Pattern of growth in weight of alate and apterous nymphs of the English grain aphid, Sitobion avenae

Daily increase in fresh weight was recorded for apterous and alate nymphs of S. avenae at 20°C. Comparison with a control group indicated that daily disturbance and weighing of nymphs did not affect significantly their growth, developmental time or survival. The increase in fresh weight of apterous and alate virginoparae at 20°C was best described by logistic equations. Alate virginoparae were significantly heavier than apterous virginoparae at birth and throughout most of their nymphal life, but they experienced a weight loss at the final ecdysis. The relative growth rate did not remain constant, but declined during development. The decline is associated with a decline in honeydew production per unit body weight. The implications of an inconstant relative growth rate and the marked loss in weight at the adult moult in alates are discussed.

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Résumé L'enregistrement de l'augmentation quotidienne du poids frais à 20°C des larves ailées et aptères de S. avenae a montré que des perturbations quotidiennes n'affectent pas significativement la croissance, la durée du développement et la survie. Les équations logistiques décrivent plus exactement l'augmentation de poids frais des aptères et des ailés virginipares à 20°C. Les virginipares ailés étaient significativement plus lourds que les virginipares aptères à la naissance et pendant la plus grande partie de la vie larvaire, mais présentaient une perte de poids à la mue finale. Le taux de croissance relative ne restait pas constant, mais diminuait au cours du développement. La diminution était associée à une diminution de la production de miellat par unité de poids du corps. La discussion porte sur les conséquences de la variation de l'augmentation du poids relatif et de la perte marquée de poids à la mue imaginale.

     

Intergall migration in aphids; a model and a test of ESS dispersal rate

Summary I present an inclusive-fitness model for the evolution of dispersal rates of the offspring of asexual organisms living in discrete sites, which vary in available resources. I also assume a stable and saturated condition and that the offspring can respond to the variation in the capacity (amount of resources) of their natal sites. The model was tested using data obtained from the intergall migration in the yezo-spruce gall aphid,Adelges japonicus. All the parameters needed for the model, which included the cost of dispersal, both dispersal rates and available resources in each site, were estimated from field examinations. The data fit the model well, suggesting the importance of kin selection in determining the dispersal rates. Both actual and ESS dispersal rates are shown as concave functions of site capacity with a minimum rate for intermediate site capacity. The effect of both actual and ESS dispersal is to reduce, but not eliminate sibling competition within natal sites, which is most severe in intermediate site capacity.     

Effect of average litter weight in pigs on growth performance,carcass characteristics and meat quality of the offspring as depending on birth weight

Offspring born from normal litter size (10 to 15 piglets) but classified as having lower than average birth weight (average of the sow herd used: 1.46 ± 0.2 kg; mean ± s.d.) carry at birth negative phenotypic traits normally associated with intrauterine growth restriction, such as brain-sparing and impaired myofiber hyperplasia. The objective of the study was to assess long-term effects of intrauterine crowding by comparing postnatal performance, carcass characteristics and pork quality of offspring born from litters with higher (>1.7 kg) or lower (<1.3 kg) than average litter birth weight. From a population of multiparous Swiss Large White sows (parity 2 to 6), 16 litters with high (H = 1.75 kg) or low (L = 1.26 kg) average litter birth weight were selected. At farrowing, two female pigs and two castrated pigs were chosen from each litter: from the H-litters those with the intermediate (H_I = 1.79 kg) and lowest (H_L = 1.40 kg) birth weight, and from L-litters those with the highest (L_H = 1.49 kg) and intermediate (L_I = 1.26 kg) birth weight. Average birth weight of the selected H_I and L_I piglets differed (P < 0.05), whereas birth weight of the H_L- and L_H-piglets were similar (P > 0.05). These pigs were fattened in group pen and slaughtered at 165 days of age. Pre-weaning performance of the litters and growth performance, carcass and meat quality traits of the selected pigs were assessed. Number of stillborn and pig mortality were greater (P < 0.05) in L- than in H-litters. Consequently, fewer (P < 0.05) piglets were weaned and average litter weaning weight decreased by 38% (P < 0.05). The selected pigs of the L-litters displayed catch-up growth during the starter and grower–finisher periods, leading to similar (P > 0.05) slaughter weight at 165 days of age. However, H_L-gilts were more feed efficient and had leaner carcasses than H_I-, L_H- and L_I-pigs (birth weight class × gender interaction P < 0.05). Meat quality traits were mostly similar between groups. The marked between-litter birth weight variation observed in normal size litters had therefore no evident negative impact on growth potential and quality of pigs from the lower birth weight group.     

Effects of dietary enrichment with a marine oil-based n-3 LCPUFA supplement in sows with predicted birth weight phenotypes on growth performance and carcass quality of offspring

Effects of a marine oil-based n-3 LCPUFA supplement (mLCPUFA) fed from weaning until the end of the next lactation to sows with a predicted low litter birth weight (LBW) phenotype on growth performance and carcass quality of litters born to these sows were studied, based on the hypothesis that LBW litters would benefit most from mLCPUFA supplementation. Sows were allocated to be fed either standard corn/soybean meal-based gestation and lactation diets (CON), or the same diets enriched with 0.5% of the mLCPUFA supplement at the expense of corn. The growth performance from birth until slaughter of the litters with the lowest average birth weight in each treatment (n=24 per treatment) is reported in this paper. At weaning, each litter was split between two nursery pens with three to six pigs per pen. At the end of the 5-week nursery period, two barrows and two gilts from each litter that had individual birth weights closest to their litter average birth weight, were moved to experimental grow–finish pens (barn A), where they were housed as two pigs per pen, sorted by sex within litter. Remaining pigs in each litter were moved to another grow–finish barn (barn B) and kept in mixed-sex pens of up to 10 littermates. After 8 weeks, one of the two pigs in each pen in barn A was relocated to the pens holding their respective littermates in barn B. The remaining barrows and gilts were individually housed in the pens in barn A until slaughter. Maternal mLCPUFA supplementation increased docosahexaenoic acid (DHA) concentration in the brain, liver and Semitendinosus muscle of stillborn pigs (P<0.01), did not affect eicosapentaenoic acid and DHA concentrations in sow serum at the end of lactation, and did not affect average daily gain, average daily feed intake or feed utilization efficiency of the offspring. BW was higher (P<0.01) in the second half of the grow–finish phase in pigs from mLCPUFA sows compared with controls in barn A, where space and competition for feed was minimal, but not barn B. Carcass quality was not affected by treatment for pigs from barn A, but maternal mLCPUFA supplementation negatively affected carcass quality in pigs from barn B. Collectively, these results suggest that nutritional supplementation of sows can have lasting effects on litter development, but that feeding mLCPUFA to sows during gestation and lactation was not effective in improving growth rates or carcass quality of LBW litters.     

Consequences of a low litter birth weight phenotype for postnatal lean growth performance and neonatal testicular morphology in the pig

The consequences of a low litter average birth weight phenotype for postnatal growth performance and carcass quality of all progeny, and testicular development in male offspring, were investigated. Using data from 25 sows with one, and 223 sows with two consecutive farrowing events, individual birth weight (BW) was measured and each litter between 9 and 16 total pigs born was classified as low (LBW), medium (MBW) or high (HBW) birth weight: low and high BW being defined as >1 standard deviation below or above, respectively, the population mean for each litter size. Litter average BW was repeatable within sows. At castration, testicular tissue was collected from 40 male pigs in LBW and HBW litters with individual BW close to their litter average BW and used for histomorphometric analysis. LBW piglets had a lower absolute number of germ cells, Sertoli cells and Leydig cells in their testes and a higher brain : testis weight ratio than HBW piglets. Overall, LBW litters had lower placental weight and higher brain : liver, brain : intestine and brain : Semitendinosus muscle weight ratios than MBW and HBW litters. In the nursery and grow–finish (GF) phase, pigs were kept in pens by BW classification (9 HBW, 17 MBW and 10 LBW pens) with 13 males and 13 females per pen. Average daily gain tended to be lower in LBW than HBW litters in lactation (P = 0.06) and throughout the nursery and GF phases (P < 0.01), resulting in an increasing difference in body weight between LBW, MBW and HBW litters (P < 0.05). Average daily feed intake was lower (P < 0.001) in LBW than HBW litters in the nursery and GF phases. Feed utilization efficiency (feed/gain) was similar for LBW and HBW litters in the nursery, but was lower (P < 0.001) in HBW than LBW litters in the GF phase. By design, slaughter weight was similar between BW classifications; however, LBW litters needed 9 more days to reach the same slaughter weight than HBW litters (P < 0.001). BW classification did not affect carcass composition traits. In conclusion, LBW litters showed benchmarks of intrauterine growth retardation, LBW had a negative impact on testicular development and germ and somatic cell populations, and was associated with decreased postnatal growth during all phases of production; however, no measurable effect on carcass composition traits was established.     

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.     

有翅型和无翅型大豆蚜卵巢和胚胎发育的差异

【目的】比较大豆蚜Aphis glycines有翅型和无翅型个体的卵巢发育,为从生理生化角度研究蚜虫翅型分化发生的繁殖适应性提供依据。【方法】在卵巢形态显微镜观察基础上,比较有翅型和无翅型大豆蚜卵巢小管数量、胚胎总数量、成熟胚胎数量以及卵巢小管中最大胚胎体积及其发育速率。【结果】有翅型和无翅型大豆蚜的3龄和4龄若蚜以及成蚜均有2个卵巢/雌,大多数蚜虫每个卵巢包含4条卵巢小管,可见一个卵巢包含5条卵巢小管的现象。有翅型和无翅型个体卵巢中胚胎总数量和成熟胚胎数量以及最大胚胎体积随发育时间增加均显著增大,但有翅型个体胚胎总数量和成熟胚胎数量以及最大胚胎体积均显著小于同一发育阶段无翅型个体。有翅型和无翅型的3龄和4龄若蚜以及成蚜卵巢中胚胎总数量与后足胫节长度均呈显著正相关关系。有翅型和无翅型大豆蚜卵巢小管中最大胚胎体积随发育时间均呈指数增长,但有翅型个体最大胚胎体积显著小于无翅型个体。【结论】有翅型大豆蚜相比于无翅型个体存在卵巢发育延迟现象,卵巢发育程度的差异可能与翅的发育相关。     

Competition and dispersal in the pea aphid: clonal variation and correlations across traits

Abstract.  1. The presence of an across-species trade-off between dispersal ability and competitive ability has been proposed as a mechanism that facilitates coexistence. It is not clear if a similar trade-off exists within species. Such a trade-off would constrain the evolution of either trait and, given appropriate selection pressures, promote local adaptation in these traits.
2. This study found substantial levels of heritable variation in competitive ability of the pea aphid, Acyrthosiphon pisum Harris (Homoptera: Aphididae), measured in terms of relative survival when reared with a single clone of the vetch aphid, Megoura viciae Buckton (Homoptera: Aphididae).
3. Pea aphids can move to new patches by either flying (longer distance dispersal) or walking (local dispersal) from plant to plant. There was considerable clonal variation in dispersal ability, measured in terms of the proportion of winged offspring produced, and ability to survive away from their host plant.
4. Winged individuals showed longer off-plant survival times than wingless forms of the same pea aphid clone.
5. There was no evidence of a relationship between clonal competitive ability and either measure of dispersal ability, although the power of the test is limited by the number of pea aphid clones used in the trial.
6. However, there was a positive correlation between clonal fecundity and the proportion of winged offspring produced. Although speculative, it is suggested that clones that are more likely to either overwhelm their host plant or attract higher numbers of natural enemies as a result of having higher fecundity are more likely to produce winged morphs.     

Effects of dietary enrichment with a marine oil-based n-3 LCPUFA supplement in sows with predicted birth weight phenotypes on birth litter quality and growth performance to weaning

The effects of a marine oil-based n-3 long-chain polyunsaturated fatty acid (mLCPUFA) supplement fed to the sow from weaning, through the rebreeding period, during gestation and until end of lactation on litter characteristics from birth until weaning were studied in sows with known litter birth weight phenotypes. It was hypothesized that low birth weight (LBW) litters would benefit more from mLCPUFA supplementation than high birth weight litters. A total of 163 sows (mean parity=4.9±0.9) were rebred after weaning. Sows were pair-matched by parity and litter average birth weight of the previous three litters. Within pairs, sows were allocated to be fed either standard corn/soyabean meal-based gestation and lactation diets (CON), or the same diets enriched with 0.5% of the mLCPUFA supplement at the expense of corn. Each litter between 9 and 16 total pigs born was classified as LBW or medium/high average birth weight (MHBW) litter and there was a significant correlation (P<0.001) between litter average birth weight of the current and previous litters within sows (r=0.49). Sow serum was harvested at day 113 of gestation for determination of immunoglobulin G (IgG) concentrations. The number of pigs born total and alive were lower (P=0.01) in mLCPUFA than CON sows, whereas the number of stillborn and mummified pigs were similar between treatments. Number of stillborns (trend) and mummies (P<0.01) were higher in LBW than MHBW litters. Tissue weights and brain : tissue weight ratios were similar between treatments, but LBW litters had decreased tissue weights and increased brain : tissue weight ratios compared with MHBW litters. Placental weight was lower (P=0.01) in LBW than MHBW litters, but was not different between treatments. Average and total litter weight at day 1 was similar between treatments. mLCPUFA increased weaning weight (P=0.08) and average daily gain (P<0.05) in MHBW litters, but not in LBW litters. Pre-weaning mortality was similar between treatments, but was higher (P<0.01) in LBW than MHBW litters. IgG concentration in sow serum was similar between treatments and litter birth weight categories. In conclusion, litter birth weight phenotype was repeatable within sows and LBW litters showed the benchmarks of intra-uterine growth retardation (lower placental weight and brain sparing effects). As maternal mLCPUFA supplementation decreased litter size overall, only improved litter growth rate until weaning in MHBW litters, and did not affect pre-weaning mortality, maternal mLCPUFA supplementation was not an effective strategy in our study for mitigating negative effects of a LBW litter phenotype.     

Low birth weight,intrauterine growth-retarded,and pre-term infants

Low birth weight, intrauterine growth retardation, and prematurity are overwhelming risk factors associated with infant mortality and morbidity. The lack of efficacious prenatal screening tests for these three outcomes illuminates the problems inherent in bivariate estimates of association. A biocultural strategy for research is presented, integrating societal and familial levels of analysis with the metabolic, immune, vascular, and neuroendocrine systems of the body. Policy decisions, it is argued, need to be based on this type of biocultural information in order to impact the difficult-to-change problems of low birth weight, intrauterine growth retardation, and prematurity. The analysis and writing of this study was funded, in part, by a grant from the National Institute of Child Health and Human Development (NICHD RO1 HD 20511). Troy D. Abell is associate professor of anthropology and adjunct associate professor of family medicine at the University of Oklahoma. His major interests are in the biocultural determinants of fetal growth and the epistemologic issues inherent in statistical reasoning in scientific inference and decision analysis.     

Transgenic production from in vivo-derived embryos: effect on calf birth weight and sex ratio

We examined transgenic-cattle production by DNA microinjection into 1-, 2-, and 4-cell embryos, analyzing the impact on calf size and subsequent viability. Embryos were either collected at an abattoir by flushing oviducts from superovulated and artificially inseminated cows (in vivo-derived) or obtained by in vitro maturation and in vitro fertilization of oocytes aspirated from excised ovaries (in vitro-derived). A human serum albumin (hSA) milk-expression DNA construct was microinjected, either in one of the visible pronuclei of in vitro- and in vivo-derived 1-cell embryos or in the nuclei of two blastomeres of 2- and 4-cell in vivo-derived embryos. Microinjection-induced mortality (lysis and developmental block) was equivalent ( approximately 40%) for all microinjected embryos. Embryos were co-cultured with BRL cells in B-2 medium containing 10% fetal calf serum (FSC). Overall, embryo development to morulae/blastocysts was significantly greater for in vivo-derived ova (15.5%) than for in vitro-derived oocytes (9.3%). All morulae and blastocysts were transferred to synchronized recipient females on Days 6-8 post-fertilization. A total of 189 calves were delivered. Birth weights were significantly greater for calves generated from in vitro-derived oocytes compared with those generated from in vivo-derived oocytes. One transgenic bull calf was obtained from the microinjection of a 2-cell embryo. Fluorescence in situ hybridization (FISH) analysis of lymphocytes detected one transgenic integration site in all cells. Transmission frequency of the hSA transgene in embryos obtained through IVM/IVF/IVC utilizing the semen of the transgenic calf confirmed that it was not mosaic.     

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.     

Seed weight and seed resources in relation to plant growth rate

Summary Relative growth rate in radish is not influenced by initial seed weight.     

Sources of sire-specific genetic variance for birth and weaning weight in Bruna dels Pirineus beef calves

This research investigated two sources of sire-specific genetic effects on the birth weight (BWT) and weaning weight (WWT) of Bruna dels Pirineus beef calves. More specifically, we focused on the influence of genes located in the non-autosomal region of the Y chromosome and the contribution of paternal imprinting. Our analyses were performed on 8130 BWT and 1245 WWT records from 12 and 2 purebred herds, respectively, they being collected between years 1986 and 2010. All animals included in the study were registered in the Yield Recording Scheme of the Bruna dels Pirineus breed. Both BWT and WWT were analyzed using a univariate linear animal model, and the relevance of paternal imprinting and Y chromosome-linked effects were checked by the deviance information criterion (DIC). In addition to sire-specific and direct genetic effects, our model accounted for random permanent effects (dam and herd-year-season) and three systematic sources of variation, that is, sex of the calf (male or female), age of the dam at calving (six levels) and birth type (single or twin). Both weight traits evidenced remarkable effects from the Y chromosome, whereas paternal imprinting was only revealed in WWT. Note that differences in DIC between the preferred model and the remaining ones exceed 39 000 and 2 800 000 DIC units for BWT and WWT, respectively. It is important to highlight that Y chromosome accounted for ∼2% and ∼6% of the total phenotypic variance for BWT and WWT, respectively, and paternal imprinting accounted for ∼13% of the phenotypic variance for WWT. These results revealed two relevant sources of sire-specific genetic variability with potential contributions to the current breeding scheme of the Bruna dels Pirineus beef cattle breed; moreover, these sire-specific effects could be included in other beef cattle breeding programs or, at least, they must be considered and appropriately analyzed.     

Hypothalamus integrity and appetite regulation in low birth weight rats reared artificially on a high-protein milk formula

High-protein (HP) milk formulas are routinely used in infants born with a low birth weight (LBW) to enhance growth and ensure a better verbal IQ development. Indirect evidence points to a link between an HP intake during early life and the prevalence of obesity in later life. We hypothesized that HP milk supplementation to LBW pups during early postnatal life would impact hypothalamic appetite neuronal pathways development with consequences, at adulthood, on energy homeostasis regulation. Rat pups born with a LBW were equipped with gastrostomy tubes on the fifth day of life. They received a milk formula with either normal protein (NP, 8.7 g protein/dl) or high protein content (HP; 13.0 g protein/dl) and were subsequently weaned to a standard, solid diet at postnatal day 21. Rats that had been fed HP content milk gained more weight at adulthood associated with an increase of plasma insulin, leptin and triglycerides concentrations compared to NP rats. Screening performed on hypothalamus in development from the two groups of rats identified higher gene expression for cell proliferation and neurotrophin markers in HP rats. Despite these molecular differences, appetite neuronal projections emanating from the arcuate nucleus did not differ between the groups. Concerning feeding behavior at adulthood, rats that had been fed HP or NP milk exhibited differences in the satiety period, resting postprandial duration and nocturnal meal pattern. The consequences of HP milk supplementation after LBW will be discussed in regard to neural development and metabolic anomalies.     

Inhibition by kinoprene of photoperiod-induced male production by apterous and alate viviparae of the aphid Myzus persicae

Photoperiod-induced male production by apterous and alate viviparae of the green peach aphid. Myzus persicae, was reduced or prevented by treating the aphids with the JH analog kinoprene (Zoecon's insect growth regulator ZR 777). Concomitant with this reduction in the number of males was an increase in the production of females. This was most clearly demonstrated for apterous viviparae that had been raised from birth under weak long-night regimes of 10–10.5 hr dark day, and exposed to 0.1% kinoprene-treated radish seedlings for 2–3 days on reaching the fourth larval instar or adulthood.Male production by alate viviparae, whose apterous mothers were born and raised for 5 days under a long-night regime of 15 hr dark day and then maintained under a short-night regime of 8 hr dark day, was completely inhibited by exposing them to kinoprene-treated plants for 2–3 days when they had reached the fourth instar.It is concluded that the kinoprene treatment affects sex chromosome replication in the oögonia of an aphid so that these germ cells develop parthenogenetically into females (2n = 12 with two X chromosomes) rather than males (2n = 11 with one X chromosome). This may result either from a direct action of absorbed kinoprene on the oögonia or from an indirect action whereby the kinoprene stimulates the insect's hormonal system to produce a hormone that stimulates development of the oögonia into females.     

Risk factors for low birth weight: Results from a case-control study in southern Spain

The main objective of this study is to examine the effect of several variables, including altitude of maternal residence, on delivering a low birth weight (LBW) newborn. A case-control study was done. Two hundred forty cases (single newborn weighing less than 2,500 g) and 374 controls (single newborn weighing more than 2,499 g) were included. Information was gathered from the clinical chart of delivering women, through a personal interview and the Spanish Census Bureau (for altitude). Predictors of LBW were assessed through stepwise logistic regression analysis. Several well-known LBW risk factors were identified: hypertension, weight gain during pregnancy, body size (mainly maternal prepregnancy weight), low social class, primiparity, and several conditions (spontaneous delivery, abruptio placentae). Altitude was an independent predictor of LBW at term (more than 37 weeks of gestational age) but not for preterm LBW. Nevertheless, a relationship between altitude and birth weight was not found in controls, although a moderate decreasing gradient with altitude was observed. The limitations of these findings are discussed. Am J Phys Anthropol 105:419–424, 1998. © 1998 Wiley-Liss, Inc.     

Genetic determinism for within-litter birth weight variation and its relationship with litter weight and litter size in the Ripollesa ewe breed

Birth weight plays a central role in lamb survival and growth, and the knowledge of its genetic determinism has become essential in worldwide selection programmes. Within this context, within-litter birth weight variation (BWV) has been suggested as an attractive trait to homogenise litters in prolific species, although it has not been analysed in sheep. The objective of this study was to ascertain whether maternal additive genetic variance exists for BWV in Ripollesa ewes, and to study its genetic, permanent environmental and residual relationships with litter weight (LW) and litter size (LS) at birth. Data were recorded in the Ripollesa experimental flock of the Universitat Autònoma of Barcelona, between 1986 and 2005, and included 1 662 litters from 380 ewes, with 712 records of BWV and 1 530 records of LW. Traits were analysed with a multivariate animal model solved through Bayesian methodologies, and with a threshold characterisation of LS. Additionally, the effect of BWV on lamb survival was studied. Additive genetic variance was observed for BWV (h² = 0.061), as well as for LW (h² = 0.200) and LS (h² = 0.141). Nevertheless, genetic correlations among those traits were not substantial (BWV and LW = 0.151; BWV and LS = − 0.219; LW and LS = − 0.320) and suffered from a high degree of uncertainly, with the null correlation included within the highest posterior interval at 95%. Within-litter birth weight variation and LS showed a negative and large permanent environmental correlation ( − 0.872), and LW and LS were negatively correlated due to residual ( − 0.762) and permanent environmental ( − 0.449) random sources of variation. Within-litter birth weight variation influenced lamb mortality during the first 7 days of life (P < 0.05), increasing and decreasing survivability in heavier and lighter littermates, respectively. Nevertheless, stillbirths and lambs died after the 1st week of life were not affected by BWV (P>0.05). The low heritability found indicates that slow genetic progress may be expected from selecting for BWV. Close to zero genetic correlations suggest that this selection will probably not affect LS and LW, although some significant permanent and residual correlations must be taken into account. Further studies are needed to understand better the genetic architecture among these three reproductive traits.