Non-lactating Females Research Articles

Genetic differences in female house mice in aggressive response to sex steroid hormone treatment

Male mice, genetically selected for aggression, characterized by short attack latency (SAL) or long attack latency (LAL), differ on several testosterone (T)-related parameters during ontogeny and adult age. The variation in aggressive behavior at adult age may be due to differences in degree of androgenization prenatally. When exposed to T at prenatal, neonatal, and/or adult age, nonlactating females also display intraspecific fighting behavior. In the present study, we investigated in females of the SAL and LAL selection lines, whether the differentiation of aggression involves processes similar to ones seen in males. Therefore, we injected females with testosterone propionate (TP) or vehicle on the day of birth, treated them after ovariectomy at adult age with T, estradiol (E), or vehicle, and tested their aggressive response. We found that neonatally vehicle-treated SAL females show a higher aggressive response to chronic T treatment at adult age than LAL females receiving the same treatment. Females of both selection lines treated with vehicle or E as adults were not aggressive. Neonatal TP treatment did not influence the adult T sensitivity and difference between selection lines in response to T at adult age. However, neonatally TP-treated SAL females showed aggressive behavior when treated with E at adult age, whereas LAL females failed to do so. These results suggest a genetic difference in susceptibility to T and E, which plays a major role prenatally, in organizing the development of sex steroid-dependent neural systems.

Male dominance rank and reproductive success in an enclosed group of Japanese macaques: with special reference to post-conception mating

The mating behaviour and reproductive success of male Japanese macaques (Macaca fuscata) were studied in relation to the female sexual cycles, which were monitored from the plasma profiles of gonadotropins and ovarian hormones. Based on observations of the mating behaviour during four successive mating seasons and paternity identification by DNA fingerprinting in 35 out of 37 offspring born in the subsequent birth seasons, the correlations between (1) male dominance rank and timing of mating, and (2) male dominance rank and reproductive success were examined. The results may be summarized as follows. (1) The number of copulations with ejaculation by any male was positively correlated with the male dominance rank, but not with the identified numbers of offspring fathered by each male. (2) Males could not choose ovulatory females as mating partners: the number of copulations with ejaculation with females during ovulatory weeks was not related to the male's rank. Monopolized copulations in consortship were mostly observed between high-ranking males and non-lactating parous females after conception. (3) Paternity testing showed that the male copulating most frequently with a female was not the identified father in 11 out of 15 cases. Prediction of the fathers of offspring was difficult even from the number of copulations occurring at around the estimated time of ovulation. An adaptive explanation of these correlations is discussed.

Involvement of Central Corticotropin‐Releasing Factor (CRF) in Suckling‐Induced Inhibition of Luteinizing Hormone Secretion in Lactating Rats

The lack of ovulation and the inhibition of reproductive functions observed in many species during lactation is closely related to the intensity of the suckling stimulus. However, the mechanisms by which suckling inhibits hypothalamic GnRH and pituitary LH secretion in rats are still unclear. Since we recently demonstrated that suckling is a persistent stimulus to the adrenococortical system of the rat, we tested the hypothesis that suckling-induced activation of central CRF release may mediate the associated inhibition of GnRH secretion. Lactating females were ovariectomized (OVX) on day 2 of lactation, and equipped with icv guide cannula on day 2 and indwelling jugular catheters on day 5 before testing on day 7. Lactating females were separated from their pups for 24 h prior to the suckling test with the following pretreatments: 1) icv injection with artificial CSF (aCSF) or a specific CRF antagonist, alpha-helical CRF (9-41), (25 micrograms/rat, CRF-AX) 15 min prior to pup reunion or 2) iv injection of normal sheep serum (NSS) or CRF antiserum (CRF-AB) 4 h prior to pup reunion. Plasma ACTH, LH and PRL concentrations were determined prior to and at various intervals after pup reunion. After 3 h of suckling, LH and PRL responses to a bolus injection of GnRH (10 ng/rat) were measured; a bolus injection of Angiotensin II (AII, 5 micrograms/rat) was administered after 4 h to test for ACTH responses. Non-lactating females injected with GnRH and AII were used as controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Extended postpregnancy estrous cycles in fernale lion-tailed macaques.

Past studies of female primate reproduction have focused on regularly cycling females, and thus the reproductive characteristics of females in other reproductive states (e.g., pregnant, or lactating) have rarely been investigated. In this study, data were collected on estrous swellings and sexual and proceptive behavior in six female lion-tailed macaques during recovery from lactational amenorrhea for the first three to five postpregnancy cycles. For these females, the length of the first lactational recovery swelling cycle averaged 81 days, nearly three times the length of cycles exhibited by nonparturient, isosexually housed females Actual swelling durations were also nearly three times the length of those seen in nonlactating females, and occupied a larger proportion of the cycle For most females, cycle duration and sexual and proceptive behavior declined progressively over successive cycles. The alpha female in each group accounted for the majority of copulations in the first three cycles, and this effect was pronounced in the first cycle. Extended postpregnancy cycles in this species may be related to female reproductive competition and /or a tactic to attract extra-group males. © 1993 Wiley-Liss, Inc.

Predicted susceptability of Dasyurus geoffroii to canid baiting programmes: variation due to sex, season and bait type

A laboratory assessment of the susceptibility of Dasyurus geoffroii to baits used to control foxes and dingoes was conducted using five types of non-poisoned baits: polony, fresh meat, meat dried by 50% and 70% of the original weight, and compressed beef crackle. Trials were designed to simulate the initial encounter of a bait by hungry wild juveniles and adults of both sexes, including lactating females. In overnight trials, juveniles and lactating females ate significantly more fresh meat per body weight (mean consumption: 23.7% for juvenile males, 21.5% for juvenile females, 23.1% for lactating females) than non-lactating adult females and adult males (combined mean, 18.3%). Maximum overnight bait consumption was 43% of body weight. These values greatly exceed those previously reported for other species of Dasyurus. Moist baits were eaten more rapidly and in larger amounts than drier baits. Seasonal factors lead to the prediction that the period when canid baiting can be conducted with the least danger to Dasyurus geoffroii is January-March.

Factors affecting oxygen consumption in wild-caught yellow-bellied marmots ( Marmota flaviventris)

1. 1. All age groups gained mass during the active season, but mass-gain of adult females was delayed during lactation. 2. 2. The relationship of body mass to metabolic rate varied widely; when the relationship was significant, R 2 varied from 10.3 to 72.6%. Body mass affects V O 2 more during lactation than at any other period. 3. 3. Mean VinO 2 of adult males was higher in June than that of adult, non-lactating females. 4. 4. V O 2 of reproductive females was significantly higher during lactation than during gestation or postlactation because specific V O 2 varied. Specific V O 2 of non-reproductive females declined over the active season. 5. 5. Specific V O 2 of all age groups declined between the premolt and postmolt periods. The reduced maintenance costs can contribute 20–46% to daily growth. 6. 6. Observed V O 2 was lower than the value predicted from intraspecific or interspecific Bm:M regressions. 7. 7. V O 2 of wild-caught marmots was lower than that of marmots maintained in the laboratory, probably because of dietary differences. 8. 8. Because basal metabolism is a stage on a food-deprivation curve, we suggest that basal metabolic rate is not an appropriate measure of the metabolic activity of free-ranging animals.

GnRH-stimulated LH and FSH release by perifused anoestrous red fox pituitary cells: gonadal steroid modulation

In this study, gonadotropin releasing hormone (GnRH)-stimulated luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretions in the red fox (Vulpes vulpes L.) have been studied during anoestrus using perifused dispersed pituitary cells. The objective was to compare LH and FSH responses to pulses of GnRH in lactating and non-lactating females and to examine the feedback of gonadal steroids. Our results indicate that the pituitary sensitivity to GnRH was greatly reduced in lactating females compared with non-lactating females. Treatment in vitro of cells during 24 h (short-term effect) by progesterone (P) or oestradiol (E2) induced an increase of LH and FSH release, indicating that even during anoestrus, pituitary cells are able to respond positively to gonadal steroids. In contrast, administration of P or E2 in vivo for several days by silastic capsules (long-term effect) induced a reduction of LH and FSH releases by pituitary cells in vitro. Thus, steroids act directly on the pituitary but their action is time- and dose-dependent. During anoestrus in the fox, particularly during lactation, P and E2 might exert a potent negative feedback control on pituitary secretion. In the red fox (Vulpes vulpes L.), the fact that GnRH-stimulated LH and FSH secretions are reduced in lactating females more than in non-lactating females, suggests that P (secreted in vivo during lactation, probably as a consequence of a luteotrophic action of prolactin) and E2 secreted jointly during episodic phases of oestrogenic activity, may be responsible for decreased pituitary responsiveness observed during early anoestrus. This action of gonadal steroids might occur in association with a specific role of prolactin or a suppressive effect of suckling.

Efficiencies of conversion of some lignocellulosic waste materials by goats

Abstract The ability of the goat to utilise some lignocellulosic materials was assessed. Fifteen West African dwarf goats comprising non-pregnant, non-lactating females, intact (uncastrated) males and castrated male goats were involved in digestion and growth studies. The lignocellulosic materials were Leucaena leaf meal, yam peels and cocoa bean shells, together making up 92% of the total diet. The diet had 24% crude protein. Data were collected on DM feed intake, weight grain, nutrient digestibilities and feed/gain ratio. The coefficient of digestibilities of the nutrients were not appreciably different ( P >0·05) between the groups of goats studied. The feed nutrient digestibilities (%) were: dry matter, 56·7; crude protein, 61·7; crude fibre, 30·7, ether extract, 99·6 and nitrogen-free extract, 67·8. The low crude-fibre digestibility was suggested to be due to the source and quality of the dietary fibre. Weight gains were between 122 and 139 g/day and were impressive. The feed conversion was 170g weight gain per kg of feed intake for the female and intact goats, and 200 g weight gain per kg of feed for the castrates. The experimental ration was considered fit for a goat fattening programme. Castration was suggested to obtain a higher efficiency of feed conversion.

WEIGHTS AND HEMATOLOGY OF WILD BLACK BEARS DURING HIBERNATION

We compared weights and hematological profiles of adult (greater than 3-yr-old) female black bears (Ursus americanus) during hibernation (after 8 January). We handled 28 bears one to four times (total of 47) over 4 yr of varying mast and berry production. Mean weight of lactating bears was greater (P less than 0.0001) than that of non-lactating females. White blood cells (P less than 0.05) and mean corpuscular volume (P = 0.005) also differed between lactating and non-lactating bears. Hemoglobin (P = 0.006) and mean corpuscular hemoglobin concentration (P = 0.02) varied among years; values were lowest during 1975, following decreased precipitation and the occurrence of a second year of mast and berry crop shortages in a three-year period. Significant (P less than 0.05) interaction between reproductive status (lactating versus non-lactating) and study year for hemoglobin, red blood cells, and packed cell volume, and increased mean corpuscular volume, suggested a greater nutritional challenge for lactating females compared to non-lactating females during the 1975 denning season. Our data suggest that hematological characteristics of denning bears may be more sensitive than weights as indicators of annual changes in nutritional status; however, other influential factors, in addition to mast and berry crop production, remain to be examined.

Humoral immune activity in CBA/Ca mice during late pregnancy and the post-partum period

Syngeneically mated CBA/Ca mice were used to measure “spontaneous” immunoglobulin (Ig) secretion in the Peyer's patches (PP), spleen and the para-aortic lymph nodes (PALN), employing a protein A plaque assay, during the latter part of pregnancy and in the post-partum period. The lactating and non-lactating females were compared with respect to humoral immune activity (plaque-forming cells) and serum Ig levels (ELISA technique). The pregnancy-induced weight changes in some lymphoid organs and the elevation in the number of plaque-forming cells in spleen (IgG and IgM PFC), PALN (IgG and IgM PFC) and the PP (IgA PFC) lasted longer in the lactating than in the non-lactating mice (owing to hormonal differences). A very strong decrease in serum IgG was observed during pregnancy and after parturition IgG levels remained depressed longer in lactating than in non-lactating mice. Interest has been focused on IgA in the study and this has been discussed as well as the possible reasons for the increased turnover of maternal serum Ig (especially IgG).

Differences in fertility and suckling patterns between primiparous and multiparous rhesus mothers (Macaca mulatta).

Primiparous females gave birth around the same time as multiparous nonlactating females, and earlier than did multiparous lactating females. No differences in birth sex ratio were found between primiparous and multiparous females. During the breeding season following birth, primiparous mothers returned to oestrus later than did multiparous mothers, and while few primiparous mothers conceived successfully during that season, most multiparous mothers did. Primiparous females suckled their infants more frequently than did multiparous females at all ages; infants of primiparous females also made more nipple contacts per bout, and had shorter sucking bouts. When mothers came into oestrus, suckling frequency drastically increased for primiparous females, but not for multiparous females, magnifying the differences between the two groups. After the first oestrus, suckling frequency declined for all mothers, but multiparous mothers had consistently lower suckling frequencies than did primiparous mothers. The high suckling frequency, and numerous nipple contacts per bout, found among primiparous mothers are likely to be related to the low reproductive chances that these females faced during the breeding season. Multiparous mothers seemed to compensate for their low suckling frequency by lengthening the suckling bouts, and this suckling pattern did not hinder their reproduction. It is argued that primiparous mothers might have to suckle their infants more frequently because they can only produce milk at slow rates, being in this way forced into a reproductively inhibiting suckling pattern. However, the delay in subsequent reproduction could be ultimately advantageous for primiparous mothers if it enhanced infant survival, and allowed the mothers to regain physical condition before reproducing again.

Stomach contents of harbour porpoises, Phocoena phocoena (L.), from the Bay of Fundy

We examined contents from stomachs of 127 harbour porpoises (Phocoena phocoena) caught in groundfish gill nets in the western Bay of Fundy during June to September, 1985–1987. Relative importance of prey species was assessed using both numerical and caloric measures. Atlantic herring (Clupea harengus) was the most important prey species, contributing 80% of the total caloric intake, with some spatial and temporal variation. Silver hake (Merluccius bilinearis) and Atlantic cod (Gadus morhua) were also important, but together comprised only 17% of the total caloric intake. No differences were found in relative prey importance between adult porpoises of different reproductive conditions, but lactating females ingested more fish and had a significantly higher total caloric intake than nonlactating females or mature males. The diet of porpoises collected from the same area in 1969–1972 consisted of a higher proportion of pelagic prey species and a lower proportion of demersal species. This may be attributed to differences in capture method, as the earlier sample of porpoises was collected at the surface, while the present animals were captured at depths of 45–100 m.

Factors influencing the self-selection of calcium in lactating rats

The effect of varying litter size and preventing milk delivery on the self-selection of calcium in lactating rats was assessed in two experiments. In Experiment 1, two groups of lactating rats, one having a litter size adjusted to four pups (n=10) on the day after parturition and the other a litter size adjusted to 16 pups (n=9), were given ad lib access to a 2.4% solution of calcium lactate, demineralised water, and a calcium deficient diet. Calcium, water and food intake were compared for these two groups both before impregnation and during 16 days of lactation. Females nursing 16 pups increased their calcium and food intake over the course of lactation more than did mothers nursing four pups. In Experiment 2, female rats were divided into four groups consisting of 10 nonimpregnated, 10 impregnated, 10 impregnated galactophore-cut, and nine sham-operated animals. To maintain pup health, and thus equivalent suckling stimulation among groups, litters of 8 pups were switched between galactophore-cut, impregnated and colony foster mothers every twelve hours. Over the course of lactation galactophore-cut dams showed an increase in calcium intake compared to nonlactating females and further, took in similar quantities of calcium to both intact and sham-operated impregnated animals in the first week of lactation. These studies showed that female rats do selectively increase their calcium intake during lactation. Moreover, this increase varies as a function of litter size and persists in the absence of milk delivery.

Effect of exogenous prolactin and bromocriptine on seasonal reproductive quiescence in the Bennett's wallaby (Macropus rufogriseus rufogriseus).

Two experiments were performed to investigate whether prolactin blocks the reactivation of the corpus luteum during seasonal reproductive quiescence in the Bennett's wallaby. In the first experiment three groups of non-lactating females (groups A C) were subjected in mid-April to photoperiods corresponding to those of the summer solstice from day 0 to day 13 of the experiment. Between days 14 and 52, photoperiods were reduced to correspond to those of the winter solstice (groups B and C). Animals in group A were maintained on the long photoperiods. Two milligrams ovine prolactin (groups A and C) or vehicle (group B) were administered on the mornings of days 14-22. In group A, no animal showed evidence of an active corpus luteum based on increased plasma progesterone levels. All animals in groups B and C exhibited reactivation of the corpus luteum. In group C, reactivation was significantly (P less than 0.01) delayed by a mean of 6.3 days. In the second experiment, two groups of nonlactating female wallabies in 'seasonal quiescence' were injected daily for 7 days with either 60 mg of the dopamine agonist bromocriptine or vehicle. The corpora lutea did not reactivate in either group. We conclude that exogenous prolactin is able to block the effect of short photoperiods in reactivating the quiescent corpus luteum during seasonal quiescence. However, the absence of an effect of bromocriptine suggests that if prolactin is the endogenous hormone responsible for maintaining seasonal quiescence it may not be under dopaminergic control at this time of year.

Body composition of the George River caribou (Rangifer tarandus caribou) in fall and late winter

The fall and late winter body composition of George River caribou was determined based on a sample of 14 calves, 9 yearlings, and 41 adult females. In fall, the fattest individuals were the adult nonlactating females with 10.62 ± 2.65% ingesta-free body fat. Ingesta-free body fat was 5.25 ± 2.47% for lactating females, 7.76 ± 0.11% for yearlings, and 3.44 ± 0.57% for calves. There was no evidence of depletion of fat reserves between fall (October–December) and mid-April in any age-class, and no change in body weights of calves. However, the ingesta-free body weights of pregnant females in April were 19.8 and 9.5% less than those of nonlactating and lactating females in fall, respectively. These differences were due mainly to a loss of water (9.8 and 7.3 kg) and protein (4.6 and 2.6 kg). This protein loss of the ingesta-free body was not compensated for by growth of the gravid uterus, which accounted for 3.5% (0.53 kg) of the total protein mass of pregnant females in mid-April. These results suggest that, between fall and late winter, the George River caribou were affected more by a deficiency in protein than a negative energy budget and that increased attention should be given to monitor protein reserves. However, in summer and early fall, these caribou accumulated only limited fat reserves as compared with other northern ungulates and the possibility of an energy deficiency during summer should be investigated.

Quantitative measurement of water consumption patterns in lactating female and neonatal Fischer 344 rats employing [ 14C]methylcellulose

Lactating female and neonatal Fischer 344 rats were given water containing [ 14C]methylcellulose, a nonabsorbed marker, over a 24-hr interval on Days 13, 15, 18, 21, 24, and 27 postpartum. The amount of water consumed was calculated based on the 14C activity recovered in the feces and gastrointestinal tract. Maternal water consumption during the first 28 days postpartum, when expressed as g/kg/day, averaged 2.5 times the level consumed by nonlactating female rats. Maternal water consumption peaked on Day 21 postpartum at 3.3 times the level measured in nonlactating female rats of comparable age. Neonatal water consumption began on Day 18 postpartum and by Day 28 postpartum was 1.9 times the level observed in nonlactating females. Average neonatal water consumption between Days 21 and 28 postpartum was 1.3 times the level for nonlactating female rats. These data indicate that when the test material is administered via the drinking water the dose levels received by the maternal and neonatal rats have been routinely underestimated, and that conclusions concerning the dose-response relationship or increased sensitivity during this period must be tempered by these results.

Dry-matter intake of Hereford and first-cross cows measured by controlled release of chromic oxide on three pasture systems

SummaryFaecal output of 287 beef cows consisting of Hereford (H × H), Simmental × Hereford (S × H), Friesian × Hereford (F × H) and Brahman × Hereford (B × H) breeding was estimated using controlled release of chromic oxide (Cr2O3). All cows were from 6 to 10 years of age and had grazed on one of three pasture systems in the subtropics of New South Wales since they were 7–8 months of age. These pastures were designated as being of high, medium and low nutritive value. Faecal organic matter output (FOMO) was estimated in each of four periods (early lactation, mid lactation, late lactation, and non-lactating) during one annual production cycle.Herbage mass exceeded 2 t/ha on all pasture systems, but estimates of organic-matter digestibility, nitrogen content and pasture composition indicated large differences in pasture quality (high > medium > low). Live weight of cows averaged 604, 488 and 393 kg live weight on the high, medium and low pastures, respectively. There were significant differences in live weight between genotypes on the medium (B × H > F × H and H × H) and low (S × H ≡ F × H ≡ B × H > H × H) pastures but not on the high pasture).FOMO and dry-matter intake (DMI) differed significantly between genotypes among lactating cows on all pasture systems. Rankings on high pastures were reasonably consistent in all periods: S × H ≡ F × H ≥ B × H ≥ H × H, as were those on low pastures, B × H ≥ S × H ≡ F × H ≥ H × H. Differences on medium pastures were significant only during mid-lactation when B × H ≡ S × H ≡ F × H > H × H. Significant differences between genotypes were observed among non-lactating cows on high pastures only, where H × H ≡ S × H ≡ F × H > B × H. Lactating females had significantly higher FOMO and DMI than non-lactating females when compared across genotypes during early lactation on all pastures.

Mineral Composition and Zinc Metabolism in Female Mice of Varying Age and Reproductive Status

Zinc metabolism of adult female C57BL/6J mice varying in age and reproductive status was studied using 65Zn. Animals were injected intraperitoneally with isotope, and whole-body and tissue turnover of 65Zn was measured. Biological half-life of whole-body 65Zn for pregnant females was 129% of that for nonpregnant, nonlactating females of similar age (25.7 and 20.0 d, respectively). Conversely, the half-life of zinc was less for lactating (11.1 d) and aged (15.3 d) females than for either pregnant or nonpregnant, nonlactating young adult females. Retention of 65Zn was generally lower for all tissues of pregnant and lactating dams than for nonpregnant, nonlactating females except for brain and tibia. In aged females, specific activity at 20 d postinjection did not differ from that of nonpregnant, nonlactating young adult females for any tissue except bone. While specific activity of tibia increased during pregnancy and lactation, it was lower in aged females than in nonpregnant, nonlactating young adult females. Increased organ content of zinc resulted from changes in zinc concentration or in organ mass or both, and was supported by increased food intake. Thus, greater food intake for these groups than for young adult females contributed to the higher turnover of tissue 65Zn. Differences in concentrations of Cu, Ca and Mg were also observed among groups for some tissues; the significance of these differences and their relationship to zinc metabolism are not clear.

Seasonal reproduction of white‐eared kob in Boma National Park, Sudan

SummaryThe reproductive phenology of migratory white‐eared kob in Boma National Park, southern Sudan, was investigated during 1981‐83. Calf production occurred during the late wet season (September‐December), well after the period of peak food abundance. Lactation continued throughout the dry season, when forage was in short supply. As a consequence, lactating females had lower fat reserves than either non‐lactating females or males. The observed calving phenology may (i) allow females time to replenish fat reserves prior to lactation and (ii) reduce the risk of predation on new‐born young.RÉSUMEÉLa phénologie reproductive du cobe de Buffon àoreilles blanches migrateur dans le Parc National de Boma, dans le sud du Soudan, fut étudiée durant les années 1981 à 1983. La naissance des jeunes se produit à la fin de la saison des pluies (septembre à décembre), bien après la période d'abondance maximale. L'allaitement se poursuit tout au long de la saison sèche, alors que le fourrage n'est pas suffisant. En conséquence, les femelles allaitantes ont moins de réserves de graisse que les autres femelles ou que les mäles. La phénologie de reproduction observée pourrait laisseu aux femelles le temps de se constituer des réserves de graisse avant la lactation et réduire le risque de prédation sur les nouveaux‐nés.

Development of an homologous radioimmunoassay for secreted prolactin from the California ground squirrel (Spermophilus beecheyi).

A sensitive homologous radioimmunoassay was developed for secreted prolactin from the California ground squirrel (Spermophilus beecheyi). S. beecheyi plasma and pituitary extracts displaced 125I-labeled S. beecheyi prolactin in a parallel manner with S. beecheyi prolactin (sbPRL). Mean minimum sensitivity of the assay was 0.21 ng/ml, and mean intra- and interassay coefficients of variation were 4.1% and 14.5%, respectively. The assay was used to measure basal prolactin concentrations in male and female ground squirrels at various stages of their annual reproductive cycles. Mean concentrations in nonpregnant, nonlactating young females, pregnant females, and lactating females were 1.63, 11.35, and 10.86 ng/ml, respectively. Mean concentrations in nonreproductive and breeding males were 1.50 and 9.81 ng/ml, respectively. Finally, the assay was used to evaluate cross-reactivity between sbPRL and prolactins and growth hormones from other rodent species. Of the tested hormones, only hamster prolactin showed any cross-reactivity with sbPRL (about 0.03%).