Gerry C. Emmans

Effective energy: a concept of energy utilization applied across species

An energy system is described in which, in both single-stomached and ruminant animals, the heat increment of feeding is considered to be linearly related to five measurable quantities. For both kinds of animals three of the quantities, with their heat increments in parentheses, are urinary N (wu; kJ/g), faecal organic matter (wd; kJ/g) and positive protein retention (wp; kJ/g). In ruminants the other two, with their heat increments in parentheses, are CH4 energy (wm; kJ/kJ) and positive lipid retention (w1; kJ/g); in single-stomached animals they are positive lipid retention from feed lipid (wII; kJ/g), and positive lipid retention not from feed lipid (wI; kJ/g). Data from suitable experiments on steers, pigs and chickens were used to test the system and to estimate wu 29.2, wd 3.80, wp 36.5, wm 0.616, wI 16.4 and wII 4.4. The values for wu, wd, wm and (wI - wII) allow an energy scale, called effective energy, to be defined for both single-stomached animals and ruminants. On this energy scale the values of wp and wI, together with the heats of combustion of protein and lipid of 23.8 and 39.6 kJ/g respectively, allow the energy requirement to be expressed as (MH + 50PR + 56LR) for both kinds of animal, where PR and LR are the rates of positive protein and lipid retention (g/d), and MH is the maintenance heat production (kJ/d) which can be estimated as 0.96 of the fasting heat production. The effective energy (EE) yielded to a ruminant animal by a feed ingredient can be estimated as EE (MJ/kg organic matter) = 1.15ME - 3.84 - 4.67DCP, where ME is the metabolizable energy value (MJ/kg organic matter) and DCP is the digested crude protein content (kg/kg organic matter) with both measured at maintenance. Alternatively, EE can be estimated as EE (MJ/kg) = GE (d - 0.228) - 4.67DCP, where GE is the gross energy (MJ/kg) and d is the energy digestibility (MJ/MJ) also measured at maintenance. The EE yielded to a single-stomached animal can be estimated as EE (kJ/g) = 1.17ME - 4.2CP - 2.44, where ME (kJ/g) is measured at, or corrected to, zero N-retention and CP (g/g) is the crude protein (N x 6.25) content of the feed ingredient. The system is simpler for ruminants, and more accurate for both kinds of animal, than those now in use. As effective energy values can be tabulated for ingredients, and are additive to the extent that ME values are additive, they can be used to formulate diets using linear programming.

The effects of varying protein and energy intakes on the growth and body composition of pigs. 2. The effects of varying both energy and protein intake.

The objective of the experiment was to define the form of the relationship between varying levels of protein and energy intake and the performance of young pigs. Forty-four young-pigs were assigned at 12 kg live weight for 6 weeks either to an initial slaughter group (n 8) or to one of the nine feeding treatments (n 4); three allowances of a high-protein food with 355 g crude protein (nitrogen x 6.25; CP)/kg (P1, P2, P3) at three levels of feeding (L, M and H). Each feeding level was met by supplementing the allowance of feed P with the appropriate amount of starch and each treatment had two males and two females. The rate of protein deposition was not affected by feeding level at the two lowest allowances of basal feed P (P1 and P2), but it increased with increasing the feeding level for the pigs on treatment P3. Males deposited more protein than females, but this effect was more pronounced with treatment P3. The rate of lipid deposition increased with each increase in the level of feeding and decreased with increasing the allowance of feed P. The calculated efficiency of protein utilization (ep) was expressed as a function of the energy:protein ratio in the feed (MJ metabolizable energy/kg digestible CP). The best model to describe the relationship was a linear-plateau model, with the maximum value for ep of 0.814 at 73 MJ/kg. This relationship provided the basis of a model that could predict the response of a growing pig to its diet as rates of protein and lipid retention.

The effects of varying protein and energy intakes on the growth and body composition of pigs: 1. The effects of energy intake at constant, high protein intake

The objective of the present experiment was to define the form of the relationship between varying levels of energy intake at constant, high protein intake and the performance of young pigs. By doing so it was expected that we could distinguish between four models that predict the pigs responses to its diet as rates of protein and lipid retention. Forty young pigs were assigned at 12 kg live weight either to an initial slaughter group (n 8) or to one of four allowances of starch intake at a constant intake of a high-protein feed (with 345 g crude protein (nitrogen x 6.25)/kg food). Half the pigs were killed after 4 weeks and half after 8 weeks on the treatments; at each slaughter point on each treatment half the pigs were entire males and half were females. Increasing the intake of starch (energy) resulted in significant increases in the rates of live weight, empty-body, protein and lipid gains of pigs slaughtered at both stages. There was no minimum positive lipid:protein ratio in the gain of the pigs. Male pigs deposited more protein and less lipid than females but this effect of sex on protein and lipid retention was seen only on the two highest allowances of starch intake. The calculated efficiency of protein utilization increased with increasing starch intake up to a maximum of 0.81, when probably the energy:protein in the diet became non-limiting. The results led to the rejection of two of the models that predict the rates of protein and lipid retention as responses to protein and energy intake, but the two remaining models could not be rejected, at least qualitatively.

The ability of pigs to control their protein intake when fed in three different ways

The ability of pigs to control their protein intake was tested in three different ways. When pigs were offered access to single feeds of different protein contents, at a constant liveweight of 20 kg, they increased their daily feed intake as the protein content of their feed was decreased (long-term protein intake regulation). When the protein content of their feed was altered daily, pigs consumed consistently higher amounts of feed when they had access to a low protein feed rather than to a high protein one (short-term protein intake regulation). When, finally, they were given a choice between two feeds of different protein contents, pigs selected a diet that met their protein requirements (as judged by their growth rates and feed efficiencies) and avoided excess of protein intake, but only if they had had previous experience of both feeds. It is suggested that pigs first need to learn about the feeds that are subsequently offered as a choice, before they can make correct dietary choices.

The effects of pathogen challenges on the performance of naïve and immune animals: the problem of prediction

Predictive frameworks for performance under both physical and social stressors are available, but no general framework yet exists for predicting the performance of animals exposed to pathogens. The aim of this paper was to identify the key problems that would need to be solved to achieve this. Challenges of a range of hosts by a range of pathogens were reviewed to consider reductions in growth beyond those associated with reductions in voluntary food intake (VFI). Pair-feeding and marginal response studies identified the extent and mechanisms of how further reductions in growth occur beyond those caused by reduced VFI. Further reductions in growth depended on the pathogen, the host and the dose and were time dependent. In some instances the reduction in VFI fully explained the reduction in growth. Marginal response experiments showed increased maintenance requirements during exposure to pathogens, but these were different for specific amino acids. There were no clear effects on marginal efficiency. Innate immune functions, repair of damaged tissue and expression of acquired immunity caused significant but variable increases in protein (amino acid) requirements. More resistant genotypes had greater requirements for mounting immune responses. The partitioning of protein (amino acids) was found to be different during pathogen challenges. Prediction of the requirements and partitioning of amino acids between growth and immune functions appears to be a crucial problem to solve in order to predict performance during pathogen challenges of different kinds and doses. The problems of accounting for reductions in performance during pathogen challenges that are described here provide a useful starting point for future modelling and experimental solutions.

Analysis of the feeding behavior of pigs using different models

Short-term feeding behavior is conventionally analysed using random process models. The assumption underlying these models have recently been questioned and this article describes the application of both random, and more biologically based, models to the feeding behavior of pigs. Feeder visits of 16 growing pigs, housed individually from 17 to 52 kg live weight, were recorded electronically over a continuous period of 35 days. Daily food intake increased linearly with time, but there was considerable individuality in the degree of order. Pigs made between 18.8 and 80.3 (mean 47.9) daily visits to the feeder. Intervals between visits could be described by two log-normal distributions. Two Gaussian density functions were fitted to the distribution of the log-transformed intervals. For the combined data from all animals the within- and between-meal intervals were 11.2 s and 100.1 min, respectively. A model with three Gaussian functions gave an improved fit to the interval distribution. The within and between meal intervals were then estimated to be 4.2 s and 93.9 min, respectively. The middle distribution of intervals ranged from 0.5 to 38.1 min. The intervals were also described by random process models; again, a three-process model gave an improved fit compared to a two-process model. The mean estimated number of meals per day from the three Gaussian model was 14.3, and from the three process random model, 16.3. A biological interpretation of the three types of interval suggests that: (1) pigs eat in meals separated by long intervals; (2) meals consist of clusters of eating bouts separated by shorter intervals, sometimes associated with drinking; (3) within each eating bout short intervals occur as pigs constantly move in and out of the feeder. It remains unclear what underlies the observed patterns of eating.

The short-term feeding behavior of growing pigs fed foods differing in bulk content

We investigated the effects of foods of different bulk on the short-term feeding behavior (STFB) of 16 individually housed pigs. The three foods used had different bulk contents [low-control (C), medium-70% wheat bran (WB), and high-70% sugar beet pulp (SBP)]. We expected the different intakes of the foods to be reflected in differences in STFB. Three hypotheses were developed based on ideas about the way in which a physical constraint to intake could arise. H(1): there would be less diurnal variation in feeding on high-bulk foods that limit food intake. H(2): feeding patterns on the bulky foods would be less flexible than those on C. H(3): a change in food type would result in food intake and STFB being rapidly altered to become appropriate to the new food. There were significant differences in food intake and STFB between the foods as intended. Pigs fed WB and SBP spent longer eating and had a slower feeding rate (FR) than pigs fed C. H(1) was rejected, as there was no difference in diurnal variation in intake between the foods. Feeding was not extended into the night on WB and SBP and the proportion of feeding that occurred during the night was the same for all three foods. H(2) was supported, as pigs fed WB and SBP were unable to maintain food intake and performance when time of access to the feeder was reduced. There was no adaptive change in STFB. H(3) was supported as a change from WB or SBP to C, or vice versa, caused a rapid change in STFB so that it became appropriate to the new food. It is concluded that physical constraints to food intake, caused by food bulk, may bring about changes in STFB and that they are important for the regulation of intake of such foods.

Unravelling the relationship between animal growth and immune response during micro-parasitic infections.

Background Both host genetic potentials for growth and disease resistance, as well as nutrition are known to affect responses of individuals challenged with micro-parasites, but their interactive effects are difficult to predict from experimental studies alone. Methodology/Principal Findings Here, a mathematical model is proposed to explore the hypothesis that a hosts response to pathogen challenge largely depends on the interaction between a hosts genetic capacities for growth or disease resistance and the nutritional environment. As might be expected, the model predicts that if nutritional availability is high, hosts with higher growth capacities will also grow faster under micro-parasitic challenge, and more resistant animals will exhibit a more effective immune response. Growth capacity has little effect on immune response and resistance capacity has little effect on achieved growth. However, the influence of host genetics on phenotypic performance changes drastically if nutrient availability is scarce. In this case achieved growth and immune response depend simultaneously on both capacities for growth and disease resistance. A higher growth capacity (achieved e.g. through genetic selection) would be detrimental for the animals ability to cope with pathogens and greater resistance may reduce growth in the short-term. Significance Our model can thus explain contradicting outcomes of genetic selection observed in experimental studies and provides the necessary biological background for understanding the influence of selection and/or changes in the nutritional environment on phenotypic growth and immune response.

The way in which the data are combined affects the interpretation of short-term feeding behavior

Short-term feeding behavior of pigs has been analyzed using random process models and log-normal models. Both were successful despite very different underlying assumptions relating to the theory of control. Feeder visits of growing pigs, housed individually from 17 to 52 kg live weight, were recorded electronically over a continuous period of 35 days. For the combined data, intervals between visits to the feeder greater than 30 min could be described well by the negative exponential model. The starting probability of a visit was constant at around 0.3, suggesting randomness. Disaggregating the data for individual pigs or for individual weeks did not change this conclusion. Intervals in the day were of a different nature to those at night, and disaggregation of the data into these two periods revealed that the negative exponential model was not satisfactory for either period. The starting probability for both periods increased with time since the last visit. This is consistent with the idea of satiety. Therefore, the apparent randomness in the data pooled across the day and night is an artefact caused by pooling itself, and is not in conflict with the satiety concept. The implications of data handling are discussed with reference to studies of the physiological control of food intake.

The effect of protein source on the diets selected by pigs given a choice between a low and high protein food.

To test the effect of the protein source on the diet selection of growing pigs, four foods of high protein concentration were made. Each food was based on a different protein meal: fish, soya bean, and two types of rape seed (with low and high glucosinolate contents), and was offered to growing pigs together with a food of low protein concentration (L), as a choice. Pigs given a choice between the fish or the soya bean meal-based food and L, selected a diet that met their protein requirements, as judged by their growth rates and food efficiency: the protein content of the selected diet declined systematically with pig weight. Pigs given a choice between the rape seed meal-based foods and L selected diets with a high proportion of L and, consequently, failed to meet their protein requirements. Given that the preference for L was more marked when the animals were given access to the rape seed meal higher in glucosinolates, it is suggested that their diet selection on these foodpairs was a tradeoff between minimising glucosinolate intake, which has potentially goitrogenic properties, and achieving a protein intake sufficient for maximum performance. This suggestion is supported by the fact that the fish meal-based food was preferred over the ones containing rape seed meal, and that the rape seed meal lower in glucosinolate content was preferred over the other when pigs were given a choice between them.