Genetic parameters were estimated for egg defects, egg production, and egg quality traits. Eggs from 11,738 purebred brown-egg laying hens were classified as salable or as having one of the following defects: bloody, broken, calcium deposit, dirty, double yolk, misshapen, pee-wee, shell-less, and soft shelled. Egg quality included albumen height, egg weight, yolk weight, and puncture score. Body weight, age at sexual maturity, and egg production were also recorded. Heritability estimates of liability to defects using a threshold animal model were less than 0.1 for bloody and dirty; between 0.1 and 0.2 for pee-wee, broken, misshapen, soft shelled, and shell-less; and above 0.2 for calcium deposit and double yolk. Quality and production traits were more heritable, with estimates ranging from 0.29 (puncture score) to 0.74 (egg weight). High-producing hens had a lower frequency of egg defects. High egg weight and BW were associated with an increased frequency of double yolks, and to a lesser extent, with more shell quality defects. Estimates of genetic correlations among defect traits that were related to shell quality were positive and moderate to strong (0.24–0.73), suggesting that these could be grouped into one category or selection could be based on the trait with the highest heritability or that is easiest to measure. Selection against defective eggs would be more efficient by including egg defect traits in the selection criterion, along with egg production rate of salable eggs and egg quality traits.
The fertility of a chicken's egg is a trait which depends on both the hen that lays the egg and on her mate. It is also known that fertility of an individual changes over the laying period. Longitudinal models including both random genetic and permanent environmental effects of both the female and her male mate were used to model the proportion of fertile eggs in a pedigree broiler population over the ages 29-54 weeks. Both the male and the female contribute to variation in fertility. Estimates of heritability of weekly records were typically 7% for female and 10% for male contributions to fertility. Repeatability estimates ranged from 24 to 33%, respectively. The estimated genetic variance remained almost constant for both sexes over the laying period and the genetic correlations between different ages were close to 1.0. The permanent environment components increased substantially towards the end of the analyzed period, and correlations between permanent environment effects at different ages declined with increasing age difference The heritability of mean fertility over the whole laying period was estimated at 13% for females and 17% for males. A small positive correlation between genetic effects for male and female fertility was found. Opportunities to improve fertility in broiler stocks by selection on both sexes exist and should have an impact throughout the laying period.
There is an intricate relationship between milk production, fertility and survival of cows, which is further confounded by management decisions on the farm. Holsteinization and selection for high milk production can be associated with reduction in cow fertility (Pryce et al., 1998; Silvia, 1998; Harris and Winkelman, 2000) because of its impact on physiological factors affecting reproduction such as energy balance, ovarian function, heat detection and conception in dairy cows (Buckley et al., 2000; Snijders et al., 2001; Westwood et al., 2002).
The effect of pregnancy on milk yield and composition has long been recognised (Erb, 1952), yet it is not currently directly accounted for in genetic evaluations. In the UK, total lactation yields are adjusted for the effect of calving interval (CI) with adjustment factors (Brotherstone, 1987) which assume a constant effect across gestation stage (GS). The effect of pregnancy however varies with gestation stage (Coulon, 1995) and is different from the effect of CI. In genetic evaluation based on test day models, it is essential to account for the direct effect of pregnancy specific to individual records. The objective of this study was to estimate the effect of gestation stage on daily milk yield and its components in first lactation.
The effect of assuming a constant residual (measurement) error structure in the analysis of test day milk records with a random regression model was investigated. Additive genetic and permanent environmental covariance components were each modelled with a 3 order orthogonal polynomial regression while measurement error was allowed to be either constant in all or some stages of lactation, or to vary from stage to stage. Coefficients of the covariance functions and residual variance components were jointly estimated by restricted maximum likelihood using the DFREML software package. There were significant increases (P<0.05) in the log-likelihood which suggests improvement in the fit of the derived covariance function as the constraint on residual error variance was removed. There was, however, little difference in estimates of the other variance components. Residual error was high in early lactation and declined rapidly to a stable value in mid/late lactation, so with a constant error assumption, residual variance was underestimated and heritability overestimated in early lactation.
The MOET open herd operated by Genus is an open-nucleus breeding programme, designed to identify superior families and individual females. The herd of 250 cows was established over the period 1987-1990, with embryos from high genetic merit dams in North America. Subsequently, replacement heifers have been bred both from donors selected within the nucleus herd, and from external donors. The herd is milked three times a day, and fed a high-quality complete diet, to maximise production and so facilitate selection. Average NMR 305 day production figures for 440 heifers were 8995 kg, at 3.88% and 3.41% protein. A relatively high proportion of the herd is kept open for embryo production, with 40% of these heifers milking beyond 400 days and 13% for over 500 days. Data from the MOET project are currently being used to model production up to and beyond 305 days, and to establish correlations between performance in early and extended lactations and between lactation length and subsequent performance. These results will be discussed in the context of options for calving interval available to high production-high genetic potential Holstein Friesian herds.
Presently, the national evaluation for fertility in Ireland is carried out for calving interval and survival using a 13 trait animal model. Breeding values are predicted from a joint analysis of calving interval, survival and milk yield in the first 3 lactations and 4 linear type traits (Angularity, Body condition score, Foot Angle and Udder depth) as predictors of calving interval and survival (Olori et al., 2002 and Pool et al., 2002).
The cuticle is an invisible glycosylated protein layer that covers the outside of the eggshell and forms a barrier to the transmission of microorganisms. Cuticle-specific staining and in situ absorbance measurements have been used to quantify cuticle deposition in several pure breeds of chicken. For brown eggs, a pre-stain and a post-stain absorbance measurement is required to correct for intrinsic absorption by the natural pigment. For white eggs, a post-stain absorbance measurement alone is sufficient to estimate cuticle deposition. The objective of the research was to estimate genetic parameters and provide data to promote adoption of the technique to increase cuticle deposition and reduce vertical transmission of microorganisms. For all pure breeds examined here, i.e. Rhode Island Red, two White Leghorns, White Rock and a broiler breed, the estimate of heritability for cuticle deposition from a meta-analysis was moderately high (0.38 ± 0.04). In the Rhode Island Red breed, the estimate of the genetic correlation between measurements recorded at early and late times during the egg-laying period was ~ 1. There was no negative genetic correlation between cuticle deposition and production traits. Estimates of the genetic correlation of cuticle deposition with shell color ranged from negative values or 0 in brown-egg layers to positive values in white- or tinted-egg layers. Using the intrinsic fluorescence of tryptophan in the cuticle proteins to quantify the amount of cuticle deposition failed because of complex quenching processes. Tryptophan fluorescence intensity at 330 nm was moderately heritable, but there was no evidence of a non-zero genetic correlation with cuticle deposition. This was complicated furthermore by a negative genetic correlation of fluorescence with color in brown eggs, due to the quenching of tryptophan fluorescence by energy transfer to protoporphyrin pigment. We also confirmed that removal of the cuticle increased reflection of ultraviolet wavelengths from the egg. These results provide additional evidence for the need to incorporate cuticle deposition into breeding programs of egg- and meat-type birds in order to reduce vertical and horizontal transmission of potentially pathogenic organisms and to help improve biosecurity in poultry.
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