Quantitative feed restriction or meal-feeding of broiler chicks alter functional development of enzymes for protein digestion.

1. Two experiments were performed on broiler chicks to determine the effect of either quantitative feed restriction (QFR) from 5 to 11 d of age or meal-feeding (MF) from d 5 to 17 on development of activity of enzymes associated with protein digestion. 2. Proteolytic activity of the proventriculus was reduced by QFR but unaffected by MF. 3. General proteolytic and carboxypeptidase A activities of the pancreas were reduced by QFR and MF. 4. Amino- and dipeptidase activities of the small intestine were increased by QFR. Dipeptidase activity was unaffected by MF. 5. Nitrogen retention of QFR chicks was lower immediately following feed restriction but not in the 2 weeks following return to ad libitum access to feed. 6. Feeding regimen alters functional development of the enzymes of protein digestion and may therefore influence growth rate of broilers.

Uterine luminal content of insulin-like growth factor (IGF)-I and endometrial expression of mRNA encoding IGF-binding proteins 1 and 2 during the oestrous cycle and early pregnancy in the ewe.

Cyclic (n = 30) and pregnant (n = 29) Merino ewes were examined (n = 3 to 5 at most time points) over Days 0-16 and 0-22 after oestrus, respectively. As IGFBP activity was detected in some plasma and ULF samples, all samples were subjected to acid-gel chromatography before assay for IGF-I. After oestrus, the overall means of both groups of ewes showed lower ULF IGF-I content (Days 3 and 12), lower plasma IGF-I concentrations (Days 3-16), higher endometrial expression of mRNA encoding IGFBP-I (Days 12-16) and lower endometrial expression of mRNA encoding IGFBP-2 (Day 8). Between Days 0 and 16 after oestrus, the pregnant ewes had lower plasma IGF-I concentrations and higher endometrial expression of IGFBP-1 mRNA than did the cyclic ewes. The presence of IGF-I in the ULF throughout the oestrous cycle and early pregnancy suggests a role of IGF-I in early pregnancy, influencing both uterine growth and embryonic survival. The concomitant endometrial expression of mRNA encoding IGFBP-1 and IGFBP-2 suggests a role of these binding proteins in the regulation of IGF-I bioavailability in the uterine environment of the ewe.

Endometrial expression of mRNA encoding insulin-like growth factors I and II and IGF-binding proteins 1 and 2 in early pregnant ewes.

The temporal variations in endometrial expression of mRNA encoding insulin-like growth factor I (IGF-I) and IGF-II, and insulin-like growth factor-binding protein 1 (IGFBP-1) and IGFBP-2 were investigated between oestrus and day 20 of pregnancy in ewes. Northern blot analysis of endometrial total RNA revealed major transcripts for IGF-I (7.1 kb), IGF-II (5.8 kb), IGFBP-1 (1.3 kb) and IGFBP-2 (1.7 kb). Some minor transcripts for IGF-II were also detected. The low endometrial expression of mRNA encoding IGF-I at day 15 of pregnancy was used as the reference point for time comparison for expression of mRNA encoding IGF-I, IGF-II and IGFBP-2. The mRNA encoding IGFBP-1 was not quantitated since the gene was expressed only on day 15 of pregnancy. Endometrial expression of mRNA encoding IGF-I was increased (P < 0.05) at oestrus and on day 8 of pregnancy relative to expression on day 15, whereas expression of mRNA encoding IGFBP-2 was decreased (P < 0.05). The major IGF-II transcript was unaffected by day of pregnancy. The temporal variation of the expression of mRNAs encoding IGF-I and IGFBP-2 suggests a role for these factors in the uterine environment during early pregnancy in ewes coinciding with rapid development of the embryo and growth of the uterus in preparation for implantation.

Effects of indomethacin on epidermal growth factor-induced renal responses in sheep.

1. The effects of indomethacin (an inhibitor of prostaglandin synthesis) on the renal responses to epidermal growth factor (EGF) were investigated in conscious sheep. 2. Ewes (n = 5 per group) received an i.v. saline infusion (150 mL/day) for days 1-8, followed by either vehicle control, 15 micrograms/h EGF, 2 mg/kg per day indomethacin or 15 micrograms/h EGF with 2 mg/kg per day indomethacin in 150 mL/day saline, i.v., over days 9-12. All ewes subsequently received an i.v. saline infusion (150 mL/day) over days 13-20. 3. Polydipsia, diuresis, transient natriuresis and reduced urine osmolality occurred during EGF treatment alone. There was no effect of EGF on fluid balance, plasma electrolyte or hormone concentrations, plasma osmolality or haematocrit or on the urinary excretion of potassium. 4. Simultaneous infusion of indomethacin with EGF attenuated (P < 0.05) the stimulatory effects of EGF infusion alone on urine volume, water intake, natriuresis and urine osmolality. 5. We conclude that prostaglandins may be involved in the diuretic/natriuretic effects of EGF, but may not be the sole mechanism involved.

Epidermal growth factor and fluid and electrolyte balance in the rat.

Epidermal growth factor (EGF) has been shown to induce a renal diuresis and natriuresis in sheep and stimulate prostaglandin synthesis from inner rat medullary collecting duct cells in culture. The aims of our study were 1) to investigate whether the renal effects of intravenous infusion of EGF were species specific and 2) to determine the mechanism of these effects by studying the interaction between EGF and indomethacin (a prostaglandin synthase inhibitor) in the conscious rat. Sprague-Dawley rats received intravenous infusions of either 0.9% saline or 0.2 or 2.0 micrograms EGF.kg-1.h-1 over a 6-day period after an initial baseline period. Infusion of 2.0 micrograms EGF.kg-1.h-1 caused an increase in urine volume (baseline: 5.5 +/- 0.2 ml to day 5: 9.0 +/- 0.4 ml, P < 0.01) and corresponding polydipsia, but not natriuresis. Administration of indomethacin with 2.0 micrograms EGF.kg-1.h-1 attenuated (P < 0.05) the diuretic (day 5 EGF + vehicle: 12.2 +/- 1.1 ml vs. EGF + indomethacin: 8.7 +/- 0.9 ml) and polydipsic effects of EGF. These studies demonstrate that intravenous infusion of EGF causes a diuretic effect in rats without natriuresis and that prostaglandins play a role in the diuretic effect of EGF in the rat.

Weight of internal organs and carcase yield of early food restricted broilers broilers.

1. Effects of food restriction on growth rate and relative growth rates of supply organs (liver, heart, lungs and kidneys, digestive tract) and demand organs (breast, back, thighs, abdominal fat) of broiler chickens were studied. 2. Birds were restricted in intake to 50% (group FI 50) or 75% (group FI 75) of ad libitum from 5 to 11 d of age; all birds were fed ad libitum from 12 to 39 d of age. 3. Relative growth rates from 12 to 39 d of age of group FI 50 were higher (P < 0.05) than group FI 75 and control group. 4. No significant differences in food conversion ratio, carcase fat and abdominal fat between groups were observed. 5. At 12 d of age, relative weight of the empty digestive tract of group FI 50 was higher (P < 0.05) than that of the control group and group FI 75. 6. The increased weight of the empty digestive tract may have contributed to the ability of the chickens to achieve compensatory growth after the restriction period.

Epidermal growth factor as a diuretic in sheep.

1. Epidermal growth factor (EGF) has recently been shown to stimulate both polydipsia and polyuria and the aim of this study was to determine which was the primary response. Ewes received a continuous intravenous saline infusion (100 ml day-1) for 12 days (days 1-12) and EGF at doses of 0 (n = 6) or 10 micrograms h-1 (n = 6) over days 5-8. The supply of water was ad libitum during days 1-4 and 9-12, but was fixed at the pretreatment mean of days 1-4 for each ewe during days 5-8. 2. During the period of fixed water intake, the EGF-treated ewes experienced mild dehydration with elevated plasma osmolality, sodium, renin and arginine vasopressin (AVP) concentrations and slightly reduced plasma atrial natriuretic peptide (ANP) concentrations. 3. When the supply of water returned to ad libitum, the EGF-treated ewes increased their water intake by 105% (5.25 +/- 0.28 vs. 2.55 +/- 0.19 l day-1) and subsequently fluid balance was restored; plasma electrolyte and hormone responses also returned to normal. 4. This experiment demonstrates that EGF infused at a dose rate of 10 micrograms h-1 I.V. into sheep has a direct renal diuretic effect.

Epidermal growth factor antagonizes vasopressin in vivo and in vitro.

Since EGF causes diuresis through a renal action and may antagonize the hydroosmotic effect of AVP in vitro we investigated the antagonistic action of EGF with AVP in vivo and the mechanism of the antagonism in vitro. Conscious ewes received i.m. injections of a selective AVP V2-receptor agonist (1-desamino, D-Arg8 vasopressin acetate, DDAVP) every 12 hours for days 5 to 16. All ewes received an i.v. isotonic saline infusion (100 ml/day) for days 1 to 8 and days 13 to 16, and i.v. EGF in 100 ml saline/day at doses of 0 (N = 8) or 10 (N = 8) micrograms/hr for days 9 to 12. DDAVP reduced both urine volume and water intake, and increased urine osmolality. In contrast, simultaneous infusion of EGF reversed the DDAVP-induced responses, resulting in a transient negative fluid balance, kaliuresis and a transient natriuresis (all P < 0.05). When EGF treatment ceased, the effects of DDAVP treatment alone gradually became apparent. From the in vitro studies, the AVP-related peptides displaced specific AVP V1- and V2-receptor antagonist radioligands from rat renal inner medullary membranes, whereas EGF had no effect. However, EGF antagonized AVP V2-stimulated cAMP production in a dose-dependent way (IC50 = 2 x 10(-7) M). Therefore, the diuretic effect of EGF is not via direct antagonism of the antidiuretic AVP V2-receptor but seems mediated by inhibition of the antidiuretic AVP V2-receptor second messenger system.

Interaction between epidermal growth factor and arginine vasopressin in renal medullary membranes.

1. Epidermal growth factor is a potent mitogen that causes natriuresis, diuresis and inhibition of arginine vasopressin-induced water reabsorption. 2. The aim of this study was to determine any interaction between epidermal growth factor and the V1 (vascular) and/or V2 (antidiuretic) arginine vasopressin receptor subtypes. 3. Radioligand binding displacement assays demonstrated that although arginine vasopressin related peptides displaced both radioligands from renal medullary membranes at low concentrations epidermal growth factor displaced neither. 4. Arginine vasopressin V2 receptor second messenger cyclic adenosine monophosphate (cAMP) production was inhibited by epidermal growth factor (IC50 2 x 10(-7) mol/L) as was sodium fluoride cAMP production but only at much higher concentrations. 5. Therefore the diuretic effect of epidermal growth factor is not via direct antagonism of arginine vasopressin receptors but seems mediated via inhibition of the V2 second messenger system.

Hormonal, fluid, and electrolyte responses of sheep during chronic intravenous infusion of epidermal growth factor.

Epidermal growth factor (EGF) has been shown to increase water intake and urine volume. To further characterize these responses the effects of EGF on fluid balance, electrolyte, and hormone profiles were examined. After an 8-day control period, ewes received intravenous EGF at doses of 0 (n = 6), 2 (low dose, n = 6), 10 (medium dose, n = 6), or 20 micrograms/h (high dose, n = 5) for 4 days. During EGF treatment, water intake and urine volume increased (both P < 0.001) in a dose-related fashion, although fluid balance was unaffected. Feed intake and fecal dry matter output were reduced (both P < 0.001) by the two higher doses of EGF. EGF had no effect on plasma potassium, sodium, or osmolality, but there was a dose-related natriuresis (P < 0.001). Treatment with EGF increased plasma renin activity and aldosterone in the medium and high dose groups (both P < 0.001). Thus chronic intravenous infusion of 10-20 micrograms EGF/h into sheep caused polydipsia, polyuria, and natriuresis with neutral fluid balance. Whether the resultant polydipsia or polyuria was the primary response to EGF remains unclear.

Role of progesterone in the control of endometrial oxytocin receptors at luteolysis in sheep.

Merino ewes were given a prostaglandin synthetase inhibitor, Finadyne (50 mg flunixin meglumine ml-1), on days 14-16 of the oestrous cycle (day of oestrus = day 0), Finadyne on days 14-16 plus PGF2 alpha on days 15-16, or progesterone on days 14-17 plus PGF2 alpha on days 15-16. Blood samples were taken once a day on days 10-14 and three times a day on days 15-16 for progesterone measurement. The concentrations of oxytocin receptors were measured in the endometrial (pooled caruncular and intercaruncular) tissues collected on day 17. Treatment of ewes with Finadyne resulted in the maintenance of high plasma concentrations of progesterone and a small, but nonsignificant, reduction in the concentrations of endometrial oxytocin receptors. Co-administration of PGF2 alpha reversed this effect of Finadyne. Treatment with both progesterone and PGF2 alpha increased the concentrations of progesterone in plasma and significantly reduced the concentrations of endometrial oxytocin receptors compared with those in the control ewes. These data indicate that withdrawal of progesterone from the circulation as a result of spontaneous luteolysis or by a PGF2 alpha-induced luteolysis caused an increase in the concentrations of oxytocin receptors. However, maintenance of plasma progesterone concentrations over the period of normal luteolysis only partially inhibited the concentrations of endometrial oxytocin receptors. There results suggest that the increase in the concentrations of oxytocin receptors at luteolysis in the naturally cycling ewes may be due to the loss of the inhibitory effects of progesterone on uterine oxytocin receptors.

Epidermal growth factor alters the electrolyte profile of lactating ewes (Ovis aries).

1. Lactating ewes were treated with mouse epidermal growth factor (EGF) at a dose rate of 0.5 mg/day for 4 days and its effects on the electrolyte profile were observed. 2. There was no effect of EGF on plasma concentrations of sodium or potassium, although urinary and total (in urine and milk) losses of both were reduced. 3. EGF-induced hypocalcaemia was associated with reduced milk calcium secretion and increased urinary calcium excretion whereas EGF-induced hypermagnesaemia was associated with reduced urinary and total magnesium losses. 4. Glomerular filtration rate was reduced during EGF infusion. 5. Chronic intravenous EGF infusion affects the electrolyte profile by altering electrolyte secretion by the mammary gland and renal electrolyte excretion.

Fluid balance, electrolyte profiles and plasma parathyroid hormone concentrations in ewes treated with epidermal growth factor.

The infusion of low doses of epidermal growth factor (EGF) into lactating ewes stimulates water intake and urine volume. The plasma concentrations and daily output of various electrolytes in milk and urine are also affected. We have investigated this further by recording the effects of EGF infusion on fluid balance, electrolyte profiles and plasma concentrations of glucose and parathyroid hormone (PTH) in non-pregnant, non-lactating ewes. Twenty-four animals (n = 8 per group) received infusions of 100 ml saline/day into the jugular vein for 10 days (days 1-10) followed by EGF at a dose rate of either 1 (low dose), 5 (medium dose) or 10 (high dose) micrograms/kg liveweight per day in 100 ml saline for 5 days (days 11-15). All ewes then received an infusion of 100 ml saline/day for 10 days (days 16-25). Most plasma and urine samples had undetectable concentrations of EGF-immunoreactive material during the periods of saline infusion. During EGF infusion, the highest amounts of EGF infusate excreted in urine were 1.6, 5.9 and 5.6% for ewes in low, medium and high dose groups respectively. Water intake increased by 17% (0.5 kg), 88% (2.5 kg) and 89% (2.3 kg) and urine volume increased by 29% (0.5 kg), 108% (2.2 kg) and 134% (2.1 kg) for the three groups respectively. Fluid balance and feed intake were not affected by EGF infusion, but the output of faecal dry matter was reduced in ewes receiving the two higher doses of EGF. All levels of EGF resulted in hypocalcaemia, increased plasma PTH concentrations and hypermagnesaemia. There was no effect of EGF on plasma concentrations of K+ and glucose or on daily urinary excretion of K+ and Mg2+. The only response to the low dose was a reduced plasma concentration of Na+ and an increased daily urinary urate excretion. The two higher doses increased the daily urinary excretion of Na+, PO4(3-) and urate, but had no effect on the respective concentrations in plasma. Urinary Ca2+ excretion was reduced only during infusion of the medium dose of EGF. The responses of most variables were similar during infusion of the medium and high doses of EGF. All three doses of EGF induced polydipsic and diuretic responses in ewes, and infusions of 5-10 micrograms EGF/kg liveweight per day affected renal excretion of Ca2+, Na+ and PO4(3-). We interpret the responses of the kidney and plasma PTH concentrations as a means of maintaining the homeostasis of plasma profiles of electrolytes.

Increase in concentration of uterine oxytocin receptors and decrease in response to 13,14-dihydro-15-keto prostaglandin F2 alpha in ewes after withdrawal of exogenous progesterone.

Ovariectomized ewes were treated with progesterone and oestradiol to induce oestrus (day of expected oestrus = day 0) and with progesterone on days 1 to 12. The concentrations of endometrial oxytocin receptors and the 13,14-dihydro-15-keto prostaglandin F2 alpha (PGFM) response induced by oxytocin were measured on days 12, 14, 16 and 18 after the cessation of progesterone treatment on day 12, by a receptor binding assay and direct radioimmunoassay, respectively. During the period of treatment, the concentrations of plasma progesterone were high and remained above 2 ng ml-1 until day 13 when they dropped rapidly to less than 0.5 ng ml-1 by day 14. The concentrations of oxytocin receptors in endometrium of control ewes were high (820.7 +/- 91.7 (SEM) fmol mg-1 protein). Treatment with progesterone significantly (P < 0.01) reduced the concentrations of the receptors on days 12 and 14 (144.1 +/- 65.0 and 200.4 +/- 45.4 fmol mg-1 protein, respectively). The receptor concentrations then increased to relatively high values on day 16 (1021.4 +/- 216.6 fmol mg-1 protein) and remained high until day 18 (677.7 +/- 103.4 fmol mg-1 protein).(ABSTRACT TRUNCATED AT 250 WORDS)

Increases in the oxytocin-induced prostaglandin F2 alpha response and reduction in the concentrations of endometrial oxytocin receptors in ewes in response to progesterone.

Ovariectomized ewes were given progesterone and oestrogen priming as steroid pretreatment and subsequently treated with progesterone, prostaglandin F2 alpha (PGF2 alpha), or both. In Expt 1, plasma concentrations of the metabolite 13,14-dihydro-15-keto-PGF2 alpha (PGFM) were measured after an i.v. injection of oxytocin. There was little PGFM response in the untreated control ewes or in the pretreated ewes. Treatment with PGF2 alpha alone had no effect (P greater than 0.05), whereas treatment with progesterone either alone or with PGF2 alpha significantly (P less than 0.05) increased the uterine PGFM response to oxytocin. In Expt 2, chronically ovariectomized ewes had high concentrations of endometrial oxytocin receptors. Treatment with PGF2 alpha alone did not alter the concentrations of the receptors. Treatment with progesterone either alone or with PGF2 alpha significantly (P less than 0.05) reduced the concentrations of the receptors. It is concluded that progesterone promotes the PGFM response to oxytocin, but simultaneously suppresses the concentrations of endometrial oxytocin receptors.

Epidermal growth factor alters milk composition and fluid balance of lactating ewes.

Lactating ewes were treated with murine epidermal growth factor (EGF) and its effects on concomitant milk production and composition were observed. Six ewes were infused via the jugular vein with 200 ml saline/day over 4 days (days 9-12 of lactation) followed by EGF at a dose rate of 0.5 mg/day in 200 ml saline over 4 days (days 13-16). All ewes then received a further infusion of 200 ml saline/day over 4 days (days 17-20). During the experiment a maintenance (lactation) diet was offered and ewes were machine-milked twice daily. An EGF-immunoreactive material was detected in mammary secretions and urine throughout the experiment, but only in plasma (1-9 micrograms/l) during the period of EGF infusion. The amount of EGF appearing in milk and urine increased from 37 micrograms and 10 micrograms respectively (day 1 of EGF infusion) to 56 micrograms and 17 micrograms respectively (day 4). EGF treatment resulted in lower milk yield and reduced concentration of lactose and protein; milk fat concentration fell after EGF infusion had ceased. Water intake increased markedly during EGF infusion and was 60% (4 kg) greater on day 4 than that measured during the first saline infusion. Urine volume also increased and was 164% (3.6 kg) greater by day 4 of EGF infusion compared with that recorded in the first saline infusion. Water retention (intake minus output in milk, urine and faeces) was significantly higher on the day after EGF infusion ceased than that found during the first saline infusion. The possibilities that the increased water intake was primary, or secondary, to a diuretic effect of EGF are discussed.

Differential effects of progesterone treatment on the oxytocin-induced prostaglandin F2 alpha response and the levels of endometrial oxytocin receptors in ovariectomized ewes.

The oxytocin-induced uterine prostaglandin (PG) F2 alpha response and the levels of endometrial oxytocin receptors were measured in ovariectomized ewes after they had been given steroid pretreatment (SP) with progesterone and estrogen to induce estrus (day of expected estrus = Day 0) and had subsequently been treated with progesterone over Days 1-12 and/or PGF2 alpha over Days 10-12 postestrus. The uterine PGF2 alpha response was measured after an i.v. injection of 10 IU oxytocin on Days 13 and 14, using the PGF2 alpha metabolite, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), as an indicator for PGF2 alpha release. The levels of oxytocin receptors in the endometrium were measured on Day 14. During the treatment with progesterone, the peripheral progesterone concentrations were elevated and remained above 1.8 ng/ml until the morning of Day 14. The PGFM responses to oxytocin in untreated controls and SP controls were low on both Days 13 and 14 whereas the levels of endometrial oxytocin receptors in the same ewes were high. Treatment with progesterone either alone or in combination with PGF2 alpha significantly (p less than 0.04) increased the PGFM response on Day 14 and reduced the levels of endometrial oxytocin receptors; treatment with PGF2 alpha alone had no effect. It is concluded that progesterone promotes the PGFM response to oxytocin while simultaneously suppressing the levels of endometrial oxytocin receptors. PGF2 alpha treatment had no effect on either the uterine secretory response to oxytocin or the levels of oxytocin receptors in the endometrium.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma concentrations of luteinising hormone and body weights during somatic maturation in intact and castrated Australorp cockerels from a line of hens selected for increased ovulation rate.

1. Plasma concentrations of luteinising hormone (LH), comb size and body weight were measured between 46 and 208 d of age in intact and castrated cockerels from lines of selected and control Australorp domestic chickens. The selected line had been selected for increased rate of lay by reducing oviposition intervals within sequences. The cockerels were reared and maintained on 15.25 h light/d. 2. Concentrations of plasma LH in the intact control cockerels were low in the 'immature' phase (less than 100 d old) and increased during the 'mature' phase (older than 175 d) with a peak occurring when the testes are beginning to grow at the onset of the 'mature' phase. In comparison with the control line of cockerels, the selected line had significantly higher plasma LH concentrations at the onset of the 'mature' phase. Selection had no effect on the mean concentration of plasma LH in either the immature phase or a few weeks after the onset of the mature phase. 3. There was no effect of selection in sibling females for higher rates of lay on changes in comb size or body weight during sexual maturation in the intact cockerels. 4. Castration at 45-46 d of age resulted in increased plasma LH concentrations and no comb growth. Plasma LH concentration increased progressively between 40-208 d. There was no difference between the two lines of cockerels in plasma LH concentration or rate of body growth after castration. 5. It is concluded that selection of females for a change in the rate of egg production has resulted in increased plasma LH concentrations in sibling males around the onset of sexual maturation. Selection appears to have caused this effect by altering an unidentified component of the inhibitory feedback mechanism which controls the tonic secretion of LH.

Lack of effect of epidermal growth factor treatment in late-pregnant ewes on subsequent lactation.

Twin-bearing ewes were treated with epidermal growth factor (EGF) to determine its effect on mammogenesis and resultant milk production and composition. The EGF was infused intravenously at a dose rate of 0.5 mg/d in 300 ml saline between days 117 and 139 of gestation; control animals received placebo infusions of saline. All animals then received continuous infusions of 300 ml/d saline on days 139-144. Following parturition 1-5 d later, ewes were milked by hand for 10 d and thereafter were machine-milked until day 16 of lactation. At this level of treatment, EGF was not detected in the circulation during infusion and feed intake was not affected. All ewes gave birth to healthy twin lambs. There were no effects of EGF on birth weights of lambs, live weights of ewes or lengths of gestation. An EGF-immunoreactive material was detected in the mammary secretions of control ewes at a mean concentration of 2 micrograms/l on day 1 of lactation. Two ewes had detectable levels on day 2, but none was found in the milk thereafter. In the EGF-infused group, concentrations of EGF in colostrum were approximately 10 times higher than in the control ewes on day 1 of lactation and EGF was detected in mammary secretions on day 2 but not in subsequent milk samples. A range of 0.3-0.5% of the EGF infused appeared in mammary secretions over the first 2 d of lactation. No other differences were observed for colostrum composition, subsequent milk yield or composition between the two groups of ewes indicating that mammary gland development and function were unaffected. The levels of EGF observed in the mammary secretions of treated and control ewes indicate that the mammary glands accumulate and store EGF in the pre partum period.

Comparisons of time intervals and plasma LH concentrations during the ovulatory cycle of broiler breeder hens maintained under either a 24 h light:dark cycle or continuous light.

The possibility that egg production in broiler breeder hens may be increased by selection for reduced oviposition interval under continuous light was investigated by comparing the pattern of pre-ovulatory releases of plasma luteinising hormone (LH) and the associated ovipositions in the same broiler hens maintained under normal cycles (15.25 h light/d) or continuous light. The lighting conditions had no effect on plasma concentrations of LH before and at the pre-ovulatory LH peak in first, mid-sequence or terminal ovulatory cycles. Plasma LH concentrations were similar during first, mid-sequence and terminal ovulatory cycles. Mid-sequence oviposition intervals and the interval between a mid-sequence LH peak and its associated oviposition were longer under continuous light than under normal lighting. Pre-ovulatory releases of LH occurred during a restricted period of day in both lighting conditions. Under continuous lighting they were probably entrained by the daily pattern of restricted feeding. Any selection programme for reduced oviposition interval under continuous lighting in broiler breeder hens should take into account the entraining effects of the daily pattern of feeding.