Molecular genetics of the adrenocortical axis and breeding for robustness

The concept of robustness refers to the combination of a high production potential and a low sensitivity to environmental perturbations. The importance of robustness-related traits in breeding objectives is progressively increasing toward the production of animals with a high production level in a wide range of climatic conditions and production systems, together with a high level of animal welfare. Current strategies to increase robustness include selection for "functional traits," such as skeletal and cardiovascular integrity, disease resistance, and mortality at various stages. It is also possible to use global evaluation of sensitivity to the environment (eg reaction norm analysis or canalization), but these techniques are difficult to implement in practice. The glucocorticoid hormones released by the adrenal cortex exert a wide range of effects on metabolism, the cardiovascular system, inflammatory processes, and brain function, for example. Protein catabolism toward energy production and storage (lipids and glycogen) supports their pivotal role in stress responses aiming at the adaptation and survival of individuals under strong environmental pressure. Large individual variations have been described in adrenocortical axis activity, with important physiopathological consequences. In terms of animal production, higher cortisol levels have negative effects on growth rate and feed efficiency and increase the fat:lean ratio of carcasses. On the contrary, cortisol has positive effects on functional traits and adaptation. Intense selection for lean tissue growth and more generally high protein output during the past decades has concomitantly reduced cortisol production, which may be responsible for the negative effects of selection on functional traits. In this paper, we review experimental evidence suggesting that the balance between production and functional traits was modified in favor of improved robustness by selecting animals with higher adrenocortical axis activity, as well as the molecular genetic tools that can be used to fine-tune this objective.     

The effects of selection of pigs on growth rate vs leanness on histochemical characteristics of different muscles

The microstructure of two type of muscles was studied in a selection experiment conducted with Dutch Large White pigs (boars and gilts) selected for either low backfat thickness (L-line) or fast growth (F-line). Second- and fourth-generation pigs were used to determine effects of selection on fiber type composition, fiber area, and capillary density in the longissimus lumborum (LL) and biceps femoris (BF) muscles. Immediately after slaughter samples were taken from the LL and BF muscles. The latter was divided into an inside (BFi) and outside (BFo) portion, which refer to the red and white portions of the biceps femoris. Serial sections were stained for ATPase (pH 4.60), succinate dehydrogenase (SDH), and alpha-amylase-periodic acid shiff (PAS) to determine fiber type and capillary density. The LL and BFo muscles had predominantly type IIBw fibers, whereas the BFi muscle had a 2 to 4 times higher amount of type I fibers. In most muscles there were more type I and fewer type IIBw fibers in F- than in L-line pigs (P < .05), except in the LL muscle of second-generation pigs and in the red part of the BF muscle of fourth-generation pigs. In both selection lines lower type I and higher type IIBw percentages were found in muscles from gilts than in those from boars (P < .05). Capillary density and fiber area of L- and F-lines showed minor differences, which could be explained by differences in weight and age of the pigs of both lines. The results suggest that selection for low backfat thickness in pig breeding compared with increased growth rate resulted in fewer oxidative and more glycolytic muscle fibers. The magnitude of the effect depended on muscle type and duration of the selection period.     

猪配套系生长性状基因效应与杂种优势的分析

测定杜长大三元杂交体系和斯格配套系各杂交组合的生长性能,计算出生长性状的杂种优势率;选用5个与生长性状紧密连锁的微卫星标记对测定个体进行基因型检测,利用混合效应线性模型计算出生长性状各位点的基因效应。结果显示:斯格配套系父母代与商品代各时期的平均日增重的差异均达到极显著水平(P<0.01),杜长大杂交体系父母代与商品代各时期的平均日增重的差异均达到显著水平(P<0.05),斯格配套系父母代和商品代与杜长大杂交体系的父母代和商品代的差异达到极显著水平(P<0.01),前期的的杂优率处于较高水平,后期及全程的杂优率不高。基因效应分析显示早期日增重的基因效应既有加性效应又有显性效应,后期日增重和全程日增重的加性效应明显,因而加性效应是日增重杂种优势的主要遗传学基础。     

乌兰察布市种猪遗传评估方案

改革开放以来,我国养猪业得到了高速发展,成为世界猪肉生产第1大国。猪肉是我国人民摄入体内动物蛋白质的主要来源,在肉食品消费中占67％左右。猪肉生产直接影响到我国人民的生活水平,随着农业结构调整,养猪业已成为增加农民收入和广大农民致富的重要手段,并逐步成为农村经济的支柱产业。     

Plasma melatonin levels in relation to the light-dark cycle and parental background in domestic pigs

To study porcine melatonin secretion in a stable environment 3 daytime (10.00-15.00) and 3 nighttime (22.00-03.00) plasma samples were collected by jugular venipuncture from 15 gilts, 16 sows, 3 boars and 48 piglets (24 females and 24 males from 8 litters) and analysed for melatonin content. Nighttime melatonin concentrations were higher than daytime melatonin concentrations (p < 0.001), whereas no effect of sampling order could be discerned. The 3 adult Hampshire boars had higher melatonin concentrations during the day and the night, than the 31 adult Yorkshire females (p < 0.05). There was no clear difference between gilts and sows in plasma melatonin. The gilts from one of the litters had higher plasma melatonin concentrations than the gilts in 3 other litters (p < 0.05). Among the 48 piglets, the increase of nocturnal melatonin secretion differed between litters (p < 0.01), whereas the influence of father was not quite significant (p = 0.12). No difference in daytime melatonin concentrations between litters could be found, and there was no difference in melatonin levels between the male and female piglets. In conclusion, this study demonstrates that domestic pigs express a nocturnal increase of melatonin secretion in a standard stable environment. For some animals the amplitude of nighttime melatonin secretion was very low, although always higher than the daytime base levels. Furthermore, the levels of nighttime melatonin secretion differed between litters, which suggests a genetic background.     

Testing genetic determinism in rate of hoof growth in pigs using Bayes Factors

Excessive growth and consequent deformity of hooves is a frequent disorder in some purebred pig populations. A test to detect possible genetic determinism related with this phenomenon was performed using the Bayes Factor (BF). Data were available for females from three purebred selection lines: Landrace (561 records), Pietrain (183) and Large White (225). Animals were scored in four categories, according to the overall growth rate of their hooves. A Bayesian analysis was performed separately for each line using a threshold model with a probit approach, and Bayes Factors between models with and without additive genetic effects were computed. Results from the three lines showed that models exhibiting genetic variability were much more probable than those that did not include a genetic component, with BF values of 312, 35 and 40 (and posterior probabilities of 0.99, 0.97 and 0.98), respectively, for the Landrace, Pietrain and Large White lines. Monte Carlo estimates of posterior means of heritabilities were medium to high (0.25, 0.41 and 0.38, respectively), and the highest posterior density region for heritability at 99% did not include zero in any of the three lines. These results allow us to conclude that genetic determinism has an important influence upon the rate of hoof growth in the pig. A potential genetic response can be achieved in the populations analysed, but further studies are needed to determine the genetic architecture of hoof growth disorders in pigs.     

Response to dietary phosphorus deficiency is affected by genetic background in growing pigs

Concern over the environmental effect of P excretion from pig production has led to reduced dietary P supplementation. To examine how genetics influence P utilization, 94 gilts sired by 2 genetic lines (PIC337 and PIC280) were housed individually and fed either a P-adequate diet (PA) or a 20% P-deficient diet (PD) for 14 wk. Initially and monthly, blood samples were collected and BW recorded after an overnight fast. Growth performance and plasma indicators of P status were determined monthly. At the end of the trial, carcass traits, meat quality, bone strength, and ash percentage were determined. Pigs fed the PD diet had decreased (P < 0.05) plasma P concentrations and poorer G:F (P < 0.05) over the length of the trial. After 4 wk on trial, pigs fed the PD diet had increased (P < 0.05) plasma 1,25(OH)(2)D(3) and decreased (P < 0.05) plasma parathyroid hormone compared with those fed the PA diet. At the end of the trial, pigs fed the PD diet had decreased (P < 0.05) BW, HCW, and percentage fat-free lean and tended to have decreased LM area (P = 0.06) and marbling (P = 0.09) and greater (P = 0.12) 10th-rib backfat than pigs fed the PA diet. Additionally, animals fed the PD diet had weaker bones and also decreased (P < 0.05) ash percentage and increased (P < 0.05) concentrations of 1alpha-hydroxylase and parathyroid hormone receptor mRNA in kidney tissue. Regardless of dietary treatment, PIC337-sired pigs consumed more feed and gained more BW than their PIC280-sired counterparts (P < 0.05) during the study. The PIC337-sired pigs also had greater (P < 0.05) HCW, larger (P < 0.01) LM area, and tended to have (P = 0.07) greater dressing percentage. Meat from the PIC337-sired pigs also tended to have greater (P = 0.12) concentrations of lactate but decreased (P = 0.07) concentrations of total glucose units 24 h postslaughter. Although plasma 1,25(OH)(2)D(3) concentrations were elevated (P < 0.05) in all the animals fed the PD diet, this elevation due to P deficiency tended (P = 0.09) to be greater in the PIC337-sired pigs after 12 wk on the treatment. The PIC337-sired pigs had stronger (P < 0.01) bones with greater ash percentage than the PIC280-sired pigs. The difference in the strength of the radii between the PIC337-sired pigs fed the PA and PD diets was greater than their PIC280-sired counterparts, which resulted in sire line x treatment interactions (P < 0.05). These data indicate differing mechanisms of P utilization between these genetic lines. Elucidating these mechanisms may lead to strategies to increase efficiency of growth in a more environmentally friendly manner.     

生猪养殖小区饲料中几种营养成分背景值的调查与思考

对生猪养殖小区三个阶段的生猪饲料的背景值进行调查,旨在为生猪的清洁生产提供决策依据。在春、夏、秋、冬每个季节分别对保育猪、育肥猪和妊娠母猪饲料进行抽样检测其粗蛋白质、总磷、铜和锌的含量。结果表明:三种生猪饲料的粗蛋白质含量均高于猪饲养标准的推荐水平;保育猪和妊娠后期母猪饲料总磷的含量基本与饲养标准推荐水平一致,而育肥猪饲料中总磷含量高于饲养标准推荐水平;三种生猪饲料的铜和锌含量均远远高于饲养标准,分别为饲养标准的9～45倍和2.7～11倍。如何给各阶段生猪提供合理营养是实现生猪清洁生产和污染变末端治理为源头控制的关键。     

Shoulder ulcers in sows are genetically correlated to leanness of young pigs and to litter weight

Abstract

The aim of this study was to estimate the heritability for shoulder ulcers (SU) and sows' body condition at weaning (BCw), and the genetic correlations between these traits and some production and reproduction traits included in the current breeding goal of sow lines. The analyses were based on data on Swedish purebred Yorkshire from nucleus as well as multiplier herds. The estimated heritabilities were for BCw 0.21, and for SU 0.13. Significant genetic correlations were found between sidefat thickness (at 100 kg) and BCw (thicker fat layer at 100 kg – better condition at weaning), between sidefat thickness and SU (thicker fat layer – less SU), between litter weight at 3 weeks and BCw (heavier litter – lower body condition) and between litter weight at 3 weeks and SU (heavier litter – more SU). The genetic correlation between BCw and SU was also significant (lower body condition – more SU).     

Evaluation of strategies for selection for lean growth rate in pigs

Lean growth rate (LGR) in pigs is a nonlinear biological function of growth rate and lean quantity. According to animal breeding theory, genetic progress for LGR is maximized with selection on a linear index of its component traits, but selection on direct EBV for LGR is also common. In this study, the performance of five criteria for selection on estimated LGR in pigs was evaluated through simulation over five generations: linear indexes of multiple-trait EBV of component traits with or without updating index weights in each generation; a nonlinear index of multiple-trait EBV of component traits; and direct selection on EBV for LGR from a single-trait model or a multiple-trait model that included LGR and component traits. The nonlinear index yielded the highest response in LGR in Generation 5, but the linear index with updating performed almost as well. Not updating weights for the linear index reduced response in LGR by 1.1% in Generation 5 (P < 0.05). Direct selection on single-trait EBV for LGR yielded the lowest responses in Generation 5. Direct selection on EBV for LGR from a multiple-trait animal model yielded a 3.1% greater response in LGR in Generation 5 than direct selection on EBV for LGR based on a single-trait animal model (P < 0.05), but yielded a 1.9% lower response than the nonlinear index. Although differences in response in LGR were limited, alternative selection criteria resulted in substantially different responses in component traits. Linear index selection for LGR placed more emphasis on lean quantity, whereas direct selection for LGR emphasized growth rate. Based on the relative changes in the responses in LGR, selection for estimated LGR based on a nonlinear index or a linear index with updating is recommended for use in the swine industry.     

Influence of genetic capacity for lean tissue growth on rate and efficiency of tissue accretion in pigs fed ractopamine.

The influence of genetic capacity for lean tissue (LT) growth on responses of pigs to ractopamine, in terms of rate and efficiency of body growth and the distribution and accretion rate of body tissues, was determined in this study. Two sources of pigs representing low and high LT genotypes were used. Within each source, two littermate barrows from each of eight litters were individually penned and given ad libitum access to a lysine-supplemented, corn-soybean meal diet (17.7% CP, 1.08% lysine) containing 0 or 20 ppm of ractopamine hydrochloride from 63 to 104 kg. Carcasses were physically dissected into muscle, fatty tissue, skin, and bone. Within each source, four additional pigs were killed for determination of initial body composition. Pigs of high LT genotype gained BW and muscle faster (P < .01), required less (P < .01) feed per unit of gain, and produced carcasses that contained more (P < .01) muscle and bone and less (P < .01) fatty tissue. Ractopamine increased (P < .01) weight gain and improved (P < .01) feed:gain ratio in both genotypes. Ractopamine enhanced the accretion rate and the amount of carcass muscle in both genotypes, but the degree of improvement was greater in pigs of the high than in those of the low LT genotype (genotype x ractopamine, P < .02). Ractopamine also reduced the accretion rate and amount of dissectible fat by a greater magnitude in the high LT genotype (genotype x ractopamine, P < .04). Based on these data, ractopamine increases muscle accretion to a greater degree in pigs with a high genetic capacity for LT growth than in those with a low capacity.     

Selection for growth rate or against back fat thickness in pigs is associated with changes in growth hormone axis plasma protein concentration and mRNA level.

Selection for increased growth rate or decreased back fat thickness results in concomitant changes in endocrine and metabolic status. Growth hormone (GH) changes in blood plasma concentration related to selection for growth rate and fat deposition were reported in pigs. The molecular mechanisms regulating selection-induced changes in GH plasma concentration remain largely unknown. We investigated selection-associated changes in GH axis parameters in 2 pig lines selected for increased growth rate (F-line), or decreased back fat thickness (L-line), respectively. First, we investigated selection-associated changes in GH pulse parameters. In both selection lines we found each generation a declining GH peak maximum concentration and area under the GH curve. GH pulse width was not associated with generation number. In both lines generation number was associated with a declined pulse interval, indicating that the number of pulses per day increased on average with 1 pulse per 24 h per generation. Second, plasma concentration of GH axis related Insulin-like growth factor-I (IGF-I) and insulin were investigated. Plasma IGF-I concentration was not associated with generation number in the F-line. Mean plasma insulin concentration declined each generation in both lines. Third, we investigated changes in GH and Pit-1 mRNA levels. In both selection lines GH and Pit-1 mRNA levels increased approximately 50% each generation. The high SD of the GH mRNA levels in both lines may suggest that the GH mRNA levels are pulsatile in vivo. We postulate a molecular mechanism that may explain how selection is associated with increased GH mRNA levels and GH pulse numbers, while lowering GH release per pulse.     

Effect of pre-weaning selection on estimates of genetic parameters and breeding values for post-weaning growth rate of beef bulls on test

Data on South African Angus cattle consisting of 45 259 records on weaning weight (WWT), 4 360 records on average daily gain from on-farm test (ADG-D) and 1 118 from centralized test (ADG-C) were analyzed to evaluate the effect of pre-weaning selection on estimates of genetic parameters and subsequent estimated breeding values (EBV) for post-weaning average daily gain. (Co)variance components and genetic parameters for weaning weight (WWT), ADG-C and ADG-D were estimated by REML procedures fitting three different animal models. Model 1 was a univariate model of WWT, ADG-C or ADG-D and did not account for the effect of pre-weaning selection on post-weaning ADG. Model 2 was a two-trait model of WWT and either ADG-C or ADG-D. Model 3 was a multi-trait animal model including WWT, ADG-C and ADG-D. Estimates of heritability for ADG-C were 0.39 ± 0.080, 0.42 ± 0.060 and 0.44 ± 0.010 from Model 1, 2 and 3 respectively. Corresponding estimates for ADG-D were 0.18 ± 0.020, 0.19 ± 0.020 and 0.21 ± 0.020 respectively. Rank correlations based on EBVs for ADG-C for all bulls were 0.92, 0.83 and 0.94 for Model 1 vs. Model 2, Model 1 vs. Model 3, and Model 2 vs. Model 3, respectively and they indicated a possible re-ranking of bulls when including or excluding a correlated pre-weaning trait. Rank correlations for ADG-D also followed a similar trend. Inclusion of pre-weaning information in genetic analysis for post-weaning average daily gain is necessary to account for selection at weaning.     

Sensitivity of the breeding values for growth rate and worm egg count to environmental worm burden in Australian Merino sheep

The objective of this study was to explore the sensitivity of breeding values for growth rate and worm egg count (WEC, cube root transformed) to environmental worm burden, measured as the average WEC for each contemporary group (CGWEC). Growth rate and WEC were measured on 7,818 naturally infected Merino lambs in eight flocks across Australia, linked through common use of AI sires. Through bivariate analysis, genetic correlations of 0.55 ± 0.23 and 0.30 ± 0.16 were found for growth rate and WEC between low and high CGWEC, respectively. In a second analysis, breeding values for growth rate and WEC were regressed on CGWEC with a random regression model. The heritability for growth rate varied from 0.23 to 0.16 from low to high CGWEC, and the heritability for WEC varied from 0.25 to 0.36. Results suggest that breeding values for both growth rate and WEC are sensitive to environmental worm burden. Animals expressed less genetic variation for growth rate and more genetic variation for WEC in high CGWEC than in low CGWEC. This form of genotype‐by‐environment interaction should therefore be considered in genetic evaluation of both growth rate and WEC, to increase the efficiency of selection for animals that are more parasite resistant and more resilient to environmental worm challenge.     

Growth rate of growing pigs is weakly correlated genetically with litter size,while the amount of genetic variation for growth rate changes with litter size

Abstract

We reasoned that if we assessed pigs for litter size and growth rate during the grow-out stage of production (25–100 kg body weight) we would find: 1) an unfavourable genetic correlation between litter size and growth rate; and 2) that the amount of additive genetic variation expressed for growth rate varies with litter size. We tested these premises by assessing 2212 litters from the Yorkshire breed for litter size, while 3038 growing pigs from 550 of these litters were assessed for growth rate during the grow-out stage of production. Genetic correlations were estimated using the additive genetic (co)variances obtained from a bivariate linear animal model fitted to litter size and growth rate. The amount of additive genetic variation expressed for growth rate as a function of litter size was estimated by fitting a univariate linear animal model with random regression on litter size. Our findings did not support the first of our premises as we found that the genetic correlation between litter size and growth rate was favourable (0.28±0.27), albeit not significantly different from zero. However, we were able to support our second premise as we found that the relationship between amount of additive genetic variation for growth rate and litter size was quadratic; the amount of additive genetic variation was highest in small and large litters (h²=0.60 and 0.65), and lowest in intermediate litter sizes (h²=0.29). These findings indicate that: 1) breeding for litter size would not reduce the growth rate of growing pigs; and 2) the amount of genetic variation for growth rate changes with litter size.     

The release of growth hormone (GH): relation to the thyrotropic- and corticotropic axis in the chicken

In the chicken and other avian species, the secretion of GH is under a dual stimulatory and inhibitory control of hypothalamic hypophysiotropic factors. Additionally, the thyrotropin-releasing hormone (TRH), contrary to the mammalian situation, is also somatotropic and equally important in releasing GH in chick embryos and juvenile chicks compared to the (mammalian) growth hormone-releasing hormone (GHRH) itself. Consequently, the negative feedback loop for GH release not only involves the insulin-like growth factor IGF-I but also thyroid hormones. In adult chickens, TRH does no longer have a clear thyrotropic activity, whereas its somatotropic activity depends on the feeding status of the animal. In addition, as in mammals, the secretion of GH and glucocorticoids is stimulated by ghrelin, a novel peptide predominantly synthesized in the gastrointestinal tract. Two chicken isoforms of the ghrelin receptor have been identified, both of which are highly expressed in the hypothalamus and pituitary, suggesting that a stimulatory effect may be directed at these levels. GH and glucocorticoids control the peripheral thyroid hormone function by down-regulating the hepatic type III deiodinating enzyme (D3) in embryos (GH and glucocorticoids) and in juvenile and adult chickens (GH). Moreover, glucocorticoids help to regulate T3-homeostasis in the brain during embryogenesis by stimulating the type II deiodinase (D2) expression. This way not only a multifactorial release mechanism exists for GH but also a functional entanglement of activities between the somatotropic-, thyrotropic- and corticotropic axis.     

浅谈楼房养猪除臭技术设计与应用

楼房养猪相较于传统平房养猪,占用面积更小,可节省用地60%以上。楼房养猪同时方便集中管理,易于采光通风和保暖;但是楼房养猪也有明显的缺点,相较于传统的平房养猪,楼房养猪作为集约化、规模化、现代化养猪的集中表现模式,建造及运营维护成本相对较高,消毒及防疫工作较为困难。高楼环境易于通风的同时,猪舍的污染问题也更加突出。猪舍给空气带来的污染不仅会影响猪舍内外的空气质量,同时还会影响猪只的繁殖、生长和发育,并将会对养殖人员与附近居民的身体健康产生重要影响。所以,必须采取相应完善的系统科学措施,处理楼房养猪中的空气除臭问题,保证生猪生活环境的清洁。文章通过结合平房养猪以及楼房养猪的特点,浅谈一下楼房养猪的除臭技术的设计与应用。