Maternal rumen and milk microbiota shape the establishment of early-life rumen microbiota in grazing yak calves.

Early-life gut microbial colonization and development exert a profound impact on the health and metabolism of the host throughout the life span. The transmission of microbes from the mother to the offspring affects the succession and establishment of the early-life rumen microbiome in newborns, but the contributions of different maternal sites to the rumen microbial establishment remain unclear. In the present study, samples from different dam sites (namely, oral, rumen fluid, milk, and teat skin) and rumen fluid of yak calves were collected at 6 time points between d 7 and 180 postpartum to determine the contributions of the different maternal sites to the establishment of the bacterial and archaeal communities in the rumen during early life. Our analysis demonstrated that the dam's microbial communities clustered according to the sites, and the calves' rumen microbiota resembled that of the dam consistently regardless of fluctuations at d 7 and 14. The dam's rumen microbiota was the major source of the calves' rumen bacteria (7.9%) and archaea (49.7%) compared with the other sites, whereas the potential sources of the calf rumen microbiota from other sites varied according to the age. The contribution of dam's rumen bacteria increased with age from 0.36% at d 7 to 14.8% at d 180, whereas the contribution of the milk microbiota showed the opposite trend, with its contribution reduced from 2.7% at d 7 to 0.2% at d 180. Maternal oral archaea were the main sources of the calves' rumen archaea at d 14 (50.4%), but maternal rumen archaea became the main source gradually and reached 66.2% at d 180. These findings demonstrated the potential microbial transfer from the dam to the offspring that could influence the rumen microbiota colonization and establishment in yak calves raised under grazing regimens, providing the basis for future microbiota manipulation strategies during their early life.

Ectoparasite fitness in auxiliary hosts: phylogenetic distance from a principal host matters.

We studied reproductive performance in two flea species (Parapulex chephrenis and Xenopsylla ramesis) exploiting either a principal or one of eight auxiliary host species. We predicted that fleas would produce more eggs and adult offspring when exploiting (i) a principal host than an auxiliary host and (ii) an auxiliary host phylogenetically close to a principal host than an auxiliary host phylogenetically distant from a principal host. In both flea species, egg production per female after one feeding and production of new imago after a timed period of an uninterrupted stay on a host differed significantly between host species. In general, egg and/or new imago production in fleas feeding on an auxiliary host was lower than in fleas feeding on the principal host, except for the auxiliary host that was the closest relative of the principal host. When all auxiliary host species were considered, we did not find any significant relationship between either egg or new imago production in fleas exploiting an auxiliary host and phylogenetic distance between this host and the principal host. However, when the analyses were restricted to auxiliary hosts belonging to the same family as the principal host (Muridae), new imago production (for P. chephrenis) or both egg and new imago production (for X. ramesis) in an auxiliary host decreased significantly with an increase in phylogenetic distance between the auxiliary and principal host. Our results demonstrated that a parasite achieves higher fitness in auxiliary hosts that are either the most closely related to or the most distant from its principal host. This may affect host associations of a parasite invading new areas.

Small intestinal morphology and sugar transporters expression when consuming diets of different energy levels: comparison between Tibetan and small-tailed Han sheep.

Some non-structural carbohydrates, especially starch, escape ruminal fermentation, are converted into glucose, and are absorbed from the small intestine. This glucose provides an important source of energy, and its usage is more efficient than glucose from carbohydrates which are fermented as short chain fatty acids in the rumen and, subsequently, undergo hepatic gluconeogenesis. Tibetan sheep graze on the harsh Qinghai-Tibetan Plateau (QTP) all year round and their carbohydrate and energy intakes fluctuate greatly with seasonal forage availability. Consequently, a high capacity to absorb glucose from the small intestine would be particularly beneficial for Tibetan sheep to allow them to cope with the inconsistent dietary intakes. This study examined how the small intestinal morphology and sugar transporters' expression of Tibetan and Small-tailed Han (Han) sheep respond to fluctuating energy intakes under the harsh conditions of the QTP. Han sheep graze on the QTP only in summer and are generally raised in feedlots. Twenty-four Tibetan sheep and 24 Han sheep, all wethers, were assigned randomly to four groups (n = 6 per breed/group), with each group offered a diet differing in digestible energy content: 8.21, 9.33, 10.45 and 11.57 MJ/kg DM. After 49 d, all sheep were slaughtered, tissues of the small intestine were collected, and measurements were made of the morphology and glucose transporters and the related regulation gene expressions. At intakes of low energy levels, Tibetan sheep had a greater villus surface area in the duodenum, jejunum and ileum and higher mRNA expression of sodium-dependent glucose transporter 1 in the duodenum and ileum (P < 0.05) than Han sheep. In the glucose transporter 2 (GLUT2) mediated glucose absorption pathway, Tibetan sheep had higher GLUT2 and taste receptor family 1 member 2 and 3 mRNA expressions than Han sheep in the duodenum, jejunum and ileum (P < 0.05). We concluded that the differences between breeds indicated a greater glucose absorption capacity in the small intestine of Tibetan than Han sheep, which would confer an advantage to Tibetan over Han sheep to an inconsistent energy intake on the harsh QTP. These findings suggested that ruminants raised under harsh environmental conditions with highly fluctuating dietary intakes, as is often the case in grazing ruminants worldwide, are able to absorb glucose from the small intestine to a greater extent than ruminants raised under more moderate conditions.

Energy substrate metabolism in skeletal muscle and liver when consuming diets of different energy levels: comparison between Tibetan and Small-tailed Han sheep.

The energy intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau (QTP) varies greatly with seasonal forage fluctuations and is often below maintenance requirements, especially during the long, cold winter. The liver plays a crucial role in gluconeogenesis and skeletal muscle is the primary tissue of energy expenditure in mammals. Both play important roles in energy substrate metabolism and regulating energy metabolism homeostasis of the body. This study aimed to gain insight into how skeletal muscle and liver of Tibetan sheep regulate energy substrate metabolism to cope with low energy intake under the harsh environment of the QTP. Tibetan sheep (n = 24; 48.5 ± 1.89 kg BW) were compared with Small-tailed Han sheep (n = 24; 49.2 ± 2.21 kg BW), which were allocated randomly into one of four groups that differed in dietary digestible energy densities: 8.21, 9.33, 10.45 and 11.57 MJ /kg DM. The sheep were slaughtered after a 49-d feeding period, skeletal muscle and liver tissues were collected and measurements were made of the activities of the key enzymes of energy substrate metabolism and the expressions of genes related to energy homeostasis regulation. Compared with Small-tailed Han sheep, Tibetan sheep exhibited higher capacities of propionate to glucose conversion and fatty acid oxidation and ketogenesis in the liver, higher glucose utilization efficiency in both skeletal muscle and liver, but lower activities of fatty acid oxidation and protein mobilization in skeletal muscle, especially when in negative energy balance. However, the Small-tailed Han sheep exhibited higher capacities to convert amino acids and lactate to glucose and higher levels of glycolysis and lipogenesis in the liver than Tibetan sheep. These differences in gluconeogenesis and energy substrate metabolism conferred the Tibetan sheep an advantage over Small-tailed Han sheep to cope with low energy intake and regulate whole-body energy homeostasis under the harsh environment of the QTP.

Astragalus membranaceus root supplementation improves average daily gain, rumen fermentation, serum immunity and antioxidant indices of Tibetan sheep.

The use of antibiotics as supplements in animal feed is restricted due to possible health hazards associated with them. Consequently, there is increasing interest in exploiting natural products to improve health and production of livestock with no detrimental side effects. In this study, we examined the effect of Astragalus membranaceus root (AMT) supplementation on DM intake, growth performance, rumen fermentation and immunity of Tibetan sheep. Twenty-four male Tibetan sheep (31 ±â€¯1.4 kg; 9 months old) were assigned randomly to one of four dietary treatments with different levels of AMT: 0, 20, 50 and 80 g/kg DM (A0, A2, A5 and A8, respectively) in addition to their basal diets. A0 acted as a control group, and measurements were recorded over a 56-d feeding period. Sheep fed with AMT had a higher average daily gain and a lower feed:gain ratio than controls (P < 0.001). Rumen concentrations of NH3-N (P < 0.001), total volatile fatty acids (P = 0.028), acetate (P = 0.017) and propionate (P = 0.031) in A5 and A8 were higher than those in A0. The addition of AMT in the feed significantly increased serum antioxidant and immunity factors of the sheep and increased the concentrations of serum interleukin, immunoglobulin and tumour necrosis factor-α (P = 0.010). We concluded that AMT can be used as a feed additive to improve growth performance and rumen fermentation and enhance the immunity of Tibetan sheep. Some responses exhibited a dose-dependent response, whereas other did not exhibit a pattern, with an increase in AMT. The addition of 50 and 80 g/kg AMT of total DM intake showed the most promising results.

Sex ratio in flea infrapopulations: number of fleas, host gender and host age do not have an effect.

This study set out to determine whether the sex ratio of fleas collected from host bodies is a reliable indicator of sex ratio in the entire flea population. To answer this question, previously published data on 18 flea species was used and it was tested to see whether a correlation exists between the sex ratio of fleas collected from host bodies and the sex ratio of fleas collected from host burrows. Across species, the female:male ratio of fleas on hosts correlated strongly with the female:male ratio of fleas in their burrows, with the slope of the regression overlapping 1. Controlling for flea phylogeny by independent contrasts produced similar results. It was also ascertained whether a host individual is a proportional random sampler of male and female fleas and whether the sex ratio in flea infrapopulations depends on the size of infrapopulations and on the gender and age of a host. Using field data, the sex ratio in infrapopulations of 7 flea species parasitic on 4 rodent species was analysed. Populations of 3 species (Nosopsyllus iranus, Parapulex chephrenis and Xenopsylla conformis) were significantly female-biased, whereas male bias was found in 1 species (Synosternus cleopatrae). In general, the sex ratio of fleas collected from an individual rodent did not differ significantly from the sex ratio in the entire flea population. Neither host gender, and age nor number of fleas co-occurring on a host affected (a) the sex ratio in flea infrapopulations and (b) the probability of an infrapopulation to be either female- or male-biased.

Comparison of nitrogen utilization and urea kinetics between yaks (Bos grunniens) and indigenous cattle (Bos taurus).

Under traditional management on the Qinghai-Tibetan Plateau, yaks () graze only on natural pasture without supplements and are forced to cope with sparse forage of low N content, especially in winter. In contrast, indigenous Tibetan yellow cattle () require supplements during the cold season. We hypothesized that, in response to harsh conditions, yaks cope with low N intakes better than cattle. To test this hypothesis, a study of whole-body N retention and urea kinetics was conducted in 2 concurrent 4 × 4 Latin squares, with 1 square using yaks and 1 square using cattle. Four isocaloric forage-concentrate diets differing in N concentrations (10.3, 19.5, 28.5, and 37.6 g N/kg DM) were formulated, and by design, DMI were similar between species and across diets. Urea kinetics were determined with continuous intravenous infusion of NN urea for 104 h, and total urine and feces were concomitantly collected. Urea production, urea recycling to the gut, and ruminal microbial protein synthesis all linearly increased ( < 0.001) with increasing dietary N in both yaks and cattle. Urinary N excretion was less ( = 0.04) and N retention was greater ( = 0.01) in yaks than in cattle. Urea production was greater in yaks than in cattle at the 3 lowest N diets but greater in cattle than in yaks at the highest N diet (species × diet, < 0.02). Urea N recycled to the gut ( < 0.001), recycled urea N captured by ruminal bacteria ( < 0.001), and ruminal microbial protein production ( = 0.05) were greater in yaks than in cattle. No more than 12% of urea recycling was through saliva, with no difference between species ( = 0.61). Glomerular filtration rate was lower ( = 0.05) in yaks than in cattle. The higher urea recycling and greater capture of recycled urea by ruminal microbes in yaks than in cattle suggest that yaks use mechanisms to utilize dietary N more efficiently than cattle, which may partially explain the better survival of yaks than cattle when fed low-N diets.

Is hypothalamic prostaglandin E2 involved in avian fever?

In chickens, the effect of Escherichia coli lipopolysaccharide (LPS) on body temperature and ex vivo hypothalamic prostaglandin E2 (PGE2) production was examined to test the possible involvement of PGE2 in mechanisms of avian fever. PGE2 is reported to be the major central mediator of fever in mammals; it has not been examined in birds. An intraperitoneal injection of LPS caused an elevation of body temperature but not an elevation of hypothalamic PGE2 production. It seems that: (a) hypothalamic PGE2 is not involved in the development of the febrile response in birds; (b) central mechanisms of avian fever differ from those in mammals.

Fiber digestion and energy utilization of fat sand rats (Psammomys obesus) consuming the chenopod Anabasis articulata.

Most herbivorous rodents consume a variety of plants and, when available, select ones low in fiber content. In contrast, the fat sand rat (Psammomys obesus), a diurnal gerbillid rodent that is wholly herbivorous, is able to survive while consuming only the halophytic chenopod Anabasis articulata. We hypothesized that these gerbils are able to digest chenopods efficiently and that fiber digestion contributes substantially to their energy budget. Digestibility of total fibers (NDF), hemicellulose, and cellulose was 51.6%, 66.4%, and 44.0%, respectively. Energy derived from fiber digestion was 211.7 kJ kg(-0.75) d(-1) and resulted mostly from hemicellulose digestion. Average daily metabolic rate was 658.4 kJ kg(-0.75) d(-1), and basal metabolic rate (BMR) was determined to be close to 192.6 kJ kg(-0.75) d(-1). Therefore, fiber digestion provided 32% of maintenance requirements and 110% of BMR requirements, one of the highest values reported thus far for placental mammals. The efficiency of utilization of the chenopod was 0.29, a low value compared to other dietary items. We concluded that A. articulata fulfills all the energy and nutrient requirements of fat sand rats, even though energy yields and efficiency of utilization of its energy is low.

Level of energy intake affects the estrous cycle in Sundevall's jird (Meriones crassus).

Effects of energy intake on the estrous cycle of the desert gerbillid, Sundevall's jird (Meriones crassus; 80 g; n=22) were studied. Females were offered either maintenance or below maintenance levels of millet seeds and ad lib. Atriplex halimus leaves and stems; drinking water was not available. Vaginal smears were used to determine sexual stage. We hypothesized that the estrous cycle ceases at low levels of energy intake and commences when sufficient energy is available. Females lost body mass linearly with a decrease in metabolizable energy intake. Estrous cycle averaged 4.46 d at maintenance energy intake but increased to an average of 7.81 d at 70% of maintenance energy intake. A cessation of the cycle occurred at an energy intake below 70% of maintenance requirements, which resulted in a body mass loss of more than 1% per day. More variability in the length of the different stages of the cycle was found with lower levels of energy intake. When offered ad lib. millet seeds and A. halimus (n=14), recovery to the normal cycle was attained within 10 d by 43% of the females and within 16 d by the rest of the females. Recovery time was longest in females that previously had the lowest energy intake. We concluded that the estrous cycle of M. crassus is sensitive to energy intake. With restricted energy intake, the estrous cycle and reproductive activities cease but can be restored with provision of adequate energy. This strategy ensures that reproduction occurs when conditions of food availability and body condition of the females are favorable.

Intake energy, energy retention and heat production in lambs from birth to 24 weeks of age.

Intake energy (IE), metabolizable energy intake (MEI), energy retention (ER) and heat production (HP) were estimated in twelve male and six female suckling lambs from birth to 4 wk of age and in nine of these male lambs after weaning from 9 to 24 wk of age. Intake energy and MEI were estimated from the milk intake and combustible energy of the milk in the suckling lambs and from digestibility trials and energy content of feed and feces in the weaned lambs. Energy retention was estimated from body composition changes and HP was calculated from MEI - ER and from the rate of O2 consumption. The O2 consumption of the ewes was also measured during late pregnancy and during lactation. In the suckling lambs, daily MEI was 277 kcal/kg.75 and ER was 112 kcal/kg.75 and as calculated from O2 consumption was 168 kcal/kg.75. Daily HP as calculated by MEI - ER was 165 kcal/kg.75. Daily maintenance HP was equal to 121 kcal/kg.75 and the efficiency of utilization of energy for ER was 70.7%. In the weaned lambs, HP as measured from O2 consumption was 10% lower than that estimated using MEI and ER. Comparison of 9- to 16-wk-old with 17- to 24-wk-old lambs, showed daily increases in MEI from 212 to 228 kcal/kg.75, in ER from 54 to 95 kcal/kg.75 and in HP from 158 to 194 kcal/kg.75, whereas there was a daily decrease in maintenance HP from 101 to 90 kcal/kg.75. Efficiency of utilization of energy for production was similar in the two postweaning periods (48.8 and 46.5%, respectively). The O2 consumption of the ewes (/kg.75) was increased over that of nonpregnant, nonlactating controls by 30% in late pregnancy, by 62% in the first month of lactation and by 50% in the second month of lactation.

Ingestion of snow by cattle.

Tritiated water was evaluated and used for determining snow and water intake by cattle. This method yielded results comparable to those obtained via simultaneous gravimetric measurement of snow and liquid water intake after adjustments were made for preformed and metabolic water from feed; the correlation coefficient was .96 and the standard error of the estimate was +/- 1.28 kg/day, or +/- 5.8% of the mean intake. Two steers were maintained in a covered, open-ended stable and were offered a maintenance diet and ad libitum liquid water. Distressed behavior was observed in these steers when they were abruptly denied liquid water and given snow in its place. They started ingesting snow after approximately 35 hr and subsequent switching from water to snow or vice versa was without apparent distress. In another study, eight pregnant beef cows were used in a 4 X 4 Latin square design consisting of four 15-day periods. The cows were either penned and given once-a-day access to water (pen water) or ad libitum access to snow only (pen snow), or they were kept in a snow-covered field and given once-a-day access to water (field water) or access only to the snow in the field (field snow). The pen water cows cunsumed 23.6 kg/day, the pen snow cows 20.6 kg/day, the field water cows 26.1 kg/day and the field snow cows 23.6 kg/day of water and (or) snow. In a subsequent experiment, the same pregnant cows were given 0, 5, 10 kg or free access to water for 15 min once each day and kept in a snow-covered field. The total daily water-plus-snow intake was similar for each of the four groups, ranging between 50 and 55 g/kg/day.

Estimation of energy expenditure from heart rate measurements in cattle maintained under different conditions.

We examined whether heart rate (HR) could be used to estimate energy expenditure (EE) in cattle. Six Hereford heifers (345 +/- 10.8 kg BW) 12 mo of age were implanted with HR radio transmitters and maintained in individual pens under the following treatments: 1) shade or sun exposure, 2) high- or low-energy diet, and 3) feeding in morning or afternoon. The HR of animals was measured every .5 h during 3 mo; measurements of oxygen consumption and HR were made simultaneously in the morning and in the afternoon while animals were resting and exercising. Average daily HR (52 +/- 4 beats/min) and average daily EE (380 +/- 9 kJ/kg(.75)) in animals on the low-energy diet were less than values in animals on the high-energy diet (94 +/- 4 beats/min and 653 +/- 9 kJ/ kg(.75), respectively). For each animal and within each diet, linear regressions best described the relationship between HR and EE in resting animals, whereas quadratic regressions best described this relationship for exercising animals. The quadratic equation for the exercising animals could also be used for resting animals. In addition, a constant value of EE per heart beat (EE pulse) for each individual resting animal was found and gave accurate estimations. This method was convenient because 1) no exercise equipment was needed to generate the regression equations and 2) EE pulse was less affected by diet than was EE estimated by regression equations. We conclude that HR, a relatively easy measurement, can be useful and accurate in estimating EE. To increase the accuracy of the estimation of EE by HR, the relationship of HR to EE should be established for each animal. In addition, the nutritional regimen for the animal in which EE is estimated should be used for the animal in establishing the relationship.

Effects of solar radiation, dietary energy, and time of feeding on thermoregulatory responses and energy balance in cattle in a hot environment.

Ten growing heifers were either exposed to or protected from solar radiation, offered a diet of either high (H) or low (L) ME, and fed either in the morning or afternoon during a hot summer. Heifers that consumed the H diet had a greater water intake, DMI, metabolizable energy intake, energy expenditure, and retained energy than heifers that consumed the L diet. Solar radiation did not have an effect on any of these variables. Furthermore, dietary energy and time of measurement had an effect on rectal temperature (Tr), respiration rate (RR), heart rate (HR), and rate of oxygen uptake (VO2); solar radiation had an effect on Tr and RR but not on HR and VO2; and time of feeding had an effect only on VO2. Heifers coped with greater heat loads by increasing RR and the difference in Tr between morning and afternoon. It seems that a lowered body temperature in the morning is a physiological mechanism used by animals to prepare for the heat load that develops during the day. Heat production (HP) and HR throughout the day were affected mainly by the time of feeding and not by the environmental heat load. Feeding in the afternoon increased HP in the cooler hours of the day when heat losses from the animal through conduction and radiation were more efficient. With a pending high heat load situation, reducing feed quality and(or) changing the time of feeding to the late afternoon could be beneficial to the animals in reducing their heat loads.

Energy requirements of the fat sand rat (Psammomys obesus) when consuming the saltbush, Atriplex halimus: a review.

The fat sand rat (Psammomys obesus; Gerbillinae), a diurnal gerbillid rodent, is herbivorous and able to thrive while consuming only the saltbush Atriplex halimus (Chenopodiaceae), a plant relatively low in energy content and high in ash and water. Before consuming A. halimus leaves, fat sand rats scraped off the outer layer with their teeth. This removed much of the electrolytes but increased gross energy and organic matter content of the leaves by only about 3.1%. Basal metabolic rate of fat sand rats was 168 kJ.kg-0.75.d-1, 57 to 60% of that expected for a eutherian mammal of its body size, and average daily metabolic rate was 499 kJ.kg-0.75.d-1, 88% of that expected for a rodent of its body mass. Field metabolic rate was 565 kJ.kg-0.75.d-1 in summer and 680 kJ.kg-0.75.d-1 in winter. The rate of energy expenditure during summer was 60% of that expected for a herbivore and 83% of that expected for a desert eutherian mammal of its body mass. The difference in rate of energy expenditure between winter and summer was taken as thermoregulatory costs. Fat sand rats appear to be well adapted to high air temperatures but less so to low air temperatures. The efficiency of utilization of energy of A. halimus for maintenance was only 0.32 and for growth only 0.30 and their respective heat increments of feeding were 0.68 and 0.70. This low utilization of feed plus its low energy yield and high water content forced fat sand rats to consume large quantities of forage for maintenance. In spite of this, there are several advantages for consuming mainly this diet, namely: (1) it provides a more stable diet throughout the year than do seeds; (2) fat sand rats have no competition for this food resource from other rodents; and (3) fat sand rat burrows are at the base of the plants and therefore they expend minimal energy for foraging.

Energy expenditure and efficiency of energy use in rodents: desert and non-desert species.

Feeding and the search for food are the predominant activities of most rodents. Since desert rodents inhabit regions of generally low food availability, it has been theorized that their energetic requirements would be lower and/or their efficiency to use energy for maintenance and growth would be higher than for rodents from more temperate regions. Indeed, the basal metabolic rate, average daily metabolic rate and field metabolic rate of desert rodents have been found to be lower than those of non-desert rodents. However, the ability to use energy intake for maintenance by desert rodents was calculated to be lower than that of non-desert rodents. In addition, granivores were not different from omnivores and herbivores in energy use efficiency, but herbivores were more efficient than omnivores.

Evidence for a negative fitness-density relationship between parent density and offspring quality for two Xenopsylla spp. parasitic on desert mammals.

We tested the hypothesis of negative fitness-density relationships and predicted that an increase in the density of parent fleas would result in lower survival rates and longer development time of pre-imagoes as well as shorter time to death from starvation of newly emerged imagoes. These predictions were experimentally tested on Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild feeding on two rodent species, Meriones crassus Sundevall or Dipodillus dasyurus Wagner. Survival of larvae and pupae, but not eggs, was negatively affected by parent density. An increase in parent density led to a decrease in the number of imagoes of the next generation. Eggs of both species developed faster when the parents were at low densities on either host. The same was true for larval X. ramesis, but not larval X. conformis. The negative effects of parent density on the duration of pupal development were evident in X. conformis, parents of which fed on both hosts, and X. ramesis from parents fed on M. crassus, whereas X. ramesis from parents fed on D. dasyurus developed faster at low densities. A negative effect of density on the development of offspring from egg to imago in X. conformis was manifested mainly when parent fleas fed on D. dasyurus, whereas the negative effect of density on offspring development in X. ramesis was manifested mainly when parent fleas fed on M. crassus. Although there was no general effect of parent density on the resistance of imago offspring to starvation, male X. ramesis from parents fed at the highest density survived starvation for significantly shorter times compared with those from parents fed at lower densities. Manifestation of the negative effect of parent density on offspring quality appears to vary with flea species and may be affected by host species.

Density dependence of feeding success in haematophagous ectoparasites.

We studied the effect of density on feeding success of 2 fleas, Xenopsylla conformis and Xenopsylla ramesis, when exploiting rodents Meriones crassus and Gerbillus dasyurus. We tested 2 alternative hypotheses: (i) that intraspecific interference competition occurs and, thus, feeding success of a flea decreases with an increase in density and (ii) that facilitation via suppression of a host defence system occurs and thus, feeding success of a flea increases with an increase in density. The mean size of a bloodmeal and the proportion of highly engorged individuals in X. conformis feeding on both hosts were affected by density. When on G. dasyurus, both the size of a bloodmeal and the proportion of highly engorged individuals were lower at low (5-15 fleas per host) than at high (25-50 fleas per host) densities. The opposite was true when this flea fed on M. crassus. The mean bloodmeal size and proportions of highly engorged X. ramesis parasitizing either host were not affected by flea density. This study showed that the density dependence of feeding success of a flea (a) varied both between fleas and within-fleas between hosts and (b) indicated either intraspecific competition or facilitation via the host in a particular flea-host association.