David W. Long

Possible roles for corticosterone and critical size in the fledging of nestling pied flycatchers

Our study was designed to see whether corticosterone (B) rises abruptly in the blood of nestling pied flycatchers (Ficedula hypoleuca) at the time they fledge, as reported recently for kestrels, and if so, why. We measured the growth and blood levels of B and selected nutrients of nestlings in broods of five, seven, and nine chicks during 1998 and 1999. In half of the broods, we clipped selected wing and tail feathers of both parents with the intention of making it more difficult for them to provide their chicks with food. We collected blood samples when the chicks were six to 10 d old (period of rapid growth) and 15 d of age or older (0–5 d before fledging). B increased substantially several days before the chicks left the nest and then declined somewhat. We found no differences in rates of growth or blood levels of B, nutrients, and hematocrit as a function of either brood size or parental handicapping. Nestlings within a day of fledging appear to have been food deprived in 1998; their glucose was significantly reduced, and B, free fatty acids, and glycerol were significantly elevated compared to levels in chicks 1–4 d younger. Such changes did not occur in 1999. Blood levels of B were significantly correlated with brood size near the day of fledging, but not earlier, in both years of the study. It was possible to predict the day on which chicks would leave the nest, using their wing length when 12 d old. These results suggest that high blood levels of B associated with food restriction and sibling competition induce chicks to fledge, provided they have reached a critical size, and that the importance of fasting, sibling competition, and B may vary from year to year.

Interval Between Preovulatory Surges of Luteinizing Hormone Increases Late in the Reproductive Period in Turkey Hens

Abstract In turkey hens, the egg production rate is relatively high early during a reproductive period, but declines as the period progresses. Among lines with different egg production potential, the interval between preovulatory surges of LH is the primary determinant of the egg production rate. The main objective of this study was to determine whether the decline in egg production rate late during an egg production period is also associated with a difference in the interval between LH preovulatory surges. A group of photosensitive turkey hens (Early) were photostimulated with continuous light (24L:0D) at 40 wk of age to induce egg laying, and serial blood samples were collected after about 3 wk of egg production. A second group of hens (Late) were housed in floor pens and photostimulated with 14L:10D at 40 wk of age for a normal 36-wk reproduction period and were then switched to 24L:0D lighting for 2 wk before collection of serial blood samples. Continuous light photostimulation was used for at least 2 wk before and during serial blood sampling to avoid potential masking effects of diurnal lighting on the interval between LH surges. The Early (n = 12) and Late (n = 16) hens were cannulated 3 days before being serially bled hourly for 10 days. The mean interval between preovulatory surges of LH was shorter in the Early hens than in the Late hens (26.1 ± 2.5 h and 34.7 ± 3.9 h, respectively). The intra-hen LH surge interval coefficient of variation was lower in the Early hens than in the Late hens (7.2% and 18.6%, respectively). The inter-hen LH surge interval coefficient of variation was similar in the Early and Late hens (9.5% and 11.2%, respectively). The incidence of blind surges of LH (those not retrospectively associated with ovipositions) was not different between Early and Late laying hens (8.4% ± 15.2% and 7.3% ± 14.6%, respectively). In conclusion, in turkey hens, longer intervals and greater intra-hen variation between LH surges were associated with a poorer rate of egg production late in the reproductive period relative to early in the reproductive period.

Circulating IGF-I in plasma of growing male and female turkeys of medium and heavy weight lines

Plasma concentrations of insulin-like growth factor-I (IGF-I) were determined in male and female turkeys from a medium weight (RBC2) and a related heavy weight line (F) from 1 to 28 wks of age. At hatch, the concentrations of IGF-I were relatively low and not different between lines or sexes. During the neonatal period (1 to 7 wks), the concentrations of IGF-I increased and were higher in the faster growing F line and in males. During the juvenile period (8 to 15 wks) the concentrations of IGF-I were higher in males but not different between lines. During the preadolescent period (16 to 21 wks), the concentrations of IGF-I were higher in males but was not different between lines in males while the females of the RBC2 line had higher concentrations than females of the F line. During the adolescent period (22 to 28 wks) the concentrations of IGF-I were higher in males but was not different between lines in males while the females of the RBC2 line had higher concentrations than females of the F line. A phenotypic correlation (+.25) between plasma IGF-I and growth rate was present after statistical absorption of model effects during the neonatal period but not at the later ages. We conclude that IGF-I concentration was positively correlated with growth rate during the neonatal period, but that this relationship changed during the preadolescent and adolescent periods so that IGF-I concentrations were not related to growth rate in males but were negatively related to growth rate in females.

Changes in plasma luteinizing hormone concentration in Turkey hens after switching from short-day to long-day photoperiods

Luteinizing hormone (LH) has been reported to increase in plasma shortly after switching photosensitive turkey hens from short-day (SD) photoperiods (6 hr light:18 hr dark) to long-day (LD) photoperiods (14 hr light: 10 hr dark). An experiment was conducted to determine the timing and nature of these changes in plasma LH concentrations after the photostimulation of photosensitive turkey hens. The turkey hens were cannulated (jugular vein) to allow serial bleeding every 15 min for 48 hr. One group (controls) was continued under the SD photoperiod, and one group (treated) was switched to the LD photoperiod by the addition of 8 hr of light to the end of the photoperiod. In the control hens, no changes were seen in the observed or calculated baseline concentrations of LH or in the frequency and amplitude of LH peaks during the 48 hr of serial bleeding. In the treated hens, the observed and baseline concentrations of LH increased during the first LD scotoperiod, with a further increase during the second LD scotoperiod. This rapid increase was due to an increase in the baseline LH concentration, whereas no consistent changes were detected in the frequency and amplitude of LH peaks.

Responses to exogenous pulsatile turkey growth hormone by growing 8-week-old female turkeys

A study was conducted in turkeys to determine the effects of pulsatile infusion of turkey growth hormone (tGH) on growth, feed conversion, carcass component parts, carcass composition, plasma metabolite concentrations, and other hormones associated with growth. Female turkeys, 8 weeks of age, were dually cannulated via the right jugular for intermittent (10 min every 2 hr) infusion of tGH at a low dosage (4.5 micrograms tGH/infusion or 54 micrograms/day), a high dosage (18 micrograms tGH/infusion or 216 micrograms/day) or vehicle infused controls (vehicle, 0.025 M NaHCO3, 0.025 M Na2CO3 + 5 mg/ml NaCitrate, pH 9.4). Treatment was for 18 days. The second cannula was used to serially bleed the turkeys (5 or 10 min between samples) at 4 and 16 days of treatment to determine concentrations of GH, glucose, triacylglycerides (TG) non-esterified fatty acids (NEFA), and uric acid (UA). Overall GH was increased 74% above the control group in the low and 195% in the high treatment group. Baseline GH was increased 52% in the high group above the control group. The amplitude of GH peaks increased 292% in the low, and 574% in the high group above the amplitude of naturally occurring peaks in the control group. Infusion of tGH for 18 days did not affect overall daily gain, feed conversion, final body weight, tibiotarsus length, weights of pectoralis major, pectoralis minor, gastrocnemius or biceps femoris muscles, or weights of liver and offal. Abdominal fat pad weight (70% decrease), and percentages of carcass fat (4.9% decline) and carcass dry matter (2.3% decline) were lower in the high treatment group. Plasma TG and glucose were unaffected by treatment. Overall plasma NEFA concentration was increased in the high treatment group, and this increase was associated with an increased in the baseline concentration and incidence of pulses of NEFA, but not with the amplitude concentration of NEFA pulses. The dynamic nature of plasma NEFA concentration observed in this study suggests single time point measurements of this metabolite may not appropriately detect treatment effects. Plasma overall uric acid (UA) was decreased in the high treatment group in comparison to the control group, and this decrease was associated with a decrease in the baseline concentration of UA but not in the amplitude concentration nor incidence of UA pulses. Plasma insulin-like growth factor-I (IGF-I) concentrations were increased in the low treatment group at 4 but not at 16 days of treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulsatile patterns of plasma growth hormone in Turkeys: Effects of growth rate, age, and sex

Male and female turkeys of a slow-growing, random bred line (RBC-2) and a fast-growing line (F), selected over 21 generations from RBC-2 for increased 16-week body weight, were intravenously cannulated and serially sampled at 10-min intervals for 6, 8, 9, 10, or 12 hr at 2, 4, 8, 14, and 24 weeks of age, respectively, for determination of the pulsatile pattern of plasma growth hormone (GH) concentration. Overall mean plasma GH concentration was greater for RBC-2 than F beginning at 4 weeks of age, when body weights of the two lines had diverged. Males exhibited both greater body weight and greater overall mean GH than females beginning at 4 weeks of age. Overall mean GH concentration, peak frequency and amplitude, and baseline concentrations declined with age for both lines. The RBC-2 line exhibited greater peak frequency, peak amplitude, and baseline mean concentration than the F line at 4, 8, and 14 weeks of age. Males exhibited greater peak frequency, peak amplitude, and baseline concentration than females at 4, 8, and 14 weeks of age. Peak duration was the most consistent profile parameter across lines, ages, and sexes, and averaged 68 min overall. Estimated GH pool size was consistently greater in males than females at all ages, and was greater in the F than RBC-2 line at 2 weeks of age when relative gain was maximal for both lines. Pool size was the GH parameter most highly correlated with body weight across treatment groups.

Frequency of luteinizing hormone surges and Egg production rate in Turkey hens

Abstract Whether the interval between preovulatory surges of LH was different between lines of turkey hens with either poor (RBC3 line, peak at 55%) or excellent rate of egg production (Egg line, peak at 85%) was examined. Laying hens were cannulated and bled hourly for 10 days at peak of production. A constant light photoschedule was used to avoid diurnal masking of innate circadian rhythms. The mean interval between LH surges in the RBC3 line was longer than in the Egg line and had a higher coefficient of variation. A few longer LH surge intervals (>72 h) were found in some RBC3 line hens (2 of 7 hens), but none were found in Egg line hens (0 of 11 hens). All progesterone (P4) surges were coupled with LH surges, but not all LH-P4 surges were coupled with ovipositions (blind LH-P4 surges). The percentage of blind LH-P4 surges was not different between lines. The baseline concentration of LH was higher in Egg line than RBC3 line hens, but LH surge amplitude, and surge duration were not different. The baseline and surge amplitude concentrations of P4 were not different between lines, nor was the concentration of estradiol-17β. The longer interval between LH surges was the major factor tested that was associated with the poorer egg production rate in RBC3 line hens in comparison to Egg line hens. A higher incidence of blind LH surges further contributed to lower egg production in RBC3 line turkey hens.

Circadian rhythm of the preovulatory surge of luteinizing hormone and its relationships to rhythms of body temperature and locomotor activity in turkey hens.

Abstract Simultaneous measurements of plasma LH, body temperature, and locomotor activity were made in laying turkey hens and are reported. Blood samples were remotely collected using a jugular cannula system, and body temperature and locomotor activity were remotely monitored using a radiotelemetry system in freely moving laying turkeys. Under a photoschedule of 14L:10D, the period for preovulatory surges of LH was 25.7 ± 0.4 h while the periods for peak body temperature and onset of sustained locomotor activity were 24.9 ± 0.4 and 25.7 ± 0.5 h, respectively. During exposure to constant light, the periods for preovulatory surges of LH, peak body temperature, and onset of sustained locomotor activity increased to 27.9 ± 0.9, 26.7 ± 0.7, and 27.4 ± 0.7 h, respectively. With the 14L:10D photoschedule, initiation of LH surges was restricted to the scotophase, but after 8 days of constant light, initiation of LH surges had dispersed throughout the 24-h subjective day and night. With constant light, the amplitude of the peak body temperature rhythm decreased, while the duration of the locomotor activity rhythm became broadened and, in some birds, disorganized. Peak body temperature and onset of locomotor activity rhythms and LH surges did not coincide, even though peak body temperature, onset of locomotor activity, and LH surges had similar periods. It is concluded that 1) the photoschedule influences the periods of the LH surge, peak body temperature, and onset of locomotor activity; and 2) a specific or direct relationship between the rhythms of LH surge, body temperature, and locomotor activity remains to be determined in laying turkey hens.

Changes in Plasma Concentrations of Luteinizing Hormone, Progesterone, and Estradiol-17β in Peripubertal Turkey Hens under Constant or Diurnal Lighting

Abstract Possible circadian fluctuations and long-term changes in concentrations of reproductive hormones in peripubertal female birds is poorly documented in comparison with mammalian species. Our objective was to document changes in concentrations of several reproductive hormones the several days before and after initial pubertal preovulatory surges of LH in turkey hens photostimulated with either constant (24L:0D) or diurnal (14L:10D) lighting. The hens were cannulated for hourly blood sampling, starting 10 days after photostimulation and continuing until all hens had laid at least two eggs. First eggs were oviposited between 16 and 24 days after photostimulation, and egg production ranged from two to nine eggs/hen during the experimental period. With both lighting treatments, concentrations of LH declined slightly, concentrations of progesterone (P4) increased, and concentrations of estradiol-17β (E2) were constant the 3–4 days prior to initial LH surges with no circadian fluctuations in hormone concentrations. Most (10 of 13) initial preovulatory surges of LH were coupled with ovulations, and all LH surges were coupled with P4 surges. Those LH and P4 surges not coupled with ovulations (blind surges) occurred with both lighting treatments, but the incidence of blind surges was higher with diurnal lighting. The interval between LH and P4 surges was longer between the first and second surges than between subsequent surges, when the interval was approximately 26 h. The duration of LH surges (7.4 ± 3.0 h) was shorter than that of P4 surges (10.0 ± 2.0 h). We conclude that, in the peripubertal female turkey, 1) prior to puberty (first LH-P4 surges), there are no circadian fluctuations in concentrations of LH, P4, and E2, 2) 3 days prior to initial LH surges, E2 concentrations are stable, LH concentrations decline slightly, and P4 concentrations increase, and 3) surges of LH are coupled to surges of P4 but LH-P4 surges are not always coupled to ovipositions (blind surges), possibly because of internal ovulations.

Evidence for the presence of 15-hydroxylated estrogens in the peripheral plasma of the laying turkey.

Abstract The purpose of this paper is to describe the estrogens other than estrone, estradiol, and estriol present in turkey plasma. Five peaks of radioimmunoassayable (RIA) estrogenic activity were detected with an estriol antiserum in ether extracts of laying turkey plasma after high-pressure liquid chromatography on a silica gel column. Estrone and estradiol were the first two peaks. Derivatives of peaks three (U 1 ), four (U 2 a), and five (U 2 b) were prepared and subjected to gas liquid chromatography-mass spectrometry. 15β-OH-estrone and 15α-OH-estrone were tentatively identified in U 1 . U 2 a was tentatively identified as 15β-OH-estradiol, and U 2 b as 15α-OH-estradiol. Reference compounds 15α-OH-estrone and 15α-OH-estradiol have been obtained. When subjected to HPLC the retention time of 15α-OH-estrone was found to correspond to the trailing edge of U 1 , and the retention time of 15α-OH-estradiol was identical to peak five (U 2 b). The definitive identification of 15β-OH-estrone and 15β-OH-estradiol awaits the availability of pure reference compounds. The presence of 15α-OH-estrone and 15α-OH-estradiol in turkey plasma in significant quantities suggests that further research concerning their physiological function is needed.