Estimating variance components and breeding values for number of oocytes and number of embryos in dairy cattle using a single-step genomic evaluation.

Reproductive technologies such as multiple ovulation and embryo transfer (MOET) and ovum pick-up (OPU) accelerate genetic improvement in dairy breeding schemes. To enhance the efficiency of embryo production, breeding values for traits such as number of oocytes (NoO) and number of MOET embryos (NoM) can help in selection of donors with high MOET or OPU efficiency. The aim of this study was therefore to estimate variance components and (genomic) breeding values for NoO and NoM based on Dutch Holstein data. Furthermore, a 10-fold cross-validation was carried out to assess the accuracy of pedigree and genomic breeding values for NoO and NoM. For NoO, 40,734 OPU sessions between 1993 and 2015 were analyzed. These OPU sessions originated from 2,543 donors, from which 1,144 were genotyped. For NoM, 35,695 sessions between 1994 and 2015 were analyzed. These MOET sessions originated from 13,868 donors, from which 3,716 were genotyped. Analyses were done using only pedigree information and using a single-step genomic BLUP (ssGBLUP) approach combining genomic information and pedigree information. Heritabilities were very similar based on pedigree information or based on ssGBLUP [i.e., 0.32 (standard error = 0.03) for NoO and 0.21 (standard error = 0.01) for NoM with pedigree, 0.31 (standard error = 0.03) for NoO, and 0.22 (standard error = 0.01) for NoM with ssGBLUP]. For animals without their own information as mimicked in the cross-validation, the accuracy of pedigree-based breeding values was 0.46 for NoO and NoM. The accuracies of genomic breeding values from ssGBLUP were 0.54 for NoO and 0.52 for NoM. These results show that including genomic information increases the accuracies. These moderate accuracies in combination with a large genetic variance show good opportunities for selection of potential bull dams.

Claw health index for Dutch dairy cattle based on claw trimming and conformation data.

The purpose of this study was to develop a model for a routine genetic evaluation of claw health traits and to develop an index including data on claw health and conformation traits. Claw health data comprised observations on 40,536 dairy cows of claw traits recorded by claw trimmers. Claw health traits scored were sole hemorrhage (SH), digital dermatitis (DD), interdigital dermatitis (ID), wall ulcer (WU), sole ulcer (SU), interdigital hyperplasia (IH), and white line disease (WL). A combined claw health trait was added as a trait to the data, combining all claw disorders. Observations on 5 feet and leg conformation traits on 41,048 animals were evaluated as predictive traits for claw health. These conformation traits were rear leg side view, rear leg rear view, foot angle, locomotion, and feet and legs. Prevalence of claw disorders ranged from 3% (WU) to 38% (SH). Overall, 69% of the animals had at least one claw disorder. Estimated heritabilities for claw health traits ranged from 0.01 (WU) to 0.13 (IH), and repeatabilities (within and across lactation) ranged from 0.15 (WU) to 0.57 (IH). Genetic correlations of claw health traits in parity 1 and parities ≥2 ranged from 0.72 to 1.00. Estimated genetic correlations among claw health traits ranged from -0.35 to 0.88 and between claw health and conformation traits ranged from -0.58 to 0.41. The breeding goal for claw health was to reduce costs due to claw disorders. The economic index for claw health, which included claw health and feet and leg conformation traits, had a reliability of 59% for an average progeny-tested bull in the Netherlands. The prevalence of claw disorders can be reduced up to 0.7% per year with selection on claw health only.

Impact of bovine somatotropin on genetic evaluation of dairy sires and cows.

Data for milk yield and bovine somatotropin (bST) injections were obtained for 92,463 lactations of 51,986 Holstein cows in 222 commercial dairy herds that had used bST during the previous 3 yr. The overall rate of bST usage in these herds was 29%, and little difference occurred across lactations. A slightly higher percentage of cows with a low pretreatment phenotypic milk yield received bST, but there was no relationship between bST usage rate and the genetic potential of the cows, as measured by the PTA for milk of the sire. The mean starting date of bST administration was 147 d of lactation. Breeding values were estimated using three different animal models. In the first model, all data regarding bST injection were ignored. The second model included a fixed effect of bST injection (0 or 1 for each lactation). In the third model, data for bST injection were used to define management groups such that cows within a particular herd, year, and season of calving that received bST during the lactation were in a different management group from their contemporaries that did not receive bST. Correlations for EBV between sire and cow either ignoring bST or treating bST as a fixed effect were > 0.999, and approximately 98% of selected individuals were chosen under both models. Use of bST information to define the management groups resulted in correlations > 0.99; the EBV from models that either ignored bST or treated bST as a fixed effect had 92 to 95% of the selected individuals chosen by the other two models. The genetic correlation between lactation milk yield with and without bST treatment, which was estimated using a multiple-trait model, was 0.98, which indicated minimal interaction of genotype and bST. In general, bST treatment had little impact on the genetic selection decisions in this study.