Immunocastrated male pigs: effect of 4 v. 6 weeks time post second injection on performance,carcass quality and meat quality

Immunocastration or vaccination against boar taint can be used as alternative for surgical castration of male piglets. The vaccine is administrated twice. After the second vaccination (V2), the pigs behave like barrows instead of boars and their feed intake increases which may result in a lower lean meat percentage. The timing of V2 is therefore crucial to find the right balance between the advantages of entire males and barrows. In this study, we evaluated the effect of time post second injection within the advised time frame (4 v. 6 weeks before slaughter) on behaviour, performance, carcass and meat quality of immunocastrated male pigs. In total, 180 animals (hybrid sow×Piétrain): 60 gilts, 60 male pigs vaccinated 6 weeks before slaughter (IM-6) and 60 male pigs vaccinated 4 weeks before slaughter (IM-4), all slaughtered at comparable slaughter weights. After 20 weeks of age, IM-6 showed more inactive behaviour at the expense of playing and aggressive behaviour. Daily feed intake (DFI), daily gain (DG) and feed conversion ratio (FCR) did not differ significantly between IM-6 and IM-4. Gilts had a lower DFI and DG in the late finishing phase and a higher FCR overall compared with both IM groups. Gilts showed a higher lean meat content compared with both IM groups. Earlier vaccination increased dressing percentage, which could partly be explained by the lower weight of the gastrointestinal tract, but not by testes weight. Meat quality traits and palatability did not differ significantly between IM-6 and IM-4. Vaccination of immunocastrates at 6 compared with 4 weeks before slaughter improved the calmness in the stable and the dressing percentage, while maintaining performance and carcass characteristics.     

Growth performance, carcass characteristics and meat quality of group-penned surgically castrated, immunocastrated (Improvac®) and entire male pigs and individually penned entire male pigs

The objective of the study was to compare growth performance, carcass characteristics, meat quality and fatty acid composition of the adipose tissue of group-penned barrows, immunocastrated boars and entire males. Furthermore, the effect of housing of entire males on the aforementioned parameters was evaluated. At 55.2 days of age, 52 Swiss Large White pigs were blocked by litter and assigned by BW to four experimental groups: barrows (C), immunocastrated boars (IC), entire males (EMG) reared in group pens and entire males (EMP) reared in individual pens. In experiment 1, the effects of the method of castration were investigated (experimental groups C, IC and EMG). In experiment 2, the effects of housing on entire male pigs were evaluated (experimental groups EMG and EMP). All pigs had ad libitum access to standard diets from weaning to 107 kg BW. The two vaccinations (Improvac®) were applied to the IC pigs at an average BW of 22.6 and 73.0 kg. In experiment 1, average daily gain (ADG) did not (P > 0.05) differ among the experimental groups. However, EMG consumed less feed and had a better feed-conversion ratio than C (P < 0.001 for each). For IC, intermediate values were observed, which differed (P < 0.001) from EMG and C. Lean meat percentage decreased (P < 0.05) from EMG to IC, and from IC to C. The androstenone and skatole levels were higher (P < 0.05) in the adipose tissue of EMG than IC and C. Shear force values were higher (P < 0.01) in the longissimus muscle of C and EMG, compared to IC. The concentration of saturated fatty acid in the adipose tissue increased (P < 0.001) from EMG to IC, and from IC to C pigs, and that of polyunsaturated fatty acid decreased (P < 0.001). In experiment 2, ADG did not (P > 0.05) differ between EMP and EMG. However, EMP pigs consumed more feed than EMG pigs and had a poorer feed efficiency (P < 0.01 for each). In conclusion, EMG pigs had a better feed efficiency than IC pigs and their carcasses were leaner, but the risk of boar tainted pork was elevated. Group-housing negatively affected average daily feed intake but not ADG of entire males. At the moment, immunocastration offers a good approach to avoid castration and minimize the risk of boar taint.     

Lysine requirements of finishing boars and gilts: A meta-analysis

The expected increase in boar (pig entire male) production while societal concerns for castration increase requires good estimations of their nutrient requirements. In this work, a meta-analytical approach was used to overcome the inconsistent results between studies that compared lysine requirements of boars and gilts. For this meta-analysis, data from 14 different studies analysing the effect of increasing dietary lysine on growth performance of finishing pigs, 70–100 kg average body weight, were extracted from 11 publications. Those studies represented 128 different treatments (53 for boars and 75 for gilts). Diets were reformulated based on NRC (2012) ingredient values to calculate standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and daily SID Lys intake using average daily feed intake (ADFI). As expected, no evidence for differences in ADFI (P = 0.303) was observed between boars and gilts. However, boars grew faster (P < 0.001) and had higher gain to feed (G:F; P < 0.001). The divergent effect of SID Lys:NE on average daily gain (ADG) and G:F was analysed in a quadratic polynomial model showing different parameters for each sex (P < 0.001). Although performance between sexes was similar at low SID Lys:NE, differences were greater at higher SID Lys:NE. Furthermore, broken-line linear, broken-line quadratic (BLQ) and quadratic polynomial (QP) models were fitted to each sex to determine SID Lys:NE and SID Lys daily intake requirements to maximize ADG and G:F. Overall, QP models showed the best fit, and reported that to reach maximum ADG 0.88 (95% CI:[0.82–0.94]) or 1.01 (95% CI:[0.91–1.11]) g SID Lys/MJ, NE was required for gilts and boars, respectively. However, boar ADG was best fitted by BLQ using SID Lys daily intake as independent variable, with the requirement for maximum ADG at 24.2 (95% CI:[21.3–27.2]) g SID Lys/day. The three models reported wide confidence intervals for the requirements at maximum performance, and consequently those were overlapped when comparing boars and gilts. Maximum boars’ productive performance when dietary lysine was not limiting was 116% of gilts, and at those levels the amount of SID Lys intake required per kg gain was similar between both sexes. Thus, because ADFI and Lys efficiency of gain was similar, the requirement differences were driven by the increased growth rate and gain to feed ratio between boars and gilts. In conclusion, the present study confirmed a greater productive response of boars compared to gilts when increasing dietary lysine.     

The effect of the MC4R gene on boar taint compounds,sexual maturity and behaviour in growing-finishing boars and gilts

Societal pressure to ban surgical castration of male piglets is rising due to animal welfare concerns, thus other methods to prevent boar taint need to be explored. Genetic selection against boar taint appears to be a long-term sustainable alternative. However, as boar taint is linked to reproductive hormones, it is important to consider possible negative side effects such as delayed sexual maturity or changes in behaviour. We reported earlier that the melanocortin-4 receptor (MC4R) marker can be used to reduce boar taint levels in fat of boars. The objective of this study was to evaluate whether MC4R marker-assisted selection for lower boar taint prevalence affects plasma levels of boar taint compounds and testosterone; sexual maturity; behaviour; skin lesions; and lameness in boars and gilts. Using an intervention study with a 2×2 design, 264 boars and gilts differing on position 893 of the MC4R gene (AA v. GG) were compared. The MC4R polymorphism did not affect the plasma concentration of either androstenone or testosterone at different time points, whereas the concentration of skatole was significantly lower (P=0.003) and the concentration of indole tended to be lower (P=0.074) in GG compared with AA boars. A higher percentage of gilts of the GG genotype were in puberty at slaughter age compared with AA gilts (P<0.001). The age of the boars at sexual maturity (as indicated by the first positive preputial smear test) did not differ between AA and GG boars. In contrast, weight of GG boars at sexual maturity tended to be lower (P=0.065). During the period from 6 weeks of age to slaughter, boars and gilts of the GG genotype showed more playing behaviour (P=0.015) and less passive and feeding behaviour (P=0.003). They showed more skin lesions on their back and caudal area (P=0.022), and tended to show more skin lesions on their head and anterior area (P=0.093) compared with AA animals. In conclusion, the polymorphism in the MC4R gene can be used as a marker without negative effects on reproduction characteristics in boars and gilts. Genetic selection towards a lower prevalence of boar taint will lead to more active pigs with more skin lesions. Management strategies may therefore be necessary to reduce skin lesions in the selected animals.     

Effect of dietary energy level in finishing phase on performance,carcass and meat quality in immunocastrates and barrows in comparison with gilts and entire male pigs

Immunocastration, a technique consisting of two vaccinations against gonadotropin-releasing hormone (GnRH), can be used as alternative to surgical castration of piglets. It reduces boar taint and allows higher economic and ecological efficiency compared to barrows. The feeding strategy of immunocastrates, however, can still be improved. After second vaccination, when immunisation becomes fully effective, feed intake of immunocastrates increases sharply. This study aimed to investigate whether energy intake of immunocastrates after second vaccination could be reduced by lowering the dietary energy level of the finishing phase, without negatively affecting animal performance and quality of pork production. We hypothesised that immunocastrates already reach their limits in voluntary feed intake after second vaccination, and therefore would not be able to compensate the lower dietary energy level, in contrast to barrows. Therefore, this study aimed to assess the effect of high-energy diet (HE, net energy (NE) = 10.2 MJ/kg) compared to low-energy diet (LE, NE = 8.8 MJ/kg) in barrows and immunocastrates and as a reference, gilts and entire male pigs on a standard high-energy diet were included. CP and standardised ileal digestible amino acid levels were similar in both diets. For each treatment, eight pen replicates of six pigs per pen were evaluated on performance, carcass quality, meat and fat quality, digestibility, economic and ecological sustainability, behaviour and effectiveness of immune response. No difference in feed intake of immunocastrates between LE and HE could be demonstrated. As a result, daily energy intake of immunocastrates was higher on HE compared to LE, which resulted in a higher daily gain on HE. Feed conversion ratio (FCR) of immunocastrates on HE did not differ significantly with FCR of entire males. Barrows did not show higher average daily gain on HE compared to LE. Nitrogen efficiency was better in HE compared to LE, without negative effects on digestibility, carcass quality, economic parameters, behaviour or immune response. Small positive effects on the palatability of the meat of immunocastrates on HE were observed, although consumers did not prefer one of both feeds. Immunocastration was successful in reducing sexual and aggressive behaviour as well as in lowering the prevalence of boar taint from 15% in EM to 0% in immunocastrates. However, in two out of 96 immunocastrates (one on HE and one on LE), the immunocastration was not fully effective. In conclusion, this study did not show advantages of feeding immunocastrates or barrows a low-energy diet.     

Reproductive status effects of pair-housed male pigs on natural,agonistic and sexual behaviours

Boar rearing, which avoids pain and suffering caused by surgical castration, provides better performance, a greater deposition of muscle tissue and leaner carcasses and thus has beneficial effects on both animal welfare and the product. Some countries that do not slaughter boars must consider their boar taint and aggressive and sexual behaviours. Considering that pigs are housed in large groups, which may complicate the formation of social hierarchies and increase fighting and mounting behaviours, some studies have conducted research with reduced numbers of pigs per pen, but these behaviours continued to be observed. However, a study of the reproductive status of pair-housed male pigs has yet to be reported. The aim of this study was to determine whether the reproductive status of uncastrated, immunocastrated and surgically castrated pair-housed male pigs alters their natural, agonistic and sexual behaviours. A total of 48 male pigs from Agroceres PIC™ genetics were assigned to three groups: surgically castrated (barrows), immunocastrated and uncastrated (boars). Natural, aggressive and sexual behaviours of the pigs were assessed by direct observations during four periods of 12 h each (six, five and three weeks before slaughter and the slaughter week). The pigs were housed in pairs from the growing phase until slaughter. Animal behaviour was observed from the finishing phase to slaughter. Carcass lesions were assessed according to five different classes (one: no injury; two to five: severely injured). Overall, boars spent more time lying and less time eating and drinking than barrows. In total of all the periods (48 h), boars expressed more aggressive and sexual behaviours than barrows, whereas immunocastrated pigs displayed similar behaviours to boars, before and after the second vaccine dose. No differences in carcass lesions between treatments and no prevalence of carcasses with severe injuries were observed. In conclusion, the reproductive status of pair-housed male pigs did not change the natural behaviour of boars, immunocastrated pigs or barrows. The agonistic and sexual behaviours of boars and barrows remained unchanged. When housing pigs in pairs, immunocastrated pigs presented similar agonistic and sexual behaviours to boars before and after the second immunocastration vaccine dose. The use of pair-housed uncastrated male pigs has generated welfare benefits for these animals, as the number of carcasses with injuries did not differ from barrows and immunocastrated pigs.     

Considerations on the performance of immunocastrated male pigs

With the ongoing social pressure on surgical castration of pigs, an increase in the population of pigs that are either not castrated or immunocastrated (IC) can be expected. In both cases, their nutrient requirements and performance will differ from surgically castrated pigs and will require changes in their management. Immunocastration is performed by giving two injections of a modified gonadotrophin-releasing hormone component along with an adjuvant, at least 4 weeks apart. This paper describes the reported differences in growth performance and carcass quality of IC male pigs in comparison with boars (BO) and barrows (BA). Theoretically, IC pigs remain physiologically boar until the second vaccination and therefore, growth may be comparable with BO until this second vaccination. From then on, IC male pigs consume more feed than BO and grow faster when fed ad libitum. IC showed a faster growth and better feed conversion ratio than BA. When fed restrictedly, BO grow faster and more efficiently than BA and IC. IC have a lower carcass yield than BA and BO, whereas meat percentage is intermediate.     

Resource efficiency and economic implications of alternatives to surgical castration without anaesthesia

This paper presents an analysis of the economic implications of alternative methods to surgical castration without anaesthesia. Detailed research results on the economic implications of four different alternatives are reported: castration with local anaesthesia, castration with general anaesthesia, immunocastration and raising entire males. The first three alternatives have been assessed for their impact on pig production costs in the most important pig-producing Member States of the EU. The findings on castration with anaesthesia show that cost differences among farms increase if the anaesthesia cannot be administered by farmers and when the veterinarian has to be called to perform it. The cost of veterinarian service largely affects the total average costs, making this solution economically less feasible in small-scale pig farms. In all other farms, the impact on production costs of local anaesthesia is however limited and does not exceed 1 €ct per kg. General anaesthesia administered by inhalation or injection of Ketamin in combination with a sedative (Azaperone, Midazolan) is more expensive. These costs depend heavily on farm size, as the inhalation equipment has to be depreciated on the largest number of pigs possible. The overall costs of immunocastration - including the cost of the work load for the farmer - has to be evaluated against the potential benefits derived from higher daily weight gain and feed efficiency in comparison with surgical castrates. The economic feasibility of this practice will finally depend on the price of the vaccine and on consumer acceptance of immunocastration. The improvement in feed efficiency may compensate almost entirely for the cost of vaccination. The main advantages linked to raising entire males are due to the higher efficiency of feed conversion, to the better growth rate and to the higher leanness of carcass. A higher risk of boar taint on the slaughter line has to be accounted for. Raising entire males should not generate more than 2.5% of boar taint among slaughter pigs, in order to maintain the considerable economic benefits of better feed efficiency of entire males with respect to castrates.     

Olfactory evaluation of boar taint: effect of factors measured at slaughter and link with boar taint compounds

There is a commitment by the European pig sector to ban surgical castration of male piglets in the European Union in 2018. One alternative to castration is to raise entire male pigs, with an increased risk of boar taint. A field study was performed to: (1) evaluate inter- and intra-farm variation in boar taint prevalence, (2) investigate factors measured at slaughter influencing boar taint and (3) evaluate the relationship between sensorial scoring by a trained panel and the concentration of boar taint components. From 34 farms, neck fat samples were collected from all entire male pigs in at least two slaughter batches per farm (78 batches; 9167 animals). In addition to olfactory boar taint analysis, data were also collected on fresh skin lesions (score 0 to 3) at the slaughter line, slaughter weight, lean meat percentage, duration of transport, time spent in lairage, total delivery duration, day length, shortening of days and outdoor mean temperature. Using the hot iron method, neck fat samples were scored (eight-point scale) for boar taint. Average boar taint prevalence (score ≥3) was 5.6±2.5% and the mean difference between the maximum and minimum prevalence per farm was 4.3±3.2%. Androstenone (AND), skatole (SKA) and indole concentrations were measured for a subset (n=254) of the samples. According to binomial univariate mixed models, entire male pigs with a higher skin lesion score had higher odds of having boar taint (P=0.031), as did fatter entire male pigs (P<0.001). In the binomial multivariate mixed model lean meat percentage (P<0.001) and outdoor mean temperature (P=0.005) remained as only significant factors. Based on our results, we can conclude that these statistically significant at least partially influence the prevalence of boar taint. According to the binomial univariate mixed models SKA concentration in liquid fat seems a better predictor for boar taint than AND. There were no significant synergetic effects between boar taint compounds.     

Biochemical, nutritional and genetic effects on boar taint in entire male pigs

Pork odour is to a great extent affected by the presence of malodorous compounds, mainly androstenone and skatole. The present review outlines the current state of knowledge about factors involved in the regulation of androstenone and skatole in entire male pigs. Androstenone is a pheromonal steroid synthesised in the testes and metabolised in the liver. Part of androstenone accumulates in adipose tissue causing a urine-like odour. Skatole is produced in the large intestine by bacterial degradation of tryptophan and metabolised by hepatic cytochrome P450 enzymes and sulphotransferase. The un-metabolised part accumulates in adipose tissue, causing faecal-like odour. Androstenone levels are mostly determined by genetic factors and stage of puberty, whereas skatole levels in addition to genetic background and hormonal status of the pigs are also controlled by nutritional and environmental factors. To reduce the risk of tainted carcasses entering the market, male pigs are surgically castrated in many countries. However, entire males compared to castrates have superior production characteristics: higher growth rate, better feed efficiency and leaner carcasses. Additionally, animal welfare aspects are currently of particular importance in light of increasing consumers' concerns. Nutrition, hormonal status, genetic influence on boar taint compounds and the methods to develop genetic markers are discussed. Boar taint due to high levels of skatole and androstenone is moderately heritable and not all market weight entire males have boar taint; it should thus be possible to select for pigs that do not have boar taint. In these studies, it is critical to assess the steroidogenic potential of the pigs in order to separate late-maturing pigs from those with a low genetic potential for boar taint. A number of candidate genes for boar taint have been identified and work is continuing to develop genetic markers for low boar taint. More research is needed to clarify the factors involved in the development of boar taint and to develop additional methods to prevent the accumulation of high concentrations of skatole and androstenone in fat. This review proposes those areas requiring further research.     

Field experience with surgical castration with anaesthesia,analgesia, immunocastration and production of entire male pigs: performance,carcass traits and boar taint prevalence

Male piglets are castrated to reduce boar taint and also to reduce aggressive and sexual behaviour. However, the procedure as traditionally performed is painful and negatively affects performance. Large-scale results about the consequences of implementing alternatives on farms are lacking. We, therefore, investigated the practical applicability of the following five alternatives that can be implemented in the short term: surgical castration (1) without pain relief (CONT, control group), (2) with analgesia (MET, Metacam, 0.2 ml, 10 to 15 min before castration), (3) with general anaesthesia (CO₂, inhalation, 100% CO₂, 25 s, 3 l/min), (4) vaccination against boar taint (IM, two injections with Improvac) and (5) production of entire males (EM). The study consisted of the following two trials: (1) an experimental farm trial with 18 animals/treatment and (2) a large field trial on 20 farms with ~120 male pigs/farm per treatment and all treatments performed on each farm. Performance results as well as data on carcass traits, boar taint (hot-iron method) and testes development and weight were collected in both trials. Neither castration nor administration of analgesia or anaesthesia had an effect on daily gain of the piglets in the farrowing crates (P>0.05). Farmer records indicated that mortality in the farrowing crates (1.1%), nursery pens (1.8%) and fattening stable (2.2%) was not influenced by MET or CO₂ compared with EM, IM or CONT (P>0.05). No significant differences were found for daily gain (P>0.05) nor slaughter age (P>0.05). Immunocastrates and EM had a better gain-to-feed ratio (P<0.05) compared with the groups of barrows (CONT, MET and CO₂). Lean meat percentage was higher for EM compared with the barrows, and intermediate for IM (P<0.05). Carcass yield was lowest for IM (P<0.05). The hot-iron method indicated that boar taint was eliminated in barrows and IM compared with EM (P<0.001). Average prevalence of strong boar taint was 3% for EM, but varied from 0% to 14% between farms. As the effect of treatment on performance as well as the level of boar taint of EM was farm dependent, farmers should be encouraged to pre-test the different alternatives in order to make a well-considered choice for the best practical and profitable alternative for their farm.     

Potential sensitivity of pork production situations aiming at high-quality products to the use of entire male pigs as an alternative to surgical castrates

The perspective of a possible ban on surgical castration of male pigs in the EU is a real challenge for pork production systems aiming at (very) high-quality products. Information was collected from a total of 272 situations in 16 European countries, including 170 situations related to EU protected designations (Database of Origin & Registration (DOOR) database) and 102 other situations related to high-quality products or differentiated production systems, in order to evaluate their potential sensitivity to the use of entire male pigs along four dimensions: BT_Inc, likelihood of increased levels of boar taint compounds compared with conventional production of entire males; BT_Per, extent to which (some of) the associated pork product(s) are susceptible to perception of boar taint by consumers; FatQQ, likelihood that the quality of (some of) the related products is decreased due to the lower fat quantity and quality in entire males; Manag, increased likelihood of animal management and welfare problems compared with conventional production of entire males. Situations corresponding to EU protected designations (DOOR situations) were on average more sensitive to entire male production but 11% of the non-DOOR situations were highly potentially sensitive, whereas one-third of the DOOR situations had low potential sensitivity. In total, 37% of the situations where castration is not formally specified as mandatory exhibited high potential sensitivity to entire male production. Three main patterns of situations were identified via ascending hierarchical clustering. A first pattern including 31% of the DOOR situations and 74% of the other ones, had potentially no increased risk compared with conventional production of entire males. A second pattern including 28% of the DOOR situations and 16% of the other ones had a high, moderate and low potential sensitivity for FatQQ, BT_Inc and Manag, respectively. The third pattern including 41% of the DOOR situations and 11% of the other situations had high potential sensitivity for BT_Inc and FatQQ, associated with moderate to high sensitivity for Manag. The approach used to evaluate the sensitivity to entire male pig production from the limited information collected for this study has many limitations. More precise approaches using more specific information are needed to evaluate the actual sensitivity of individual situations to the use of entire male pigs. Still, the present study provides a first global insight on the capacity of European production systems aiming at high-quality products to use entire male pigs as an alternative to surgical castration.     

Pig meat quality from entire males

This paper constitutes an updated review of the production and meat quality aspects of rearing entire male pigs. Since a major obstacle in rearing entire males is the incidence of boar taint, possible methods for detection are also summarised. Safe and fast methods for detection of boar taint would be valuable in avoiding complaints from consumers. Pig meat quality is determined by many aspects, among which odour and taste are the most important attributes. Odour may be negatively affected by the presence of a pheromonal steroid, androstenone, and a fermentation product of l-tryptophan, skatole. Male pigs are surgically castrated in many countries to minimise the risk of accumulation of high levels of androstenone and skatole. Raising entire male pigs is more profitable because they have superior production characteristics and improved meat quality due to leaner carcasses and higher protein content, as compared to castrated pigs. Furthermore, surgical castration is negative from an animal welfare point of view. In most studies, no differences in sensory quality have been found between lean meat from entire male pigs with low levels of androstenone and skatole and pork from castrates and females. The question that remains is: which substances are responsible for boar taint besides androstenone and skatole and whether they need to be considered? The threshold values used for androstenone and skatole might also be too high for highly sensitive persons. Recent research shows that a human odorant receptor, ORD7D4, is involved in sensitivity to androstenone. If the ORD7D4 genotypes of consumer and expert panels are known, this might facilitate consumer studies in the future. There is still a great need for rapid on/at-line detection methods in abattoirs for identifying carcasses with unacceptable levels of boar taint compounds. Several emerging rapid technologies with a potential for boar taint detection have been investigated. They represent various measurement principles such as chemical sensor arrays (electronic noses), mass-spectrometry fingerprinting, ultra-fast gas chromatography, gas-phase spectrometry and biosensors. An industrial detection method should allow 100% correct classification of both acceptable and not-acceptable samples with regard to boar taint sorting criteria. There are, however, still too high a percentage of false negatives ranging from 5% to 20%. In addition, these methods do not yet seem to fulfil the industrial specifications with regard to cost efficiency, simplicity and analysis time. There is still no dedicated measurement technology available for on/at-line detection of boar-tainted carcasses that measures both androstenone and skatole.     

Impact of boar exposure on puberty attainment and breeding outcomes in gilts

We examined the most effective method of boar exposure for the attainment of puberty in 89 gilts. At 160 days of age, we allocated gilts to daily direct contact with a vasectomized boar after movement of pen groups of gilts to a detection-mating area (DGB: n = 30); daily direct contact with boars in the gilt home pens (DBG: n = 31); or daily fenceline contact between boars and gilts housed in individual gilt stalls (FBG: n = 28). DGB gilts were younger (P < or = 0.05) than FBG gilts at puberty. Direct boar contact reduced the interval from initial boar contact to puberty in DGB and DBG gilts, compared to fenceline contact in FBG gilts (P < 0.05). There was no difference (P > or = 0.05) between treatment for pubertal weight, backfat, lifetime growth rate, or duration of first pubertal estrus. Backfat depth and leptin concentration at 160 days of age were positively correlated (P < or = 0.05). We detected no relationships between leptin or IGF-1 concentration at 160 days of age and the interval from initial exposure to a vasectomized boar to puberty (P > 0.05). Based on objective criteria, fenceline contact with a boar (BC) during artificial insemination improved the quality of artificial insemination compared to no boar contact (NC) (P < 0.05).     

Effect of social conditions during rearing on mating behaviour of gilts

The mating behaviour of 28 gilts was studied. The gilts were reared under two different social conditions known to affect both their puberty attainment and reproductive parameters during early pregnancy. The different social conditions were applied from an average age of 137 days onwards. Ten gilts were housed individually, having neither tactile nor visual contact with other pigs. The remaining gilts (n=18) were housed pairwise, having additional contact with gilts in adjacent pens and daily boar contact from 180 days of age onwards. At third oestrus, the gilts were artificially inseminated and subsequently introduced to one of three vasectomized boars for a period of 20 min. The gilts were slaughtered 10±1 days after insemination.

The mating behaviour varied considerably between individual gilts, partly because of differences in mating behaviour between the two groups of gilts. More (P<0.05) individually housed gilts showed a standing response latency upon introduction of the boar. During this latency period, the individually housed gilts initiated contact with the boar. Once the standing response was elicited, mating behaviour was similar in gilts of both social groups. One individually housed gilt did not show a standing response and consequently was not mated. The mating behaviour of the boars did not differ for the gilts of the two social conditions.

It was concluded that the social conditions of gilts during rearing affected their introductory sexual behaviour. The relationship with reproductive performance during early pregnancy is discussed.     

Gilt development and mating in commercial swine herds with varying reproductive performance

The primary objectives were to improve standard operating procedures for gilt development and mating, based on a comparison of practices among commercial Japanese herds with varying reproductive performance. Questionnaires were sent to 115 herds; the 96 herds (83.5%) responding were classified, on the basis of the upper and lower 25th percentiles of pigs weaned per mated female per year, into high-, intermediate- or low-performing herds. During gilt development, high-performing herds switched to a gilt developer diet at an earlier age than low-performing herds (P < 0.05). More high-performing herds performed first insemination “immediately,” with second insemination “6 to 12 h” after first estrus detection than low-performing herds (P < 0.05). However, there were no differences (P > 0.05) among productivity groups with regard to the use of nutritional flushing or percentage of AI used. In multilevel analyses (17,582 service records), gilts in herds using direct boar contact were 13.73 d younger at first mating than those in the herds using indirect boar contact (P < 0.05), but age was not related to feeding practices or the number of days of boar contact per week (P > 0.05). First-serviced gilts in the herds that performed first insemination “immediately” after first estrus detection had an 8.3 to 8.4% higher farrowing rate (FR) than those in herds that performed first insemination at “6 to 12 h” and “24 h” (P < 0.01). Reserviced gilts in the herds with first insemination “immediately” after first estrus detection had 7.5% higher FR than those in herds with first insemination at “6 to 12 h” (P < 0.05). Meanwhile, first-serviced and reserviced gilts in herds that restricted feed after insemination had 0.23 and 0.17 more pigs born alive (PBA) than gilts in the herds that did not restrict feed (P < 0.05). However, PBA was not related to time of insemination (P > 0.05). In conclusion, to improve gilt reproductive performance, we recommend stimulating gilt estrus by using direct boar contact, performing first insemination “immediately” after first estrus detection, and restricting feed intake after insemination.     

On-farm prevalence of and potential risk factors for boar taint

Boar taint is an unpleasant taste and odor that can occur in entire male pigs and is caused by androstenone, skatole, and to a lesser extent indole accumulating in fat tissue. In the present observational study, we evaluated an extensive list of such potential risk factors which influence boar taint: social hierarchy and puberty attainment, housing, health, preslaughter conditions, season, feed, carcass composition, slaughter weight or age, and breed. Details on these factors were collected by interviews with the participating farmers, observations on each farm by trained observers and farmers, as well as slaughterhouse data. Twenty-two farms (in West- and East-Flanders, ranging from 160 to 600 sows, selected on suitability) raising entire male pigs were included in the study to evaluate the link between boar taint and potential risk factors related to the farm and slaughter batch (114 slaughter batches and 16 791 entire male pigs in total). Average olfactory boar taint prevalence was 1.8 ± 0.8%. Boar taint prevalence varied also within farms up to a maximum range between slaughter batches of 9.1% which suggests an effect of factors varying between slaughter batches such as season or other variables varying between slaughter batches. Less aggressive behavior at the end of fattening as well as lower skin lesion scores at fattening as well as at slaughter could be associated with less boar taint. The same might be said for sexual behavior, though less convincingly from this study. Measures that reduce aggression and stress have therefore have the potential to lower boar taint prevalence. The same might be said for sexual behavior, though less convincingly from this study. Furthermore, boar taint prevalence was generally higher in winter than in summer, which is relevant from a planning perspective for the slaughterhouses to seek alternative markets. Finally, increased CP gave significantly lower boar taint prevalences. This may to some extent be explained by the negative association between boar taint and lean meat percentage, as increased dietary CP levels promote the carcass lean meat percentages which can then be associated with lower boar taint levels.     

Influence of sex and immunocastration on feed intake behavior,skatole and indole concentrations in adipose tissue of pigs

Feed intake behavior was studied between 9 weeks of age and slaughter in a total of 36 gilts, 32 immunocastrates, 33 surgically castrated barrows and 33 boars from 36 litters. Consequences for the concentration of substances contributing to off odor of pork (skatole, indole) were evaluated. Animals were kept in groups of 12 pigs of the same sex and treatment and fed ad libitum (13.4 MJ ME, 17% CP, 1.1% lysine). Individual feed intake behavior was recorded continuously by an electronic feeder. Immunocastration was carried out with two injections of Improvac with at least 4 weeks between both injections (1st: 12 to 17 weeks of age, 2nd: 19 to 21 weeks of age). Feed intake/day increased from an average of 0.91 ± 0.02 kg/day up to 3.15 ± 0.04 kg/day before slaughter. This increase was associated with a 50% reduction in the number of meals/day (from 15.8 ± 0.44 to 7.2 ± 0.29 meals/day). The larger meal sizes resulted from an increase in both, the duration of feed intake/meal and the feed intake rate (g/min). In addition, sex and treatment differences were observed: Feed intake in boars was lower than in all other groups due to a reduction in the number of meals/day and in the time spent feeding/day. In females, time spent feeding/day was quite similar to boars, but resulted from a higher number of meals of shorter duration. Barrows had a significantly higher feed intake because of a higher number of meals/day resulting in more time spent feeding/day. The feed intake rate was similar in boars, gilts and barrows and showed an increasing trend during the study, starting from about 15 g/min up to four times the amount. Immunocastration affected feed intake behavior severely, especially the meal size increased dramatically because of higher feed intake rate, which exceeded that of all other groups by 25% at the end of the study. The number of meals/day was not influenced by immunocastration and was almost identical to that of boars. Highest skatole concentrations were measured in fat of boars, whereas indole concentrations were higher in immunocastrates than in all other groups. In gilts and barrows, skatole concentrations were related to growth rate. Additionally, the feeding rate was an important factor explaining the variability in skatole/indole concentrations in adipose tissue. The physiological mechanisms however need further clarification.     

Animal welfare implications of surgical castration and its alternatives in pigs

This paper constitutes a review on the welfare aspects of piglet castration that considers the scientific literature published after 2004. Castrating during the neonatal period (1 to 3 days of age) is clearly painful. In addition, inflammatory processes may take place at the sites of incision, thus adding further pain to the procedure. Surgical castration with general and local anaesthesia, in combination with long-term analgesia, has been shown to reduce pain but the additional handling and injection of the anaesthetic, the effectiveness and limited safety margins have to be thoroughly evaluated. Raising entire males during the whole fattening period or immunocastration of males towards the end of the fattening period are other alternatives with welfare benefits in young pigs compared to current surgical castration, but with some potential welfare drawbacks regarding handling stress and behaviour during fattening. Based on the current knowledge, it can be concluded that sperm sexing and raising entire males after genetic control of boar taint are potentially preferable alternatives to current practices, but need further research, as these methods are not yet available.     

Influence of breed and slaughter weight on boar taint prevalence in entire male pigs

Piétrain (P), Large White (LW) and Belgian Landrace stress negative (BN) boars were slaughtered at 50, 70, 90 or 110 kg live weight to investigate breed differences and the effect of slaughter weight on boar taint prevalence. Boar taint was quantified by four different methodologies: sensory evaluation of neckfat heated with a hot iron in the slaughterhouse, sensory evaluation of meat by consumer panels, sensory evaluation of fat and meat by expert panels and laboratory analysis of indole, skatole and androstenone in backfat. Skatole levels in backfat were significantly higher for LW and BN than for P boars. The androstenone levels and the hot iron method revealed a significant interaction between breed and slaughter weight. On the other hand, experts detected an effect of weight on the androstenone odour perception, which was significantly higher in fat from boars slaughtered at 90 kg compared with 50 kg, and significantly higher in meat from boars slaughtered at 110 kg compared with 50 kg. Consumers did not detect differences in the sensory characteristics among breeds or slaughter weight. These results indicate opportunities to minimise the risk of boar taint in entire male pigs by carefully selecting a combination of breed and slaughter weight. Along with the optimal slaughter weight, the effectiveness of reducing boar taint by lowering slaughter weight appeared to be breed dependent.