Effect of age, sex, genotype and environment on fat deposition in broiler chickens—A review

Scanning electron microscopic observations on the intestinal villi in growing White Leghorn and broiler chickens from 1 to 30 days of age

1. To obtain intestinal morphological data demonstrating the faster growth rate in broiler (BR) than in White Leghorn (WL) chickens, villi of the duodenum, jejunum and ileum were examined from 1 to 30 d of age by scanning electron microscopy. 2. At the first day after hatching, villi of each intestinal segment showed a finger-like shape in both breeds. Villi developed to a plate-like shape in the duodenum, a wave-like shape in the jejunum and a tongue-like shape in the ileum at 30 d of age via the common plate-like villi at 10 d of age. The fundamental villous shape and arrangement seem to be accomplished by 10 d of age; two types of obliquely elongated plate-like villi showed a zigzag arrangement, adjoining at an angle of 40 degrees to 60 degrees like an oblique T-shape. It is suggested that such a villous arrangement would be more effective for nutrient absorption by inducing a long zigzag flow of ingesta. 3. Compared with WL, even at the first day after hatching BR had many more developed epithelial cell protrusions over the whole apical surface of the duodenal villi. In WL the protrusions were not so apparent and located only in the central area of the villous tip. Furthermore, at 10 d of age BR showed more developed and larger villi, many wider microvilli at the apical portion of villi and more active extrusions of epithelial cells from the tip of the duodenal and jejunal villi. 4. These morphological characteristics of villi in early life in BR suggest a greater absorptive surface area and a more active intestinal function, permitting the faster growth rate of BR immediately after hatching.

Effect of dietary concentrations of fat and energy on fat deposition in broilers divergently selected for high or low abdominal adipose tissue

1. Fat deposition in abdominal, mesenterial, sartorial and gizzard adipose tissues (AT), liver, breast muscle, skin and carcase was studied in male broilers, selected for high (HF) and low (LF) abdominal fat and fed on diets differing in energy density and total fat content. 2. There were no significant differences in body weight in the experimental groups. The relative weight (g/kg body weight) of the dissected adipose tissues was higher in HF than in LF birds. Fat concentration in the AT (sartorial excepted), skin and body was higher in the HF compared with the LF birds. The lines did not differ significantly in liver and breast muscle fat content. 3. Abdominal AT was affected by selection or dietary fat more than other AT and total body fat. 4. In the HF birds increasing energy density from 12.3 to 13.4 MJ/kg (dietary fat kept constant: 5.46 g/MJ) significantly increased the weight of the abdominal, mesenterial and sartorial AT. Increasing dietary fat (at both energy densities) decreased the weight of the AT, whereas increasing both energy and fat did not affect it. In the LF birds, similar but milder and insignificant trends were observed. It is suggested that this interaction has biological significance.

Lack of interactive effect of nicarbazin and dietary energy-to-protein ratio on performance and abdominal fat pad weight of broiler chicks

An experiment was carried out, in a factorial arrangement, with female broiler chicks during the period from 8 to 49 days of age. Combined effects were evaluated of dietary energy-to-protein ratio (E:P; 130 vs. 170 from 8 to 28 days of age and 140 vs. 190 from 28 to 49 days of age) and nicarbazin supplementation (0 vs. 125 mg/kg) on performance and fattening. At 49 days of age, feed intake was not affected either by dietary E:P or by nicarbazin supplementation. The latter significantly depressed weight gain (P less than .01) and feed efficiency (P less than .001), but did not affect abdominal fat pad weight. The wide E:P significantly decreased feed efficiency (P less than .01) and increased abdominal fat pad weight (P less than .001). Neither of the parameters was affected by the interaction between nicarbazin and dietary E:P. It was suggested that the growth-depressing effect of nicarbazin was due to its effect on increasing the metabolic rate, an increase which did not affect fattening as measured by abdominal fat pad weight.

Estimates of genetic parameters in turkeys. 2. Body weight and carcass characteristics

Data were taken from 1,088 individuals--504 females (F) and 584 males (M)--produced by 34 sires and 168 dams from a randombred control line (RBC2) of turkeys maintained at the Ohio Agricultural Research and Development Center, Wooster, OH. Turkeys were used to estimate genetic and phenotypic parameters among 16-wk body weight and a number of body composition characteristics. Heritabilities (h2) were estimated from sire components of variance for 16-wk weights of muscles of breast (BM: F = .08, M = .35); thigh (TM: F = .12, M = .17); and drum (DM: F = .30, M = .44); weights of leaf fat (LF: F = .13, M = .51) and total abdominal fat (AF: F = .21, M = .55); and total percentage carcass fat (%F:F = .06, M = .24), percentage protein (F = .07, M = .20), and percent moisture (F = nonestimable, M = .11). The h2 of percentage carcass ash was nonestimable from both data sets due to negative estimates of the sire variance components. Due to the non-normal distributions of some of the fat measures, the fat measure data were converted to natural logarithms. Genetic estimates from the transformed data were similar to those from the nontransformed data. Genetic correlation (rG) estimates indicated a positive genetic association between body weight (BW) and all the fat characteristics measured. The BW was highly correlated with BM (F = .48, M = .86), TM (F = .81, M = 1.01), and DM (F = 1.04, M = .70). However, BW was correlated to a lesser degree with LF (F = .02, M = .27), AF (F = .25, M = .32), and %F (F = .93, M = .50). The BM was only moderately correlated with TM (F = .43, M = .28) and DM (F = .73, M = .27). The TM and DM were highly correlated (F = 1.02, M = .84). The existence of these correlations, which are less than unity, indicate that selection for BW alone will lead to increasing levels of fat in commercial turkeys, and to disproportionate increases in breast vs. leg muscles.

Evaluation of bioelectrical impedance for estimation of body composition in 8-week-old broilers

Bioelectrical measurements (resistance and reactance) were obtained from 35 male and 45 female 8-wk-old broilers using a tetrapolar technique. Body weight, dorsal body length (BL), thigh diameter (TD), and proximate analysis (percentage fat, protein, and moisture) were also ascertained. Twenty birds of each sex were randomly assigned to a calibration group and the remaining birds to a prediction group. Data for birds in the calibration group were used to generate regression equations for estimating whole body composition. Data from birds in the prediction group were collected for possible validation of the calibration equations. Repeatability values for resistance (Re), reactance (Xc), and composition variables were equal to or greater than .78. Coefficients of determination (R2) among percentage body moisture, fat, and protein and body and bioelectrical measurements in males were .41, .36, and .24 (P less than .05), respectively. Percentage moisture in females was predicted by TD2/BL (R2 = .22, P less than .05). Body composition was not adequately predicted by variables measured in this study.

Fat deposition in a broiler sire strain. 4. Performance of broiler progeny of four differently selected sire lines

Cocks from four lines selected for a low amount of abdominal fat (AF), a favorable feed conversion ratio (FC), and high body weight after restricted (GR) or ad libitum (GL) feeding were mated to commercial broiler breeder hens. A total of 3,600 broiler progeny in three hatches from these matings was reared by line in litter pens. At 41 days of age GR and GL line progeny had significantly heavier body weights, poorer feed conversion ratio, and higher percentages of abdominal fat than AF and FC line progeny. At comparable body weights (AF, 1,893; FC 1,918; GR, 1,848; and GL, 1,897 g) feed conversion was most favorable for FC line progeny (1.72), AF and GL line progeny did not differ (1.77), and GR line progeny had the poorest feed conversion ratios (1.79). The AF line progeny had the lowest percentage abdominal fat (1.88%), followed by FC line progeny (2.20%), GL line progeny (2.91%), and GR line progeny (3.10%). As in the pure lines, selection for body weight after restricted feeding was not effective in obtaining leaner and more efficient chickens. When compared with differences between pure lines, results of the broiler progeny matings indicate that body weight, feed conversion, and percentage abdominal fat are inherited largely in an additive manner.

Fat deposition in a broiler sire strain. 5. Comparisons of economic efficiency of direct and indirect selection against fatness

In a simulation study, selection for weight gain in a broiler sire strain was compared with 1) one and two stage index selection for weight gain and feed conversion and 2) weight gain, slaughter yield, and percentage abdominal fat. Weight gain per day was assigned an economic value of 1.138 Dutch cents (ct)1/g; feed conversion, -138.18 ct/1.0; slaughter yield, 0 or 7.55 ct/%; and percentage abdominal fat, 0 or -10 ct/%. When selection was completely or almost completely (as in two stage selection) based on weight gain, percentage abdominal fat increased; otherwise it decreased. Weight gain, feed conversion, and slaughter yield improved with all selection methods examined. Due to the high positive correlation between feed conversion and percentage abdominal fat, selection for an index of weight gain and feed conversion gave about the same reduction in percentage abdominal fat as selection for an index of weight gain, slaughter yield, and percentage abdominal fat. Selection response of the four traits was dependent more on selection methods than on sets of economic values. Based on economic values, selection for an index of weight gain and feed conversion gave 1.70 to 3.35 times the financial gain of selection for weight gain only, and selection for an index of weight gain, slaughter yield, and percentage abdominal fat gave 1.15 to 3.12 times that attained by selection only for weight gain. The extra financial gains exceeded by far the estimated additional costs of the index selection methods.

Effect of early nutrition on fattening and growth of broiler chicks at 7 weeks of age

1. Six experiments were carried out with male and female broiler chicks in a factorial arrangement to evaluate the combined effects of fat concentration or energy-to-protein (E:P) ratio in diets fed from 1 to 7 or 14 d of age, and of the E:P ratio in diets fed from 1 or 2 to 7 weeks of age on fattening and performance of the birds. 2. Diets with a wide E:P ratio fed from 1 or 2 to 7 weeks consistently and significantly increased abdominal fat pad size at 7 weeks of age. On the other hand, in 5 of the experiments, the nutritional treatments from 1 to 7 or 14 d did not significantly affect this variable in chicks fed on diets with either the narrow or the wide E:P ratio. 3. Body weights and food utilisation at 7 or 14 d were consistently and significantly improved by increasing dietary fat concentration and using diets with a narrow E:P ratio. However, at 7 weeks of age, in only two of the experiments were body weights still significantly affected by early nutrition. 4. Diets with a wide E:P ratio consistently and significantly reduced the performance of chicks up to 4 weeks of age. Nevertheless, at 7 weeks of age the performance of these chicks tended to be better (at times significantly so) in most of the experiments, despite their excess fattening.