Biomedical subjects

D H Baker

Publications and source records attributed to D H Baker.

At least 91 records · Page 5Linked to original sources

PubMed1996

Efficacy of a lysine-tryptophan blend for growth of chicks.

Two chick experiments were conducted to compare the growth-promoting efficacy as well as the toxicity of a new source of L-tryptophan and L-lysine, Tryptosine (16.1% tryptophan, 56.3% lysine). A corn-feather meal-soybean meal basal diet was made singly deficient in either lysine or tryptophan, and graded doses of lysine or tryptophan from either Tryptosine or feed-grade sources of lysine and tryptophan were supplemented. Linear (P < .01) weight gain responses occurred, and responses to lysine or tryptophan in Tryptosine were similar to those obtained with equal doses of lysine or tryptophan provided by feed-grade sources of L-lysine.HCI or L-tryptophan. The toxicity trial involved additions of 1, 2, or 4% lysine with .29, .58, or 1.16% tryptophan to a lysine- and tryptophan-adequate corn-soybean meal diet. Both amino acids were provided as either Tryptosine or as feed-grade sources of lysine and tryptophan. Weight gain and feed intake were reduced in a linear fashion (P < .01) as levels of the two excess amino acids increased. The decreases caused by Tryptosine were similar to those caused by equivalent levels of excess feed-grade lysine and tryptophan.

Animals↗

PubMed1996

Sulfur amino acid requirement and cystine replacement value of broiler chicks during the period three to six weeks posthatching.

Three experiments were conducted with commercial broiler chicks to determine the SAA requirement during the growth period 3 to 6 wk posthatching. A 20% CP corn-peanut meal basal diet (3,200 kcal ME(n)/kg) was analyzed to contain 0.23% Met and 0.28% cystine. True digestibility assessment in cecectomized cockerels revealed that Met and cystine in the basal diet were 81 and 75% digestible, respectively. Therefore, the basal diet contained 0.19% digestible Met and 0.21% digestible cystine. When fully fortified with DL-Met, growth rate and feed efficiency of chicks fed the corn-peanut meal diet were equal to that of chicks fed a 20% CP Met-fortified corn-soybean meal diet. In the SAA requirement assay, Ross x Hubbard male chicks were fed graded increments of DL-Met (0.03%) and L-cystine (0.03%) to achieve digestible SAA concentrations of 0.40, 0.46, 0.52, 0.58, 0.64, and 0.70%. Weight gain and feed efficiency responded quadratically (P < 0.01) to increasing doses of SAA. The estimated requirement for maximal feed efficiency was higher than that for maximal weight gain. Both visual appraisal and curve fitting procedures suggested a requirement of close to 0.61% digestible SAA. When extrapolated to a corn-soybean meal diet where SAA true digestibility is 87.5%, the total SAA requirement calculates to be 0.70% of the diet. However, because commercial corn-soybean meal diets typically contain supplemental Met, which is only 81% efficient (wt:wt) in furnishing cystine, the estimated total SAA requirement for chicks fed 20% CP Met-fortified corn-soybean meal diets with 3,200 kcal of ME/kg would probably approximately 0.72% of the diet. A DL-Met vs L-cystine supplementation assay suggested that digestible cystine can supply no more than 52% of the total requirement for digestible SAA of chicks during the 3- to 6-wk growth period.

Amino Acids, Sulfur↗

PubMed1996

Digestible threonine requirement of broiler chickens during the period three to six and six to eight weeks posthatching.

Four experiments were conducted to determine the digestible Thr requirement of commercial broiler chickens (Ross x Hubbard) during the period 3 to 6 and 6 to 8 wk posthatching. Threonine-deficient corn-peanut meal basal diets (3,200 MEn/kg) contained 20% CP and 0.50% Thr for 3- to 6-wk-old birds, and 18.3% CP and 0.50% Thr for 6- to 8-wk-old birds. True digestibility assessment using cecectomized roosters indicated that Thr was 81% digestible in both basal diets. Thus, both diets contained 0.40% digestible Thr. Growth rate and feed efficiency of chicks fed the corn-peanut meal basal diets supplemented with surfeit Thr was equal to that of chicks fed a 20% CP Met-fortified corn-soybean meal diet. Graded doses of Thr produced marked responses (P < 0.05) in weight gain and feed efficiency in birds of both age groups. Maximal feed efficiency was achieved at 0.61% digestible Thr in 3- to 6-wk-old birds and at 0.52% digestible Thr in 6- to 8-wk-old birds. Extrapolating these digestible Thr requirements to total requirements for chicks consuming corn-soybean meal diets (Thr digestibility = 87%) results in estimates of 0.70 and 0.60% for broiler chickens during the growth periods 3 to 6 and 6 to 8 wk posthatching, respectively. These estimates are lower than those of NRC (1994) but are in close agreement with those obtained from ideal protein calculations, i.e., Thr requirements should be 70% of lysine requirements for chicks 3 to 8 wk of age.

Aging↗

PubMed1995

1 alpha-Hydroxylated cholecalciferol compounds act additively with microbial phytase to improve phosphorus, zinc and manganese utilization in chicks fed soy-based diets.

Seven experiments were conducted to determine the efficacy of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and microbial phytase in improving P, Zn and Mn utilization of chicks fed P, Zn- and Mn-deficient soy protein diets containing surfeit levels of cholecalciferol. Efficacy of 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) was also studied. A dose titration study indicated that supplemental phytase at 1200 units/kg diet would increase bone ash by at least 65% when added to a corn-soybean meal diet containing 0.43 g P/100 g (0.1 g nonphytate P/100 g). These responses were similar to those obtained from supplemental P (0.1 g/100 g) as KH2PO4 or from added 1,25-(OH)2D3 (10 micrograms/kg). Dietary addition of both 1200 units phytase and 10 micrograms/kg 1,25-(OH)2D3 elicited bone ash responses that were near 100%. When chicks were fed a Zn-deficient soy-concentrate diet (13 mg Zn/kg), diet supplementation with 1,25-(OH)2D3 or phytase increased growth rate by 40% and tibia Zn content by > 100%; adding 1,25-(OH)2D3 together with phytase increased tibia Zn content by 160%. Utilization of both Zn and Mn contained in the corn-soybean meal diet also was markedly enhanced by supplemental phytase, 1,25-(OH)2D3, or the combination. The cholecalciferol analog 1 alpha-OH D3 was found to improve dietary P utilization maximally (70% bone ash response) at a dose of 20 micrograms/kg diet, and effects were additive when 1 alpha-OH D3 was fed in the presence of phytase.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Phytase↗

PubMed1995

Effects of acute exercise on hepatic lipogenic enzymes in fasted and refed rats.

The effects of an acute bout of prolonged exhaustive exercise on the activities of hepatic lipogenic enzymes have been investigated. Male Sprague-Dawley rats were randomly divided into three groups: fasted for 48 h without refeeding (FA) and fasted for 48 h and refed a diet high in fructose (RF) or in cornstarch (RC). One-half of each group of rats exercised on a treadmill at 20 m/min, 5% grade, until exhaustion and the other half rested for the same amount of time without food. Dietary intakes during refeeding were kept equal between the exercised and rested control animals. Activities of all hepatic lipogenic enzymes measured, i.e., fatty acid synthase (FAS), L-type pyruvate kinase (L-PK), ATP citrate lyase, malic enzyme, and glucose-6-phosphate dehydrogenase, were induced dramatically by fasting-refeeding and were significantly higher in the RF than in the RC rats (P < 0.05). FAS activity was increased 19- and 39-fold, respectively, in the RC and RF rats compared with the FA rats. Exercise decreased FAS activity to approximately one-third of the resting control value in both RC and RF rats (P < 0.05) but not in FA rats. L-PK activity was elevated by 55% in RC and 100% in RF rats compared with FA rats (P < 0.05). FA and RF rats also showed a reduction of L-PK activity with exercise. No significant alteration of other lipogenic enzymes was observed after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP Citrate (pro-S)-Lyase↗

PubMed1995

Optimum ratio to lysine of threonine, tryptophan, and sulfur amino acids for finishing swine.

Forty-eight crossbred (PIC line 26 x Camborough 15) pigs were used in two finishing trials to compare the ideal ratios of threonine (Thr), tryptophan (Trp), and sulfur amino acids (SAA) to lysine (Lys) determined for young pigs to a proposed ratio of these amino acids for finishing pigs. Trial 1 involved 20 barrows and 20 gilts that were self-fed in sex groups of two. Trial 2 was a Latin square design that used four barrows and four gilts that were individually fed in metabolism cages. Separate diets were used for the early (EF = 56 to 90 kg) and late (LF = 90 to 112 kg) finishing periods. Diets were formulated from a corn-soybean meal mixture and contained 11% CP and .55% digestible lysine for EF pigs and 10% CP and .50% digestible lysine for LF pigs. Negative-control diets in both the EF and LF periods were designed to be slightly deficient in lysine and to contain digestible Thr (65%), Trp (18%), and SAA (60%) at the ideal ratio to digestible Lys determined for 10- to 20-kg pigs. The experimental diet in both the EF and LF periods was formulated to contain digestible Thr (70%), Trp (20%), and SAA (65%) at the proposed ideal ratio to digestible Lys for finishing pigs. In Trial 1, increased ratios of Thr, Trp, and SAA improved gain:feed ratio, whole-body and carcass protein concentration, and whole-body and carcass protein accretion. In Trial 2, LF pigs responded to the increased ratios of Thr, Trp, and SAA with decreased urinary nitrogen excretion and increased N retention.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids, Sulfur↗

PubMed1995

Ideal digestible lysine level for early- and late-finishing swine.

Two hundred sixteen crossbred (PIC line 26 x Camborough 15) pigs were used in three trials to determine optimal digestible lysine levels during early (EF = 50 to 95 kg) and late (LF = 90 to 110 kg) finishing periods. Pigs were self-fed in sex groups of two in all trials. The assay diets for EF and LF periods were 11 and 10% CP corn-soybean meal diets, respectively, supplemented with threonine, methionine, tryptophan, valine, and isoleucine. Corn-soybean meal positive-control diets were included in each trial (14.5% CP for EF and 13.5% CP for LF). This dietary CP regimen was shown to give the same performance and carcass quality as a 17% CP corn-soybean meal diet fed during both EF and LF. Plateau portions of the lysine response curves resulted in performance levels that were equal to or greater than those achieved with pigs fed the 14.5/13.5% CP positive-control diets. Early-finishing pigs responded (P < .05) to graded doses of digestible lysine (.41 to .71%) for daily weight gain, gain:feed, longissimus muscle area, 10th-rib fat depth, lean gain, and plasma urea N. Digestible lysine requirement estimates based on average plateau points were .58% for EF barrows and .64% for EF gilts. Late-finishing pigs responded (P < .05) to digestible lysine doses (.35 to .65%) for daily weight gain, gain:feed, lean gain, and plasma urea N. Digestible lysine requirement estimates based on average plateau points were .49% for LF barrows and .52% for LF gilts.

Aging↗

PubMed1995

Estimates of zinc and iron bioavailability in pork liver and the effect of sex of pig on the bioavailability of copper in pork liver fed to male and female chicks.

Four chick experiments were conducted to investigate possible explanations for why Cu bioavailability in pork liver is zero. One possible explanation was that pork liver contains compounds, such as Zn, that directly or indirectly inhibit Cu utilization. It has also been suggested that sex differences may influence Cu bioavailability. The effect of freeze-dried (FD) pork liver from gilts vs barrows was first examined. Neither FD gilt liver nor FD barrow liver provided any bioavailable Cu to chicks. The effect of sex of the chicks used in the assay (i.e., male chicks vs female chicks) was also examined, but there were no sex-dependent differences (P > .10) in the slopes of the standard curve generated by added Cu from CuSO4 or in the responses to added FD pork liver. Based on bone Zn uptake, Zn bioavailability in FD barrow liver and FD gilt liver was not different (P > .04) from that in ZnSO4, but Fe bioavailability (hemoglobin repletion assay) was approximately 40% (P < .05) of that in FeSO4 in both FD gilt liver and FD barrow liver.

Animal Feed↗

PubMed1995

Copper bioavailability in pork liver and in various animal by-products as determined by chick bioassay.

Three chick experiments were conducted to investigate possible explanations for why pork liver provides no bioavailable Cu to chicks. Autoclaving, acid-hydrolysis, and protease-digestion increased (P < .01) Cu bioavailability in pork liver to 32, 46, and 63%, respectively, from virtually 0% of the Cu in unprocessed pork liver (relative to CuSO4, which was set at 100%). Addition of EDTA at 200 mg/kg to the diet containing 1 mg of Cu/kg from unprocessed pork liver also resulted in an increased (P < .07) Cu bioavailability, to 23%. Tissues representing different sources of endogenous Cu in the pig also were evaluated for their Cu bioefficacy. Freeze-dried (FD) porcine bile did not have any bioavailable Cu, whereas spray-dried porcine plasma contained Cu that was as available (99%) as that in CuSO4. In addition, when FD pork liver or FD porcine bile was added to the basal diet containing .5 mg of Cu/kg from CuSO4, Cu bioavailability in CuSO4 was reduced (P < .05) to 34% and 19%, respectively, of values obtained with CuSO4 alone. An additional experiment was conducted to estimate Cu bioefficacy in selected animal-source feed ingredients. Copper bioavailability in all-beef meat and bone meal, all-pork meat and bone meal, mixed-species meat and bone meal, high-bone meat and bone meal, poultry byproduct meal, and hog hair meal was 4, 53, 28, 8, 42, and 9%, respectively, relative to CuSO4. Feather meal did not provide any bioavailable Cu to chicks.

Animal Feed↗

PubMed1995

Effect of microbial phytase and 1,25-dihydroxycholecalciferol on dietary copper utilization in chicks.

Bile Cu accumulation in Cu-depleted chicks fed Cu concentrations between .56 and 1.56 mg Cu/kg (0, .5, or 1 mg supplemental Cu/kg) was used to investigate the effect of microbial phytase at 600 U/kg and 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] at 10 micrograms/kg on Cu bioavailability from dehulled soybean meal (SBM) and cottonseed meal (CSM). The bioavailability of Cu (relative to CuSO4.5H2O, which was set at 100%) in SBM and CSM was 43 and 39%, respectively. Phytase addition (600 U/kg diet) decreased Cu bioavailability in SBM to 21%, but did not affect that in CSM (34%). Copper bioavailability in SBM was not affected by addition of 1,25-(OH)2D3 (10 micrograms/kg diet), but that in CSM was nearly doubled by 1,25-(OH)2D3 supplementation.

6-Phytase↗

PubMed1995

Effect of high copper dosing on hemicellulose digestibility in cecectomized cockerels.

A precision-fed cockerel digestibility assay using ground corn cobs was conducted to test a theory that birds fed pharmacological doses of Cu (250 mg Cu/kg diet) may exhibit a higher hemicellulose digestibility due to increased release of lysosomal enzymes in the bile. Finely ground corn cobs were crop intubated into adult cockerels that had been pretested on diets containing either 0 or 250 mg Cu/kg (from CUSO4.5H2O). Copper-loaded cockerels showed higher (P < .05) true dry matter digestibility, hemicellulose digestibility, and TMEn than the control cockerels. True dry matter digestibility of corn cobs was 11.1% in Cu-loaded cockerels, which was nearly double that observed (6.2%) in control cockerels. Hemicellulose digestibility also increased from 22.1% in control cockerels to 36.6% in Cu-loaded cockerels. Copper-loaded cockerels obtained some TMEn (117.7 kcal/kg) from corn cobs, whereas the control cockerels obtained no TMEn from the corn cob intubation. The preliminary results presented herein demonstrate that pharmacological doses of dietary Cu may improve hemicellulose digestibility, which may in part explain the growth-promoting effect of Cu.

Animal Nutritional Physiological Phenomena↗

PubMed1995

Iron requirement of chicks fed a semipurified diet based on casein and soy protein concentrate.

An Fe depletion and repletion study was conducted to determine the Fe requirement of chicks fed a casein-dextrose diet containing soy protein concentrate. Weight gain, hematocrit, hemoglobin, and serum total Fe showed marked increases when graded levels (0, 5, 10, 20, 30, 40, and 50 mg/kg) of Fe from analytical grade FeSO4.7H2O were added to an Fe-deficient basal diet containing 46.5 mg Fe/kg. Subjecting the hemoglobin data to broken-line analysis indicated that the Fe requirement was 38.5 mg/kg of supplemental Fe (i.e., total dietary Fe of 85 mg/kg). Heart hypertrophy was observed in Fe-deficient chicks, but Fe supplementation (more than 20 mg/kg) alleviated the problem.

Animals↗

PubMed1995

Zinc stores in chickens delay the onset of zinc deficiency symptoms.

Three chick assays were conducted to evaluate Zn depletion rates in whole body and various tissues. In Assay 1, chicks fed a corn-soybean meal diet containing 1,037 mg Zn/kg had twice as much Zn in intestine and bone and 50% more Zn in liver and whole body than chicks fed 37 mg Zn/kg (P < .01). In Assay 2, the minimum Zn requirement for growth of chicks consuming a chemically defined, amino acid diet was 10.6 mg Zn/kg. In Assay 3, chicks were fed the chemically defined diet containing either 300 or 10.6 mg Zn/kg during an 8-d pretest period, after which they were fed either 0 or 10.6 mg Zn/kg for 9 d. Tissue Zn concentrations were determined on Days 0, 1, 2, 3, 4, 5, 7, and 9 of the test period. Following the pretest period, Zn was higher in the liver, tibia, and small intestine, but not in muscle, of chicks fed 300 mg Zn/kg than of those fed 10.6 mg Zn/kg (P < .01). Growth of chicks switched from 10.6 to 0 mg Zn/kg was less than for chicks maintained on 10.6 mg Zn/kg by Day 5 (P < .05), whereas chicks switched from 300 to 0 mg Zn/kg did not display a growth depression relative to the control until Day 8 (P < .05). Zinc that accumulated in the liver and small intestine of chicks fed the 300 to 0 Zn regimen declined until Day 3 of the test period, whereas tibia Zn decreased until Day 8. Chicks fed the 10.6 to 0 regimen did not display a substantial decrease in small intestine, liver, or tibia Zn. The data confirm that Zn can accumulate in bone, liver, and intestine and can subsequently be released for use during a period of Zn deficiency. The data also indicate that chicks fed a diet containing the minimum requirement of Zn cannot accumulate reserves of Zn that become available for use during a subsequent period of Zn depletion.

Animal Nutritional Physiological Phenomena↗

PubMed1994

Copper-amino acid complexes are partially protected against inhibitory effects of L-cysteine and L-ascorbic acid on copper absorption in chicks.

Chick experiments were conducted to investigate whether two new Cu-amino acid complexes, Cu-methionine (Cu-Met) and Cu-lysine (Cu-Lys), would differ from a standard Cu source (analytical-grade CuSO4) in their reaction to the inhibitory dietary effects of physiologic doses of L-cysteine (4000 mg/kg diet) or L-ascorbate (1000 mg/kg diet) on Cu absorption. Whether absorbed actively (as evaluated by a bile Cu assay at low Cu doses) or passively (as evaluated by a liver Cu assay at high Cu doses), cysteine inhibited Cu absorption more than did ascorbate. In addition, the inhibitory effects of cysteine and ascorbate were not additive, but they enhanced the inhibitory effect of Zn when evaluated at low Cu doses. Ascorbate inhibited Cu utilization from CuSO4 to 58.0% of the unsupplemented reference group at low Cu doses, which was greater (P < 0.05) than the inhibitory effect of ascorbate of Cu-Lys (78.7%) or Cu-Met (89.1%). Cysteine inhibited Cu utilization from CuSO4, Cu-Lys and Cu-Met at low Cu dose levels to 49.1, 44.1 and 50.2%, respectively, of unsupplemented reference groups of each source. These values were not different from each other. On the other hand, cysteine inhibited Cu utilization from CuSO4 to 8.5% of the unsupplemented reference group at high Cu doses, which was greater (P < 0.05) than the inhibitory effect on Cu-Lys (29.5%) or Cu-Met (39.9%). Ascorbate reduced Cu utilization from CuSO4, Cu-Lys and Cu-Met at high Cu doses to 72.8, 63.7 and 68.3%, respectively, of unsupplemented control groups of each source.

Animals↗

PubMed1994

Iron deficiency reduces the efficacy of tryptophan as a niacin precursor.

A niacin-deficient purified amino acid diet that contained adequate (40 mg/kg) or deficient (10 or 15 mg/kg) iron was used to assess the growth promoting efficacy of tryptophan as a niacin precursor. Basal diets contained 1400 mg/kg tryptophan, a level that was established as meeting the requirement for tryptophan per se in diets containing excess nicotinic acid. Chicks fed the iron-deficient diets had markedly lower hemoglobin concentrations than those fed the iron-adequate diets. Regardless of iron level, chicks exhibited linear growth responses to either nicotinic acid or tryptophan supplementation. Using multiple-linear regression of weight gain on supplemental tryptophan or nicotinic acid intake, the efficiency (wt:wt) of tryptophan conversion to niacin activity (i.e., tryptophan slope divided by nicotinic acid slope) was a mean of 1.77% (56:1) for chicks fed the iron-deficient diet. This was significantly (P < 0.05) lower than the 2.39% (42:1) efficiency calculated for chicks fed the iron-adequate diet. Thus, iron deficiency reduced tryptophan utilization (for NAD synthesis) but had no effect on nicotinic acid utilization. The results suggest that pellagra in populations having endemic anemia and protein-energy malnutrition may be due not only to inadequate intakes of bioavailable niacin but also to inadequate intakes of bioavailable iron.

Animals↗

PubMed1994

Manganese utilization in the chick: effects of excess phosphorus on chicks fed manganese-deficient diets.

Young chicks were used in a 16-d feeding study to evaluate the effects of excess dietary P on Mn utilization. The basal casein-dextrose diet (1.4 mg Mn/kg) was supplemented with 0, 3.5, 7.0, or 10.5 mg Mn/kg from MnSO4.H2O and was fed in the absence or presence of .8% excess dietary P (equal P contributions from KH2PO4 and NaH2PO4). Diets containing .8% excess P were also supplemented with .8% excess Ca (CaCO3) to keep the Ca:P ratio above 1:25 so as to prevent anorexia associated with excess dietary P per se. Both growth rate and total tibia Mn responded linearly (P < .01) to Mn supplementation in chicks fed the normal level of P, but those fed excess P responded erratically. Excess P did not affect growth or tibia Mn in chicks fed the basal diet, but birds fed diets with supplemental inorganic Mn grew slower (P < .01) and had lower (P < .01) quantities of Mn in tibia when excess P was supplemented. Manganese content in the tibia of chicks fed excess P was 55% of that in chicks fed an adequate level of P.

Animal Feed↗

PubMed1994

Ideal amino acid profile for chicks during the first three weeks posthatching.

Two chick bioassays with chemically defined amino acid (AA) diets were conducted to compare three different AA profiles: the NRC 1984 and NRC 1994 requirement profile and the Illinois Ideal Chick Protein (IICP) AA profile. The two battery studies involved chicks during the 2nd and 3rd wk after hatching. In Assay 1, indispensable AA (including glycine and proline) were ratioed to lysine according to requirement ratios present in NRC 1984 and NRC 1994, with digestible lysine set at either deficient (.80% of diet) or superadequate (1.12% of diet) levels for the purified diet in question. All diets were kept isonitrogenous (2.83% N) by varying the level of L-glutamic acid. At .80% lysine, chicks fed the NRC 1994 AA profile gained 60% faster (P < .01) than those fed the NRC 1984 AA profile. With excess digestible lysine (1.12%) and all other indispensable AA increased proportionately, chicks fed NRC 1994 still out-gained those fed NRC 1984 by 13% (P < .05). Ratios of AA (with respect to lysine) in NRC 1994 were equal to or higher than those in IICP, except for histidine. This was due to a lower estimated lysine requirement in NRC 1994 than that used for IICP. When NRC 1994 was compared with IICP in a chick bioassay involving isonitrogenous diets (2.36% N) and digestible lysine set at a deficient level of .90%, weight gain and feed efficiency were similar between diets. This result suggested that most of the indispensable AA in the NRC 1994 AA profile were too high relative to lysine, probably because lysine, the reference AA, was too low relative to the other AA.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1994

Digestible lysine requirement of male and female broiler chicks during the period three to six weeks posthatching.

Experiments were conducted to determine the dietary digestible lysine requirement of male and female broilers (Ross x Ross) during the period 22 to 43 d posthatching. An amino acid-fortified basal diet containing corn, feather meal, and soybean meal as intact protein sources provided .63% total lysine, 20% CP, and 3,200 kcal MEn/kg. The basal diet contained .51% true digestible lysine as determined with a precision-fed cecectomized adult cockerel assay. Growth rate and feed efficiency of birds fed the basal diet fortified with a surfeit level of L-lysine were equal to those of birds fed a methionine-supplemented corn-soybean meal positive control diet (20% CP; 3,200 kcal MEn/kg). Graded levels of synthetic L-lysine (0, .1, .2, .3, .4, .5, .6%) were added to the basal diet to produce growth response curves. Subjecting the growth data to broken-line analysis indicated that the digestible lysine requirement for maximum body weight gain was .85% for males and .78% for females. The requirement for optimum feed efficiency was higher: .89% for males and .85% for female broilers. Breast meat (Pectoralis major) yield increased quadratically in response to lysine addition, and the responses suggested that the lysine requirement for maximal breast yield was not greatly different from that predicted from the feed efficiency data. Abdominal fat (percentage of live body weight) increased from the first to the second increment of lysine, but it then declined as lysine level was increased further.

Adipose Tissue↗