Low Birth Weight Pigs Research Articles

Effects of dietary l-methionine supplementation on the growth performance, carcass characteristics, meat quality, and muscular antioxidant capacity and myogenic gene expression in low birth weight pigs.

The aim of the present study was to investigate the effects of dietary Met supplementation on the growth performance, carcass characteristics, meat quality, and muscular antioxidant capacity and myogenic gene expression in low birth weight (LBW) pigs. Thirty normal birth weight (NBW) and 60 LBW female piglets were selected at birth. In each litter, after weaning, 1 of the LBW piglets (LBW-CON group) and 1 of the NBW piglets (NBW-CON group) were fed the basal diets and 1 LBW littermate was fed the basal diet supplemented with Met (LBW-MET group). Thus, all pigs were distributed into groups of 3 treatments × 6 replicates (pens) × 5 piglets per replicate up to 180 d of age. Compared with NBW-CON pigs, LBW-CON pigs had decreased ADG ( = 0.004) and ADFI ( < 0.001) during the postweaning period and greater backfat thickness ( = 0.015) at slaughter. In addition, LBW-CON pigs exhibited compromised meat quality, as evidenced by a greater drip loss at 24 h postmortem( = 0.037) and a lower pH at 45 min postmortem ntents of malondialdehyde (MDA; = 0.046) and protein carbonyl ( = 0.028) in the LM. The LBW pigs fed the Met-supplemented diets had a greater amount of reduced glutathione (GSH; = 0.009) but a lower level of MDA ( = 0.015) in the LM compared with the LBW-CON pigs. Methionine supplementation increased the pH at 24 h postmortem (pH) value ( = 0.004) but reduced the drip loss at both 24 ( = 0.016) and 48 h ( = 0.005) postmortem of LBW-MET pigs in comparison with the LBW-CON pigs. The Met-supplemented diets increased the -adenosyl-methionine content ( = 0.006), DNA methyltransferase activity ( = 0.007), and CpG methylation levels of the sites +27 ( = 0.008) and +160 ( = 0.009) of myostatin (MSTN) exon 1 but decreased the mRNA expression of MSTN ( = 0.011) in the LM of the LBW-MET group compared with the LM of the LBW-CON group. Additionally, when compared with the LBW-CON group, the area of LM ( = 0.037) was significantly increased in the LBW-MET group, in parallel with the upregulated mRNA abundance of myogenin ( = 0.025), myocyte enhancer factor 2A ( = 0.036), and myocyte enhancer factor 2D ( = 0.015). In conclusion, Met supplementation increases pH and decreases drip loss in the LM of LBW-MET pigs, along with a greater GSH content but a lower MDA accumulation. Also, the LBW-MET pigs showed a greater LM area, which may be associated with the improved expression of myogenic genes.

Testing post-weaning food motivation in low and normal birth weight pigs in a runway and operant conditioning task

Low birth weight (LBW) pigs face more welfare challenges than their normal birth weight (NBW) siblings. Understanding the underlying mechanisms of cognitive and learning abilities in these pigs may help to improve their welfare. Early competition in life over resources, combined with the higher need for nutrient intake, make it likely that LBW pigs have a higher motivation for food than NBW pigs. This study aimed to compare the motivation to obtain food rewards between LBW and NBW pigs, using variable numbers of rewards in two separate tasks; a runway and an operant conditioning task (the nose wheel task). Ten pairs of littermates were used. From each litter, one low birth weight piglet (mean birth weight±SEM: 854±33g) and one normal birth weight piglet (1332±53g) was selected. Pigs were tested in the runway task at 12 weeks of age and the operant nose wheel task at 19 weeks of age. Both tasks consisted of a baseline phase (two rewards), a high reward phase (eight rewards) and an extinction phase (no rewards). Statistical analyses using mixed models showed that NBW animals left the start box faster than LBW animals in the high reward phase in the runway task. However, their run time in this phase was not shorter and no other birth weight effects were found in any other phase or measure in this task nor in the nose wheel task. All animals decreased their run time in the runway task between the baseline phase and high reward phase, and increased their run time in the extinction phase (p<0.05). Likewise, in the nose wheel task, all animals reached a higher number of total rewards gained and spent a lower percentage of time away from the feeder in the high reward phase compared to the baseline phase (p<0.05). Additionally, they showed a decrease in motivation during the extinction phase (p<0.05). Our results indicate that there is no difference in motivation to obtain food rewards between LBW and NBW pigs. However, both the results of the runway and the nose wheel task show a phase effect between the baseline, high reward and the extinction phase. This is in accordance with the underlying theory that animals have a higher motivation for resources that are more desired. Therefore, we show that both tasks are sensitive enough to measure motivation for food rewards in pigs, and are consequently useful to study factors influencing pig motivation.

Dysfunction of Insulin‐like Growth Factor Signaling in Skeletal Muscles of Low Birth Weight Neonatal Pigs

Low birth weight (LBWT) neonates experience restricted fetal muscle development and impaired postnatal muscle growth. Our previous data suggest that protein synthesis is lower while protein degradation is not different in skeletal muscle of LBWT compared to normal birth weight (NBWT) neonatal pigs. We hypothesized that decreased protein synthesis in skeletal muscle of LBWT pigs is a consequence of dysfunction of insulin‐like growth factor (IGF) signaling cascade. Twenty four LBWT and NBWT male pigs were euthanized to collect blood and longissimus dorsi (LD) muscle samples. Plasma IGF‐I concentration was measured using a commercial ELISA kit, mRNA expression by real‐time PCR and protein expression and phosphorylation by western blot. Plasma IGF‐I concentration and mRNA expression of IGF‐I and IGF binding protein 5 (IGFBP 5) were lower in LD muscle of LBWT pigs (P &lt; 0.05). However, mRNA and protein expression of IGF‐I receptor was higher in the LD muscle of LBWT compared to NBWT pigs (P &lt; 0.05). Protein expression of eukaryotic initiation factor 4E binding protein 1 (4EBP1) and phosphorylation of ribosomal protein S6 kinase 1 (S6K1) were lower in LD muscle of LBWT compared to their NBWT siblings (P &lt; 0.05). These results suggest that in spite of the increased abundance of IGF‐I receptor in muscles of LBWT pigs, there is a reduction in the expression of downstream effectors of IGF‐I. As a result, IGF signaling is compromised and could contribute to impaired postnatal muscle growth in LBWT compared to NBWT neonatal pigs.Support or Funding InformationVirginia Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture, U.S. Department of Agriculture (S.W. El‐Kadi)

Early postnatal feed restriction reduces liver connective tissue levels and affects H3K9 acetylation state of regulated genes associated with protein metabolism in low birth weight pigs

Intrauterine growth retardation is associated with metabolic consequences in adulthood. Since our previous data indicate birth weight-dependent effects of feed restriction (R) on protein degradation processes in the liver, it should be investigated whether effects on connective tissue turnover are obvious and could be explained by global changes of histone H3K9me3 and H3K9ac states in regulated genes. For this purpose, female littermate pigs with low (U) or normal (N) birth weight were subjected to 3-week R (60% of ad libitum fed controls) with subsequent refeeding (REF) for further 5weeks. The 3-week R-period induced a significant reduction of connective tissue area by 43% in the liver of U animals at 98 d of age, which was not found in age-matched N animals. Of note, after REF at 131 d of age, in previously feed-restricted U animals (UR), the percentage of mean connective tissue was only 53% of ad libitum fed controls (UK), indicating a persistent effect. In U animals, R induced H3K9 acetylation of regulated genes (e.g. XBP1, ERLEC1, GALNT2, PTRH2), which were inter alia associated with protein metabolism. In contrast, REF was mostly accompanied by deacetylation in U and N animals. Thus, our epigenetic data may give a first explanation for the observed birth weight-dependent differences in this connective tissue phenotype.

Translation Initiation Signaling in Myotubes from Normal and Low Birth Weight Neonatal Pigs

Skeletal muscle growth is impaired in low birth weight (LBWT) compared to normal birth weight (NBWT) neonates. Our previous studies showed that skeletal muscle protein synthesis is lower and IGF‐І receptor expression is higher in LBWT than NBWT neonatal pigs. The objective of the current study was to investigate the effect of IGF‐І stimulation on the regulation of translation initiation signaling in primary myotubes from LBWT and NBWT neonatal pigs. Primary satellite cells were isolated from Longissimus dorsi muscle of male LBWT and NBWT pigs (n = 4). Cells were allowed to proliferate to ~80% confluence, and differentiate to form myotubes. At 2.5 day of differentiation, myotubes were treated with IGF‐І at physiological levels (0, 25 and 50 ng/ml) after fasting in serum‐free media for 3 h. Myotubes were harvested in lysis buffer, and the expression of translation initiation signaling proteins were measured by Western blotting. IGF‐І stimulation significantly increased protein kinase B (PKB/Akt), eukaryotic initiation factor 4E binding protein (4EBP1) and ribosomal protein S6 kinase beta‐1 (S6K1) phosphorylation in myotubes from LBWT and NBWT pigs (P &lt; 0.05). However, total S6K1 expression was significantly lower (P &lt; 0.05) and 4EBP1 phosphorylation was higher (P = 0.09) in myotubes of LBWT compared with NBWT pigs. Our data suggest IGF‐І stimulation does not differentially regulate translation initiation signaling in myotubes from LBWT and NBWT pigs. S6K1 expression is reduced in primary myotubes from LBWT pigs, which likely indicates impaired translation initiation signaling in myotubes from LBWT compared with NBWT pigs.

Compensatory growth feeding strategy does not overcome negative effects on growth and carcass composition of low birth weight pigs

The aim of this study was to evaluate whether the compensatory growth feeding strategy could be a suitable solution for overcoming the negative effects on growth, carcass composition and meat quality of low birth weight pigs. Forty-two Swiss Large White barrows from 21 litters were selected at weaning and categorized into either being light (L; >0.8 and <1.3 kg) or heavy (H; >1.7 kg) birth weight pigs. From 27.8 kg BW, pigs were assigned within birth weight group to one of three feeding groups: AA: ad libitum access to the grower and finisher diet, RR: restricted access to the grower and finisher diet or RA: restricted access to the grower diet and ad libitum access to the finisher diet. At slaughter, the longissimus (LM) and semitendinosus (STM) muscles were removed from the right side of the carcass. Weight, girth and length of the STM and the LM area were determined after muscle excision. Carcass characteristics and meat quality traits were assessed. Using mATPase histochemistry, myofibre size and myofibre type distribution were determined in the LM and STM. Because of longer days on feed, total feed intake was greater (P<0.01) and feed efficiency was lower (P<0.01) in L than H barrows. Regardless of the birth weight group, AA and RA barrows grew faster (P<0.05) than RR barrows. During the compensatory growth period, RA barrows grew faster (P<0.05) than AA or RR barrows. Growth efficiency did not differ between RA and RR barrows but was greater (P<0.05) compared with AA barrows. Carcasses of L barrows were fatter as indicated by the lower (P⩽≤0.05) lean meat and greater (P⩽0.02) omental and subcutaneous fat percentage. Lean meat percentage was lower (P⩽0.05) in AA and RA than RR barrows. These differences caused by ad libitum feed access tended to be greater (feeding regime × birth weight group interaction; P<0.08) in L than H barrows. In L barrows, slow oxidative, fast oxidative glycolytic and overall average myofibre size of the LM and the fast glycolytic myofibres and overall average myofibre size of the dark portion of the STM were larger (P⩽0.03) than in H barrows. The study revealed that the compensatory growth feeding strategy was inadequate in overcoming the disadvantages of low birth weight.

Decision-making under risk and ambiguity in low-birth-weight pigs.

Low birth weight (LBW) in humans is a risk factor for later cognitive, behavioural and emotional problems. In pigs, LBW is associated with higher mortality, but little is known about consequences for surviving piglets. Alteration in hypothalamic-pituitary-adrenal axis function in LBW pigs suggests altered emotionality, but no behavioural indicators have been studied. Decision-making under uncertain conditions, e.g., risk or ambiguity, is susceptible to emotional influences and may provide a means of assessing long-term effects of LBW in piglets. We tested LBW (N=8) and normal-birth-weight (NBW; N=8) male pigs in two decision-making tasks. For decision-making under risk, we developed a simple two-choice probabilistic task, the Pig Gambling Task (PGT), where an 'advantageous' option offered small but frequent rewards and a 'disadvantageous' option offered large but infrequent rewards. The advantageous option offered greater overall gain. For decision-making under ambiguity, we used a Judgement Bias Task (JBT) where pigs were trained to make an active response to 'positive' and 'negative' tone cues (signalling large and small rewards, respectively). Responses to ambiguous tone cues were rated as more or less optimistic. LBW pigs chose the advantageous option more often in later blocks of the PGT, and were scored as less optimistic in the JBT, than NBW pigs. Our findings demonstrate that LBW pigs have developed different behavioural strategies with respect to decision-making. We propose that this is guided by changes in emotionality in LBW piglets, and we provide behavioural evidence of increased negative affect in LBW piglets.

High specification starter diets improve the performance of low birth weight pigs to 10 weeks of age.

Piglets born with low birth weights (LBiW) are likely to be lighter at weaning. Starter regimes tailored for pigs of average BW therefore may not be optimal for LBiW nursery performance. The objective was to determine if LBiW pigs benefit from a high specification starter regime and the provision of extra feed (additional allowance of last phase diet of the starter regime) in comparison to a standard commercial regime. Additionally, the effect of starter regime on performance of normal birth weight (NBiW) pigs at weaning was determined and compared to that of LBiW pigs. Finally, the cost effectiveness of the treatments was determined. The experiment was therefore an incomplete 2 × 2 × 2 factorial design, as the provision of extra feed was given only to LBiW pigs (n = 6 replicates per treatment; 5 pigs per replicate). Treatments comprised birth weight (LBiW or NBiW), starter regime (high specification [HS] or standard starter [SS]), and extra feed 3 quantity (yes [YF] or no [NF], for LBiW pigs only; feed 3 corresponded to the last phase diet of the starter regime). At weaning (d 28), pigs were randomly assigned within each birth weight category to treatment groups. Nutritional treatments were fed ad libitum on a kilogram/head basis for approximately 3 wk followed by a common weaner diet fed ad libitum until d 70. Starter regime (P = 0.019), feed 3 amount (P = 0.010), and their interaction (P = 0.029) had an effect on ADG of LBiW pigs from d 28 to 49, with pigs on HS followed by YF (HY) performing best. An improvement in feed conversion ratio (FCR) was noted between d 28 and 49 for pigs fed the additional feed 3 (P = 0.030); between d 49 and 70, the only residual effect seen was of starter regime (P = 0.017) on ADG. In contrast, there was no significant effect of starter regime from d 28 to 70 on ADG, ADFI, or FCR of NBiW pigs. By d 49 and 70, LBiW pigs on regime HY weighed the same as NBiW pigs (d 70 BW; 30.0 vs. 30.6 kg; P = 0.413), with similar growth rates from d 28 to 70 (0.570 vs. 0.533 kg/d; P = 0.137). Despite highest feed cost for regime HY at US$12.30 per pig, its margin over feed was greatest ($23.40). Conversely, regime SS gave the best margin over feed for NBiW pigs at $22.70 per pig. In conclusion, a postweaning feeding regime formulated for LBiW pigs improved the ADG and FCR to the end of the nursery phase enabling them to achieve the same weight as NBiW. Targeting the provision of the high quality expensive regime only to light pigs will ensure maximum growth and increased profitability.

A high-protein formula increases colonic peptide transporter 1 activity during neonatal life in low-birth-weight piglets and disturbs barrier function later in life.

Dietary peptides are absorbed along the intestine through peptide transporter 1 (PepT-1) which is highly responsive to dietary protein level. PepT-1 is also involved in gut homeostasis, both initiating and resolving inflammation. Low-birth-weight (LBW) neonates are routinely fed a high-protein (HP) formula to enhance growth. However, the influence of this nutritional practice on PepT-1 activity is unknown. Intestinal PepT-1 activity was compared in normal-birth-weight (NBW) and LBW piglets. The effect of HP v. normal-protein (NP) formula feeding on PepT-1 activity and gut homeostasis in LBW piglets was evaluated, during the neonatal period and in adulthood. Flux of cephalexin (CFX) across the tissue mounted in Ussing chambers was used as an indicator of PepT-1 activity. CFX flux was greater in the ileum, but not jejunum or colon, of LBW than NBW piglets during the neonatal period. When LBW piglets were formula-fed, the HP formula increased colonic CFX during the 1st week of life. Later in life, intestinal CFX fluxes and barrier function were similar whether LBW pigs had been fed NP or HP formula. However, colonic permeability of HP- but not NP-fed pigs increased when luminal pH was brought to 6·0. The formyl peptide N-formyl methionyl-leucyl-phenylalanine conferred colonic barrier protection in HP-fed piglets. Heat shock protein 27 levels in the colonic mucosa of HP-fed LBW pigs correlated with the magnitude of response to the acidic challenge. In conclusion, feeding a HP formula enhanced colonic PepT-1 activity in LBW pig neonates and increased sensitivity of the colon to luminal stress in adulthood.

Efficacy of 1,3-butanediol for enhancement of neonatal pig survival

Pre-partum feeding of 1,3-butanediol to sows has been shown to improve the metabolic status and survival rate of neonatal pigs. To evaluate the efficacy of short-term, pre-partum feeding of 1,3-butanediol on pig and sow productivity on a large scale and low concentration was the focus of the research. The secondary objective was to determine if pre-partum feeding of 1,3-butanediol had any effect on survival rate and weight gain of lesser body weight pigs, sow body weight and subsequent sow reproductive performance. In a large commercial unit, 2537 sows were fed one of two pre-partum diets (0% or 4.55% 1,3-butanediol) on Day 108±3 of pregnancy. 1,3-butanediol provided 8% of the total metabolizable energy. Pigs born live in those litters were equalized by cross-fostering among sows receiving the same pre-partum diet. Pigs were weaned from the sows at 16±3 days post-partum and return of sows to estrus and conception rates were determined. Pre-partum feeding of 1,3-butanediol reduced (P=0.01) pre-weaning pig mortalities from 1.44 to 1.24 pigs per litter. The reduction in pig mortality was independent of length of 1,3-butanediol feeding (4 to 11 days). In a subset of 750litters, four lesser birth-weight pigs from each litter were tagged and monitored to determine the effect of 1,3-butanediol on survival rates and pre-weaning weight gain of pigs with the greatest mortality risk. 1,3-butanediol reduced (P=0.01) pre-weaning mortality of these low birth weight pigs by 5.27%. Based on these data, short-term pre-partum feeding of 1,3-butanediol effectively improves pre-weaning pig productivity at a lower concentration than previously reported.

Management strategies to improve the performance of low birth weight pigs to weaning and their long-term consequences1,2

Performance of pigs from birth to slaughter is a result of a complex interaction of factors, with the early stages of a pig's life likely to affect lifetime performance. During the preweaning stage, piglets are reliant on the sow for nutrition, and sibling competition is likely to affect growth, in particular for low birth weight (LBiW) piglets. The objective of the experiment was to determine the effect of litter composition (littermate weight) and milk supplementation during lactation on the performance of LBiW pigs to weaning and the long-term consequences of treatment to slaughter. The experiment was a 2 × 2 factorial with littermate weight (normal or LBiW) and provision of supplementary milk from d 1 to 28 (yes or no) as factors. A total of 265 piglets were selected within 24 h of birth and cross-fostered to create 2 litter types (LOW = LBiW pigs [≤ 1.25 kg] only and MX = both LBiW and normal birth weight pigs [1.6 to 2.0 kg]); half of the litters within a type were supplemented with milk and the other half were not. The behavior of litters given milk was recorded to identify milk consumption patterns. Piglets were weaned at d 28 and kept in their litters until d 70 and then subsequently housed in mixed groups until slaughter. No difference was observed at any stage in the ADG of pigs given access to supplementary milk or not (P > 0.05) nor was there any significant interaction between milk provision and litter composition (P > 0.05). However, LOW litters drank significantly more supplementary milk than MX litters (P < 0.001). There was a significant effect of litter type on ADG from d 14 to 28, with LBiW pigs in LOW litters performing better than those in MX litters (0.252 versus 0.217 kg/d; P < 0.05). At weaning, LBiW piglets in LOW litters weighed over 500 g more than those in MX litters (P < 0.05). In MX litters there was a significant interaction between birth weight and supplementary milk on the CV of BW from d 14 to slaughter (P < 0.05). In conclusion, grouping LBiW piglets with similar sized littermates preweaning can improve preweaning performance by reducing competition from heavier littermates; however, this advantage does not persist after weaning. Although supplementary milk does not improve LBiW pig performance before or after weaning, it affects their drinking behavior and can reduce the variation in the BW of LBiW piglets in mixed litters to slaughter.

Birth weight alters the response to postnatal high-fat diet-induced changes in meat quality traits and skeletal muscle proteome of pigs

Low birth weight (LBW) exerts persistent effects on the growth and development of offspring. The present study was conducted to test the hypothesis that LBW alters the response of pigs to high-fat (HF) diet-induced changes in meat quality and skeletal muscle proteome. Normal-birth weight (NBW) and LBW piglets were fed a control diet or a HF diet from weaning to slaughter at 110kg body weight. Most of the meat quality traits were influenced by LBW. Meat quality analysis revealed that LBW piglets had a greater ability to deposit intramuscular lipids than their heavier littermates when fed a HF diet. Increased shear force, lower pH45 min and drip loss were observed in the skeletal muscle of LBW piglets compared with NBW piglets. Proteomic analysis revealed forty-six differentially expressed proteins in the skeletal muscle of LBW and NBW piglets fed the control diet or HF diet. These proteins play a central role in cell structure and motility, glucose and energy metabolism, lipid metabolism, and cellular apoptosis, as well as stress response. Of particular interest is the finding that LBW altered the response to HF diet-induced changes in the expression of proteins related to stress response (heat shock protein) and glucose and energy metabolism (pyruvate kinase, phosphoglycerate mutase, enolase and triosephosphate isomerase). Taken together, our findings revealed that the HF diet-induced changes in the expression of glucose and energy metabolism-related proteins varied between NBW and LBW piglets, which provides a possible mechanism to explain higher intramuscular fat store in LBW pigs when fed a HF diet.

Successive and conditional discrimination learning in pigs

We studied the ability of pigs to discriminate tone cues using successive and conditional discrimination tasks. Pigs (n = 8) were trained in a successive discrimination Go/No-Go task (Experiment 1) to associate a Go-cue with a reward at the end of a runway and a No-Go-cue with the absence of reward. Latency to reach the goal-box was recorded for each cue-type. Learning of a conditional discrimination task was compared between low-birthweight (LBW, n = 5) and normal-birthweight (NBW, n = 6) pigs (Experiment 2) and between conventional farm (n = 7) and Göttingen miniature (n = 8) pigs (Experiment 3). In this active-choice task, one cue signalled a response in a right goal-box was correct and a second cue signalled a response in a left goal-box was correct. Cues were differentially rewarded. The number of sessions to learn the discrimination and number of correct choices per cue-type were recorded. In Experiment 1, four out of eight pigs showed learning on the task, that is, a higher latency to respond to the No-Go-cue, within 25 sessions. In Experiment 2, eight out of 11 pigs learned the discrimination within 46 sessions. LBW learners learned faster than NBW learners. In Experiment 3, all 15 pigs learned the task within 16 sessions. Göttingen miniature pigs learned faster than conventional farm pigs. While some methodological issues may improve the Go/No-Go design, it is suggested that an active-choice task yields clearer and more consistent results than one relying on latency alone.

Meat Science And Muscle Biology Symposium: In utero nutrition related to fetal development, postnatal performance, and meat quality of pork1

Intrauterine growth restriction (IUGR) occurs naturally in pigs and leads to low birth weight of piglets due to undernutrition caused by placental insufficiency. For 2 main reasons, low birth weight causes economic loss. First, low birth weight pigs have a greater mortality and increasing the litter size causes more low birth weight piglets within litters. Second, surviving low birth weight piglets have reduced performance (i.e., ADG, feed conversion rate, and percentage meat). To develop dietary strategies for preventing IUGR, knowledge of the biological basis of IUGR is required. Muscle fiber number, formed during myogenesis, is correlated positively with performance traits and has been shown in several studies to be reduced in low birth weight pigs. Postnatal muscle hypertrophy is due to satellite cell number per fiber at birth and their rate of proliferation as well as protein deposition (i.e., protein synthesis and degradation). Previous studies and some recent ones indicate that low birth weight littermates in mice are born with fewer satellite cells and studies on pigs show that the rate of satellite cell proliferation may vary within litters. Proteomics studies show that protein synthesis and degradation is downregulated in IUGR pigs and low birth weight pigs also produce meat with less tenderness. Alternative maternal feeding strategies to prevent IUGR have been examined. Increasing maternal global nutrition had no beneficial effect on performance and muscle growth traits in several studies. Feeding excess maternal dietary protein also did not influence muscle growth traits whereas moderately decreased maternal dietary protein may decrease muscle fiber number and performance. On the other hand, addition of L-carnitine to the maternal gestation or lactation diet may increase birth and weaning weights or the muscle fiber number, respectively, in low birth weight pig offspring. Finally, promising data have been obtained on reproductive traits in pigs after addition of functional AA, such as arginine and glutamine, to the gestational diet. Although much is known about the biological basis of IUGR, we still need to learn much more about the mode of action before maternal dietary strategies can be developed to prevent IUGR.

Maturation of digestive function is retarded and plasma antioxidant capacity lowered in fully weaned low birth weight piglets

The digestive function of low birth weight (LBW) pigs post-weaning has been poorly studied. Therefore, newborns from eleven hyperprolific sows were weighed, weaned at 27·2d and fed a starter diet until sampling. Sampling was done between 18 and 28d post-weaning. An LBW piglet (n 19) was defined as a piglet having a birth weight less than 1kg and less than the lower quartile of litter birth weights. Normal birth weight (NBW) piglets (n 13) were having a birth weight close to the mean litter birth weight. For each piglet, eighty-eight variables were determined. Data were analysed with linear models with type of piglet and litter as predictors. A principal component analysis was performed to determine the most important discriminating variables. In the LBW pig, the development of the digestive tract post-weaning was delayed: lower small-intestinal weight:length ratio due to a thinner tela submucosa and tunica muscularis and a higher secretory capacity, both in the distal jejunum. These observations might be a consequence of lower circulating insulin-like growth factor-1 (IGF-1) concentrations (126 (se 10·0) v. 158 (se 12·0)ng/ml for LBW and NBW, respectively) and a lower density of IGF-1 receptors in the proximal small intestine. Additionally, the plasma antioxidant capacity was lower for the LBW pig. Taken together, in the LBW piglet, the normal gut maturation post-weaning was retarded and this did not seem to be related to the weaning transition as such.

Effects of piglet birth weight and litter size on the preweaning growth performance of pigs on a commercial farm (2009)

A total of 2,204 pigs (PIC 327 sired) were used to evaluate the effects of piglet birth weight and litter size on preweaning piglet performance. At a commercial sow farm, all pigs born alive for 22 consecutive days were identified individually at birth with a numbered ear tag. Each sow was assigned a body condition score (BCS; 1 = very thin to 5 = very fat), and the number of total born, live born, and born dead as well as the individual gender, birth weight, and identification of piglets were recorded within 18 h of parturition and before the movement of pigs to equalize litter size. During lactation, all pigs fostered, removed, or found dead were weighed, and the event was recorded. No litters were provided creep feed or supplements during lactation. Pigs were individually weighed and assigned a BCS (1 = emaciated, 2 = thin, or 3 = full-bodied) at weaning over 6 weaning days during a 19-d period, which resulted in a mean weaning age of 25 d. For data analysis, individual birth weight was used to assign pigs to 4 birth weight categories (≤ 2.3 lb, 2.4 to 3.3 lb, 3.4 to 4.3 lb, and ≥ 4.4 lb), and the number of total born in each pig’s litter of origin was used to assign pigs to 3 total born categories (≤ 11, 12 to 14, and ≥ 15). As expected, birth weight was greater (P < 0.0001) for pigs of heavier birth weight categories. Pigs of heavier birth weight categories were associated (P < 0.02) with a decreased number of total and live born. Also, preweaning ADG, weaning weight, weaning BCS, and preweaning mortality were improved (P < 0.0001) for pigs of heavier birth weight categories. Birth weight decreased (P < 0.04) for pigs of greater total born categories, and an increased sow BCS was associated (P < 0.0001) with total born category ≥ 15. As expected, the litter total born, as well as live born and number born dead, increased (P < 0.0001) with greater total born categories. Preweaning ADG (0.51, 0.50, and 0.50 lb/d, respectively) and weaning weight (16.3, 15.9, and 15.8 lb, respectively) were modestly improved (P < 0.04) for pigs from the smallest total born category compared with the 2 larger categories. These data indicate that low-birthweight pigs had poorer preweaning growth performance and survivability. Although larger litters resulted in a greater number of low-birth-weight pigs, the number of heavier pigs also increased. In addition to increasing litter size, maximizing reproductive and economic efficiency of swine requires identifying methods to improve birth weight and performance of the lightest pigs born.

Growth and development of adipose tissue and gut and related endocrine status during early growth in the pig: impact of low birth weight

With genetic selection, the increase in litter size has led to higher variation in within-litter birth weights in pigs. This has been associated with a reduction in mean birth weights and a rise in the proportion of piglets weighing less than 1 kg at birth. Low birth weight pigs exhibit lower postnatal growth rates and feed efficiency, which may be explained by an inadequate digestion and/or nutrient use as a consequence of prenatal undernutrition. It is now documented that there is a relationship between birth weight and subsequent pattern of growth and development of tissues and organs. During the neonatal period, the rapid somatic growth is accompanied by tremendous anatomical, physiological and chemical composition changes. The present review focuses primarily on the influence of low birth weight on adipose tissue and the gastrointestinal tract growth and development during the suckling period. The importance of the somatotropic axis, insulin, thyroid hormones, glucocorticoids, epidermal growth factor and leptin in the regulation of these developmental processes is also considered.

Insulin sensitivity in juvenile and adult Large White pigs of low and high birthweight.

We have previously demonstrated poor glucose tolerance in adult pigs of naturally occurring low birthweight. The aim of this study was to examine sensitivity to insulin in juvenile (3-month-old) and adult (12-month-old) pigs of low and high birthweight. Low (<1.47 kg) and high (>1.53 kg) birthweight piglets from 15 litters were studied at 3 (n=47) and 12 (n=17) months of age. At each age the selected pigs were tranquilised and catheters were inserted into the dorsal aorta and caudal vena cava under general anaesthesia. After recovery, insulin sensitivity was measured as the glucose decrement (mmol.l(-1).min(-1)) during the first 10 min after an intravenous insulin bolus (0.5 IU/kg). Data (means +/- SEM) were analysed by the Student's t test, ANOVA and linear regression. The body weight of low birthweight female, but not male, pigs remained smaller than that of high birthweight pigs at 3 and 12 months of age. At 3 months, thinness at birth and rapid catch-up growth in the first month of life were associated with increased insulin sensitivity in males. In females thinness at 3 months was associated with reduced sensitivity to insulin. At 12 months, early postnatal catch-up growth was associated with insulin resistance, irrespective of sex, when all data were combined. The glucose intolerance previously observed in young adult pigs of low birthweight is probably due to insulin resistance. Early catch-up growth in low birthweight pigs was the clearest predictor of adult insulin resistance.

The effects of birth weight on basal cardiovascular function in pigs at 3 months of age.

In man, epidemiological studies have shown that low birth weight (BW) is associated with an increased risk of cardiovascular disease in later life. In this study, the long-term consequences of variations in natural BW on basal cardiovascular function were investigated in pigs at 3 months of postnatal age. Low (< 1.41 kg; n = 20) and high (> 1.52 kg; n = 20) BW Large White piglets were selected from a total of 12 litters for study at 3 months of age. Basal mean arterial pressure (MAP) and heart rate (HR) were recorded for approximately 30 min using standard recording equipment and basal arterial blood samples were taken for hormone analyses. Concentrations of angiotensin-converting enzyme (ACE) were also measured in kidney, lung and plasma. Basal MAP, but not HR, in 3-month-old pigs was significantly inversely related to BW and positively related to the ratio of head length to BW. Postnatal growth rate of low BW pigs was slower than that of high BW pigs such that low BW piglets remained significantly smaller at 3 months of age. There were no differences in basal plasma adrenaline or cortisol concentrations between low and high BW pigs. However, basal plasma noradrenaline concentrations were significantly elevated in low BW compared to high BW pigs. Renal and pulmonary ACE levels were significantly reduced in low BW compared to high BW pigs. These data show that basal MAP in 3-month-old pigs is negatively associated with BW and positively correlated to disproportionate size at birth. This effect was associated with an increase in basal plasma noradrenaline concentrations.

Muscle cellularity and birth weight

ABSTRACTA study of the effects of low birth weight on muscle cellularity was performed on 48 pedigree Large White pigs selected, from a total of 17 litters, on the basis of their weight at birth. Where possible, the largest male (mean birth weight of 1544 g), smallest male (1135 g), and runt (776 g) littermates were chosen. Fresh frozen, whole mid belly, sections of m. semitendinosus and samples of m. trapezius from each animal were stained for the demonstration of acid pre-incubated myosin adenosine triphosphatase. The use of this stain demonstrated groups of positively stained, slow-contracting, myofibres which were each surrounded by a compliment of negatively stained, fast-contracting, fibres which together constituted ‘metabolic bundles’. The positions of metabolic bundles are indicative of the presence of single primary myofibres in the foetal muscle, all the other myofibres in the metabolic bundles being derived from subsequently formed secondary fibres. Determination of total myofibre number and primary fibre number were made for m. semitendinosus together with an estimation of the secondary to primary fibre-number ratios for both this muscle and for m. trapezius. Low birth weight was associated with a permanently reduced total muscle fibre number, proportionately in the order of 0·19 (P &lt; 0·001) between large and runt littermates. A reduced muscle fibre number was not always associated with low birth weight, but when this was the case it was generated through a reduced secondary to primary fibre-number ratio (P &lt; 0·01). Primary fibre number was not significantly affected in low birth-weight pigs except in extreme cases of runting.