Biomedical subjects

R W Rosebrough

Publications and source records attributed to R W Rosebrough.

At least 19 recordsLinked to original sources

PubMed2006

The relationship of body composition, feed intake, and metabolic hormones for broiler breeder females.

Three hundred twenty Cobb 500 broiler breeder pullets at 21 wk of age were selected from a flock fed according to Cobb Breeder Management Guide specifications. One hundred sixty pullets at 21 wk of age were switched to ad libitum feeding, and the remaining 160 pullets continued to be control-fed. The pullets were photostimulated at 22 wk and maintained until 36.5 wk. Plasma samples were obtained, BW was determined, and hens were killed for determination of body composition at the following periods: 24 h prior to photostimulation, 2.5 wk after photostimulation, 24 h after first egg, and 36.5 wk following peak egg production. Compared with ad libitum-fed breeders, the restricted breeders had a higher percentage carcass protein and lower percentage carcass fat at all sampling periods. Total egg numbers were greater, and abnormal eggs were less for the restricted pullets compared with the ad libitum-fed pullets at 36.5 wk. Carcass percentage fat of ad libitum-fed pullets was positively related to plasma glucagon, insulin-like growth factor-II (IGF-II), and 17beta-estradiol but negatively related to plasma insulin, insulin/glucagon M ratio, insulin-like growth factor-I (IGF-I), thyroxine (T4), and triiodothyronine (T3). Carcass percentage fat of feed-restricted pullets was negatively related to IGF-I, IGF-II, and T4. The T4 was the most important hormone for predicting the percentage carcass fat in ad libitum-fed pullets, and IGF-I was the most important hormone for predicting the percentage carcass fat in feed-restricted pullets. The percentage carcass protein for ad libitum-fed breeders was positively correlated to IGF-I, T4, T3, insulin/glucagon M ratio, and insulin. Carcass percentage protein for feed-restricted breeders was positively correlated to IGF-I, IGF-II, T4, and glucagon. Stepwise regressions for predicting percentage carcass protein for breeders fed by both systems shows that T3 and IGF-I concentrations were the most important for ad libitum-fed breeders, whereas IGF-II and T4 were best for feed-restricted breeders. The hormone status of breeders may be a key indicator to help predict the body composition and thus support management decisions for maintaining optimum production.

Animal Feed↗

PubMed2005

Studies on doses of methimazole (MMI) and its administration regimen on broiler metabolism.

We designed three experiments to determine both the optimal dose of and time on experiment for methimazole (MMI; 1-methyl-2-mercaptimidazole). Our goals were to determine if chicken growth was related to thyroid hormone levels and if intermediary metabolism changed along with changes in thyroid hormone levels. Initiating MMI at one week of age decreased (P<0.01) plasma thyroid levels and growth in four-week old birds. In contrast, initiating MMI at two and three weeks of age decreased (P<0.05) hormone levels without affecting growth as severely. Although initiating MMI at two weeks of age depressed (P<0.05) plasma thyroid hormones at four weeks, there was little change in vitro lipogenesis at four weeks. Again, initiating MMI at one week of age decreased body weight, plasma thyroid hormones and in vitro lipogenesis at four weeks of age. In addition, this treatment also decreased (P<0.05) malic enzyme activity at this same age period. The second experiment showed that MMI, initiated at 14 days, had no significant effect on 28-day body weight and again decreased both plasma T(3) and T(4) but T(3) replacement increased plasma T(3) in both 14-28-day treatment groups. All body weights were similar at 30 days, however. Lastly, diets containing graded levels of MMI decreased thyroid hormones and body weight (0>0.25>0.5>1 g MMI/kg). In contrast, only the two higher levels (0.5 and 1 g MMI/kg) decreased in vitro lipogenesis. Growth depression, caused by MMI feeding, can occur without changes in lipid metabolism. The length of MMI administration may be as important as dose level in obtaining effects (growth, thyroid hormone depression and inhibition of lipogenesis).

Animals↗

PubMed2005

Regulation of uncoupling proteins 2 and 3 in porcine adipose tissue.

This study was performed to determine whether or not uncoupling protein 2 (UCP2) and UCP3 expression in porcine subcutaneous adipose tissue are hormonally regulated in vitro and whether their expression is correlated with changes in metabolic activity. Tissue slices (approximately 100 mg) were placed in 12-well plates containing 1 mL of DMEM/F12 with 25 mM Hepes, 0.5% BSA, pH 7.4. Triplicate slices were incubated with basal medium or hormone supplemented media at 37 degrees C with 95% air/5% CO2. Parallel cultures were maintained for either 2 or 24 h to evaluate metabolic viability of the tissue. Slices were transferred to test tubes containing 1 mL of DMEM/F12 with 25 mM Hepes, 3% BSA, 5.5 mM glucose, 1 microCi 14C-U-glucose/mL and incubated for an additional 2 h at 37 degrees C. Glucose metabolism in 2-h incubations did not differ from 24-h (chronic) incubations, indicating viability was maintained (P>0.05). Expression of UCP2 and UCP3 was assessed in slices following 24h of incubation with various combinations of hormones by semi-quantitative RT-PCR. Expression of UCP2 was induced by leptin (100 ng/mL; P<0.05). Growth hormone (100 ng/mL) inhibited UCP2 expression (P<0.05). Expression of UCP3 was inhibited by growth hormone (100 ng/mL; P<0.05), tri-iodothyronine (10 nM; P<0.05) or leptin (100 ng/mL; P<0.05). Changes in UCP expression could not be associated with overall changes in glucose metabolism by adipose tissue slices in chronic culture.

Adipose Tissue↗

PubMed2004

Methimazole, thyroid hormone replacement, and lipogenic enzyme gene expression in broilers.

The purpose of this experiment was to determine the possible relationship between certain indices of lipid metabolism and specific gene expression in chickens fed methimazole to simulate hypothyroidism. Male broiler chickens (Gallus gallus) growing from 7 to 28 days of age were fed diets containing 18% crude protein and either 0 or 1 g methimazole per kilogram of diet. At 28 days, these two groups were further subdivided into groups receiving 18% crude protein diets containing either 0 or 1 mg triiodothyronine (T3) per kilogram. Birds were sampled at 28, 30, and 33 days. Measurements taken included in vitro lipogenesis (IVL), malic enzyme (ME) activity, isocitrate dehydrogenase, aspartate amino transferase, and the expression of the genes for ME, fatty acid synthase (FAS), and acetyl coenzyme carboxylase (ACC). Hypothyroidism decreased IVL and ME at 28 days of age; however, T3 supplementation for 2 days restored both IVL and ME. Paradoxically, continuing T3 replenishment for an additional 3 days decreased IVL but did not decrease ME activity. In contrast, supplemental T3 decreased IVL in euthyroid birds, regardless of the dosing interval, but had no effect on ME activity. Although methimazole decreased ME gene expression, there was only a transitory relationship between enzyme activity and gene expression when plasma T3 was restored with exogenous T3. These data may help to explain some of the apparent reported dichotomies in lipid metabolism elicited by changes in the thyroid state of animals. In addition, most metabolic changes in response to feeding T3 occurred within 2 to 5 days, suggesting that changes in intermediary metabolism preceded morphological changes. In conclusion, the thyroid state of the animal will determine responses to exogenous T3.

Animals↗

PubMed2004

Further studies on dietary protein reversals and lipid metabolism in the broiler.

Although changes in dietary protein levels change metabolism in the broiler chicken, there is little information concerning the time course of the process of adaptation. Therefore, male Hubbard broiler chickens were fed diets containing either 12 or 30% crude protein from 7 to 28 d of age and then were switched to the opposite level for an additional 9 d. Birds were bled and killed at 0, 2, 5, 7and 9 d following the reversals. Data taken at these intervals included those involved in vitro lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities and plasma hormones and metabolites. Birds fed the lower level of crude protein were smaller in growth from 7 to 28 d. Feeding these birds a higher protein diet from 28 to 37 d improved both growth and feed efficiency in comparison to controls. Lipogenesis was also greater and plasma insulin-like growth factor-I (IGF-I) less in birds fed the lower protein diet. Switching dietary treatments increased and decreased lipogenesis as birds were switched from high to low and low to high protein diets, respectively. Half-maximal changes were observed 2 d after the reversal and maximal changes 5 d after the reversal. In contrast, switching dietary treatments decreased and increased plasma IGF-I as birds were switched from high to low and low to high protein diets, respectively. Half-maximal changes were observed 2 d after the reversal. Of the three hepatic enzymes monitored, malic enzyme activity most closely followed the rapid changes in IVL. In the present study, plasma IGF-I may be a more sensitive indicator of changes in dietary protein than changes in intermediary metabolism.

Aging↗

PubMed2003

Methimazole and thyroid hormone replacement in broilers.

Seven-day-old chickens were fed diets containing 18% crude protein + 0 or 1g methimazole/kg to produce either euthyroid or hypothyroid groups of birds at 28 days of age. These two groups were then offered diets containing either 0 or 1mg triiodothyronine (T(3))/kg diet. Birds were sampled at 0, 2, 5, and 8 days following the onset of the T(3) treatment. Measurements taken at these intervals included in vitro hepatic lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities (malic enzyme, ME; isocitrate dehydrogenase, ICD; and aspartate amino transferase, AAT), plasma hormones (T(3); thyroxine, T(4); insulin like growth factors I, IGF-I; and insulin like growth factors II, IGF-II) and metabolites (glucose; fatty acids, NEFA; triglyerides; uric acid). Hypothyroidism decreased IVL and ME at 28 days of age; however, T(3) supplementation for 2 days restored both IVL and ME. Paradoxically, continuing T(3) replenishment for an additional 3-6 days decreased IVL without affecting ME activity. In contrast, supplemental T(3) decreased IVL in euthyroid birds, regardless of the dosing interval, but had no effect on ME activity. Methimazole decreased plasma T(3), T(4), uric acid, and IGF-I, but did not affect IGF-II at 28 days. Giving T(3) to birds previously on methimazole increased plasma IGF-I as did feeding a control diet. Supplemental T(3) increased NEFA in both euthyroid and hypothyroid birds, but only for a short period following the initiation of supplementation (2 days post-supplementation). These data may help to explain some of the apparent reported dichotomies in lipid metabolism elicited by changes in the thyroid state of animals. In addition, most metabolic changes in response to feeding T(3) occurred within 2-5 days, suggesting that changes in intermediary metabolism preceded morphological changes. In conclusion, the thyroid state of the animal will determine responses to exogenous T(3).

Animals↗

PubMed2003

Hormonal regulation of postnatal chicken preadipocyte differentiation in vitro.

This study was designed to develop a culture system from the stromal-vascular fraction of chicken adipose tissue that can be used to characterize hormones that promote preadipocyte differentiation. Abdominal adipose tissue was excised from 2 to 4-week-old male broilers (Gallus domesticus) by sterile dissection. The stromal-vascular cell fraction from the adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. These preadipocytes were seeded in six well culture plates and proliferated to confluency in 10% fetal bovine serum in DMEM/F12 (50:50) medium. At confluency, experiments were initiated to determine hormonal requirements for differentiation. Insulin (100 nM) stimulated expression of citrate lyase and sn-glycerol-3-phosphate dehydrogenase relative to lactate dehydrogenase in the presence of 2.5% chicken serum (P<0.05), but not with 10% chicken serum (P>0.05). Triiodothyronine (T(3), 1 nM) and insulin-like growth factor 1 (100 ng/ml) had no effect on differentiation. Dexamethasone (Dex, 1 microM) stimulated differentiation in 2.5 or 10% chicken serum (P<0.05). Insulin, Dex and 2.5% chicken serum stimulated enzymatic differentiation to the extent of 10% chicken serum, but heparin (10 U/ml) addition, in combination with insulin and Dex was necessary to stimulate lipid filling of adipocytes.

Adipocytes↗

PubMed2002

Dietary protein regulates in vitro lipogenesis and lipogenic gene expression in broilers.

The purpose of this experiment was to determine the possible relationship between certain indices of lipid metabolism and specific gene expression in chickens fed graded levels of dietary crude protein. Male, broiler chickens growing from 7 to 28 days of age were fed diets containing 12, 21 or 30% protein ad libitum. In addition, another group of birds was fed on a regimen consisting of a daily change in the dietary protein level (12 or 30%). This latter group was further subdivided such that one-half of the birds received each level of protein on alternating days. Birds were sampled from 28 to 30 days of age. Measurements taken included in vitro lipogenesis, malic enzyme activity the expression of the genes for malic enzyme, fatty acid synthase and acetyl coenzyme carboxylase. In vitro lipogenesis and malic enzyme activity were inversely related to dietary protein levels (12-30%) and to acute changes from 12 to 30%. In contrast, expression of malic enzyme, fatty acid synthase and acetyl CoA carboxylase genes were constant over a dietary protein range of 12-21%, but decreased by feeding a 30% protein diet (acute or chronic feeding). Results of the present study demonstrate a continued role for protein in the regulation of broiler metabolism. It should be pointed out, however, that metabolic regulation at the gene level only occurs when feeding very high levels of dietary protein.

Acetyl-CoA Carboxylase↗

PubMed2002

Carry over effects of dietary crude protein and methimazole in broiler chickens.

Seven day old male broiler chickens were fed diets containing 12, 18 or 24% crude protein + 0 or 1 g methimazole/kg diet for 21 days to examine the interaction of the birds' thyroid status and crude protein levels on metabolism. Methimazole (1-methyl-2-mercaptimidazole) inhibits thyroidal production of thyroid hormones and results in hypothyroidism. Birds were fed a diet containing 18% crude protein for an additional 21 days to determine the carry over effects of treatments. Birds were killed at 28 and 49 d. In vitro lipogenesis was inversely related (P < 0.05) to dietary protein levels in control birds at 28 d. Dietary methimazole attenuated (P < 0.05) this effect, resulting in a common rate similar to that attained in the birds fed the highest level of protein without methimazole. Birds fed methimazole for an initial 21-day period (7 to 28 d of age) had greater lipogenic rates (P < 0.05) at 49 d than did their control counterparts. In contrast, methimazole increased (P < 0.05) abdominal fat pad (AFP) lipoprotein lipase (LPL) at both age periods, indicating increased ability by the AFP to remove triglycerides from systemic circulation. Observations at 49 d suggest that perturbations in the thyroid of the young bird may substantially change metabolism in later life. Results also show that obesity in hypothyroid birds cannot be explained by increases in de novo lipogenesis, but probably relates to changes in LPL activity.

Adipose Tissue↗

PubMed2001

Dietary adrenergic active compounds and the response of broilers to isoproterenol and cyclic adenosine monophosphate in vitro.

Broiler chickens, growing from 7-28 days of age, were fed diets containing 18% protein and 0, 1, 10 or 100 mg/kg yohimbine (alpha 2-adrenergic antagonist) or metaproterenol (beta-adrenergic agonist) to determine the role of adrenergic agents in the regulation of feeding behavior and metabolism. Data from this experiment suggest that beta-adrenergic agonists have slight effects on feed intake, growth and more pronounced effects on metabolism in the broiler chicken. In vitro lipogenesis (IVL) was determined by incubating liver explants for 2 h at 37 degrees C in the presence of cAMP or isoproterenol (ISO) and [2-14C]acetate and by measuring acetate incorporation into total hepatic lipid. Metaproterenol and yohimbine (100 mg/kg) depressed growth from 7 to 28 days. Both metaproterenol and yohimbine (100 mg/kg) decreased (P < 0.05) IVL compared to controls. These dietary additions also decreased (P < 0.05) hepatic malic enzyme activity without affecting the activities of either isocitrate dehydrogenase or aspartate aminotransferase.

Adrenergic alpha-Antagonists↗

PubMed2000

Supplemental triiodothyronine, feeding regimens, and metabolic responses by the broiler chicken.

There are conflicting results concerning the role of the thyroid hormones in lipid metabolism. The experiments in this report were designed to examine the role of T(3) in modifying responses obtained by shifting birds from moderate to low protein diets. Birds were grown from 7 to 28 d on a diet containing 18% protein. At this time, birds were switched to a diet containing 12% protein +/- T(3) The switch was accomplished either immediately or after a 24 hr fast. Measurements taken included in vitro lipogenesis (IVL), hepatic enzyme activities and plasma metabolites and thyroid hormones. Simply switching to birds to the low protein diet increased IVL, but rates were similar for three days following the switch. Feeding T(3) in this same regimen resulted in lower, but again, constant rates of IVL. In contrast, although switching protein levels after a 24 hr fast increased IVL, the rate after two days of refeeding was nearly double that following one day. This accentuated response was somewhat attenuated by including T(3) in the diet. Neither fasting nor refeeding altered plasma T(3) relative to ad libitum values. Supplemental dietary T(3) increased plasma T(3) and results were not affected by feeding regimens. Plasma T(4) was greatest in birds fasted for 24 hr and least in birds fed T(3) suggesting that feeding regimens may regulate the conversion of T(4) to T(3) It is suggested from this study that some of the effects of alterations in dietary feeding regimens can be modulated by T(3)

Animals↗

PubMed2000

Altered chicken thyroid hormone metabolism with chronic GH enhancement in vivo: consequences for skeletal muscle growth.

In contrast to most vertebrates, GH reportedly has no effect upon somatic growth of the chicken. However, previous studies employed only one to two dosages of the hormone, and limited evidence exists of a hyperthyroid response that may confound its anabolic potential. This study evaluated the effects of 0, 10, 50, 100 and 200 microgram/kg body weight per day chicken GH (cGH) (0-200 GH) infused i.v. for 7 days in a pulsatile pattern to immature, growing broiler chickens (9-10 birds/dosage). Comprehensive profiles of thyroid hormone metabolism and measures of somatic growth were obtained. Overall (average) body weight gain was reduced 25% by GH, with a curvilinear, dose-dependent decrease in skeletal (breast) muscle mass that was maximal (12%) at 100 GH. This profile mirrored GH dose-dependent decreases in hepatic type III deiodinase (DIII) activity and increases in plasma tri-iodothyronine (T(3)), with bot! h also maximal (74 and 108% respectively) at 100 GH. No effect on type I deiodinase was observed. At the maximally effective dosage, hepatic DIII gene expression was reduced 44% versus controls. Despite dose-dependent, fold-increases in hepatic IGF-I protein content, circulating IGF-I was not altered with GH infusion, suggesting impairment of hepatic IGF-I release. Significant, GH dose-dependent increases in plasma non-esterified fatty acid and glucose, and overall decreases in triacylglycerides were also observed. At 200 GH, feed intake was significantly reduced (19%; P<0.05) versus controls; however, additional control birds pair-fed to this level did not exhibit any responses observed for GH-treated birds. The results of this study support a pathway by which GH impacts on thyroid hormone metabolism beginning at a pretranslational level, with reduced hepatic DIII gene expression, translating to reduced protein (enzyme) ex! pression, and reflected in a reduced level of peripheral T(3)-degrading activity. This contributes to decreased conversion of T(3) to its inactive form, thereby elevating circulating T(3) levels. The hyper-T(3) state leads to reduced net skeletal muscle deposition, and may impair release of GH-enhanced, hepatic IGF-I. In conclusion, GH has significant biological effects in the chicken, but profound metabolic actions predominate that may confound positive, IGF-I-mediated skeletal muscle growth.

Adipose Tissue↗

PubMed1999

Influence of dietary protein on insulin-like growth factor binding proteins in the chicken.

We determined the effect of dietary protein on the distribution of insulin-like growth factor (IGF) binding proteins in chicken plasma. Three groups of male broilers (n = 6 per group) were fed (ad libitum) isocaloric diets containing 12, 21 or 30% dietary protein. Birds were fed respective diets beginning at 7 days of age and killed at 28 days. No differences were observed between adequate (21%) and high (30%) protein intakes for any of the parameters investigated (growth criteria, plasma levels of IGF-I, growth hormone or IGF-binding proteins). Feeding protein deficient diets (12%) resulted in a 34% decrease in body weight, 17% decrease in feed intake and a 39% increase in feed/gain ratio. IGF-binding proteins in plasma samples were separated by SDS-PAGE and transferred to nitrocellulose sheets. Nitrocellulose blots were probed with [125I]chicken IGF-II. Four regions of binding activity corresponding to 70, 43, 30 and 24 kDa were observed in all samples. Birds consuming 12% dietary group protein had less than 50% of the 43-kDa binding activity of birds consuming 21 or 30% dietary protein. The 30-kDa binding activity was 42% lower in the 12% dietary protein group compared to birds consuming adequate protein. In contrast, 70- and 24-kDa binding activities were not influenced by dietary protein. Chickens consuming 12% dietary protein had higher levels of growth hormone and lower levels of IGF-I than those consuming 21 or 30% dietary protein. These data indicate that in chickens, the circulating levels of at least two independent IGF-binding proteins are influenced by dietary protein.

Animals↗

PubMed1999

New insights into the mechanism and actions of growth hormone (GH) in poultry.

Despite well documented anabolic effects of GH in mammals, a clear demonstration of such responses in domestic poultry is lacking. Recently, comprehensive dose-response studies of GH have been conducted in broilers during late post-hatch development (8 to 9 weeks of age). GH reduced feed intake (FI) and body weight gain in a dose-dependent manner, whereas birds pair-fed to the level of voluntary FI of GH-infused birds did not differ from controls. The reduction in voluntary FI may involve centrally mediated mechanisms, as hypothalamic neuropeptide Y protein and mRNA were reduced with GH, coincident with the maximal depression in FI. Growth of breast muscle was also reduced in a dose-dependent manner. Circulating IGF-I was not enhanced by GH, despite evidence that early events in the GH signaling pathway were intact. A GH dose-dependent increase in circulating 3,3',5-triiodothyronine(T3) paralleled decreases in hepatic 5D-III monodeiodinase activity, whereas 5'D-I activity was not altered. This confirms that a marked hyperthyroid response to GH occurs in late posthatch chickens, resulting from a decrease in the degradative pathway of T3 metabolism. This secondary hyperthyroidism would account for the decreased skeletal muscle mass (52) and lack of enhanced IGF-I (53) in GH-treated birds. Based upon these studies, it is now evident that GH does in fact have significant effects in poultry, but metabolic responses may confound the anabolic potential of the hormone.

Animals↗

PubMed1999

Dietary fat and triiodothyronine (T3) interactions in the broiler chicken.

Male, Indian River, broiler chickens growing from 7 to 28 d were fed on diets containing 180 g crude protein, 300, 600 or 1200 kcal fat calories and 0 or 1 mg T3/kg diet. Birds were bled and sacrificed at d 28, 29 and 30. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and feed consumption and hepatic enzyme activities. Plasma metabolites as well as thyroid hormones were also determined. Dietary fat levels did not influence growth or feed intake. In contrast, T3 decreased growth and feed intake by 25% without altering the efficiency of feed utilization. Dietary T3 and additional fat decreased IVL and lipogenic enzyme activities. Dietary T3 increased plasma T3 and decreased plasma T4. Dietary fat energy levels had no effect upon plasma thyroid hormone levels. Although both additional dietary fat and T3 modify broiler lipid metabolism, there was no additional treatment effect when high-fat diets were supplemented with T3. In contrast to previous reports, T3 did not increase any parameter associated with lipid metabolism.

Animal Feed↗

PubMed1999

Dietary fat and protein interactions in the broiler.

An experiment was conducted to study the interrelationships between dietary fat and protein levels in the regulation of lipid metabolism in the broiler chicken. Birds were fed diets containing 300, 600, or 1,200 kcal ME from fat (corn oil) with either 124 or 190 g CP/kg. Two additional experimental diets contained 234 or 285 g CP and 300 kcal ME from fat. Regardless of fat level, birds fed the diets containing 124 g CP/kg weighed less and were less efficient than birds fed diets containing 190 g CP/kg. The diet containing 600 kcal as fat decreased lipogenesis and malic enzyme activity (P < 0.05) in birds fed the diet containing 190 g CP/kg diet, but not in birds fed the diet containing 124 g CP/kg. Birds fed the latter level of protein required at least 1,200 kcal as fat to express any significant decrease in lipogenesis or malic enzyme activity (P < 0.05). Dietary fat did not affect plasma levels of triiodothyronine (T3), thyroxine (T4), or insulin-like growth factor-I (IGF-I). Feeding diets containing 124 g CP/kg resulted in decreased plasma T4 and IGF-I and elevated T3 (P < 0.05). Increasing dietary protein (compared to increasing dietary fat) increased body weights, IGF-I, T4 and decreased lipogenesis, malic enzyme activity, and T3. Both of these regimens involve decreasing dietary carbohydrate at equal rates, but results differed. Although replacement of dietary carbohydrates with either fat or protein reduce precursors for fat synthesis, both energy sources have additional unique effects on metabolism. Dietary protein levels modulate metabolic effects of dietary fat.

Animal Feed↗

PubMed1999

Dietary protein effects on the broiler's adaptation to triiodothyronine.

The purpose of this experiment was to study the effects of dietary protein on metabolic adaptations in birds given triiodothyronine (T3) at 28 d of age. Knowledge about the role of dietary protein in thyroid metabolism is lacking. Male broiler chickens were fed diets containing either 120 or 300 g crude protein/kg from 7 to 28 d. At this time, one-half of each group was given that diet supplemented with 1 mg/kg T3. Birds were sampled at 0, 2, 5, 7, 9 and 12 d following the initiation of the T3 treatments. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities and plasma thyroid hormones and metabolites. As expected, IVL was greater at 28 d in birds fed the lower level of protein. Moreover, when T3 was added to either diet, IVL decreased by 50% after 5 d. Plasma IGF-I and T4 were greater while T3 and GH were less when birds were fed the higher level of crude protein. Plasma T3 increased and T4 decreased 3 d following the addition of T3 to diets containing either level of crude protein. Most metabolic changes in response to feeding T3 occurred within 2 to 5 d, suggesting that changes in intermediary metabolism preceded morphological changes that we have previously seen. In addition, dietary protein levels may not affect adaptive responses to T3.

Adaptation, Physiological↗

PubMed1998

Further studies on carry-over effects of dietary crude protein and triiodothyronine (T3) in broiler chickens.

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing either 120 or 210 g crude protein and 0 or 1 mg triiodothyronine (T3)/kg diet to study in vitro lipogenesis (IVL). In addition, a carry-over period (180 g crude protein/kg diet from 28 to 40 d of age) was used to test the persistence of prior treatment effects. The higher protein level increased, but T3 decreased (P < 0.01) growth and feed consumption at 28 d of age. The lower protein level increased (P < 0.05) and T3 decreased IVL in 28-d-old chickens. These effects were only sustained for 6 d following the switch to a common diet at 28 d. IVL at 40 d of age was not affected by either crude protein or T3 fed during the 7-28 d period. The higher protein level increased plasma insulin-like growth factor-1 during the period from 7 to 28 d; however, this effect lasted for only 6 d following the switch to a common diet. Plasma growth hormone (GH) at 28 d of age was inversely related to dietary protein level. Changing to a common level of crude protein did not change plasma GH values at 12 d, indicating that the nutritional state of the young chicken may affect GH at a later period of life. Metabolic changes noted in this study were rapid and maintained for a short period of time following the feeding of a common diet.

Analysis of Variance↗