L. Brossard

Influence of some sow characteristics on within-litter variation of piglet birth weight

Within-litter variation of piglet birth weight (BW0) is associated with an increased piglet mortality and a high variability in pig weight at weaning and weight or age at slaughter. Data collected in two experimental herds were used to quantify within-litter variability in BW0 and to assess the influence of factors mainly related to the sow. Within 24 h after birth, piglets born alive were individually weighed and stillborn piglets were collectively (first data set) or individually (second data set) weighed. The first data set was restricted to litters with no or only one stillborn piglet (3338 litters). It was used to assess the influence of genetic selection on BW0 variation by comparing litter characteristics before (1994 to 1996) and after (2001 to 2004) the development of hyperprolific sows in this herd. The second data set included all litters (n = 1596) from sows born between 2000 and 2004. For each litter, mean BW0 (mBW0) and its coefficient of variation (CVBW0) were calculated. Then, variance analyses were performed to test the influence of litter size, parity, year of sow birth and season at conception. Prolificacy improvement was associated with an increased CVBW0 in litters from pure Large White (LW) and Landrace × Large White (LR × LW) crossbred sows. The CVBW0 averaged 21% and was significantly influenced by litter size and parity. It increased from 15% to 24% when litter size varied from less than 10 piglets to more than 15 piglets. The proportion of small piglets (i.e. weighing less than 1 kg) increased concomitantly. The CVBW0 was not repeatable from a parity to the following. It was lowest for first and second parities (20%) and thereafter increased progressively. The CVBW0 was positively related to sows backfat thickness gain during gestation. Taking into account litter size, parity, year of sow birth and season at conception explained 20% of BW0 variation. Thus, major part of heterogeneity is due to other factors, presumably including embryo genotype, on the one hand, and factors that influence embryo and foetus development, such as epigenetic factors, on the other hand.

Genetics of residual feed intake in growing pigs: Relationships with production traits, and nitrogen and phosphorus excretion traits

Residual feed intake (RFI) is defined as the difference between the observed ADFI and the ADFI predicted from production and maintenance requirements. The objectives of this study were to evaluate RFI as a selection criterion to improve feed efficiency and its potential to reduce N and P excretion in 4 pig breeds. Data were collected between 2000 and 2009 in French central test stations for 2 dam breeds [French Landrace (LR) and Large White (LWD)], and 2 sire breeds [Large White (LWS) and Piétrain (PP)]. Numbers of recorded pigs were 6407, 10,694, 2342, and 2448 for the LR, LWD, LWS, and PP breeds, respectively. All PP animals were genotyped for the halothane mutation. This data set was used to calculate RFI equations for each of the 4 breeds, and to estimate genetic parameters for RFI together with growth, carcass, and meat quality traits, and N and P excretion during the test period (35 to 110 kg BW). The RFI explained 20.1% in PP, 26.5% in LWS, 27.6% in LWD, and 29.5% in LR of the phenotypic variability of ADFI. The PP breed differed from the others in this respect, probably due to a lower impact of the variation of body composition on ADFI. Heritability estimates of RFI ranged from 0.21 ± 0.03 (LWD) to 0.33 ± 0.06 (PP) depending on the breed. Heritabilities of N and P excretion traits ranged from 0.29 ± 0.06 to 0.40 ± 0.06. The RFI showed positive genetic correlations with feed conversion ratio (FCR) and excretion traits, these correlations being greater in the sire breeds (from 0.57 to 0.86) than in the dam breeds (from 0.38 to 0.53). Compared with FCR, RFI had weaker genetic correlations with carcass composition, growth rate, and excretion traits. Estimates of genetic correlations between FCR and excretion traits were very close to 1 for all breeds. Finally, excretion traits were, at the genetic level, correlated positively with ADFI, negatively with growth rate and carcass leanness, whereas the halothane n mutation in PP was shown to reduce N and P excretion levels. To conclude, new selection indexes including RFI can be envisaged to efficiently disentangle the responses to selection on growth rate and body composition from those on feed efficiency, with favorable impacts on N and P excretions, particularly in sire pig breeds. However, the switch from FCR to RFI in selection indexes should not resolve the genetic antagonism between feed efficiency and meat quality.

Modelling the variation in performance of a population of growing pig as affected by lysine supply and feeding strategy.

Considerable progress has been made in the nutritional modelling of growth. Most models typically predict (or analyse) the response of a single animal. However, the response to nutrients of a single, representative animal is likely to be different from the response of the herd. To address the variation in response between animals, a stochastic approach towards nutritional modelling is required. In the present study, an analysis method is presented to describe growth and feed intake curves of individual pigs within a population of 192 pigs. This method was developed to allow end-users of InraPorc (a nutritional model predicting and analysing growth in pigs) to easily characterise their animals based on observed data and then use the model to test different scenarios. First, growth and intake data were curve-fitted to characterise individual pigs in terms of BW (Gompertz function of age) and feed intake (power function of BW) by a set of five parameters, having a biological or technico-economical meaning. This information was then used to create a population of virtual pigs in InraPorc, having the same feed intake and growth characteristics as those observed in the population. After determination of the mean lysine (Lys) requirement curve of the population, simulations were carried out for each virtual pig using different feeding strategies (i.e. 1, 2, 3 or 10 diets) and Lys supply (ranging from 70% to 130% of the mean requirement of the population). Because of the phenotypic variation between pigs and the common feeding strategies that were applied to the population, the Lys requirement of each individual pig was not always met. The percentage of pigs for which the Lys requirement was met increased concomitantly with increasing Lys supply, but decreased with increasing number of diets used. Simulated daily gain increased and feed conversion ratio decreased with increasing Lys supply (P < 0.001) according to a curvilinear-plateau relationship. Simulated performance was close to maximum when the Lys supply was 110% of the mean population requirement and did not depend on the number of diets used. At this level of Lys supply, the coefficient of variation of simulated daily gain was minimal and close to 10%, which appears to be a phenotypic characteristic of this population. At lower Lys supplies, simulated performance decreased and variability of daily gain increased with an increasing number of diets (P < 0.001). Knowledge of nutrient requirements becomes more critical when a greater number of diets are used. This study shows the limitations of using a deterministic model to estimate the nutrient requirements of a population of pigs. A stochastic approach can be used provided that relationships between the most relevant model parameters are known.

The standardized ileal digestible valine-to-lysine requirement ratio is at least seventy percent in postweaned piglets.

To reduce the impact of animal production on the environment, the CP content of the diet can be reduced by limiting the excess supply of AA. Improving the balance between AA relative to the requirement of the animal implies that we need to have accurate knowledge of the requirement of individual AA. The purpose of this study was to determine the Val requirement in postweaned piglets (12 to 25 kg) because Val is considered to be potentially limiting to performance after Lys, Met (and Cys), Thr, and Trp. The first experiment was carried out to identify a diet limiting in Lys supply. In this experiment, piglets were offered 1 of 3 diets: a low-CP diet containing low or adequate Lys concentrations [providing 1.0 and 1.2% standardized ileal digestible (SID) Lys, respectively] or a normal-CP diet with 1.2% SID Lys. Average daily gain of piglets receiving the diet containing 1.0% SID Lys was significantly less than that of piglets receiving diets containing 1.2% SID Lys at low or normal CP (486 vs. 522 g/d, respectively; P < 0.01). In Exp. 2, four diets with 1.0% SID Lys were used in a 2 x 2 factorial design, in which diets contained 57 or 70% SID Val:Lys in combination with 50 or 60% SID Ile:Lys. Independent of the Ile supply, feed intake and daily BW gain were, respectively, 15 and 20% less in piglets receiving diets providing 57% SID Val:Lys compared with piglets receiving 70% SID Val:Lys (P < 0.001). The Ile content of the diet did not affect feed intake or daily BW gain (P > 0.10). Experiment 3 was conducted to evaluate the response of piglets to an increasing Val supply provided by 2 sources of l-Val differing in the degree of purity. Increasing the Val supply from 58 to 66% SID Val:Lys resulted in a linear increase in both feed intake and daily gain by 24 and 30%, respectively (P < 0.001). No difference was observed between both sources of l-Val (P > 0.10). Experiment 4 was a dose-response study using 5 concentrations of Val supply (ranging from 60 to 80% SID Val:Lys). The estimated SID Val:Lys requirements for maximizing ADFI, ADG, and G:F were, respectively, 74, 70, and 68% using a linear-plateau model, and 81, 75, and 72% using a curvilinear-plateau model. Plasma Val, plasma alpha-ketoisovaleric acid, Ile, and Leu concentrations after an overnight fast increased with increasing Val supply (P < 0.001). The results of these experiments indicated that the SID Val:Lys was at least 70%, which was slightly greater than the current NRC recommendation.

Quantitative assessment of the effects of space allowance, group size and floor characteristics on the lying behaviour of growing-finishing pigs.

To obtain quantitative information that can be later used in animal welfare modelling, the relationship between the lying behaviour of growing-finishing pigs (initial body weight (BW) between 19 and 87 kg) and different factors related to the housing conditions, with a potential negative effect on their welfare, was studied by means of a meta-analytical approach. Data from 22 experiments reported in 21 scientific publications were collected. The space allowance, expressed on an allometric basis by means of a k-value (m2/BW0.667), the group size (n) and the floor characteristics (fully and partly slatted v. non-slatted floor), as well as their significant two-way interactions were used as fixed effects, and the experiment was used as a random factor to take into account the interexperiment effect. Further regression analyses were performed on the predicted values of observations in order to improve the adjustment of data. A significant quadratic relationship was established between space allowance (k-value, P < 0.05; squared k-value, P < 0.01) and the percentage of time spent lying. A significant interaction between the k-value and the floor type was also found (P < 0.05), showing that the relationship between space allowance and lying behaviour is affected by the presence or absence of slats. Threshold k-values were obtained using broken-line analyses, being about 0.039 for slatted floors and almost double for non-slatted floors. Compared to other studies, these values suggest that the ability to rest as space availability decreases may be compromised before a reduced performance becomes apparent. Group size did not show a significant effect. Additional information should be added to the model, as further data become available, to adjust the proposed parameters as well as to try to include the effect of other important aspects such as that of ambient temperature.

The effect of immunization against GnRF on nutrient requirements of male pigs: a review

In most countries, male pigs are physically castrated soon after birth to reduce the risk of boar taint and to avoid behaviours such as fighting and mounting. However, entire male pigs are more feed efficient and deposit less fat than barrows. In addition, many animal welfare organizations are lobbying for a cessation of castration, with a likelihood that this could lead to inferior pork unless an alternative method is used to control boar taint. An alternative to physical castration is immunization against gonadotrophin releasing factor (GnRF) which allows producers to capitalize on the superior feed efficiency and carcass characteristics of boars without the risk of boar taint. From a physiological perspective, immunized pigs are entire males until shortly after the second dose, typically given 4 to 6 weeks before slaughter. Following full immunization, there is a temporary suppression of testicular function and a hormonal status that resembles that of a barrow. Nutrient requirements will be different in these two phases, before and after full immunization. Given that there have been few published studies comparing the lysine requirements of entire males and barrows in contemporary genotypes, it is useful to use gilt requirements as a benchmark. A series of meta-analyses comparing anti-GnRF immunized boars and physical castrates and use of nutritional models suggest that the lysine requirement of entire males before the second immunization is 5% higher than for gilts, from 25 to 50 kg BW, and by 8% from 50 to 95 kg. Given that the penalty in growth performance for having inadequate dietary lysine is greater in males than in gilts or barrows, it is important to ensure that lysine requirements are met to obtain the maximum benefits of entire male production during this phase. After the second immunization, the lysine requirement of immunized males decreases and may become more like that of barrows. In addition, a consistent effect of full immunization is a marked increase in voluntary feed intake from about 10 days after the second dose. Putting these together, the estimated lysine requirement, expressed in terms of diet composition, falls to 94% of the gilt level. Although general principles can be described now, further research is needed to fully define the lysine requirements of immunized boars. It is important that the temporal pattern of tissue deposition rates and feed intake be explored to be incorporated into models to predict nutrient requirements over the period of rapidly changing metabolism.

Response of piglets to the valine content in diet in combination with the supply of other branched-chain amino acids

The branched-chain amino acids (BCAA) valine (Val) and isoleucine (Ile) are considered to be among the next-limiting amino acids for growth in piglets. In earlier studies, we estimated the standardized ileal digestible (SID) Val : Lys (lysine) requirement to be at least 70%, whereas the Ile : Lys requirement may be as low as 50%. Because the BCAA partially share a common route of catabolism, the supply of one BCAA may affect the availability of the other BCAA. Four experiments were conducted to determine the response of 6-week-old piglets to the Val supply in relation to the other BCAA. A deficient supply of Val or Ile typically results in a reduction in average daily feed intake (ADFI). Experiment 1 was designed to determine the effect of a limiting Val supply, independent of the effect on feed intake. In a dose-response study using restrictively fed piglets, nitrogen retention did not increase for an SID Val : Lys supply greater than 64%. In the remaining experiments, piglets were offered feed ad libitum using ADFI, average daily gain (ADG) and gain-to-feed ratio as response criteria. The interaction between the Val and leucine (Leu) was studied in Experiment 2 in a 2 × 2 factorial design (60% and 70% SID Val : Lys, and 111% and 165% SID Leu : Lys). Performance was considerably lower in piglets receiving 60% Val : Lys compared with those receiving 70% Val : Lys and was lowest in piglets receiving the diet with low Val and high Leu content. To further evaluate the interaction between Val and Leu, a dose-response study was carried out in which the response to Val supply was studied in combination with high Leu supply (165% Leu : Lys). Using a curvilinear-plateau model, the average SID Val : Lys requirement was 72%. However, low Val supply (60% SID Val : Lys) reduced performance by 13% to 38%, which was much greater than what we observed in earlier studies. Experiment 4 was carried out to test the hypothesis that the Val requirement is not affected by low Ile supply (50% SID Ile : Lys). Performance was not improved for Val : Lys supplies greater than 65%, which may indicate that Ile (and not Lys) was second-limiting in this study. In conclusion, the first response of piglets to deficient Val supply appears to be a reduction in ADFI, rather than a reduction in ADG or nitrogen retention. A large supply of Leu may not affect the Val requirement per se, but may aggravate the consequences of Val deficiency.

The standardized ileal digestible isoleucine-to-lysine requirement ratio may be less than fifty percent in eleven- to twenty-three-kilogram piglets.

Most studies concerning the Ile requirement in pigs have been carried out using blood products as a protein source, and these have a relatively low Ile content relative to the other branched-chain AA (BCAA). There are indications that an excess supply of one BCAA can affect the utilization of the other BCAA. Little information is available concerning the Ile requirement in pigs when the supply of the other BCAA is moderate (e.g., in cereal- and soybean meal-based diets). The objective of the present study was to evaluate the response of piglets to Ile supplementation under different nutritional conditions. In all experiments, piglets were housed individually and had ad libitum access to feed during a 3-wk period. The first experiment was carried out to study the response of piglets to an increasing Ile supply by using 2 sources of l-Ile differing in degree of purity. Piglets received either a control diet with 48% standardized ileal digestible (SID) Ile:Lys or 1 of 4 other diets containing graded levels of either source of l-Ile to provide 52 or 56% SID Ile:Lys. All diets were formulated to provide 1.00% SID Lys in the diet. Feed intake and growth were not affected by Ile level or Ile source. Experiment 2 was performed to exclude a possible interaction between Ile and Lys supply. In a 2 x 2 factorial arrangement, 2 levels of Lys (1.00 and 1.15% SID Lys) and 2 levels of Ile (48 and 60% SID Ile:Lys) were used. Growth and G:F were 8 and 7% greater in piglets receiving the diet with the greater Lys content, but the Ile:Lys did not affect performance. No interactions were observed between the Lys and Ile supplies. In Exp. 3, a 2 x 2 factorial arrangement was used to test the effect of protein source (spray-dried blood cells or corn gluten meal) and Ile supply (50 or 65% SID Ile:Lys) on performance in piglets. Both protein sources had an elevated BCAA content but differed in Leu and Val contents. Protein source or Ile supply did not affect feed intake, growth, or G:F in the piglets. Plasma concentrations after an overnight fast reflected the difference in AA concentrations of the diets. In conclusion, the results of these experiments indicate that the SID Ile:Lys requirement may be not greater than 50% in piglets receiving cereal- and soybean meal-based diets with a moderate BCAA content. In contrast to other studies, we could not confirm that the Ile requirement was affected by BCAA content of the diet.

Review: divergent selection for residual feed intake in the growing pig.

This review summarizes the results from the INRA (Institut National de la Recherche Agronomique) divergent selection experiment on residual feed intake (RFI) in growing Large White pigs during nine generations of selection. It discusses the remaining challenges and perspectives for the improvement of feed efficiency in growing pigs. The impacts on growing pigs raised under standard conditions and in alternative situations such as heat stress, inflammatory challenges or lactation have been studied. After nine generations of selection, the divergent selection for RFI led to highly significant (P<0.001) line differences for RFI (−165 g/day in the low RFI (LRFI) line compared with high RFI line) and daily feed intake (−270 g/day). Low responses were observed on growth rate (−12.8 g/day, P<0.05) and body composition (+0.9 mm backfat thickness, P=0.57; −2.64% lean meat content, P<0.001) with a marked response on feed conversion ratio (−0.32 kg feed/kg gain, P<0.001). Reduced ultimate pH and increased lightness of the meat (P<0.001) were observed in LRFI pigs with minor impact on the sensory quality of the meat. These changes in meat quality were associated with changes of the muscular energy metabolism. Reduced maintenance energy requirements (−10% after five generations of selection) and activity (−21% of time standing after six generations of selection) of LRFI pigs greatly contributed to the gain in energy efficiency. However, the impact of selection for RFI on the protein metabolism of the pig remains unclear. Digestibility of energy and nutrients was not affected by selection, neither for pigs fed conventional diets nor for pigs fed high-fibre diets. A significant improvement of digestive efficiency could likely be achieved by selecting pigs on fibre diets. No convincing genetic or blood biomarker has been identified for explaining the differences in RFI, suggesting that pigs have various ways to achieve an efficient use of feed. No deleterious impact of the selection on the sow reproduction performance was observed. The resource allocation theory states that low RFI may reduce the ability to cope with stressors, via the reduction of a buffer compartment dedicated to responses to stress. None of the experiments focussed on the response of pigs to stress or challenges could confirm this theory. Understanding the relationships between RFI and responses to stress and energy demanding processes, as such immunity and lactation, remains a major challenge for a better understanding of the underlying biological mechanisms of the trait and to reconcile the experimental results with the resource allocation theory.

Meta-analysis of the response of growing pigs to the isoleucine concentration in the diet

The efficiency of nitrogen utilization will be highest when the amino acid (AA) supply approaches the requirement of the animal. With the availability of different crystalline AA, it is theoretically possible to formulate low-protein diets for growing pigs in which seven AA are co-limiting for performance. In such a diet, the concentration of Lys, Met, Met + Cys, Thr, Trp and Val and a seventh AA would exactly match the requirement. To determine the extent to which low-protein diets can be used, it is important to have reliable information about the requirements for these AA. Isoleucine is often considered the seventh-limiting AA in diets for growing pigs; however, information about the Ile requirement is limited and sometimes conflicting. The purpose of this study was to carry out a meta-analysis of the available literature information to determine the Ile requirement in growing pigs. A total of 46 Ile dose-response experiments were identified that used at least four concentrations of Ile in the diet. Because of differences in experimental design, both the Ile concentration and the response criteria were standardized. In 13 dose-response experiments, there was no indication of a response to an increasing Ile concentration. For the other 33 experiments, a response to the increasing Ile concentration was observed and the Ile requirement estimates ranged from 53% to 114% of that of the National Research Council (1998). An Ile concentration below the requirement resulted in important reductions in both feed intake and growth. A 10% reduction in the Ile concentration (below the requirement) resulted in a 15% reduction in feed intake and a 21% reduction in daily gain. The use of blood products in the diet was the main factor determining whether a response to the Ile concentration was observed or not. Blood meal and blood cells are protein sources with a very low Ile concentration, but with high or very high concentrations of Leu, Val, Phe and His. Some of these AA compete with Ile for catabolic pathways or transport across the blood-brain barrier, thereby potentially increasing the requirement for Ile. In diets without blood products, the Ile requirement appears to be lower than the currently recommended requirement. On the basis of the outcome of this study, we recommend a Ile : Lys requirement ratio of at least 50% on a standardized ileal digestible basis.