Bovine OPU-derived oocytes can be matured in vitro for 16-28 h with similar developmental capacity.

The aim of this study was to determine the optimal maturation culture period of ovum pick up (OPU)-derived cumulus oocytes complexes (COCs) in relation to their developmental capacity. Embryo production, embryo cryotolerance, post-transfer embryonic survival and calf characteristics such as gestation length, birthweight and sex ratio were investigated. This retrospective study covers the analyses of ovum pick up -in vitro production and calving results from a commercial programme that took place between March 1994 and September 2004. Donors were both heifers (of which approximately 90% pregnant) and cows (of which approximately 10% pregnant). Embryo production analyses were based on 7800 OPU sessions conducted from January 1995 until January 1999. Analyses of calving rate were based on 13 468 embryo transfers performed during January 1995 until May 2002. Analyses on calf characteristics were based on 2162 calves born between March 1994 and September 2004. The in vitro maturation culture period ranged from 16 to 28 h. The mean production rate of transferable embryos was 16.5% (1.2 embryos per OPU session). Length of maturation culture period did not affect the production of transferable embryos. Mean calving rate was 40.9% and 38.7% for fresh and frozen/thawed embryos, respectively. Calving rate was not affected by the maturation culture period. Mean birthweight, gestation length and proportion of male calves were 46 kg, 281.9 days and 52.8%, respectively. Maturation culture period did not affect these variables. In conclusion, this study shows that the in vitro maturation culture period within the range of 16-28 h does not affect in vitro embryo production, embryo cryotolerance, post-transfer embryonic survival and calf characteristics, suggesting that all COC batches collected by OPU on the same day, can be fertilized in one IVF session without a significant loss in the production from oocyte to calf.

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.

Use of combinations of in vitro quality assessments to predict fertility of bovine semen.

Predicting in vivo fertility of bull ejaculates using in vitro-assessed semen quality criteria remains challenging for the breeding industry. New technologies such as computer-assisted semen analysis (CASA) and flow cytometry may provide accurate and objective methods to improve semen quality control. The aim of this study was to evaluate the relationship between semen quality parameters and field fertility of bull ejaculates. A total of 153 ejaculates from 19 Holstein bulls have been analyzed using CASA (postthawing semen motility and morphology) and several flow cytometric tests, including sperm DNA integrity, viability (estimated by membrane integrity), acrosomal integrity, mitochondria aerobic functionality and oxidation. Samples were analyzed both immediately after thawing and after 4 hours at 37 °C. A fertility value (FV), based on nonreturn rate at 56 days after insemination and adjusted for environment factors, was calculated for each ejaculate. Simple and multiple regressions have been used to correlate FV with CASA and flow cytometric parameters. Significant simple correlations have been observed between some parameters and FV (e.g., straight line velocity [µm/s], r(2) = -0.12; polarized mitochondria sperm (%), r(2) = 0.07), but the relation between simple parameter and FV was too week to predict the fertility. Partial least square procedure identified several mathematical models combining flow cytometer and CASA variables and had better correlations with FV (adjusted r(2) ranging between 0.24 and 0.40 [P < 0.0001], depending on the number of included variables). In conclusion, this study suggests that quality assessment of thawed bull sperm using CASA and flow cytometry may provide a reasonable prediction of bovine semen fertility. Additional work will be required to increase the prediction reliability and promote this technology in routine artificial insemination laboratory practice.

Evaluation of classifiers that score linear type traits and body condition score using common sires.

Subjective visual assessment of animals by classifiers is undertaken for several different traits in farm livestock, e.g., linear type traits, body condition score, or carcass conformation. One of the difficulties in assessment is the effect of an individual classifier. To ensure that classifiers rank animals consistently, i.e., the repeatability between classifiers and within classifier, genetic links across routinely scored observations may be used to validate scoring of individual classifiers. Eighteen classifiers of NRS scored 18 traits, and body condition for 91,589 first-lactation heifers, daughters of 601 sires. Genetic parameters were estimated in a series of bivariate analyses. In turn, observations of each individual classifier were trait 1 and all observations of all other classifiers were grouped as trait 2. Likelihoods were used to test whether additive genetic or residual variances for each classifier (trait 1) differed significantly from the grouped records (trait 2), and to test whether the genetic correlation between trait 1 and trait 2 was significantly smaller than unity. Arbitrary criteria were set to mark traits for individual classifiers when a significant deviation was found: genetic correlations of < or = 0.40, and more than 15% deviation for the standard deviation. One classifier had relatively low heritabilities, but high genetic correlations with the others. This might indicate that the repeatability within classifier should be improved. Another classifier had high genetic correlations with the others, but his sire variances were significantly higher than average for most traits. For the genetic correlations, each classifier averaged 3.3 traits marked, ranging from 0 to 9. Overall feet and legs, rump width, central ligament, and foot angle received most marks (12 to 6 classifiers), but no disagreement existed on the definition (i.e., no mark) for body condition score, stature, rump angle, teat length, overall udder, and teat placement. These simple and cheap marks can be used in training sessions to improve the quality of the scoring system.