Piglet Survival Research Articles

A survey of sow management at farrowing in the UK

AbstractFarrowing is an important period in pig production, with sow health and piglet mortality representing a welfare issue and an economic loss. Sow health and welfare is critical for piglet survival and good management can improve welfare and productivity. This study investigated the management of sows around farrowing and attitudes of UK pig farmers towards sow pain and difficulty farrowing. Farmers were asked how often they provided night checks, used farrowing induction and administered pharmaceutical products during and after farrowing. Farmers and veterinarians were asked if they used or prescribed anti-inflammatories for farrowing-related health issues. Farmers were asked if pain at farrowing was a problem for gilts and sows and what percentage they considered to have difficulty farrowing. Convenience sampling using a number of distribution methods was used. Sixty-one farmers and 52 veterinarians responded. Of the farmer respondents, ten worked on outdoor and 51 on indoor farms. Night checks were reported as frequently provided and farrowing induction was rare. Many respondents reported using oxytocin substitutes at least sometimes during (74%) or after (54%) farrowing. Azaperone was reported to be used at least sometimes by 45% of respondents during and 33% after farrowing. Farmers indicated that pain at farrowing was more often a problem for gilts than sows and 5% of gilts and 4% of sows were considered to have farrowing difficulty. The high level of supervision around farrowing, with the use of night checks, is encouraging and could improve welfare. Frequent use of oxytocin substitutes, which promote farrowing and milk let-down may negatively impact sow and piglet welfare and could be masking poor mothers that fail to perform well without intervention. This study provides interesting information regarding the management of sows around farrowing, which could inform future research and education to improve sow and piglet welfare in the periparturient period.

Consequences for Piglet Performance of Group Housing Lactating Sows at One, Two, or Three Weeks Post-Farrowing.

Housing lactating sows with piglets in a multi-suckling pen from around 14 days post-farrowing is common practice in Swedish organic piglet production. However, nursing-suckling interaction is less frequent in multi-suckling pens than in individual farrowing pens, thus affecting piglet performance, e.g., piglet growth. Moreover, piglet mortality is higher in systems using multi-suckling pens. Three management routines whereby lactating sows with piglets were moved from individual farrowing pens to multi-suckling pens at one, two, or three weeks post-farrowing were compared in terms of nursing-suckling interaction and piglet performance. Correlations between nursing-suckling interaction, piglet performance, and piglet mortality were also examined. In total, 43 Yorkshire sows with piglets were included in the study. Nursing-suckling interaction and all piglet performance parameters except piglet mortality did not differ between management routines. Piglet mortality in the individual farrowing pens did not differ between management routines, but piglet mortality in the multi-suckling pen was lower (P<0.05) when piglets were group housed at three weeks compared with one week post-farrowing. Overall piglet mortality was positively correlated with mortality in the multi-suckling pen for piglets group housed at one week (r = 0.61: P<0.05) and at two weeks post-farrowing (r = 0.62: P<0.05) but not for piglets group housed at three weeks post-farrowing. In conclusion, overall piglet mortality could be reduced if sows and piglets are group housed at three weeks post-farrowing and piglet survival the first week post-farrowing is improved.

Factors influencing colostrum yield by sows

ABSTRACT An adequate colostrum intake, in order to ensure the survival and weight gain of piglets, depends on the sow's ability to produce enough colostrum for the whole litter. The aim of this study was to evaluate factors involved in colostrum yield (CY) variability related to the sow, the litter and the farrowing process. The experiment was conducted with 96 Camborough 25(r) sows of parities one to seven, whose farrowing was spontaneous. Colostrum production of each sow was estimated by summing up the colostrum intake of each piglet in the litter, estimated by an equation that takes into account the birth weight and weight gain during the first 24h of life. The multiple regression model explained 28% of variation in CY, with 24% and 4% respectively of variation being explained by the litter birth weight and the width of the first mammary glands. Litter birth weight was positively correlated with the number of total born (r= 0.73) and born alive piglets (r= 0.83). When categorised into two groups of colostrum yield (LOWCY; ≤3.4kg; n= 46 vs HIGHCY; &gt;3.4kg; n= 50), LOWCY sows had fewer total born and born alive piglets and lighter litters (P&lt;0.05). The logistic regression analysis showed that sows from parities 1, 2 and &gt;3 had greater odds (P≤0.05) of belonging to the LOWCY group than parity 3 sows. Sows with two or more obstetrical interventions had higher odds (P&lt;0.05) of belonging to the LOWCY group than sows without interventions during farrowing. The higher colostrum yield observed in sows of parity 3 and sows with less than two obstetrical interventions during farrowing was associated with a greater number of nursed piglets. This study showed that total birth weight of born alive piglets is the most important factor involved in colostrum yield variability, indirectly representing the number of piglets nursed by the sow.

074 Birth weight threshold for identifying piglets at-risk for preweaning mortality

Several studies have suggested there is a critical relationship between piglet birth weight and preweaning mortality. Thus, the objective of the current work was to identify a birth weight threshold value for preweaning mortality. Birth weight and survival data from two studies involving a combined total of 4,068 piglets from 394 litters on four commercial farms (three European, one U.S.) were compiled for a pooled, multistudy analysis. Overall preweaning mortality across the two studies was 12.2%. Key variables used in the analysis were piglet birth weight (measured within 24 h of birth) and corresponding survival outcome (dead or live) by weaning at 3-4 wk of age. A mixed effects logistic regression model was fit to estimate the relationship between preweaning mortality and birth weight. A random effect of study was included to account for overall differences in mortality between the two studies. A piecewise linear predictor was selected to best represent the drastic decrease in preweaning mortality found as birth weight increased in the range of 0.5-1.0 kg and the less extreme change in weight above 1.0 kg. The change point of the birth weight and preweaning mortality model was determined by comparing model fit based on maximizing the likelihood over the interval ranging from 0.5 to 2.3 kg birth weight. Results from the analysis showed a curvilinear relationship between birth weight and preweaning mortality where the birth weight change point value or threshold value was 1.11 kg. In the combined data set, 15.2% of pigs had birth weights ≤1.11 kg. This subpopulation of pigs had a 34.4% preweaning mortality rate and represented 43% of total preweaning mortalities. These findings imply interventions targeted at reducing the incidence of piglets with birth weights ≤1.11 kg have potential to improve piglet survivability. Additional research is needed to validate 1.11 kg as the birth weight threshold for increased risk of preweaning mortality.

Development of a methodology to describe udder conformation in sows

The aim of this study was to develop a methodology to measure sow udder conformation to use in studying the correlation between udder traits and piglet survival, health and performance. The steps in the investigation were (i) to assess the repeatability of measures, (ii) to determine if there was an important difference between the two sides of the udder, (iii) to assess the extent of variation between sows, and finally (iv) to verify if the measures differ in a systematic way over the days shortly before farrowing. A total of 24 sows were scored for six conformation traits of the udder measured twice a day, every day from the sows’ entrance into the farrowing crates until farrowing (1 to 4 days later). The data were recorded from both sides when the sow was lying and when she was standing. The measurements taken were: inter-teat distance within the same row (SAMER; mm between the adjacent teat bases); distance from the base of the teats to the abdominal midline, recorded only in a lying posture (B); distance between the teat base and the adjacent teat on the opposite row, recorded only in a standing posture (OPPR), distance from the base of the teats to the ground (FLOOR); teat length (LEN) measured from the tip to the base, and diameter (DIA) measured at the tip of the teat. Intraclass correlation coefficients (ICC) revealed that most udder conformation traits were highly repeatable (ICC>0.8); only DIA and FLOOR had lower repeatability (ICC=0.7). Measurements did not differ by side. In general, the greatest proportion of variance occurred at the sow level. Traits changed little in the days before farrowing, except for a change 1 day before farrowing in DIA, FLOOR and OPPR. Measures which used anatomical landmarks as the reference point were more reliable than those using the floor of the pen. Udder conformation measures can be used as a reliable phenotype for further study. They can be collected on any day shortly before farrowing, and only from one side and in one posture to save time.

Effect of radiant heat at the birth site in farrowing crates on hypothermia and behaviour in neonatal piglets

It has been documented that floor heating of the farrowing area in loose housed sows improves survival of piglets significantly. However, today, the majority of farrowing pens are designed with crating of sows and slatted floor at the birth site. The aim of this study was to investigate whether providing radiant heat at the birth site to new-born piglets in pens with crated sows reduced hypothermia, time to first milk intake and growth of the piglets during the 1st week. Second parity Danish Landrace×Yorkshire sows (n=36) were randomly divided into two groups: Control (CG) and heat (HG). In the area behind the sow (zone 1), two radiant heat panels were mounted above the slatted floor in the HG. The farrowings were attended, and the heaters were turned on at birth of first piglet and turned off 12 h after. Birth time, time to leave zone 1, time to first contact with udder and time to first suckling were registered by direct observation. The piglet’s rectal temperature (RT) was measured 15, 30, 60, 120, 180, 240 min after birth and 12, 14 and 24 h after birth of first piglet. Piglets were weighed at birth, 24 and 48 h and 7 days after birth. Data were analysed in a mixed model in SAS. The drop in RT was lower in HG compared with CG (P=0.002), and the RT in HG remained higher than in CG from 30 to 240 min after birth (P<0.05), whereas no difference was found at 12 h after birth of first piglet (P=0.92). Piglets in HG stayed longer in zone 1 than those in CG (P=0.01), whereas time to reach udder (P=0.35) and to first suckling (P=0.56) did not differ. No difference in weight gain was found between piglets in HG and CG at 24 h (P=0.23), 48 h (P=0.28) and 7 days after birth (P=0.44). Birth weight had a positive effect on RT (P<0.001) and reduced time to leave zone 1 (P<0.01), reach udder (P<0.001) and time to first suckling (P<0.001). The results showed that radiant heating behind the sows reduced hypothermia in new-born piglets and indicate that providing heat during the first half hour after birth is important.

Reference values for immunocrit ratios to assess maternal antibody uptake in 1-day-old-piglets

Colostrum intake is an essential component for piglet survival. Assessing colostrum intake, and consequently transfer of immunoglobulins (Igs), has been difficult to quantitate in swine. In this study, the authors first sought to subjectively determine the least stressful method to collect necessary sample quantities for Ig quantitation. The immunocrit ratio (IR) method was used to quantify a benchmark Ig level for a commercial production system. Lastly, the authors sought to identify associations between IR and production parameters. The cephalic vein provided consistent sample volumes and caused minimal animal distress. Additionally, a small volume of serum (30 μL) can be used for IR testing. An IR benchmark was determined to be 0.098 for this production system. For this study, no significant associations were found between pre-weaning mortality or average daily weight gain and IR. Birth weight and parity had significant effects (P &lt; .05) on IR, with parity 1 litters having lower IR than higher parity litters. Using the IR technique to identify IR benchmarks for piglets will help producers improve colostrum intake opportunities in piglets with suboptimal Ig levels. The IR method ascertains whether piglets are receiving adequate maternal antibodies until their own immune systems are developed.

Effects of dietary valine:lysine ratios on lactation performance of primiparous sows nursing large litters

Eighteen sows were used to determine the effect of dietary valine:lysine (val:lys) ratios on lactation performance in primiparous sows and litter performance. Sows, raised in individual pens, were randomly assigned to 1 of 2 experimental diets containing different standardized ileal digestibility (SID) val:lys ratios of 0.80 or 0.85. Corn-soybean-wheat-based diets were formulated to achieve the dietary treatments (0.86% or 0.87% SID lysine, and 0.69% or 0.74% SID valine). All diets were formulated to have 3,450 kcal metabolizable energy/kg. The experiment lasted 24 d. At the end of the experiment, body weight loss, backfat loss, average daily feed intake, and days to return to estrus were not affected by the different dietary val:lys ratios. Furthermore, no difference was observed in number of piglets weaned, piglet survival rate, weaning litter weight, litter weight gain, piglet weaning body weight, piglet gain, or piglet daily gain between the two dietary treatments. However, increasing the dietary val:lys ratio increased arginine and threonine concentrations in the milk. Dietary val:lys ratios of 0.80 and 0.85 do not affect the lactation performance of primiparous sows nursing large litters, but increase the arginine and threonine concentrations in milk as the dietary val:lys ratio are increased.

Effects of natural resistance-associated macrophage protein 1 and toll-like receptor 2 gene polymorphisms on post-weaning piglet survivability

Predicting resistance or susceptibility to infectious diseases on the basis of the genotypes of animals regarding disease or immune related genes could be important in animal production. We evaluated the potential influence of the genetic polymorphisms of four immune related genes, porcine beta defensin 4, interferon-induced GTP-binding protein Mx1, natural resistance-associated macrophage protein 1 (Nramp1), and Toll-like receptor 2 (TLR2) on post-weaning piglet survivability in farms. We selected a single SNP that satisfied the criteria of non-synonymous substitutions and the minor allele frequency >0.1 from each gene, and performed PCR–RFLP. Distributions of allele and genotype frequencies of the SNPs were, in general, significantly different among the five breeds (Berkshire, Yorkshire, Duroc, Landrace, and Korean native pigs. Initially, 371 randomly collected Yorkshire × Landrace F1 piglets consisting of post-weaning survival (n = 185) and non-survival groups (n = 186) were genotyped for the selected SNPs. For the Nramp1 and TLR2 SNPs, genotype frequencies were significantly different between the two groups (P < 0.05). To confirm the results, additional animals that were collected in a different time-period were genotyped for the Nramp1 (n = 390) and TLR2 (n = 240) SNPs. The results using the combined samples (n = 761) were consistent with the initial analysis (P < 0.01), suggesting that the genetic polymorphisms of Nramp1 and TLR2 affect post-weaning piglet survivability. The relative risks, i.e. odds ratios, between the beneficial and non-beneficial genotypes to piglet survivability were 4.88 and 29.65 for the Nramp1 and TLR2 SNPs, respectively.

Effects of bovine colostrum on performance, survival, and immunoglobulin status of suckling piglets during the first days of life

Supplementation of bovine colostrum (BC) has shown to improve growth performance, intestinal development, and immune response in early-weaned pigs. Little is known about whether BC may have similar effects in neonatal piglets. In the present study, the effect of BC supplementation on mortality, growth performance, and blood parameters (plasma proteins and white blood count) of suckling piglets in the first 10&amp;nbsp;days of life was investigated under practical conditions with special emphasis on low birth weight piglets. In total, 258 newborn piglets from 30 multiparous sows in a commercial breeding unit were randomly assigned to two different treatment groups. Piglets received either 1 ml of BC orally on days 1&amp;ndash;3 of life (group BC, n = 128) or 1 ml of saline (0.9%) (control (CON) group; n = 130). Body weight was measured on days 1, 4, and 10 of life. Blood was collected on days 1 and 4 from 60 piglets per group. No differences in mortality, body weight, and average daily weight gain were observed between treatment groups in days 1&amp;ndash;10. However, compared to CON, particularly in low birth weight piglets the administration of BC supported (P &amp;lt; 0.01) their survival. Group BC exhibited lower plasma total protein (P = 0.03) and beta-globulin (P = 0.02) concentrations compared to group CON. In conclusion, BC improved low and normal birth weight piglets&amp;rsquo; survival during their first 10 days of life. Further research is needed to clarify whether the survival rate is related to earlier gut closure indicated by lower plasma protein levels, which might be beneficial due to a lower uptake of potential antigenic substances.

Preferences for pig breeding goals among organic and conventional farmers in Sweden

Organic and conventional pig farmers’ preferences regarding breeding goal traits important in pigs were investigated using an advanced internet-based questionnaire. Farmers were asked what pig traits they spontaneously considered important, to rank 15 given traits and to weigh traits against each other given the estimated genetic change (calculated based on selection index theory). Organic and conventional farmers ranked both functional and production traits highly. For example, more than 70 % of farmers from both production systems ranked piglet survival, fertility, sow longevity, leg health, feed conversion, piglet birth weight, piglet and slaughter pig growth as being of high or moderate importance (1–10/15). Litter size and shoulder ulcers were ranked higher by respondents from conventional farms, while parasite resistance and roughage consumption were ranked higher by respondents from organic farms. Regarding estimated desired genetic change, respondents from organic farms favoured health traits while conventional farmers favoured growth traits. In order to obtain genetic improvement in those traits, farmers gave low priority to carcass quality and litter size. Due to the variations in farmers’ breeding goal trait preferences demonstrated here, it is clearly important to take farmers’ preferences into consideration when developing future pig breeding strategies.

Parâmetros genéticos para características de prolificidade nas raças Landrace e Large White

Dados de suínos das raças Landrace (LD) e Large White (LW) foram utilizados para estimar componentes de variância para número total de leitões nascidos (NTN), nascidos vivos (NV) e de leitões vivos ao quinto dia (LV5). Usou-se o método da máxima verossimilhança restrita (REML) para estimar componentes de variância. O modelo misto incluiu os efeitos fixos de mês e ano de nascimento e da inseminação da porca e ordem de parto. Análises unicaracterísticas incluíram os efeitos genético direto, genético materno e de ambiente permanente. Análises multicaracterísticas foram feitas para estimar correlações genéticas. Os modelos unicaracterísticas foram comparados e o que continha apenas o efeito genético direto foi considerado o mais adequado. As estimativas de herdabilidade para NTN foram de 0,15 para LW e de 0,08 a 0,12 para LD, dependendo do modelo, para NV foram de 0,14 para LW e de 0,05 a 0,12 para LD, e para LV5, variaram de 0,11 a 0,12 para LW e de 0,03 a 0,08 para LD. As correlações fenotípicas e genéticas entre as três características foram altas e favoráveis. Conclui-se que a seleção para aumento do LV5 pode ser uma via interessante para o aumento do tamanho da leitegada, da sobrevivência de leitões e da habilidade materna em suínos.

Achieving optimum performance in a loose-housed farrowing system for sows: The effects of space and temperature

Piglet survival relies on interactive influences of the sow, her piglets and their environment. There are a number of design challenges in a loose-housed farrowing and lactation system to optimise this dynamic, including achieving farrowing in the desired location (i.e. a protected nest area) and minimising crushings. The PigSAFE (Piglet and Sow Alternative Farrowing Environment) pen was developed with these challenges in mind. It has different areas to fulfil different biological and managerial needs, including a solid-floored nest area with piglet protection features (sloped walls, heated creep) intended for farrowing. Two hypotheses regarding pen design features to optimise farrowing location and improve piglet survival were tested: (i) greater space would improve maternal behaviour; and (ii) a heated nest-site would be more attractive to the farrowing sow. PigSAFE was adapted to give a LARGE treatment, 9.7m2 in total with a nest area of 4.0m2, and a SMALL treatment, same design but 7.9m2 in total with a nest area of 3.3m2. The nest floor was heated to either 30°C (T30) or 20°C (T20) from 48h before until 24h after farrowing. A 2×2 factorial design saw 88 Large White×Landrace sows randomly assigned to space and temperature treatments. Generalised linear mixed models were used to analyse performance data. Farrowing location analysis involved dividing the pen into seven areas (L1–L7); L1 deemed the safest location for the piglets to be born (in the nest, furthest from dunging area, closest to creep) and L7 the least protected (in the dunging area). Of all the piglets born 97% were born in the nest area. The majority of sows started farrowing in L1 (56%), with 39% of remaining piglets being born in this location. There was a significant Space×Temperature interaction for farrowing location (P=0.011) with SMALL_T20 achieving the most L1 births. Temperature had no significant influence on piglet survival (Total mortality P=0.401; Live-born mortality P=0.826). However space influenced mortality, with significantly greater live-born mortality when sows were afforded a larger farrowing space (LARGE=18.1% vs. SMALL=10.9% P=0.028). There were no significant interactions between space and temperature for either total mortality (P=0.394) or live-born mortality (P=0.685). The overall design successfully promoted farrowing in the nest location, irrespective of nest size and floor temperature. The higher piglet mortality in the LARGE treatment suggests that the larger nest size was less protective for the piglets and thus a smaller nest, within an adequate total pen size for differentiation of functional areas, would be recommended.

Adaptation of Piglets Using Different Methods of Stress Prevention.

Simple SummaryStressful events play a major negative role in the modern technology of weaned piglets. These events include but are not limited to weaning itself, lack of maternal milk, loss of maternal bonding, mixing of different litters, transportation to growing-finishing farms, and housing conditions. Various additives (phenazepam, aminazine, vitamins E and C, the extract Eleutherococcus senticosus, and ultraviolet irradiation) at different doses and combinations with or without ultraviolet irradiation were used to evaluate their effect on the viability and growth rate of piglets after weaning. Content of lipids in the blood and liver, antioxidant activity (AOA) and lipid peroxidation (LPO) significantly decreased or increased with the use of the additives. Feeding a mixture of additives increased survival rate, average daily gain, and live weight at the end of the experiment.The purpose of this study was to evaluate the viability and growth rate of piglets after weaning, the content of lipids in the blood and liver, antioxidant activity (AOA) and lipid peroxidation (LPO) when various additives are used in feed. The experiments were performed on two crosses of piglets obtained from Large White breed sows and Landrace breed boars. Twenty to 28 animals were randomly assigned per group. The following additives were tested: the benzodiazepine phenazepam, the neuroleptic aminazine, vitamins E and C, and the extract Eleutherococcus senticosus (Araliaceae). Different doses and combinations of the additives against ultraviolet irradiation were used. The addition of these substances improved the growth rate and viability of piglets. AOA increased under the influence of all factors studied, especially with the addition of extract of Eleutherococcus in feed in combination with aminazine and UV-irradiation (p < 0.01). However, the addition of Eleutherococcus extract and aminazine intensified LPO (p < 0.01), but use of UV irradiation helped to decrease LPO values (p < 0.01). Feeding a mixture of additives per pig per day of 3 mL of Eleutherococcus extract, 80 mg of 25% tocopherol, and 500 mg of ascorbic acid increased survival rate, average daily gain, and live weight at the end of the experiment. Thus, the use of prophylactic antistress and sedative drugs during weaning helps AOA normalize LPO of red blood cells; enhance post weaning growth of the pigs by 4.8% to 24.6% and increases piglet survival rate by 5% to 5.1%.

Establishment of a special pathogen free Chinese Wuzhishan Minipigs Colony.

To meet the increasing demands of specific pathogen free (SPF) minipigs in biomedical researches, 8 pregnant Chinese Wuzhishan minipigs (WZSP) sows with clear background were chosen to obtain SPF WZSP by hysterectomy. At 111 ± 2 days of the pregnancy, piglets were aseptically taken out from the sows and artificially suckled for 40 to 45 days in the positive isolators. Then, the piglets defined as F0 were transferred to barrier environment and fed with standard feeds. The original SPF colony was formed for breeding by selected piglets from F0 group of 6–8 months old. Biological characteristics of SPF WZSP were collected and further compared to those of conventional (CV) WZSP, including growth performance, reproductive performance, hematology and blood biochemistry, and major pathogens detection. As a result, 61 F0 piglets were obtained from 8 candidate sows, and 55 out of them survived. After strictly selection, 35 F0 piglets were used to form the original SPF colony, which produced 14 litters of SPF piglets defined as F1. Piglet survival rates, growth performance, and reproductive performance of SPF WZSP were similar to CV WZSP. Some hematology and blood biochemistry parameters showed significant differences between SPF and CV WZSP. Eighteen kinds of pathogens were identified to be free in F0 and F1 SPF colony by repeated pathogen detections. In conclusion, we established a satisfied SPF WZSP colony maintaining original characteristics, free of controlled diseases, and being proved to be a suitable laboratory animal.

Post-mortem findings and piglet mortality in relation to strategic use of straw at farrowing

Piglet survival is the outcome of complex interactions between the sow, the piglet and their environment. In order to facilitate nest-building and to provide a suitable environment for the newborn piglets, a strategic method to supply loose housed sows with large quantities of straw at farrowing has been developed by Swedish piglet-producing farmers. The objectives of this cohort study were to use post-mortem findings to assess the causes of death and to quantify the effect of a large quantity of straw provided before farrowing compared to limited small daily amounts on stillbirths, post-mortem findings in piglets dying within 5 days after birth and the pre-weaning mortality. On each of four commercial piglet-producing farms in South-West Sweden, one batch of sows was studied during two consecutive lactations. At inclusion, sows were randomly assigned to two treatment groups, and sows remaining in the batch during the next lactation switched treatment group. In the STRAW group (n=181litters) sows were provided with 15–20kg of chopped straw 2 days prior to the calculated date of farrowing. Sows in the CONTROL group (n=182 litters) received 0.5–1kg of chopped straw on a daily basis plus about 2kg for nest-building when the stockperson judged the sow to be about to farrow. After onset of farrowing, additionally 1–2kg was given. Post-mortem examination was performed in all piglets that died within 5 days after birth (n=798). The three major post-mortem findings were starvation (34%) crushing by the sow (28%), and enteritis (24%). In conclusion, strategic use of large quantities of straw reduced the number of stillborn piglets per litter by 27% (p=0.007). Under the conditions studied, the pre-weaning mortality of liveborn piglets was not affected by treatment; however, the distribution of post-mortem findings differed with fewer piglets dying due to starvation and more due to crushing and enteritis in STRAW litters.

Heritable environmental variance causes nonlinear relationships between traits: application to birth weight and stillbirth of pigs.

There is recent evidence from laboratory experiments and analysis of livestock populations that not only the phenotype itself, but also its environmental variance, is under genetic control. Little is known about the relationships between the environmental variance of one trait and mean levels of other traits, however. A genetic covariance between these is expected to lead to nonlinearity between them, for example between birth weight and survival of piglets, where animals of extreme weights have lower survival. The objectives were to derive this nonlinear relationship analytically using multiple regression and apply it to data on piglet birth weight and survival. This study provides a framework to study such nonlinear relationships caused by genetic covariance of environmental variance of one trait and the mean of the other. It is shown that positions of phenotypic and genetic optima may differ and that genetic relationships are likely to be more curvilinear than phenotypic relationships, dependent mainly on the environmental correlation between these traits. Genetic correlations may change if the population means change relative to the optimal phenotypes. Data of piglet birth weight and survival show that the presence of nonlinearity can be partly explained by the genetic covariance between environmental variance of birth weight and survival. The framework developed can be used to assess effects of artificial and natural selection on means and variances of traits and the statistical method presented can be used to estimate trade-offs between environmental variance of one trait and mean levels of others.

Pre-partum straw-directed behaviour by sows in farrowing pens is positively associated with piglet survival

Animal Production Science (continuing Australian Journal of Experimental Agriculture) publishes original research into applied agriculture including animal production, animal-plant interactions, pasture and fodder crops, field crops, extension and horticulture

A ‘two-stage’ farrowing and lactation system: piglet survival and growth performance

A ‘two-stage’ farrowing and lactation system: piglet survival and growth performance

Neonatal split suckling improves survival of small piglets

Neonatal split suckling improves survival of small piglets