Storage of milk powders under adverse conditions. I. Losses of lysine and of other essential amino acids as determined by chemical and microbiological methods

Whole-milk powders containing 25 g water/kg were stored for up to 9 weeks in sealed aluminium containers at elevated temperatures. Lysine and other essential amino acids were measured by chemical and microbiological methods. Storage at 60 degrees resulted in the progressive formation of lactulosyl-lysine. After 9 weeks, 30% of the lysine groups were present in this form. The powders still retained their natural colour and the levels of tryptophan, methionine, cyst(e)ine and leucine remained unchanged. Storage at 70 degrees resulted in the formation of lactulosyl-lysine followed by its complete degradation with the development of browning. Available tryptophan, methione, leucine and isoleucine decreased progressively during storage. The different methods for lysine determination gave widely dissimilar results. The direct fluorodinitrobenzene (FDNB) technique and reactive lysine from furosine were considered to be the most reliable methods. The FDNB-difference, dye-binding lysine, Tetrahymena and Pediococcus methods all seriously underestimated reactive or available lysine in heat-damaged milk powders. Tetrahymena and Pediococcus appeared to utilize lactulosyl-lysine as a source of lysine. The results are discussed in relation to storage and distribution of milk powders in hot climates.     

Effects of substitution of tricaproin for tallow and of protein concentration in milk substitutes on nitrogen and energy balance in the preruminant lamb

1. Results of 138 nitrogen balance studies from experiments with forty male Limousin and nineteen male Ile de France preruminant lambs were used to estimate total N requirements and to assess the effects of dietary tricaproin inclusion, protein concentration, lysine and methionine supplementation and the age of lambs on protein retention. In addition, energy balances were obtained in twenty-four of the Limousin lambs from birth up to 3 weeks of age by means of a slaughter technique. 2. For milk substitute unsupplemented with amino acids, tricaproin inclusion increased N balance slightly (P less than 0.001) when a medium-protein concentration (260 g/kg dry matter (DM] was used, in 2-week-old lambs (+4.3%) and in 5-week-old Limousin lambs (+5.3%), or very markedly when a high-protein concentration (320 g/kg DM) was used, in 2-week-old lambs (+14.5%) and in 5-week-old lambs (+18.6%). Protein requirements decreased from 300 g/kg DM in 3-week-old lambs to 270 g/kg DM in 5-week-old lambs for the control milk containing tallow-coconut oil mixture (0.67:0.33 by wt) and was increased above 300 g/kg DM at all ages in the case of experimental milk containing tallow-coconut oil-tricaproin mixture (0.33:0.33:0.33, by wt). 3. For milk containing either a medium- or a high-protein concentration and supplemented with lysine and methionine, inclusion of tricaproin increased N balance (P less than 0.01) to a similar extent (+8.5 up to +14.3%) in 1 to 2- and 3-week-old Limousin lambs. An increase in N concentration in the milk had no effect in 1- and 2-week-old lambs, but led to a decreased N balance in 3-week-old lambs. Protein requirements decreased from 310 g/kg DM in 1-week-old lambs to 190 g/kg DM in 3-week-old lambs for the milk containing tallow-coconut oil or from 300 g/kg DM in 2-week-old lambs to 210 g/kg DM in 3-week-old lambs for the milk containing tallow-coconut oil-tricaproin. 4. For the Ile de France lambs given milk supplemented with lysine and methionine, tricaproin inclusion did not alter N balance. Protein requirements decreased from 370 g/kg DM in 2-week-old lambs to 270 g/kg DM in 4-week-old lambs for milk containing both kinds of fat mixtures.(ABSTRACT TRUNCATED AT 400 WORDS)     

The amino acid requirements of the preruminant calf.

1. Ten calves (50--58 kg live weight) were given a diet consisting of diluted whole milk, wheat gluten and supplemented with appropriate nutrients including amino acids but deficient in lysine. The lysine reequirements of these calves, which were growing at approximately 0.25 kg/d, were estimated from responses to lysine supplementation of this diet. From plasma urea, plasma lysine, nitrogen retention and apparent digestibility of N responses the estimated lysine requirements were 8.5, 7.5, 7.2 and 7.6 g/d respectively. 2. From the mean lysine requirement (7.8 g/d) and the ratio, lysine: otheressential amino acids in carcasses of similar calves the estimated requirements were (g/d): methionine 2.1, cystine 1.6, threonine 4.9, valine 4.8, isoleucine 3.4, leucine 8.4, tyrosine 3.0, phenylalanine 4.4, histidine 3.0, arginine 8.5, tryptophan 1.0.     

Reactions of proteins with oxidizing lipids. 1. Analytical measurements of lipid oxidation and of amino acid losses in a whey protein-methyl linolenate model system

The reactions between protein-bound amino acids and oxidizing lipid were investigated in a whey protein-methyl linolenate (C18:3)-water model system. The extent of fat oxidation was followed by measuring oxygen uptake, hydroperoxide formation and hydrocarbon (ethane and pentane) formation. Significant losses occurred with lysine (up to 71%), tryptophan (up to 31%) and histidine (up to 57%). Methionine was extensively oxidized to its sulphoxide but less than 2% was further oxidized to the sulphone. No other amino acids were affected. Increasing storage temperature (20 degrees, 37 degrees, 55 degrees) resulted in an enhancement of fat oxidation reactions and amino acid degradation. Increasing water activity (0.28, 0.65, 0.90) increased losses of lysine and tryptophan but had no influence on the oxidation of methionine, the level of remaining hydroperoxides or O2 uptake. Hydrocarbons were decreased. Limitation of O2 uptake to 1 mol/mol lipid instead of excess O2 (O2 uptake about 2.5 mol/mol lipid in 4 weeks) significantly reduced the degradation of lysine and tryptophan but had less influence on the oxidation of methionine. The level of remaining hydroperoxides was increased but hydrocarbons were unaffected.     

An evaluation of total and digestible lysine as a predictor of lysine availability in protein concentrates for young pigs

Forty pigs between 23 and 51 d of age were given, ad lib., diets containing 7.9 g lysine/kg. The diets contained wheat and one of five protein concentrates: milk, peanut (Arachis hypogaea) meal, cotton-seed (Gossypium herbaceum) meal, meat meal or lupins (Lupinus augustifolius). Twenty of the pigs were given an indigestible marker, 103Ru-labelled Tris-(1,10-phenanthroline)-ruthenium(II) chloride, between 51 and 56 d of age and were killed at 56 d of age. A further forty pigs, between 23 and 51 d of age, were given the same diets supplemented with 3 g L-lysine hydrochloride/kg. The weight gains of the pigs given the diets containing 7.9 g lysine/kg (95-153 g/d) were significantly less (P less than 0.05) than those of the pigs given the diets containing 10.9 g lysine/kg (274-340 g/d). Weight gains of pigs given the diets containing meat meal were less than those of pigs given diets containing milk, peanut meal or lupins. Feed conversion ratios decreased and N balances increased with increasing lysine content of the diets. Apparent digestibilities of dry matter (DM) and nitrogen of the diets containing meat meal and cotton-seed meal were less than those of the other three diets, but there was no effect of lysine content of the diets on these indices. The major site of DM and N absorption for the diet containing milk was the duodenum while for the other four protein concentrates the jejunum and ileum were the major absorption sites. Apparent digestibility of lysine from the five diets ranged from 0.54 to 0.75. The retention of the apparently absorbed lysine in weight gain was 0.86-0.94, and there was no significant (P greater than 0.05) difference between diets which suggested that the apparent digestibility of lysine could be an indicator of its availability.     

The optimal amino acid supplementation of barley for the growing pig. 1. Response of nitrogen metabolism to progressive supplementation.

1. In five experiments, involving 142 female pigs weighing on average 33 kg, estimates were made of the amounts of essential amino acids which minimized urinary N excretion when diets with barley as the only source of protein were given at the rate of 120 g/kg0.75 per d. 2. With additions of lysine (4.0 g/kg diet) and threonine, (1.2 g/kg diet) to barley urinary N excretion decreased from 0.91 to 0.36 g/kg0.75 per d, corresponding to an increase in biological value (bv) from 0.51 to 0.86. 3. With these additions of lysine and threonine, there were no responses to additions of tryptophan, methionine or isoleucine, or to further additions of lysine or threonine, but addition of histidine significantly reduced N excretion. 4. No optimal addition of histidine could be determined; the mean rate of N excretion after addition of histidine (not less than 0.3 g/kg diet) was 0.27 g/kg0.75 per d, corresponding to a BV of 0.93. 5. There was a variation between pigs from different litters in their responses to added histidine. Those with low rates of N excretion on the unsupplemented diet did not respond to additions of histidine, but those with high rates did. 6. It is concluded that additions of only three amino acids can greatly improve the nutritive value of barley protein for the growing pig and that the amino acid composition of the supplemented protein closely approaches the ideal; it is also similar to whole-body tissue protein.     

Nutritional limitations to increased production on pasture-based systems

The constraints to high levels of milk production imposed by a high-quality-pasture diet, and development of feeding strategies to overcome these limitations, were examined by modelling the nutritional status of New Zealand Friesian and North American Holstein-Friesian dairy cows grazing high-quality pasture. The Cornell Net Carbohydrate and Protein System (CNCPS) was used to predict sensitivity of milk production to a 10% change in the composition of pasture nutrients. The rate at which fibre and protein were degraded in the rumen and the value given to effective fibre and lignin content significantly affected the supply of metabolisable energy and protein, and the profile of amino acid supply. The first limiting factor in milk production when only high-quality pasture was fed was metabolisable energy supply, while specific amino acids, particularly methionine and lysine, limited milk production when > 20 g/kg diet consisted of a grain supplement. Compared with cows fed a total mixed ration in confinement, North American Holstein-Friesians grazing all pasture produced less milk (29.6 v. 44.1 kg/d). Of the difference in milk production 61% could be attributed to a lower DM intake (19 kg/d v. 23.4 kg/d). Predictions using the CNCPS indicated that supply of metabolisable energy was the first-limiting factor for milk production from high-quality pasture (251 g crude protein (N x 6.25)/kg, 432 g neutral-detergent fibre/kg, 77% in vitro DM digestibility), rather than metabolisable protein or amino acids. In addition, these nutritional limitations imposed by pasture diets will be greater for dairy cow genotypes that have not been selected for high performance within a pasture system.     

Amino acid composition of the diet in a region of Southern Tunisia.

As part of a study of the effects of lysine supplementation of wheat products in Southern Tunisia one qualitative and four quantitative surveys of food consumption were carried out. The average diet provided 7.1 MJ (1,670 kcal), 42 g of protein and 1,280 mg of lysine per person per day. The overall dietary protein thus supplied only 31 mg of lysine/g of protein, or about 56% of the level recommended by the FAO/WHO Expert Committee on Protein Requirements. Addition of lysine to all wheat products to a final effective concentration of 0.2% would raise the dietary lysine level to 45 mg/g protein, or 82% of the FAO/WHO recommended level, at which time threonine would become limiting. Irrespective of whether the FAO/WHO pattern of 1973, breast milk, cow's milk, whole egg or a modification of the FAO pattern of 1957 was used to assess the quality of the protein in the diet, lysine was the first, and threonine the second limiting amino acid (except in comparison with breast milk, which showed tryptophan as the second limiting amino acid). In no case did there appear to be any problem with the sulfur-containing amino acids.     

Responses to post-ruminal infusions of casein and arginine, and to dietary protein supplements in lactating goats.

1. In Expt 1 a study was made in goats of responses in terms of milk production, nitrogen utilization and plasma amino acids to abomasas infusions of casein (45 g/d) in goats given 2.5 kg/d of a ration containing crude protein (N x 6.25) at 109 (L1) or 146 (H1) g/kg. 2. In Expt 2 a study was made in goats of responses in terms of milk production, nitrogen utilization, plasma amino acids and growth hormone levels to abomasal infusions of casein (45 g/d) or arginine (25 g/d) in goats given 2.3 kg/d of a ration containing crude protein (N x 6.25) at 104 g/kg (L2). These observations were made also in goats given a ration containing crude protein at 136 g/kg (H2). 3. Milk production in Expt 1 was 2.75, 2.45 and 2.76 kg/d on L1+casein, H1 and H1+casein treatments respectively, the response to casein infusion being significant (P less than 0.05). Milk production in Expt 2 was 1.90, 2.04, 1.96 and 1.96 kg/d on L1, L2+casein, L2+arginine and H2 treatments respectively, and the differences were not significant. 4. Total N intake in Expt 1 was 49, 58 and 64 g/d on L1+casein, H1 and H1+casein treatments respectively. Faecal N was similar on the three treatments (14 g/d), urinary N was 15, 23 and 30 g/d and milk N was 14, 12 and 14 g/d on the respective treatments. Total N intake in Expt 2 was 33, 40, 43 and 44 g/d on L2, L2+casein, L2+arginine and H2 treatments respectively. Faecal N was similar on the four treatments (12 g/d), urinary N was 7, 10, 13 and 14 g/d and milk N was 9, 9, 8 and 8 g/d on the respective treatments. 5. The concentration of indispensable amino acids in plasma was increased by casein infusion in both experiments. It was 1279, 825 and 1133 micrometers/l on L1+casein, H1 and H1+casein treatments respectively in Expt 1, and 1081, 1582, 1055 and 1163 micrometers/l on L2, L2+casein, L2+arginine and H2 treatments respectively in Expt 2. 6. The concentration of arginine in plasma was doubled 1 h after the onset of arginine infusion in Expt 2, Growth hormone levels in plasma were not increased when arginine levels rose following arginine infusion. and did not differ between treatments. 7. The results of the two experiments showed that the stimulatory effect on milk production of intra-abomasal infusion of casein was not reproduced by increasing the dietary intake of protein or by infusing arginine. The results of the second experiment showed that abomasal infusion of arginine did not stimulate production of growth hormone and that growth hormone apparently was not implicated in the effects of casein infusion on milk production.     

Assessment of ascorbic acid stability in different multilayered parenteral nutrition bags: critical influence of the bag wall material

BACKGROUND: The recent development of multilayered bags has minimized ascorbic acid oxidation in parenteral nutrition (PN) admixtures. However, the gas-barrier property of multilayered bags depends on their plastic material. This study compared ascorbic acid stability in different multilayered bags under experimental conditions. METHODS: Oxygen permeability of a newly developed 6-layered bag (6-L) was compared with a highly mechanical-resistant 3-layered bag (3-L(R)) and a highly flexible 3-layered bag (3-L(F)) using gas chromatography. Ascorbic acid stability was assessed by iodine titration in bags filled with 2.5 L H(2)O and 40 g carbohydrates after setting residual O(2) content at < or =1 or > or =5 ppm. The effect of storage at 4 degrees C, 21 degrees C, and 40 degrees C on ascorbic acid stability was assessed over 48 hours in a complete PN admixture (ie, 330 g carbohydrates, 100 g lipids, 96 g amino acids and trace elements) using high-pressure liquid chromatography. RESULTS: Oxygen permeability was markedly reduced in 6-L bags (0.5 mL O(2) /m(2)/d) compared with 3-L(R) (150 mL O(2) /m(2)/d) and 3-L(R) (1500 mL O(2)/m(2)/d). Accordingly, ascorbic acid was more stable in 6-L bags (half-life [T(1/2)] = 16 days up to 40 degrees C) than in 3-L(R) (T(1/2) = 9 days at 4 degrees C, 47 hours at 21 degrees C and 29 hours at 40 degrees C) and 3-L(F) (T(1/2) = 15 hours at 4 degrees C, 10 hours at 21 degrees C, and 6 hours at 40 degrees C). During the first 6 hours after PN admixture compounding, an additive ascorbic acid loss of 4.6 +/- 0.5 mg/L/ppm O(2) occurred because of residual O(2) in the bag. CONCLUSIONS: The new combination of plastic layers and careful O(2) monitoring during the filling process allowed near to complete prevention of ascorbic acid degradation in multilayered PN bags during 48 hours, regardless of the storage temperature.     

Efficiency of utilization of wheat and milk protein in healthy adults and apparent lysine requirements determined by a single-meal [1-13C]leucine balance protocol

BACKGROUND: We recently reported better wheat-protein utilization and a higher apparent lysine requirement than would be predicted, because of adaptive mechanisms of lysine conservation. However, such findings may be subject to the feeding protocol of frequent small meals. OBJECTIVE: We used a [1-13C]leucine balance, large single-meal protocol to estimate the utilization of wheat and the consequent lysine requirements. DESIGN: Wheat and milk utilization were compared in 5 adults infused for 9 h with L-[1-13C]leucine, in the postabsorptive (0-3 h) and postprandial (3-9 h) states after ingestion of a single meal of either milk (30.4 kJ/kg; 32% of energy as protein) or a mixture of wheat gluten and whole wheat (29.2 kJ; 26.7% of energy as protein). Premeal nitrogen balance was predicted from [1-13C]leucine oxidation and postmeal balance predicted from cumulative increased leucine oxidation, enabling evaluation of the metabolic demand for protein, the efficiency of postprandial protein utilization (PPU), and the requirements for wheat protein and lysine. RESULTS: Mean (+/-SD) PPU was 0.61 +/- 0.03 and 0.93 +/- 0.02 for wheat and milk (P < or = 0.001), respectively, and the estimated average wheat-protein requirement (0.6 g.kg(-1).d(-1)/PPU) was 0.98 +/- 0.05 g.kg(-1).d(-1), indicating a lysine requirement of 18.3 +/- 1.0 mg. kg(-1).d(-1). CONCLUSIONS: Measured wheat utilization efficiency at 0.61 was considerably higher than the value predicted from wheat lysine intake and milk protein lysine deposition (ie, 0.222 +/- 0.004). These results confirm our previous finding that lysine conservation allows wheat protein to be utilized more efficiently than expected and is consistent with a lysine requirement in fully adapted individuals of 19 mg.kg(-1).d(-1), as indicated by recalculated nitrogen balance data.     

Lactation performance of rural Mesoamerindians.

Anthropometry, body composition and dietary intake of 30 lactating Otomi Indians of Capulhuac, Mexico, were studied to identify maternal factors which potentially limit lactation and thereby infant growth. Human milk production, milk composition, and maternal dietary intake, body weight, skinfold thicknesses, and body composition were measured at 4 and 6 months postpartum. The 2H2O dose-to-mother method was used to estimate milk production and maternal total body water (TBW). Fat-free mass (FFM) was calculated as TBW/0.73. Body fat was computed as body weight minus FFM. Human milk samples were analyzed for energy, nitrogen, lactose and fat using standard analytical methods. Maternal diet was assessed by three 24-h intake recalls. Mean (SD) milk production was 885 (146) and 869 (150) g/d at 4 and 6 months, respectively. Milk concentrations of protein nitrogen (1.23 (0.17) mg/g) and lactose (66.6 (2.8) mg/g) were comparable to, but the concentrations of fat (22.2 (6.7) mg/g) and energy (0.54 (0.06) kcal/g) were lower than, values observed in economically privileged populations. Maternal height, weight, and BMI were 1.47 (0.06) m, 50.3 (6.0) kg, and 23.4 (3.1) kg/m2, respectively. Maternal TBW, FFM and body fat were 55.8 (4.6)%, 76.4 (6.3)%, and 23.6 (6.4)%, expressed as a percentage of body weight, respectively. Maternal energy and protein intakes averaged 1708 (338) kcal/d and 40 (10) g/d, respectively. Milk production was negatively correlated with maternal body fat (P = 0.006). Energy and fat concentrations in the milk of the Otomi women were positively related to their weight (P = 0.002), BMI (P = 0.05), and body fat (P = 0.004). Energy concentrations in milk were not related to rates of milk production (r = 0.24; P = 0.23). Nor was milk production or composition significantly associated with maternal dietary intake. Lactation performance of these Otomi women correlated significantly with maternal body size and composition, but not current dietary intake.     

螺旋藻对四氧化二氮导致的动物损伤的防护效应研究

目的探讨螺旋藻(SP)对四氧化二氮导致的动物损伤的防护作用。方法采用在静式染毒柜内吸入N2O4方式构建动物损伤模型,染毒柜体积120L,柜内温度保持在(25.0±0.5)℃,染毒柜内N2O4注入剂量为45μl,每隔5min向柜内补充N2O41μl,吸入染毒时间为30 min。ICR雄性小鼠随机分为正常对照,N2O4单纯染毒,SP低浓度+染毒,SP中浓度+染毒和SP高浓度+染毒,共5组,每组15只。SP分别以0.5、1.0、1.5g/kg配成灌喂液,提前4d经口灌胃,每只灌喂0.4 ml。第5日灌胃后1h进行染毒,前后共灌胃5d。脱臼法处死后取材,测定肺组织SOD、GSH-Px活性和MDA含量;取肺组织切片观察病理变化。结果 1.0g/kg SP分别提高SOD 38.9%,GSH-Px 73.9%,MDA 83.0%。肺组织病理观察显示:SP组较单纯染毒组病变轻。结论 SP对四氧化二氮导致的动物损伤有显著的防护作用。     

Responses to postruminal infusions of graded levels of casein in lactating goats

1. A study was made in goats of the response in terms of milk production, nitrogen utilization, plasma amino acids and amino acid uptake by the mammary gland, to postruminal infusion of casein. Goats in early lactation, housed in metabolism cages, were fed on 2-5 kg basal ration/d (containing 111 g crude protein (N X 6-25)/kg) and were given, by infusion into the abomasum, 0, 15, 30 or 45 g casein/d. 2. Milk production increased from 2-41 kg/d on the basal ration to 2-52, 2-80 and 2-94 kg/d in response to infusions of 15, 30 and 45 g casein/d respectively. Milk composition was unaffected except for milk fat, which was slightly decreased during infusions of the higher levels of casein. 3. The goats were found to be in positive N balance on the basal ration. Milk N output increased with casein infusion; the increase was equvalent to a miximum of 49% of the infused N. 4. The concentration of glucose in arterial blood plasma was decreased at the highest level of casein infusion but that of plasma urea N was unaffected by treatments. 5. Casein infusions increased the concentrations of total indispensable amino acids and the ratio, indispensable: dispensable amino acids in arterial plasma. Arterial concentrations and mammary extractions of most indispensable amino acis were increased, but only a few increases were statistically significant (Pless than 0-05); 6. Comparison of individual indispensable amino acids absorbed from the intestine with output in milk indicated that methionine was probably the first limiting amino acid. 7. The results of the experiment were compared to those of similar experiments with cows that have been reported by other workers. The possible ways in which the infused casein may have caused the responses were discussed. However, no firm conclusions regarding the mechanism involved could be drawn from the results of the present study.     

Water intake and excretion, urinary solute excretion and some stress indicators in mink (Mustela vison): effect of ambient temperature and quantitative water supply to lactating females

Lactation is a physiologically demanding period in mink production, during which kit and dam losses may occur. Ambient temperature and quantitative water supply are thought to affect animal performance and well-being, but conclusive data in the literature are sparse. Therefore, effects of ambient temperature (Ta; low, about 5 degrees; medium, about 15 degrees; high, average 20-25 degrees) and water supply (ad libitum (N), or 10% extra supplementation in the food (E)) were investigated regarding effects on quantitative water intake and excretion, urine osmolality and solute excretion, and urinary cortisol and catecholamines as stress indicators in an experiment with twelve lactating mink with litters of three to seven kits in three consecutive periods, lasting 3, 3 and 2 d respectively. Kit ages ranged from 15 to 20 d at the end of the experiment. Water requirement for milk production (factorial calculations) and water available for evaporation (balance component) were estimated. Period, and hence mainly Ta, had a significant influence on intake of metabolizable energy, quantitative water intake and excretion, but there was less effect of water supply. The total water intake and excretion were very high in relation to the weight of the animals as an effect of lactation. Water intake and excretion, and urinary Na excretion, seemed to be less accurately regulated compared with corresponding functions in non-lactating animals. Rectal temperature increased with increasing Ta, possibly as a means of decreasing evaporative water loss. Water output in milk was estimated to increase from 118 g/d at low Ta to 134 g/d at high Ta. The amounts of water available for evaporation were estimated to be 42, 58 and 69 g/kg0.75 at low, medium and high Ta. Cortisol data did not indicate that the animals experienced negative stress. It was concluded that prolonged periods of high Ta may be hazardous for lactating mink because of decreased intake of metabolizable energy resulting in energy deficit and excessive mobilization of body reserves simultaneously as the requirement for intake of water increases considerably.     

Maintenance threonine requirement and efficiency of its use for accretion of whole-body threonine and protein in Atlantic salmon (Salmo salar L.) fry

Eighteen groups of seventy Atlantic salmon (Salmo salar L.) fry (initial mean body weight 0.8 (sd 0.01) g) were fed on semi-purified diets containing graded levels of l-threonine (Thr) in 15 litres aquaria at a temperature of 14.5+/-1 degrees C. Doses of Thr represented 1, 31, 41, 51, 62, 72, 83 and 93 % of its ideal level for optimum protein deposition. Indispensable amino acids other than Thr were included in the same proportion (on a g/16 g N basis) as in the Atlantic salmon fry whole-body carcass. Following 36 d of feeding and a 36 h fast, fry were killed for whole-body protein and amino acid analysis. Weight gain (r2 0.98), protein accretion (r2 0.97), and Thr accretion (r2 0.97) were linear (P<0.01) functions of Thr intake. Slope of the Thr accretion regression line showed that the efficiency of Thr utilisation above maintenance was 76 %. At zero Thr intake, fry lost 5.4 mg Thr/kg body weight0.75 per d. The Thr maintenance requirement was 7.2 mg/kg body weight0.75 per d and the Thr requirement for growth was 66 mg for 1 g protein deposition. Increasing doses of Thr resulted in increased (P<0.05) concentrations of histidine and lysine, and decreased concentrations of isoleucine in whole-body protein. The maintenance need for Thr represented 13.4 % of the total need for Thr. The data suggest that efficiency of Thr utilisation above maintenance is constant at all levels of Thr intake between 1 and 93 % of the level required for optimum protein deposition.     

Measurement of milk intake: tracer-to-infant deuterium dilution method

The tracer-to-infant deuterium dilution method for the measurement of milk intake was evaluated in twenty breast-fed and twenty formula-fed infants. The isotope method was compared with conventional direct-weighing techniques. Human milk intake was assessed by 5 d test-weighing. Intakes of formula, supplemental foods, and water were determined by pre- and post-weighing of feeding bottles. An oral dose of 200 mg 2H2O/kg body-weight was given to each infant, and urine was sampled daily for 14 d. 2H enrichment of the urine was measured by gas-isotope-ratio mass spectrometry. Milk intakes estimated from the deuterium dilution method were consistently higher than those from direct-weighing; the mean difference between methods was 106 (SD 47) g/d or 14% for the breast-fed group and 70 (SD 155) g/d or 8% for the formula-fed group. Estimates of intake for some infants varied substantially between the two methods of measurement. When the estimated values of human milk intake were corrected for environmental water influx and insensible water loss during breast-feeding, the relative bias decreased to 5%. Correction of the estimated values of formula intake for environmental water influx decreased the relative bias to 1-2%. The acceptability of the deuterium dilution method to determine milk intake depends on the goals and the tolerance for error in group and individual intake estimates of a given study.     

Infused and ingested labeled lysines: appearance in human-milk proteins

Incorporation of two labeled forms of lysine into human-milk proteins was studied in fasted lactating subjects to determine whether highly labeled proteins could be produced for subsequent nutritional studies and whether the kinetics of milk synthesis could be studied in humans with stable isotope techniques. Five subjects, maintained on formula diets, received L-[13C1]lysine (27 mumol/kg) as an IV bolus and L-[15N2]lysine (27 mumol/kg) as an oral bolus 4 h postprandially. Milk samples were collected at 30, 45, 90, 150, 240, and 360 min. Tracer lysine levels in the hydrolysate of unfractionated milk protein were determined by gas chromatography-mass spectrometry isotope ratiometry. After a delay of at least 45 min, significant labeling of milk protein was detected and reached a maximum at 150 min with cumulative percent does recovery over 6 h of 0.5%. Human-milk proteins can be labeled for nutritional investigations and in vivo kinetics of milk protein synthesis can be studied with stable isotope techniques.     

The utilization of lysine by young pigs from nine protein concentrates compared with free lysine in young pigs fed ad lib

1. Pigs (n 195) between 21 and 49 d of age were given a basal diet containing wheat, wheat gluten and cotton-seed meal which was supplemented with one of nine protein concentrates or free L-lysine. The diets were given ad lib. in two experiments. 2. Increasing the lysine content of the diets from 6.9 to 10.1 g/kg increased the weight gains of the pigs from 89 to 317 g/d in the first experiment. In the second experiment the weight gains were increased from 68 to 213 g/d by increasing the lysine content of the diets from 5.9 to 9.5 g/kg. 3. The utilization of lysine from the protein concentrates was compared with the utilization of free L-lysine. 4. The utilization of lysine fro weight gain compared with free lysine was 0.86-0.88 for meat meals, 0.95-0.99 for soya-bean meal, 0.69-0.75 for cotton-seed meal, 0.90 for lupins (Lupinus augustifolius) and 0.99 for milk.     

Protein and energy metabolism of lactating Granadina goats

Twelve goats of the Granadina breed in mid- and late lactation were used in two consecutive years to determine their protein and energy requirements for lactation. The animals were individually fed on diets based on pelleted lucerne (Medicago sativa) hay and barley. A total of six balance experiments were carried out. Gas exchange was measured using open-circuit respiration chambers. Milk yield ranged widely from 0.649 to 1.742 kg/d in the first year and from 0.222 to 1.989 kg/d in the second year, a steady decline in milk output being observed as lactation progressed. Milk composition remained rather constant during the midstage of lactation, with an average content (/kg milk) for total solids, total nitrogen, fat and gross energy of 149.7 g, 5.39 g, 58.8 g and 3.59 MJ respectively. Total endogenous N, endogenous urinary N and maintenance requirement for N in lactating goats were estimated to be 244, 218 mg N/kg body-weight (W)0.75 per d and 478 mg total N/kg W0.75 per d respectively from regression equations. A constant efficiency of use of dietary N for milk N plus retained N of 51.0% was found. By regressing milk energy plus apparent body energy retention or loss on metabolizable energy (ME) intake, the maintenance energy requirement was estimated to be 401 kJ ME/kg W0.75 per d. When estimating the corrected milk yield as milk energy + (0.84 x negative energy retentio) + (1.05 x positive energy retention), regression analysis indicated that the overall efficiency of use of ME for lactation was 66.7%. Also, from a plot of apparent body energy retention v. milk energy yield, both expressed as a percentage of ME intake above maintenance, the efficiency with which ME was used to promote energy retention in the body during lactation was calculated to be 0.907 times that for milk secretion.