Comparison of neutral fat and free fatty acids in high lipid-low carbohydrate diets for the growing chicken

Characteristics of lipids and their feeding value in swine diets

In livestock diets, energy is one of the most expensive nutritional components of feed formulation. Because lipids are a concentrated energy source, inclusion of lipids are known to affect growth rate and feed efficiency, but are also known to affect diet palatability, feed dustiness, and pellet quality. In reviewing the literature, the majority of research studies conducted on the subject of lipids have focused mainly on the effects of feeding presumably high quality lipids on growth performance, digestion, and metabolism in young animals. There is, however, the wide array of composition and quality differences among lipid sources available to the animal industry making it essential to understand differences in lipid composition and quality factors affecting their digestion and metabolism more fully. In addition there is often confusion in lipid nomenclature, measuring lipid content and composition, and evaluating quality factors necessary to understand the true feeding value to animals. Lastly, advances in understanding lipid digestion, post-absorption metabolism, and physiological processes (e.g., cell division and differentiation, immune function and inflammation); and in metabolic oxidative stress in the animal and lipid peroxidation, necessitates a more compressive assessment of factors affecting the value of lipid supplementation to livestock diets. The following review provides insight into lipid classification, digestion and absorption, lipid peroxidation indices, lipid quality and nutritional value, and antioxidants in growing pigs.

Apparent metabolizable energy of glycerin for broiler chickens

Three energy balance experiments were conducted to determine AMEn of glycerin using broiler chickens of diverse ages. In experiment 1, two dietary treatments were fed from 4 to 11 d of age. Dietary treatments consisted of a control diet (no added glycerin) and a diet containing 6% glycerin (94% control diet + 6% glycerin). Four dietary treatments were provided in experiment 2 (from 17 to 24 d of age) and 3 (from 38 to 45 d of age). Diets in experiment 2 and 3 were 1) control diet (no added glycerin); 2) 3% added glycerin (97% control diet + 3% glycerin); 3) 6% added glycerin (94% control diet + 6% glycerin); and 4) 9% added glycerin (91% control diet + 9% glycerin). Diets in experiment 1 and 2 were identical, but the diet used in experiment 3 had reduced nutrient levels based on bird age. In experiments 2 and 3, broilers were fed 91, 94, 97, and 100% of ad libitum intake so that differences in AMEn consumption were only due to glycerin. A single source of glycerin was used in all experiments. Feed intake, BW, energy intake, energy excretion, nitrogen intake, nitrogen excretion, AMEn, and AMEn intake were determined in all experiments. In experiment 1, AMEn determination utilized the difference approach by subtracting AMEn of the control diet from AMEn of the test diet. In experiments 2 and 3, AMEn intake was regressed against feed intake with the slope estimating AMEn of glycerin. Regression equations were Y = 3,331x -72.59 (P < or = 0.0001) and Y = 3,348.62x -140.18 (P < or = 0.0001) for experiments 2 and 3, respectively. The AMEn of glycerin was determined as 3,621, 3,331, and 3,349 kcal/kg in experiments 1, 2, and 3, respectively. The average AMEn of glycerin across the 3 experiments was 3,434 kcal/kg, which is similar to its gross energy content. These results indicate that AMEn of glycerin is utilized efficiently by broiler chickens.

Effects of feeding high carbohydrate or high fat diets. 1. Growth and metabolic status of the posthatch poult following immediate or delayed access to feed

Three experiments were conducted with turkey poults to determine the effects of diet and delayed placement on growth and selected aspects of carbohydrate metabolism. Immediately after hatch, poults were placed in batteries and allowed either immediate access to feed and water (FED) or feed and water withdrawal for 48 h (WH). In the first two experiments, diets contained a high proportion of carbohydrate from corn (CHO; 60% of diet) or a lower proportion of corn (26%) and 10% supplemental animal-vegetable fat (FAT). The WH poults weighed less than FED poults at 5 d postfeeding (DPF; P < or = 0.05) but not at 13 DPF. Similarly, poults fed the CHO diet were heavier 5 DPF, whereas poults fed the FAT diet were heavier at 13 DPF (P < or = 0.05). Regardless of feeding regimen (WH vs FED), all poults were nearly depleted of hepatic glycogen prior to feeding. At 2 DPF, poults fed the CHO diet had more hepatic glycogen concentrations compared with those fed the FAT diet (P < or = 0.002). In addition, one-half of the WH poults fed the CHO diet had plasma glucose concentrations in excess of 500 mg/dL at 2 DPF. In Experiment 3, similar feeding regimens and diets were used with the addition of a third diet containing a synthetic medium-chain triglyceride emulsion (MCT) as the supplemental fat source. Poults fed the FAT and MCT diets were 41 g heavier than poults fed the CHO diet at 13 DPF (P < or = 0.05). Similar to the results of Experiment 2, poults fed the CHO diet had increased hepatic glycogen concentrations at 2 DPF, and within the WH treatment at 2 DPF, 30% of the poults had plasma glucose concentrations in excess of 500 mg/dL. Metabolic consequences of delayed placement were also found. At both 4 and 7 DPF, WH poults had a reduced capacity for glucose clearance 60 min after a glucose load (250 mg; P < or = 0.05). The current experiments demonstrate that supplemental fat may ease the metabolic shift toward glycolysis after hatching, thereby improving growth through 2 wk of age.

Studies on acid oils and fatty acids for chickens III. Effect of chemical composition on metabolisable energy of by-products of vegetable oil refining

1. Fourteen by-products of oil refining, selected for their variability in free fatty acid and unsaponifiable contents, were analysed chemically with the objective of relating the determined ME values of the products to chemical composition by means of multiple linear regression analysis. Refined sunflower oil was included as a reference fat. 2. Twenty-one 2-week-old chicks were used to determine fat digestibilities and AMEn values of diets, using the total collection method. Fats were included in a wheat-soyabean meal diet at 100 g/kg. Multiple linear regression analysis was used to express the ME values of fats as functions of the parameters measured (moisture, gross energy, impurities, unsaponifiables, non eluted material, free fatty acid content, unsaturated: saturated ratio, peroxide value, TBA test). 3. The ME of the fat products lay in the range l2.62 to 24.35 MJ/kg, and 29.26 MJ/kg for refined sunflower oil. Free fatty acid content of the fats was shown to be a poor predictor of their ME values, whereas non eluted material (NEM) of the fat products showed a good correlation with their ME. A regression equation could be derived (R2 0.6548; SEE 2.0064) with the unsaturated: saturated ratio (U:S) and NEM. An ME prediction equation based on the U:S, NEM and unsaponifiable content is also proposed (R2= 0.7l68; SEE= 1.9058).

[Glycerol as a feed ingredient for broiler chickens]

In a first trial glycerol was tested as a feed ingredient for broiler chickens. The influence of glycerol supplementation on weight gain, feed intake, feed conversion ratio and N-balance was proved. 90 Broiler chickens (Lohmann Meat) were fed ad libitum in 6 groups with nearly isoenergetic diets based on corn and soybean meal with 23% crude protein and 0; 5; 10; 15; 20 or 25% pure glycerol in the DM. During a feeding period of 31 days animals had have a very good intake of all experimental diets. The highest weight gains were observed in the groups with 5 and 10% glycerol (34.9 and 35.3 g/animal.d, resp.). However, this effect was not significant compared to the control group (34.3 g/animal.d), but was significant superior to the gain of groups with 20 and 25% glycerol in the diet (30.2 and 26.6 g/animal.d, resp.). The feed conversion ratio was unchanged up to 10% glycerol (1.65 kg/kg gain) and rose to 2.08 kg/kg gain with 25% glycerol. Up to 20% glycerol the N-balance (1.6 to 1.8 g N/animal.d) was positively correlated with the glycerol content in the diet (r = 0.98). The estimation of the plasma glycerol level 2 hours after feeding indicated a remarkable increase already with a 5% supplementation of glycerol from 0.65 (control) to 4.36 mmol/l. Further supplementation caused on average 11 to 54 mmol glycerol/l varying considerably between the individual animals. In general 25% glycerol in the diet caused the lowest performance and pathological changes in the crop epithelium, liver and kidneys. From the point of view of weight gain, feed intake, and feed conversion ratio as well as N-balance a supplementation of 5 to 10% glycerol seems to be beneficial.

[Use of free fatty acids in animal nutrition]

The description of the processes of absorption of free fatty acids in monogastric animals and in ruminants is the first part of the review. The feeding problems of free fatty acids are discussed in the second part. In pig diets is a level up 6% free fatty acids in the dry matter of the ration not disadvantageous. In the feeding of ruminants additionally free fatty acids reduce the fermentation processes in the rumen. Only protected free fatty acids (Ca-fatty acids) are favourable in feeding systems for high yielding cows.

Ascites in broilers. 1. Experimental factors evoking symptoms related to ascites

Male broilers of two genetically related stocks with divergent growth rates and feed conversion ratios were used to study metabolic backgrounds on the occurrence of pulmonary hypertension, heart failure, hypoxemia, and ascites in poultry. An experiment with a 2 x 2 x 2 x 2 factorial split-plot arrangement of treatments with 96 groups of 12 broilers was performed. Effects of stock and environmental factors such as ambient temperature, dietary fat, and dietary energy on performance, energy metabolism, oxygen consumption, hematocrit values, and mortality were investigated in broilers from 1 to 5 wk of age. Dissimilar responses of the two stocks to environmental factors reflected genotype by environment interactions and revealed metabolic disorders related to heart failure and ascites. The results indicated that in the stock with the lower feed conversion ratio, a fast protein accretion was achieved together with a reduced ability to convert chemical energy to metabolic heat and to deposit body fat directly from ingested fat. Birds with a low feed conversion ratio show less flexibility in metabolic adaptation to a changing environment, which can account for the development of ascites.

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.

A rat bioassay for measuring the comparative availability of carbohydrates and its application to legume foods, pure carbohydrates and polyols

An assay was developed to evaluate the bioavailability of dietary carbohydrate by slope-ratio analysis of weight gain and plasma ketones of rats fed a carbohydrate-free diet supplemented with glucose as a standard and selected food items, pure carbohydrates and polyols. The diet was based on 35% food grade oleic acid, 12% casein protein supplemented with methionine (0.3%) and arginine (0.2%), 7.5% soybean oil, 37% cellulose, minerals and vitamins. Glucose, as the reference standard, or test materials were incorporated in the diet by replacing equi-energetic amounts of oleic acid and adjusting cellulose to equalize total weight. Optimal levels of protein (casein) and triglyceride (soybean oil) in the basal diet were defined as those levels above which additional protein or fat would serve only to provide endogenous glucose from their glucogenic amino acids and glycerol constituents. A standard dose-response curve was obtained by feeding diets containing 0%, 1% and 2% glucose. Similar dose response curves were obtained by feeding test materials. Under these experimental conditions, additional glucose or additional protein were growth stimulating and casein had approximately 50% of the value of an equal weight of glucose, which was consistent with its content of glucogenic amino acids. The specific carbohydrate value of a food was estimated in the assay by subtracting the calculated glucogenic value of its digestible protein from the total response. The apparent availability of the carbohydrates (i.e., nitrogen-free extract) in soybean meal, lima bean (Phaseolus lumatus), and chick pea (Cicer arietinum) were 35, 70, and 80%, respectively, as available as glucose. Galactose, a 1:1 mixture of galactose + glucose, fractose and starch were as available as glucose. Lactose, ribose, sorbitol, and xylitol were 50 to 65% as available as glucose while mannitol and inulin were not available to a significant extent. Possible metabolic bases for these differences are discussed.

Intracellular distribution of hepatic and renal gluconeogenic enzymes in embryonic and growing chickens

The intracellular distribution of hepatic and renal gluconeogenic enzymes in 20-day-old chicken embryos and 4-week-old chickens (Gallus domesticus: New Hampshire male X Columbian female) has been studied. Pyruvate carboxylase, fructose-1,6-diphosphatase, and glucose-6-phosphatase were found primarily in the mitochondrial, cytosolic, and microsomal fractions, respectively. Phosphenolpyruvate carboxykinase was present not only in the mitochondria but also in the cytosol of the chicken liver and the kidney. The intracellular distribution of the liver enzyme differed from that of the kidney enzyme in chicken embryos as well as in growing chickens.

Host dietary starch and Moniliformis (Acanthocephala) in growing rats

During the course of three experiments, groups of male weanling rats were allowed to feed ad libitum on isoenergetic diets containing 0, 1, 2, 3 and 4% starch. The growth of rats, which were infected with either 20 or 40 cystacanths of Moniliformis dubius , was compared with the growth of similar uninfected rats which had been fed on the same diet. No differences could be detected between the uninfected and infected rats for a given diet apart from the lowered liver glycogen of the infected rats which had consumed the diet containing most starch during one of the experiments. Under the experimental conditions used, the growth of both the host and the parasite appeared to be closely related to the amount of starch ingested by the host. Thus, the results may be interpreted as demonstrating that the presence of a suitable source and quantity of available glucose in the diet of the rat is important for the growth of Moniliformis .

Effect of feeding a carbohydrate-free diet on the growth and metabolism of preruminant kids

1. Experiments were done using 8-d-old kids to determine the metabolic effect of feeding a carbohydrate-free diet, and the effects of supplementation of this diet with a small amount of glycerol, sodium propionate or glucose. 2. The experimental (carbohydrate-deficient) diets permitted growth nearly equal to that with the control diet (cow's milk). The kids given the experimental diets generally had lower levels of blood glucose than those given the control diet. 3. With all experimental diets there were increases in the concentrations of plasma lipid and total liver lipid and a decrease in the concentration of liver glycogen; supplementation of the carbohydrate-free diet with glycerol, sodium propionate or glucose had no additional effect on these values. 4. The ingestion of cow's milk produced hyperglycaemia 2 h after feeding, while in kids given the carbohydrate-free diet there was no increase in blood glucose level. The concentration of plasma free fatty acids in the kids given the carbohydrate-free diet was higher than that in control animals 24 h after feeding, suggesting that the kids given the experimental diet preferentially utilize free fatty acids as an energy source.

Lipid biosynthesis in the chick. A consideration of site of synthesis, influence of diet and possible regulatory mechanisms

Studies in vitro and with intact chicks support the view that liver is the major site of lipid biosynthesis in the chicken. Adipose tissue is relatively unimportant as a site of fatty acid biosynthesis in this species although it does have the ability to esterify fatty acids to triglycerides. The available evidence, therefore, suggests that in the chicken, and presumably other avian species, fatty acids are synthesized in liver and are transported as triglycerides in the plasma low-density lipoproteins to the adipose tissue for storage. Fasting, even for short periods of time, markedly depresses the capacity for hepatic lipogenesis in the chick. Food restriction for 2 hr. depresses hepatic lipogenesis by about 90% and refeeding for 1 hr./or/the intravenous administration of glucose or fructose restores the lipogenic capacity. Feeding diets high in fat or protein cannot be adequately explained on the basis of the reduction of dietary carbohydrate which accompanies increased dietary protein or fat levels. Dietary fat and protein appear to exert their effects on hepatic lipid synthesis by different mechanisms. The depression in hepatic fatty acid synthesis brought about by fasting or fat-feeding is accompanied, and probably preceded, by an increased plasma free fatty acid level. Under these conditions hepatic fatty-acyl CoA levels increase while free CoA levels are reduced. Long-chain acyl CoA derivatives are capable of inhibiting acetyl CoA carboxylase activity as well as citrate transport. The reduced availability of free CoA may limit the citrate cleavage reaction. Dietary alterations influence the hepatic lactate-pyruvate ratio of chicks, however the changes observed are not always consistent with the changes observed in rat liver. Chicks fed high-protein diets have a decreased hepatic lactate/pyruvate ratio indicative of a more oxidized cytoplasmic environment. This change in redox state may be associated with control of fatty acid synthesis in chicks fed high-protein diets. Thyroxine and glucagon affect hepatic fatty acid synthesis in the chick, however insulin appears to play a lesser role.

Studies on the growth and changes in metabolism of rats fed on carbohydrate-deficient fatty acid-based diets supplemented with graded levels of maize starch

1. Experiments were conducted to determine the effects of the supplementation of carbohydrate-deficient fatty acid-based (FA) diets with 18·7, 37·5, 75, 150 and 300 g maize starch (MS)/kg on the growth and metabolism of the growing rat. Further, the effects of fasting on rats given the FA diet were compared with those given the high-carbohydrate (CHO) diet. Due to the significant decrease in food consumption of rats given the FA diet, the effects of pair-feeding the CHO and the FA diet were also investigated.

2. The isoenergetic replacement of fatty acids with increasing amounts of MS in the FA diet given to rats increased their weight gain and concentration of glucose in their plasma. These increases, however, tended to level off for weight gain and glucose concentration, respectively, at about 18·7 g and 75 g MS/kg diet. The same type of replacement decreased the concentration of ketones in the plasma but the decrease levelled off at the high concentration of 300 g MS/kg diet. Activities of liver glucose-6-phosphatase (EC3.1.3.9) and glucokinase (EC2.7.1.2) decreased and increased respectively with increasing concentration of maize starch in the diet. These changes tended to level off at concentrations of about 75–150 g MS/kg diet.

3. Fasting for 18 h decreased the concentration of glucose in plasma of both the FA- and the CHO-fed rats, while fasting of the CHO-fed rats depressed the concentration of glycogen in the liver but did not influence that of the FA-fed rats. Pair-feeding the CHO diet to the FA diet produced similar weight increases during the 8-week experimental period.

Influence of meal-feeding on some of the effects of dietary carbohydrate deficiency in rats

1. Experiments were conducted to investigate the effects of feeding rats on a diet based on a mixture of maize oil fatty acids as the only source of non-protein energy (fatty acid diet) and the influence on these effects of giving such a diet in a single daily meal lasting 2 h.

2. In comparison with a triglyceride diet in which the non-protein energy was in the form of maize oil, feedingad lib.with the fatty acid diet produced no significant changes in body-weight gain, plasma glucose and plasma ketones concentrations, liver glycogen concentration and protein efficiency ratio.

3. In comparison with the triglyceride diet, meal-feeding with the fatty acid diet produced significantly lower body-weight gain and protein efficiency ratio; moreover, it significantly lowered plasma glucose and liver glycogen concentrations.

4. Rats meal-fed on the fatty acid diet synthesized glucose from protein, as evidenced by the significantly higher liver glycogen concentration detected 6 h after the meal had been eaten, but the increase was significantly lower than in the animals fed on the triglyceride diet. Also, 6 h after the meal had been eaten, the amount of meal remaining in the stomach of rats meal-fed on the fatty acid diet was significantly higher than in those fed on the triglyceride diet.