Biomedical subjects

W H Burke

Publications and source records attributed to W H Burke.

At least 19 recordsLinked to original sources

PubMed1999

The effects of in ovo administration of testosterone or an antiandrogen on growth of chick embryos and embryonic muscle characteristics.

Based on earlier studies from our laboratory, we hypothesized that higher levels of plasma androgens in male embryos stimulate greater muscle development and are responsible for the greater muscle mass of male chickens after hatching. The results of these studies show that androgen supplementation by in ovo injection of testosterone prior to incubation had no effect on weight of 12-, 16-, or 20-d-old male chicken embryos or on characteristics of their Pectoralis superficialis muscle. In contrast, weight of 12 d-old female embryos was depressed and the protein concentration and protein content of the P. superficialis was reduced in 16-d-old female embryos. Interference with the actions of endogenous androgens by preincubation in ovo injection of Flutamide, an antiandrogen, resulted in significant linear and quadratic relationships between the dose of Flutamide injected and the weight, protein content, and DNA content of the P. superficialis of 16-d-old female embryos. Increases over the lower part of the dose range (0 to 1.74 micromol per egg) were followed by a decrease at the highest dose (2.9 micromol per egg). The DNA content of the P. superficialis of 16-d-old female embryos was similarly affected when Flutamide was injected on Day 8 of incubation, whereas the protein content and protein concentration of the muscle was increased in 20-d-old female embryos. There were no significant changes in the weight, protein content, or DNA content of the P. superficialis of male embryos when Flutamide was injected before or on Day 8 of incubation.

Androgen Antagonists↗

PubMed1999

Gonadal development and growth of chickens and turkeys hatched from eggs injected with an aromatase inhibitor.

It was the purpose of these experiments to describe gonadal development and posthatching growth of genetic female chickens and turkeys following in ovo injection of the aromatase inhibitor Fadrazole (CGS 16949A) prior to incubation. In ovo injection of Fadrazole (CGS 16949A) resulted in the development of testes-like gonads in the majority of day-old genetic female chickens and turkey poults. Ninety-eight to 99% of these birds have masculine-type male genitalia at 1 d of age. Microscopic examination of the gonads of day-old genetic female chicks hatched from Fadrazole-treated eggs showed the presence of atypical seminiferous tubules in 3 of 18 individuals and the presence of ovarian follicles in 3 of 18 individuals. No germinal elements were seen in 12 individuals. The gonads in the majority (8/11) of day-old female poults from treated eggs showed the presence of atypical seminiferous tubules. Three of 11 individuals had structures characterized as disorganized or degenerate follicles. Between the day of hatch and 6 wk, gonads in an increasing proportion of female chickens from Fadrazole-treated eggs had normal appearing ovarian follicles. A similar trend was seen in the female turkeys between hatch and 12 wk of age. There were no differences in BW of female chickens hatched from Fadrazole-treated eggs and those from control eggs between the day of hatch and 6 wk of age. The pectoral muscle mass and fat pad weights of these birds did not differ. In one experiment, the BW of female turkeys hatched from Fadrazole-treated eggs was significantly greater than that of controls and equal to that of males at 3 and 6 wk of age. Thereafter, both types of females were of equal weight and significantly lighter than males. Fadrazole treatment did not affect pectoral muscle mass of either sex of turkeys.

Adipose Tissue↗

PubMed1998

Sexual dimorphism in broiler chick embryos and embryonic muscle development in late incubation.

Studies were conducted to compare the weights and the characteristics of the Pectoralis superficialis, Semimembranosus, and Gastrocnemius of male and female chicken embryos at 16 and 20 d of incubation. Male embryos were significantly heavier than females at 16 d of incubation, but not at 20 d. The cross-sectional area of myofibers in the P. superficialis of 20-d-old female embryos was greater than that of males and the area of Semimembranosus myofibers was greater at 16 and 20 d. The Semimembranosus apparent myofiber number of 16-d-old male embryos was greater than of females (P = 0.002). There was a significant increase in apparent myofiber number in this muscle between 16 and 20 d of incubation but there was no sex difference at 20 d. The number of Type I myofibers per 30,000 microm2 area of the Gastrocnemius of 20-d-old male embryos was greater than that in females (P = 0.06). There were no significant sex differences in the protein concentration, DNA concentration, or protein:DNA ratio in the muscles at either age when data were pooled across the whole population. There were significant differences in these characteristics between sire families and in some sire families significant sex differences were noted. The protein:DNA ratio of the muscles increased between 16 and 20 d of incubation and the mitotic index decreased. These data suggest that the muscles of male embryos have more but smaller, myofibers than females, which may be responsible for the sex difference in embryo weight and provide the framework for the greater posthatching muscle growth.

Animals↗

PubMed1997

Characteristics of the pectoralis superficialis and semimembranosus of broiler strain chickens, bantam chickens, and the reciprocal crosses.

At hatch, chicks from bantam sire x broiler dam (BaBr) matings were as heavy as those from broiler sire x broiler dam (BrBr) matings. Both were heavier than pure bantam chicks (BaBa) or chicks from broiler strain sires and bantam dams (BrBa), but weights of the latter two genotypes were identical. The Pectoralis superficialis and Semimembranosus of pure bantam chicks weighed less than those of pure broiler chicks throughout the studies. Muscle weights in the BaBr chicks were markedly heavier than those of genetically similar BrBa chicks at hatch. Genetic influences were quickly expressed and weights of muscles in these two groups had converged by 14 d of age. Myofiber cross-sectional areas at 1 d of age were not clearly associated with genotype or maternal environment, but clear patterns had begun to develop by 4 d of age. Myofiber area of both muscles was greater in BrBr than BaBa chicks by this age and after. Myofiber areas in the reciprocal crosses converged toward each other and away from the pure line chicks. By 11 d, the area of Pectoralis myofibers of BrBr chicks was greatest, those of the reciprocal crosses was intermediate and equal to each other, and that of BaBa chicks was least. A similar trend was apparent in Semimembranosus fibers by 11 d but the differences did not become significant until 21 d of age. Significant differences in myofiber number of the Semimembranosus were present (BrBr > BaBr > BrBa > BaBa). Thus, differences in muscle mass were the result of differences in both fiber number and fiber size.

Analysis of Variance↗

PubMed1997

Comparison of embryos and chicks that developed as single individuals in double yolk eggs with those that developed in single yolk eggs.

Body weight and muscle characteristics of 18- to 20-d-old broiler strain embryos developing in double yolk eggs (DY) that contained one embryo and one infertile ovum were compared with embryos in single yolk eggs (SY). Similar comparisons were made in the posthatching period. In some DY eggs, the embryos were bathed in a watery yolk-like fluid with no distinct second yolk present (Type 1 embryo). In others, the second yolk was contained within the vitelline membrane and surrounded by a vascularized membrane (Type 2). These embryos were heavier than Type 1 or embryos in SY eggs by 20 d of incubation. Their Pectoralis superficialis were heavier and had significantly more protein and DNA. Chicks that hatched from the DY eggs were heavier than those that hatched from SY eggs and they had heavier P. superficialis through at least 14 d of age. Pectoralis superficialis myofibers of chicks from DY eggs had greater cross-sectional area than those from SY eggs. Myofibers in the Semimembranosus of 7- and 14 d-old chicks from DY eggs tended to be larger than those from SY eggs, but the differences were not significant. There was no difference in apparent myofiber number in the Semimembranosus of the two types of chicks. The difference in BW between the two types of chicks diminished over time, so that by 42 d of age they were virtually identical. In summary, a nutritionally enriched in ovo environment resulted in embryos and chicks with enhanced growth and muscle mass, but the effects of enrichment diminished during posthatching life and eventually disappeared.

Animals↗

PubMed1996

Effects of an in ovo injection of an anti-androgen on embryonic and posthatching growth of broiler chicks.

Experiments were conducted to determine whether in ovo injection of Flutamide, a non-steroidal anti-androgen, would affect posthatching growth of broiler chickens. Before doing these studies it was necessary to develop a bioassay to demonstrate that Flutamide had anti-androgenic actions when injected in ovo. In ovo injection of 0.06 to 1.74 mumol of testosterone propionate (TP) per egg on the 8th d of incubation caused a dose-related decrease in weight of the bursa of Fabricius of newly hatched chicks. In subsequent experiments, 1.74 mumol of Flutamide significantly decreased the bursal regression produced by 0.58 mumol of TP when both substances were injected on Day 8 of incubation and bursal weights were taken on the day of hatch. Having established that Flutamide could block the effects of high doses of exogenous TP, it was reasoned that it could block the action of much lower endogenous levels. In two of the three experiments, injection of Flutamide on the 8th d of incubation resulted in a dose-related decrease in 21- and 49-d BW of male broiler chickens. The material had no effect on BW of males in one experiment and had no effect on BW of females at any age in any of the experiments. The data suggest that interference with the actions of endogenous androgens during embryonic life suppresses the posthatching growth of male broilers.

Androgen Antagonists↗

PubMed1996

Influence of male broiler breeder dietary energy intake on reproduction and progeny growth.

A study was conducted to test the effects of dietary energy intake on reproduction in genetically similar broiler breeder males and on the subsequent growth of their progeny. Fifty-nine 1-d-old pedigree broiler breeder male chicks were raised to breeding age. At 33 wk of age, 33 males were chosen and placed in one of three groups of 11 males per group and fed either 370, 330, or 290 kcal per bird per d. Each group contained both full and half brothers and had similar 6- and 33-wk mean body weights. There was a significant negative effect of decreased dietary energy intake on sperm concentration and total live sperm per milliliter of ejaculate, whereas there was no significant effect on ejaculate volume or percentage dead sperm per ejaculate. Four groups of hens (21 wk of age) with 18 hens per group, were randomly assigned to each male dietary treatment group. Hens were artificially inseminated with 50 microL neat pooled semen from one of the three male treatment groups. There was a significant linear effect of diet on fertility, with no significant effect on hatch of fertile, hatch of eggs set, or embryonic mortality. There was no effect of sire energy intake on offspring body weights at 0, 3, or 6 wk of age. Hens were similarly artificially inseminated and sperm penetration determined for 9 consecutive d postinsemination. There was a significant quadratic relationship between sperm penetration of the perivitelline layer overlying the germinal disc and day postinsemination for each of the three male treatment groups. In addition, mean sperm penetration was 62.3, 42.9, and 6.6 holes in the germinal disc perivitelline layer for the high, medium, and low energy groups, respectively. Following 16 wk of dietary energy treatment, there was a significant linear effect of diet on mean testes weight, mean testes weight as a percentage of male body weight, and male body weight.

Animals↗

PubMed1995

Daily energy allotments and performance of broiler breeders. 1. Males.

The effects of daily energy intake on reproductive performance of Arbor Acres males and on growth of their offspring was studied. In Experiment 1, 21 males were placed in individual pens with 12 females. Three rations, differing in energy, were fed from 24 to 57 wk of age with seven males receiving either 300, 340, or 380 kcal ME/d. In Experiment 2, 32 individually caged males were given daily allotments of 280, 320, 360, or 360 kcal ME/d from 26 to 32 wk of age and 300, 340, 380, or 380 kcal ME/d from 32 to 38 wk. Rations of the two groups of males fed the highest energy level differed in formulation, one being the same wheat short-based basal ration as fed to the two lower energy groups, only with additional fat, and the other being a corn-soybean-based ration. Body weight and testes weight were increased with increased energy allotment in both experiments but carcass composition was unaltered. There were no significant effects of energy intake on fertility or hatchability in either experiment. Even though mean differences were not significant, fertility in two pens dropped to near zero at 38 wk in Experiment 1. Semen characteristics and plasma testosterone concentrations were unaffected by energy intake in Experiment 2. There was a significant linear increase in 6-wk BW of broilers associated with the increase in sire energy intake in each of three batches of broilers grown in Experiment 1 and in one of two batches of broilers grown in Experiment 2.

Animals↗

PubMed1995

Daily energy allotments and performance of broiler breeders. 2. Females.

Arbor Acres broiler breeder hens, 21 to 61 wk of age, were given the daily ME level recommended by the primary breeder for their age and level of production (100% AA) or were given 94 or 88% of that amount. The reduction in daily energy allotment had no effect on age at 50% or age at peak production, but there was a highly significant linear decrease in the eggs per hen from 165 +/- 2.8 in hens given 100% AA to 149 +/- 3.2 and 141 +/- 3.8 in hens given 94 and 88% AA. The percentage of nonlaying hens between 44 and 60 wk of age was substantially increased as daily energy allotment was reduced. The percentage settable eggs was significantly lower in the 100% AA group, but no differences in fertility or hatchability were seen. Chicks per hen fell from 123 +/- 2.4 to 116 +/- 2.4 to 102 +/- 2.6 as energy allotment was progressively reduced. Dietary energy allotment had no effect on egg weight, shell weight, shell characteristics, or proportion of albumen and yolk. Chick weight was unaffected but chicks' liver weight increased with increasing dam energy intake. Percentage lipid in hens' carcasses increased with increasing energy intake and percentage protein and percentage ash decreased.

Animals↗

PubMed1995

Posthatching growth and pectoralis muscle development in broiler strain chickens, bantam chickens and the reciprocal crosses between them.

Body weight, pectoralis muscle weight, pectoralis protein and DNA concentration, and plasma GH and IGF-I concentrations of broiler chicks (BrBr), bantam chicks (BaBa) and reciprocal crosses between them (BaBr and BrBa) were measured between 0 and 42 days after hatching. At hatch, body weight and pectoralis weight of the two types of chicks from broiler eggs (BrBr and BaBr) were equal to each other but greater than the two types of chicks from bantam eggs (BaBa and BrBa), which were not different from each other. BrBr chicks grew more rapidly than crossbreds and BaBa chicks grew more slowly. Weights of the reciprocal crosses (BaBr and BrBa) were markedly different at day of age, but converged by day 14. The increase in pectoralis muscle mass of BrBr chicks exceeded that of the reciprocal crosses which in turn exceeded that of BaBa chicks. The increase in pectoralis DNA content and protein content followed the same pattern. The DNA unit size, as expressed by the protein:DNA ratio, was markedly lower in pure bantam chicks from 14 to 42 days of ages, whereas the unit size did not differ between the intermediate sized reciprocal crosses and the large bodied broiler chicks. Differences in muscle mass were primarily achieved by differences in the number of DNA units although a difference in unit size was also a factor. There were no clear relationships between growth and plasma growth hormone or insulin-like growth factor I concentrations. Thus while satellite cell proliferation is primarily responsible for genotypic differences in muscle mass, the plasma growth hormone-IGF-I axis does not appear to be regulating their proliferation.

Age Factors↗

PubMed1994

Photostimulation changes the pattern of luteinizing hormone secretion in turkey hens.

Changes in the secretory pattern of luteinizing hormone (LH) were determined in turkey hens during initiation of reproduction. Photosensitive hens were switched from a short day photoschedule of 6L:18D (light:dark) to 14L:10D and serially bled six times during the next 6 weeks of photostimulation and early after ovulatory cycles had begun. The pattern of LH secretion at 0-1 day of photostimulation was characterized by a low baseline concentration of LH with numerous low frequency, high amplitude pulses. This pattern changed at Days 4-5 and 11-12 of photostimulation (hens photostimulated but not yet laying) to a pattern characterized by a high baseline with few ill defined pulses of very short duration. Once the hens had initiated egg production, ovulatory surges of LH (duration of 358 +/- 104 min) were superimposed on the basic pattern seen during photostimulation. The ascending limb of the ovulatory surge was much shorter in duration than the descending limb. No diurnal variation was detected in baseline concentration before or during photostimulation or after egg production had begun. It was concluded that photosensitive turkey hens secrete LH in low frequency; high amplitude pulses superimposed on a low baseline. During photostimulation, this pattern changes to one characterized by a high baseline with few pulses of low amplitude and short duration. This pattern of secretion is stimulatory to the ovary and continues until egg laying begins when it is modified by ovulatory surges of LH, characterized by short duration ascending limbs and longer duration descending limbs, which are superimposed on the high baseline pattern noted during photostimulation.

Animals↗

PubMed1994

Response of broiler breeder hens to forced molting by hormonal and dietary manipulations.

Experiments were conducted to compare dietary and hormonal techniques for molting broiler breeder hens. In the first experiment, production dropped to 5% 3 wk after hens were restricted to an intake of one half of their calculated energy requirement (FR). Egg production levels of hens given a single i.m. injection of the Lupron Depot formulation of leuprolide acetate (LA) in a dose intended to provide 10 micrograms/kg BW per d for 30 d dropped to 9.5% whereas production dropped to 33% in hens receiving 5 micrograms and was unchanged by 2.5 micrograms. Postmolting fertility and hatchability of eggs from the FR and the 10-micrograms LA groups were not different. In the second experiment, postinjection egg production, oviduct weight, and uterus weight were depressed, in a dose-related manner, when hens received 0, 10, or 22 micrograms LA/kg per d. In a third experiment, egg production dropped to zero within 2 wk when hens were deprived of feed (FD) or deprived of feed and light (FD+LR), whereas it reached zero in 4 wk in hens fed only 30 g of wheat shorts per d (FR). Lupron Depot at a dose intended to deliver 30 micrograms/kg BW per d, reduced egg production to 9.5% by the 3rd wk. Twenty-eight weeks postmolting, egg production ranged from 84 to 98 eggs per hen in the molted groups and 56 eggs per hen in the unmolted controls. Fertility ranged from 82.1% in the FD+LR groups to 69.8% in the unmolted controls, whereas chick production averaged 36, 50, 59, 60, and 68 chicks per hen in the unmolted controls and in hens molted by LA, FR, FD, or FD+LR, respectively.

Animals↗

PubMed1994

Effect of early castration on body weight, muscle growth, and bone characteristics of male Nicholas strain turkeys.

Body weight of male Nicholas strain turkeys, castrated at 8 to 10 d of age, averaged .60, 2.20, 5.26, 8.26, and 10.83 kg at 3, 6, 9, 12, and 15 wk of age, respectively. These weights did not differ significantly from those of sham-operated control birds, but were significantly less than those of unoperated controls at 12 and 15 wk of age. Pectoralis major weights of 15-wk-old castrated turkeys were not significantly different than the sham-operated controls, but were less than those of intact controls. Pectoralis weights, expressed as a percentage of BW, did not differ among these groups. There were no differences in tarsometatarsal lengths, weight, or percentage ash among the groups. The incidence of tibial dyschondroplasia ranged from 66.7 to 80.0%, with average scores ranging from 1.00 to 1.42, with no differences among groups. Plasma testosterone concentrations of unoperated and sham-operated controls averaged .16 and .26 ng/mL at 15 wk, whereas concentrations in 7 of 12 castrates were undetectable and amounts in the other 5 castrates averaged .03 ng/mL.

Animals↗

PubMed1994

Sex differences in weight of turkey embryos.

Wet and dry weights of 12-, 16-, and 20-d-old embryos from Hybrid strain and Nicholas strain commercial cross turkeys were determined, and the relationships between embryo weights and the preincubation weight of the eggs in which they were developing was determined by regression analyses. The wet weight of Hybrid strain male embryos was significantly greater than that of females at each age, whereas wet weight of male Nicholas embryos was greater than females at 16 and 20 d. Average dry weights of male embryos of both strains exceeded those of females at 16 and 20 d but differences were not significant. Significant linear regressions of embryo wet and dry weights on egg weight were present in the Hybrid strain males at 12 and 16 d of incubation and in females at 16 d only. The regression of Nicholas embryo wet weight on egg weight approached significance in 12-d-old males and 20-d-old females.

Animals↗

PubMed1994

Coordinate pattern of secretion of luteinizing hormone and testosterone in mature male turkeys under continuous and intermittent photoschedules.

Secretory patterns of luteinizing hormone (LH) and testosterone (T) were determined in sexually mature male turkeys housed under Continuous [14 h light (L): 10 h dark (D), n = 3)] or Intermittent [8 x (1L:2D), n = 3] photoschedules. Jugular vein cannulas were implanted on Day 0 and serial blood samples were taken at 5-min intervals for 12 h on Day 3 and again 4 to 7 d later. Most increases in T concentration were preceded by an increase in LH concentration for both photoschedules. Treatment differences for overall mean T [1.77 +/- .58 (SE) ng/mL], baseline T (.92 +/- .30 ng/mL), T peak number (6.1 +/- 1.2 per 12 h), T peak amplitude (2.77 +/- 1.70 ng/mL), or T peak length (79 +/- 24 min) were not significant (P > .05). The number of LH peaks was greater in the Continuous than Intermittent group (11.7 +/- .6 vs 6.8 +/- 1.4 per 12 h, P < .05), but there were no treatment differences in overall mean LH (4.56 +/- 2.09 ng/mL), baseline LH (4.10 +/- 2.11 ng/mL), LH peak amplitude (2.80 +/- .92 ng/mL), or LH peak length (15.9 +/- 3.1 min). There were no differences in T or LH concentrations between the photo- and scotophases in the continuous group, and pulses of both were seen in both phases in both lighting treatments. It was concluded that minor differences in patterns of LH secretion may occur between Continuous and Intermittent stimulatory lighting treatments in sexually mature male turkeys.

Animals↗

PubMed1994

Molting single comb White Leghorns with the use of the Lupron Depot formulation of leuprolide acetate.

Reproductive tract regression and cessation of egg production was induced in 80-wk-old Hy-Line W36 strain hens by an i.m. injection of Lupron Depot at a dose calculated to release 60 micrograms of leuprolide acetate (LA)/kg of BW for 30 d, by restriction of feed intake (FR) for 28 d, or by total feed deprivation (FD) for 7 d followed by feed restriction for 21 d. Egg production in LA and FD groups dropped to 24 and 19% in the first 7 d after initiation of the treatments and to 3.5 and 0% in the 2nd wk. Production of the FR group dropped to 38% during the 1st wk and to 1.7% in the 2nd wk. Production of both nutritionally deprived groups remained near zero through the 5th wk, whereas it increased to 8.2% in the LA group at that time. Hens injected with LA reached 50% production at about 37 vs 45 d for both nutritionally deprived groups. Egg production of control groups remained unchanged during this time. Shell characteristics did not differ significantly among the molted groups throughout most of the 16 wk of the experiment. However shell weight and shell weight per unit surface area of eggs from LA-treated hens were significantly (P < or = .05) lower than those of FR, but not FD, hens at several times. Mean values for shell characteristics of eggs from unmolted hens were significantly lower than those of molted hens. There were no differences in albumen quality between any of the groups at any time.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

The role of plasma growth hormone, prolactin, triiodothyronine and tetraiodothyronine in the regulation of growth and sex differences in body weight of turkeys.

An attempt was made to alter male:female (M:F) body weight ratios in two strains (S12 and S72) of turkeys by selective matings; to study their post-hatching growth patterns and to relate growth patterns to plasma growth hormone (GH), prolactin (Prl), tetraiodothyronine (T4), and triiodothyronine (T3) concentrations. Selection for high and low M:F body weight ratio (HR and LR) was essentially ineffective in both strains. Sex differences in body weight were first significant in S12 at day of age and in S72 at 6 wk. Plasma GH and Prl rose during the first 2 wk of age and fell thereafter while T3 levels decreased and T4 levels increased over time. Differences in plasma hormones between lines and sexes within strains were noted, but showed no consistent patterns. Correlations between GH and growth were mostly negative. When significant, regressions between body weight and GH or gain and GH were generally negative. Significant correlations between Prl and body weight in males were negative whereas they were of mixed sign in females. Correlations between T3 levels from 2 to 8 wk of age and body weight over this same period were mostly positive in males whereas those at later ages and in females were mostly negative. Few significant correlations between T4 and weight were found. These findings suggest that the regulation of growth in turkeys is quite different than that of mammals and that hormones known to regulate growth in some species may not do so in others.

Age Factors↗

PubMed1993

Precocious puberty in tamoxifen-treated cockerels: hypothalamic gonadotrophin-releasing hormone-I and plasma luteinising hormone, prolactin, growth hormone and testosterone.

1. The administration of the anti-oestrogen, tamoxifen (TAM) to juvenile chicks results in precocious puberty. In the present study the effects of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin-releasing hormone (cGn-RH-I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juvenile White Leghorn cockerels. 2. The increase in hypothalamic GnRH-I content which occurs during sexual development was advanced in TAM-treated birds, in association with precocious testicular development, an early rise of plasma testosterone content and enhanced comb growth. 3. Plasma LH concentrations behaved similarly and were higher in the TAM-treated than in control birds, during most of the experimental period. Plasma PRL concentration, which is high at hatching, decreased more quickly in TAM-treated than in control birds; plasma GH values were not consistently affected by TAM treatment. 4. Both the growth and the involution of the bursa of Fabricius in the TAM-treated cockerels preceded that in the control chicks. 5. It is concluded that TAM treatment induces precocious puberty in the cockerel by blocking the negative feedback action of aromatised testicular androgens on the hypothalamus.

Animals↗