Dietary Amino Acid Levels Research Articles

The influence of short-term feeding of amino acid-deficient diets and high dietary leucine levels on the intramuscular fat content of pig muscle

AbstractThe objective of the study was to investigate the influence of amino acid-deficient diets and high dietary leucine levels offered for intervals of either 21 or 35 days pre-slaughter on the intramuscular fat content of pig muscle. Twenty-four hybrid gilts were offered individually ad libitum one of four diets that comprised combinations of amino acid levels (supplemented or deficient: 5·6 v. 4·0 g lysine per kg) and low or high leucine levels (10·3 v. 30·3 g leucine per kg). Live weights at the start of the study were 74·5 and 87·0 kg for pigs on the 35- and 21-day feeding regimens, respectively. There were no significant effects of dietary amino acid level, leucine level, or feeding interval on food intake, daily live-weight gain or food efficiency. Pigs given the amino acid-deficient diets had lower killing-out proportions (736 v. 747 (s.e. 3·4) g/kg; P < 0·05) and longissimus dorsi muscle areas (32·6 v. 35·7 (s.e. 0·71) cm2, P < 0·01) than those given amino acid-supplemented diets. Subjective score for longissimus dorsi colour indicated that pigs on the high leucine diet had darker muscle than those on the low leucine diet. Intramuscular fat contents of the longissimus dors i muscle at the Wth/llth rib and the 3rd/4th lumbar vertebra and of the semimembranosu s muscle were increased by 19, 18 and 18 g/kg, respectively (P < 0·05), for pigs given amino acid-deficient compared with those given amino acid-supplemented diets. Dietary leucine level had no significant effect on intramuscular fat level. Pigs given the diets for 35, compared with 21, days had higher fat levels in the semimembranosu s muscle (52 v. 30 (s.e. 5·2) g/kg; P < 0·01) but not in the other two muscle locations studied. This study suggests that relatively short-term feeding of amino acid-deficient diets can produce substantial increases in intramuscular fat levels.

The effects of dietary protein and energy levels of diets offered during lactation on the lactational and subsequent reproductive performance of first-litter sows

AbstractA total of 315 first parity sows were used in two experiments to establish the lactational and subsequent reproductive performance of first-litter sows in response to varying levels of dietary amino acids and digestible energy (DE) offered during lactation. In the first experiment, sows were offered five diets ranging in lysine content from 6·2 to 15·1 g/kg. In the second experiment sows were offered five diets with a similar lysine: DE ratio (0·88 to 0·85 g/MJ) but ranging in DE content from 12·6 to 15·1 MJ/kg. Voluntary food intake during lactation was unaffected by lysine or DE content of the diets. Piglet pre-weaning growth was similarly unaffected by dietary DE content but responded in a curvilinear manner with increasing dietary lysine. Sow body-weight loss during lactation was unaffected by dietary lysine but declined with increasing DE content up to 13·8 MJ/kg. Backfat loss was lowest for sows offered the lowest lysine diet and tended to reach a plateau at a dietary level of 10·6 g lysine per kg. In response to dietary DE content, backfat loss tended to be highest for sows offered the diet of lowest DE content and declined with increasing DE content up to 15·1 MJ DE per kg. The subsequent weaning to remating interval was unaffected by dietary DE content. Subsequent litter size was similarly unaffected by dietary DE content but was significantly higher for sows offered the two higher, compared with the two lower, lysine diets (10·7 v. 9·6 born alive, s.e.d. 0·5, P < 0·05). The results suggest that current amino acid recommendations for lactating first-litter sows are inappropriate and may be constraining both milk production and subsequent reproductive performance.

Effect of Different Dietary Amino Acid Levels on Growth and Whole Body Amino Acid Composition of Rohu Fry

In a 6-week laboratory trial, two fish meal-based diets containing 45 and 49% protein and different levels of amino acids were evaluated for their effects on growth and whole body amino acid composition of rohu, Labeo rohita (Ham.), fry. The studies showed that the differences in dietary levels of protein and amino acids were reflected in growth of fish whch registered 81 and 110% weight gains with the diets containing 45 and 49% protein, respectively, but had no significant influence on their whole body amino acid composition.

Methionine and Total Sulfur Amino Acid Requirements Influenced by Stage of Production

Nine consecutive flocks of SCWL pullets were started at 13-wk intervals and housed in individual laying cages. Beginning with the fourth flock, four different age groups of hens from the same genetic line were housed in the same environment and fed the same experimental diets to test the hypothesis that the methionine and total sulfur amino acid (TSAA) requirements of hens vary with age and stage of production. For the last eight weeks of each 13-wk period, estimates were made of methionine and TSAA requirements for maximum egg production, egg weight, and egg mass. Results indicate that the methionine and TSAA requirements do not diminish with age and stage of production. Requirements were greater for the middle and final quarters of production than for the initial quarter. Peak daily requirements for methionine were 384, 380, and 402 mg/day for egg production, egg weight, and egg mass, respectively. These results indicate that the application of a phase feeding program based upon a reduction in protein or amino acid requirement as hens age has no scientific basis. Adjustments should be made in dietary amino acid levels to compensate for changes in daily feed intake as influenced by environmental changes, feather covering, or other factors in order to maintain a constant amino acid intake, but adjustment based on age or stage of production is not justified.

Estimation by regression analysis of endogenous amino acid levels in digesta collected from the distal ileum of pigs.

An experiment was conducted to estimate by simple linear regression the levels of endogenous amino acids in digesta collected from the distal ileum in pigs. Six barrows, average initial BW 35 kg, were fitted with a simple T-cannula at the distal ileum and fed six diets according to a 6 x 6 Latin square design. Six cornstarch-based diets containing six levels of CP from soybean meal (4, 8, 12, 16, 20, and 24% CP, respectively) were formulated. Chromic oxide (.4%) was included as the digestibility marker. Each experimental period consisted of 8 d. Ileal digesta were collected, at 2-h intervals, for a total of 24 h during d 7 and 8. There were linear relationships (P < .001) between dietary contents of apparent ileal digestible and total amino acids, irrespective of the ranges in graded dietary levels of amino acids. Determined with the regression technique, the endogenous levels of the indispensable amino acids (grams/kilogram of DMI) were as follows: arginine, .64; histidine, .23; isoleucine, .46; leucine, .69; lysine, .47; methionine, .13; phenylalanine, .31; threonine, .69; and valine, .54. Differences in the ranges of graded dietary levels of amino acids resulted in large differences in the estimated amounts of endogenous amino acids in ileal digesta. Furthermore, it seems that the levels of endogenous amino acids, as grams/kilogram of DMI, were constant at different dietary levels of amino acids, whereas the contributions of endogenous amino acids, as percentages of their dietary contents, decreased curvilinearly with increasing dietary contents. Therefore, apparent ileal digestibilities of amino acids were quadratically related to their dietary contents until plateau digestibilities were reached, whereas the true ileal digestibilities of amino acids were independent of their respective dietary contents. Furthermore, true ileal amino acid digestibilities should be determined from their corresponding plateau apparent ileal digestibilities. In conclusion, the levels of endogenous amino acids in ileal digesta can be determined reliably from the linear relationships between dietary contents of apparent ileal digestible and total amino acids. An important methodological consideration in the determination of endogenous amino acids by regression analysis is to design an appropriate range of graded dietary levels of amino acids.

Dietary Formulation with Cottonseed Meal on a Total Amino Acid Versus a Digestible Amino Acid Basis

The results of previous experiments indicated that performance of chicks fed corn-cottonseed meal (CSM) diets was inferior to performance of chicks fed a corn-soybean meal (SBM) diet and that true digestibilities of amino acids (AA) in CSM were lower than those in SBM. Therefore, the current study evaluated the formulation of diets containing expander-solvent CSM on an equivalent total AA basis vs an equivalent digestible AA basis compared to a corn-SBM diet. True digestibility of AA in the CSM, corn, and SBM were determined using the precision-feeding assay with cecectomized roosters and TMEn was determined using conventional roosters. One-week-old male chicks were then fed diets containing corn and SBM only or diets containing increasing levels of CSM from 5 to 40% that were formulated to be equal in total or digestible AA to the corn-SBM diet. All diets contained 20.7% CP and 3,200 kcal TMEn/kg. Weight gain and feed efficiency of chicks fed 20% or more CSM on a total AA basis were less (P < .05) than those of chicks fed the corn-SBM diet. Growth performance of chicks fed up to 20% CSM on a digestible basis was equivalent to that of chicks fed the corn-SBM diet, but dietary levels of 30 or 40% CSM depressed performance even on a digestible basis. Increasing most essential AA by 15% in the 40% CSM (digestible basis) diet had no effect on performance. True digestible AA and ME values determined in chicks were similar to those determined in roosters. These results indicate that formulation of diets containing CSM on a digestible AA basis is superior to formulation on a total AA basis and that at least 20% CSM could be fed to chicks if the diet contains adequate levels of digestible AA and Fe to bind gossypol. The results also indicated that the depression in performance from feeding 30 or 40% CSM diets was not associated with dietary AA levels.

Effect of Phase Feeding of Amino Acid on Performance of Laying Hens During Laying Period.

To investigate the effect of phase feeding of amino acids for laying hens during laying period, the laying period from 20 to 80 weeks of age was divided into 3 phases as 20-30, 30-60 and 60-80 weeks of age, and the hens were fed with 8 feeding programs. Five dietary amino acids (lysine, methionine, threonine, isoleucine and tryptophan) levels were adjusted to 100, 115 and 130% of the NRC requirement. The hens in non phase feeding groups were fed 130, 115, 100% (groups 1, 2, 3) and commercial diet as a reference (group 9). The hens in phase feeding groups were fed with following programs: 130-115-115 (group 4), 130-115-100 (5), 130-100-130 (6), 115-115-100 (7) or 100-130-130% (8) for phase I-II-III. The oviposition was recorded every day and egg weight was measured every Monday, Wednesday and Friday throughout the experimental period. And the eggshell strength, eggshell weight and Haugh unit were estimated every 10 weeks after 30 weeks of age.The first egg age and egg weight were not different among dietary amino acid levels. However the hens in 100% diet groups decreased their body weight considerably after the start of laying. Their performance was also inferior to other groups. When the dietary amino acid level was decreased from 130 to 115 to 100% gradually (group 5), there was no difference in the performance throughout the experimental period compared with 130% diet (group 1). However, the length of laying peak in experimental groups was shorter than that in reference group. The egg weight of hens fed 130% diet was the largest. The eggshell strength and Haugh unit were decreased with age. But the effective phase feeding program to maintain the egg quality was not determined.

Threonine Requirement in Female Broilers Affected by Age and Dietary Amino Acid Levels.

The reported threonine requirement for the maximum performance of broilers ranges widely. To clarify the reasons of these wide ranges, two experiments were conducted using female Arbor Acres strain broilers. In Experiment 1, to elucidate the effect of age on the threonine requirement, six feeds containing graded concentrations of dietary threonine from 0.70 to 0.90% were supplied to the broilers at four growing stages from 5 to 15, 15 to 25, 25 to 35 and 35 to 45 days of age. In Experiment 2, to confirm the effect of age and amino acid levels on the threonine requirement, the feeds containing two levels of amino acids, 90 and 100% of the NRC requirement, with six graded concentrations of threonine were supplied to the broilers at 8 to 18 and 28 to 35 days of age. At the end of each experiment, the body weight gain and feed consumption were recorded. The dietary threonine requirement expressed as a percentage of diet and crude protein level for the maximum body weight gain and feed efficiency decreased with age and had a tendency to increase with increasing dietary amino acid levels. The amount of threonine per kg body weight gain increased with age, but the effect by increasing dietary amino acid levels was not clear.

Influence of Dietary Levels of Protein and Sulfur Amino Acids on the Subacute Toxicity of Methylmercury in Mice.

The influence of diet on the subacute toxicity of methylmercury (MeHg) was investigated using C57BL/6N male mice, each fed a 24.8% protein diet (normal protein diet, NPD), a 7.5% protein diet (low protein diet, LPD) or LPD supplemented by methionine and cystine to NPD level (amino acid supplemented diet, ASD). When MeHg was consecutively administered to each group of mice (20 μmol/kg per day), median survival times were 11, 18 and 30 d in ASD-, LPD- and NPD-fed mice, respectively. Toxic symptoms including ataxia and loss of body weight were in that order. Hg accumulation rate in brain was faster in LPD-fed mice than in NPD-fed mice, and was further enhanced in ASD-fed mice. The fact that Hg in plasma low molecular weight (LMW) fraction was in the order of ASD->LPD->NPD-fed mice, would be one reason for the difference in the brain Hg accumulation. Hg levels in liver, blood and plasma showed a monotonous increase, and their terminal Hg levels were similar in the three groups. Renal Hg levels increased rapidly and almost never changed from the 7th d in the three groups. Urinary excretion of Hg in LPD-fed mice was markedly lower than in NPD-fed mice throughout the experimental period ; that in ASD-fed mice, which was the highest at least for the first few days, began to decline earliest. No difference was observed in fecal Hg levels during the early part of the experiment. Our results suggest that diet is an important factor determining the susceptibility to subacute MeHg toxicity, and that accelerated Hg accumulation rate in the brain caused by diet would result in higher susceptibility to subacute MeHg toxicity.

Response of the pea aphid ( Acyrthosiphon pisum) to variation in dietary levels of sugar and amino acids: the significance of amino acid quality

Growth, survivorship and food intake were measured for newborn pea aphids maintained on one of 25 chemically-defined diets varying in sucrose and amino acid content (200–1000 and 50–250 mM, respectively), with amino acids comprising 20:80 essential/non-essentials (e:n). Survivorship varied positively with dietary amino acid concentration, while dry weight growth was strongly affected by concentration of amino acids and sucrose, and also by the ratio of sucrose to amino acids (s:aa). Peak performance was achieved on the diet containing 800 mM sucrose and 200 mM amino acids. This was a lower s:aa ratio than that which supported maximal growth in previous experiments for aphids reared on diets containing 50:50 e:n. Comparison of plots for final dry weight against s:aa ratio indicated that the 20:80 e:n amino acid mixture supported growth ca. 60% of that on the 50:50 e:n mix. When the scaling of the s:aa ratio was adjusted accordingly, the plots for 20:80 and 50:50 e:n converged in all but elevation; a difference which represented the extra growth costs of feeding on 20:80 e:n diets. Analysis of diet consumption showed that these costs were associated with, and perhaps attributable to, inhibition of compensatory feeding.

Influence of dietary levels of protein and sulfur amino acids on the fate of methylmercury in mice

We previously reported that the fate of methylmercury (MeHg) in mice was affected by dietary protein levels. To study the mechanism of this alteration, we investigated the effect of sulfur amino acid supplement for a lowered protein diet on the fate of MeHg. C57BL/6N male mice were fed on a 24.8% protein diet (normal protein diet, NPD), a 7.5% protein diet (low protein diet, LPD), or LPD supplemented by methionine and cystine so as maintain the normal levels (amino acid supplemented diet, ASD) for 5 days. NPD-fed mice were used as controls. The mice were orally administered MeHg chloride (20 μmol/kg), and were examined after 24-h distribution and excretion of Hg. The Hg level in brain increased with LPD feeding and was further enhanced by ASD feeding. The hepatic Hg level increased only with ASD feeding. Although Hg levels in kidney, blood and plasma did not change with LPD feeding, these decreased with ASD feeding. The urinary Hg level that decreased with LPD feeding was recovered and exceeded by far the control levels with ASD feeding. When mice were intravenously injected with MeHg-bovine serum albumin, the Hg uptake rate in the brain increased in LPD-fed mice and was further enhanced in ASD-fed mice. The brain uptake of intravenously injected l-[ 14C]phenylalanine was also accelerated with LPD or ASD feeding, which indicated that LPD or ASD feeding increased activity of neutral amino acid transport in the brain. This would cause increased Hg uptake in the brain, since MeHg reaches the brain through this transport system. Hg ratio in plasma low molecular weight fraction increased in ASD-fed mice, but not in LPD-fed mice. This might contribute to the further enhanced Hg uptake in the brain with ASD feeding. Analysis of thiol compounds in plasma and urine revealed increased levels with ASD feeding. The present results suggest that insufficiency of sulfur amino acids in LPD is one reason for the alteration in the fate of MeHg induced by LPD feeding. It is also suggested that the change in neutral amino acid transport caused by LPD feeding is involved in the alteration in the fate of MeHg.

Determination of apparent ileal amino acid digestibility in pigs: effect of dietary amino acid level1

Studies were carried out to investigate the effect of dietary amino acid level on apparent ileal amino acid digestibility. Six barrows, average initial BW 35 kg, were fitted with a simple T-cannula at the distal ileum and fed six diets according to a 6 x 6 Latin square design. Six cornstarch-based diets containing six levels of CP from SBM (4, 8, 12, 16, 20, and 24% CP, respectively) were formulated. Chronic oxide was included as a digestibility marker. Each experimental period consisted of 8 d. After a 6-d adaptation period, ileal digesta were collected for 24 h during d 7 and 9 at 2-h intervals. The pigs were fed twice daily, equal amounts, at 0800 and 2000. The dietary allowance was 1,600 g/d during the first period and increased by 100 g each following period. There was a quadratic increase (P < .05) in apparent ileal amino acid digestibility as the dietary CP content was increased from 4 to 24%. Initially, the apparent ileal amino acid digestibilities increased sharply then gradually reached their plateaus, after which there were no further increases and the digestibility values became independent of the dietary amino acid levels. The lower end points of 95% confidence intervals of the plateau ileal digestibility values were defined to be the initial plateau digestibilities. The dietary CP and amino acid contents, corresponding to the initial plateau digestibility values, represent the dietary threshold levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutrient regulation in the pea aphid Acyrthosiphon pisum: application of a novel geometric framework to sugar and amino acid consumption

Abstract. A recently developed framework was applied to investigate the responses of newborn pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), to simultaneous variations in dietary suerose and amino acid levels. The location of functional ‘targets’ for intake and growth were determined experimentally using performance criteria. Behavioural rules employed by insects to approach these targets were investigated by reference to the geometry of arrays of intake and growth across a range of diets. First‐instar aphids were fed one of thirty‐one chemically‐defined diets ranging in sucrose concentration from 200 to 1000 mM and amino acid concentration from 25 to 250 mM. Insect survivorship, dry weight, protein‐ and carbohydrate‐derived growth were high for all diets except those with the lowest nutrient levels. Peaks in final dry weight and protein content identified the intake target as the point reached by larvae fed the 600 mM sucrose, 75 mM amino acid diet. Aphids regulated sucrose primarily by consumption (i.e. behaviourally), whereas amino acids were regulated post‐ingestively (i.e. by physiological mechanisms).

Effects of Dietary Amino Acid and Metabolizable Energy Levels on Performance of Native Chicken, Hinai-dori.

The present study was conducted to study the effects of dietary amino acid and metabolizable energy (ME) levels on the performance of Hinai-dori at different ages, and to obtain the basic information of Hinai-dori preceding a series of experiment to determine the requirement of individual essential amino acids.Three Hinai-dori chicks of both sexes per dietary group were confined individually in wire cages and were fed the experimental diets ad libitum from 7 to 21, 42 to 56 and 77 to 91 days of age in Experiments 1, 2 and 3, respectively. Experiments have a 3×5 factorial arrangement of treatment with three ME and five amino acid levels. The body weight and feed intake were recorded on the 14th day on the experimental diet.There was no sexual difference in the response to dietary amino acid and ME levels for any of the parameters determined. The body weight gain and feed efficiency were improved with increasing of amino acid levels. The feed intake was not affected by amino acid levels. The body weight gain, feed efficiency and feed intake were not affected by ME levels. The amino acid level for the maximum body weight gain and feed efficiency decreased with age. The maximum body weight gain was observed at the period from 42 to 56 days of age.

Effect of Dietary Amino Acid Level on Change from Starter to Grower Diets for Broiler Chickens

Two experiments were conducted to determine effects of time of changing from starter to grower feed for broilers as influenced by amino acid density of the diet. Diets were formulated to provide a minimum of 100, 110, and 120% of suggested amino acid levels for male broilers. Starter diets were fed to 0, 7, 14, and 21 days of age with grower diets fed to 40 days, and finisher diets from 40 to 45 days of age. Broilers were processed to examine treatment effects on carcass composition and parts yield.Although amino acid content of the diet significantly affected a number of live performance parameters, there was no interaction of time of diet change and amino acid composition of diets. Mean weight of broilers at 40 days was significantly reduced when birds were placed on grower diets at 0 days, but mean weight at 45 days did not differ significantly among treatments. Mean 45-day weight of females placed on grower feed at 0 days was significantly less than that of females placed on grower feed at 7 or 14 days, but did not differ significantly from that of females placed on grower feed at 21 days of age. Time of change from starter to grower diets had no significant effect on feed utilization, calorie utilization, mortality, dressing percentage, abdominal fat content, or parts yield of male or female broilers. When diets were changed from starter to grower at 0, 7, or 14 days of age, there was a linear increase in breast meat yield of males as the amino acid content increased; however, when diets were changed from starter to grower at 21 days of age, there were no differences in breast meat yield among males fed the different amino acid levels.Based upon prevailing feed prices and performance data from the present experiments, changing from starter to grower diets at 7 or 14 days of age would result in the lowest feed cost to produce a pound of chicken, with no loss in live performance.

Effects of Amino Acid Restriction During Starter and Grower Periods on Subsequent Performance and Incidence of Leg Disorders in Male Large White Turkeys

Male Nicholas Large White turkeys were fed diets formulated to meet a minimum of 100, 110, or 120% of NRC (1984) amino acid recommendations. There were three periods when 75% of recommended standards were fed: 0 to 3 wk, 0 to 6 wk, or 6 to 12 wk. A fourth (control) group was not restricted at any time. Four pens of 12 males were fed each amino acid by restriction combination. At 18 wk, leg scores were assigned to all birds and representative samples of birds processed for parts yield.All birds fed restricted diets had significantly lower BW at 18 wk than unrestricted controls but did not differ in feed utilization. Dietary amino acid levels significantly influenced BW and feed utilization, but there was no interaction with restriction times. There were no significant effects of amino acid levels or restriction times on incidence of leg disorders. Breast meat yields (quantity and percentage of carcass) were significantly influenced by both restriction time and amino acid levels. There seemed to be little if any compensatory gain following amino acid restriction in these studies.

Interactive effects of thermal environment and dietary amino acid and fat levels on rate and efficiency of growth of pigs housed in a conventional nursery.

In four trials, 480 weanling pigs were housed in a conventional nursery maintained at 20 or 30 degrees C, which represented a cool and hot thermal environment, respectively. They were allowed ad libitum access to corn-soybean meal-dried whey diets containing .7, 1.0, or 1.3% lysine and 0 or 5% added fat (choice white grease). The pigs were weaned between 27 and 33 d of age (7.27 +/- .90 kg) and penned in groups of five for the duration of the 42-d trials. Pigs housed in the cool environment consumed more feed (P < .01), gained more weight (P < .01), and utilized feed more efficiently (P < .01) than those in the hot environment. As dietary lysine levels were increased in the 20 and 30 degrees C environments, daily weight gains and gain:feed ratios increased linearly (P < .01) from d 0 to 21 and quadratically (P < .01) from d 21 to 42. However, the magnitudes of the increases were less in the cool environment, resulting in temperature x lysine interactions (P < .05). As the pig's feed intake, body weight, and heat production increased over time, the 20 and 30 degrees C environments became progressively warmer relative to the animal's zone of thermoneutrality. The associated reductions over time in energy and lysine intakes relative to the pigs' maintenance needs resulted in an increase in the concentration of dietary lysine needed to maximize rate and efficiency of gain in the 30 degrees C environment but not in the 20 degrees C environment (temperature x lysine x period interaction, P < .10).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Dietary Amino Acid Level on Response to Time of Change from Starter to Grower Diets for Broiler Chickens

Four trials were conducted to determine the effects of time of changing from starter to grower feed for broilers, as influenced by the amino acid composition of the diet. All diets were formulated to provide a minimum of 100, 110, or 120% of suggested amino acids for male broilers. In the first two trials, starter diets were fed to 17, 21, 25, or 29 days of age. In the third trial, starter diets were fed to 14, 18, 22, or 26 days of age. In the fourth trial, starter diets were fed to 14, 17, 21, or 24 days of age. Grower diets were fed to 40 days and finisher diets to 45 days of age. Broilers from the third trial were processed to examine effects on carcass composition.Although amino acid content of the diet significantly affected a number of live performance and carcass parameters, there was no interaction of time of diet change and amino acid composition of diets. In the first two studies, the 45-day weight of male broilers was reduced significantly (P < .05) when changed from starter to grower diets at 17 days of age. Weight of females, mean weights, total feed consumed, feed utilization, calorie conversion, and mortality were not affected significantly by time of change. In the third and fourth trials, day of change had no significant effects on live performance of broilers. Carcass dressing percentage of males was reduced significantly when starter diets were fed to 29 days; no other effects on carcass characteristics were observed. These data suggest that broilers may be changed from starter to grower diets as early as 14 to 17 days of age, especially if sexes are combined.

Effects of Dietary Amino Acid Level and Duration of Finisher Period on Performance and Carcass Content of Broilers Forty-Nine Days of Age

Two studies were conducted to evaluate feeding reduced levels of amino acids (AA) to broilers during the finisher period. Birds grown to 42 days on nutritionally complete diets were fed diets formulated to contain a minimum of 70, 80, 90, 100, or 110% of recommended AA levels for periods of 3, 5, or 7 days prior to slaughter at 49 days of age. Body weight, feed intake, feed utilization, dressing percentage, and abdominal fat content were determined.For finisher periods of 3 to 5 days, a reduction in recommended dietary AA levels may be utilized without impairment of body weight gains of broilers. Extending the finisher period to 7 days resulted in significant (P < .05) reduction of body weight gains on diets with AA levels less than 90% of recommended levels. Feed utilization was more sensitive to reduction in AA levels and may be affected adversely even by a 5-day withdrawal period. Dressing percentage was reduced in some instances, and abdominal fat generally increased when reduced AA levels were fed. The economics of feeding reduced AA levels must be considered in evaluating the results of the present studies.

Influence of time lag in amino acid absorption on nitrogen retention in rats

Depending on the form of nitrogen sources, there is a time lag in amino acid absorption. However, the influence of such a time lag on nitrogen retention is not known. In the present experiment we created a time lag in amino acid absorption and observed nitrogen retention in rats. Two unbalanced amino acid mixtures were prepared. The equal amount of combination of these mixtures makes the amino acid pattern of egg protein. Rats were given these two unbalanced amino acid mixture diets alternatively at 08:00–09:30 hr, 11:00–12:30 hr, 14:00–15:30 hr, and 17:00–18:30 hr for 14 days. Control rats were given egg-protein-pattern amino acid mixture diet at the same time and periods as the experimental group. Dietary amino acid levels were 5% and 10%. Although the control and experimental rats ate similar amounts of each amino acid, there was a time lag in the amino acid absorption. Plasma aminograms, hematologic values, body protein concentration, and growth were very similar. The results indicate that nitrogen utilization is not influenced by a relatively small time lag in amino acid absorption.