Digestible Energy Ratio Research Articles

Effect of feed intake on heat production and protein and fat deposition in milk-fed veal calves

Energy requirements for veal calves have not been updated recently despite the increased age at slaughter and the predominance of the Prim’Holstein breed in Europe. The objectives of this study were to determine the effects of four feeding levels (FLs) on protein and fat deposition and heat production in milk-fed calves at three stages of fattening and to determine energy requirements of calves. At each stage, 16 Prim’Holstein male calves (mean body weight (BW): 73.4, 151.6 and 237.4 kg) were fed a milk replacer at 79%, 87%, 95% or 103% of a reference FL. Measurements for one stage were conducted over 4 successive weeks in two open-circuit respiration chambers and consisted of a 6-day nitrogen and energy balance followed by a fasting day for estimating fasting heat production (FHP) of the calves. Heat production (HP) measurements were analyzed using a modeling approach to partition it between HP due to physical activity (AHP), feed intake (thermic effect of feeding (TEF)) and FHP. There was no effect of FL and stage on apparent digestibility coefficients, except for a tendency for increased digestibility coefficient of fat as animals got older. The metabolizable energy (ME)/digestible energy (DE) ratio did not depend on FL but decreased (P < 0.01) as animals got older in connection with marked increases in urinary glucose and urea excretion. The AHP and TEF components of HP were not affected by stage or FL and averaged 8.4% and 7.8% of ME intake, respectively. The FHP, expressed per kg BW0.85, increased with increasing FL, suggesting that also ME requirement for maintenance (MEm) may depend on FL. For an average intake of 625 kJ ME/kg BW0.85 per day (95% of the reference FL), FHP was 298 kJ/kg BW0.85 per day. Energy retention as protein and fat increased with increasing FL resulted in higher BW gain. But the rate of increase depended on stage of growth. The slope relating protein deposition to FL was lower in the finishing phase than in the growing phase, while the slope for lipid deposition was greater. Protein and fat contents of BW gain were not affected by FL but increased as animals got older. From these results, the energy requirements of veal calves are proposed according to a new approach, which considers that MEm (expressed per kg BW0.85) depends on ME intake (kJ/kg BW0.85) according to the following relationship: MEm = 197 + 0.25 × ME intake. The corresponding marginal efficiencies of ME utilization for protein and fat deposition are then 82% and 87%, respectively.

The effects of dietary protein:energy ratio and amino acid pattern on nitrogen utilization and excretion of rainbow trout Oncorhynchus mykiss (Walbaum)

This study was undertaken to investigate: (1) the effects of both deficiencies and excesses in essential amino acids (EAAs) from an estimated optimum dietary EAA pattern on nitrogen (N) utilization and excretion of rainbow trout Oncorhynchus mykiss, (2) the effects of dietary digestible protein (PD): digestible energy (ED) ratio (PD:ED) on N utilization and excretion of O. mykiss and (3) the potential interaction of these two factors. A 3 × 3 factorial experiment was conducted, with the two factors EAA pattern and PD:ED ratio. The three levels of EAA pattern were: (1) optimum EAA pattern, (2) 60% deficiencies in the three amino acids arginine, histidine and lysine, and (3) 60% excesses in the three amino acids arginine, histidine and leucine. The three levels of PD:ED ratio were 18, 21 and 24 g MJ−1. Amino acid deficiencies from an optimum amino acid pattern caused reductions in mean N retention of 29 to 37%, with the greatest reduction associated with the lowest PD:ED ratio, and similar substantial increases in total N and ammonia‐N excretion at all of the dietary PD:ED ratios investigated. Amino acid excesses, however, did not negatively affect N retention or excretion. Increasing PD:ED ratio was associated with decreasing N retention and increasing N excretion over the range of dietary protein and lipid levels tested. Results of this study showed that a diet with optimum dietary amino acid pattern and lowest PD:ED ratio produced the highest N retention (47% of ingested N) and the lowest total N and ammonia‐N excretion of O. mykiss.

Effects of Dietary Energy Concentration and Lysine on the Digestible Energy Ratio for Apparent Amino Acid Digestibility in Finishing Barrows

This experiment was performed to investigate the effects of two energy levels and four lysine:digestible energy (DE) ratios on the apparent digestibility of nutrients in finishing pigs. The experiment was conducted using a 2x4 randomized complete block (RCB) design with three replicates. Twenty-four cross-bred finishing barrows ((LandracexYorkshire)xDuroc) with an average body weight of 64.2±0.69 kg were assigned to one of eight treatments. Each barrow was placed in an individual metabolism crate and dietary treatment and water was provided ad libitum. Diets were designed to contain lysine:ME ratios of 1.5, 1.8, 2.1 and 2.4 g/Mcal at 3.35 and 3.6 Mcal/kg of diet in a 4x2 factorial arrangement. Dry matter (DM), ash, Ca and P digestibility were not affected by energy density or lysine:DE ratios. Crude fat digestibility increased as the energy density increased from 3.35 to 3.6 Mcal of DE/kg. Increasing the lysine:DE ratio also increased crude protein digestibility. There were no interactions between energy density and lysine:DE ratio in terms of nutrient digestibility. Nitrogen excretion via feces was not affected by energy density and lysine:DE ratio, while nitrogen excretion via urine was significantly affected by energy density and lysine:DE ratio. The apparent digestibility of all amino acids except for isoluecine, arginine and aspartic acid as well as average values of essential amino (EAA), non-essential amino acids (NEAA) and total amino acid digestibility (p>0.05) were not affected by energy density. The apparent digestibility of all amino acids except for leucine, proline, alanine and tyrosine, NEAA and total amino acid digestibility were significantly affected by lysine: DE ratio (p<0.05). Interactive effects of energy and lysine:DE ratio also significantly affected amino acid digestibility except for isoleucine, alanine, cystine, leucine, phenylalanine, glutamine and proline (p<0.05). In conclusion, these results suggest that maintaining the appropriate lysine:DE ratio becomes more important as the energy density of the diet increases. Consequently, increasing the lysine:DE ratio can result in increased crude protein digestibility and urinary nitrogen excretion, although apparent protein digestibility and nitrogen excretion were not affected by energy density Furthermore, increasing the lysine:DE ratio also increased the apparent digestibility of essential amino acids, except for leucine, regardless of energy density. The optimum lysine:DE ratio for maximum essential amino acid digestibility of the 64.2±0.69 kg pig is approximately 2.4 g of lysine/Mcal ofDE.

Effect of the Dietary Ratio of Digestible Energy to Crude Protein on Growth and Feed Conversion in Juvenile Pacific White Shrimp Litopenaeus vannamei under Similar Levels of Daily Protein Consumption

AbstractWe evaluated the effect of the dietary ratio of digestible energy (DE) : Crude protein (CP) on growth performance and nutrient utilization in juvenile Pacific white shrimp Litopenaeus vannamei fed various diets with a constant daily protein input. Juveniles (weight = 0.94 ± 0.04 g [mean ± SE]; n = 30) were stocked in an indoor recirculating‐water system (173‐L polyethylene tanks; 20 shrimp/tank) and were assigned to four different treatments. Two treatments consisted of 30% and 40% CP diets (30 isoenergetic [ISO]‐100% and 40 ISO‐75%, respectively) with a constant level of DE (3.28 kcal/g). Two treatments consisted of 30% and 40% CP diets with variable levels of DE (2.70 and 3.6 kcal/g, respectively) that maintained a constant DE : CP ratio of 9 kcal/g of protein (30 ratio [RAT]‐100% and 40 RAT‐75%, respectively). At the end of the 49‐d trial, final weight and weight gain did not differ among the treatments. However, feed conversion ratio (FCR) was significantly lower (P &lt; 0.01) for the 40 RAT‐75% and 40 ISO‐75% groups than for the 30 ISO‐100% and 30 RAT‐100% groups. Final body composition (dry matter, CP, and gross energy) and protein conversion efficiency were not significantly different among the four treatments. However, energy conversion efficiency was significantly higher for the 40 ISO‐75% group than for the 30 ISO‐100% group. This study demonstrates that when the level of energy is appropriate, increasing dietary protein content allows for reduced feed inputs without affecting shrimp growth performance, while actually improving FCR and water quality due to presumably lower wastage of feed.

Effect of isoenergetic diets with different protein and lipid content on the growth performance and heat increment of rainbow trout

The heat increment of feeding (HiE) is the metabolic cost associated with feeding, typically measured in fish as the increase in oxygen consumption (MO2) over some estimate of standard metabolic rate (SMR). The present study sought to accurately measure HiE using a variety of different methods in order to remove the influence of routine fish activity and excitement which could overestimate HiE. Protein handling makes up a large component of HiE. Thus, there is an expectation that variations in dietary protein content could influence HiE. Therefore, growth performance parameters were assessed in juvenile rainbow trout fed daily to satiation one of three isoenergetic diets with equivalent carbohydrate content (12%) but variable protein (P) and lipid (L) content [theoretical protein:lipid levels were: 55%:10% (HP:LL); 45%:15% (MP:ML) and 35%:20% (LP:HL)]. The estimated dietary digestible protein (DP) to digestible energy (DE) ratios of 19.8, 24.8 and 29.8 g/MJ bracketed the recommended levels of 22–25 g/MJ for juvenile rainbow trout. HiE values for the same groups of fish that were maintained on the test diets after the growth trial were subsequently assessed following a single meal (by gavage) of 2% of their body mass so that the growth performance parameters could be compared with the HiE estimates. Some growth performance parameters (i.e., specific growth rate, feed efficiency and dry feed intake) did not vary significantly among fish fed the diets, whereas percent protein deposition was inversely related to dietary protein content and the dietary DP to DE ratio. The dissimilar diet treatments did not result in differences in values for SMR, RMR, peak MO2 or time-to-peak MO2 or in estimates for HiE. The mean SMR from all fish combined across treatments was 50.4±3.4 mg O2/kg/h. MO2 increased significantly above SMR by 4-h postprandial and peaked at 116.2±7.7 mg O2/kg/h, representing an increase of 131%. The metabolic cost of the diets (as a % of DE) was low, and best estimates ranged between 4.0 and 4.8%.

The effect of dietary energy concentration and total lysine/digestible energy ratio on the growth performance of weaned pigs

Amino acids should be defined in relation to dietary energy concentration in diets for young pigs. However, the literature contains diverse estimates of the optimum lysine:digestible energy (DE) ratio for weanling pigs performing at levels commonly observed in commercial practice. Further, there is a poor understanding of the reponse of the weanling pig to dietary energy concentration. A growth experiment was conducted to define the optimum total lysine:DE ratio for pigs from 4 to 8 wk of age. Dietary treatments were arranged as a 2 × 5 factorial: low (LDE, 3.4 Mcal kg-1) or high DE (HDE, 3.6 Mcal kg-1) and the following total lysine:DE ratios: 3.7, 4.0, 4.3, 4.6, or 4.9 g Mcal-1). The experiment ran for 28 d, beginning 7 d post-weaning, using four pigs per pen and six pens per diet for a total of 240 pigs (27 ± 2 d; 7.5 ± 1.1 kg). No DE × lysine:DE ratio interactions were detected for any performance parameter (P &gt; 0.05). The average daily feed intake (ADFI) was 4% greater with pigs on LDE than HDE diets (DE,P &lt; 0.05), but was not affected by lysine:DE ratio (P &gt; 0.05). Conversely, DE did not affect average daily gain (ADG) (P &gt; 0.05), but increased quadratically (day 0 to 14; P &lt; 0.05) and (day 0 to 28; P &lt; 0.10) with increasing lysine:DE ratio. Feed efficiency increased linearly with increasing lysine:DE ratio (P &lt; 0.05) and was 4% greater with the HDE than LDE diets (P &lt; 0.05). The optimum total lysine:DE ratio for ADG was determined to be 4.46 and 4.27 g Mcal-1 for pigs between 7.5 to 13 kg and 7.5 to 22.5 kg BW, respectively. Key words: Pig, total lysine, digestible energy, growth

Reduced protein intake during the weaner period has variable effects on subsequent growth and carcass composition of pigs

In total, 960 pigs (480 castrated males and 480 gilts), selected at ~28 days of age, were used to investigate the effect of restricting protein intake for a short period between 4 and 14 weeks of age. Pigs were selected over an 8-week period in groups of 120 pigs (three pens of 20 castrated males and three pens of 20 gilts per week). Pigs were given ad libitum access to commercial diets from weaning to slaughter. Pens of 20 pigs of each sex were allocated to one of six treatments: control (no restriction), restriction from 4 to 7 weeks of age, restriction from 7 to 10 weeks of age, restriction from 10 to 14 weeks of age, restriction from 4 to 10 weeks of age or a restriction from 4 to 14 weeks of age. During the period of restriction, pigs were offered ad libitum commercial diets that had been reduced in dietary lysine to digestible energy ratio by ~15%. Restricting protein intake between 7 and 10, 4 and 10 and 4 and 14 weeks of age reduced daily gain during the period of restriction. Pigs restricted from 7 to 10 weeks of age had reduced average daily feed intake (5.6%) from 7 to 10 weeks, followed by a reduction in average daily feed intake (5.5%) and improved feed efficiency (6.1%) in the subsequent period from 10 to 17 weeks of age. Daily gain for the entire experimental period was similar for all treatment groups, except those restricted from 7 to 10 weeks of age (3.9% lower than the controls), although there was no treatment effect on carcass weight. Interestingly, backfat was reduced by 10% in these animals compared with the controls, which may be economically beneficial in markets where producers are paid on backfat and carcass weight, such as those selling domestically in the Australian market. Economic benefits of reduced feed costs during both the restriction and realimentation periods were also observed when pigs were restricted from 10 to 14 weeks of age. Any economic benefits from short periods of protein restriction will vary depending on the specific market conditions and the local cost of feed protein sources.

Dietary composition manipulation to enhance the performance of juvenile barramundi (Lates calcarifer Bloch) reared in cool water

Barramundi Lates calcarifer reared in cool water (20-22 degrees C) grow slowly and feed is used poorly compared with fish in warm water (28-32 degrees C). Two comparative slaughter growth assays were carried out with juvenile barramundi to see if increasing the digestible energy (DE) and/or the n-3 highly unsaturated fatty acid (n-3 HUFA) content of the feed would improve growth of fish raised in cool water. Increasing the DE content of the feed from 15 to 17 or 19 MJ kg(-1) while maintaining a constant protein to energy ratio in Experiment 1 brought about significant improvements in feed conversion ratio (FCR) (from 2.01 to 1.19) and daily growth coefficient (DGC; from 0.69 to 1.08%/day) for fish at 20 degrees C. For fish at 29 degrees C, improvements, while significant, were of a lesser magnitude: from 1.32 to 0.97 for FCR and from 3.24 to 3.65%/day for DGC. Increasing the absolute amount of dietary n-3 HUFA, expressed as the sum of eicosapentaenoic and docosahexaenoic fatty acids, from 0.5% to 2.0% in Experiment 2 improved DGC linearly and FCR curvilinearly for fish at 29 degrees C whereas at 20 degrees C, DGC was not affected while FCR improved slightly (from 1.83 to 1.68). Feed conversion ratio was optimized with a dietary n-3 HUFA of about 1.5%. Providing barramundi with a feed that is high in DE (viz 19 MJ kg(-1)) and a digestible protein to DE ratio of 22.5 g MJ(-1) is a practical strategy for improving the productivity of barramundi cultured in cool water whereas increasing dietary n-3 HUFA conferred very little additional benefit.

Protein and energy digestibility and gonad development of the European sea urchin Paracentrotus lividus (Lamarck) fed algal and prepared diets during spring and fall

Protein and energy are two of the main limiting factors for sea urchin growth. However, the requirement of daily protein and energy to maximize gonadal production is still unknown. Paracentrotus lividus were fed three experimental diets: Ulva lactuca, Gracilaria conferta and a prepared diet for 2 months in the fall of 1999 and spring of 2000. Sea urchins from a laboratory-cultured population of equal age, weight and test diameter were used. Apparent digestibility coefficients (ADC%) for protein and energy, using acid-insoluble ash as a marker, were measured for all experimental diets. Apparent digestibility coefficients for protein was high (>75%) for all diets. Energy digestibility varied among the diets and was lowest for G. conferta (50-62%). The three diets contained varying digestible protein (DP) to digestible energy (DE) ratios of 25, 26 and12 mg kJ-1 for U. lactuca, G. conferta and the prepared diet respectively. Digestible protein intake was similar for all treatments, but DE intake was greater for sea urchins fed the prepared diet in both seasons. As a result, the gonad production was significantly higher for urchins fed the prepared diet, suggesting that energy was limiting in the algal diets. Paracentrotus lividus spawned during the spring experiment, resulting in protein loss in all treatments. Protein loss was lowest in the sea urchins fed the prepared diet. Enhanced gonadal growth and gamete development of P. lividus resulted from the higher dietary energy content of the prepared diet.

Response of the tropical spiny lobster Panulirus ornatus to protein content of pelleted feed and to a diet of mussel flesh

In an 8-week growth experiment, juvenile spiny lobsters (Panulirus ornatus) grew best on a feed containing at least 610 g kg−1 crude protein on a dry matter basis (DM) and a digestible protein to digestible energy ratio of 29.8 mg kJ−1. The study entailed a six treatment by four replicate randomized block experiment with 222 wild-caught P. ornatus of mean initial weight (±SD) of 2.5 ± 0.19 g. The lobsters were fed one of five isolipidic feeds (approximately 130 g kg−1 DM) in which the crude protein was serially incremented between 330 and 610 g kg−1 DM, or a reference diet comprising the flesh of frozen green-lip mussels. Lobsters fed the pelleted feeds had high survival (79 ± 4.5%) and responded to increasing dietary crude protein content with progressively higher growth rates, with the daily growth coefficient improving from 0.72% day−1 with 330 g kg−1 crude protein to 1.38% day−1 with 610 g kg−1 crude protein. Both growth rate and survival were low with the mussel diet (0.80% day−1and 41 ± 4.5%, respectively). These results demonstrate that tropical spiny lobsters grow well when fed high-protein, high lipid, pelleted feeds, but feeding on a sole diet of freshly thawed green-lip mussels was unsatisfactory.

Essential amino acid supplementation to fish meal-based diets with low protein to energy ratios improves the protein utilization in juvenile rainbow trout Oncorhynchus mykiss

Two 10-week feeding experiments were conducted to evaluate the supplemental effect of essential amino acids (EAA) to fish meal-based diets with low digestible crude protein (DCP) to digestible energy (DE) ratio (DCP / DE) on the growth and protein utilization in juvenile rainbow trout. In each experiment, the control diet having DCP / DE of 24 g/MJ was compared to three lower DCP / DE diets of ratios of 17 and 16 g/MJ in Experiment 1 and 2, respectively. The ingredients containing protein in the control diet were proportionally reduced in the low DCP / DE diets. To the low DCP / DE diets, EAA were: 1) unsupplemented; 2) supplemented to meet the requirements; and 3) supplemented corresponding to 1.2 times the requirements. Each diet was fed to apparent satiation twice a day to juveniles (initial body weight of 21 and 17 g, respectively) at 17 °C. In both experiments, the growth of fish was not affected by the dietary treatments, however, the feed efficiency was significantly improved in fish fed the low DCP / DE diet supplemented with EAA at 1.2 times the requirements. Whole body fat content increased whereas the crude protein content decreased in fish fed the low DCP / DE diets relative to those for the control diet, however, the crude protein content of fish fed the low DCP / DE diet supplemented with EAA at 1.2 times the requirements was significantly higher than fish fed the low DCP / DE diet without the EAA supplementation. Accordingly, percentage nitrogen retention was 50–52% in the group fed diets with the higher levels of supplemental EAA compared to 35–36% in the control diet group. By the supplementation of EAA at 1.2 times the requirements, the concentrations of most of free EAA in plasma, liver, and dorsal white muscle of the low DCP / DE diet group increased to identical levels of fish fed the control diet. Taurine concentration in the plasma and tissues showed an opposite postprandial change to that of ordinal amino acids: the concentration decreased after feeding and the lowest levels were noted at around 15 h after feeding. The results of these experiments indicate that juvenile rainbow trout grow well on 16 g DCP/MJ DE diets based on fish meal, and EAA supplementation to these diets improves the protein utilization and thus reduces nitrogen loading into the environment.

The effects of dietary digestible protein and digestible energy content on protein retention efficiency of juvenile silver perch Bidyanus bidyanus (Mitchell)

Effects of varying dietary digestible protein (DP) and digestible energy (DE) on protein retention efficiency (PRE), weight gain, protein deposition and carcass composition for silver perch (Bidyanus bidyanus, Mitchell) were studied. Using digestibility data for silver perch, we formulated three series of diets with different DE contents (13, 15 or 17 MJ DE kg−1). For each series, a ‘summit’ diet containing an excess of protein for silver perch (based on previous research) and a ‘diluent’ diet with only 10–13% DP were formulated. By blending the summit and diluent diets together in different ratios, five diets with different DP contents were produced for each DE series. A commercial diet was also included to give 16 experimental diets in total. Eight juvenile fish (mean initial weight 1.2 g) were stocked into each of 64 × 70-L acrylic aquaria and then each of the 16 diets was randomly allocated to four replicate aquaria. Tanks were supplied with partially recirculated water (75%) at 25–27°C. Fish were fed restrictively, twice per day, based initially on 3.5% body weight day−1 with 40% of the ration given at 08:30 hours and 60% given at 15:00 hours for 59 days. Quadratic functions were fitted to each energy series to describe the relationship between DP content of diets and PRE (the asymptote of these functions were used to predict maximum PRE). For low DE (13 MJ kg−1), mid-DE (15 MJ kg−1) and high DE (17 MJ kg−1), the dietary DP contents to give maximum PRE were 24.7%, 26.1% and 30.1% respectively. Carcass fat decreased with increasing DP and increasing DP:DE ratio. Varying the dietary protein and DE also influenced other indices of fish performance. ‘Optimum’ dietary protein therefore depends on several factors. For fish fed, restrictively, the protein content needed to maximize PRE is lower than the content needed to maximize weight gain or minimize carcass fat. For fish fed to satiation, the lowest protein content for maximum weight gain is lower than for fish fed restrictively.

Optimum dietary ratio of digestible protein and energy for juvenile American eel, Anguilla rostrata , fed practical diets

Triplicate groups of juvenile American eel, Anguilla rostrata, initial weight 8.2 ± 0.24 g, were fed to satiation herring meal based diets formulated with digestible protein/digestible energy (DP/DE) ratios of 19, 20, 21, 22 and 23 g DP MJ DE−1 (as-fed basis) for 84 days. Data were collected to determine the effect of dietary DP/DE ratio on feed intake (FI), mean weight (MW), specific growth rate (SGR), feed conversion ratio (FCR), apparent digestibility (AD) of major nutrients, rate of phosphate excretion (RPE) and nutrient retention efficiency (RE). Highest MW, SGR and lowest FCR (P 0.05) with mean AD coefficients for organic matter, protein, energy and phosphorous of 86.3, 94.1, 89.2 and 34.7%, respectively. Lipid AD was significantly higher (P 0.05) on RPE and it averaged 0.05 ± 0.002 g phosphate kg fish−1 day−1. Nitrogen retention efficiency (NRE) significantly (P 0.05) at an average of 31.6 ± 0.67%. Energy retention efficiency (ERE) significantly (P < 0.05) increased to 42.9 ± 1.24% as DP/DE ratio increased to 22 g DP MJ DE−1 and thereafter significantly (P < 0.05) decreased. Lipid retention efficiency (LRE) increased significantly (P < 0.05) to 75.7 ± 0.85% as dietary DP/DE ratio increased to 23 g DP MJ DE−1. Non-linear quadratic regression of ERE against dietary DP/DE ratio yielded an estimated optimum DP/DE ratio for juvenile American eel of 22.1 g DP MJ DE−1.

Urinary energy losses in dogs fed commercial extruded foods.

Energy and nitrogen losses in the urine were recorded in 134 individual balances with adult (1- to 2-year-old) female Beagles that were fed 23 dry extruded dog foods ranging in crude protein (CP) content from 242 to 360 g/kg dry matter. The energy equivalent of urinary nitrogen was estimated as 33.9 kJ/g N. Both energy losses in the urine corrected for the nitrogen balance, and the metabolizable energy (MEn): digestible energy (DE) ratio were found to be closely related to diet CP content (r : 0.851 and 0.820). The MEn content of extruded dog foods can be accurately calculated from the DE content, either by subtracting 4.59 MJ/kg CP or estimating the MEn/DE ratio from the food CP content by the following equation: MEn/DE=0.98 - 3.44 +/- 0.517 x CP (kg/MJ DE).

Modification of body composition by altering the dietary lysine to energy ratio during rearing and the effect on reproductive performance of gilts

AbstractFifty-four lean genotype crossbred gilts were allocated at 118 days of age among three diets with different protein concentrations to give lysine: energy (g/MJ digestible energy) ratios: high (0·9), medium (0·6) and low (0·3) given twice daily at 2·9 × maintenance energy. At 160 days of age, gilts were treated with exogenous gonadotropin (PG600™) and animals were examined daily for signs of oestrus. Animals were slaughtered after the second oestrus, if they had shown behavioural oestrus, or at the age of 212 days. Reproductive tracts were recovered for counting of corpora lutea and albicantia. L gilts were lighter than M or H gilts at puberty induction (80, 95, 97 (s.e. 0·73) kg for L, M, H respectively, P &lt; 0·001), with greater backfat thickness (10·8,10·0, 9·2 (s.e. 0·21) mm P2,P &lt; 0·001), lesser longissimus muscle depth (57·4, 65·9, 64·3 (s.e. 0·77) mm, P &lt; 0·001) and poorer food conversion ratio during rearing (3·87, 2·48, 2·42 (s.e. 0·098) kg food per kg gain, P &lt; 0·001). There was no statistically significant difference in the total number of animals that responded to the puberty induction, although L had a greater latency to oestrus than H. Ovulation rate at this induced oestrus was significantly lower in L gilts than in M or H gilts (12·5, 17·3, 21·5 (s.e. 1·32), P &lt; 0·02). A lower proportion ofL, compared with M or H gilts showed spontaneous ovulation in a subsequent cycle (0·15, 0·75, 0·77, %2 = 12·72, P &lt; 0·005). It proved possible, by means of low protein (lysine) diets, to increase body fat reserves in breeding gilts but protein restriction in the rearing phase negatively affected aspects of reproductive performance.

Regulation of hepatic lipogenesis by dietary protein/energy in juvenile European seabass ( Dicentrarchus labrax)

A growth trial was conducted with groups of European seabass having an initial weight of 6 g to study the lipogenic action of dietary protein and non-protein energy supplies. Six experimental diets were formulated to contain one of two crude protein levels (43 and 52%) with digestible protein (DP) to digestible energy (DE) ratios ranging from 19 to 26 mg/kJ. At the end of the growth trial (12 weeks), the activities of liver glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49), malic enzyme (ME, EC 1.1.1.40), ATP citrate lyase (ACL, EC 4.1.3.8), acetyl-CoA carboxylase (ACoAC, EC 6.4.1.2) and fatty acid synthetase (FAS, EC 2.3.1.38) were measured. Digestibility of main dietary components was also determined over a three-week period. At each protein level, an increase in dietary DE led to improved growth performance, protein efficiency, daily N deposition and to a reduction of N loss. Best results were achieved at 40% DP and a DP/DE ratio of 19–20 mg/kJ. G6PD, ME and ACoAC were found to be the key regulatory enzymes in the lipogenic pathway, with G6PD being the main NADPH-generating enzyme. Activities of G6PD, ME, ACL and FAS were reduced with increasing fat intake. Activities of G6PD, ME and ACL were increased with increasing starch intake. ACoAC activity was negatively correlated with starch intake and positively with fat intake.

Dietary protein/energy ratios for Atlantic salmon in relation to fish size: growth, feed utilization and slaughter quality

Four extruded diets differing in protein/fat concentrations, 378/389 g kg−1, 425/346 g kg−1, 480/308 g kg−1 and 524/256 g kg−1 were tested in a digestibility trial and a growth study. Apparent digestibility of protein and fat were not significantly different among the diets when tested in 1-kg Atlantic salmon, Salmo salar L., in sea water. The diets represented a range of digestible protein to digestible energy ratios (DP/DE ratios) of 14.1, 16.4, 18.8 and 21.9 g MJ−1. The 138-day growth study was performed with triplicate groups of Atlantic salmon of 1.0 and 2.5 kg initial weight. Irrespective of size; growth, feed conversion ratio (FCR), nitrogen and energy retention were poorer in fish fed the diet with DP/DE ratio of 14.1 g MJ−1 compared with the fish fed the other diets. A DP/DE ratio of 16.4 g MJ−1 was sufficient to produce maximum growth for the large fish, while the DP/DE ratio of 18.8 g MJ−1 produced the highest growth in the small fish. In the large fish, the lowest FCR was obtained on a DP/DE ratio of 16.4 g MJ−1, while there was no clear difference in FCR within the small fish when diets of DP/DE ratios of 16.4–21.9 g MJ−1 were fed. The carcass-to-body ratio in the small fish decreased with decreasing DP/DE ratios. The fish fed the diet of 21.9 g MJ−1 had significantly lower fat and dry matter and higher protein content than fish of similar size fed the other diets. Increased dietary lipid content seemed to improve astaxanthin deposition in the small fish, while the large fish showed no significant differences in astaxanthin deposition due to dietary treatment. This study indicates that a DP/DE ratio of 14.1 g MJ−1 in high-energy diets for Atlantic salmon in sea water is below the optimal DP/DE ratio for growth and feed utilization, and that the optimal DP/DE ratio decreases with increasing fish weight. DP/DE ratios around 19 g MJ−1 for fish weighing 1 to 2.5 kg, and 16–17 g MJ−1 for fish weighing 2.5 to 5 kg, are suggested to be optimal.

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 &lt; 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.

Effects of dietary protein/energy ratio, ration size, dietary energy source and water temperature on nitrogen excretion in rainbow trout

Postprandial nitrogen excretion was measured on groups of rainbow trout of mean body weight (MBW) 35g, fed, from maintenance to near satiation, diets containing graded levels of digestible energy (14 to 20 kJ/g dry matter) with digestible protein (DP)/digestible energy (DE) ratios of 18 and 23 mg/kJ at each protein level (DP: 32.5 or 37% dry matter). Irrespective of the diet and the ration size, urea-N excretion amounted to 15-16% of ammonia-N excretion. The higher the dietary DP/DE ratio, the greater was the amount of ammonia excreted. At high ration levels (1.5% and 2% of MBW/d), N excretion was 39-40% of digestible N intake for diets with a DP/DE ratio of 18 mg/kJ and 44% of digestible N intake for diets with a DP/DE ratio of 23 mg/kJ irrespective of the dietary protein level. At lower ration levels, N excretion as percent of N intake was higher than at higher feeding levels. Another experiment was performed to compare the effect of dietary lipid and digestible carbohydrate on ammonia excretion in rainbow trout reared at two water temperatures (8°C and 18°C). Neither water temperature nor dietary sources of non-protein energy had any significant effect on N excretion expressed as proportion of digestible N intake.

Effects of dietary protein/energy ratio, ration size, dietary energy source and water temperature on nitrogen excretion in rainbow trout

Postprandial nitrogen excretion was measured on groups of rainbow trout of mean body weight (MBW) 35g, fed, from maintenance to near satiation, diets containing graded levels of digestible energy (14 to 20 kJ/g dry matter) with digestible protein (DP)/digestible energy (DE) ratios of 18 and 23 mg/kJ at each protein level (DP: 32.5 or 37% dry matter). Irrespective of the diet and the ration size, urea-N excretion amounted to 15-16% of ammonia-N excretion. The higher the dietary DP/DE ratio, the greater was the amount of ammonia excreted. At high ration levels (1.5% and 2% of MBW/d), N excretion was 39–40% of digestible N intake for diets with a DP/DE ratio of 18 mg/kJ and 44% of digestible N intake for diets with a DP/DE ratio of 23 mg/kJ irrespective of the dietary protein level. At lower ration levels, N excretion as percent of N intake was higher than at higher feeding levels.Another experiment was performed to compare the effect of dietary lipid and digestible carbohydrate on ammonia excretion in rainbow trout reared at two water temperatures (8°C and 18°C). Neither water temperature nor dietary sources of non-protein energy had any significant effect on N excretion expressed as proportion of digestible N intake.