Gestational Caloric Restriction Alters Adipose Tissue Methylome and Offspring's Metabolic Profile in a Swine Model

Limited nutrient supply to the fetus results in physiologic and metabolic adaptations that have unfavorable consequences in the offspring. In a swine animal model, we aimed to study the effects of gestational caloric restriction and early postnatal metformin administration on offspring's adipose tissue epigenetics and their association with morphometric and metabolic variables. Sows were either underfed (30% restriction of total food) or kept under standard diet during gestation, and piglets were randomly assigned at birth to receive metformin (n = 16 per group) or vehicle treatment (n = 16 per group) throughout lactation. DNA methylation and gene expression were assessed in the retroperitoneal adipose tissue of piglets at weaning. Results showed that gestational caloric restriction had a negative effect on the metabolic profile of the piglets, increased the expression of inflammatory markers in the adipose tissue, and changed the methylation of several genes related to metabolism. Metformin treatment resulted in positive changes in the adipocyte morphology and regulated the methylation of several genes related to atherosclerosis, insulin, and fatty acids signaling pathways. The methylation and gene expression of the differentially methylated FASN, SLC5A10, COL5A1, and PRKCZ genes in adipose tissue associated with the metabolic profile in the piglets born to underfed sows. In conclusion, our swine model showed that caloric restriction during pregnancy was associated with impaired inflammatory and DNA methylation markers in the offspring's adipose tissue that could predispose the offspring to later metabolic abnormalities. Early metformin administration could modulate the size of adipocytes and the DNA methylation changes.

Genomic architecture of carcass and pork traits and their association with immune capacity

Carcass and pork traits have traditionally been considered of prime importance in pig breeding programmes. However, the changing conditions in modern farming, coupled with antimicrobial resistance issues, are raising the importance of health and robustness-related traits. Here, we explore the genetic architecture of carcass and pork traits and their relationship with immunity phenotypes in a commercial Duroc pig population. A total of nine traits related to fatness, lean content and meat pH were measured at slaughter (∼190 d of age) in 378 pigs previously phenotyped (∼70 d of age) for 36 immunity-related traits, including plasma concentrations of immunoglobulins, acute-phase proteins, leukocytes subpopulations and phagocytosis. Our study showed medium to high heritabilities and strong genetic correlations between fatness, lean content and meat pH at 24 h postmortem. Genetic correlations were found between carcass and pork traits and white blood cells. pH showed strong positive genetic correlations with leukocytes and eosinophils, and strong negative genetic correlations with haemoglobin, haematocrit and cytotoxic T cell proportion. In addition, genome-wide association studies (GWASs) pointed out four significantly associated genomic regions for lean meat percentages in different muscles, ham fat, backfat thickness, and semimembranosus pH at 24 h. The functional annotation of genes located in these regions reported a total of 14 candidate genes, with BGN, DPP10, LEPR, LEPROT, PDE4B and SLC6A8 being the strongest candidates. After performing an expression GWAS for the expression of these genes in muscle, two signals were detected in cis for the BGN and SLC6A8 genes. Our results indicate a genetic relationship between carcass fatness, lean content and meat pH with a variety of immunity-related traits that should be considered to improve immunocompetence without impairing production traits.

Incorporation of feeding behaviour traits to increase the genetic gain of feed efficiency in Pietrain pigs

Improved feed efficiency is an essential goal for the sustainability of pig production in economic and environmental terms. Traits such as feed conversion rate (FCR), residual feed intake (RFI), residual body weight gain (RG) and feeding behaviour, such as duration (TPV) and feeding rate per visit (FR) can now be measured by automatic feeding systems. The aim of this study was to evaluate the benefits of incorporating feeding behaviour traits into a selection index to improve feed efficiency in a nucleus of purebred Pietrain pigs. Data on body weight, feed intake and duration were recorded at each visit in 1608 animals. The information contained in 843,605 visits was grouped by animal ID to obtain a set of feed efficiency and feeding behaviour traits. These traits were obtained in three periods (first, second and total period). Bayesian models were built to estimate the posterior marginal distribution of the variance components. The heritabilities were between 0.44 and 0.59 for feeding behaviour traits and between 0.31 and 0.49 for feed efficiency traits. The FCR and RFI showed a considerable genetic correlation with daily feed intake (~0.65). FCR showed a genetic correlation with feeding behaviour traits, such as feed intake per visit (FPV) (0.44) and FR (0.33). Furthermore, the fast-eating pigs were less efficient. This was due to the positive genetic correlation found between the FR and the FCR (0.33) and the RFI (0.23), and the negative correlation found with the RG (-0.28). On the other hand, the inclusion of the feeding behaviour traits into a selection index slightly increased the selection response for FCR (4%) and RFI (1.8%). However, there was an increase of up to 19% in the selection response for RG and an improvement in accuracy from 0.59 to 0.70. Therefore, we concluded that it would be interesting to include feeding behaviour traits in a selection index to improve the selection response and accuracy of feed efficiency traits.

The leptin receptor gene affects piglet behavior and growth

Piglets with low birth weight present low vitality after farrowing, often leading to impaired weight gain during lactation. A recessive missense variant (C > T) for increased appetite and fatness in the porcine leptin receptor gene (rs709596309) causes a negative maternal effect on the weight of piglets at weaning. However, it is not known whether this variant already exerts an effect on the birth weight and vitality of newborn piglets and on their growing capacity during lactation. An experiment was conducted using 668 purebred Duroc piglets (131 CC, 311 CT, and 226 TT) from 74 multiparous sows (9 CC, 43 CT, and 22 TT) and 14 boars (1 CC, 10 CT, and 3 TT). All piglets were individually weighed at birth and tested for vitality, which was assessed on a scale from 1 (low vitality) to 3 (high vitality) based on behavioral observations, including the status of the piglet immediately before the test. Only non-adopted piglets were considered for piglet performance at weaning. Inferences on the effect of the genotype on birth and weaning traits were done on a Bayesian setting based on 2-trait bivariate models including the effects of the piglet and the litter, as well as the genotype of the sow and the piglet, the sex of the piglet, and the parity number. Vitality and the status of the piglet before the test were analyzed using a liability threshold (probit) model. As compared to other genotypes, TT newborn piglets were 28 g heavier, were more vital (the probability of being scored as highly vital was 6.5% higher) and were more often found suckling before the test (the probability of being suckling at test was 6.5% higher). As a result, they grew more during lactation (153 g) and were heavier at weaning (169 g) than littermates of the two other genotypes, thus partly compensating for the limited maternal capacity of TT sows. Our findings provide evidence that appetite-influencing genes, such as the leptin receptor gene, have developmental implications from very early life stages.

A Methodology to Quantify Resilience in Growing Pigs

Simple Summary

The concept of resilience can be defined as the ability of animals to maintain their productivity despite the stressors that might occur during the rearing period. Despite the growing interest in the genetic determinism of resilience and its possible inclusion in selection objectives, there is no straightforward method to measure this trait. Several quantifying methods estimate resilience based on productivity such as body weight or milk production, or non-productivity related traits such as immunity or stress responses. The objective of this study was to elaborate novel resilience indicators in growing pigs based on both productivity (body weight) and non-productivity (acute-phase proteins) related traits. We propose the deviation from the expected growth curve and the increment of the acute-phase protein haptoglobin, after applying a common vaccine, as resilience indicators in growing pigs under standard rearing conditions. We showed that the suggested resilience indicators are under a genetic control, show a substantial variability in the population, and may be improved through selection.

Abstract

There is a growing concern about the genetic determinism of resilience and its possible implementation in breeding programs. The objective of our study was to elaborate novel resilience indicators in growing pigs based on the deviation from the expected growth curve and the increment of the acute-phase protein haptoglobin (HP) after applying a common vaccine. A total of 445 pigs were vaccinated with an attenuated Aujeszky vaccine at 12 weeks of age. Deviation from the expected body weight (ΔBW) given the growth curve of unvaccinated pigs at 28 days post-vaccination (DPV) and the increment of HP at 4 DPV (ΔHP) were suggested as resilience indicators. Challenged pigs that maintained their productivity and had a minor activation of HP were deemed resilient, whereas pigs that had low ∆BW values and a high activation of HP were deemed susceptible. Pigs were also classified based on ∆BW and ∆HP relative to the expected BW at 28 DPV and to the basal level of HP, respectively. The concordance was high between both methods, indicating that ΔBW and ΔHP are not sensitive to the animal’s expected BW nor the basal level of HP. The heritability estimates were moderate for ∆BW (0.33) and low-to-moderate for ∆HP (0.16). Our study suggests ΔBW and ΔHP as novel resilience indicators in pigs. The suggested indicators capture different aspects of resilience, are easy to measure, and are genetically controlled. Thus, they may be improved through selective breeding. Further analyses are needed to validate our findings.

Antagonistic maternal and direct effects of the leptin receptor gene on body weight in pigs

Maternal effects on offspring growth can impact survival and evolution of natural and domesticated populations. Genetic correlation estimates often support a negative relationship between direct and maternal effects. However, the genetic underpinnings whereby this antagonism operates are unclear. In pigs, sow feeding status and body composition condition piglet development and growth. We hypothesized that variants in genes impacting these traits may be causative of maternal influences that could be antagonistic to the direct effects for piglet growth. A recessive missense mutation (C>T) in the porcine leptin receptor (LEPR) gene (rs709596309) has been identified as the possible causal polymorphism for increased feed intake and fatness. Using data from a Duroc line, we show that the TT sows exerted a negative impact on the body weight of their offspring at the end of the growing period of similar extent to the positive direct effect of the TT genotype over each individual. Thus, TT pigs from TT dams were about as heavy as CC and CT (C–) pigs from C–dams, but TT pigs from C–dams were around 5% heavier than C–pigs from TT dams. In contrast, body composition was only influenced by LEPR direct effects. This antagonism is due to a higher propensity of TT pigs for self-maintenance rather than for offspring investment. We show that TT pigs consumed more feed, favored fatty acid uptake over release, and produced lighter piglets at weaning than their C–counterparts. We conclude that LEPR underlies a transgenerational mechanism for energy distribution that allocates resources to the sow or the offspring according to whether selective pressure is exerted before or after weaning.

Linoleic acid metabolic pathway allows for an efficient increase of intramuscular fat content in pigs

Background

Intramuscular fat (IMF) content is a relevant trait for high-quality meat products such as dry-cured ham, but increasing IMF has the undesirable correlated effect of decreasing lean growth. Thus, there is a need to find selection criteria for IMF independent from lean growth. In pigs, the proportion of linoleic (C18:2) and arachidonic (C20:4) acids decline with fat deposition and therefore they can be considered as indicators of fatness. The aim of this research was to estimate the genetic variation for C18:2 and C20:4 in IMF and their genetic correlations with IMF and lean growth traits, with the objective to assess their potential as specific biomarkers of IMF. The analysis was conducted using a full-pedigreed Duroc resource line with 91,448 records of body weight and backfat thickness (BT) at 180 days of age and 1371 records of fatty acid composition in the muscle gluteus medius.

Results

The heritability estimates for C18:2 and C20:4 in IMF, whether expressed in absolute (mg/g of muscle) or in relative (mg/g of fatty acid) terms, as well as for their ratio (C20:4/C18:2), were high (> 0.40), revealing that the C18:2 to C20:4 pathway is subjected to substantial genetic influence. Litter effects were not negligible, with values ranging from 8% to 15% of the phenotypic variance. The genetic correlations of C18:2 and C20:4 with IMF and BT were negative (- 0.75 to - 0.66, for IMF, and - 0.64 to - 0.36, for BT), if expressed in relative values, but almost null (- 0.04 to 0.07), if expressed in absolute values, except for C18:2 with IMF, which was highly positive (0.88). The ratio of C20:4 to C18:2 also displayed a stronger genetic correlation with IMF (- 0.59) than with BT (- 0.10).

Conclusions

The amount of C18:2 in muscle can be used as an IMF-specific biomarker. Selection for the absolute amount of C18:2 is expected to deliver a similar response outcome as selection for IMF at restrained BT. Further genetic analysis of the C18:2 metabolic pathway may provide new insights into differential fat deposition among adipose tissues and on candidate genes for molecular markers targeting specifically for one of them.

The Recipients' Parity Does Not Influence Their Reproductive Performance Following Non-Surgical Deep Uterine Porcine Embryo Transfer

With the development of the non-surgical deep uterine (NsDU) embryo transfer (ET) technology, the commercial applicability of ET in pigs is now possible. There are, nevertheless, many factors that influence NsDU-ET effectiveness that need to be addressed. The aim of this study was to evaluate the effects of the weaned recipients' parity on fertility and prolificacy following NsDU-ET. The recipients (n = 120) were selected based on their reproductive history and body condition and grouped into three categories according to their parity: primiparous sows, sows of parity 2 and sows of parities from 3 to 5. Thirty fresh embryos (morulae and unhatched blastocysts) were non-surgically transferred into one uterine horn of each recipient. It was possible to insert the NsDU-ET catheter through the cervix along a uterine horn in 98.3% of the recipients. The parity had no influence on the difficulty grade of the insertions or on the percentage of correct insertions. The cervix and uterine wall were not perforated during the insertions, and vaginal discharge was not observed after transfer in any of the recipients. There were no differences in the pregnancy rates (74.8%), farrowing rates (71.2%) or litter sizes (9.6 ± 3.3) between groups. Also, there were no differences between groups regarding to the piglets' birthweights or piglet production efficiency. In conclusion, these results demonstrate that weaned sows from parity 1 to 5 are appropriate to be used as recipients in NsDU-ET programs, which increase the possibilities for the utilization of ET in the recipient farms.

Sperm quality and fertility of boar seminal doses after 2 days of storage: does the type of extender really matter?

The present approach was designed to evaluate the extender effects on sperm quality and fertility of short-term refrigerated seminal doses from Landrace boars lodged in husbandry-controlled conditions. For this purpose, we analyzed the sperm quality of seminal doses diluted in short-term (Beltsville Thawing Solution) and extra-long-term (Duragen) extenders from Days 0 to 2 of storage at 17 °C during an 8-month period. Pregnancy rates and litter size were evaluated from double inseminations within an interval of 12 hours (36 and 48 hours of refrigeration) of multiparous females using seminal doses diluted in each extender type. Sperm quality was assessed from the analyses of sperm motility and kinetics, sperm viability, expressed as plasma and acrosome membrane integrity, membrane lipid disorder, intracellular calcium levels, and acrosin activity. Results indicated significant differences between the extenders in the sperm quality of seminal doses. Therefore, the seminal doses diluted in Duragen had higher percentages of progressive motile spermatozoa and membrane-intact spermatozoa than those diluted in Beltsville Thawing Solution throughout all the experimental months. Nevertheless, despite these differences in preserving the sperm quality, pregnancy rates (>90%) and litter sizes (>10 piglets born per litter) were similar between the extenders. Our results had great relevance from a practical point of view because they reported lack of an extender effect on the reproductive performance of seminal doses during short-tem storage.

Successful non-surgical deep uterine transfer of porcine morulae after 24 hour culture in a chemically defined medium

Excellent fertility and prolificacy have been reported after non-surgical deep uterine transfers of fresh in vivo-derived porcine embryos. Unfortunately, when this technology is used with vitrified embryos, the reproductive performance of recipients is low. For this reason and because the embryos must be stored until they are transferred to the recipient farms, we evaluated the potential application of non-surgical deep uterine transfers with in vivo-derived morulae cultured for 24 h in liquid stage. In Experiment 1, two temperatures (25 °C and 37 °C) and two media (one fully defined and one semi-defined) were assessed. Morulae cultured in culture medium supplemented with bovine serum albumin and fetal calf serum at 38.5 °C in 5% CO2 in air were used as controls. Irrespective of medium, the embryo viability after 24 h of culture was negatively affected (P<0.05) at 25 °C but not at 37 °C compared with the controls. Embryo development was delayed in all experimental groups compared with the control group (P<0.001). Most of the embryos (95.7%) cultured at 37 °C achieved the full or expanded blastocyst stage, and unlike the controls, none of them hatched at the end of culture. In Experiment 2, 785 morulae were cultured in the defined medium at 37 °C for 24 h, and the resulting blastocysts were transferred to the recipients (n = 24). Uncultured embryos collected at the blastocyst stage (n = 750) were directly transferred to the recipients and used as controls (n = 25). No differences in farrowing rates (91.7% and 92.0%) or litter sizes (9.0 ± 0.6 and 9.4 ± 0.8) were observed between the groups. This study demonstrated, for the first time, that high reproductive performance can be achieved after non-surgical deep uterine transfers with short-term cultured morulae in a defined medium, which opens new possibilities for the sanitary, safe national and international trade of porcine embryos and the commercial use of embryo transfer in pigs.

An earlier uterine environment favors the in vivo development of fresh pig morulae and blastocysts transferred by a nonsurgical deep-uterine method

This study aimed to evaluate the effect of recipient-donor estrous cycle synchrony on recipient reproductive performance after nonsurgical deep-uterine (NsDU) embryo transfer (ET). The transfers (N=132) were conducted in recipients sows that started estrus 24 h before (–24 h; N=9) or 0 h (synchronous; N=31), 24 h (+24 h; N=74) or 48 h (+48 h; N=18) after the donors. A total of 30 day 5 morulae or day 6 blastocysts (day 0=onset of estrus) were transferred per recipient. The highest farrowing rates (FRs) were achieved when estrus appeared in recipients 24 h later than that in the donors (81.1%), regardless of the embryonic stage used for the transfers. The FR notably decreased (P<0.05) when recipients were –24 h asynchronous (0%), synchronous (61.3%) or +48 h asynchronous (50%) relative to the donors. No differences in litter size (LS) and piglet birth weights were observed among the synchronous and +24 h or +48 h asynchronous groups. While a +24 h asynchronous recipient was suitable for transfers performed with either morulae (FR, 74.3%; LS, 9.2 ± 0.6 piglets) or blastocysts (FR, 84.6%; LS, 9.8 ± 0.6 piglets), a + 48 h asynchronous recipient was adequate for blastocysts (FR, 87.5%; LS, 10.4 ± 0.7 piglets) but not for morulae (FR, 30.0%; LS, 7.3 ± 2.3 piglets). In conclusion, this study confirms the effectiveness of the NsDU-ET technology and shows that porcine embryos tolerate better a less advanced uterine environment if they are nonsurgically transferred deep into the uterine horn.

The effects of superovulation of donor sows on ovarian response and embryo development after nonsurgical deep-uterine embryo transfer

This study aimed to evaluate the effectiveness of superovulation protocols in improving the efficiency of embryo donors for porcine nonsurgical deep-uterine (NsDU) embryo transfer (ET) programs. After weaning (24 hours), purebred Duroc sows (2-6 parity) were treated with 1000 IU (n = 27) or 1500 IU (n = 27) of eCG. Only sows with clear signs of estrus 4 to 72 hours after eCG administration were treated with 750 IU hCG at the onset of estrus. Nonhormonally treated postweaning estrus sows (n = 36) were used as a control. Sows were inseminated and subjected to laparotomy on Days 5 to 6 (Day 0 = onset of estrus). Three sows (11.1%) treated with the highest dosage of eCG presented with polycystic ovaries without signs of ovulation. The remaining sows from nonsuperovulated and superovulated groups were all pregnant, with no differences in fertilization rates among groups. The number of CLs and viable embryos was higher (P < 0.05) in the superovulated groups compared with the controls and increased (P < 0.05) with increasing doses of eCG. There were no differences among groups in the number of oocytes and/or degenerated embryos. The number of transferable embryos (morulae and unhatched blastocysts) obtained in pregnant sows was higher (P < 0.05) in the superovulated groups than in the control group. In all groups, there was a significant correlation between the number of CLs and the number of viable and transferable embryos, but the number of CLs and the number of oocytes and/or degenerated embryos were not correlated. A total of 46 NsDU ETs were performed in nonhormonally treated recipient sows, with embryos (30 embryos per transfer) recovered from the 1000-IU eCG, 1500-IU eCG, and control groups. In total, pregnancy and farrowing rates were 75.1% and 73.2%, respectively, with a litter size of 9.4 ± 0.6 piglets born, of which 8.8 ± 0.5 were born alive. There were no differences for any of the reproductive parameters evaluated among groups. In conclusion, our results demonstrated the efficiency of eCG superovulation treatments in decreasing the donor-to-recipient ratio. Compared with nonsuperovulated sows, the number of transferable embryos was increased in superovulated sows without affecting their quality and in vivo capacity to develop to term after transfer. The results from this study also demonstrate the effectiveness of the NsDU ET procedure used, making possible the commercial use of ET technology by the pig industry.

Genetic evaluation combining purebred and crossbred data in a pig breeding scheme

Genetic evaluations using purebred data alone and combined purebred and crossbred information were performed for lean meat percentage in a pig breeding scheme. One purebred (PB) model and 2 crossbred models (CCPS1 and CCPS2) were used in the analyses. Data were obtained from the Selección Batallé S.A. Company (Riudarenes, Spain) and spanned a period of 4 yr (2006 to 2009). The data corresponded to 3 nuclei of purebred populations, Landrace (LD), Duroc (DU), and Pietrain (PI); 1 multiplying farm with animals from a 2-way cross (TB1; DU × LD); and commercial farms with animals from a 3-way cross (TB2; TB1 × PI). Genetic parameters were similar across the models, with the exception of purebred PI. The DU and LD purebreds presented large heritabilities (0.5 to 0.6) for lean meat percentage, whereas the PI purebred showed a lower heritability (approximately 0.1) for the PB model and moderate heritability for the CCPS1 and CCPS2 models (0.2 to 0.3). The mean reliability of the predicted purebred breeding values was clearly increased when the CCPS1 and CCPS2 models were used. Moreover, a reranking of the animals with important changes in the selection decisions was observed in the PI purebred. In a simulation study, the CCPS1 model achieved a greater response to selection than the PB model for the PI purebred. On another hand, between the CCPS1 and CCPS2 models, CCPS1 was slightly superior in terms of predictive ability, exhibiting a greater robustness. These results illustrate the usefulness of using crossbred models to evaluate lean meat percentage in this pig breeding scheme.

Mapping of quantitative trait loci for cholesterol, LDL, HDL, and triglyceride serum concentrations in pigs

The fine mapping of polymorphisms influencing cholesterol (CT), triglyceride (TG), and lipoprotein serum levels in human and mouse has provided a wealth of knowledge about the complex genetic architecture of these traits. The extension of these genetic analyses to pigs would be of utmost importance since they constitute a valuable biological and clinical model for the study of coronary artery disease and myocardial infarction. In the present work, we performed a whole genome scan for serum lipid traits in a half-sib Duroc pig population of 350 individuals. Phenotypic registers included total CT, TG, and low (LDL)- and high (HDL)-density lipoprotein serum concentrations at 45 and 190 days of age. This approach allowed us to identify two genomewide significant quantitative trait loci (QTL) for HDL-to-LDL ratio at 45 days (SSC6, 84 cM) and for TG at 190 days (SSC4, 23 cM) as well as a number of chromosomewide significant QTL. The comparison of QTL locations at 45 and 190 days revealed a notable lack of concordance at these two time points, suggesting that the effects of these QTL are age specific. Moreover, we have observed a considerable level of correspondence among the locations of the most significant porcine lipid QTL and those identified in humans. This finding might suggest that, in mammals, diverse polymorphisms located in a common set of genes are involved in the genetic variation of serum lipid levels.

Association of CA repeat polymorphism at intron 1 of insulin-like growth factor (IGF-I) gene with circulating IGF-I concentration, growth, and fatness in swine

Evidence is accumulating that intronic polymorphic cytosine-adenosine (CA) repeats may play a role in gene expression. In this work, we investigated whether a polymorphic CA short tandem repeat (STR) located at the first intron of the pig insulin-like growth factor I (IGF-I) gene influences plasma IGF-I concentration in pigs as well as phenotypic variation in growth and fatness traits. We measured plasma IGF-I levels at one to four time points from 35 to 215 days of age in 340 performance-tested Landrace and Duroc pigs previously genotyped for the IGF-I STR. Data were analyzed within breed with a linear mixed model with the number of CA repeats as a covariate. At least five alleles were segregating in each breed, differing in one to seven repeats. The results showed that in each breed, circulating IGF-I at 160 days of age increased with the length of the shortest allele, accounting for an average trend of 4.38 +/- 1.28 ng/ml of IGF-I per additional repeat (P = 0.001). Longer repeats were associated with early growth in Landrace boars (1.92 +/- 0.92 kg per CA at 160 days; P = 0.038) and with back fat thickness (-0.57 +/- 0.20 mm per CA; P = 0.005) and lean content (7.52 +/- 3.00 g/kg per CA at 105 kg; P = 0.013) adjusted for carcass weight in Duroc barrows, as expected from the effect of circulating IGF-I on these traits. The consistency of the results across populations supports the hypothesis that the length of the CA repeats at intron 1 of the IGF-I gene is associated with circulating IGF-I levels, and that this effect is not neutral with respect to growth and fatness.

Feeding time and feeding rate and its relationship with feed intake, feed efficiency, growth rate, and rate of fat deposition in growing Duroc barrows

Because feed is the major cost to pork production, management practices and breeding strategies are aimed at optimizing feed intake. Knowledge about the shape of feed intake and feeding behavior curves may be of interest for optimization of lean meat production. This study investigated trends based on daily measurements of feeding behavior in 200 Duroc barrows, originating from 5 sires and 200 dams, during growth. Daily values were examined between 88 and 188 d of age. Furthermore, phenotypic correlations between feeding length and feeding rate, and feeding frequency, feed intake, residual feed intake, growth rate, and rate of fat deposition were investigated for a period between 95 and 175 d of age. No differences were observed between sires for parameter estimates of a curvilinear function fitted to data on feeding length as a function of age, but the effect of sire was significant (P < 0.01) for values at individual ages up to 132 d of age. Feeding rate (feed ingested for each minute spent eating) increased in a linear fashion with age (average R(2) = 0.80) and differently so for different sires (P < 0.05 for the intercept and P < 0.01 for the regression coefficient). Because the increase in BW is linear over this time period (average R(2) = 0.99), the results suggest that feeding rate increased with increased BW and is related to the physical capacity for feed intake. Results indicate that pigs that ate faster also ate more (r = 0.29, P < 0.001), grew faster (r = 0.40, P < 0.001), and grew fatter (r = 0.28, P < 0.001), but had no greater or lower residual feed intake (r = -0.01). The linear regression slope of feeding rate on age seemed inherent to the individual and was correlated with feed intake but not with residual feed intake. Feeding length may be selected for in order to regulate absolute feed intake at different stages of growth.

The relationship between residual feed intake and feed intake behavior in group-housed Duroc barrows1

Because feed is the major input in pork production, conversion of feed into lean tissue at minimum costs has been a focus for improvement. Several researchers have proposed using residual feed intake (RFI) rather than feed conversion ratio (FCR) for genetic improvement of feed efficiency. Little is known about the variation in RFI in pigs. As several studies suggest a greater RFI is related to greater animal activity levels, the current study investigated the phenotypic relationship between RFI and feed intake (FI) behavior of 104 group-housed growing Duroc barrows allowed ad libitum access to feed. Feed intake, BW gain, feeding time (TIME), feeding frequency (VISITS), RFI, and FCR were calculated for 5 periods of 14, 23, 28, 21, or 23 d in length (periods 1 through 5, respectively) on animals that were between 73 to 95 d of age at the start of the testing period. Barrows that grew faster consumed more feed (P < 0.001), and barrows that consumed more feed were fatter (P < 0.01). There were no correlations between VISITS and TIME, between VISITS and FI, or between VISITS and RFI. Barrows that spent more time at the feeder, however, consumed more feed (P < 0.05) and had greater RFI in periods 1, 3, and 5 (P < 0.05). As expected, FI and FCR were highly correlated with RFI (P < 0.001). These results suggest that a greater FI rather than greater feed intake activity resulted in greater RFI values.