Additive genetic and permanent environmental variance components for test day milk traits in Black-White cattle

Genetic Parameters Estimation of Milking Traits in Polish Holstein-Friesians Based on Automatic Milking System Data

The automatic milking system (AMS) provides a large amount of information characterizing the course of each milking cow, which is not available in the conventional system. The aim of our study was to estimate heritability and genetic correlations for milk yield (MY), milking frequency (MF), and speed (MS) for 1713 Polish Holstein-Friesian primiparous cows milked in barns with an AMS. Daily heritability indicators estimated using second-order Legendre polynomials and Random Regression Models showed high variation during lactation, ranging 0.131-0.345 for MY, 0.153-0.322 for MF, and 0.336-0.493 for MS. The rates of genetic correlation between traits ranged: 0.561-0.929 for MY-MF, (-0.255)-0.090 for MF-MS, (-0.174)-0.020 for MY-MS. It is possible to carry out effective selection for milking speed, which provides an opportunity to increase the number of cows per milking robot, and thus increase the profitability of production in the herd. The results proved that selection for milk yield and daily milking frequency is also feasible. The research showed a high, positive genetic correlation between milking frequency and milk yield, which allows us to conclude that preferring breeding cows with a natural tendency to frequent visits to the milking robot should indirectly improve the genetic basis of milking.

Genetic Analysis of Milk Yield in First-Lactation Holstein Friesian in Ethiopia: A Lactation Average vs Random Regression Test-Day Model Analysis

The development of effective genetic evaluations and selection of sires requires accurate estimates of genetic parameters for all economically important traits in the breeding goal. The main objective of this study was to assess the relative performance of the traditional lactation average model (LAM) against the random regression test-day model (RRM) in the estimation of genetic parameters and prediction of breeding values for Holstein Friesian herds in Ethiopia. The data used consisted of 6,500 test-day (TD) records from 800 first-lactation Holstein Friesian cows that calved between 1997 and 2013. Co-variance components were estimated using the average information restricted maximum likelihood method under single trait animal model. The estimate of heritability for first-lactation milk yield was 0.30 from LAM whilst estimates from the RRM model ranged from 0.17 to 0.29 for the different stages of lactation. Genetic correlations between different TDs in first-lactation Holstein Friesian ranged from 0.37 to 0.99. The observed genetic correlation was less than unity between milk yields at different TDs, which indicated that the assumption of LAM may not be optimal for accurate evaluation of the genetic merit of animals. A close look at estimated breeding values from both models showed that RRM had higher standard deviation compared to LAM indicating that the TD model makes efficient utilization of TD information. Correlations of breeding values between models ranged from 0.90 to 0.96 for different group of sires and cows and marked re-rankings were observed in top sires and cows in moving from the traditional LAM to RRM evaluations.

The polymorphism in the beta4-defensin gene and its association with production and somatic cell count in Holstein-Friesian cows

The aim of this study was to find a polymorphism of the bovine beta4-defensin gene and search for its association with milk yield and composition and with the somatic cell count in milk. The data were from the years 1999 to 2004 on 212 Holstein-Friesian (HF) dairy cows, descended from 70 sires. Based on the sequence of the bovine beta4-defensin gene (GenBank no. AF008307) the primers were designed for the amplification of the 924-bp or 393-bp long fragments. The 924-bp long fragment was sequenced and the sequence was compared with that available in the GenBank. Ten putative nucleotide sequence polymorphisms were found in the intron of the bovine beta4-defensin gene. One of them, a C-->T transition at position 2239, that creates a new NlaIII (Hin1II) restriction site, was genotyped with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in a cohort of 212 HF cows. The CC genotype was the most common (72%). The heterozygous CT genotype was found in 26% of the genotyped cows and four cows (2%) were TT homozygotes. In order to determine the relationship between the polymorphism of the beta4-defensin gene and milk production traits a multi-trait repeatability test-day animal model was used. The Derivative-free Multivariate analysis program was used for computation. The differences between estimates for genotypes were checked using Student's t-test. The model included the animal genotype, year-season of calving and parity as fixed effects and the animal additive genetic effect and permanent environmental effect of individual cows as well as dates of the tests as random effects. Significant associations were found between the RFLP-NlaIII and milk fat, protein and lactose contents. Also, a significant effect was shown of the defensin genotype on the somatic cell count in the milk.

Genetic parameters for first and second lactation milk yields of Polish black and white cattle with random regression test-day models

Single- and two-trait random regression models were applied to estimate variance components of test-day records of milk, fat, and protein yields in the first and second lactation of Polish Black and White cattle. The model included fixed herd test-day effect, three covariates to describe lactation curve nested within age-season classes, and random regressions for additive genetic and permanent environmental effects. In two-parity models, each parity was treated as a separate trait. For milk and the two-parity model, heritabilities were in the range of 0.14 to 0.19 throughout first lactation and 0.10 to 0.16 throughout second lactation. For fat, heritabilities were within 0.11 to 0.16 and 0.11 to 0.22 throughout first and second lactations, respectively. For protein in the two-parity model, heritabilities were within 0.10 to 0.15 throughout most of first lactation and within 0.06 to 0.15 throughout the most of second lactation. For milk, genetic correlations between the first and second parities were 0.6 at the beginning of the lactation, rising to 0.9 in the middle, and 0.8 at the end of the lactation. For fat, the corresponding correlations were 0.6, 0.8, and 0.7, respectively, and for protein were 0.6, 0.8, and 0.8, respectively. Heritability estimates for all traits were flatter for the two-parity model. Relatively smooth genetic and permanent environmental variances with the two-parity model indicated that large swings of heritabilities could be artifacts of single-trait random regression models. High correlations between most of test day records across lactations suggested that a repeatability model could be considered as an alternative to a multiple-trait model to analyze multiple parities.