Do breeds of pig differ in the efficiency with which they use a limiting protein supply?

Issues arising from genetic selection for growth and body composition characteristics in poultry and pigs

Breeders of poultry and pigs have selected for some combination of increased growth rate, decreased fatness and increased muscularity. Increasingly various fitness traits are included in the index used. The consequences of such selection include complex effects on nutritional and environmental requirements, at least some of which are reliably predictable using suitable models. Appropriate changes to the environment and to nutrition as selection proceeds will help to avoid unwanted effects occurring. Among the predictable effects are that higher ratios of nutrients to energy, and lower temperatures, will be needed by the improved genotypes. Selection for growth rate must eventually exhaust the capacity of the support systems – digestive, respiratory, circulatory and excretory – to cope with the increased metabolic rate. Selection for increased yield of valuable parts will cause these problems to occur earlier. While it is possible to predict that these problems will occur it cannot be predicted when they will. Breeders need to be aware of these problems, and use all possible routes to help them in reducing their severity. Where the appropriate actions for fitness selection, and nutritional and environmental modifications, are taken the occurrence of the problems will be delayed.

Nutrient utilisation in grower pigs fed a protein concentrate blended with sweet potato roots either boiled or ensiled with or without vines

Blending sweet potato (Ipomoea batatas L. (Lam)) with a protein concentrate for pig feed is a common strategy used by small-scale livestock farmers across Africa, Asia and the Pacific. However, high dietary fibre in sweet potato (SP) forage may reduce nutrient utilisation and energy metabolism and reduce the growth rate of young pigs. A 32-day metabolic trial with grower pigs using a 4 × 4 Latin square design tested the hypothesis that there would be no difference in apparent total tract digestibility (ATTD) of nutrients, energy and nitrogen (N) balance in 25 kg grower pigs (Large White × Landrace × Duroc) fed diets based on a blend of 43–40% protein supplement with 57–60% of DM as SP roots either boiled (BR43) or ensiled alone (ER43) or ensiled with vines (ERV40). Blended SP diets provided ~14–15% crude protein (CP), 16.1–16.3 MJ digestible energy (DE)/kg DM and 0.54–0.58 g lysine/MJ DE. The control diet (STD) contained 16.5% CP, 14.8 MJ DE/kg DM, 0.58 g lysine/MJ DE. The major findings were as follows: (1) DM intake was higher (P < 0.05) for BR43 than ER43, ERV40 and STD diets, which were similar; (2) DM ATTD and energy utilisation were higher (P < 0.05) in pigs fed SP diets; (3) carbohydrate (N-free extracts) ATTD was higher (P < 0.05) in pigs fed BR43 and ER43 diets, while CP ATTD of both these diets was similar to that of STD and higher than that of ERV40; (4) ATTD of fats (ether extracts), CP, carbohydrates (N-free extracts) and total phosphorus was lower (P < 0.05) on ERV40, but fibre ATTD was higher; (5) N intake and N retained were similar (P > 0.05) for pigs fed BR43, ER43 and STD diets but lower for ERV40 (P < 0.05). Boiled or ensiled SP roots provided high nutrient and energy utilisation in growing pigs, but the inclusion of SP vines lowered ATTD, energy utilisation and N retained from the mixed diet (ERV40). It is concluded that boiled or ensiled SP root are equally valuable as blended feed for grower pigs. However, at 30%DM, ensiled SP vine in blended feed led to reduced grower-pig performance.

Modelling the effects of thermal environment and dietary composition on pig performance: model logic and concepts

A deterministic, dynamic pig growth model is described that predicts the effects of genotype and the thermal and nutritional environments on food intake, growth and body composition of growing pigs. From the daily potential for protein gain, as determined by pig genotype and current state, the potential gains of the other chemical components, including ‘desired’ lipid gain, are calculated. Unconstrained voluntary food intake is predicted from the current protein and lipid contents of the pig, and the composition of the food, as that which is needed to permit potential growth to be achieved. The model allows compensatory lipid gain. The composition of the food is described in terms of its digestible energy content (DEC), ideal digestible crude protein content (IDCPC) and bulkiness. Both energy and protein can be limiting resources and the bulk of the food may constrain intake. The animal’s capacity for bulk is a function of its size. The thermal environment is described by the ambient temperature, wind speed, floor type and humidity and sets the maximum (HLmax) and minimum (HLmin) values possible for heat loss. A comparison with heat production (HP) determines whether the environment is hot (HP > HLmax), cold (HP < HLmin) or thermoneutral (HLmin< HP < HLmax). A constraint on intake operates in hot environments, while in cold environments, there is an extra thermal demand. If conditions are thermoneutral no further action is taken. Daily gains of each of the chemical components are calculated by partitioning energy intake between protein and lipid gains according only to the energy to protein ratio of the food. The model builds on the work of others in the literature as it allows predictions on how changes in: (i) the kind of pig; (ii) the animal’s current state, which is particularly relevant in cases of compensatory growth; (iii) the dietary composition, and; (iv) the climatic environment, affect food intake and growth, whilst maintaining simplicity and flexibility.

Energy requirement of growing pigs under commercial housing conditions

Scientifically derived recommendations for the energy supply to growing pigs are generally based on estimates of the metabolisable energy (ME) requirements for maintenance (MEm) and protein (MEp) and fat (MEf) retention. It is supposed that animals are kept within the zone of thermoneutrality and that their physical activity is not elevated. These assumptions might not always be true for practical housing conditions, and it is difficult to quantify the additional energy needed for thermoregulation and physical activity. Hence, at a given ME intake, differences can occur between the actual growth rates and those predicted from the recommendations. To quantify such differences, three trials were carried out under commercial farming conditions with pigs growing from 25 to 120 kg body weight (BW). In each trial, 624 castrated male and female pigs were allocated to four feeding groups distributed over 24 double pens. The rations were provided according to the animals' feed intake capacity and BW was recorded every three weeks. Protein, fat and energy retention (RE) was derived from carcass composition and BW gain. The difference between ME intake and MEm plus ME required for growth (MEg = RE/kpf) was calculated and seen as the ME required for purposes other than maintenance and growth (MEx). MEx accounted for 2.0%, 17.0% and 21.4% of the animals' ME intake in Trials 1, 2 and 3, respectively, and was higher in female than in castrated male pigs when related to metabolic BW. It was concluded that total ME requirements of pigs kept under commercial housing conditions can be considerably higher than ME requirements predicted from feeding standards since they usually ignore MEx. MEx can be used as an indicator for the quality of housing systems. Further studies are needed to identify the key factors responsible for MEx to allow for more precise recommendations for the energy supply to commercially raised pigs.

Administration of loperamide and addition of wheat bran to the diets of weaner pigs decrease the incidence of diarrhoea and enhance their gut maturation

The influence of fibre inclusion and transit time regulation on the performance, health status, microbial activity and population, physico-chemical characteristics of the hindgut digesta and intestinal morphology in early weaned pigs were examined. For these experiments, wheat bran (WB) was used as fibre source and loperamide as a drug (LOP) to increase the digesta transit time. In Expt 1, a total of 128 early weaned pigs were randomly distributed in a 2 × 2 factorial combination of WB inclusion (0v.40 g/kg) and LOP administration (0v.0·07 mg/kg body weight) during 13 d. For Expt 2, a total of twenty-four piglets were allotted to three dietary treatments for 15 d with the same basal diet (control diet) as Expt 1; a diet with 80 g/kg of WB and the combination of WB and LOP. In Expt 1, LOP improved the average daily feed intake and average daily gain of the animals (P = 0·001 and 0·007, respectively). The same result was obtained when WB was combined with LOP. The WB–LOP group also showed a higher concentration of SCFA (P = 0·013), acetic acid (P = 0·004) and propionic acid (P = 0·093). On the other hand, WB inclusion reduced the organic matter and crude protein digestibility (P = 0·001) and tended to decrease the enterobacteria population (P = 0·089). In Expt 2, WB increased the butyric acid concentration (P = 0·086). We concluded that the inclusion of WB to modify the intestinal microbiota activity combined with LOP may be beneficial to animal health and performance.

Partitioning of limiting protein and energy in the growing pig: testing quantitative rules against experimental data

Literature solutions to the problem of protein and energy partitioning in the growing pig are quantitatively examined. Possible effects of live weight, genotype and food composition on the marginal response in protein retention to protein and energy intakes, on protein and energy-limiting foods are quantified. No evidence was found that the marginal response in protein retention to ideal protein supply, when protein intake is limiting, is affected by live weight, genotype or environmental temperature. There was good evidence that live weight does not affect the marginal response in protein retention to energy intake when protein intake is not limiting. Limited data for different genotypes suggested no effects on this response. A general quantitative partitioning rule is proposed that has two key parameters; e(p)* (the maximum marginal efficiency for retaining the first limiting amino acid) and R* (the maximum value of R, the energy to protein ratio of the food, MJ metabolisable energy (ME)/kg digestible crude protein (DCP), when e(p)* is just achieved). When R<R* the material efficiency of using ideal protein is (e(p)*/R*) x R. The value of e(p)* was determined to be 0.763 (SE 0.0130). There was no good experimental evidence that e(p)* is different for different amino acids. The best estimate of R* was 67.9 (SE 1.65) MJ ME/kg DCP. Live weight, genotype and temperature did not affect the values of either parameter. A more general understanding of partitioning, including the effects of 'stressors' such as disease, may be achieved by using the preferred rule as a starting point.

Pattern of protein retention in growing boars of different breeds, and estimation of maximum protein retention

Protein and energy metabolism in boars of different breeds, 10 each of Hampshire, Duroc and Danish Landrace was measured in balance and respiration experiments by means of indirect calorimetry in an open-air circulation system. Measurements were performed in four periods (Period I-IV) covering the body weight range from 25 to 100 kg. In order to achieve maximum protein retention (RP) a daily intake of digestible protein > 12 g/kg0.75 and metabolisable energy > 1100 kJ/kg0.75 was assumed to be necessary. Protein retention of Danish Landrace boars was inferior to that of Hampshire and Duroc boars in Periods III and IV, and therefore, 55 measurements on Hampshire and Duroc boars fulfilling the chosen criteria for digested protein and ME intake were used for calculation of maximum protein retention, giving the following significant quadratic relationship: RP [g/d] = 11.43.W0.75-0.144.W1.50 (n = 55, RSD = 15.2, CV = 9.2%, R2 = 0.851) with a summit of 227 g/d at 135 kg BW. In Period I, when BW was below 30 kg, 12 measurements fulfilled the chosen criterion for digested protein but not for ME, and these data were used comparatively. Protein retention of boars with a low ME intake in Period I was significantly below that of boars with a high ME intake (93 g/d vs. 107 g/d; P = 0.02). In summary, the present data have shown that boars of high genetic potential have capacity for maximum protein retention of about 230 g/d, and that there was a significant quadratic relationship between protein retention and metabolic body weight, indicating that maximum protein retention was not reached until 135 kg BW. Differences in capacity for protein retention were recorded between boars of different breeds, with Duroc and Hampshire boars being superior to Danish Landrace boars. Additionally, the crucial importance of a sufficient ME supply early in the growth period was underscored by a lower protein accretion rate of boars given a daily ME supply below 1100 kJ ME/kg0.75 at an approximate BW of 25 kg.

Major determinants of fasting heat production and energetic cost of activity in growing pigs of different body weight and breed/castration combination

A total of sixty-five observations on heat production during fasting and physical activity were obtained in four groups of pigs differing in breed and/or castration (Meishan (MC) and Large White (LWC) castrates and Large White (LWM) and Piétrain (PM) males) with body weight (BW) ranging between 25 and 60 kg. Pigs were fed ad libitum before fasting. Heat production was measured using indirect calorimetry. Fasting heat production (FHP) was proportional to the body weight raised to the power 0.55, but with group-specific proportionality parameters (810, 1200, 1220 and 1120 kJ/kg BW0.55 per d for MC, LWC, LWM and PM respectively). Group effects could be removed by expressing FHP as a function of muscle, viscera and fat: FHP (kJ/d) = 457(muscle)0.81 + 1969(viscera)0.81 - 644(fat)0.81. It is hypothesized that different breeds with equal muscle and visceral mass, can have different FHP. The negative coefficient for fat would then be the result of a low FHP rather than a cause of it. Because a large part of the variation in tissue composition between groups was due to MC group, a separate equation for the lean groups was established. For lean pigs, FHP could be expressed as a function of muscle and viscera alone: FHP (kJ/d) = 508(muscle)0.66 + 2011(viscera)0.66. Both type of pig and BW affected the number of bouts of physical activities (i.e. standing or sitting) per day, the duration of activity and the total cost of activity. Energetic cost of activity was proportional to the muscle mass raised to the power 0.91 (FHPactivity (kJ/h activity) = 21.0(muscle)0.91). Physical activity represented less than 10% of the total heat production in fasting growing pigs housed alone in metabolic cages and kept in a quiet environment.