dose of 229 μg/kg of metabolic body weight (BW0.75) of pegylated super human leptin antagonist (PEG-SHLA) via the i.v. or subcutaneous (s.c.) route. Plasma PEG-SHLA concentration reached a peak of 1,528 ± 78 ng/mL after 1 min and a nadir of 71 ± 9 ng/mL after 24 h with the i.v. route versus a peak of 423 ± 43 ng/mL after 300 min and a nadir of 146 ± 22 ng/mL after 24 h for the s.c. route; the t1/2 of PEG-SHLA was 394 ± 29 min for the i.v. route and 433 ± 58 min for the s.c. route. Finally, plasma concentration of PEG-SHLA was modeled when given either i.v. or s.c. at a dose of 229 μg/kg BW0.75 every 12 h. Once a steady state was reached, peak and lowest concentrations PEG-SHLA over the 12-h windows were 2,269 and 403 ng/mL for the i.v. route and 814 and 555 ng/mL for the s.c. route. Weighted PEG-SHLA concentrations over the 12-h period were 1,455 and 713 ng/mL for the i.v. and s.c. route, translating into 364- and 178-fold excess over endogenous plasma leptin. These data confirm the effectiveness of pegylation in extending the t1/2 of leptin antagonists in newborn lambs and in increasing their circulation in fold excess over endogenous leptin.

Epigenetics and developmental programming of welfare and production traits in farm animals

The concept that postnatal health and development can be influenced by events that occur in utero originated from epidemiological studies in humans supported by numerous mechanistic (including epigenetic) studies in a variety of model species. Referred to as the 'developmental origins of health and disease' or 'DOHaD' hypothesis, the primary focus of large-animal studies until quite recently had been biomedical. Attention has since turned towards traits of commercial importance in farm animals. Herein we review the evidence that prenatal risk factors, including suboptimal parental nutrition, gestational stress, exposure to environmental chemicals and advanced breeding technologies, can determine traits such as postnatal growth, feed efficiency, milk yield, carcass composition, animal welfare and reproductive potential. We consider the role of epigenetic and cytoplasmic mechanisms of inheritance, and discuss implications for livestock production and future research endeavours. We conclude that although the concept is proven for several traits, issues relating to effect size, and hence commercial importance, remain. Studies have also invariably been conducted under controlled experimental conditions, frequently assessing single risk factors, thereby limiting their translational value for livestock production. We propose concerted international research efforts that consider multiple, concurrent stressors to better represent effects of contemporary animal production systems.

Variation in physiological profiles may explain breed differences in neonatal lamb thermoregulation

Ability to adapt rapidly from the uterine environment to self-thermoregulation following birth is a vital requirement for neonatal lamb survival. This investigation reports factors that could explain differences in thermoregulation among breeds that differ in lamb survival. Breeds such as the Merino and Border Leicester have previously been shown to be divergent for birthweight, cold resistance and lamb survival. Cross-bred (Poll Dorset Border Leicester (PDBL, n = 9) and Poll Dorset Merino (PDM, n = 25)) and pure-bred (Border Leicester (BL, n = 35) and Merino (M, n = 46)) lambs were recorded for the thermogenic measures rectal temperature at birth, cold resistance (time for rectal temperature to fall to 35°C while in a cooled water bath) and cold recovery (time to restore rectal temperature after cold exposure) at 1 day of age. In pure-bred lambs, 1 kg increase in weight resulted in a 0.25°C increase in rectal temperature at birth (P < 0.001) and 4.2 min increase in cold resistance (P < 0.001). In contrast, cross-bred lambs did not exhibit any relationship between birthweight and rectal temperature at birth, although they displayed a 3.2 min greater cold resistance for every 1 kg increase in birthweight (P < 0.001). BL-derived lambs were more cold resistant than M lambs (cross-bred: PDBL, 67.1 ± 2.5 min; PDM, 56.4 ± 1.6 min; P < 0.01; and pure-bred: BL, 58.1 ± 1.5 min; M, 53.2 ± 1.3 min; P < 0.01). The quadratic relationship of glucose concentration over time during cold exposure differed with lamb breed. PDBL exhibited higher peak glucose concentrations than did PDM (11.0 mmol/L and 8.9 mmol/L, respectively; P < 0.01). BL took longer to reach peak glucose concentration (50 min) than did M (40 min) and this peak value was higher (BL, 9.4 mmol/L; M, 7.7 mmol/L; P < 0.001). In conclusion, variations in birthweight and glucose metabolism are associated with breed differences in thermogenesis of neonatal lambs.

Reproduction Symposium: hypothalamic neuropeptides and the nutritional programming of puberty in heifers

Nutrition during the juvenile period has a major impact on timing reproductive maturity in heifers. Restricted growth delays puberty, whereas elevated BW gain advances the onset of puberty. The initiation of high-frequency episodic release of GnRH and, consequently, LH during the peripubertal period is crucial for maturation of the reproductive axis and establishment of normal estrous cycles. Nutritional signals are perceived by metabolic-sensing cells in the hypothalamus, which interact with estradiol-receptive neurons to regulate the secretory activity of GnRH neurons. The orexigenic peptide, neuropeptide Y (NPY), and the anorexigenic peptide derived from the proopiomelanocortin (POMC) gene, melanocyte-stimulating hormone α (αMSH), are believed to be major afferent pathways that transmit inhibitory (NPY) and excitatory (αMSH) inputs to GnRH neurons. The neuropeptide kisspeptin is considered a major stimulator of GnRH secretion and has been shown to mediate estradiol's effect on GnRH neuronal activity. Kisspeptin may also integrate the neuronal pathways mediating the metabolic and gonadal steroid hormone control of gonadotropin secretion. Recent studies in our laboratories indicate that functional and structural changes in the pathways involving NPY, POMC, and kisspeptin neurons occur in response to high rates of BW gain during the juvenile period in heifers. Changes include regulation of expression in NPY, POMC, and KISS1 and plasticity in the neuronal projections to GnRH neurons and within the neuronal network comprising these cells. Moreover, an intricate pattern of differential gene expression in the arcuate nucleus of the hypothalamus occurs in response to feeding high concentrate diets that promote elevated BW gain. Genes involved include those controlling feeding intake and cell metabolism, neuronal growth and remodeling, and synaptic transmission. Characterizing the cellular pathways and molecular networks involved in the mechanisms that control the timing of pubertal onset will assist in improving existing strategies and facilitate the development of novel approaches to program puberty in heifers. These include the use of diets that elevate BW gain during strategic periods of prepubertal development.

The metabolic profile of growing lambs fed diets rich in unsaturated fatty acids

The effect of two diets enriched with unsaturated fatty acids--one containing the addition of dried distillers grains with solubles (DGS) and the other the addition of false flax--Camelina sativa cake (CS)--on some metabolic parameters and hormone concentration in growing lambs was determined in this experiment. A total of 21 ram lambs of the Polish Whiteheaded mutton sheep were divided into three groups (the control, receiving DGS and CS). The diets were administered to animals for 6 weeks. During the experiment, peripheral blood was collected. Glucose (GL), total cholesterol (CH), triglycerides (TG), free fatty acids (FFA), insulin (IN), leptin (LE), triiodothyronine (T3) and thyroxine (T4) were assayed in serum. The age-dependent reduction in CH and TG limited by both experimental diets were observed. A significant increase in FFA concentration was observed in samples collected in the last, that is, third, time period. This was most probably caused by a 12-h pre-slaughter fasting period. A significantly lower dynamic of FFA increase in that experimental period was found in animals receiving the experimental feed. Insulin concentration in DGS-receiving lambs was increased, in contrast to the CS-receiving lambs, in which it was lower when compared to the control. LE concentration was decreased by both experimental diets, more markedly in the DGS-receiving animals. No differences between the experimental groups and the control were observed in T3 and T4 concentrations. The effect of 12-h pre-slaughter fasting was statistically highly significant for the levels of examined blood markers and hormones, except for TG and IN in the group of lambs receiving the experimental diet with CS.

Impact of embryo donor adiposity, birthweight and gender on early postnatal growth, glucose metabolism and body composition in the young lamb

Intrauterine growth restriction (IUGR) is a risk factor for metabolic syndrome, notably when associated with rapid postnatal catch-up growth. A sheep paradigm was used to assess relationships between prenatal and early postnatal growth trajectories, metabolism and body composition. Singletons (single-sire embryo transfer from obese and control donors) were gestated and suckled by overnourished adolescent dams and categorised by birthweight as IUGR or normal (N). Gestation length was equivalent in both categories and all lambs were delivered spontaneously preterm (PT; mean (± s.e.m.) 139.8 ± 1.7 days; term = 145–147 days). The IUGR lambs were smaller at birth, but fractional growth rates (FGR) for eight anthropometry parameters were higher and independent of gender (except thorax girth; males (M) < females (F)). At Day 48, fasting glucose (IUGR > N; M > F) and first-phase insulin response (to 20 min; IUGR < N; M < F) after glucose were influenced by prenatal growth and gender. Embryo donor adiposity influenced glucose tolerance only. Plasma insulin, insulin-like growth factor-1 (M > F) and leptin (M < F) were influenced by gender but not prenatal growth. At necropsy (Day 77), IUGR plus PT lambs had decreased carcass and visceral organ weights, but carcass composition was not different from N plus PT. In contrast, M were heavier, with lower internal fat mass, carcass fat percentage and perirenal fat leptin mRNA than F. Therefore, IUGR was associated with increased postnatal FGR and altered glucose handling, but, without absolute catch-up growth, gender had the predominant influence on postnatal leptinaemia and adiposity.

Late foetal life nutrient restriction and sire genotype affect postnatal performance of lambs

This experiment investigates the effects of maternal nutrient restriction in late gestation on the offsprings' postnatal metabolism and performance. Forty purebred Shropshire twin lambs born to ewes fed either a high-nutrition diet (H) (according to standard) or a low-nutrition (L) diet (50% during the last 6 weeks of gestation) were studied from birth until 145 days of age. In each feeding group, two different sires were represented, 'growth' (G) and 'meat' (M), having different breeding indices for the lean : fat ratio. Post partum all ewes were fed the same diet. Lambs born to L-ewes had significantly lower birth weights and pre-weaning growth rates. This was especially pronounced in L-lambs born to the M-ram, which also had markedly lower pre-weaning glucose concentrations than the other three groups of lambs. L-lambs converted milk to live weight with an increased efficiency in week 3 of life. Their glucose concentrations and growth rates were both increased. Plasma glucose concentrations in LM-lambs became similar to those observed in H-lambs post-weaning. However, LM-lambs continued to be lighter than the other groups throughout the experimental period and were unable to compensate for the reduced weight at birth despite having the highest daily fractional growth rates. LG-lambs had the highest plasma glucose concentrations of all four groups of lambs, and they indeed reached body weights comparable to those of the H-lambs by 145 days of age. The increased growth rate post-weaning in L-lambs was not reflected in fat deposition, as L-lambs had lower fat deposition than H-lambs. This may relate to the lower plasma insulin levels found in the L-lambs than in the H-lambs. In conclusion, a 50% reduction of maternal nutrient supply in the last 6 weeks of gestation reduces the birth weight and pre-weaning growth of the offspring due to lower milk intake. Growth rates can be restored when an adequate post-weaning diet is provided, but the prenatal nutrition may programme postnatal metabolism differentially depending on genotype, thus affecting the ability of the ad libitum-fed lamb to achieve a given body weight by a certain age.

Selected hormonal and neurotransmitter mechanisms regulating feed intake in sheep

Appetite control is a major issue in normal growth and in suboptimal growth performance settings. A number of hormones, in particular leptin, activate or inhibit orexigenic or anorexigenic neurotransmitters within the arcuate nucleus of the hypothalamus, where feed intake regulation is integrated. Examples of appetite regulatory neurotransmitters are the stimulatory neurotransmitters neuropeptide Y (NPY), agouti-related protein (AgRP), orexin and melanin-concentrating hormone and the inhibitory neurotransmitter, melanocyte-stimulating hormone (MSH). Examination of messenger RNA (using in situ hybridization and real-time PCR) and proteins (using immunohistochemistry) for these neurotransmitters in ruminants has indicated that physiological regulation occurs in response to fasting for several of these critical genes and proteins, especially AgRP and NPY. Moreover, intracerebroventricular injection of each of the four stimulatory neurotransmitters can increase feed intake in sheep and may also regulate either growth hormone, luteinizing hormone, cortisol or other hormones. In contrast, both leptin and MSH are inhibitory to feed intake in ruminants. Interestingly, the natural melanocortin-4 receptor (MC4R) antagonist, AgRP, as well as NPY can prevent the inhibition of feed intake after injection of endotoxin (to model disease suppression of appetite). Thus, knowledge of the mechanisms regulating feed intake in the hypothalamus may lead to mechanisms to increase feed intake in normal growing animals and prevent the wasting effects of severe disease in animals.

Leptin in farm animals: where are we and where can we go?

Fat affects meat quality, value and production efficiency as well as providing energy reserves for pregnancy and lactation in farm livestock. Leptin, the adipocyte product of the obese (ob) gene, was quickly seen as a predictor of body fat content in animals approaching slaughter and an aid to assessing reproductive readiness in females. Its participation in inflammation and immune responses that help animals survive infection and trauma has clear additional relevance to meat and milk production. Furthermore, almost a decade of discoveries of nucleotide polymorphisms in the leptin and leptin receptor genes has suggested useful applications relating to feed intake regulation, the efficiency of feed use, the composition of growth, the timing of puberty, mammogenesis and mammary gland function and fertility in cattle, pigs and poultry. The current review attempts to summarise where research has taken us in each of these aspects and speculates on where future research might lead.

Placental restriction increases adipose leptin gene expression and plasma leptin and alters their relationship to feeding activity in the young lamb

Low birth weight and catch-up growth predict increased adiposity in children and adults. This may be due in part to leptin resistance, as adults who were born small exhibit increased plasma leptin concentration relative to adiposity. Placental restriction (PR), a major cause of intrauterine growth restriction, reduces size at birth and increases feeding activity and adiposity by 6 wk in sheep. We hypothesized that PR would increase plasma leptin concentration and alter its relationship with feeding activity and adiposity in young lambs. Body size, plasma leptin, feeding activity, adiposity, leptin, and leptin receptor gene expression in adipose tissue were measured (12 control, 12 PR). PR reduced size at birth and increased adiposity. Plasma leptin concentration decreased with age, but to a lesser extent after PR and correlated positively with adiposity similarly in control and PR. PR increased plasma leptin concentration and perirenal adipose tissue leptin expression. Feeding activity correlated negatively with plasma leptin concentration in controls, but positively after PR. PR increases adipose tissue leptin expression and plasma leptin concentration, however, this increased abundance of peripheral leptin does not inhibit feeding activity (suckling event frequency), suggesting PR programs resistance to appetite and energy balance regulation by leptin, leading to early onset obesity.

Protein restriction during gestation and/or lactation causes adverse transgenerational effects on biometry and glucose metabolism in F1 and F2 progenies of rats

Substantial evidence suggests that poor intrauterine milieu elicited by maternal nutritional disturbance may programme susceptibility in the fetus to later development of chronic diseases, such as obesity, hypertension, cardiovascular disease and diabetes. One of the most interesting features of fetal programming is the evidence from several studies that the consequences may not be limited to the first-generation offspring and that it can be passed transgenerationally. In the present study, female rats (F0) were fed either a normal-protein diet [control diet (C); 19 g of protein/100 g of diet] or a low-protein diet [restricted diet (R); 5 g of protein/100 g of diet]. The offspring were termed according to the period and the types of diet the dams were fed, i.e. CC, RC, CR and RR (first letter indicates the diet during gestation and the second the diet during lactation). At 3 months of age, F1 females were bred to proven males, outside the experiment, to produce F2 offspring. At weaning, F2 offspring were divided by gender. RC1 offspring (with the number indicating the filial generation) were born with low birthweight, but afterwards they had catch-up growth, reaching the weight of the CC1 offspring. The increased glycaemia in RC1 offspring was associated with insulin resistance. CR1 and RR1 offspring had impaired growth with no changes in glucose metabolism. RC2 offspring had high BM (body mass) at birth, which was sustained over the whole experiment in male offspring. The F2 generation had more alteration in glucose metabolism than the F1 generation. CR2 and RC2 offspring had hyperglycaemia accompanied by hyperinsulinaemia and insulin resistance in both genders. CR2 offspring had an increase in body adiposity with hyperleptinaemia. In conclusion, low protein during gestation improves BM, fat mass and growth rate in F1 rats, but has adverse effects on glucose and leptin metabolism, resulting in insulin resistance in adult F1 and F2 offspring. Low protein during lactation has adverse effects on glucose, insulin and leptin metabolism, resulting in insulin resistance in adult F2 offspring. These findings suggest that low protein during gestation and/or lactation can be passed transgenerationally to the second generation.

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Maternal undernutrition during early to mid-gestation in the ewe results in altered growth, adiposity, and glucose tolerance in male offspring

This study utilized maternal undernutrition from early to midgestation in the ewe to determine the impact(s) of intrauterine growth restriction on postpartum growth of male offspring and the potential mechanisms involved. Multiparous ewes were fed 50% (nutrient-restricted) or 100% (control-fed) of their nutrient requirements (NRC, 1985) between d 28 and 78 of gestation, and then all ewes were fed 100% of the NRC requirements from d 79 through lambing. Male lambs born to nutrient-restricted (n = 9) and control-fed (n = 9) ewes exhibited similar BW (5.8 vs. 6.0 +/- 0.3 kg) and crown-rump lengths (53.8 vs. 55.4 +/- 1.0 cm) at birth. At 63 and 250 d of postnatal age, wether lambs were subjected to a glucose tolerance test, in which a bolus of glucose was administered i.v. to evaluate changes in glucose and insulin concentrations. After i.v. glucose administration at 63 d of age, lambs from nutrient-restricted ewes exhibited a greater area under the curve for glucose (AUCg; 6,281 vs. 5,242 +/- 429; P < 0.05) and insulin (AUCi; 21.0 vs. 8.6 +/- 1.9; P < 0.001) than lambs from control-fed ewes. After glucose administration at 250 d of age, lambs from nutrient-restricted ewes had greater AUCg (7,147 vs. 5,823 +/- 361; P < 0.01) but a lower AUCi (6.4 vs. 10.2 +/- 1.9; P = 0.05) than lambs from control-fed ewes. Lambs from nutrient-restricted ewes were heavier (26.6 vs. 21.8 +/- 2.3 kg; P < 0.05) and had more backfat (0.30 vs. 0.21 +/- 0.03 cm, P < 0.05) by 4 mo of age than the lambs from control-fed ewes. At slaughter at 280 d of age, lambs from nutrient-restricted ewes remained heavier than lambs from control-fed ewes, had greater (P < 0.05) amounts of kidney and pelvic-area adipose tissue, and tended (P < 0.10) to have reduced LM and semitendinosus muscle weights as a percentage of HCW. These data demonstrate that a bout of maternal undernutrition during early to midgestation in sheep increased BW and fat deposition during adolescence and dysregulated glucose uptake in the absence of any change in birth weight.

Prenatal programming of postnatal productivity and health of livestock: a brief review

Human epidemiological evidence has suggested that metabolic perturbations during fetal life may increase predisposition to cardiovascular disease, type 2 diabetes and obesity in later life. A growing number of controlled experiments on sheep and other large animal species are adding to the already large body of experimental evidence from rat studies in supporting the ‘fetal origins’ hypothesis. Of particular practical relevance are findings that maternal undernutrition in late pregnancy can predispose lambs to glucose intolerance and increased adiposity in early adulthood. This effect may be exacerbated by high energy intakes and limited capacity for muscle growth in undernourished or growth-retarded lambs during early postnatal life. Recent Australian studies have demonstrated the effects of prenatal nutrition on postnatal growth and meat production in beef cattle, and on quantity and quality of wool production in sheep.

Fetal origins of insulin resistance and obesity

A number of epidemiological studies worldwide have demonstrated a relationship between poor early growth and an increased susceptibility to insulin resistance, visceral obesity, type 2 diabetes and other features of the metabolic syndrome in adulthood. However, the mechanistic basis of this relationship and the relative roles of genes and the environment remain a subject of debate. The 'thrifty phenotype' hypothesis proposes that poor fetal nutrition leads to programming of metabolism and an adult phenotype that is adapted to poor but not plentiful nutrition. The maternal reduced-protein rat model has been used to examine the importance of the maternal environment in determining susceptibility to adult disease. Pregnant and lactating rat dams are fed a diet containing 80 g protein/kg as compared with 200 g protein/kg, which leads to growth restriction in utero. Offspring of low-protein dams have increased susceptibility to diabetes, insulin resistance and hypertension when fed a palatable high-fat diet that promotes obesity. Administration of leptin during pregnancy and lactation to these protein-restricted dams produces offspring that have increased metabolic rate and do not become obese or insulin resistant when fed on a high-fat diet. Increased glucocorticoid exposure, particularly during late gestation, has been linked with insulin resistance in adulthood. High levels of fetal glucocorticoids may result from a decreased activity of placental 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2, which normally protects the fetus from high maternal glucocorticoid levels. Leptin administration to protein-restricted dams inhibits the suppression of 11beta-HSD-2 and may be one mechanism by which the metabolic syndrome is prevented.

Effects of Age and Nutrition on Expression of CD25, CD44, and l-Selectin (CD62L) on T-cells from Neonatal Calves

Effects of the plane of nutrition and age on the proliferation and activation of lymphocyte subsets from milk replacer-fed calves were investigated in vitro. Holstein calves were fed a standard (0.45 kg/d of a 20% crude protein, 20% fat milk replacer, n = 4) or intensified (1.14 kg/d of a 28% crude protein, 20% fat milk replacer, n = 4) diet from 1 to 8 wk of age. Average daily weight gain of intensified-diet (0.66 kg/d) calves was greater than that of standard-diet (0.27 kg/d) calves. Relative to the pokeweed mitogen-induced responses of CD4(+) cells from steers (5 to 6 mo of age), CD4(+) cells from 1-wk-old calves showed decreased proliferative activity, delayed increase in CD25 expression, and no demonstrable increase in CD44 expression or decrease in CD62L expression. Calf CD8(+) and gammadeltaT-cell receptor(+) cells, unlike T-cells from the older animals, did not demonstrate decreased expression of CD62L after stimulation with mitogen. The increased expression of CD44 by mitogen-stimulated gammadeltaT-cell receptor(+) cells from older animals was not seen in gammadeltaT-cell receptor(+) cells from 1-wk-old calves. At wk 8 of age, mitogen-induced proliferation and expression of activation antigens by T-cells from standard-fed calves were similar to responses of T-cells from steers indicating rapid maturation of T-cell function during the neonatal period. Feeding calves an intensified milk replacer was associated with decreased proliferation of mitogen-stimulated CD4(+), CD8(+), and gammadeltaT-cell receptor(+) cells; decreased CD25 expression by mitogen-stimulated CD4(+) and CD8(+) cells; and decreased CD44 expression by mitogen-stimulated CD8(+) cells. These results indicate that the functional capacity of the calf's T-cell population becomes more adult-like during the first weeks of life and suggest that nutrition modulates T-cell function during this period of immune maturation.

Leptin expression in ruminants: nutritional and physiological regulations in relation with energy metabolism

Leptin, mainly produced in adipose tissue (AT), is a protein involved in the central and/or peripheral regulation of body homeostasis, energy intake, storage and expenditure, fertility and immune functions. Its role is well documented in rodent and human species, but less in ruminants. This review is focused on some intrinsic and extrinsic factors which regulate adipose tissue leptin gene expression and leptinemia in cattle, sheep, goat and camel: age, physiological status (particularly pregnancy and lactation) in interaction with long-term (adiposity) and short-term effects of feeding level, energy intake and balance, diet composition, specific nutrients and hormones (insulin, glucose and fatty acids), and seasonal non-dietary factors such as photoperiod. Body fatness strongly regulates leptin and its responses to other factors. For example, leptinemia is higher after underfeeding or during lactation in fat than in lean animals. Physiological status per se also modulates leptin expression, with lactation down-regulating leptinemia, even when energy balance (EB) is positive. These results suggest that leptin could be a link between nutritional history and physiological regulations, which integrates the animal's requirements (e.g., for a pregnancy-lactation cycle), predictable food availability (e.g., due to seasonal variations) and potential for survival (e.g., body fatness level). Reaching permissive leptin thresholds should be necessary for pubertal or postpartum reproductive activity. In addition to the understanding of leptin yield regulation, these data are helpful to understand the physiological significance of changes in leptin secretion and leptin effects, and how husbandry strategies could integrate the adaptative capacities of ruminant species to their environment.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Plasma leptin status in young calves: effects of pre-term birth, age, glucocorticoid status, suckling, and feeding with an automatic feeder or by bucket

Plasma leptin concentrations depend on energy intake and fat stores and are modified by hormones, such as glucocorticoids. We have measured plasma leptin concentrations in pre-term calves (born on day 277 of gestation) during the first week of life, in full-term calves (290 days of gestation), fed similar amounts of nutrients with colostrum or a milk-derived formula, combined with or without dexamethasone treatment (to simulate a high glucocorticoid status), during the first five days of life, and in calves fed with an automatic feeder or by bucket or suckling on dams up to day 28. Leptin concentrations increased (P<0.05) from birth to day 7 in pre-term calves. In full-term calves leptin concentrations were stable from day 1 to day 4 in colostrum-fed animals, but decreased (P<0.05) and were lower (P<0.05) if fed a formula with similar amounts of energy and macronutrients as colostrum. Concentrations increased (P<0.05) from day 1 to day 2 in calves suckling on dams and then remained elevated, but did not change and were lower in calves fed with the automatic feeder or by bucket than in suckling calves. Dexamethasone only slightly elevated leptin concentrations. There was no episodic secretion pattern, and there were no consistent associations of leptin with various metabolites and hormones. In conclusion, plasma leptin in young calves with respect to effects of nutrition (low energy intake) and hormones (glucocorticoids) and in association with metabolic changes behaved differently from what is known in mature cattle.