Prolactin Assays Research Articles

Macroprolactinaemia: contribution to hyperprolactinaemia in a district general hospital and evaluation of a screening test based on precipitation with polyethylene glycol.

For a period of 12 months all samples submitted for serum prolactin (PRL) assay and with PRL > 700 mU/L were examined by gel filtration chromatography. In 17 (25%) of 69 samples we found macroprolactin. The Delfia and Immuno 1 immunoassay systems gave similar PRL results with samples containing macroprolactin whereas the ACS 180 system gave lower results. With the Delfia and Immuno 1 systems samples containing substantial quantities of macroprolactin showed low recovery of PRL after precipitation with polyethylene glycol 6000 (PEG 6000) and this technique can be used as a screening test for macroprolactinaemia. We conclude that macroprolactinaemia is a common phenomenon and, in assays which detect this species, is a common cause of hyperprolactinaemia. Macroprolactinaemia may contribute to the difficulty in establishing an upper limit of the reference range for serum PRL. In our experience, patients with macroprolactinaemia do not exhibit features of the hyperprolactinaemia syndrome and it is important to recognize macroprolactin as the cause of hyperprolactinaemia to avoid unnecessary investigation and treatment.

Sleep in rats rendered chronically hyperprolactinemic with anterior pituitary grafts

A hyperprolactinemic rat model [rats bearing anterior pituitary grafts under the capsule of the kidney (AP-grafted rats)] was used to study sleep-wake activity and cortical brain temperature (T crt). Fisher 344 male rats ( n = 24) were implanted with anterior pituitaries from rat pups; the control rats ( n = 12) were sham-operated. Sleep–wake activity and T crt were recorded for 2 days between weeks 3 and 7 after surgery. The hyperprolactinemic state of the rats was confirmed by plasma prolactin (PRL) assays on week 7 and by determination of PRL mRNA levels in the anterior pituitary of the AP-grafted rats. Neither growth hormone plasma concentration nor pituitary mRNA levels were affected by the pituitary grafts. Duration of non-rapid eye movement sleep (NREMS) was slightly enhanced in the AP-grafted rats. A large increase in rapid eye movement sleep (REMS) during the 12-h light period was the major effect of the implantation of the extra pituitaries. Both the duration and the frequency of the REMS episodes increased and persisted for weeks 4–7 post-implantation. The nocturnal states of vigilance, T crt, and intensity of NREMS (EEG slow wave activity) were not altered. The results clearly indicate that the enhancements in REMS persist during hyperprolactinemia, and support the hypothesis that PRL possesses REMS-promoting activity.

A Descriptive Model for the Kinetics of a Homogeneous Fluorometric Immunoassay

A descriptive mathematical model was chosen to fit the antigen-antibody association kinetics of a new homogeneous immunometric assay for prolactin, involving time-resolved fluorescence detection (TRACE® technology, Time Resolved Amplified Cryptate Emission). We paid special attention to the methodology and criteria applied, to yield a convenient and statistically valid model, designed to allow potential exploitation of kinetic information in the data processing of the assay. We compared specific parameterizations of an hyperbolic model, the Gompertz, and the monomolecular models on the basis of morphological considerations, a statistical analysis of fit, and an assessment of the parameters estimation quality, over a wide range of antigen concentrations. The monomolecular model gave the best fit, and the most precise and stable estimation of its parameters. The study of parameter properties confirmed this choice.

Potential hook effect in prolactin assay in patients with giant prolactinoma

<b>Potential hook effect in prolactin assay in patients with giant prolactinoma</b>

Sensitivity and specificity of paired capillary prolactin measurement in diagnosis of seizures

Serum prolactin levels may increase after epileptic seizures, but the increase is transient. We developed an assay of prolactin from capillary blood applied to filter paper than can be performed at home. Blood was obtained by finger stick 15 and 75 min after a seizure-like clinical episode in 50 patients undergoing video-EEG monitoring. A positive result by immunoradiometric assay (IRMA) was set at a level ⩾6.7 ng/ml 15 min after a neurologic event or at a twofold decrease from 15 to 75 min. In all, 25 of 36 epileptic events and 1 of 14 nonepileptic events generated capillary prolactin levels >6.7 ng/ml, for a sensitivity of 69% and a specificity of 93%. If simple partial seizures were excluded, sensitivity increased to 80%. A twofold decrease from 15 to 75 min occurred in 25 of 36 epileptic events and in 2 of 14 nonepileptic events, for a sensitivity of 69% and a specificity of 86%. Paired capillary blood testing for prolactin is useful for diagnosis of seizures; results are comparable to those obtained by venous sampling. In our study group, assays of a second finger stick obtained 1 h after the first did not increase the sensitivity or specificity of the test. Our results suggest that capillary blood finger stick for prolactin is useful for diagnosis of seizures.

Cellular basis for elevated prolactin secretion during incubation behavior in Bantam chickens: analysis by reverse hemolytic plaque assay.

Incubation behavior in birds is characterized by elevated serum prolactin (PRL) levels. The objective of this study was to determine the cellular basis for increased PRL secretion. Incubation behavior of Bantam hens was induced by allowing the hens to accumulate their eggs. In experiment 1, hens were allowed to accumulate their eggs in floor pens for 0, 2, 12, or 24 days (Day 0, Day 2, Day 12, and Day 24 hens, respectively). Anterior pituitaries were dissociated into individual cells with trypsin, and the resulting cells were then subjected to reverse hemolytic plaque assays for PRL. The percentage of PRL-secreting cells and serum PRL levels were higher in Day 24 hens than in the other groups (p < 0.05; n = 3 separate trials). In experiment 2, hens were allowed to accumulate their eggs for 2, 14, 18, or 24 days (Day 2, Day 14, Day 18, and Day 24 hens, respectively). The percentage of PRL-secreting cells and levels of serum PRL were greater in Day 18 and Day 24 hens than in Day 2 hens (p < 0.05; n = 4). Results from Day 14 hens were intermediate and different (p < 0.05) from those from both Day 2 and Day 18 groups. Data indicate that an increase in the proportion of PRL secretors occurred between 14 and 18 days after hens began to accumulate their eggs. The area of plaques formed by lactotrophs from Day 14 and Day 18 hens was also increased (p < 0.05). In experiment 3, hens were allowed to accumulate their eggs for 0 and 24 days (Day 0 and Day 24 hens, respectively). Their anterior pituitaries were dissected into cephalic, middle, and caudal regions, and the percentage of PRL cells were analyzed in each region separately. The percentage of PRL secretors was increased (p < 0.05) in Day 24 compared to Day 0 hens in both the cephalic and middle regions of the anterior pituitary but not in the caudal portion. We conclude that increased PRL secretion during incubation behavior involves the recruitment of additional pituitary cells into the PRL-secreting population and an increase in the capacity of these cells to secrete hormone (p < 0.05). Furthermore, this increase in PRL-secreting cells is localized to the cephalic and middle regions of the anterior pituitary.

100. - Differential effects of typical and atypical antipsychotic medication on plasma prolactin levels

100. - Differential effects of typical and atypical antipsychotic medication on plasma prolactin levels

Uneven Regional Distributions of Prolactin- and Growth Hormone-Secreting Cells and Sexually Dimorphic Proportions of Prolactin Secretors in the Adenohypophysis of Adult Chickens

Prolactin (PRL) and growth hormone (GH) proteins are structurally similar and are thought to be evolutionarily derived from a common gene. In addition, data indicate that GH and PRL cells differentiate from a common stem cell. In adult birds, females have higher levels of serum PRL than males. Levels of serum GH are reported to be higher in young male birds than in females and equal between sexes in adult birds. Furthermore, previous studies using immunocytochemistry found that PRL- and GH-containing cells were located primarily in the cephalic (Cp) and caudal (Cd) lobes. respectively, of the anterior pituitary. Two experiments were conducted to study the cellular basis for differences in PRL and GH secretion between genders or anatomical location in adult chickens. In Experiment I, anterior pituitaries from broiler breeder adult hens and roosters were subjected to reverse hemolytic plaque assays (RHPA's) for PRL and GH. The percentage of PRL-secreting cells was significantly greater in females than in males (46.1 ± 4.5% and 26.1 ± 2.4%, respectively: P < 0.001; n = 6). However, there were no significant differences between the proportions of GH-secreting cells between sexes (25.8 ± 3.1% and 30.0 ± 3.9% in females and males, respectively). Average area of plaques formed was different between sexes in GH plaque assays under basal conditions (162,465.9 ± 29,911.8 μm2 and 53,834.9 ± 31,033.5 μm2, for males and females, respectively P < 0.05). However, no differences were found in the presence of GH-releasing hormone. In Experiment II, anterior pituitaries from Leghorn hens were dissected into three regions: the extreme portions of the Cp and Cd lobes and the remaining or middle portion. The cells from each region were subjected to RHPA's for PRL and GH. We found that 52.0 ± 4.1% of all cells from the Cp lobe secreted PRL. This proportion was greater (P < 0.01; n = 4) than that found in the Cd lobe, where 2.4 ± 0.4% of all cells released PRL. In contrast, the percentage of GH-secreting cells was higher in the Cd lobe than in the Cp lobe (61.0 ± 2.3% and 0.8 ± 0.5%, respectively: P < 0.01). As expected, the middle portion contained substantial numbers of both cell types. These findings suggest that sexual dimorphism in serum PRL levels in adult chickens is due, in part, to an increased cell population of PRL secretions in females. Furthermore, PRL- and GH-secreting cells are distributed unevenly throughout the anterior pituitary of chickens, with the PRL secretors localized to the Cp lobe and the GH secretors to the Cd lobe.

Plasma Prolactin Concentrations in the Horse—Response to Opioid Receptor Blockade with Naloxone and Comparison of two Prolactin Assay Systems

Plasma Prolactin Concentrations in the Horse—Response to Opioid Receptor Blockade with Naloxone and Comparison of two Prolactin Assay Systems

Stress and nursing in the pig: Role of HPA axis and endogenous opioid peptides

To determine the effect of stress on nursing, and the roles of HPA activity and opioid peptides, nine sows had their piglets removed for 2 h and were treated as follows: (a) control; (b) nose-snare restraint for 20 min; (c) naloxone injections (IV 2 mg/kg); and (d) snare + naloxone. After the treatment, the piglets were returned, milk ejections were timed, and the sows' blood sampled every 10 min for cortisol, growth hormone (GH), and prolactin assays. Piglet removal increased cortisol and decreased prolactin and GH. This was reversed when the piglets were returned. Restraint increased cortisol and decreased GH, but did not affect prolactin. Naloxone alone increased cortisol and decreased GH but did not increase the effect of restraint. The rise in GH following the piglets' return was abolished by the combination of restraint and naloxone. Neither restraint nor naloxone delayed the latency to first milk ejection or reduced the frequency. No unsuccessful nursings were observed. First milk ejections occurred when cortisol levels were elevated. Stress-induced activity of the hypothalamo-pituitary-adrenocortical (HPA) axis does not inhibit milk ejection in the pig, but this is not due to a protective opioid action. Endogenous opioids protect lactogenic hormones against inhibition by stress.

Effects of prenatal cocaine exposure on haloperidol-induced increases in prolactin release and dopamine turnover in weanling, periadolescent, and adult offspring.

Offspring of dams given 40 mg/kg cocaine SC on gestational days (GD) 8-20 (E8-20) (C40), dams given 0.9% saline SC on E8-20 that were pair fed and watered to C40 dams (PF), and untreated control dams given ad lib access to food and water (LC) were challenged with haloperidol (0.0, 0.05, 0.10, or 0.50 mg/kg) at either 21, 35, or 60 days postnatally (P21, 35, 60). One hour postinjection, animals were sacrificed, trunk blood collected for assay of prolactin, and the striatum (ST) and nucleus accumbens (NAc) removed. The ratio of the dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid to dopamine (DA) as well as the ratio of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) to serotonin (5-HT) were determined in these brain regions as an index of DA and 5-HT turnover, respectively. Assessment of 5-HIAA/5-HT ratios did not indicate any reliable dose or prenatal treatment effects. Reminiscent of previous findings obtained in C40 offspring at P11 (35), P21 C40 offspring exhibited a slightly reduced sensitivity to haloperidol relative to LC controls both in terms of DA ratios in the NAc as well as plasma prolactin levels. These findings were also evident in PF controls suggesting that they may be the result of prenatal undernutrition. Furthermore, this reduced sensitivity was not evident at the older test ages. At P60, planned comparisons revealed haloperidol-induced increases in prolactin levels in C40 males but not PF or LC males; these findings could potentially reflect feminization in males following prenatal cocaine exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine responsiveness of human prolactinoma cells as determined by the reverse hemolytic plaque assay.

The responsiveness in vivo to dopamine of prolactin (PRL) secretion in patients with prolactinoma was compared with that in vitro of single cells obtained from the same prolactinomas by surgical operations. Six patients with prolactinoma showing various degrees of hyperprolactinemia were challenged by bromocriptine suppression test (2.5 mg, peroral) before operation. Bromocriptine administration caused a decrease in the serum PRL concentration ranging 24-95% and there was no correlation between the basal PRL level and bromocriptine-induced inhibition. Monodispersed pituitary cells obtained from the prolactinomas by operation were subjected to a reverse hemolytic plaque assay for PRL to determine PRL secretion at the single cell level under basal conditions as well as in response to dopamine. The percentage of plaque-forming cells under basal conditions ranged 15-55% among the prolactinomas. The percentage of plaque-forming cells and plaque area were decreased in a dose-dependent manner by 10(-7) - 10(-5) M dopamine for the pituitary cells obtained from some adenomas but not for those from other adenomas. When the inhibition rates in vitro due to 10(-5) M dopamine in these two parameters were compared with the inhibition rate in vivo in the serum PRL concentration due to bromocriptine, it was found that there was a significant correlation between them. These results show that the reverse hemolytic plaque assay can be used to determine in vitro responsiveness to dopamine of PRL secretion from single prolactinoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Flumazenil effects on growth hormone response to gamma-hydroxybutyric acid

Gamma-hydroxybutyric acid (GHBA) has been recently introduced for alcohol detoxication but few data are available concerning the central mechanism of action of this gamma-aminobutyric acid (GABA) catabolite. GHBA ability to stimulate growth hormone (GH) and prolactin (PRL) secretion has been reported: the involvement of GABA, dopamine or serotonin systems acting on pituitary hormones has been hypothesized. In the present study we investigated GH and PRL responses to GHBA with or without flumazenil (a benzodiazepine receptor antagonist) i.v. pretreatment. Our study included nine male healthy volunteers (aged 23.2 +/- 2.5 years) who were submitted to three tests in random order: (1) oral GHB administration; (2) oral GHBA and i.v. flumazenil administration; (3) oral placebo and i.v. saline administration. Blood samples for GH and PRL assays were collected during the three tests at -15, 0, 15, 30, 45, 60 and 90 min. GHBA induced a significant increase in GH plasma levels; flumazenil pretreatment antagonized GHBA action on GH secretion. No changes were obtained with placebo and saline administration. A subpopulation of GABA receptors or GHBA-specific receptors seems to be involved in GHBA action. The benzodiazepine receptor antagonist flumazenil was able to influence the sensitivity and the neuroendocrine consequences of GHBA binding site stimulation.

Prolactin assay for fescue toxicity in sheep

Abstract Fungal endophyte (Acremonium spp.) toxicity affects sheep and cattle grazing a number of forages, including ryegrasses (Lolium spp.) and tall fescue (Festuca nrundinacea). The endophyte in tall fescue is responsible for ill thrift, as indicated by low weight gains or weight loss(1) and decreased reproductive efficiency(2), and is associated with increased body temperatures. Extensive research has been undertaken in the USA to determine ways of reducing the impact of fescue toxicity on the beef industry(3), whilst New Zealand research is directed toward both ryegrass and fescue endophyte toxicity and its impact on sheep(4)(5) and cattle(6) production. Much of this work involves field evaluations of productive performance in animals fed toxic and non-toxic forage, so that it is important to be sure that treatment effects are due to the endophyte.

Prolactin heterogeneity: a limitation on the evaluation of results from prolactin assays due to differences in immunoassays and the different bioactivities of prolactin forms.

Prolactin exists in biological fluids in several molecular forms. This raises two questions: (1) whether the assay of prolactin by immunotechniques is valid and reliable and (2) whether the different forms have different physiological roles, which might be exploited to improve diagnostic accuracy and data interpretation by the use of appropriate methods. To investigate these questions, prolactin from human amniotic fluid was separated, by concanavalin A-Sepharose affinity chromatography, into bound, retarded and unbound fractions (bound prolactin fraction, retarded prolactin fraction, unbound prolactin fraction), which were characterized by electrophoresis, immunoblotting and glycan detection blot. Virtually no contamination was found in the bound prolactin fraction, and the unbound prolactin fraction and retarded prolactin fraction were 74-83% pure according to densitometry of the electrophoretic and immunoblot patterns. High variability was found among the individual patterns. Glycan detection in the blotted fractions revealed that the bound prolactin fraction bands corresponding to M(r)25,000-29,000 were weakly glycolysated, whereas the bands of M(r)60,000-64,000 were significantly glycan-positive. Immunoreactive bands of unbound prolactin fraction and retarded prolactin fraction also stained positively for glycans. Using two commercial prolactin kits, the bound prolactin fraction forms were virtually undetectable. To demonstrate that the prolactin forms may depend on the hypothalamic state, two behaviourly different breeds of cattle were used as an animal model for studying hypothalamic activities. The number of immunoreactive bands, representing the prolactin forms, and the change of the forms in response to thyroliberin differed strikingly among the groups. The bioactivity of the forms was examined in bovine granulosa, oviductal, endometrial and spleen cells, and in murine splenocytes, the latter being activated by concanavalin A or allogeneically to create in vitro conditions that may have relevance for situations in vivo. The rate of incorporation of [3H]thymidine in murine splenocytes was dose-dependently enhanced only by bound prolactin fraction. The increase was abolished by purified anti-prolactin antiserum. However, the standard prolactin from the kits inhibited the proliferation even in low dose (1.25 microgram/l) and the inhibition was abolished in part by bound prolactin fraction. Thymidine incorporation into the bovine cells was significantly increased by low concentrations (2 micrograms/l) of unbound prolactin fraction and retarded prolactin fraction. Oviduct epithelial cells and splenocytes were stimulated by unbound prolactin fraction but not by retarded prolactin fraction in a dose of 16 micrograms/l. Thymidine incorporation into granulosa cells was inhibited by retarded prolactin fraction (16 micrograms/l) but not by unbound prolactin fraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid resolution of visual abnormalities with medical therapy alone in patients with large prolactinomas

Large prolactin-secreting pituitary adenomas with suprasellar extension are often complicated by visual field defects, for which surgical decompression is the accepted treatment. However, surgical management of large prolactinomas is often not curative. This report describes a group of six unselected male patients who presented with visual field defects and reduced visual acuity due to large pituitary tumours with suprasellar extension. All six patients also had loss of libido and/or impotence. A rapid serum prolactin estimation enabled the diagnosis of prolactinoma to be made, and CT revealed a large pituitary adenoma with suprasellar extension. The patients were treated with bromocriptine, in doses increasing from 2.5 to 20 mg daily, as the sole therapy. Symptoms were relieved and serum prolactin levels were restored to normal or near normal; visual field defects resolved and visual acuity recovered in all patients. A repeat CT showed evidence of tumour shrinkage especially of the suprasellar extension, in all the patients. A diagnosis of prolactinoma should always be considered in a patient with a large pituitary tumour. The clinical history and a rapid prolactin assay will confirm the diagnosis. Treatment with bromocriptine leads to rapid improvement in perimetry and visual acuity as well as tumour shrinkage, obviating the need for pituitary surgery.

Effect of lactation feed intake on endocrine status and metabolite levels in sows

Two experiments were performed to study the endocrine response of sows to changes in feed intake during lactation. The hormonal status of 24 (exp. 1) and 15 (exp. 2) lactating sows subjected to different feed intakes was determined. During a 28-d lactation, the sows were full-fed (FF) or restrict-fed 3 kg d−1 (RF) of a diet formulated to contain 12.4 MJ DE kg−1 and 16% crude protein. On days 2 and 28 postpartum, blood samples were collected by means of indwelling vena cava cannulae from 12 FF and 12 RF (exp. 1) and 8 FF and 7 RF (exp. 2) sows. Metabolic status was assessed by plasma assay for glycerol, free fatty acids, blood urea nitrogen, glucose and creatinine. Endocrine status was determined by plasma assay for growth hormone (GH), insulin, cortisol, prolactin, glucagon, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). On day 2 postpartum, there were no treatment differences (P &gt; 0.05) in plasma concentrations of any of the components studied. On day 28 postpartum, the RF sows had higher (P &lt; 0.05) plasma concentrations of glycerol and creatinine, higher (P &lt; 0.05) concentrations of GH and cortisol and lower (P &lt; 0.05) concentrations of insulin than FF sows. Both mean plasma LH and FSH levels increased (P &lt; 0.05) between days 2 and 28 of lactation. Furthermore, total LH and FSH secretion determined on day 28 was higher in FF than in RF sows (P &lt; 0.05). It is suggested that the hormone changes associated with excessive catabolism in the RF sows during lactation could be functionally related to the difference in gonadotrophin secretion measured at the end of lactation. Key words: Sow, lactation, nutrition, endocrine status

Single and dual hormone secretors in GH3 cultures respond differently to hypothalamic factors

Recent studies using both normal and tumoral pituitary cell cultures have demonstrated that growth hormone (GH) and prolactin (PRL) secreting populations contain cells which release either one or both of these hormones. In order to determine whether these two cell types can be differentially regulated by hypothalamic factors we performed the following study employing plaque assays for GH and PRL. Using cultures of GH3 cells, a rat tumor cell line which contains both of these cell types, we found that the hypothalamic factors vasoactive intestinal peptide (VIP) and thyrotropin releasing hormone (TRH) when used together had a greater influence on plaque formation than when each was used individually. This suggested that cells were present in culture that responded to one peptide but not the other. Estradioltreated cultures (which contain only dual-secreting cells) were then evaluated for VIP and TRH responsiveness and found to respond to TRH but not VIP. Finally, we assessed the peptide sensitivity of cultures that were exposed to a conjugate of VIP and the A-chain of ricin (a potent cytotoxin). In addition to eliminating VIP-responsive cells, this treatment markedly reduced the proportions of cells secreting GH-only while having no appreciable influence on dual-hormone secretors. When taken together, our findings indicate that single and dual secretors respond differently to at least two hypothalamic secretagogues and suggest that regulatory differences between these cell types may be important in the control of GH and PRL secretion.

Improved enzyme immunosorbent assay for mouse prolactin using penicillinase as label

Enzyme immunosorbent assay (EIA) for mouse prolactin was established by modifying a method originally developed for human prolactin by Shrivastav et al. This simple, sensitive, rapid, and reproducible assay utilizes penicillinase as the labeling enzyme, rabbit anti-mouse prolactin antibody (Ab) and goat anti-rabbit Ig Ab as the first and second antibodies. Prolactin reference preparations and enzyme-conjugated prolactin were mixed with the first Ab and incubated for 0.5 h at 4°C (24–48 h for serum samples). Then, the sample mixture was transferred to the wells of microtiter plate coated with the second Ab. After being kept at room temperature for 2 h, the plate was washed and filled with substrate solution (penicillin V). Absorbance at 620 nm was measured with an ELISA reader to quantitate the amount of conjugated prolactin bound to the second Ab. The prolactin levels obtained by this assay exhibited good correlation with those measured by radioimmunoassay (R (RIA) ( y = 0.95 x + 9.14, r = 0.943), and the sensitivity of EIA was equivalent to that of RIA (1.7 ng/ml). The CVs of intra-assay and inter-assay by EIA for mouse serum samples ranged comparably to those by RIA.

The effect of extended photoperiod on performance, behaviour and prolactin levels of finishing dairy bred steers and heifers

Previous studies have shown that bovine performance can be improved by manipulating photoperiod. This may be an acceptable alternative to the use of exogenous hormones but responses have been inconsistent. The objective of this trial was to determine the response of finishing cattle to extended photoperiod.Sixty-four Hereford x Friesian steers and 48 Charolais x Friesian heifers were finished in consecutive years over the winter housing period under either natural daylength (Control) or daylength extended to 16 hours (16 hour). Lights were installed to provide 16 hour animals with 400 lux at animal eye level. A photocell and timeswitch combination ensured that lights were switched on if natural light levels were below this level between 04.00 and 20.00 GMT. Animals were penned in groups of eight and silage was weighed in daily to each pen. Animals were weighed fortnightly and feed conversion ratios calculated. Prolactin assays were carried out on blood samples taken monthly from 10 animals per treatment. Steer and heifer behaviour was monitored over 24 hours on three occasions.