The effect of diet on liver glycogen and body composition in the chick

Issues arising from genetic selection for growth and body composition characteristics in poultry and pigs

Breeders of poultry and pigs have selected for some combination of increased growth rate, decreased fatness and increased muscularity. Increasingly various fitness traits are included in the index used. The consequences of such selection include complex effects on nutritional and environmental requirements, at least some of which are reliably predictable using suitable models. Appropriate changes to the environment and to nutrition as selection proceeds will help to avoid unwanted effects occurring. Among the predictable effects are that higher ratios of nutrients to energy, and lower temperatures, will be needed by the improved genotypes. Selection for growth rate must eventually exhaust the capacity of the support systems – digestive, respiratory, circulatory and excretory – to cope with the increased metabolic rate. Selection for increased yield of valuable parts will cause these problems to occur earlier. While it is possible to predict that these problems will occur it cannot be predicted when they will. Breeders need to be aware of these problems, and use all possible routes to help them in reducing their severity. Where the appropriate actions for fitness selection, and nutritional and environmental modifications, are taken the occurrence of the problems will be delayed.

Effect of dietary energy and protein content on growth and carcass traits of Pekin ducks

A study was conducted to determine the influence of dietary energy and protein concentrations on growth performance and carcass traits of Pekin ducks from 15 to 35 d of age. In experiment 1, 14-d-old ducks were randomly assigned to 3 dietary metabolizable energy (11.8, 12.8, and 13.8 MJ/kg) and 3 crude protein concentrations (15, 17, and 19%) in a 3 × 3 factorial arrangement (6 replicate pens; 66 ducks/pen). Carcass characteristics were evaluated on d 28, 32, and 35. In Experiment 2, 15-d-old ducks (6 replicate cages; 6 ducks/cage) were randomly allotted to the 9 diets that were remixed with 0.5% chromic oxide. Excreta were collected from d 17 to 19, and ileal digesta was collected on d 19 to determine AME_n and amino acid digestibility. In Experiment 1, there were interactions (P < 0.05) between dietary metabolizable energy and crude protein (CP) on body weight (BW) gain and feed intake, wherein BW gain increased more to increasing dietary CP as dietary metabolizable energy increased. However, feed intake was only influenced by dietary crude protein at 11.8 MJ ME/kg and not 12.8 or 13.8 MJ/kg. As dietary CP increased from 15 to 19%, breast meat yield increased by 10.8% on d 35 (P < 0.01). Conversely, increasing metabolizable energy from 11.8 to 13.8 MJ/kg increased dressing percentage, breast skin, and subcutaneous fat, but decreased breast meat yield (% but not weight) on d 35 (P < 0.01). In Experiment 2, the determined AME_n for diets formulated to contain 11.8, 12.8, or 13.8 MJ ME/kg were 11.66, 12.68, and 13.75 MJ/kg, respectively; determined standardized ileal digestible Lys was 0.95, 1.00, and 1.21% for diets formulated to contain 15, 17, or 19% crude protein, respectively. The best body weight gain and feed conversion ratio was obtained when ducks were fed a high dietary AME_n (13.75 MJ/kg) and high CP (19%, 1.21% SID Lys). These results provide a framework for subsequent modeling of amino acid and energy inputs and the corresponding outputs of growth performance and carcass components.

Strain-cross response of heavy male broilers to dietary lysine in the finisher feed: live performance and further-processing yields

A total of 2,560 male broilers from eight commercial strain-crosses were growth to 42 days of age on common starter (1 to 21 days; 23.06% CP, 3,217 kcal ME/kg) and grower (21 to 42 days; 20.14% CP, 3,224 kcal ME/kg) rations. All strain-crossed subsequently received finisher diets (17.95% CP; 3,186 kcal ME/kg) containing either .85 or .95% lysine from 42 to 53 days of age. Further-processing yields were determined on 12 birds per pen, selected within +/- 10% of the replicated pen (8 pens per strain-cross, 40 birds per pen) average weight. The strain-crosses differed significantly (P less than .05) in BW (1, 21, 42, and 53 days), weight gain (WG), feed:gain ratio (1 to 21 and 21 to 42 days), and mortality rate (1 to 21 days). The lysine effect during the finisher period was significant for 53-day BW and WG from 1 to 53 days. Chilled carcass (CC) and abdominal fat (AF) weights, CC yield (percentage, excluding AF), AF yield (percentage of CC weight), Pectoralis major, Pectoralis minor, total deboned breast (TDB), drumstick, thigh, wing, and residual "cage" and skin yields varied among the strain-crosses. A significant weight and yield response to lysine was observed for TDB. Variation observed among strain-cross in live performance, further-processing yields, and response to additional lysine is attributed to differences in rate of growth and degree of maturity at market age. Furthermore, the lysine requirement during the finisher period for optimum breast meat yield may be higher than that recommended by the National Research Council in 1984.

Nutritional effects on the growth and fatness of broilers

1. Broiler chickens given diets high in protein, or choice-fed on a high protein balancer, had much lower abdominal fat contents than those reported in many recent experiments. The values for males were 10.8 g/kg liveweight at 56 d at 2.43 kg liveweight in one experiment in Scotland and 16.0 g/kg liveweight at 42 d at 1.93 kg liveweight in another in South Africa. For females the values were 18.8 g/kg liveweight at 56 d at 2.15 kg liveweight in Scotland and 15.7 g/kg liveweight at 42 d at 1.60 kg in South Africa. 2. The content of abdominal fat was, in general, increased by reducing the protein content of the diet or by dilution of the food with oil or starch. It was, in general, reduced by diluting the food with dietary fibre which also reduced liveweight gain. 3. The results are consistent with the idea that chickens attempt to control their food intake so that they achieve a particular fatness. This level of fatness differs between the sexes and between degrees of maturity.

Effects of dietary fat level and lysine:energy ratio on energy utilization and tissue synthesis by broiler chicks

An experiment was designed to estimate the effect of dietary fat (20 or 80 g/kg) on the responses of broiler chicks to changes in the ratios of bioavailable lysine (LB) to true metabolizable energy corrected to zero nitrogen balance (TMEn) in their diets. A comparative slaughter experiment used an initial slaughter group of 44 10-day-old male chicks; an additional 120 chicks from the same population were used in the 14-day experiment. Dietary treatments comprised two basal diets differing in fat content and formulated to have similar nutrient:TMEn ratios. Each basal diet was supplemented with four levels of lysine to provide four LB:TMEn ratios calculated, and subsequently found, to be the same in each basal diet series. Each of the eight diets was diluted with five levels of cellulose to ensure a range of intakes under ad libitum feeding. Three individually housed chicks were assigned to each of the 40 diets. Carcasses were assayed for water, nitrogen, lipids, ash, and gross energy; changes in these variables during the experiment were the response criteria. The fat content of the diet had no effect (P greater than .05) on the chick responses to LB:TMEn ratios. At a fixed energy intake the body weight gain, retained water, retained energy as protein and retained ash increased with the LB:TMEn ratio, with no conclusive evidence of a maximum response having been reached for any variable at an LB:TMEn ratio of .83 g/MJ. Retained energy was independent (P greater than .05) of the LB:TMEn ratio but the energy retained as neutral lipids tended to decrease as the ratio increased. The data support the view that the lysine requirement of the broiler chick varies according to the response criterion used in its assessment.

Evaluation of a diet dilution technique for measuring the response of broiler chickens to increasing concentrations of lysine

Three experiments were conducted on male broiler chickens between one and three weeks of age to determine their response to dietary lysine concentrations. Serial dilutions of a summit diet shown to be first-limiting in lysine were fed in all experiments. The balance between amino acids in these diets was maintained within narrow limits. Intake of the most-limiting amino acid was the most important factor determining growth rate; protein intake as such was of little or no importance. The efficiency of utilisation of dietary lysine for protein growth was calculated to be 65.05 mg/g protein gain, representing a net efficiency of 0.85. The diet dilution technique overcomes the major disadvantage of the graded supplementation method for determining the requirements of amino acids, namely that of the amino acid balance changing systematically in successive dietary treatments.

Effect of dietary protein and energy on broiler carcass composition and efficiency of nutrient utilization

Day-old broilers were offered diets varying in dietary protein (16, 20, 24, 28, 32, 36%) and energy (2600, 2800, 3000, 3200, 3400, 3600 kcal [metabolizable energy] ME/kg) to 49 days of age to determine the effect of alteration in nutrient density on carcass composition and efficiency of nutrient utilization. Abdominal and total carcass fat contents responded similarly to alterations in dietary protein and energy, whether expressed on a percentage or absolute weight basis. However, maximum protein deposition occurred with the 20% crude protein diet, in contrast to the increase in percent carcass protein observed above this level. Although percent carcass protein decreased throughout the energy range tested, absolute carcass protein remained constant regardless of the dietary energy level. Dietary protein exerted similar effects on both absolute and percent carcass moisture. However, an increase in dietary energy resulted in a decrease in percent carcass moisture and an increase in absolute carcass moisture. Protein utilization decreased with each increment of dietary protein but increases in dietary energy resulted in small increases in protein utilization throughout the range tested. Changes in dietary protein and energy resulted in small differences in efficiency of energy utilization. Regression equations derived for carcass composition demonstrated that although diet composition is inadequate as a predictor of carcass parameters, the addition of carcass moisture (%) to the equation improves the reliability of the estimate. Equations for the prediction of nutrient utilization from diet composition are also presented.

Changes in liver glycogen of broilers during coccidiosis

Liver glycogen levels of broilers with Eimeria acervulina, E. Brunetti, or E. tenella fell during the acute phase of the infection with the maximum effect at 5-6 days post-inoculation (DPI). During the early recovery phase (6-8 DPI), liver glycogen levels in the E. acervulina-infected birds increased to levels up to 3 times greater than those found in uninoculated control birds. A lesser increase was occasionally seen in E. tenella-infected birds. Pair feeding studies showed that the decrease in liver glycogen was not related to the amount of feed consumed. The magnitude of the glycogen overshoot at 7 DPI was not related to the depression of weight gain at 5 and 6 DPI. When feed was withheld from birds, liver glycogen levels of uninoculated control birds fell rapidly within 1 h after feed withdrawal. In birds infected with E. acervulina, liver glycogen levels remained high even after 3 h starvation. Injection of glucagon indicated that glycogen could be mobilized in both infected and uninfected birds.

A comparative study of trout and chicks regarding dietary effects on glycogen concentration in liver and muscle during feeding and subsequent to feed withdrawal

1. Glycogen concentrations in liver and skeletal muscle were compared in rainbow trout and in chicks of two genetic sources. 2. Tissue glycogen concentrations were determined during feeding and after feed withdrawal in response to diets high in carbohydrate and oil, respectively. 3. Livers of trout and chicks were heavier and glycogen concentrations were higher in both liver and muscle of trout and chicks fed high-carbohydrate diets. 4. Feed withdrawal resulted in gradual but steady declines in trout glycogen over a 16-day period but caused sharp declines in liver glycogen in chicks followed by a rebound and a more gradual decline within a 5-day period. 5. Feed withdrawal from trout caused declines in muscle glycogen followed by rebounds which occurred more rapidly when the high-carbohydrate diet had been fed. 6. Feed withdrawal had little effect on muscle glycogen in broiler-type chicks. In White Leghorn chicks there was a general decline in muscle glycogen which showed marked fluctuations when the high-fat diet had been fed.

Analysis of liver glycogen in chicks

The glycogen levels in homogenates from livers from 3- to 4-week-old broilers were measured using alkaline digestion and ethanol precipitation followed by direct hydrolysis with amyloglucosidase. Glycogen was determined with glucose oxidase. Glycogen levels were not affected by rapid freezing in liquid nitrogen and storage at -10 C. Glycogen was stabile at 4 C for at least 1 hr; however, at room temperature, over 50% of the glycogen was lost within 1 hr. Homogenization with .05 M ethylenediaminetetraacetate (EDTA) prevented this loss. Liver glycogen decreased rapidly (within 1 hr) after feed withdrawal and was sometimes undetectable within 2 hr. There was considerable variation in glycogen levels among individual birds. Liver glycogen levels were up to 50% higher at 1100 than at 0800 hr.

Effects of storage conditions in vitro on the assay of chick liver glycogen

1. The reproducibility of an enzymic method for assaying chick liver glycogen was found to be +/- 1.6%. 2. Storage of liver at either -21 or -70 degrees C for up to 4 weeks, after freezing in liquid nitrogen, had no significant effect on glycogen concentration. However, the concentration of free glucose increased by about 50% during this time. 3. Storage of liver in ice-cold saline for up to 3 h proved unsatisfactory because of a significant loss of glycogen. 4. There was no significant difference in immediate glycogen concentration in liver tissue that was freeze-clamped, frozen in liquid nitrogen or collected into ice-cold saline. The free glucose concentration was higher, when estimated immediately after, with the latter two methods of collection of liver tissue.