Severe undernutrition in growing and adult animals. 17. The ultimate results of rehabilitation: pigs

Impact of single or repeated short-term heat challenges mimicking summer heat waves on thermoregulatory responses and performances in finishing pigs

The objectives of this study were to determine the effects of single or repeated short heat stress (HS) challenges that mimicked summer heat waves on performance and thermoregulatory responses in finishing pigs. A total of 45 crossbred castrated males were tested in three consecutive replicates of 15 pigs. Within each replicate, pigs were assigned to one of five treatments. Pigs in treatment group TTT were maintained in thermoneutral conditions (22 °C) for the entire experiment (45 d). Pigs in treatment group HHH were subjected to an HS challenge (32 °C for 5 d) at 113, 127, and 141 d of age (in experimental periods P1, P2, and P3, respectively). Pigs in treatment groups HTT, THT, and TTH were subjected to the HS challenge at 113, 127, or 141 d of age, respectively. Each 5-d challenge was preceded by a 3-d prechallenge period and followed by a 7-d recovery period. Pigs were housed in individual pens and fed ad libitum. HS significantly reduced average daily feed intake (ADFI) and the average daily gain (ADG). Expressed as a percentage of the performance observed during the prechallenge period, ADFI decreased by 12%, 22%, and 26% and ADG decreased by 12%, 43%, and 72% in the HTT, THT, and TTH groups, respectively. Regardless of the experimental group, no compensatory performance was observed during the recovery period, suggesting that HS has a long-lasting effect on animal performance. Pigs subjected to HS had an immediate increase in core body temperature (T_core), skin temperature, and respiratory rate, all of which gradually decreased during the HS challenge. Based on T_core measurements, hypothermia was observed during the recovery period in each of the three experimental periods, especially for pigs in the HHH and the HTT groups but only during the first HS cycle. Repeated exposure to HS for the HHH group resulted in heat acclimation responses characterized by a lower increase in T_core and lower decrease in ADFI during P2 and P3 than during P1.

Modelling the feed intake response of growing pigs to diets contaminated with mycotoxins

Quantifying robustness of farm animals is essential before it can be implemented in breeding and management strategies. A generic modelling and data analysis procedure was developed to quantify the feed intake response of growing pigs to perturbations in terms of resistance and resilience. The objective of this study was to apply this procedure to quantify these traits in 155 pigs from an experiment where they received diets with or without cereals contaminated with the mycotoxin deoxynivalenol (DON). The experimental pigs were divided equally in a control group and three DON-challenged groups. Pigs in each of the challenged groups received a diet contaminated with DON for 7 days early on (from 113 to 119 days of age), later on (from 134 to 140 days of age) or in both periods of the experiment. Results showed that the target feed intake trajectory of each pig could be estimated independently of the challenge. The procedure also estimated relatively accurately the times when DON was given to each challenged group. Results of the quantification of the feed intake response indicated that age and previous exposure to DON have an effect on the resilience capacity of the animals. The correlation between resistance and resilience traits was modest, indicating that these are different elements of robustness. The feed intake analysis procedure proved its capacity to detect and quantify the response of animals to perturbations, and the resulting response traits can potentially be used in breeding strategies.

Progressive limit feeding to maximize profit in the feedlot1

Our objective was to examine the potential of limit feeding that keeps a previously growing animal at a constant size (termed progressive limit feeding) to maximize profit using a 3D surface to integrate the effects of animal size, feeding rate, and time in the feedlot. The constant size contours of the surface were determined using a combination of results. We used data from a study of growing beef cattle being fed to maintain specified sizes coupled with modern growth rate data for animals fed ad libitum in a feedlot. These feed rate contours were best-fit declining exponentials. They shared the same exponent and they originated on the ad libitum curve, thus defining the entire possible growth surface. The asymptotes of these exponentials coincided with the interspecies mean for the metabolic body size of mature animals. This surface also demonstrated the phenomenon of compensatory growth. We proved that the most profitable growth path across this surface is of a particular form under realistic assumptions. Specifically, we proved that the profit maximizing growth path in the feedlot began with a period of progressive limit feeding and then allowed ad libitum feeding to the same market time as experienced by the standard continuous ad libitum fed animal. The opportunity cost of holding the progressively limit-fed animal longer in the feedlot than the animal fed ad libitum quickly overpowered any profit gained by limit feeding. Consequently the progressively limit-fed animal on the optimal feeding path at sale time was slightly smaller but potentially more profitable than the animal fed ad libitum, both slaughtered at the same time. It may also have an economically favorable body composition. Thus we have demonstrated a process for maximizing profit in the feedlot. The approach involved developing a growth surface to integrate the effects of progressive limit feeding and subsequent compensatory growth. After refinement this same process could be applied to other livestock.

Describing and predicting potential growth in the pig

Most animal growth models contain an explicit growth function. It determines the pattern of growth over the lifetime of the animal and defines an upper limit to growth rate (the potential). The criterion of the ‘goodness-of-fit’ to one or more sets of data is frequently used to select a suitable growth function. Alternative criteria are described here that can be used to choose between forms that describe potential growth. Of the functions reviewed only a few fulfilled all of the proposed criteria. Of these the Logistic and Gompertz functions were favoured because of an economy of parameters and their ability to describe relative growth rate as a simple function of size. The Logistic function was rejected on the grounds of its numerical consequences for growth in pigs over a wide range of degrees of maturity, leaving the Gompertz function to be tested for its ability to make sensible predictions of potential growth. Pre-natal growth data, assumed to occur under non-limiting conditions as long as the mother is not subjected to extremely adverse nutritional conditions or incidence of infection, were used to estimate the values of the two Gompertz function parameters-the growth coefficient and the initial condition-given an estimate of mature size. The values were comparable with literature estimates based on post-natal growth and predictions of growth rate over a wide range of degree of maturity were thus sensible. On these grounds, and because it uses few parameters all with biological meaning, the Gompertz function is proposed as a suitable descriptor of potential growth.

Modelling the relation between energy intake and protein and lipid deposition in growing pigs

When modelling the effect of a changing nutrient supply to growing animals, it is important to distinguish the individual response curve of an animal from the change in this response that may occur during growth. A data analysis model is proposed where, for an individual animal, the relation between protein deposition (PD) and metabolizable energy (ME) intake above maintenance (MEp) is curvilinear, so that PD intersects the origin and reaches its maximum at the maximum protein deposition rate (PDmax). An increase of MEp beyond that required to attain PDmax would not change PD. The MEp not used for protein synthesis can be used for lipid deposition (LD). The relation between PD and LD on the one hand and ME on the other hand can then be described as a function of the maintenance energy requirement (MEm), PDmax, the level of ME required to attain PDmax (F; as a multiple of MEm) and the energetic efficiencies of PD (kp) and LD (kf). Of these statistics, only kp and kf were assumed to be independent of body weight (BW), age or genotype. Variation in PDmax was described as a Gompertz function (of age) whereas variation in F was assumed a linear function of BW. Maintenance energy requirement was expressed as a power function of BW. To evaluate the model, 145 nitrogen and energy (indirect calorimetry) balances were obtained from three types of pigs (Large White castrated males (cLW) and Piétrain × Large White castrated males (cPP× ) and males (bPP×)) ranging in BW between 45 and 100 kg and housed under thermoneutral conditions. Animals were allotted to one of four energy levels ranging from 0·70 to 1·00 of ad libitum intake. The MEm was not different between genotypes (849 kJ/kg BW0·60) whereas the kp and kf were 0·56 and 0·75, respectively. For castrated animals on ad libitum intake, PDmax started limiting PD at approximately 130 days of age (78 and 86 kg BW for cLW and cPP×, respectively). Before this age and for bPP×, PD was limited by MEp. In bPP×, the difference between PD and PDmax was small (less than proportionately 0·05). The F did not change with BW for bPP× (2·85 × MEm) whereas for the other genotypes, it decreased linearly from 4·47 at 45 kg to 2·00 at 100 kg of BW. Due to its nature, the model allows estimation of PDmax even when energy is restricting PD.

The effect of genotype and sex on the patterns of protein accretion in pigs

Protein accretion curves were derived using food intake, growth and body composition data from a total of 320 pigs, which comprised castrated males and gilts from five genotypes. The 32 pigs from each genotype/sex subclass were offered ad libitum a series of isoenergetic diets (13·8 MJ metabolizable energy per kg) designed to provide a non-limiting intake of nutrients and to allow maximum protein deposition rates. Four pigs from each subclass weren slaughtered at each of the live weights (kg) 25, 44, 65, 85, 100, 115, 130 and 150. Daily food intake (dF/dt) was described as an increasing exponential function of age (t), live weight (W) as an increasing exponential function of cumulative food consumed (F), and protein weight (Pr) as an allometric function of live weight (W). The rate of protein accretion in the body of pigs [d(Pr)/dt] was calculated as d(Pr)/dt = (dF/dt).(dW/dF).(dPr)/dW). Bootstrap procedures were used to estimate standard errors for the food intake, growth and compositional parameters and to obtain the confidence bands for the dependent variables (dF/dt, W, Pr and d(Pt)/dt).

Protein accretion rate as a function of live weight was curvilinear, increasing to a maximum, then decreasing with increasing live weight. There were significant differences between subclasses in the maximum rate of protein accretion, although there was no relationship between this rate and the live weight, stage of maturity, or age at which maximum protein accretion occurred. Describing protein accretion as a multiplicative function of food intake, food efficiency and the partitioning of nutrients in the body allowed changes in the magnitude and shape of the protein accretion curve to be ascribed to one, or a combination, of the above mechanisms.

A comparison of phase feeding and choice feeding as methods of meeting the amino acid requirements of growing pigs

Two experiments are reported in which a comparison was made of phase feeding and choice feeding as methods of meeting the changing amino acid requirements of growing pigs. In the first experiment, three feeding strategies were used: a system in which a single food (165 g protein per kg food) was offered throughout the growth period; a phase-feeding system, using five different treatments; and three choice-feeding treatments, in which the two diets offered differed only in their protein concentrations. The second experiment consisted of six treatments, three of which constituted a single feeding system, being a high, a medium, (the control) and a low protein food (240, 165 and 100 g protein per kg); there were two phase-feeding treatments, of three and five phases; and one treatment in which a choice was offered of the high and the low protein foods. In both experiments, group data were collected on Landrace × Large White pigs, sexes separate, during the growing period (30 to 90 kg). All pigs were weighed weekly, as was the amount of food consumed in each pen of 10 animals. Phase feeding improved food conversion efficiency (+4·4 g/kg) and caused a decline in both food intake (−45·3 g) and P2 backfat thickness (−0·4 mm) with each increment in the number of phases used. Results of the choice feeding treatments were not statistically significantly different from either the control or the phase feeding treatments. The intake of dietary protein was higher in the choice treatments than in the control (420 v. 370 g in experiment 1 and 345 v. 334 g in experiment 2). Where the two foods on offer differed only in protein content, pigs reduced the proportion of high protein food in the combination chosen by 0037 and 0·059 per week in the two experiments respectively, these linear trends being statistically highly significant. They were less successful in differentiating between the high protein food and maize, the proportion of high protein food chosen decreasing at a statistically significant rate of 0018 per week, but where the maize had not been supplemented with vitamins and minerals there was no significant trend in the way in which the pigs selected their diet, demonstrating the importance of the correct design of the two foods on offer in a choice-feeding programme.

Severe undernutrition in growing and adult animals

1. Pigs, held by undernutrition to a weight of about 5.5 kg till they were a year old, were then rehabilitated on an excellent growing ration, and killed when they were fully mature.

2. Undernutrition of this degree of severity delayed the growth and development of the teeth, but relatively less than that of the body or the jaws.

3. The teeth became abnormally sited and the shape of the mandible changed.

4. During rehabilitation, some of the crowns and most of the roots of the molar teeth failed to reach their proper size.

5. Some of the molar teeth remained permanently impacted and out of alignment.

6. The fine structure of the teeth, particularly of those parts formed during the period of undernutrition, was still abnormal when the animals were killed.

Effects of feed restriction and subsequent refeeding on energy utilization in growing pigs

An experiment was carried out to evaluate the metabolic utilization of energy in crossbred barrows during feed restriction and subsequent refeeding. Ten pigs, initially weighing 52 kg, were used in 5 blocks of 2 littermates each. A 7-d adaptation period (P1) was used in which pigs were offered feed at 2.60 MJ of ME.kg of BW(-0.60).d(-1). This adaptation period was followed by a 7-d period (P2), in which 1 pig of each block continued to receive feed at the same level of feeding, whereas for its littermate a 40% reduction in feed intake was imposed (i.e., 1.55 MJ of ME.kg of BW(-0.60).d(-1)). During the subsequent 7-d period (P3), both pigs were offered feed at 2.60 MJ of ME.kg of BW(-0.60).d(-1). After P3, pigs were fasted for 1 d. Heat production (HP) was measured for all pigs during the last 3 d of P1 and on all days for P2 and P3. Heat production was measured using an open-circuit respiration chamber. Energy and N balances were determined for P1, P2, and P3. The HP was partitioned into HP due to physical activity, the short-term thermic effect of feeding, and resting HP. Feed restriction during P2 decreased (P < 0.01) total HP, resting HP, short-term thermic effect of feeding, and retained energy, whereas HP due to physical activity was not affected by feed restriction (P = 0.50). Likewise, fecal and urinary N loss, protein gain, lipid gain, and ADG were reduced during feed restriction (P < 0.01). There were no differences in components of HP and metabolic utilization of energy between the 2 groups during P1 and P3. Nevertheless, urinary N loss was decreased (P < 0.05) and ADG increased (P < 0.01) during P3 for pigs that were restricted in P2. Compensatory growth after a period of feed restriction does not seem to be related to a change in the metabolic utilization of energy for gain but more likely is due to gain in water and gut contents.

A role for suppressed thermogenesis favoring catch-up fat in the pathophysiology of catch-up growth

Catch-up growth is a risk factor for later obesity, type 2 diabetes, and cardiovascular diseases. We show here that after growth arrest by semistarvation, rats refed the same amount of a low-fat diet as controls show 1) lower energy expenditure due to diminished thermogenesis that favors accelerated fat deposition or catch-up fat and 2) normal glucose tolerance but higher plasma insulin after a glucose load at a time point when their body fat and plasma free fatty acids (FFAs) have not exceeded those of controls. Isocaloric refeeding on a high-fat diet resulted in even lower energy expenditure and thermogenesis and increased fat deposition and led to even higher plasma insulin and elevated plasma glucose after a glucose load. Stepwise regression analysis showed that plasma insulin and insulin-to-glucose ratio after the glucose load are predicted by variations in efficiency of energy use (i.e., in thermogenesis) rather than by the absolute amount of body fat or plasma FFAs. These studies suggest that suppression of thermogenesis per se may have a primary role in the development of hyperinsulinemia and insulin resistance during catch-up growth and underscore a role for suppressed thermogenesis directed specifically at catch-up fat in the link between catch-up growth and chronic metabolic diseases.

Redistribution of abdominal fat after a period of food restriction in rats is related to the type of dietary fat

The aim of the present experiment was to test the hypothesis that during refeeding a redistribution of intra-abdominal fat takes place and that both the recovery of weight and the redistribution of intra-abdominal fat are related to the type of dietary fat. The experimental study was carried out using male Sprague-Dawley rats. Three groups of animals were fed diets with three different fatty acid profiles. Each group contained two branches, one fed normally and the other fed initially with a 50 % energy reduction followed by refeeding ad libitum with the same isoenergetic diet as the control branch, giving a total of six treatments. Measurements were made of the final and incremental weight of the rat, weight of the intra-abdominal adipose tissue (total intra-abdominal, epididymal, omental and retroperitoneal adipose tissue weight), and feed efficacy (weight increment/metabolizable energy intake). Carcass, epididymal, omental, and muscle lipid contents, carcass protein and energy density were also measured. The results revealed that diets rich in fish oil or olive oil increase catch-up growth more than diets rich in saturated fats. During refeeding the lipid content in the adipose tissue increases while that of muscle tissue decreases. A diet rich in saturated fats induces a relative increase in the amount of intra-abdominal adipose tissue. The lipid content in adipose and muscle tissues and the distribution of intra-abdominal fat can all be modified by the type of dietary fat.

Changes in adipose tissue of the rat due to early undernutrition followed by rehabilitation. 1. Body composition and adipose tissue cellularity

1. Male Black and White Hooded rats were allocated at birth to foster mothers in litters of three, nine or sixteen. At weaning animals from each of these litter sizes were ad lib.-fed on a stock diet forming three ad lib.-fed control groups. At weaning further animals from litters of nine and sixteen were fed on the stock diet in restricted amounts until 12 weeks of age. These undernourished animals were then rehabilitated by being allowed ad lib. access to the stock diet. 2. Five animals from each group were killed at various stages of the experiment, their bodies analysed for fat and nitrogen, and the size and number of cells determined in four specific fat depots. 3. The previously undernourished rats failed to make a complete recovery and were significantly smaller than ad lib.-fed animals from the same litter at 32 weeks of age when the experiment was terminated. 4. The previously undernourished rats from litters of nine deposited a significantly greater porportion of fat in their bodies during rehabilitation than ad lib.-fed animals from litters of nine over the same gain in body-weight. The previously undernourished rats from litters of sixteen deposited the same proportion of fat in their bodies during rehabilitation as ad lib -fed animals from litters of three, nine and sixteen over the same gain in body-weight. 5. There were no significant differences in apparent or total fat cell numbers between ad lib.-fed animals and undernourished-rehabilitated animals at any of the four sites studied at 32 weeks of age.

Deposition of fat in the body of the rat during rehabilitation after early undernutrition

1. Male and female rats aged 3 weeks were divided into two groups. One group of each sex was allowed unlimited access to the stock diet, the other group was given the stock diet in restricted amounts for 10 weeks so that the males gained only 19 g and the females 21 g in comparison with 176 g and 116 g for the well-nourished males and females respectively. The undernourished animals were then rehabilitated by being allowed the stock dietad lib.

2. Five animals of each sex were killed at various stages of the experiment, their bodies analysed for fat and nitrogen, and the size and number of fat cells determined in specific fat depots.

3. The undernourished rats failed to make a complete recovery and were significantly smaller than the controls of the same sex at 172 d of age when the experiment terminated.

4. The previously undernourished rats deposited significantly more fat in their bodies during rehabilitation than the control animals in the same number of days and over the same gain in body-weight.

5. There were no significant differences in the number of cells containing fat at the abdominal fat site between the undernourished and rehabilitated animals and the controls at any stage, nor were there any significant differences in apparent fat cell numbers between the control and rehabilitated animals at any of the other sites studied when the experiment ended at 172 d.

The determinants of growth and form

An animal can only achieve its full genetic potential if it has lived its life in an ideal environ­ment. Few environments are ideal; they may be unfavourable for numerous reasons and for different lengths of time. Indeed, variations on these themes are almost infinitely possible, but concrete examples will be selected and their effects on the lives of animals and of man demonstrated. Time comes into all this, but its importance and the difference between chronological and biological time have not been properly appreciated. The interactions of time and the environment on the growth of animals and of their organs are complex, but recent work on malnutrition and growth has given us some insight into the matter. Theories that have been formulated are discussed, but none of those yet put forward explain all the facts that can be demonstrated experimentally, and studies that might provide clues have been neglected.

Clinical and experimental results of removing the large intestine soon after birth

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The relationship between an elevated serum amino acid ratio and the development of other biological abnormalities in the experimentally malnourished pig

1. Weanling pigs were fed under three dietary regimens, control, low protein and total calorie restricted.

2. In the protein-deficient group the amino acid ratio did not start to become elevated until growth was impaired and total serum protein and albumin concentration began to fall.

3. In the protein-deficient group, but not in the control or undernourished animals, the magnitude of the ratio was statistically correlated with the rate of growth, appetite, serum protein and albumin concentration and hydroxyproline excretion.

4. The results provide information on the relationship between the serum amino acid ratio and nutritional status.

Severe undernutrition in growing and adult animals. 19. The metabolic rates and body temperature of calorie-deficient and protein-deficient pigs

1. The body temperatures and resting oxygen consumptions of calorie-deficient and protein-deficient pigs have been measured at 12, 21, 26, 30, 36 and 40°.

2. A fall in the environmental temperature was followed by a rise of the same order in the oxygen consumptions of the two groups of animals, and past and present evidence indicates that the rise in normal animals of the same size is similar.

3. The rectal temperatures and oxygen consumptions of the protein-deficient pigs were higher at all the above temperatures than those of the calorie-deficient animals but not as high as those of normal animals.

4. The differences in rectal temperatures and oxygen consumptions were highly significant at 30°, which is probably within or near the zone of thermal neutrality of all the animals.

Experimental resection of the intestine in newborn pigs

1. The whole of the lower half of the small intestine, with the exception of the last few cm of the ileum, has been removed from sixteen suckling pigs, 3–4 kg in weight.

2. The operation is technically easy, but the exposure and handling of the intestines may produce crippling adhesions.

3. The postoperative management presents no serious nutritional difficulties.

4. If the operation is successful the animals become functionally normal, if slightly small, adults.