There is evidence indicating that using the current UK energy feeding system to ration the present sheep flocks may underestimate their nutrient requirements. The objective of the present study was to address this issue by developing updated maintenance energy requirements for the current sheep flocks and evaluating if these requirements were influenced by a range of dietary and animal factors. Data (n = 131) used were collated from five experiments with sheep (5 to 18 months old and 29.0 to 69.8 kg BW) undertaken at the Agri-Food and Biosciences Institute of the UK from 2013 to 2017. The trials were designed to evaluate the effects of dietary type, genotype, physiological stage and sex on nutrient utilization and energetic efficiencies. Energy intake and output data were measured in individual calorimeter chambers. Energy balance (Eg) was calculated as the difference between gross energy intake and a sum of fecal energy, urine energy, methane energy and heat production. Data were analysed using the restricted maximum likelihood analysis to develop the linear relationship between Eg or heat production and metabolizable energy (ME) intake, with the effects of a range of dietary and animal factors removed. The net energy (NEm) and ME (MEm) requirements for maintenance derived from the linear relationship between Eg and ME intake were 0.358 and 0.486 MJ/kg BW0.75, respectively, which are 40% to 53% higher than those recommended in energy feeding systems currently used to ration sheep in the USA and the UK. Further analysis of the current dataset revealed that concentrate supplement, sire type or physiological stage had no significant effect on the derived NEm values. However, female lambs had a significantly higher NEm (0.352 v. 0.306 or 0.288 MJ/kg BW0.75) or MEm (0.507 v. 0.441 or 0.415 MJ/kg BW0.75) than those for male or castrated lambs. The present results indicate that using present energy feeding systems in the UK developed over 40 years ago to ration the current sheep flocks could underestimate maintenance energy requirements. There is an urgent need to update these systems to reflect the higher metabolic rates of the current sheep flocks.

Variations in feeding behaviour between animals result from individual variations in their metabolism as affected by diet composition. The study aimed to link the within-day dynamics of voluntary feed intake and those of blood metabolites and insulin in growing pigs having ad libitum access to feed and receiving diets differing in dietary fibre levels and aleurone supplementation. A total of forty pigs (body weight: 35 kg) had access to diets provided ad libitum, which differed by fibre content (13 or 18 % neutral-detergent fibre) and aleurone supplementation (0, 2 or 4 g/kg). Feeding behaviour was individually recorded for 1 week. The kinetic of plasma metabolites and insulin was followed for 1 h after a voluntary test meal. Dietary fibre level did not affect the daily feed intake but increased meal size and meal duration. Aleurone supplementation (4 g/kg) decreased the daily feed intake and number of meals. Dietary fibre level only decreased insulin concentration measured 15 min after meal beginning. Aleurone supplementation (4 g/kg) decreased glycaemia in the first hour after the meal and insulinaemia 15 min after the meal. Free access to feed led to high variability in pre-prandial metabolites and insulin concentrations, resulting in different test meal size irrespective of diet composition. Animals were then spread over different profiles combining feeding behaviour and fasted status to explain different profiles of regulation of feed intake. Plasma metabolites and insulin kinetics were affected by diet composition but also by animal characteristics. Individual variability should be considered when diet composition is used to modulate feeding behaviour.

This experiment was conducted to investigate the effects of guanidinoacetic acid (GAA) on productive performance, intestinal morphometric features, blood parameters and energy utilisation in broiler chickens. A total of 390 male broiler chicks (Ross 308) were assigned to six dietary treatments based on a factorial arrangement (2×3) across 1–15 and 15–35-d periods. Experimental treatments consisted of two basal diets with standard (STD; starter: 12·56 MJ/kg and grower: 12·97 MJ/kg) and reduction (LME; starter: 11·93 MJ/kg and grower: 12·33 MJ/kg) of apparent metabolisable energy (AME) requirement of broiler chickens each supplemented with 0, 0·6 and 1·2 g/kg GAA. Supplemental 1·2 g/kg GAA decreased the negative effects of feed energy reduction on weight gain across starter, growing and the entire production phases (P<0·05). Energy retention as fat and total energy retention were increased when birds received LME diets supplemented with 1·2 g/kg GAA (P<0·05). Net energy for production (NEp) and total heat production increased in birds fed LME diets containing 1·2 g/kg GAA (P<0·05). A significant correlation was observed between dietary NEp and weight gain of broilers (r 0·493; P=0·0055), whereas this relationship was not seen with AME. Jejunal villus height and crypt depth were lower in birds fed LME diets (P<0·05). Serum concentration of creatinine increased in broilers fed LME diets either supplemented with 1·2 g/kg GAA or without GAA supplementation (P<0·05). Supplemental GAA improved performance of chickens fed LME diet possibly through enhanced dietary NEp. The NEp could be preferred over the AME to assess response of broiler chickens to dietary GAA supplementation.

Currently, energy evaluation of fish feeds is performed on a digestible energy basis. In contrast to net energy (NE) evaluation systems, digestible energy evaluation systems do not differentiate between the different types of digested nutrients regarding their potential for growth. The aim was to develop an NE evaluation for fish by estimating the energy efficiency of digestible nutrients (protein, fat and carbohydrates) and to assess whether these efficiencies differed between Nile tilapia and rainbow trout. Two data sets were constructed. The tilapia and rainbow data set contained, respectively, eight and nine experiments in which the digestibility of protein, fat and energy and the complete energy balances for twenty-three and forty-five diets was measured. The digestible protein (dCP), digestible fat (dFat) and digestible carbohydrate intakes (dCarb) were calculated. By multiple regression analysis, retained energy (RE) was related to dCP, dFat and dCarb. In tilapia, all digestible nutrients were linearly related to RE (P<0·001). In trout, RE was quadratically related to dCarb (P<0·01) and linearly to dCP and dFat (P<0·001). The NE formula was NE=11·5×dCP+35·8×dFAT+11·3×dCarb for tilapia and NE=13·5×dCP+33·0×dFAT+34·0×dCarb–3·64×(dCarb)2 for trout (NE in kJ/(kg0·8×d); dCP, dFat and dCarb in g/(kg0·8×d)). In tilapia, the energetic efficiency of dCP, dFat and dCarb was 49, 91 and 66 %, respectively, showing large similarity with pigs. Tilapia and trout had similar energy efficiencies of dCP (49 v. 57 %) and dFat (91 v. 84 %), but differed regarding dCarb.

The objective of this study was to develop a novel methodology that enables pig diets to be formulated explicitly for environmental impact objectives using a Life Cycle Assessment (LCA) approach. To achieve this, the following methodological issues had to be addressed: (1) account for environmental impacts caused by both ingredient choice and nutrient excretion, (2) formulate diets for multiple environmental impact objectives and (3) allow flexibility to identify the optimal nutritional composition for each environmental impact objective. An LCA model based on Canadian pig farms was integrated into a diet formulation tool to compare the use of different ingredients in Eastern and Western Canada. By allowing the feed energy content to vary, it was possible to identify the optimum energy density for different environmental impact objectives, while accounting for the expected effect of energy density on feed intake. A least-cost diet was compared with diets formulated to minimise the following objectives: non-renewable resource use, acidification potential, eutrophication potential, global warming potential and a combined environmental impact score (using these four categories). The resulting environmental impacts were compared using parallel Monte Carlo simulations to account for shared uncertainty. When optimising diets to minimise a single environmental impact category, reductions in the said category were observed in all cases. However, this was at the expense of increasing the impact in other categories and higher dietary costs. The methodology can identify nutritional strategies to minimise environmental impacts, such as increasing the nutritional density of the diets, compared with the least-cost formulation.

A total of 364 female Ross 308 chicks (1 d old) were used in the present study conducted in floor pens to investigate the effects of graded levels of supplementary bacterial phytase on dietary energy utilisation and growth performance. For this purpose, four maize–soyabean-based diets were offered to the birds from 0 to 21 d of age. These included a suboptimal P negative control (NC, 3·0 g/kg non-phytate P), NC+250 phytase units (FTU)/kg feed, NC+500 FTU and NC+2500 FTU. The effect of phytase activity on bird growth performance was best described as a linear relationship between increasing dose and increased feed intake (P< 0·001), but was quadratic for body-weight gain (P= 0·002) and feed efficiency (P= 0·023). There was no significant response (P>0·05) of dietary apparent metabolisable energy (AME) to supplementary phytase. The birds fed phytase increased their retention of total carcass energy in a linear fashion (P= 0·009) with increased phytase dose. The efficiency of dietary AME used for overall carcass energy retention also improved (P= 0·007) in a linear manner with increased dietary phytase activity. Dietary net energy for production (NEp) increased (P= 0·047) with an increase in phytase dose following a linear pattern, as an increase of 100 FTU increased dietary net energy by 15·4 J (estimated within the range of doses used in the present experiment). Dietary NEp was more highly correlated with performance criteria than dietary AME, and it seems to be a more sensitive way to evaluate broiler response to phytase supplementation.

The concentrations of utilisable energy per unit of price is important information to allow choices to be made between feedstuffs for practical dietary formulations. There has been a long lasting debate as to whether net energy (NE) or metabolisable energy (ME) is preferable. Only one large data set of empirically determined net energy concentrations (NEp) of feedstuffs for poultry has been published. Although the ME system for describing the utilisable energy concentrations of feedstuffs is now widely used, different metabolised nutrients (protein, fat and carbohydrate) are utilised with different relative efficiencies for energy deposition. More recently, methods of predicting the NE of feeds from equations have been suggested. These include information on nutrient digestibility with or without determined ME values with corrections according to the efficiency by which the nutrients are utilised. The objectives of the present study were, firstly, to evaluate the relationship between determined apparent metabolisable energy (AME) and determined NEp concentrations for a range of poultry feedstuffs and, secondly, the relationship between four different NE prediction equations and determined NEp concentrations was evaluated using the same data set. There was a positive linear regression (p < 0.001) between the determined AME and NEp concentrations in a data set of 62 feedstuffs with a range of AME from 0.1 to 20.5 MJ/kg. This regression equation accounted for 92.8% of the variance in NEp. Each 1.0 MJ increase in AME gave a 0.69 MJ increase in NEp. However, this data set had a large proportion of low energy feedstuffs that are unlikely to be used in modern proprietary poultry diets. A subset of these data that included 40 feedstuffs with an AME range of 8.0–18.0 MJ/kg was also examined. The regression between determined AME and NEp concentrations in this smaller data set only accounted for 77.7% of the variance in NEp. There was evidence (p < 0.01) that AME overestimated the NEp concentrations of high protein feeds of animal origin compared with cereals, cereal byproducts and high protein vegetable feeds. Three NE prediction equations that require knowledge of the digestibility coefficients for protein, ether extract and carbohydrates all improved the precision of the NEp prediction. However, a fourth prediction equation that requires only AME and crude protein determinations gave an equally precise estimate of NEp.

Digestible energy (DE), metabolizable energy (ME) and net energy for maintenance (NEm) values of a set of fourteen diets were measured in six adult sows fed at and below their maintenance energy level. The efficiency of ME for NEm was estimated from heat production (HP) measurements (indirect calorimetry) at these different feeding levels. HP was partitioned between HP due to physical activity, thermic effect of food (TEF) and fasting heat production (FHP). The amounts of DE digested in the small intestine or in the hindgut were measured. Equations for prediction of NEm from dietary characteristics were calculated. HP at maintenance level averaged 400 kJ/kg body-weight0.75, 16 and 19% of the total being due to physical activity and TEF respectively. The efficiency of ME for NEm averaged 77·4% with higher values for digestible diethyl ether extract (100%) and starch + sugar (82 %). The efficiencies of digestible crude protein (N × 6·25) and digestible residue averaged 69 and 56 % respectively. The energy absorbed from the small intestine was used more efficiently than the energy fermented in the hindgut (82 v. 59%). These values are comparable with those obtained in growing pigs. The NEm content of diets can be predicted accurately from equations including DE (or ME) values and some dietary chemical characteristics.