Review: Improving pig survival with a focus on birthweight: a practical breeding perspective.

Survival of growing pigs through to slaughter age is not only a key driver of profitability but also has implications for animal welfare. Changing preweaning mortality by over 3% gives a similar change in profit per pig as changing postweaning mortality by 1%. There is significant scope to improve both traits through management and breeding to improve survival. The aim of this literature review was to explore the relationship between litter size and piglet birthweight and the detrimental impact this negative association has had on pig survival, along with genetic strategies that have been implemented in breeding programmes. It is suggested that the primary effect of litter size on mortality was indirect, through the effects of litter size on individual piglet birthweights. The circumstances affecting the litter a piglet was born into were the most important for determining the birthweight of individual piglets, rather than the genetic make-up of the individual piglet itself. Therefore, breeding programmes should include the average piglet birthweight of a litter (i.e., a sow trait) rather than individual piglet birthweight to maintain the weight of piglets at birth. The relative weighting of litter size and average piglet birthweight should be done in a manner that avoids selecting heavy pigs from small litters. Additional genetic strategies to improve survival include survival at the litter level, or survival of individual piglets or enhanced through the use of genomic information. At the litter level, litter size at day 5 and weaning can be considered as sow traits, but the use of these traits depends on the recording environment. At the individual piglet level, pre- and postweaning survival can be recorded as 0/1 traits and analysed directly. Although heritabilities are low for all these traits, genetic improvements can be made. For preweaning survival, the genes of the nurse sow are more important than the genes of the individual piglet. The nurse sow model captures both the lactation and gestation effects, and the information obtained when piglets born from different litters are reared together. However, once a piglet is weaned, its own genes became more important for the expression of postweaning mortality outcomes. Finally, for a successful selection programme, combining the average piglet birthweight at the litter level and mortality data based on individual piglet records (not solely birthweight) might yield the best response in piglet survival.

Development of breeding values for susceptibility to virulent footrot in sheep: A strategy to accommodate variable disease progression at time of scoring.

Genetic evaluations utilising footrot scores from industry flocks in their essence, incorporate data from a wide range of challenge environments, resulting in potentially large differences in means, variances and distribution of scores across challenges. The date that commencement of infection occurs is generally unknown, and progression of the infection varies with the prevailing environmental and management conditions, virulence of the bacterium Dichelobacter nodosus, as well as the genetic potential and (permanent) environmental ability of animals to resist footrot. In practice, animals are unlikely to be repeatedly scored to identify the best time for comparison, or monitor development of disease progression. Furthermore, field challenges are limited by the need to treat animals before their welfare is compromised. Therefore, the duration and intensity of infection varies and this affects comparisons between animals for their susceptibility. Diseases such as footrot are characterised by multiple categorical scores reflecting clinical stages that describe the progression and relative impact of the disease. This provides the opportunity for the transformation of the data to a standardised prevalence. Scoring events from multiple footrot field challenges under a standardised protocol were used to establish a series of transition matrices to describe disease progression between scores over time. These transition matrices were used to standardise challenge events to the more severe scoring events, observed later in the challenge. The accuracy of the transition technique was tested by comparing the ranking of animals and sires against the observed scores. Transitioning the data from low disease prevalence to the higher prevalence at the subsequent scoring event improved the correlations between the scoring events, at the animal level, by upwards of 0.10 across challenges. The utilisation of a transition matrix to transform low prevalence disease challenges by taking into account the natural biological rate of progression through the clinical stages of the disease provides a more accurate technique to account for variation in disease prevalence. The transition technique increases the acceptable range of disease expression targeted by producers when scoring virulent footrot challenges reducing the need for repeat scoring and allowing earlier treatment and reducing the impact of the disease on the host animal.

Poorer lifetime growth performance of gilt progeny compared with sow progeny is largely due to weight differences at birth and reduced growth in the preweaning period, and is not improved by progeny segregation after weaning.

Gilt progeny (GP) are born and weaned lighter than sow progeny (SP) and have higher rates of mortality. This study aimed to quantify the performance and survival differences between GP and SP throughout the entire production cycle from birth to sale. Furthermore, the study looked at the effects of segregating GP and SP compared with commingling during rearing within common pens. It was hypothesized that GP would be lighter than SP at every age and have lower rates of survival accompanied by higher rates of medication, and that segregating GP and SP would improve the growth and survival of both groups. All progeny born to 109 gilts (parity 1) and 94 sows (parities 2 to 8) were allocated to 4 postweaning treatments at birth: GP separately penned, GP mixed with SP in a common pen (GM), SP separately penned, and SP mixed with GP in a common pen (SM), with littermates split among treatments. The GM and SM pigs were penned together after weaning. Individual live weight of all progeny was recorded at birth (birth weight [BWT]), weaning (28 d; weaning weight [WWT]), 10 wk of age (10-wk weight [10WT]), and sale (22-23 wk; sale weight [SWT]). Individual HCW, backfat depth, loin depth, and dressing percentage were measured at slaughter. All postweaning mortalities and medications were recorded. The GP had a lighter BWT ( = 0.032), WWT ( < 0.001), 10WT ( < 0.001), and SWT ( < 0.001) than SP as well as a lower HCW ( < 0.001) and dressing percentage ( = 0.012). Postweaning performance differences were mostly attributable to the lighter WWT of GP compared with that of SP when WWT was fitted as a covariate. The GP had a higher mortality in the immediate postweaning period (weaning to 10 wk of age; = 0.028) and from weaning to sale ( = 0.012) than SP, which was also attributable to lower WWT. The GP exhibited a higher incidence of mortality ( = 0.011) due to respiratory tract infection in the grower-finisher period, despite similar medication rates ( = 0.83). Segregation of GP and SP between pens presented no benefit in terms of growth and survival of both groups while requiring added labor and production considerations and, therefore, is not recommended. This study confirms that GP are lighter than SP, on average, at every stage of life from birth to slaughter and that their performance before weaning is an important determinant for whole-of-life performance.

Social genetic effects influence reproductive performance of group-housed sows.

Group housing of gestating sows has implications for reproductive performance due to detrimental interactions between sows within groups. Reproductive records ( = 10,748) were obtained for 8,444 pedigreed nucleus sows housed in a single facility, formed into 1,827 static groups during gestation. Only data from complete groups were used to estimate genetic parameters for total born (TB), number born alive (NBA), and gestation length (GL) and to compare models extended to account for group effects. Censored data for sows which did not farrow (0.8% of records) were augmented with biologically meaningful values. Group sizes ranged from 2 to 10, in pens designed to hold 4, 8, or 10 sows per pen. Sows were grouped by parity, line, and mating date after d 35 of pregnancy. Heritability estimates were generally constant across all model alternatives at 0.11 ± 0.02 for TB and NBA and 0.32 ± 0.03 for GL. However, models for all traits were significantly ( < 0.05) improved through inclusion of terms for nongenetic group and social genetic effects (SGE). Group effects were no longer significant in models containing both terms. The proportional contributions of SGE () to phenotypic variances were very low (≤0.002 across traits), but their contributions to calculated total genetic variance (T) were significant. The differences between h and T ranged between 3 and 5% under simple models, increasing to 8 to 14% in models accounting for both covariances between additive direct (A) and SGE and the effects of varying group size on the magnitude of estimates for SGE. Estimates of covariance between A and SGE were sensitive to the modeling of dilution factors for group size. The models of best fit for litter size traits used a customized dilution based on sows/pen relative to the maximum sows/pen. The best model supported a reduction in SGE with increased space per sow, independent of maximum group size, and no significant correlation between A and SGE. The latter is expected if A and SGE reflect different trait complexes. It is suggested that the SGE estimated for reproductive traits represented the expression of an unobserved phenotype, such as sow aggression, of an individual on its pen mates. Further investigation into the use of competitive effects models for genetic evaluation of reproductive traits for group-housed sows could be considered a strategy to improve welfare and performance of group-housed sows.

A longitudinal study of weight and fatness in sows from selection to parity five, using random regression.

This study examined the changes in BW, fatness, and genetic parameters for these traits over a sow's productive life, using random regression. Data for BW (kg) and fat depth at the P2 site (mm) were recorded repeatedly on 3,324 sows from selection to culling. There were up to 19 recording events, defined as: 20, 21, 26, and 29 wk of age, followed by records at mating, d 110 of gestation (d110), and weaning, for parities 1 through 5. In this population, sows continued growing through parity 5 but achieved 90% of this BW by 22 mo, which is the average age at remating after parity 3. In contrast, sows increased fat levels until just before parity 1 farrowing, when a plateau in permanent reserves was essentially established. Heritability estimates were 0.31 ± 0.08 and 0.36 ± 0.08 for BW and fatness, on average, from the random regression analyses. However, the greatest heritabilities were estimated from data recorded before the first farrowing and diminished with increasing age as residual variation increased. Trajectories of heritability estimates for both BW and fat from random regression show that genetic variation is available for selection to alter sow development patterns. However, due to relatively low genetic correlations between early and later BW, repeated BW measurements would be required to effectively alter mature sow BW, in particular. The solutions for development patterns were obtained for individual sows from the random regression model and were used to extrapolate the expected individual sow BW at 30 mo. Genetic solutions, including the intercept and slope for BW and fatness, were used to rank sows into quartiles. Results suggested that genetically heavier/fatter sows are more likely to successfully enter and stay in the breeding herd, thus demonstrating increased lifetime performance. However, there is also evidence to suggest that sows with high growth potential expressed later in life were disadvantaged with respect to their longevity and productivity. Therefore, a breeding goal combining efficient lean growth in finishers with limits to mature sow size could be beneficial to sow herd performance.

Body development in sows, feed intake and maternal capacity. Part 1: performance, pre-breeding and lactation feed intake traits of primiparous sows.

This study examined the genetic and phenotypic associations between finisher performance, pre-breeding body condition of the gilt, subsequent lactation feed intake and survival of the primiparous sow to farrow in the second parity. Complete data were available on ~2200 sows, along with additional cohort and historical performance data. Genetic variation was observed for average lactation feed intake (heritability: 0.18 ± 0.04), with a significant proportion of observed variation in average intake attributable to variation in lactation length. Weight and body condition (fatness) at finishing were very highly correlated genetically (0.89 ± 0.03 and 0.90 ± 0.02) and moderately correlated phenotypically (0.58 ± 0.01 and 0.58 ± 0.01) with weight and body condition before mating. Estimates of genetic (r(g)) and phenotypic (r(p)) correlations between feed intake recorded at finishing and average lactation feed intake (LADI) were moderate (r(g) = 0.26 ± 0.16 and 0.42 ± 0.22) and low (r(p) = 0.07 ± 0.02 and 0.08 ± 0.03), with r(g) dependent on the models and data subsets used for lactation intake. Non-unity genetic correlations imply that different genetic control mechanisms regulate feed intake during growth and lactation. Moderate genetic correlations between lactation feed intake with live weight (TWT) or growth rate (TADG) recorded at selection and live weight before mating (0.42 ± 0.11, 0.42 ± 0.11 and 0.37 ± 0.15) were considerably higher than the corresponding phenotypic correlations for LADI with TADG or 29WT (0.09 ± 0.02 and 0.08 ± 0.02). Correlations between fatness at selection (TFAT) or mating (29FT) and LADI were negative but not significantly different from 0. Overall, these data suggest that there is exploitable genetic variation for feed intake during lactation, and that selection is possible if lactation feed intakes are recorded. However, genetic correlations suggest that early growth seems to be related to lactation feed intake capacity. There was generally no strong evidence that selection for lean growth potential in dam lines will substantially diminish sow lactation intake capacity as a correlated response.

Body development in sows, feed intake and maternal capacity. Part 2: gilt body condition before and after lactation, reproductive performance and correlations with lactation feed intake.

Data on sow body weight (BW) and fatness (n = ~2250 pregnant sows) and reproductive data (including historical: n = ~18 000) were used to examine the genetic and phenotypic associations between body condition before and after farrowing, gestational outcomes, lactation feed intake and the gilts' ability to survive unculled to farrow in the second parity. Within-trait genetic correlations were very high between weight (0.77 ± 0.06) and fat depth (0.91 ± 0.04) recorded before farrowing and at weaning. Litter size traits were generally uncorrelated genetically with aspects of sow BW and body condition. However, genetic correlations indicated that sows producing heavier piglets at birth had litters with increased gain (0.36 ± 0.16), and were characterised by greater weight (-0.72 ± 0.08) and fat change (-0.19 ± 0.15) during lactation, reflected to a lesser extent by lower weight (-0.12 ± 0.11) and fatness (-0.17 ± 0.10) at weaning. Genetic correlations (r(a)) between reproductive traits and lactation feed intake were generally low, but favourable. However, lactation intake was positively correlated with measures of sow size (r(a) = ~0.55), such that selection for lactation feed intake would likely be accompanied by increased mature sow size. Phenotypic correlations (r(p)) showed that sow survival to the second parity (FAR12) was positively influenced by litter size and fat depth at weaning, supporting attributes of increased fatness before farrowing, less weight loss during lactation and an increased lactation intake.

Selection to reduce residual feed intake in pigs produces a correlated response in juvenile insulin-like growth factor-I concentration.

Data from a selection experiment for residual feed intake (RFI) were used to estimate genetic correlations between measures of efficiency and performance traits with juvenile IGF-I, and to demonstrate direct and correlated responses to selection. The heritability of IGF-I was 0.28 +/- 0.06 and genetic correlations of IGF-I with feed intake (0.26 +/- 0.17), backfat (0.52 +/- 0.11), and feed conversion ratio (0.78 +/- 0.14) were moderate to large. The estimated and realized genetic correlations between RFI and IGF-I were 0.63 +/- 0.15 and 0.84. In contrast, genetic correlations between IGF-I and lifetime or test period growth did not differ (P > 0.05) significantly from zero (0.06 +/- 0.14 and -0.19 +/- 0.14). Selection for decreased RFI produced a direct response in RFI, as expected, and was accompanied by downward correlated responses in ADFI, juvenile IGF-I, backfat, and growth traits, listed in order of decreasing relative magnitude, and an increased loin muscle area. The correlated response in IGF-I to selection on RFI demonstrates that this physiological measure is genetically associated with efficiency, and is thus useful as an early information source to estimate genetic merit for efficiency before performance testing. Decreased juvenile IGF-I is associated with leaner, more efficient animals.

Sire breed comparisons for meat and eating quality traits in Australian pig populations.

Sire breed comparisons for carcase (n = 1169), meat and eating quality (n = 686) traits were obtained using data recorded on progeny of known pedigree sired by Duroc (DU), Large White (LW), Landrace (LR) and Duroc Synthetic (DS) boars from crossbred (LW/LR) sows. Animals were reared in eco-shelters in large single-sex contemporary groups and slaughtered on an age constant basis at 22 weeks of age. Compared to progeny from other sire groups, animals sired by purebred Duroc boars tended to have improved eating quality traits (higher intramuscular fat and lower shear force) at the expense of poorer carcase characteristics (higher subcutaneous and belly fat). Animals sired by DS boars tended to be heavier and leaner than those sired by LW, LR or DU boars; intramuscular fat but not belly fat was correspondingly lower, while tenderness was generally consistent with that of the DU progeny. Significant variability of sire progeny groups within sire breed suggests that sire breed selection, potentially used for improving traits such as meat quality in commercial progeny, will be less accurate in the absence of sire-specific information, which is typically poorly recorded in this class of traits.

Variance components for live weight, body measurements and reproductive traits of pair-mated ostrich females.

Estimates of genetic parameters for reproductive traits, live weight and body measurements were obtained using data from a pair-mated ostrich flock at Oudtshoorn in South Africa. Reproductive traits included total egg and chick production, along with hatchability percentage. Live weight, chest circumference and tail circumferences were recorded at the commencement and cessation of breeding. Heritability estimates (h(2)) were 0.23 for egg production, 0.20 for chick production, 0.10 for hatchability, 0.20 to 0.34 for live weight, 0.12 for chest circumference and 0.30 to 0.38 for tail circumference. Female permanent environmental effects (c(2)) amounted to 0.18 for egg production, 0.18 for chick production, 0.21 for hatchability, 0.32 to 0.36 for live weight and 0.23 to 0.32 for chest circumference. Service sire exerted significant effects only on hatchability (0.22) and subsequently chick production (0.09). Genetic correlations of reproductive traits with live weight were low to moderate, variable in sign, and did not differ significantly from zero. Correlations between live weight recorded at the beginning and end of the breeding season were unity for additive genetic and permanent environmental effects. Egg and chick production were highly correlated genetically and phenotypically, with the genetic correlation exceeding the theoretical limit. In unconstrained analyses, hatchability was positively related to chick production, including at the service sire level. Selection gains in the current flock and future generations are likely. No significant adverse relationships were found between live weight, body measurements and reproductive traits.

The heritability of the expression of two stress-regulated gene fragments in pigs.

Pigs reared in commercial production units sometimes encounter stressors that significantly decrease growth performance. It is hypothesized that response to stress challenges could potentially be used as selection criteria. This study aimed to investigate, in a commercial setting, the heritability of two target genes previously shown to be induced in response to stress, and related to growth performance, in an experimental situation. Blood samples (n = 2,392) were collected from three separate breeding lines of pedigreed and performance-tested boars between 24 to 25 wk of age. The expression levels of a novel fragment, '29a,' and the calcitonin receptor gene (CTR) were quantified using quantitative real-time PCR (qRT-PCR) on a subset (n = 709) of the blood samples. Gene expression levels were corrected for the efficiency of PCR reactions and also computed directly from threshold cycle (Ct) values. Resulting data showed a skewed nonnormal distribution of expression levels for the target genes relative to the endogenous control, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and were highly variable. Analyses were subsequently performed using untransformed and log-transformed data, with outliers identified and deleted in edited data sets. Regardless of the transformation or editing procedures for outliers applied, there was negligible genetic variation for the expression of target genes relative to GAPDH. In contrast, repeatabilities of replicate samples were generally high (between 0.54 and 0.67). Absolute expression levels for GAPDH and 29a were lowly heritable (h2 of about 0.04), although estimates did not exceed their SE. Subsetting the data according to whether the target gene had a higher or lower level of expression than GAPDH was then performed using the relevant Ct values. In the subset where the target gene was more highly expressed than GAPDH, a moderate estimate of heritability (0.18 +/- 0.10) for the log-transformed absolute expression level of 29a was obtained, whereas the estimate for its expression relative to GAPDH was lower (0.09 +/- 0.07). Estimates of heritability did not increase in the subset of low expression data. The limitations of using gene expression measures as potential selection criteria in commercial situations are discussed.