Effects of aminoglutethimide phosphate administration on the incidence of pregnancy and number of live fetuses in superovulated rats

This study examined the effects of aminoglutethimide phosphate (AGP) administration on the incidence of pregnancy and number of live fetuses in superovulated rats. Immature (31- to 33-day-old) young (8- to 9-week-old) and (14- to 16-week-old) rats were treated with 20 or 40 IU of PMSG and the same dosses of hCG at 52 to 54 hour-intervals (GTH rats). One half of the GTH rats were injected with 10 mg AGP twice a day for the first 3 days of pregnancy (AGP rats). Pregnancy rates of all AGP rats (95 to 100%) were much higher than the GTH rats (12.7). Young and adult AGP rats treated with 20 IU of GTH had 14.7 and 15.3 live fetuses per dam, respectively. These numbers of live fetuses increased to 17.8 and 18.4 after treatment with 40 IU of GTH. These values were significantly greater than those of the control rats (12.3 to 12.8; P<0.01), but the fetal weights were lower. The results show that AGP administration improves pregnancy rates and the number of live fetuses in young and adult superovulated rats.     

Genetic parameters for canalisation analysis of litter size and litter weight traits at birth in mice

The aim of this research was to explore the genetic parameters associated with environmental variability for litter size (LS), litter weight (LW) and mean individual birth weight (IW) in mice before canalisation. The analyses were conducted on an experimental mice population designed to reduce environmental variability for LS. The analysed database included 1976 records for LW and IW and 4129 records for LS. The total number of individuals included in the analysed pedigree was 3997. Heritabilities estimated for the traits under an initial exploratory approach varied from 0.099 to 0.101 for LS, from 0.112 to 0.148 for LW and from 0.028 to 0.033 for IW. The means of the posterior distribution of the heritability under a Bayesian approach were the following: 0.10 (LS), 0.13 (LW) and 0.03 (IW). In general, the heritabilities estimated under the initial exploratory approach for the environmental variability of the analysed traits were low. Genetic correlations estimated between the trait and its variability reached values of -0.929 (LS), -0.815 (LW) and 0.969 (IW). The results presented here for the first time in mice may suggest a genetic basis for variability of the evaluated traits, thus opening the possibility to be implemented in selection schemes.     

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.     

Selection response for litter size at birth and litter weight at weaning in the first parity in mice

Summary Five 60-pair lines of mice were selected for seven generations for the following criteria: number born alive (LSO), random selection of litters (LC), number born alive divided by the weight of the dam at 9 weeks (LSO/DWT), total litter weight weaned divided by the weight of the dam at 9 weeks (LWT/DWT), and weight of litter weaned (LWT). All traits were measured in the first parity only and litters were not standardized. Realized heritabilities for LSO, LWT, LSO/DWT, and LWT/ DWT were 0.10± 0.06, 0.11±0.07, 0.22 ± 0.04, and 0.22 ± 0.08, respectively. Selection response for the two ratio lines was due to correlated responses in the respective numerators, LSO and LWT, as DWT did not decrease. In terms of improving LWT, selection for LWT/ DWT was three times as effective as selection for LSO/ DWT.     

Effects of litter size on sympathetic activity in young adult rats

Rearing animals in small litters induces a permanent increase in body weight and body fat. To determine whether changes in sympathoadrenal activity contribute to this effect, litter size was adjusted the day after birth and maintained until weaning at 21 days. Sympathetic nervous system (SNS) activity was measured in adult animals using [(3)H]norepinephrine ([(3)H]NE) turnover in peripheral tissues. Although litter size was without effect on [(3)H]NE turnover in chow-fed animals, acceleration of [(3)H]NE turnover by dietary sucrose was completely abolished in heart and attenuated in interscapular brown adipose tissue and kidney of rats reared in small litters. Body and epididymal fat-pad weights were heavier in rats reared in small litters; however, weight gain in response to dietary enrichment with sucrose did not differ as a function of litter size. Thus litter size alters dietary activation of the SNS, and this effect presumably reflects changes in central nervous system regulation.     

Influence of month and climatic factors on the period of birth,litter size,birth weight and preweaning mortality of sheep in Ghana

Relationships between month and clinatic factors-rainfall, ambient temperature, relative humidity (RH) and temperature-humidity index (THI)-with time of parturition, litter size, birth weight and preweaning mortality were studied in Djallonke and Dja lonke x Sahelian sheep. Births (4142) occurred all year round although there were significant differences in the number of births per month. Maximum litter size did not coincide with the maximum births. Peak conceptions occurred in the early parts of the major rainy season. There were also significant differences in birth weights and mortalities (%) per month. Maximum and minimum values (of birth weighs and mortalities) occurred in the latter part of the rainy seasons and dry periods respectively. There were significant positive correlations between litter size and cumulative rainfall in the 4th–6th months periods prior to lambing. Birth weights of both males and females were positively and significantly associated with minimum temperature and cumulative rain-fall in the 2- and 3-months period prior to lambing respectively. There were significant positive correlations between mortality and minimum and maximum RH and cumulative rainfall in the 3 months after lambing.     

Analysis of litter size and average litter weight in pigs using a recursive model

An analysis of litter size and average piglet weight at birth in Landrace and Yorkshire using a standard two-trait mixed model (SMM) and a recursive mixed model (RMM) is presented. The RMM establishes a one-way link from litter size to average piglet weight. It is shown that there is a one-to-one correspondence between the parameters of SMM and RMM and that they generate equivalent likelihoods. As parameterized in this work, the RMM tests for the presence of a recursive relationship between additive genetic values, permanent environmental effects, and specific environmental effects of litter size, on average piglet weight. The equivalent standard mixed model tests whether or not the covariance matrices of the random effects have a diagonal structure. In Landrace, posterior predictive model checking supports a model without any form of recursion or, alternatively, a SMM with diagonal covariance matrices of the three random effects. In Yorkshire, the same criterion favors a model with recursion at the level of specific environmental effects only, or, in terms of the SMM, the association between traits is shown to be exclusively due to an environmental (negative) correlation. It is argued that the choice between a SMM or a RMM should be guided by the availability of software, by ease of interpretation, or by the need to test a particular theory or hypothesis that may best be formulated under one parameterization and not the other.     

Assessing survey measures of infant birth weight and birth size in Ecuador

The purpose of this study was to assess the utility of using maternal assessments of infant birth size as proxy measures for birth weight in Ecuador, a country in which a sizeable proportion of births take place at home, where birth weight is typically not recorded. Four thousand and seventy-eight women who experienced a live singleton birth between January 1992 and August 1994 were interviewed in the Ecuador Demographic and Maternal-Child Health Survey. All women were asked if their child was weighed at birth, his/her weight, and what they considered to be his/her birth size relative to other newborns. The consistency between birth size and birth weight measures was assessed, and the differences between infants with and without reported birth weights were explored. The authors conclude that maternal assessments of birth size are poor proxy indicators of birth weight. Estimates of low birth weight based on maternal assessments of birth size as very small should be recognized as underestimates of the actual prevalence of low birth weight. Moreover, infants for whom birth weights are missing should not be considered similar to those for whom weight was reported. Those without reported birth weights are more likely to be low birth weight. Thus, relying solely on reports of numeric birth weight will underestimate the prevalence of low birth weight.     

Effects of teat number on litter size in gilts

This study was carried out to investigate the effects of teat number and interval at first estrus and mating on litter size in Duroc, Landrace and Yorkshire gilts. Gilt body weight at first estrus was from 101.5 kg to 115.3 kg and gilts normally attained puberty at 170.5-181.5 days of age. Breed differences among Duroc, Landrace and Yorkshire in body weight and age at first estrus and mating were found. Total teat number of Duroc, Landrace and Yorkshire were 12.5, 14.9 and 13.7, respectively. Teat interval from pectoral to inguinal region and from left to right at first estrus and mating did not show any differences among the breeds. In conclusion, 14 or more teat number compared to 11-13 teat number in gilts increased litter size at birth and at 21 day weaning.     

Effects of graded doses of the pesticide heptachlor on body weight,mating success,oestrous cycle,gestation length and litter size in laboratory rats

Adult female Sprague-Dawley rats were injected with 5 or 20 mg/kg body weight heptachlor solution every other day for up to 18 days. They were weighed every day and the stage of oestrus determined by vaginal smears. One experimental group was mated and pregnancy characteristics studied. Heptachlor affected body weights, cycle patterns, length of gestation period and litter sizes in a dose-related manner. At a dose of 20 mg/kg body weight, heptachlor caused a significant decrease in average body weight (P < 0.01), disrupted and/or prolonged oestrous cycles, decreased mating success (P < 0.001), slightly increased gestation length (P < 0.05) and decreased litter size (P < 0.01).     

Effects of birth weight on later intelligence

Abstract

Identical twins are used to show the long‐term effects of birth weight when genetic and many environmental factors are controlled. Female twins between the ages of 6 and 10 are evaluated for performance IQ and other measures of activity. No relationship was found between any of these measures and birth weight except for IQ. The heavier cotwin had the higher IQ score even when the birth weight of each twin was above 2,500 grams. Birth order was not associated with intelligence within the twin pairs.     

Effects of litter size on maternal care, body weight and infant development in golden hamsters (Mesocricetus auratus)

The effects of litter size on maternal care, body weight and infant development of golden hamsters were investigated from a longitudinal perspective. Litters were culled to 1,3,6 and 9 pups, and the behavior and body weight of mothers and pups were recorded from the 5th to the 25th postpartum day. We noted that the time spent by mothers in bodily interactions with pups decreased as a function of litter size; maternal pup retrievals reached their maximum around the 13-15th day, which coincided with the increased locomotor activity of pups at this time; the total number of pup retrievals by the mother increased as a function of the litter size, but mothers of larger litters were more 'efficient' (i.e. they failed less frequently in exhibiting a full sequence of retrievals) and exhibited a low litter-size proportional mean number of retrievals. All mothers gradually lost body mass throughout lactation, and decrease in body weight was significantly related to litter size. The mean body weight gain (%) by pups decreased as a function of litter size, but we also noted that single and larger litter pups exhibited a decreased body mass (grams) by the 15th day, suggesting that infant development may be impaired at both extremes of experimental conditions. We concluded that the behavior of mothers and pups was affected by the litter size, and it appeared that the litter had an optimal size-not so large as to overlap the mother's physical capacity, and not so small as to fail to compensate for the parental investment.     

Single-trait and antagonistic index selection for litter size and body weight in mice

Individual selection based on female performance only was conducted in four lines of mice: L⁺ for increased litter size, W⁺ for increased 6-week body weight, L^-W⁺ for a selection index aimed at decreasing litter size and increasing 6-week body weight and L⁺W^- for a selection index aimed at increasing litter size and decreasing 6-week body weight. A fifth line (K) served as an unselected control. All litters were standardized to eight mice at one day of age. Expected heritability was based on twice the regression of offspring on dam (h²_d), which contains additive genetic variance due to direct (σ²_Ao) and maternal (σ²_Am) effects and their covariance (σ_AoAm). Responses and correlated responses were measured either deviated (method 1) or not deviated (method 2) from the control line. Realized heritabilities (h²_R) for litter size were 0.19 ± 0.04 (1) and 0.16 ± 0.03 (2), which were similar to h ²_d of 0.17 ± 0.04. The h² _R for 6-week body weight of 0.55 ± 0.07 (1) and 0.44 ± 0.07 (2) agreed with h²_d of 0.42 ± 0.02. Realized genetic correlations (r*_GR) between litter size and 6-week body weight calculated from the double-selection experiment were 0.52 ± 0.10 (1) and 0.52 ± 0.13 (2), which were not significantly different from the base population estimate of r* _Gd = 0.63 ± 0.14. Divergence (L^-W ⁺ minus L⁺W^-) in the antagonistic index selection lines was 0.21 ± 0.01 index units (I = 0.305 P_W - 0.436 P_L, where P _W and P_L are the phenotypic values for 6-week body weight and litter size, respectively.). The h² _R of index units of 0.14 ± 0.02 calculated from divergence agreed with h²_d of 0.14 ± 0.04. Divergences in litter size (-0.19 ± 0.07) and 6-week body weight (0.46 ± 0.10) were in the expected direction. Antagonistic index selection yielded about one-half the expected divergence in litter size, while divergence in 6-week body weight was only slightly less than expected. Realized genetic correlations indicated that litter size, 6-week body weight and index units each showed positive pleiotropy with 3-week body weight, postweaning gain and weight at vaginal introitus and negative pleiotropy with age at vaginal introitus. Sex ratio and several components of fitness (days from joining to parturition, percent fertile matings and percent perinatal survival) did not change significantly in the selected lines.     

Effects of simulated increases in body weight from birth on the growth of limb bones in rats

The purpose of this study was to subject groups of newborn male and female Sprague-Dawley rats each to a specific 10% simulated increase in body weight, to a maximum of a doubling of body weight, to study the effects of quantified, increased, intermittent, compressive forces on limb bone growth. Chronic centrifugation was employed. After 90 days of centrifugation the rats were sacrificed. The humerus, radius, ulna, femur, and tibia were removed from each animal, cleared of all soft tissues, measured and weighed. Tukey's Studentized multiple range test was performed to identify aggregations (sets) of force groups between which there are significant differences. The data suggest that newborn male and female rats subjected to simulated increases in body weight, within the range used for this study, undergo enhanced general body growth and limb bone growth.