Estimation of genetic parameters for partial egg production periods by means of random regression models

We estimated genetic parameters for egg production in different periods by means of random regression models, aiming at selection based on partial egg production from a generation of layers. The production was evaluated for each individual by recording the number of eggs produced from 20 to 70 weeks of age, with partial records taken every three weeks for a total of 17 periods. The covariance functions were estimated with a random regression model by the restricted maximum likelihood method. A model composed of third-order polynomials for the additive effect, ninth-order polynomials for the permanent environment, and a residual variance structure with five distinct classes, was found to be most suitable for adjusting the egg production data for laying hens. The heritability estimates varied from 0.04 to 0.14. The genetic correlations were all positive, varying from 0.10 to 0.99. Selection applied in partial egg production periods will result in greater genetic profit for the adjacent periods. However, as the distance in time between periods increases, selection becomes less efficient. Selection based on the second period (23 to 25 weeks of age), where greater heritability was estimated, would note benefit the final egg-laying cycle periods.     

Estimation of random regression parameters

The problem of the best linear unbiased estimation (BLUE) of random regression parameters is considered. It is proved that increasing informations about the mean value of the parameters both extend the class of estimable linear functionals and improve on the estimation. In all investigated cases the uniqueness of BLUE is proved. In the case of known mean values the BLUE is shown to be numerically equivalent with the MMSEE almost everywhere. A numerical example shows the improvements of BLUE due to increasing informations about the mean values of the parameters.     

Estimation in regression models with externally estimated parameters

In many regression applications, some of the model parameters are estimated from separate data sources. Typically, these estimates are plugged into the regression model and the remainder of the parameters is estimated from the primary data source. This situation arises frequently in compartment modeling when there is an external input function to the system. This paper provides asymptotic and bootstrap-based approaches for accounting for all sources of variability when computing standard errors for estimated regression model parameters. Examples and simulations are provided to motivate and illustrate the ideas.     

Effects of Enterococcus faecalis on egg production,egg quality and caecal microbiota of hens during the late laying period

This study was conducted to determine the effects of diet supplementation of laying hens with Enterococcus faecalis (EF) on egg production, egg quality and caecal microbiota. A total of 360 Hy-Line Brown laying hens (72 weeks old) were divided into three groups with four replicates of 30 birds each. The laying hens were fed with the basal diet (Control), the basal diet + 3.75 · 10⁸ cfu EF/kg (Group I) or the basal diet + 7.5 · 10⁸ cfu EF/kg (Group II). The experiment lasted for 45 d. Eggs and caecal samples were collected at the end of the experiment. Results showed that dietary supplementation with EF did not affect the average daily egg weight, cracked egg rate, mortality and egg quality. However, EF supplementation caused a significantly increased laying rate and decreased feed/egg ratio (p < 0.05). The differences in caecal microbiota between Group II and the Control were significant. The relative abundance of Verrucomicrobia and Cyanobacteria at the phylum level, Rikenellaceae, Christensenellaceae and Veillonellaceae at the family level, and the Faecalibacterium, Christensenellaceae R-7 group and Eubacterium coprostanoligenes group at the genus level changed significantly in Group II compared with the Control (p < 0.05). In conclusion, the tested dietary supplementations with EF improved product performance and affected the caecal microbial community structure of laying hens during the late laying period.     

复合酶制剂降解黄曲霉毒素 B1对蛋鸡生产性能和蛋品质的影响

试验旨在研究葡萄糖氧化酶(Glucose Oxidase,GOD)和过氧化氢酶(catalase,CAT)复合酶制剂降解污染饲料中黄曲霉毒素B1(Aflatoxin B1,AFB1)对蛋鸡生产性能和蛋品质的影响。选用210只180日龄京粉蛋鸡,随机分为7组(CK、BA1、BA2、BA3、BD1、BD2和BD3),7个处理组分别是饲喂不添加污染玉米和复合酶的CK组,污染饲料中含有17.22,53.27和134.56μg/kg AFB1的BA1,BA2和BA3组,在有毒玉米中添加0.5%复合酶的BD1、BD2和BD3组。结果显示,蛋鸡的生产性能和蛋品质在BA1、BA2和BA3组均有不同程度下降,在BD1、BD2 3期(T1,T2和T3)和BD3组第1期(T1)均达到对照组水平,BD3组第3期与BA3组同期相比,蛋鸡月产量从9枚提高到17枚,受精蛋孵化率从41%提高到57%,蛋黄重量从14.34 g提高到15.53 g,单枚蛋重从42.39 g提高到48.49g,蛋壳厚度从0.28 mm提高到0.31 mm。由此可知,复合酶制剂基本消除或减轻了AFB1对蛋鸡生产性能和蛋品质不良影响。     

Plumage condition in laying hens: genetic parameters for direct and indirect effects in two purebred layer lines

Background

Feather pecking is a major welfare issue in laying hen industry that leads to mortality. Due to a ban on conventional cages in the EU and on beak trimming in some countries of the EU, feather pecking will become an even bigger problem. Its severity depends both on the victim receiving pecking and on its group mates inflicting pecking (indirect effects), which together determine plumage condition of the victim. Plumage condition may depend, therefore, on both the direct genetic effect of an individual itself and on the indirect genetic effects of its group mates. Here, we present estimated genetic parameters for direct and indirect effects on plumage condition of different body regions in two purebred layer lines, and estimates of genetic correlations between body regions.

Methods

Feather condition scores (FCS) were recorded at 40 weeks of age for neck, back, rump and belly and these four scores were added-up into a total FCS. A classical animal model and a direct–indirect effects model were used to estimate genetic parameters for FCS. In addition, a bivariate model with mortality (0/1) was used to account for mortality before recording FCS. Due to mortality during the first 23 weeks of laying, 5363 (for W1) and 5089 (for WB) FCS records were available.

Results

Total heritable variance for FCS ranged from 1.5% to 9.8% and from 9.8% to 53.6% when estimated respectively with the classical animal and the direct–indirect effects model. The direct–indirect effects model had a significantly higher likelihood. In both lines, 70% to 94% of the estimated total heritable variation in FCS was due to indirect effects. Using bivariate analysis of FCS and mortality did not affect estimates of genetic parameters. Genetic correlations were high between adjacent regions for FCS on neck, back, and rump but moderate to low for belly with other regions.

Conclusion

Our results show that 70% to 94% of the heritable variation in FCS relates to indirect effects, indicating that methods of genetic selection that include indirect genetic effects offer perspectives to improve plumage condition in laying hens. This, in turn could reduce a major welfare problem.     

Progesterone injection and egg production in turkey hens

An arrest in laying associated with either a polyovarian follicle (POF) or a polycystic ovarian follicle (PCOF) syndrome has been reported in turkey hens photostimulated at an early age with a constant-light photoperiod. Hens expressing the POF or PCOF syndrome had stopped laying for several weeks, but the ovary contained an increased number of mature-size and larger follicles (POF hens), which were cystic (PCOF) in some of the hens. Hens with the POF or PCOF syndrome had plasma progesterone (P(4)) concentrations that were relatively high and without surges. We hypothesized that high plasma P(4) concentrations may block ovulatory surges of LH but not the growth or maintenance of hierarchical follicles leading to development of the POF or PCOF syndrome in turkey hens. In the first six studies, hens were photostimulated with either a 14L:10D or a 24L:0D photoperiod and, after laying for 1-38 wk, were then injected daily for up to 14 days with P(4) (up to 1.50 mg kg(-1) day(-1)) and necropsied. At all ages, the oviposition rate was reduced at a P(4) dosage of 0.17 mg kg(-1) day(-1). With dosages of 0.33 mg kg(-1) day(-1) or greater, however, ovipositions stopped in most hens within approximately 2 days. For hens laying for less than 15 wk, oviductal weight and number of hierarchical follicles of P(4)-injected hens were not different from control vehicle-injected hens, but the numbers of mature, cystic, and atretic follicles were increased. For hens laying for 38 wk, when treated with P(4), oviductal weight and number of hierarchical follicles decreased, but number of atretic follicles increased. No effect of photoperiod was found on egg production, oviductal weight, or follicle number, and none of the hens developed POF or PCOF syndrome in these experiments. Two additional experiments were conducted with hens early in the reproductive period that had been photostimulated with 14L:10D or 24L:0D and injected with P(4) (0.33 mg kg(-1) day(-1)) for 10 or 12 days but not necropsied until 3 wk after the last injection. Most of the hens photostimulated with the 24L:0D photoperiod and injected with P(4), and a few of the hens photostimulated with the 14L:10D photoperiod and injected with P(4), had developed the PCOF syndrome when necropsied. The hens with the PCOF syndrome had high levels of P(4) when necropsied. From these studies, we concluded that the PCOF syndrome can be induced early in the reproduction period by photostimulating turkey hens with a 24L: 0D photoperiod, injecting them for 10 to 12 days with P(4) at a dosage of 0.33 mg kg(-1) day(-1), and then waiting 3 wk for the PCOF syndrome to develop.     

Using a feed-grade zinc propionate to achieve molt induction in laying hens and retain postmolt egg production and quality

A commercial-feed-grade form of zinc propionate was examined as a potential feed amendment at a concentration of 1% zinc to induce molt in 90-wk-old hens. Dietary treatments consisted, of 4 treatment groups of 28 birds each randomly assigned to either (1) molted conventionally by feed withdrawal, (2) 1% zinc as Zn acetate, (3) 1% zinc as Zn propionate, or (4) nonmolted control for 9 d. Ovary weights of hens fed Zn acetate or Zn propionate were not significantly different from each other, but hens fed Zn acetate or Zn propionate were significantly (p<0.05) lighter than the ovary weight of nonmolted control hens. Zinc concentrations in the kidney and liver were significantly (p<0.05) increased in both Zn acetate- and Zn propionate-molted hens when compared to either nonmolted control-fed hens or feed-withdrawal molted hens. Over the entire 3-mo postmolt period, there were no significant differences in interior or exterior egg qualities among the four treatments Egg production of hens fed Zn acetate was significantly lower than feed-withdrawal hens, Zn propionate-fed hens, or nonmolted control hens (p<0.05). The data of the current study demonstrated that feeding a feed grade of Zn propionate (1% Zn)-supplemented diet can induce molt and retain postmolt egg quality and production comparable to hens molted by feed withdrawal.     

Effects of dietary chromium and zinc on egg production, egg quality, and some blood metabolites of laying hens reared under low ambient temperature

This experiment was conducted to evaluate the effects of chromium (chromium picolinate, CrPic) and zinc (ZnSO₄·H₂O) on egg production, egg quality, and serum insulin, corticosterone, glucose, cholesterol, and total protein concentrations of laying hens reared under a low ambient temperature (6.8°C). One hundred twenty laying hens (Hy-Line; 32 wk old) were divided into 4 groups, 30 hens per group. The laying hens were fed the control diet (T1) or the control diet supplemented with either 400 μg of Cr/kg of diet (T2), 30 mg of Zn/kg of diet (T3), or 400 μg of Cr plus 30 mg of Zn/kg of diet (T4). Although the dry matter intake (DMI) was similar (p>0.05) for all treatment groups, supplemental chromium and zinc either individually or together increased live-weight change, egg production, and improved feed efficiency (p<0.05). However, no significant differences were observed between T4 and T2 or T3. Compared to T1, supplemental chromium and zinc increased egg weight, eggshell weight, eggshell thickness, egg specific gravity, and Haugh unit (p<0.05) in T2, T3, and T4 groups, among which there was no significant difference. Serum insulin concentration increased (p<0.05) and corticosterone concentration decreased (p<0.05) with dietary chromium and zinc supplementation. Serum glucose and cholesterol concentrations decreased (p<0.05) and protein concentrations increased (p<0.001) with dietary chromium and zinc supplementation in all treatment groups. The results of this study indicated that either supplemental dietary chromium or zinc increased plasma insulin and decreased corticosterone concentrations and that had a positive effect on performance of laying hens under low ambient temperature.     

Effect of Ligustrum lucidum and Schisandra chinensis on the egg production, antioxidant status and immunity of laying hens during heat stress

The experiment was conducted to evaluate the effect of two plants belonging to Chinese herbal medicines, Ligustrum lucidum (LL) and Schisandra chinensis (SC), on the laying performance, antioxidant status and immunity of hens during heat stress. The results showed that diets supplement with 1% of either LL or SC had beneficial effects on egg production and FCR of hens during heat stress (p < 0.05), compared with the control group. Either LL or SC significantly reduced malondialdehyde (MDA) concentration of heart, liver, sera and egg yolk. In addition, glutathione reductase (GR) activity of tissues and sera of the birds was significantly elevated by supplementation LL or SC. Furthermore, LL or SC supplementation significantly elevated lymphoblastogenese of the birds and the antibody values against Newcastle disease virus (NDV). The results suggest that diets supplement with 1% of either LL or SC may enhance egg production, immune function, and antioxidant status of hens during heat stress.     

Effect of Ligustrum lucidum and Schisandra chinensis on the egg production,antioxidant status and immunity of laying hens during heat stress

Abstract

The experiment was conducted to evaluate the effect of two plants belonging to Chinese herbal medicines, Ligustrum lucidum (LL) and Schisandra chinensis (SC), on the laying performance, antioxidant status and immunity of hens during heat stress. The results showed that diets supplement with 1% of either LL or SC had beneficial effects on egg production and FCR of hens during heat stress (p < 0.05), compared with the control group. Either LL or SC significantly reduced malondialdehyde (MDA) concentration of heart, liver, sera and egg yolk. In addition, glutathione reductase (GR) activity of tissues and sera of the birds was significantly elevated by supplementation LL or SC. Furthermore, LL or SC supplementation significantly elevated lymphoblastogenese of the birds and the antibody values against Newcastle disease virus (NDV). The results suggest that diets supplement with 1% of either LL or SC may enhance egg production, immune function, and antioxidant status of hens during heat stress.     

Genetic parameters for test day milk yields of first lactation Holstein cows by random regression models

Covariance components for test day milk yield using 263 390 first lactation records of 32 448 Holstein cows were estimated using random regression animal models by restricted maximum likelihood. Three functions were used to adjust the lactation curve: the five-parameter logarithmic Ali and Schaeffer function (AS), the three-parameter exponential Wilmink function in its standard form (W) and in a modified form (W*), by reducing the range of covariate, and the combination of Legendre polynomial and W (LEG+W). Heterogeneous residual variance (RV) for different classes (4 and 29) of days in milk was considered in adjusting the functions. Estimates of RV were quite similar, rating from 4.15 to 5.29 kg². Heritability estimates for AS (0.29 to 0.42), LEG+W (0.28 to 0.42) and W* (0.33 to 0.40) were similar, but heritability estimates used W (0.25 to 0.65) were highest than those estimated by the other functions, particularly at the end of lactation. Genetic correlations between milk yield on consecutive test days were close to unity, but decreased as the interval between test days increased. The AS function with homogeneous RV model had the best fit among those evaluated.     

Genetic parameters of body weight in sheep estimated via random regression and multi-trait animal models

Variance components for five consecutive measurements of body weight in Polish sheep were estimated using random regression and multi-trait animal models. The data included between 7856 and 31694 body weight records at 5 age classes from birth to 150 days of age. The random additive genetic, maternal environmental and individual permanent environmental effects were fitted. All variance components were increasing over time (not at equal rates), which reflects increasing phenotypic mean and variance with age. Direct heritability tended to increase with age, whereas the effect of dam was reduced for older ages, and the proportion of permanent environmental component was relatively stable. Generally, similar tendencies were registered for estimates obtained via multi-trait animal model. The results confirm that there is a scope for genetic improvement in growth pattern in Polish sheep.     

Multivariate parametric random effect regression models for fecundability studies

Delay until conception is generally described by a mixture of geometric distributions. Weinberg and Gladen (1986, Biometrics 42, 547-560) proposed a regression generalization of the beta-geometric mixture model where covariates effects were expressed in terms of contrasts of marginal hazards. Scheike and Jensen (1997, Biometrics 53, 318-329) developed a frailty model for discrete event times data based on discrete-time analogues of Hougaard's results (1984, Biometrika 71, 75-83). This paper is on a generalization to a three-parameter family distribution and an extension to multivariate cases. The model allows the introduction of explanatory variables, including time-dependent variables at the subject-specific level, together with a choice from a flexible family of random effect distributions. This makes it possible, in the context of medically assisted conception, to include data sources with multiple pregnancies (or attempts at pregnancy) per couple.