Effect of caponization and testosterone implantation on hepatic lipids and lipogenic enzymes in male chickens

This study was conducted to determine the role and effects of testosterone in lipogenesis by measuring and analyzing the lipid composition and lipogenic enzyme activity of livers from capons treated with various doses of exogenous testosterone implant. Healthy and uniform male Single Comb White Leghorn chickens were caponized at 12 wk of age. Sixteen-week-old capons were randomly selected for a 10-wk experiment. Fifteen intact males and 15 capons were used for trial 1. In trial 2, 10 sham-operated males and 40 capons were used. The capons were randomly divided into 4 independent treatments with sialistic implants of cholesterol (1.62 mm i.d., 3.6 mm o.d., 9.24 +/- 0.36 mg; CHOL), low testosterone (1 mm i.d., 3 mm o.d., 5.88 +/- 0.23 mg), medium testosterone (1.62 mm i.d., 3.16 mm o.d., 9.81 +/- 0.17 mg), or high testosterone (2 mm i.d., 4 mm o.d., 16.7 +/- 0.24 mg). In trial 1, the results showed that caponization increased total hepatic lipid and triacylglycerol contents and decreased the nonesterified fatty acid content (P < 0.05) compared with the intact male. Meanwhile, caponization increased nicotinamide adenine dinucleotide phosphate -malic dehydrogenase (MDH) activity and MDH mRNA content (P = 0.09) simultaneously. In trial 2, comparing treatments with the various implantation doses of testosterone, the liver triacylglycerol content of capons the medium-dose implantation was decreased as compared with those receiving CHOL (P < 0.05). The total lipid and phospholipid contents of liver were decreased in capons receiving the high-dose implantation (P < 0.05), whereas the relative weight and nonesterified fatty acid content were increased (P < 0.05) and reached the same level as those in the sham treatment (P > 0.05). With an increased implantation dose, MDH activity of capons receiving the medium dose or higher was not different from those receiving the CHOL and sham treatments (P > 0.05). The increase in MDH activity at the transcriptional and translational levels suggests that caponization may positively regulate hepatic lipogenesis. In contract, implantation of testosterone up to the threshold concentration depressed hepatic lipogensis and lipid accumulation.

Caponization and testosterone implantation effects on blood lipid and lipoprotein profile in male chickens

To understand the role of lipid metabolism in increasing body fat accumulation after caponization of male chickens, trials were conducted to determine the effects of levels of testosterone implantation on lipoprotein composition. Male chickens were caponized at 12 wk and selected at 16 wk for a 10-wk feeding experiment. Fifteen male and 15 caponized (capon) chickens were used in trial 1. Ten sham operated chickens (sham) and 40 capons were randomly divided among 4 treatments in trial 2; the treatments were as follows: implantation of cholesterol (1.62 mm i.d. x 3.16 mm o.d., 9.24+/-0.36 mg) or implantation of testosterone at low (1 mm i.d. x 3 mm, o.d., 5.88+/-0.23 mg), medium (1.62 mm i.d. x 3.16 mm, o.d., 9.81+/-0.17 mg), or high (2 mm i.d. x 4 mm, o.d., 16.7+/-0.24 mg) dose. The results of trial 1 showed that caponization decreased (P < 0.05) blood testosterone concentrations and increased (P < 0.05) abdominal fat weight and relative abdominal fat weight in capons. Caponization also increased low density lipoprotein (LDL), high density lipoprotein (HDL), LDL protein, and HDL protein and decreased LDL-free cholesterol (LDL-FC), HDL-FC, and HDL-phospholipid (HDL-PL) percentages (P < 0.05). In trial 2 capons implanted with increasing testosterone levels exhibited proportional increases in blood testosterone concentration, although blood testosterone concentration in implanted capons were not fully restored to those of the sham group. High dose testosterone implantation inhibited abdominal fat accumulation and increased glucose and glycerol concentrations compared with the cholesterol implantation. Caponization of male chickens decreased the androgen level and increased the blood triacylglyceride content. Caponization also changed the lipoprotein profiles, which resulted in increased lipid storage capacity. The testosterone concentration, therefore, must achieve threshold concentrations to inhibit lipid accumulation in the testosterone implanted capon.

Effects of sources of protein and enzyme supplementation on protein digestibility and chyme characteristics in broilers

1. The purpose of this study was to evaluate the effects of protein source and enzyme supplementation on protein digestibility and chyme characteristics in broilers. 2. One hundred and twenty growing (13 d old) and 60 finishing (34 d old) Arbor Acre strain commercial male broilers were selected and placed into individual metabolic cages. 3. The experiment was a 5 x 2 factorial arrangement with 5 different sources of protein: casein, fish meal, soybean meal (SBM), soy protein concentrate (SPC), maize gluten meal (MGM) and two levels of protease (bromelain), 0 and 65 CDU/kg diets. 4. The diets were iso-nitrogenous and semi-purified, with Cr2O3 as an indicator for determination of ileal digestibility and chyme characteristics. 5. Apparent ileal protein digestibility (AIPD) in both growing and finishing chickens was highest on the casein diet, followed by fish meal, SBM, SPC and MGM. 6. Enzyme inclusion did not improve protein digestibility, but significantly decreased the digesta pH value in the gizzard and increased pH in the ileum in the 3-week-old broilers. 7. The digesta pH values in the gizzard and duodenum were significantly lower in the SBM and fish meal groups compared with the other protein groups. The molecular weight distribution pattern of the soluble protein in the chyme of the gastrointestinal (GI) segments showed a similar trend, regardless of the enzyme inclusion or the stage of growth. 8. The molecular weight profile of soluble protein changed dynamically in the casein fed broilers from the gizzard to ileum and the low molecular weight proteins, < 7 kDa, reached maximum levels at the ileum. The molecular weight profile of the soluble protein in the SBM and SPC changed between the jejunum and the ileum and in the intermediate molecular soluble protein weight (7 to 10 kDa) was significantly decreased. This indicated that the hydrolysis process began from the middle to the posterior end of the small intestine. 9. Similar profiles were also shown with fish meal protein. The pattern of distribution, however, did not show any prominent change in the GI segments of the MGM group. 10. The pepsin, trypsin and chymotrypsin protease activity in the gizzard and duodenum were highest in the casein group and lowest in the MGM group as compared with the other protein groups. 11. The rate change in the patterns of molecular weight distribution in soluble protein and the digestive enzyme activity provide indications of the partial digestibility of different protein sources. The exogenous enzyme, bromelain, did not show any beneficial effect on protein digestion.