1st Litter Research Articles

19 Overview of the National Pork Board replacement gilt feet and leg evaluation trial

Abstract Replacement gilt feet and leg conformation traits are subjectively evaluated at early ages (150 d) in order to select acceptable replacements. The objectives of this study were to: 1) evaluate replacement gilt feet and leg conformation (FLC) using subjective and objective measurement methods, 2) estimate objective joint angle changes over two parities, and 3) evaluate the effect of three diets differing in standardized ileal digestible (SID) lysine concentrations on FLC traits using the objective evaluation method. Crossbred Large White × Landrace gilts (n = 641) were used. Gilts were moved to GDU at 77 days-of-age and randomly allotted to three ad libitum fed dietary treatments providing similar ME but differing in SID lysine concentrations (low, medium, and high) during the grow-finisher period. All animals received common gestation and lactation diets. Feet and leg conformation traits were evaluated at 100 d, 200 d, 1st litter (392 ± 25 d) and 2nd litter (548 ± 49 d) weaning events. Subjective evaluation was done on a scale from 1 to 5. Data were analyzed using mixed linear model methods. The majority of gilts received the intermediate score (i.e. 3) when joint angles were subjectively evaluated. No differences (P ≥ 0.05) were observed for knee, front pastern and hock objective joint angles between subjective scores assigned. Differences in subjectively evaluated rear pastern (P < 0.05) were observed, where objective joint angles associated with scores of ≤ 2 and 3 were lower than score of ≥ 4. There was no interaction between dietary treatment and objective evaluation time-period for any FLC traits studied (P > 0.05). Females with greater knee, hock, front and rear pastern objective joint angles at 100 d of age, continued to have greater joint angles (0.2 ± 0.04 degrees; P < 0.001) later in life. Front and rear pastern joint angles decreased (P < 0.001) and hock joint angles increased from 100 d to end of study (P < 0.001).

Use of repopulation for optimizing sow reproductive performance and piglet loss

The objective of this study was to analyse sow reproductive performance and piglet loss from birth to weaning before and after repopulation of a selected farm. The observation was carried out on a productive sow farm; 160 sows were included in the experiment. Before repopulation, 80 sows from the 1stto the 5thlitter were evaluated. The original population of sows was removed. Repopulated (newly stocked) group consisted of 80 gilts at the 1stlitter. Newly delivered gilts with a status of minimum disease were placed into a decontaminated stable with a strict batch, black and white breeding system with stringent hygienic provisions. The piglets were weaned at the mean age of 28 ± 3 days. A very highly significant difference (P≤ 0.001) in favour of the repopulated group of sows was found in the evaluation of the total number of piglets, the number of live-born piglets and the number of stillborn piglets in %; a significant difference (P≤ 0.05) in favour of the repopulated group of sows was found in the number of stillborn piglets. In reared piglets and losses of piglets, both in numbers and percentage, a highly significant difference (P≤ 0.001) was found in favour of the repopulated group. This study brings important information on the benefits of repopulation pig breeding.

Genetic parameters for feed intake, litter weight, body condition and rebreeding success in primiparous Norwegian Landrace sows

The aim of this study was to estimate genetic parameters for feed intake recorded as farmers’ perception of young sows’ appetite for the first 3 weeks of lactation (APP) and feed intake recorded for one day in the 3rd week of lactation (FEED), litter weight (LW) at 3 weeks, sow body condition at weaning (BC) and the following five reproduction traits: weaning-to-service interval of 1 to 7 days (WSI7), weaning-to-service interval of 1 to 50 days (WSI50), delayed service or not (DELAYED), pregnant on first service or not (PREGNANT) and litter size in 2nd parity (NBT2). The analyses included data on 4606 Norwegian Landrace 1st-parity sows and their litters. The Gibbs sampling method was used. The traits DELAYED and PREGNANT were analysed as threshold traits and APP, FEED, LW, BC, WSI7, WSI50 and NBT2 were analysed as linear traits. The heritability estimates for APP and FEED were low (<0.1), whereas the estimates for DELAYED and PREGNANT were rather high (0.4 and 0.3). The heritability estimate for BC was 0.2. The genetic correlations confirmed the complexity of breeding for sow performance; selection for heavy 1st litters may lead to lower body condition at weaning, which in turn leads to lower reproductive performance and smaller litters in 2nd parity. Selection for higher sow feed intake would improve body condition, but the simple way of measuring feed intake tested in this study (APP and FEED) cannot be recommended because of the low heritability obtained for these traits.

Birth timing for mountain lions (Puma concolor); testing the prey availability hypothesis.

We investigated potential advantages in birth timing for mountain lion (Puma concolor) cubs. We examined cub body mass, survival, and age of natal dispersal in relation to specific timing of birth. We also investigated the role of maternal age relative to timing of births. We captured mountain lion cubs while in the natal den to determine birth date, which allowed for precise estimates of the population birth pulse and age of natal dispersal. A birth pulse occurred during June–August. Body mass of cubs was related to litter size and timing of birth; heaviest cubs occurred in litters of 2, and those born after 1 July. Cubs born within pulse months exhibited similar survival to those born out of the pulse. We found that cubs born April–June dispersed at younger ages than those born after 1 July. There was less variation in birth timing for 1st litters of females than older females. We hypothesize that cubs born after the peak in births of neonate prey are advantaged by the abundance of vulnerable prey and those cubs and mothers realize an evolutionary advantage.

Home ranges of Bengal tiger (Panthera tigris tigris L.) in Pench Tiger Reserve, Madhya Pradesh, Central India

The home range size is an important parameter required for effective conservation and management of a species. Home ranges of three radio collared Bengal tigers (Panthera tigris tigirs) (one adult female or AF, one adult male or AM and one sub-adult male or SAM) were studied between March 2008 and December 2011 in Pench Tiger Reserve (PTR), Madhya Pradesh, Central India. Using 95% Minimum Convex Polygon (MCP), the estimated home range of AF (n= 750 locations) was 43 km², AM (n= 118 locations) was 55.1 km2 and SAM (n= 734 locations) was 52.2 km2. Using 95% Fixed Kernel (FK), the home range of AF was 32.1 km², AM was 64.1 km2 and SAM was 19.1 km2. The core area of activity for each tiger as determined by 50% Fixed Kernel (FK) method was 6.2 km² for AF, 13.4 km2 for AM and 4.1 km2 for SAM. The estimated overlap area between AM and AF using 95% FK was 19.2 km² (65 %), whereas it was 15.4 km² (48%) between AF and SAM. The AF recruited three, four and five cubs in her 1st, 2nd and 3rd litter respectively. Minimum 44% of the original natal area was used by AF at the time of raising her 2nd litter and 46% in her 3rd litter. Though there was a gradual increase of annual home range observed for first two years but the core activity area remained considerably same for AF over the study period. The study revealed that minimum of 25 to 30 km² area was required for a breeding female in PTR where wild prey density (348.2/km²) was found to be high with adequate ground cover for the successful raising of cubs up to dispersal stage. The findings highlight the need for developing a long term monitoring system for tigers in PTR and surrounding habitats to understand the survival and dispersal patterns.

Reproductive performance of second parity sows: Relations with subsequent reproduction

The objective of this study was to determine relations between reproductive performance, i.e. being a repeat breeder and litter size, in 2nd parity and reproductive performance in later parities. In addition, relations between the 1st and 2nd parity litter size and litter size in later parities were determined. First, 184,135 records from 46,571 sows were used to analyze the effect of being a repeat breeder in 2nd parity on subsequent farrowing rate, litter size and parity number at culling. Second, 161,521 records of 39,654 sows were used to analyze the effect of litter size from 1st insemination in 2nd parity, being either low (≤10 piglets total born), medium (11–13) or high (≥14), on subsequent litter size, farrowing rate and parity number at culling, with litter size in 1st parity included in the model as well. In total 15.7% of the sows inseminated in 2nd parity were a repeat breeder in 2nd parity. Being a repeat breeder in 2nd parity did not affect litter size in subsequent parities, however it decreased farrowing rate in parity 3 (4.1%) and 4 (3.4%), but not in later parities (P<0.05). Repeat breeders in 2nd parity were culled on average 2 parities earlier compared with non-repeat breeders (resp. parity 5 vs. 7, P<0.05). Sows with a low litter size in 2nd parity showed a lower litter size in parity 3 and up compared with sows with a medium or high litter size in 2nd parity (P<0.05). The magnitude of this effect, however, decreased if litter size in 1st parity increased. For example, the difference in piglets born in parity 3–5 between sows with a low and high litter size in 2nd parity was −4.6 piglets for sows with a low litter size in 1st parity. This difference decreased to −3.3 piglets for sows with a high litter size in 1st parity. Sows with a high litter size in 2nd parity had 2% lower farrowing rate in parity 3, but not in later parities. Sows with a low litter size in 2nd parity were culled 1 parity earlier compared with sows with a medium or high litter size in 2nd parity. This study showed that a large part of the sows with poor reproductive performance in 2nd parity can be expected to have a poor reproductive performance in subsequent parities. The effect of 2nd parity litter size on subsequent litter size, however, depends on 1st parity litter size.

Evaluation of the anticoccidial efficacy of Cycostat® in experimentally infected breeding rabbits housed under conventional conditions.

&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;The present study was designed in order to evaluate the effi cacy and safety of Cycostat® 66G in the prevention and control of coccidiosis in breeding does after experimentally induced infection with common &lt;/span&gt;&lt;em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;Eimeria &lt;/span&gt;&lt;/em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;spp. at the age of 18 wk. The inoculum was prepared based on faecal samples collected on farms in the Czech Republic. A total of 94 young and pregnant does were divided into 4 groups and enrolled in the study. The zootechnical, clinical and parasitological results of 2 control groups were compared, a non-infected non-treated (NI-NT) and an infected non-treated (I-NT), and 2 infected and dietary supplemented groups, with 50 (I-50) and 66 mg/kg (I-66) robenidine, respectively. Does in the I-NT group showed a significant drop in weight gain and feed intake during the fi rst 14 d after inoculation. No treatment related effects on the weight development of the does were observed, although does in the I-NT group always had approximately ± 200 g lower body weight. Litter size (live born) was not signifi cantly different at either the fi rst or second parturition and amounted to 9.0, 8.2, 10.1 and 9.8 (1st litter) and 11.3, 10.4, 10.1 and 11.0 (2nd litter) in NI-NT, I-NT, I-50 and I-66 does, respectively. At weaning, both in the 1st and 2nd cycle, the highest litter weight was obtained in the I-50 and I-66 groups. Litter weaning weight values for I-66 (litter 2) were higher but not significant (&lt;/span&gt;&lt;em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;P=&lt;/span&gt;&lt;/em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;0.069) compared to the NI-NT litters. The lowest young mortality was also observed in the I-66 litters, both in the first and second cycles. Between 6 to 11 d after inoculation, the oocyst excretion of both supplemented groups was reduced by more than 90% in comparison to the I-NT. Supplementation with Cycostat® 66G diminished the excretion of &lt;/span&gt;&lt;em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;E. flavescens &lt;/span&gt;&lt;/em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;and &lt;/span&gt;&lt;em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;E. intestinalis&lt;/span&gt;&lt;/em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;, the most pathogenic species, by 100%. The excretion of &lt;/span&gt;&lt;em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;E. magna &lt;/span&gt;&lt;/em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;was reduced by &amp;gt;90 and 100% for the I-50 and I-66 groups, respectively. The reduction in oocyst excretion of &lt;/span&gt;&lt;em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;E. media &lt;/span&gt;&lt;/em&gt;&lt;span style="font-size: 11pt; font-family: 'Calibri','sans-serif';" lang="EN-US"&gt;was less pronounced. It was concluded that Cycostat® 66G supplemented in the feed at a concentration of 50 or 66mg/kg was able to prevent coccidiosis in breeding does after experimental inoculation.&lt;/span&gt;

Genetic analysis of reproductive performance in Landrace sows and its correlation to piglet growth

The aim of this study was to investigate the reproductive performance of sows, including the interval from weaning to service after 1st litter and litter size in the following (2nd) parity, as well as the direct and maternal genetic effects of piglet growth on these reproduction traits. Data on 15 946 Norwegian Landrace sows' 1st and 2nd parity, and on 106,962 piglets born in 11,323 1st parity litters were included in the analyses. In total, five traits were analysed. Weaning-to-service interval was based on a 1- to 7-day interval (WSI7) or a transformed 1- to 50-day interval (WSI50). A third reproduction trait was total number of piglets born in 2nd parity (NBTnext). Piglet weight was included in the analyses, either as average piglet weight in the litter at 3 weeks of age (meanW3) or as individual piglet weight gain during the first 3 weeks of life (IWG03). Genetic parameters were estimated with animal models, including both direct and maternal effects for IWG03. Heritability estimates for WSI7, WSI50 and NBTnext were 0.08, 0.03 and 0.09 respectively. For meanW3, the heritability estimate was 0.21. For IWG03, the direct and maternal heritability estimates were 0.15 and 0.10 respectively. Negative and unfavourable genetic correlations were estimated between meanW3 and NBTnext ( r g = − 0.37), and between IWG03 maternal and NBTnext ( r g = − 0.39). The ability to raise fast growing, heavy piglets seems to have an unfavorable effect on total number born in next litter but not on the weaning-to-service interval.

Within-litter variation of birth weight in hyperprolific Czech Large White sows and its relation to litter size traits, stillborn piglets and losses until weaning

Data from about 2900 litters (approximately 40,000 piglets) originating from 1063 Czech Large White hyperprolific sows were analyzed. The phenotypic and genetic relations between litter size traits, piglet mortality during farrowing and from birth to weaning and several statistics referring to the distribution of the birth weight within litter were analyzed. All genetic parameters were estimated from multi-trait animal models including the following factors: mating type (natural service or insemination), parity, linear and quadratic regression on age at first farrowing (1st litter) or farrowing interval (2nd and subsequent litters), herd-year-season effect and additive-genetic effect of the sow. The phenotypic correlations of the mean birth weight with the total number of piglets born and piglets born alive were −0.30. Traits describing the variability of the birth weight within litter (range, variance, standard deviation, coefficient of variation) were mostly positively correlated with litter size. A statistically significant phenotypic correlation (−0.09 to −0.15) between mean birth weight and losses at birth and from birth to weaning was found. The heritability for the number of piglets born, piglets born alive and piglets weaned was around 0.15. The number of stillborn piglets had only a very low heritability less than 0.05, whereas the heritability for losses from birth to weaning was 0.13. The heritabilities of the mean, minimal and maximal birth weight were 0.16, 0.10 and 0.10, respectively. The heritability for all statistics and measures referring to the variability of the birth weight within litter was very low and did never exceed the value of 0.05. An increase in litter size was shown to be genetically connected with a decrease in the mean piglet birth weight and an increase in the within-litter variability of birth weight. Selection on litter size should be accompanied by selection on mortality traits and/or birth-weight traits. Losses from birth to weaning and the minimal birth weight in the litter were proposed as potential traits for a selection against piglet mortality.

Test of the First-Cohort Advantage Hypothesis with Feathertail Gliders (Marsupialia)

The first-cohort advantage hypothesis (FCAH) was formulated to explain patterns of biased sex ratios in litters of Virginia opossums (Didelphis virginiana). Females of this species typically produce 2 litters each season, and litters born early in a season are male-biased and those born later in the season are female-biased. Males born earlier are older and heavier in the next breeding season and likely to secure more mates. The hypothesis predicts fitness benefits to mothers that have more males in their 1st litter (the 1st cohort) each season. The feathertail glider (Acrobates pygmaeus), in Victoria, Australia, is another species that produces 2 litters per year and not all males mature before the start of the breeding season after their birth. Hence, feathertail gliders also might be expected to show a pattern of sex bias in litters consistent with the FCAH. They do not. This paper uses data from 2 field studies of feathertail gliders in Victoria over the past 18 years. Sex ratios were recorded for 53 first- and 42 second-cohort litters. There was a trend toward male-biased litters in the 1st cohort, but also in the 2nd, and neither group differed significantly from a binomial distribution of sex ratios. This provides no support for the FCAH in this species. This may be due to the much less sharply defined breeding seasons in feathertail gliders compared to those of Virginia opossums, and to their greater longevity.

Maternal parity and diet (n-3) polyunsaturated fatty acid concentration influence accretion of brain phospholipid docosahexaenoic acid in developing rats.

The long-chain PUFA, docosahexaenoic acid [22:6(n-3), DHA], a major component of neuronal membrane phospholipids, accumulates in brain during late prenatal and early neonatal development and is essential for optimal attentional and cognitive function. Because all nutrition is supplied to the developing fetus/neonate by the mother and maternal DHA status is affected by parity, this study examined the effects of maternal diet and parity on DHA accretion in the developing brain. Whole brain total phospholipid fatty acid composition was determined by TLC and GC in weanling male Long-Evans rats (n = 5) from the 1st, 2nd, 3rd, or 4th litters of dams fed diets containing alpha-linolenic acid (ALA), containing ALA and preformed DHA (ALA + DHA), or lacking ALA (low-ALA). First-litter low-ALA offspring exhibited a decrease in phospholipid fatty acid DHA content to 68% of 1st-litter ALA pups. DHA in 2nd-litter low-ALA pups was further decreased to 55% of 1st-litter ALA pups, but further decreases were not observed in subsequent litters. DHA levels increased 15-20% in 2nd to 4th-litter ALA + DHA pups and 11% in 4th-litter ALA pups compared with 1st-litter ALA pups. These findings demonstrate that maternal diet and parity interact to affect offspring brain DHA status and suggest that maternal multiparity may place offspring at greater risk of decreased accretion of brain DHA if the maternal diet contains insufficient (n-3) PUFA.

REPRODUCTIVE PERFORMANCE AS A FUNCTION OF INBREEDING IN PRAIRIE VOLES (MICROTUS OCHROGASTER)

Most studies of inbreeding depression have confounded levels of inbreeding of parents with those of offspring. We used 4 experimental groups of prairie voles (Microtus ochrogaster) in which both parents and offspring were noninbred, parents and offspring were inbred, or parents and offspring differed in their level of inbreeding. For each pair, we recorded latency to the production of the 1st litter, number of litters produced and number of young born in 120 days, litter weights from birth to weaning, and parental behavior. Noninbred parents produced more litters and young and showed shorter interlitter intervals than did inbred parents. Inbred offspring weighed less at birth and weaning. We found no significant differences in parental behaviors among groups. Our results demonstrate that inbreeding depression occurs in prairie voles, and that it may be influenced more by physiological changes in inbred parents or young than by behavioral deficiencies in inbred parents. However, larger sample sizes could reveal that parental behavior does have an effect.

Stimulation of the Immune Response in B6C3F1 Mice by Genistein Is Affected by Exposure Duration, Gender, and Litter Order

The objective of this study was to determine whether immune responses could be differentially modulated by the phytoestrogen genistein (GEN) in mice from the 1st and 2nd litters, and whether the effects were persistent or reversible. B6C3F1 mice were exposed to a control or GEN-containing diet at 25, 250, and 1250 microg/g for the 1st litters, and 500 microg/g for the 2nd litters from d 0 of gestation to postnatal day (PND) 22, and through feeding after weaning. At PND42, anti-CD3 antibody-stimulated splenic T-cell proliferation and the percentages of T cells were increased in mice from the 1st litters at 250 and 1250 microg/g GEN but not from the 2nd litters. At PND84, the activity of IL-2-treated NK cells was significantly increased by GEN in mice from the 2nd litters but not from the 1st litters. The activity of cytotoxic T cells (CTLs) was also significantly increased by GEN in male mice from the 2nd litters. However, the increases in the CTL activity were not significant when the male mice were shifted from GEN-containing food to control food at PND22. Additionally, the increases in T-cell activities in female mice from the 1st litters and male mice from the 2nd litters were associated with a decrease in the percentage of CD4+CD25+ T regulatory cells. Overall, the results demonstrated that GEN could enhance the immune responses in mice from the 1st and 2nd litters; however, the effects varied depending on the exposure duration, gender, and litter order.

Shetland Sheepdog Leukodystrophy

Three litters of Shetland Sheepdog pups born to the same bitch and 2 different sires were studied because of uncontrollable seizures or progressive neurologic dysfunction. Four pups from the 1st litter, 1 from the 2nd litter, and 4 from the 3rd litter had severe diffuse spongy degeneration of the white matter of the brain and spinal cord. An inherited basis for this syndrome was suspected. The purpose of this study was to evaluate the pups with currently available screening tests for the metabolic, biochemical, infectious, and toxicologic causes of leukodystrophy seen in humans and animals. Computed tomography scans revealed diffuse hypomyeli‐nation in the affected pup. Complete postmortem examination, including histopathology and electron microscopy, delineated a leukodystrophy resembling human Canavan's disease, but amino acid and organic acid metabolism abnormalities were not detected. No etiology for Shetland Sheepdog leukodystrophy has been found, but this condition represents another familial disease in the purebred dog population.

AGE-SPECIFIC EFFECT OF PARITY ON LITTER SIZE IN THE COMMON VOLE (MICROTUS ARVALIS)

Abstract The “triangular” pattern of reproduction in arvicoline rodents predicts small fecundity early and late in life and high fecundity in the middle. In producing this pattern, the effects of maternal age and parity are typically highly confounded. We present results of a laboratory study designed to disentangle these effects in the common vole (Microtus arvalis) by analyzing variation in sizes of the first 2 litters born to 3 age classes of females subjected to photoperiods of 8 h and 16 h of light. Although the youngest females, paired at 2 weeks of age, decreased size of the 2nd litter in either light environment, the older 2 classes, paired at 3–4 months and 1 year of age, increased their 2nd litters, as predicted by the triangular pattern. This age-specific effect of parity could be explained by differences in the size of 1st litters.

Experience with younger siblings facilitates maternal responsiveness in pubertal Norway rats.

The latency of maternal behavior (MB) onset induced by cohabitation with pups (sensitization) increases in female and male Long-Evans rats from 24 days of age (1-2 day latency) to 42 days of age (4-5 day latency). This decline in maternal responsiveness at Day 42 did not occur in 50% of rats ("responders") which lived with their dam and younger siblings (conceived during the postpartum estrus) for either 4 or 11-18 days after their birth. In contrast to cessation of suckling at about Day 25 postpartum in the absence of a 2nd litter, when a 2nd litter was born greater than Day 26 or less than Day 26 postpartum, suckling continued for a mean of 32 and 35.5 days, respectively (and up to Day 40). Also, time spent suckling during the 10 days following the birth of the 2nd litter was more than five times as great if the 2nd litter was born with little or no delay (less than Day 26). The offspring from the 1st litter spent about 80% of the diurnal observation time in proximity to the dam and younger siblings, and instances of nurturance (retrieving, crouching, licking) toward the young littermates were observed. However, the only dam-litter interaction significantly related to subsequent maternal responsiveness by 1st litter offspring was a positive relation between the prior incidence of aggression by mothers towards juveniles and sensitization latency.

Effects of age and parity on litter size and offspring sex ratio in golden hamsters (Mesocricetus auratus).

Golden hamsters that were mated repeatedly from 55 days of age produced 6-12 litters. Litter size at birth rose between the 1st and 2nd litters, peaked on the 3rd, and declined steadily after the 5th litter. Offspring sex ratio (% male) at birth followed a similar pattern: increasing between the 1st and 2nd litters, remaining high through the 3rd, and becoming increasingly female-biased thereafter. Weaning success decreased sharply after the 6th litter and most dams failed to raise any young to weaning after the 9th litter. These sequential effects on litter size, offspring sex ratio and weaning success were also observed in females mated once at different ages, but they occurred considerably later in life, i.e. increasing parity hastened the effects of advanced age. These age- and parity-related changes in litter composition are consistent with the Trivers-Willard hypothesis that physiologically-stressed females would skew offspring sex ratios to favour daughters. However, since the observed changes in sex ratio were probably due to differential prenatal mortality, their adaptive significance is unclear.

Helminths and the transmammary route of infection.

SUMMARYThe transfer of infective larval stages of helminths via the mammary glands is probably more common than generally recognized. Recent investigations of both natural and experimental infections of various animals have shown that the transmammary transmission of some helminths is a major avenue of infection. Other studies indicate that there are at least 13 helminth parasites which may be transmitted as prenatal infections and at least 17 transmitted via the mammary glands. The majority of these are nematodes. However, in one case the tetrathyridia of the cestode Mesocestoides was observed. In this report the life-cycle and transmission of 2 species of diplostomatid trematodes in the genus Pharyngostomoides is described. The raccoon, Procyon lotor, is the only definitive host; a planorbid snail, Menetus dilatatus, and a branchiobdellid annelid, Cambarincola osceola, a commensal on crayfishes, are intermediate hosts. Records for a period of 11 years are now available for the maternal transmission and longevity of this trematode. During this time one infected female raccoon was maintained in the laboratory on a diet of commercial dog food, sweet potatoes and corn. She produced 25 offspring, most of which were infected with Pharyngostomoides, through the 6th litter. There was a declining number of worms in each litter, ranging from nearly 2000 in one of the 1st litter, to none in the 7th litter. After nearly 12 years she continues to pass a few trematode ova. Rather than assume she has retained the same adult worms for 12 years, it is reasonable to conclude that mesocercariae move through her body and eventually mature in the intestine. Because the mesocercariae have a predilection for the lactating mammary gland, it seems likely that a hormonal influence is present. The transmammary transmission of larvae is a viable alternative in the life-cycles of a number of helminths, and in some instances it is probably the major route of infection.

Effect of litter size on milk yield in the rat.

The amount of milk removed from rats during 1 hour's suckling after a separation period of 8 hours was estimated by weighing their pups. In the 1st experiment litters of 9 pups were suckled by all rats. At test sucklings held daily on days 6-15 of lactation, pups were reallocated to give 3, 6, 9, 12 or 15 pups per dam. The largest amount of milk was removed at suckling by groups of 12 pups. In a 2nd experiment, rats were constantly sucked by litters of either 3, 6, 9, 12 or 15 pups from birth to slaughter at 15 days post partum. Rats with 12 and 15 pups yielded the most milk, nearly twice as much as those suckling only 6 or 9 pups. Litters of 3 pups consumed less than 1/3 of the amount consumed by litters of 6 or 9 pups.

Sex ratio and weaning bodyweight differences in the offspring of unisexually- and bisexually-reared cross-fostered rats.

When mated, unisexually-reared female rats produced a significant excess of females in their litters, while males predominated significantly in litters produced by bisexually-reared females. The percentage of female offspring produced by both types of females declined with successive litters. 1st litter offspring of unisexually-reared females were significantly heavier, and generally less variable in weight at weaning than the comparable offspring of bisexually-reared females, a difference which was apparently maternally-induced. These differences in weaning bodyweight disappeared, or were reversed in favour of the offspring of bisexually-reared females, in 2nd litters.