Genetic analyses for conformation traits in South African Jersey and Holstein cattle

(Co)variance components for linear type traits of South African Jerseys and Holsteins were estimated. Heritability estimates are mostly in agreement with other studies although some estimates for the Jersey population are lower. Genetic trends for conformation traits of the South African Holstein show that cows are becoming taller and more angular, while udder traits have also improved. Teat lengths are becoming shorter in both breeds. Genetic trends of the Jersey indicate little or no selection for conformation traits, except for traits highly correlated with production, i.e. rear udder width, rear udder height and dairy form. South African Journal of Animal Science Supp 2 2004:47-4

Derivation of standard lactation curves for South African dairy cows

Standard Lactation Curves were derived for South African Holstein and Jersey cows, using 20 herd-, 18 age- and six season classes. Six herd classes were below and 13 above the average production level for both breeds. A standard lactation curve was estimated for each combination of herd-, age- and season class, which resulted in 2 160 curves per trait per breed. Variation in Holstein yields was much larger than that of Jerseys, causing different herd classes to be defined for both breeds. South African cows displayed more variation in yields compared to those of Holstein cows in the Netherlands and Ireland. Season of calving had a pronounced effect on the shape of the Standard Lactation Curve, while the combination of calving age and lactation affected both the shape and level of the curves. Expected yields were therefore higher during the whole lactation in higher compared to lower herd classes.The results of this study form the basis for inclusion of records in progress and short lactations in national genetic evaluation. Keywords: Calving age, Herd levels, Holstein, Jersey, Standard Lactation Curves, Season of calving South African Journal of Animal Science Vol.33(2) 2003: 70-7

Procedures for estimation of genetic persistency indices for milk production for the South African dairy industry

Procedures have been developed for calculation of a Persistency Index for South African dairy breeds. This index is based on the Canadian Persistency Index, which is simple and easy to understand. Data used in this study were test-day records of the first three lactations, as included in the National Dairy Genetic Evaluations of South Africa, of the Ayrshire, Guernsey, Holstein and Jersey breeds. Interpolation, using the Wilmink curve, was done on these test-day records to calculate 60-day and 280-day yields for each cow and lactation. Variance components have been estimated for these yields to be used in breeding value estimations, using bivariate evaluations and a repeatability model. To obtain independence of persistency from total milk yield, 305-day milk yield estimated breeding values were included as covariates in the genetic model for estimation of breeding values for 60- and 280-day yields. The Persistency Index will be released for sires with progeny following each national dairy genetic evaluation, allowing the South African dairy industry to select for changes in persistency in future. Keywords: Ayrshire, Guernsey, Holstein, Jersey, Repeatability model, test-day recordsSouth African Journal of Animal Science Vol. 38 (3) 2008: pp. 224-23

Breeding value estimation for somatic cell score in South African dairy cattle

Two fixed regression testday models were applied for variance component estimation and prediction of breeding values for somatic cell score, using testday records of the first three lactations of South African Holstein and Jersey cows. The first model (ML-model) considered the testdays of the different lactations as different traits in a multiple-trait animal model and the second analysis (RM-model) treated later lactation records as repeated measures of the first lactation. Heritabilities from the RM-model were more in the range of literature estimates compared to that of the ML-model, i.e. 0.19 + 0.003 for the Holstein breed and 0.18 + 0.003 for the Jersey breed. Rank correlations indicated that minor changes occur in the ranking of proven sires between breeding values obtained from the ML- and RM-models. Although genetic correlations between parities are not unity, the RM-model estimates more competitive variances and requires extensively less computer time to predict breeding values compared to the ML-model and are therefore recommended for breeding value estimation on a national basis. South African Journal of Animal Science Supp 2 2004: 32-3

Test-day models for South African dairy cattle for participation in international evaluations

Variance components and breeding values of production traits and somatic cell score of South African Guernsey, Ayrshire, Holstein and Jersey breeds have been estimated using a multi-lactation repeatability test-day model, including tests of the first three lactations as repeated measures and fitting the permanent environmental effect across lactations. Multitrait evaluations were done for the production traits (milk, butterfat and protein) and single trait evaluations for somatic cell score. Heritability estimates were comparable with yield and somatic cell score estimates obtained by test-day models from other countries (17-24% for milk yield; 10-13% for butterfat yield; 14-19% for protein yield and 6-8% for somatic cell score). Proofs of qualifying sires were sent to the International Bull Evaluation Service (INTERBULL) for participation in the March 2005 test runs. Genetic correlations between South Africa and other participating countries, estimated by INTERBULL, compared well with those amongst the other participating countries. Trend validation tests were successful using this methodology for all traits and breeds except for somatic cell score of the Guernsey breed, due to insufficient data for this trait. South Africa can now participate in routine INTERBULL evaluations to obtain Multiple Across Country Evaluation (MACE) breeding values, using this methodology. South African Journal of Animal Science Vol. 36(1) 2006: 58-7

Comparison of breeding values and genetic trends for production traits estimated by a Lactation Model and a Fixed Regression Test-day Model

A comparison of breeding values and genetic trends of production traits from two models is made. One set of breeding values and trends was estimated by the September/October 2003 South African National Genetic Evaluation, using a Lactation Model (LM). The other set was obtained in the 2004 South African National Genetic Evaluation, using a Fixed Regression Test-day Model (TDM). This comparison is made for Ayrshire, Guernsey, Holstein and Jersey cows participating in the South African Dairy Animal Improvement Scheme. Specific differences between the two models were documented, with differences in statistical methodology and inclusion of test-day records of the first three parities in the TDM vs. only first lactation 305-day yields in the LM, as the main differences. Significant reranking of especially cows and unproven sires occurred between the models. Genetic trends of the TDM were not as steep as those from the LM, as the trait that was selected was first lactation yield, while the TDM trends reflect genetic progress over the first three parities. South African Journal of Animal Science Vol. 36(2) 2006: 71-7

Adjustment of heterogenous variances and a calving year effect in test-day models for national genetic evaluation of dairy cattle in South Africa

South Africa implemented test-day models for genetic evaluations of production traits, using a Fixed Regression Test-Day Model (FRTDM), which assumes equal variances of the response variable at different days in milk, the explanatory variable. Data at the beginning and at the end of lactation period, have higher variances than tests in the middle of the lactation. Furthermore, first lactations have lower mean and variances compared to second and third lactations. This is a deviation from the basic assumptions required for the application of repeatability models. A modification was therefore implemented to reduce the effect of deviating from this assumption. Test-day milk, butterfat and protein yield records of Jersey cows, participating in the South African Milk Recording Scheme, were therefore pre-adjusted such that the variances are on the same scale. Variance components estimated using the adjusted records were higher than using unadjusted records. Convergence of breeding value estimation is reached significantly faster when using adjusted data (± 4000 iterations) compared to unadjusted records (± 15 000 iterations). Although cow and bull rankings were not influenced much, significant changes in breeding values for individual animals and genetic trends of especially young animals, were found. South African Journal of Animal Science Vol. 36(3) 2006: 165-17

Rate of inbreeding and effective population size in four major South African dairy cattle breeds

Pedigree information on the registered South African Ayrshire (n = 47 116), Guernsey (n = 18 766), Holstein (n = 892 458) and Jersey (n = 314 403) breeds was analyzed to determine the rate of inbreeding and effective population sizes for the period 1960 to 2003. Inbreeding coefficients were calculated using the Animal Breeder's Tool Kit. The mean inbreeding coefficients for 2003 were 2.02%, 2.04%, 2.30%, and 3.05% for the Ayrshire, Guernsey, Holstein and Jersey, respectively. The corresponding rates of inbreeding per year were 0.05%, 0.05%, 0.06%, and 0.07% indicating that inbreeding is accumulating at a slightly higher rate in Jersey compared to the other three breeds. However, the rates of inbreeding in the current study are still considerably lower than the acceptable rate of less than 0.5% per year. Estimates of effective population sizes were 148, 165, 137, and 108 for the Ayrshire, Guernsey, Holstein and Jersey, respectively. Results indicate that the impact of inbreeding on genetic variability is still minimal. However, the impact of inbreeding on phenotypic performance on traits of economic importance was not investigated in the current study and should therefore receive future consideration. South African Journal of Animal Science Vol. 36(1) 2006: 50-5

Emotion Coregulation in Mother-Child Dyads: A Dynamic Systems Analysis of Children with and without Autism Spectrum Disorder

Few studies have investigated patterns of emotion coregulation in families of children with Autism Spectrum Disorder (ASD) or contrasted the ways in which their emotion coregulation patterns differ from families of typically developing (TD) children. To address this gap, we used a dynamic systems approach to compare flexible structure and emotional content of coregulation between mothers and children (3-7 years) with ASD (n = 47) and TD children (n = 26). Mother-child play interactions in the home were videotaped and emotion-engagement states were coded in micro-level 5-s intervals based on behavioral and affective expressions. Analyses indicated that mother-child dyads in the ASD group spent more time than dyads in the TD group in mismatched emotion-engagement states (e.g., child negative/mother positive), and children with ASD spent more time than TD children engaged exclusively with objects. Mother-child dyads in the TD group stayed longer in mutual positive engagement states. Compared to dyads in the TD group, mother-child dyads in the ASD group exhibited greater flexibility (i.e., a wider range of emotional-engagement states, more frequent changes in states, and less time in each state). These findings suggest that mothers and their children with ASD do not sustain dyadic positive engagement patterns in a low-stress environment. Findings confirmed the preference of children with ASD for objects over social partners, even when they are at home with their mothers, and elucidated a challenging mother-child interactional style. Results have implications for mother-child interventions aimed at regulating negative emotional states and sustaining positive ones in families raising children with ASD