R. W. Rosebrough

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.

Protein and energy relations in the broiler chicken. 8. Comparison involving protein- and lysine-adequate and inadequate diets on lipid metabolism.

Chickens were fed on diets containing either 12.8 MJ, 150 g crude protein (nitrogen x 6.25)/kg or 12.8 MJ, 200 g crude protein/kg to determine differences in metabolism. The diet containing 12.8 MJ, 150 g crude protein/kg contained either 8 or 12 g lysine/kg. Treatment variables examined in vitro were lipogenesis, glucose production and hepatic enzyme activities to compare metabolism in chicks fed on a low-protein, lysine-supplemented diet and a diet formulated to contain the required amount of lysine from intact protein. Growth was similar in chicks fed on diets containing either 12.8 MJ, 154 g crude protein with 12 g lysine/kg or 12.8 MJ, 200 g crude protein/kg. Net glucose production was greater (P less than 0.05) in liver explants from chickens fed on diets containing either 12.8 MJ, 154 g crude protein with 12 g lysine/kg or 12.8 MJ, 200 g crude protein/kg than in explants from chickens fed on 12.8 MJ, 150 g crude protein with 8 g lysine/kg. Pyruvate use for glucose production was greater (P less than 0.05) in chickens fed on a diet containing 12.8 MJ, 150 g crude protein with 8 g lysine/kg. The findings from the present study suggest that crystalline and natural lysine additions to chick diets may influence metabolism differently.

Effect of early feed restriction in male broiler chicks on plasma metabolic hormones during feed restriction and accelerated growth

1. Plasma GH was greater (P less than 0.05) on day 12 in ad libitum-fed birds compared to restricted chicks. Conversely, maximum GH levels were found to occur in the nutrient restricted chicks during the period of accelerated growth (day 42). 2. A significant decline in circulating insulin concentrations with advancing age was evident in both ad libitum-fed and restricted chicks. 3. Feed restriction significantly suppressed circulating T3 in restricted chicks, with concentrations returning to control levels upon refeeding. 4. A significant increase in T4 with advancing age was evident in both treatment groups, with T4 being significantly greater in controls compared to restricted chicks at 54 days of age.

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 5D-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.

Crude protein and supplemental dietary tryptophan effects on growth and tissue neurotransmitter levels in the broiler chicken

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing 120, 210 and 300 g crude protein/kg diet and 0, 1.67 or 16.7 g added tryptophan (TRP)/kg diet. The hypothesis tested was that crude protein levels and TRP would affect both growth and neurotransmitter metabolism. Heart, brain and pancreatic neurotransmitter (noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxy-indole-3-acetic acid (5-HIAA)) concentrations were determined by HPLC separation and electrochemical detection. Malate dehydrogenase (2-oxoglutarate decarboxylating) (NADP+) (MDH(NADP+); EC 1.1.1.40), isocitrate dehydrogenase (NADP+) (ICD(NADP+); EC 1.1.1.42) and aspartate aminotransferase (AAT; EC 2.6.1.1) activities were also measured. Supplemental TRP decreased growth and feed intake. Increasing dietary crude protein decreased MDH(NADP+), but increased (ICD(NADP+) and AAT activities. Additional dietary TRP decreased MDH(NADP+) activity, but had no effect on other enzyme activities. Cardiac NA concentrations were directly related to dietary crude protein levels while pancreatic levels were inversely related. An increase in dietary crude protein decreased both brain NA and DA. Supplemental dietary TRP increased both 5-HIAA and 5-HT. Changes in feed intake caused by different levels of both dietary crude protein and TRP are accompanied by altered levels of neurotransmitters. The present study indicates that much larger amounts of TRP are required to make simultaneous changes in feed intake and neurotransmitters.

Influence of early plane of nutrition on enzyme systems and subsequent tissue deposition

The occurrence of compensatory growth is of great significance because of its potential effects on body composition (muscle versus adipose development) at maturity. Studies have been conducted with chickens in which feed intake is limited to meet their maintenance energy requirements for 6-d period, beginning 6-d post-hatch. Following realimentation, the birds undergo compensatory growth that results in a greater proportion of lean versus adipose tissue at 8 wk of age compared to birds given ad libitum access to feed. During energy restriction, hepatic enzyme activity associated with lipogenesis and in vitro lipogenesis were suppressed, followed by an over-shoot at realimentation, and a subsequent suppression in activity during compensatory growth. The concentrations of metabolic hormones were not effected by nutrient restriction. Early post-hatch feed restriction was found to delay the proliferation of adipocytes but did not affect the development of normal adipocyte size. In summary, early feed restriction of short duration in chickens induces permanent changes in the mechanisms responsible for adipose tissue development.

CHICKEN HEPATIC METABOLISM IN VITRO. PROTEIN AND ENERGY RELATIONS IN THE BROILER CHICKEN--VI. EFFECT OF DIETARY PROTEIN AND ENERGY RESTRICTIONS ON IN VITRO CARBOHYDRATE AND LIPID METABOLISM AND METABOLIC HORMONE PROFILES*

1. Ross male broiler chicks growing from 14 to 28 days of age were fed 14 and 20% protein diets (4 kcal day-1/body wt0.66) or 20 and 28% protein diets (2.8 kcal day-1/body wt0.66) in a 2 x 2 factorial arrangement to determine the effects of protein and energy intakes on in vitro lipogenesis (IVL) and net glucose production (NGP). Plasma concentrations of insulin, glucagon, thyroid hormones (T3 and T4) and somatomedin-C (Sm-C) were estimated by radioimmunoassay. 2. There was a significant (P less than 0.05) decrease in IVL in the chicks given the higher daily protein intake. 3. The higher protein intake increased (P less than 0.05) NGP while the lower energy intake decreased (P less than 0.05) NGP. 4. Insulin, both thyroid hormones and Sm-C were affected by dietary energy and protein intakes.

In vitro lipid metabolism, growth and metabolic hormone concentrations in hyperthyroid chickens

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing energy:protein values varying from 43 to 106 MJ/kg protein and containing 0 or 1 mg triiodothyronine (T3)/kg diet to study effects on growth, metabolic hormone concentrations and in vitro lipogenesis. In vitro lipid synthesis was determined in liver explants in the presence and absence of ouabain (Na+, K(+)-transporting ATPase (EC 3.6.1.37) inhibitor) to estimate the role of enzyme activity in explants synthesizing lipid. Growth and feed consumption increased (P < 0.01) when the energy:protein value decreased from 106 to 71 MJ/kg protein; however, both variables decreased as the value was further decreased from 53 to 43 MJ/kg protein. Triiodothyronine depressed (P < 0.01) growth, but not food intake. Large energy:protein diets (> 53 MJ/kg protein) and dietary T3 lowered (P < 0.01) plasma growth hormone. Large energy:protein diets (> 53 MJ/kg protein) increased (P < 0.01) lipogenesis, plasma growth hormone (GH) and decreased plasma insulin-like growth factor 1 (IGF-1). Also, T3 decreased plasma GH, IGF-1 in vitro lipogenesis. Ouabain inhibited a greater proportion of in vitro lipogenesis in those explants synthesizing fat at a high rate. Both dietary T3 and in vitro ouabain decrease lipogenesis, but, when combined, the effects are not cumulative.

The role of feeding regimens in regulating metabolism of sexually mature broiler breeders

A trial was conducted to determine the effects of different rearing feed regimens on plasma hormone and metabolite levels and hepatic lipid metabolism and gene expression on sexually mature broiler breeders. Cobb 500 birds were divided into 2 groups at 4 wk and fed either an everyday (ED) or skip-a-day (SKP) regimen. At 24 wk of age, all birds were switched over to an ED regimen. At 26.4 wk, breeder hens were randomly selected and killed at intervals after feeding. Livers were sampled from 4 hens at 4-h intervals for 24 h for a total of 28 samples per treatment. Blood was sampled from 4 hens per sampling time; sampling times were 0, 30, and 60 min and 2 and 4 h after feeding and then every 4 h up to 24 h for a total of 36 samples per treatment. Main feeding regimen, time, and interaction effects were analyzed. Significant interaction effects were found between time and feeding regimen for acetyl-coenzyme A carboxylase and malic enzyme mRNA expression. The peak for acetyl-coenzyme A carboxylase expression was higher in ED-reared birds, whereas the peak for malic enzyme expression was higher in SKP-reared birds. Overall, plasma levels of insulin-like growth factor-II were higher in SKP-reared birds. Overall, plasma corticosterone levels were also higher in SKP-reared birds and significant interaction effects between time and feeding regimen were seen. The expression of apolipoprotein A1 was significantly higher in ED-reared birds: significant interaction effects were also noted. Other researchers also found some of the differences observed in the present study in 16-wk-old pullets. In summary, different feeding regimens alter metabolic responses, some of which carry over into sexual maturity.

In vivo measurement of body composition of chickens using quantitative magnetic resonance

Quantitative magnetic resonance (QMR) is a nuclear magnetic resonance-based method for measuring the fat, lean, and water content of the total body of the live animal. The purpose of this study was to evaluate the use of QMR for measuring the body composition of chickens while comparing QMR results to those obtained by dual x-ray absorptiometry (DXA) and chemical analysis (CA). A total of 191 birds were scanned live (nonanesthetized) by QMR, killed, and then scanned by DXA. The birds were Ross 708 broiler chickens and ranged in weight from 786 to 3,130 g. In addition, 48 of the carcasses were chemically analyzed for total body lipid, water, and ash content. Compared with CA, QMR underestimated the percentage of total body fat by 34% whereas DXA overestimated the percentage of fat by 50% (10.35 ± 3.35 by CA vs. 6.73 ± 3.90 by QMR and 15.55 ± 4.01 by DXA; P < 0.05). Both QMR and DXA measurements of percentage total body fat were highly correlated with the CA measurement (R(2) = 0.94 and 0.68, respectively). Both QMR and DXA estimates of total body water were close to the CA measurement (1,166 ± 277 g by CA vs. 1,214 ± 279 g by QMR and 1,217 ± 255 g by DXA; P > 0.05), with R(2) values of 0.90 and 0.91, respectively. Based on regression analysis, when prediction equations were applied to the entire group of birds, the QMR and DXA measurements of total body water and total body lean mass were in good agreement, with no significant difference (1,125 ± 244 g vs. 1,135 ± 246 g and 1,377 ± 311 g vs. 1,403 ± 309 g, respectively; P > 0.05) and highly correlated (R(2) = 0.97 for both). Likewise, the QMR measurement of total body fat agreed closely with that measured by DXA (164 ± 48 g and 167 ± 47 g, respectively) and was highly correlated (R(2) = 0.72). The results of this study demonstrate that with proper calibration, both QMR and DXA can provide accurate measurements of the body composition of chickens. The major advantage of the QMR method is that no anesthesia is required, thus facilitating the ease of measurement and repeated measurements.