Tissue growth and development in crossbred lambs sired by ten breeds

The relative growth of carcass tissues and the partitioning of fat between depots was examined in a total of 1400 crossbred lambs from the Meat and Livestock Commission's (MLC) Ram Breed Evaluation. The evaluation was carried out over a five-year period in 10 commercial flocks of Scottish Blackface, Scotch Haltbred (Border Leicester × North Country Cheviot) and Mule (Bluefaced Leicester × Swaledale) ewes. An average of 43 sires from each of the following sire breeds was involved: Border Leicester, Dorset Down, Hampshire Down, Ile de France, North Country Cheviot, Oxford Down, Southdown, Suffolk, Texel and Wensleydale. Lambs of each cross were slaughtered over a range of 9 kg selected on the basis of estimated adult body size to cover the fatness range within which most lambs are slaughtered in Great Britain.Flocks were analysed as two groups: early flocks, from which most lambs were slaughtered before October, and late flocks. Results for early flocks are given in this Abstract. Results for late flocks were similar but they tended to fatten less quickly.Allometric growth coefficients for tissues on side (half carcass) weight were: lean, 0.77±0.015 (S.E.); total separable fat, 1.82±0.039; bone, 0.51±0.025. Perinephric and retroperitoneal fat, and subcutaneous fat, grew relatively faster than total separable fat: 1.16±0.028 and 1.16±0.011, respectively. Intermuscular fat grew relatively more slowly: 0.80±0.012. Sire breed differences were recorded (P<0.001) for the weight of each of the tissues at equal side weight. Texel crosses had the highest lean weight and Southdown crosses the lowest.At the same total lean weight, Texel crosses tended to have less lean in the loin and more in some of the other joints, especially the shoulder, than other crosses.     

Genetic parameters for various random regression models to describe the weight data of pigs

Various random regression models have been advocated for the fitting of covariance structures. It was suggested that a spline model would fit better to weight data than a random regression model that utilizes orthogonal polynomials. The objective of this study was to investigate which kind of random regression model fits best to weight data of pigs. Two random regression models that described weight of individual pigs, one using orthogonal polynomials, and the other using splines, were compared. A comparison with a multivariate model, Akaike's information criterion, and the Bayesian-Schwarz information criterion were used to select the best model. Genetic, permanent environmental, and total variances increased with age. Heritabilities for the multivariate model ranged from 0.14 to 0.19, and for both random regression models the heritabilities were fluctuating around 0.17. Both genetic and phenotypic correlations decreased when the interval between measurements increased. The spline model needed fewer parameters than the multivariate and polynomial models. Akaike's information criterion was least for the spline model and greatest for the multivariate model. The Bayesian-Schwarz information criterion was least for the polynomial model and greatest for the multivariate model. Residuals of all models were normally distributed. Based on these results, it is concluded that random regression models provide the best fit to pig weight data.     

Changes in food intake and circulating leptin due to gastrointestinal parasitism in lambs of two breeds

A reduction in food intake is a prominent feature of many infectious diseases. However, the underlying mechanisms of parasite-induced anorexia in sheep are poorly understood. Here, we tested the hypotheses (a) that the degree of parasite-induced anorexia in lambs is influenced by their growth potential and (b) that nematode infection results in elevated plasma leptin concentration in lambs. The hypotheses were tested with Suffolk x Greyface (S) and Scottish Black-face (B) lambs that are known to differ in their growth potential (S lambs are of greater growth potential than B lambs). During a primary parasite infection, 24 out of 48 lambs per breed were trickle-infected with 7,000 infective Teladorsagia circumcincta larvae per day, 3 d/wk, for a period of 12 wk (experiment I). The lambs were then dewormed, and after a 2-wk interval, half of the 24 lambs per breed that were previously infected were reinfected for another 12 wk with the same parasite and dose as used in the primary infection (experiment II). In both experiments, infected lambs were fed grass pellets for ad libitum intake, whereas noninfected lambs were fed grass pellets for either ad libitum or restricted intakes. The S lambs were more susceptible than B lambs to nematode infection, as judged from the differences in fecal egg counts (P = 0.007). Parasitized lambs of the more susceptible breed (S) showed anorexia [i.e., a decrease in intake of 13% compared with uninfected controls (P = 0.01)], whereas no significant reduction in food intake was observed in lambs of the more resistant breed (B). Reexposure to nematode infection of previously infected animals tended to result in renewed anorexia in S lambs but not in B lambs (P = 0.08) in a similar extent as during primary infection. Plasma leptin concentrations did not differ between ad libitum-fed infected and control lambs but were greater in infected than in noninfected lambs at a similar level of food intake during both the primary (P = 0.02) and the secondary parasitic infection (P = 0.004) in both breeds. The results show that leptin may be involved in the response of lambs to infection but that it is unlikely that leptin alone is responsible for the parasite-induced anorexia in lambs.     

Area use of two sheep breeds in contrasting summer alpine grazing environments in southern Norway

In Norway, approximately 2 million sheep are released for summer grazing onto highly heterogeneous outer-fields. The crossbred Norwegian White Sheep (NWS) is dominating, whereas the lighter short-tailed gregarious Spælsau (SP) is the second most abundant of the total Norwegian sheep population. We fitted 51 ewes with GPS collars in two contrasting alpine environment, Spekedalen (poor pasture) and Brathøa sauhavnelag (rich pasture), during the summer grazing seasons 2013 and 2014. We modelled breed differences in summer area use and found no significant effect of breed or pasture quality. No breed?* pasture interaction was found. Information of pasture quality and breed characteristics is vital to understand the resource–animal interplay and may prove important for sheep management.     

Population structure and genetic characterization of two native Danish sheep breeds

ABSTRACT

Genetic diversity in livestock animals has become recognized as important genetic resource for future sustainable livestock production. Especially native breeds, adapted to their local environment, are of considerable interest. Here, we report a genome-wide characterization of two native Danish sheep breeds, the Danish Landrace sheep and the Danish White-Headed Marsh sheep. We investigated the genetic diversity both at national and European breed level using a European-derived reference panel. The native Danish breeds are genetically distinct from other Nordic breeds. Their closest relatives are Border Leicester, Galway, and Texel. Apart from gene flow between native Danish breeds, Texel admixture was most dominant. For Danish Landrace sheep, a population split into two genetically distinct sub-populations was detected. Compared to other livestock species, genomic inbreeding was moderate. However, among European-derived sheep the native Danish breeds were among the 10 most inbred investigated, illustrating the need for sustainable management strategies to preserve genetic diversity.     

Performance of hair sheep composite breeds: resistance of lambs to Haemonchus contortus

This study was designed to evaluate breed differences in resistance to Haemonchus contortus in lambs. A total of 181 ewe lambs representing crossbred Dorsets (DO) and Dorpers (DP; out of 1/2-Dorset, 1/4-Rambouillet, 1/4-Finnsheep ewes) and straight-bred Katahdins (KT) were evaluated over 3 yr. An additional 144 DO, DP, KT, and Barbados Blackbelly x St. Croix (HH) wethers were evaluated over 2 yr. Lambs were weaned at 60 to 90 d of age. After deworming at about 4 mo of age, ewe lambs received approximately 10,000 infective larvae and were evaluated for parasite resistance in drylot, whereas wethers were evaluated on pasture under conditions of natural infection. Each sex was analyzed separately. Egg counts per gram of feces (FEC), log-transformed FEC (LFEC), packed cell volumes (%), and body weights (kg) measured at 3, 4, 5, and 6 wk after deworming and reinfection were analyzed. Breed influenced all traits (P < 0.05) except BW in ewe lambs and PCV in wethers. Year and week influenced (P < 0.05) all traits. At most times, DP had the highest FEC, DO had the lowest PCV, and KT and HH had lower FEC and higher PCV than either DO or DP. Clearly, Dorper sheep were not more resistant to parasites than DO, but they were able to cope with infection better by maintaining similar or higher (P < 0.05) PCV and similar BW. Katahdin and HH were more resistant, with lower FEC (P < 0.05) than DO or DP. Breed differences were more apparent when infection levels were higher; DO and DP were less affected when infection levels were low and when animals were on a better plane of nutrition. Caribbean hair sheep originated in hot, humid regions of West Africa. They and the derivative Katahdin breed seem relatively resistant to parasitism. The Dorper, in contrast, was developed in more arid regions and exhibited little parasite resistance.     

猪品种遗传多样性的研究进展

从猪品种的体型外貌、染色体带型、血型和蛋白质以及DNA分子水平等几个方面对猪的遗传多样性进行论述 ,并对遗传多样性的度量参数作了分析。认为猪种遗传多样性的研究是保种和利用的理论基础 ,从形态到DNA分子水平对猪品种遗传多样性的研究在遗传资源大量流失的今天具有重要意义。     

Genetic parameters for various random regression models to describe total sperm cells per ejaculate over the reproductive lifetime of boars

The objective of this study was to model the variances and covariances of total sperm cells per ejaculate (TSC) over the reproductive lifetime of AI boars. Data from boars (n = 834) selected for AI were provided by Smithfield Premium Genetics. The total numbers of records and animals were 19,629 and 1,736, respectively. Parameters were estimated for TSC by age of boar classification with a random regression model using the Simplex method and DxMRR procedures. The model included breed, collector, and year-season as fixed effects. Random effects were additive genetic, permanent environmental effect of boar, and residual. Observations were removed when the number of data at a given age of boar classification was < 10 records. Preliminary evaluations showed the best fit with fifth-order polynomials, indicating that the best model would have fifth-order fixed regression and fifth-order random regressions for animal and permanent environmental effects. Random regression models were fitted to evaluate all combinations of first- through seventh-order polynomial covariance functions. Goodness of fit for the models was tested using Akaike's Information Criterion and the Schwarz Criterion. The maximum log likelihood value was observed for sixth-, fifth-, and seventh-order polynomials for fixed, additive genetic, and permanent environmental effects, respectively. However, the best fit as determined by Akaike's Information Criterion and the Schwarz Criterion was by fitting sixth-, fourth-, and seventh-order polynomials; and fourth-, second-, and seventh-order polynomials for fixed, additive genetic, and permanent environmental effects, respectively. Heritability estimates for TSC ranged from 0.27 to 0.48 across age of boar classifications. In addition, heritability for TSC tended to increase with age of boar classification.     

Managing genomes of conserved livestock breeds with historical introgression to decrease genetic overlap with other breeds

Recovering the native genetic background of a breed and increasing the founder genome equivalent (FGE) that is contributed by a breed to the gene pool of the species can increase its value for conservation. The suitability of several strategies was compared, whereby a hypothetical multi‐breed population, the core set, was used to approximate the genetic diversity of the species. Twenty‐five generations of management were simulated based on genotypes of German Angler cattle. The scenarios were compared when the kinship reached 0.10. The native contribution (NC) increased in a population with 400 births per generation from 0.317 to 0.706, whereas 1,000 births enabled to reach 0.894. This scenario maximized the NC, constrained the native kinship, and the kinship of the core set so that its genetic diversity could not decrease. It increased the proportions of mainstream breeds because their genes were removed from the target breed. A substantial increase of the FGE was achieved in some other scenarios, which arose from reduced genetic overlap and from increased diversity within the breed. The latter factor is especially important for breeds with high contributions to the core set.     

Estimates of genetic parameters and selection strategies to improve the economic efficiency of postweaning growth in lambs

The objectives of this study were to estimate (co)variance components for growth and feed efficiency measures, and to compare selection strategies to improve economic efficiency of gain. Variance components for pre- and postweaning growth, body weight, and measures of feed efficiency were estimated from data collected on 1,047 Targhee lambs over 7 yr. Approximately 21 d after weaning, lambs were group-fed for 4 wk, with ad libitum access to a diet of 37% whole barley grain and 63% pelleted alfalfa hay. Lambs were then individually fed for 6 wk. Lambs were then returned to group feeding for another 4-wk period. The mean feed conversion ratio (gain/intake) for the individual feeding period was 0.11. Mean postweaning ADG for the total 14-wk feeding period was 0.26 kg. (Co)variance components were estimated from single- and two-trait animal models using REML. The selection strategies compared included direct selection, index selection, and restricted index selection. Estimates of (co)variances derived from single- and two-trait models were similar, except for mid-test body weight. Preweaning growth had a low heritability estimate (0.03 +/- 0.04) compared with postweaning growth measures (0.25 to 0.39), but all measures of growth were highly correlated (r2 > 0.98). Heritability estimates of measures of gain efficiency were variable (total feed intake = 0.39; feed conversion ratio = 0.26; residual feed intake = 0.26). Total feed intake was strongly correlated genetically with feed conversion ratio (0.79) and residual feed intake (0.77). The estimate of genetic correlation between feed conversion ratio and residual feed intake was low (0.23). Comparison of selection strategies showed the superiority of index selection (ADG, total feed, body weight) for economic improvement compared with other strategies. Economic response to direct selection for ADG was at least twice that for direct selection for feed conversion ratio or against total feed intake, and that for restricted indices (selecting against residual feed, while holding body weight and/or gain constant). Selection for ADG may be a practical approach for indirectly improving efficiency of gain in lambs.     

Genetic and environmental effects on growth to 1 year and viability of lambs from a crossbreeding study of D'man and Sardi breeds.

Genetic effects were estimated for growth to 1 yr and viability to 90 d of 882 lambs from a diallel cross of Sardi (S), D'man (D), and D'man x Sardi (DS) male and female parents. Sardi direct genetic effects were significantly higher than those of D'man for weights at birth and up to 2 mo, but the difference decreased thereafter and was in favor of D'Man at 6 mo. Sardi maternal ability was better than that of D'man for weights at all ages. Estimates of individual heterosis were small and negative for weight at birth, weight at 1 mo, and lamb viability and positive for other body weights; the estimate was significant for 12-mo weight. Estimates of maternal heterosis were small and did not approach significance for any trait. Epistatic recombination effects were generally small, but negative for all traits and significantly so for viability to 30 d. In general, the results, combined with those on reproduction and total lamb production of ewes of these groups, reported elsewhere, indicate that a population produced by inter se mating of animals 50% D, 50% S breeding is expected to have higher total lamb production than either purebred.     

Breed and sex differences in growth curves for two breeds of dog guides

A desirable dog guide weighs 18 to 32 kg as an adult. Male and female German shepherd dogs and male and female Labrador retrievers were weighed between birth and 18 mo of age, with at least one weight recorded after 290 d of age. Growth curves were constructed from 10,484 observations on 880 dogs using the Gompertz function in the form Wt = W(max)exp(-e[-(t-c)/b]), where Wt is weight at time t, Wmax is mature body weight, b is proportional to duration of growth, c is age at point of inflection, and t is age in days. Estimates for mature body weight were 2.4 +/- .3 kg higher for Labrador retrievers than for German shepherd dogs and 4.7 +/- .2 kg higher for males than for females. Male Labrador retrievers were closest to the upper limit for desirable weight, with an average estimated mature weight of 31.4 +/- .3 kg. Duration of growth, 4b + c, was not different between the breeds; however, the estimate for males was 8 +/- 5d longer than for females. Female Labrador retrievers had the shortest estimate for growth of 319 +/- 6 d. The estimate for age at the point of inflection was 3.6 +/- 1.2 d greater for males than for females, but not different between breeds. A better understanding of growth curves for dog guides may aid in estimating mature weight at a young age, thus allowing earlier breeding and training decisions to be made and increasing genetic change per year.     

Comparison of different nonlinear functions to describe Nelore cattle growth

This work aims to compare different nonlinear functions for describing the growth curves of Nelore females. The growth curve parameters, their (co)variance components, and environmental and genetic effects were estimated jointly through a Bayesian hierarchical model. In the first stage of the hierarchy, 4 nonlinear functions were compared: Brody, Von Bertalanffy, Gompertz, and logistic. The analyses were carried out using 3 different data sets to check goodness of fit while having animals with few records. Three different assumptions about SD of fitting errors were considered: constancy throughout the trajectory, linear increasing until 3 yr of age and constancy thereafter, and variation following the nonlinear function applied in the first stage of the hierarchy. Comparisons of the overall goodness of fit were based on Akaike information criterion, the Bayesian information criterion, and the deviance information criterion. Goodness of fit at different points of the growth curve was compared applying the Gelfand's check function. The posterior means of adult BW ranged from 531.78 to 586.89 kg. Greater estimates of adult BW were observed when the fitting error variance was considered constant along the trajectory. The models were not suitable to describe the SD of fitting errors at the beginning of the growth curve. All functions provided less accurate predictions at the beginning of growth, and predictions were more accurate after 48 mo of age. The prediction of adult BW using nonlinear functions can be accurate when growth curve parameters and their (co)variance components are estimated jointly. The hierarchical model used in the present study can be applied to the prediction of mature BW in herds in which a portion of the animals are culled before adult age. Gompertz, Von Bertalanffy, and Brody functions were adequate to establish mean growth patterns and to predict the adult BW of Nelore females. The Brody model was more accurate in predicting the birth weight of these animals and presented the best overall goodness of fit.     

A diallel crossing experiment with two breeds of laying fowl

Light Sussex and Brown Leghorn flocks were concurrently bred pure and crossed in both directions for 6 years in an experiment to test for genetic interactions (“nicking”) between individual sires and dams. The traits measured in survivors to 450 days of age were (i) egg production, 126–250 days, (ii) egg production, 250–450 days, (iii) egg production, 126–450 days, (iv) mature egg weight, (v) age at sexual maturity and (vi) pullet weight at 18 weeks.

There was little response to selection in the primary trait, egg production to 450 days. Crossbreds showed a degree of heterosis in averages of egg production and there were consistent reciprocal differences between crossbreds in egg weight and pullet weight. It was impossible to distinguish between sex linkage and maternal effects in the determination of these differences.

Analyses of variance were complicated by the breed difference and by heterogeneity of variances, but yielded little evidence of interaction in egg production either between sires and breed of dams or between dams and sires. Some significant interactions were noted in egg weight and pullet weight. A weighted covariance technique yielded high positive correlations between purebred and crossbred sire family means, and confirmed that genetic interactions were unimportant. Thus reciprocal recurrent selection would not have been advantageous for improving egg production of crossbreds from the two flocks.     

Response of two breeds of chickens to Ascaridia galli infections from two geographic sources

Comparative resistance to different isolates of Ascaridia galli was investigated in a local chicken breed from Jordan (LC) and in the Lohmann LSL white chicken (LW) strain. In two trials, birds of LC and LW were inoculated orally at 1-day old with 250 embryonated A. galli eggs. In the first trial a German source of A. galli was used, whereas in the second trial, a Jordan source of A. galli was used. At week 7 of infection, infected LC birds harbored significantly (P<0.05) fewer worms and excreted less A. galli eggs than infected LW birds. A. galli isolated from Jordan were less infectious than A. galli from Germany. Results suggest that the variation in genetic background between LC and LW is involved in the resistance to A. galli infection. A. galli isolates from different geographic areas differ in their ability to infect different chicken genotypes.