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PubMed2000

Effects of stress on reproduction in non-rodent mammals: the role of glucocorticoids and sex differences.

The means by which stress influences reproduction is not clearly understood, but may involve a number of endocrine, paracrine and neural systems. Stress impacts on the reproductive axis at the hypothalamus (to affect GnRH secretion) and the pituitary gland (to affect gonadotrophin secretion), with direct effects on the gonads being of less importance. Different stressors have different effects and there are differences in response to short- and long-term stress. Many short-term stresses fail to affect reproduction and there are reports of stimulatory effects of some 'stressors'. There are species differences in the way that specific stressors affect reproduction. Sex differences in the effects of a particular stressor have been delineated and these may relate to effects of stress at different levels of the hypothalamo-pituitary axis. The significance of stress-induced secretion of cortisol varies with species. In some instances, there appears to be little impact of short-term increases in cortisol concentrations and protracted increases in plasma concentration seem to be required before any deleterious effect on reproduction is apparent. Issues of sex, sex steroid status, type of stressor and duration of stress need to be considered to improve understanding of this issue.

Animals↗
PubMed2001

Reproductive phase depedent circadian variation in the pineal biochemical constituents of Indian palm squirrel, Funambulus pennanti.

In mammals, pineal gland is intimately concerned with the co-ordination of rhythm physiology. Biochemical characteristics of pineal gland in man and other mammals may provide strong, yet sometimes elusive support for the belief in functional individuality and probable importance of this tiny gland. In seasonal breeding animals, pineal gland function is very much dependent on the reproductive status. Therefore, the aim of this experiment is to note the circadian rhythmicity of different biochemical constituents of pineal gland during active and inactive phases of reproductive cycle of a seasonally breeding rodent, F. pennanti. In the present study, pineal biochemical constituents i.e. protein and cholesterol showed higher values during daytime (1400 h). The plasma melatonin level presented two peaks during active (April; at 1800 h and 0200 h) and inactive (December; at 1400 h and 0200 h) phases of reproductive cycle. The pineal protein, cholesterol and plasma melatonin values in term of basal and peak levels were higher during the reproductive inactive/pineal active phase. Therefore, pineal--also known to have antigonadotropic properties and cholesterol which appears conjugated with pineal serotonin, presented circadian rhythmicity along with the plasma level of melatonin. This rhythmicity noted in present study was dependent on the reproductive and pineal activity status, and might be regulated by the sex steroid receptor present on the pineal gland.

Animals↗
PubMed2004

Environmental color affects Nile tilapia reproduction.

We investigated the effects of environmental color on the reproductive behavior of Nile tilapia, Oreochromis niloticus. Two environmental colors were tested by covering the aquarium (60 x 60 x 40 cm) with white (12 groups) or blue (13 groups) cellophane and observing reproductive behavior in groups of 2 males (10.27 +/- 0.45 cm) and 3 females (10.78 +/- 0.45 cm) each. After assignment to the respective environmental color (similar luminosity = 100 to 120 Lux), the animals were observed until reproduction (identified by eggs in the female's mouth) or up to 10 days after the first nest building. Photoperiod was from 6:00 h to 18:00 h every day. Food was offered in excess once a day and water quality was similar among aquaria. Daily observations were made at 8:00, 11:00, 14:00 and 17:00 h regarding: a) latency to the first nest, b) number of nests, c) gravel weight removed (the male excavates the nest in the bottom of the aquarium), d) nest area, and e) mouthbrooding incubation (indication of reproduction). The proportion of reproducing fish was significantly higher (6 of 13) in the group exposed to the blue color compared the group exposed to the white color (1 of 12; Goodman's test of proportions). Moreover, males under blue light removed significantly larger masses of gravel (blue = 310.70 +/- 343.50 g > white = 130.38 +/- 102.70 g; P = 0.01) and constructed wider nests (blue = 207.93 +/- 207.80 cm(2) > white = 97.68 +/- 70.64 cm(2); P = 0.03) than the control (white). The other parameters did not differ significantly between light conditions. We concluded that reproduction in the presence of blue light was more frequent and intense than in the presence of white light.

Animals↗
PubMed2005

[Proximal determinants of fertility: reproductive behavior among Chamibida indigenous women in Antioquia, Colombia].

The aim of this study was to determine the reproductive timing used by Chamibida indigenous women in Antioquia, Colombia. This socio-demographic study used the reproductive history technique and was conducted in the year 2000. Two hundred and thirty-four homes on the Cristianía indigenous reservation were visited to obtain 253 reproductive histories (83.1% of the women ages 15 to 49). Reproductive behavior was characterized by sexual debut at age 17.8 years (mean), with short intergenesic intervals in 69.0% and an adjusted fertility rate of 5.12 children. This reproductive pattern differs from all other indigenous groups and subgroups in Antioquia. As an explanation, Chamibida women are familiar with and accept Western birth control methods, besides having more access to formal schooling. Current Colombian health system policies are far from appropriate, since they fail to take the indigenous groups' specificities into account.

Adolescent↗
PubMed2006

[Sexual behaviors and incidence of sexual and reproductive health programs among poor secondary students and public university students in Cali, Colombia].

In order to qualitatively evaluate sexual behaviors or practices and the incidence of sexual and reproductive health programs in adolescent and postadolescent users educated in Cali, Colombia, two quota samples were carried out, one in schools in poor neighborhoods of the city and one at Valle University (UNIVALLE). In addition, a limited number of twelve open interviews was made among two different student population groups, the schools and the university. The study addresses the sexual behaviors of adolescents and postadolescents, contraceptive methods and prevention of STDs and HIV/AIDS, and the uses of sexual and reproductive health programs by both populations, controlling for social class (socioeconomic stratum), gender, and race. Two sexual and reproductive health programs were taken as reference: that of PROFAMILIA (Pro-Wellbeing of the Colombian Family Association), and the sexual and reproductive health program of the University Medical Service of the UNIVALLE. Results show how the behaviors and responses to sexual and reproductive health programs are mediated by multiple sociological categories that orient the analysis.

Acquired Immunodeficiency Syndrome↗
PubMed2003

Reproductive patterns and feeding habits of three nectarivorous bats (Phyllostomidae: Glossophaginae) from the Brazilian Cerrado.

The reproductive patterns and feeding habits of three sympatric nectarivorous bats, Glossophaga soricina, Anoura caudifera, and A. geoffroyi were studied in the Pousada das Araras Natural Reserve, located in Central Brazil. The bats were captured with mist nets from August 2000 to July 2001. Reproductive condition was determined by external analyses of the specimens and feeding habits from fecal samples. Glossophaga soricina was the most abundant species (65%), followed by A. geoffroyi (30%) and A. caudifera (5%). Significant differences were observed in the sex-ratio of the two more abundant species. Anoura geoffroyi showed a monoestrous pattern; its reproductive peaks occurred between the end of the dry season and the beginning of the rain season. A seasonal bimodal pattern was recorded for G. soricina, with pregnant specimens showing one peak observed in the dry season and another in the middle of the rainy season. The reproductive pattern of A. caudifera could not be satisfactorily defined because of the small sample size. However, this species apparently has a reproductive cycle similar to that of G. soricina. The patterns observed in this study seem to be related with the climate in the Brazilian savanna (Cerrado), with two well-defined seasons (dry and wet). By adjusting the parturition close to or in the rain season the three species could be favoring a greates survival rate for the offspring, since the critical lactation period would then occur in a time of maximum food availability. The three bat species showed a generalist diet, consuming fruits, pollennectar, and arthropods. Significant differences were observed in the diet of G. soricina: fruits and arthropods predominated in the dry season and pulp (fruits) in the rainy season. Males and females of this species ate the same items in similar proportions. Although A. geoffroyi has not showed a preference for a specific item, consumption of fruits and arthropods was generally greater than that of pollen.

Animals↗
PubMed2001

An empirical model of the optimal timing of reproduction for female amphipods infected by trematodes.

Life-history theory predicts that hosts should reproduce when first infected by parasites if hosts are capable and if parasites have a lower cost on current than on future reproduction of hosts. We constructed an empirical model to explore fitness of females of the intertidal amphipod Corophium volutator that reproduced soon versus long after infection by the trematode Gynaecotyla adunca. For uninfected females, the optimal time to reproduce was at their maximum body length. However, for females infected by low or high intensities of trematode metacercariae, reproductive potential (realized fecundity) was highest for females that mated immediately after becoming infected. Even after removing a high cost of delaying reproduction for infected amphipods (high likelihood of depredation by sandpipers, which are final hosts of G. adunca), realized fecundity remained highest if reproduction occurred immediately following infection by trematodes. Results from our model support the view that early reproduction of female amphipods following infection by G. adunca is an adaptive life-history response to parasitism.

Adaptation, Physiological↗
PubMed1992

Reproductive effects of placing micro-implants of melatonin in the mediobasal hypothalamus and preoptic area in rams.

The reproductive effects of placing micro-implants of melatonin in the mediobasal hypothalamus (MBH) and preoptic area (POA) were monitored in Soay rams. Groups of animals were initially conditioned to alternating 16 weekly periods of long days (16 h light: 8 h darkness; 16L:8D) and short days (8L:16D) for at least 9 months to entrain the seasonal reproductive cycle. All experiments were then initiated at 10 weeks under long days when the animals were sexually inactive. In experiment 1, rams were exposed to short days for 14 weeks or maintained on long days to illustrate the photoperiodically induced re-activation and regression of the reproductive axis. In experiments 2-4, rams received micro-implants of melatonin in the MBH or POA, or received control treatments (sham-operated or no surgery) for 12-14 weeks while maintained on long days (total of 12 animals/treatment). The melatonin implants consisted of 22-gauge stainless-steel cannulae with melatonin fused inside the tip and were placed bilaterally in the brain. Incubation of the implants in Tricine-buffered saline (pH 8.0) at 37 degrees C showed that the release rate of melatonin was relatively constant after an initial peak in week 1 (means +/- S.E.M.: 3.42 +/- 0.43 micrograms/24 h). Rams with melatonin implants placed in the MBH, but not in the POA, showed a consistently earlier re-activation of the reproductive axis compared with the control animals in all three experiments (12/12 for MBH vs 2/12 for POA). The mean time to maximum testicular diameter was 12.2 +/- 0.9, 21.6 +/- 1.8 and 22.3 +/- 1.2 weeks for the MBH, POA and combined control groups respectively (MBH vs control, P less than 0.01; analysis of variance). The premature growth of the testes in the MBH group was associated with an earlier increase in the blood plasma concentrations of FSH and testosterone, and the appearance of the sexual skin coloration. Removal of the implants resulted in a decline in all reproductive parameters. The melatonin treatments did not cause a detectable increase in the peripheral concentrations of melatonin, or affect the diurnal rhythm in melatonin which reflected the long-day photoperiod. When implants containing 125I-labelled melatonin were introduced into the brain the associated radioactivity was localized to within 1 mm of the implants. The overall results demonstrate that the constant administration of melatonin into the MBH blocks the effect of the endogenous long-day melatonin signal and induces gonadal redevelopment.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Expression of the crustacean hyperglycaemic hormones and the gonad-inhibiting hormone during the reproductive cycle of the female American lobster Homarus americanus.

Crustacean reproduction is regulated by a complex chain of hormonal interactions in which the crustacean hyperglycaemic hormones A and B (CHH-A and CHH-B) and the gonad-inhibiting hormone (GIH) play a primary role. These neurohormones are produced in the same neuroendocrine cells of the X-organ sinus gland complex, situated in the eyestalks of the American lobster, Homarus americanus. In order to obtain more information on the synthesis, storage, release and function of these three neuropeptides during the reproductive cycle, we studied the levels of their mRNAs in the X-organ, their peptide storage in the sinus gland and their concentration in the haemolymph at different stages of the female reproductive cycle. A high CHH-A mRNA level was found only in the previtellogenic stage, while elevated mRNA levels were determined for CHH-B in the mature as well as the previtellogenic stage. High CHH storage levels in the sinus gland were found during previtellogenesis. The total amount of CHH (CHH-A plus -B) in the haemolymph was significantly higher during maturation. A low level of GIH mRNA in the X-organ and a low amount of the GIH I isoform in the sinus gland were found only in the immature stage. In contrast, GIH haemolymph levels were high during the immature and previtellogenic stages. We conclude that CHH-A and -B are involved in triggering the onset of vitellogenesis and that CHH-B in particular is responsible for stimulating oocyte maturation before spawning, while GIH prevents the start of vitellogenesis in the ovary. Moreover, our results show that the balance between the haemolymph levels of the CHHs and GIH may tune the synchronization of reproduction and molting during the biannual reproductive cycle of the American lobster.

Animals↗
PubMed2005

Reproductive impairment in zebra finches (Taeniopygia guttata).

The effects of polychlorinated biphenyls (PCBs) as compounds that may disrupt endocrine activity and, consequently, alter reproductive performance were investigated in altricial zebra finches (Taeniopygia guttata). The breeding performance and breeding cycle of zebra finches differed significantly between nonexposed birds and those experimentally pulse-exposed to Aroclor 1248, a PCB compound (40 microg/bird). Aroclor-exposed birds showed significantly increased numbers of clutches laid, nests constructed per pair, incubation time per pair, and percentage of hatchling mortality compared to controls. Not all reproductive parameters were affected. Those traditionally regarded as indicators of reproductive capacity (number of eggs laid per clutch, number of eggs laid per pair, hatchlings per clutch, and fledglings per clutch) did not differ statistically between exposed and control birds. Findings support the hypothesis that very low PCB doses may be associated with endocrine disruption. It is suggested that evaluation of reproductive parameters related to parental care is more adequate to assess endocrine disruption than is evaluation of reproductive success parameters. Given its short breeding cycle, altricial breeding behavior, and other advantages not possessed by precocial birds, we propose using the zebra finch for evaluations of chemicals with endocrine-disruptive activity.

Animals↗
PubMed2001

Effects of field exposure to diazinon on small mammals inhabiting a semienclosed prairie grassland ecosystem. I. Ecological and reproductive effects.

The widespread use of cholinesterase-inhibiting pesticides in the environment presents increasing concerns about their effects on human, wildlife, and ecosystem health. As a group, these pesticides are generally highly toxic and have great potential for negatively affecting nontarget organisms. Small mammals have proven to be ideal biomonitors of environmental contaminants, and were used here to test for possible effects of a widely used cholinesterase-inhibiting insecticide, diazinon, in a natural field setting. Using 12 0.1-ha terrestrial mesocosms, we examined the effects of low-level diazinon exposure on the small mammal communities inhabiting semienclosed grassland ecosystems. Our primary objective was to test the hypothesis that diazinon, applied at two different recommended label application rates, would not cause any observable adverse ecological or reproductive effects on small mammal populations and communities. Experimental small mammal communities consisting of Sigmodon hispidus, Microtus ochrogaster, Reithrodontomys fulvescens, and Mus musculus were stocked at natural densities and sex ratios inside empty mesocosms. Diazinon 4E was applied at two different maximum recommended label application rates, 0.56 kg a.i./ha (1x) and 4.5 kg a.i./ha (8x), and controls remained unsprayed, with four enclosures (replicates) per treatment. Two 30-d trials were run during peak rodent breeding seasons and enclosures were sampled on days 2, 16, and 30 of each trial. Recovery of small mammals was not significantly different among treatments, although fewer animals were recovered from the diazinon-exposed enclosures in both trials. Analysis of trapping data suggested that the normally strong competitive relationship between Sigmodon and Microtus may be altered by the pesticide, favoring Microtus in the diazinon-exposed enclosures. Incidence of reproductive condition was found to be reduced 20 to 80% and 33 to 100% in diazinon-exposed males and females, respectively. Reproductive productivity, including percentage of pregnant females and of females giving birth, was significantly reduced in diazinon-exposed animals. Percentage of pregnant females ranged from 13.6 to 43.5% in diazinon-exposed animals compared to 40 to 80% for control animals, and percentage of females giving birth ranged from 0 to 17% in diazinon-exposed animals compared to 22 to 50% for control animals. Generally, the effects found in this study suggest that diazinon was relatively persistent in the sprayed enclosures and that oral routes of exposure (consumption of dead and dying arthropods, grooming) may have been important. Ecological relationships and reproduction in both herbivorous and omnivorous mammals were negatively impacted by diazinon exposure. Overall, ecological relationships in the enclosed prairie grassland ecosystem were disrupted by diazinon, probably through a combination of sublethal effects, particularly reproductive effects, impacting individuals and their populations. This suggests that negative impacts on populations and community structure and function may persist longer than diazinon persists in the environment.

Animals↗
PubMed2005

A two-generation reproductive toxicity study of diethyl phthalate (DEP) in rats.

A two-generation reproductive toxicity study was performed to evaluate the effects of diethyl phthalate on parental reproductive performance, including features of the endocrine system and development and growth of offspring at dietary dose levels of 0, 600, 3000 and 15000 ppm. In F0 and F1 parents, no treatment-related adverse effects were observed in clinical findings, body weights, food consumption, reproductive parameters, and gross or histopathological findings in any treated group. Increased liver weights and enhanced activities of metabolic enzymes were observed in F0 males at 15000 ppm. F0 males also exhibited an increase in the content of CYP3A2, a cytochrome P450 isozyme, at 15000 ppm, and a decrease in the levels of serum testosterone at 3000 and 15000 ppm, suggesting sex steroid metabolism might be changed. However, these were not considered adverse effects because the degree of change was too slight to affect the reproductive capability to produce progeny. Body weight gains before weaning were inhibited in F1 and F2 pups and vaginal opening was slightly delayed in F1 females at 15000 ppm. No changes were observed in the reproductive performance. Therefore, the no-observed-adverse-effect level (NOAEL) from this study is considered to be 15000 ppm for parental animals, and 3000 ppm for development and growth of the pups.

Administration, Oral↗
PubMed1990

Management practices and their association with reproductive health and performance in Colorado beef herds.

An observational study was conducted to quantify the effects of management practices on reproductive performance and disorders of beef cows. The study population consisted of 44 randomly selected Colorado cow-calf herds monitored for disease and reproductive events as part of the National Animal Health Monitoring System. The managers of the herds were surveyed with a standardized questionnaire to determine specific management characteristics of their operations. Data were analyzed using the random-effects multiple logistic regression model. Outcomes of interest were calving rate, herd incidence rates of dystocia and combined reproductive disorders, and calf mortality rate. A higher calving rate was associated (P less than .01) with a decreased percentage of replacement females in the herd, a shorter breeding season, a smaller herd size, and a lower percentage of bulls being used as yearlings. Incidence rates of both dystocia and combined reproductive disorders were found to be lower (P less than .01) in herds that were fed cottonseed cake as a winter supplement, but higher (P less than .01) in herds that were fed grass hay as a winter supplement. Herds located in the mountains of Colorado had lower (P less than .01) incidence rates of dystocia and reproductive disorders than herds located in the eastern plains. Calf mortality rate was found to be higher (P less than .05) with calving seasons that began earlier in the year. Higher calf mortality rates were associated (P less than .05) with an increased incidence of dystocia, the commingling of cattle on summer range, and smaller herd size.

Animal Feed↗
PubMed1992

The effect of natural toxins on reproduction in livestock.

Reproductive efficiency is the most important economic factor in livestock production. Thus, the hypothalamo-pituitary-gonadal regulatory axis, accessory sexual organ functionality, and the complex events involved in fertilization, implantation, and embryonic and fetal development may be sensitive to therapeutic agents, environmental pollutants, and natural toxicants. There are many factors that adversely affect reproduction, one of which is toxic substances in the diets of animals. Toxic materials can affect reproductive success by causing abortions, interfering with libido, estrus, oogenesis, or spermatogenesis, causing emaciation and subsequent abnormal mating behavior, birth defects, and increasing the time between parturition and rebreeding. Examples of natural toxicants in poisonous plants interfering with reproduction are numerous. Abortion in livestock from locoweeds, ponderosa pine needles, broom snakeweeds, fescue, and others are reported in studies. Selenium and seleniferous forage inhibit estrus in cattle and swine. Emaciation and temporary illness from sneezeweeds, bitterweed, locoweed, larkspur, lupines, and others may interfere with mating. Embryonic loss and birth defects from Veratrum, lupines, locoweeds, poison hemlock, and so on, may occur. As suggested, toxins have many diverse and economically adverse effects on reproductive performance in livestock.

Animals↗
PubMed1992

Effects of nutrient deficiencies and excesses on reproductive efficiency of livestock.

Successful reproduction is dependent on a host of macro- and micronutrients and ceases well before an animal expires from deficiency of a particular nutrient. This review focuses on the functional roles phosphorus, vitamin A and beta-carotene, protein, and energy play in reproductive processes. Although it is not known whether deficiencies of these nutrients limit reproduction through common or discrete mechanisms, appropriate quantities of these nutrients are required for optimal reproduction. Mechanisms through which nutritional status is perceived by the hypothalamic-pituitary-gonadal axis remain unclear but seem to impinge on hypothalamic regions that selectively regulate production and release of pituitary trophic hormones. Body condition, or degree of fatness, seems to be the most reliable indicator of well-being of an animal, and, when coupled with changes in BW, provides a useful method to assess reproductive potential.

Animal Nutritional Physiological Phenomena↗
PubMed2001

Level of dietary energy during prepubertal growth and reproductive development of gilts.

Development of gilts that conceive early and continue to produce offspring is a primary objective of swine production. The objective of this study was to determine the degree of feed restriction during development required to optimize reproductive performance and efficiency in gilts. The effects that various patterns of growth had on reproductive development and performance of gilts through d 30 of gestation were investigated. At 13 wk of age and 41 kg BW, 192 white crossbred gilts were penned individually and assigned to receive 87.5%, 75%, 62.5%, and 50% of predicted ad libitum energy intake. The study was replicated in two seasons. At 25 wk of age, gilts were moved to group pens and allowed ad libitum access to feed, and estrous detection was initiated. Gilts were inseminated at first observed estrus and those recycling were remated. Post-mating gilts were fed 1.5x maintenance in stalls. Gilts that did not return to estrus 17 to 30 d after mating were slaughtered at 30 d of gestation. Reproductive tracts were collected and numbers of corpora lutea and live embryos were recorded. Feed restriction during development resulted in differences in BW and backfat thickness at the start of the breeding period and differences in feed intake during breeding. Gilts subjected to the greatest feed restriction during development consumed the greatest quantity of feed during breeding. Feed intake during breeding was associated with BW and backfat gain during breeding. The treatment group that entered breeding lightest and leanest (50% of predicted ad libitum intake) had the least number of days to first estrus, followed by the fattest, heaviest group (87.5% of predicted ad libitum intake). Treatment groups did not differ (P > 0.38) in ovulation rate or live embryo numbers. Significant relationships between quantity of GE consumed during development and variables considered important in reproductive development and performance were evident, such as BW and fatness at start of breeding and first detected estrus, and ovulation rate. Variation in dietary energy during the development period impacted many aspects of reproductive development and performance. However, coupling restricted energy intake during development with ad libitum intake during breeding negated many of the effects of feed restriction during the development period.

Animal Feed↗
PubMed2001

The effect of litter size before weaning on subsequent body development, feed intake, and reproductive performance of young rabbit does.

An experiment was performed to study the effect of litter size before weaning on subsequent body development and composition, feed intake, and reproductive performance of young rabbit does with the objective to improve reproductive performance. Litter size (LS) before weaning (treatment) was 6, 9, or 12 kits. After weaning (30 d), 58 female kits per treatment (in two successive replicates) were reared and fed for ad libitum intake to 14.5 wk of age (end of rearing). At 14.5 wk of age, receptive does were inseminated. Nonreceptive and nonpregnant does were inseminated at 17.5 wk of age. The experiment ended when the second litter was weaned. Part of the animals was slaughtered to determine body composition at the end of the experiment (replicate one) and at the end of rearing (replicate two). At weaning, BW differed among treatments (P < 0.05; 855, 773, and 664 +/- 15 g for LS6, 9, and 12, respectively). Compensatory growth was observed. At the end of rearing, LS12 does were smaller (P < 0.05) than LS9 and LS6 does (3,524, 3,778, and 3,850 +/- 48 g, respectively). After first lactation, no difference in BW among treatments was found. Compared with LS6, empty body weight (BW minus gut, bladder, and uterus content) of LS12 contained more (P < 0.05) nitrogen (32.5 vs 31.1 +/- 0.3 g/kg), more (P < 0.05) ash (30.7 vs 28.3 +/- 0.6 g/kg), and less (P < 0.05) fat (168.6 vs 200.2 +/- 8.6 g/kg). No differences in body composition among treatments were found at the end of the experiment. During rearing, LS12 had the lowest (P < 0.05) daily feed intake (152, 164, and 169 +/- 2 g/d for LS12, 9, and 6, respectively). During the reproductive period, no differences in feed intake among treatments were found. Kindling rate (the number of kindlings per number of inseminations) was not influenced by treatment. In the first parity, total litter size (number of alive and stillborn kits) was lower (P < 0.10) for LS12 than for LS9 (6.4 vs 8.6 +/- 0.5, respectively). When first mating was delayed by 3 wk, an increased (P < 0.05) total litter size was found regardless of treatment (7.5 and 9.4 +/- 0.3 for 14.5, and 17.5 wk, respectively). Decreasing litter size before weaning from nine to six kits did not alter future reproductive performance. Based on results of this study, it seems advisable to perform a limited standardization level (at nine kits) after kindling and postpone first mating to an older age (17.5 wk) to improve reproductive performance.

Animal Husbandry↗
PubMed2002

Relationships between body weight at first mating and subsequent body development, feed intake, and reproductive performance of rabbit does.

A retrospective study was performed to evaluate the relationships between BW at first insemination and subsequent body development, feed intake, reproductive performance, and culling rate of rabbit does. Young rabbit does are vulnerable to body energy deficit in first lactation, resulting in decreased reproductive performance and high replacement rate. Heavy does at first insemination might be able to benefit from the extra amount of BW to cope with the energy deficit during first lactation. Data of three experiments were used in which does were given ad libitum access to feed during rearing and inseminated at 14.5 wk of age. The first two parities of each doe were recorded. Does were categorized in three groups based on their BW at 14.5 wk of age (first insemination): heavy (BW > or = 4,000 g), medium (BW 3,500 to 4,000 g), and small (BW < 3,500 g). Among does that kindled, differences in BW at first insemination were related to differences in voluntary feed intake and body growth rate during rearing. Heavy does consumed more feed per day (+ 45 g/d, P < 0.001) and had a higher BW gain (+ 12 g/d, P < 0.001) than small does from weaning (4.5 wk) to 14.5 wk of age. Body weight at first insemination did not affect BW, feed intake, and culling rate during the first two parities. Heavy does were heavier at first insemination and remained so throughout the reproductive period, but they followed a similar BW curve as medium and small does. A higher BW at first insemination (14.5 wk of age) improved litter size in the first parity (8.9, 7.7, and 6.4 for heavy, medium, and small does, respectively, P < 0.05). Extra BW at start of reproduction improves litter size in the first parity but does not contribute to an improved feed intake or increased BW development during reproduction.

Animal Husbandry↗