This study aimed to evaluate the heritability (h²) estimates of some important udder conformation traits, their relationship to each other and with production, and their phenotypic and genetic trends over a 10-year period in relatively high-yielding Holstein-Friesian cows. A total of 15,032 cows from six herds in Hungary were tested for milk (MY), butterfat (FY), and protein (PY) production yields over 305 days in first lactation. In addition, their udder conformation was scored for udder attachment (FU), rear udder height (RUH), central ligament (CL), udder depth (UD), front teat placement (FTP), and udder texture (UT) on a 1–9 linear udder score scale. REML and BLUP single-step animal model and linear regression model were used for data analysis and estimation. The production traits of the cows were quite reasonable, with 10,179.4 kg milk, 380.3 kg fat, and 333.1 kg protein in a standard lactation of 305 days. The scores of the udder conformation traits (5.4 to 6.1) were slightly above the mean of 5 on a linear scale of 1–9. The h² for MY, FY, and PY were obtained from 0.30 to 0.35, while those for udder traits were from 0.22 to 0.41. Phenotypic (rp) and genetic (rg) correlations for the relationship between production and udder conformation were weak or negligible (ranged from −0.33 to +0.15). Most of the associations between different udder traits were generally weak, but moderate positive correlations were observed between FU and UD (rp = 0.42, rg = 0.50 or 0.57), and between FU and UT (rp = 0.36, rg = 0.33 or 0.35). There were increasing genetic trends in the milk production (b = 2.2 to 16.5), but the studied udder conformation traits did not change over time (b = 0.00 to 0.03). In our study, despite an increase in milk yield over the studied ten-year period, udder conformation traits did not change. Therefore, considering that udder conformation scores were slightly above average and that udder traits were included in the selection index, we believe that it may be necessary to reconsider the udder conformation scoring system and its inclusion in the selection index.

In this study, 1,616,549 Holstein-Friesian females were genotyped for genomic evaluation of genetic merit (BVGenomic). Genotyping was performed using the EuroGenomics MD v3.0 chipset on the Illumina microarray scanner platform operated by an accredited Illumina laboratory. In addition, international and national reference populations were used for traditional BLUP breeding value (BV) estimation for both individuals (BVBLUP) and parents (BVPedigree). A single-step BLUP animal model was used for this estimation. A sample of 190 first lactation progeny cows from a single herd, reared and kept under consistent environmental conditions, was used to validate the three types of BV estimation methods. Correlation and regression analysis were used to study the association between the phenotypic performance and the results of three different estimation models. The average production of the 305-day standard lactation was 10,910.5 kg milk, 397.86 kg butterfat and 365.33 kg protein. Comparative analyses showed that BVBLUP had the highest accuracy, followed by BVGenomic, while BVPedigree was the least reliable, R² = 0.37 to 0.48; 0.09 to 0.23; 0.02 to 0.06, respectively.

By analyzing the genome of Hungarian Holstein Friesian cows, we looked for genomic regions which have an effect on the milk, fat, and protein yield. Among the sampled animals and the investigated nucleotides, nine were simultaneously associated with milk, fat, and protein yield. Among the nine variants, two had opposite effects; for example, while increasing the value of milk yield, the other one or two parameters’ values decreased. The acquired knowledge can help in the planning of breeding schemes to avoid unwanted interactions among the abovementioned yield parameters.

The objective of this study was to estimate the heritability of dairy production traits and that for dimensional traits and to calculate the correlation between the two heritability values in a Holstein Friesian cow herd bred in Hungary. Data of 15,032 Holstein Friesian cows born in the period 2008–2018 from 666 sires were collected for the study in 6 large dairy herds. Among the conformation traits, stature (ST), chest width (CW), body depth (BD), and rump width (RW), and for production traits, in the first lactation of cows, the 305-day milk yield (MY), milk butterfat yield (FY), and milk protein yield (MY) were evaluated. Heritability estimates of ST, CW, BD, and RW were 0.49, 0.25, 0.31, and 0.30, and those of MY, FY, and PY were 0.40, 0.35, and 0.30, respectively. BD and RW had no phenotypic (b = −0.01) or genetic (b = 0.00–0.01) change. The production traits (MY, FY, PY) increased to a greater extent (b = 2.2–43.3) than the examined conformation traits over time. Consequently, it is indicated that the selection for dairy production did not result in an increase in the studied dimensional traits.

Calving interval (CI) data (N = 37,263) from 17,319 cows born 2008–2018 in six herds were assessed. The data were made available by the National Association of Hungarian Holstein Friesian Breeders in Hungary. The effects of some genetic and environmental factors, population genetic parameters, breeding value (BV) of sires, and phenotypic and genetic trends of the CI were estimated. The GLM method was used for studying different effects on the CI. BLUP animal model was used for heritability (h²) and BV estimation. Linear regression analyses were applied for the trend calculation. The mean of the CI was 412.2 ± 2.0 days. The h² of the CI proved to be low (0.07 ± 0.01 and 0.08 ± 0.01). There were relatively high differences among the sires in the estimated BV. Based on the phenotypic trend calculation, the CI of cows showed decreasing direction by an average of 1.80 days per year (R² = 0.94; p < 0.01). In the case of genetic trend calculation, the average BV of sires in the CI has decreased −4.94 and −0.31 days per year (R² = 0.91 and 0.41; p < 0.01).

The conformation of dairy cows, referring to their physical form and the arrangement of body parts, plays a critical role not only physiologically but also economically. It is intricately linked to key sustainability traits such as milk production, reproduction, and longevity. Research has revealed genetic correlations between body conformation traits and first lactation milk yield ranging from 0.48 to 0.54, and correlations between fertility and type traits vary from zero to 0.79. The relationships between productive life or herd life and type traits range from –0.06 to 0.16, with negative correlations observed for characteristics such as rump angle, rear leg set, udder depth, and teat length. Larger cows with slightly positive conformation traits are associated with longer herd life. Specifically, cows with well-attached fore udders, high rear udder attachment, strong central ligaments, close front teat placement, and moderately long teats are linked to the longest functional, productive lives. The heritability estimates for conformation traits are moderate, ranging from 0.20 ± 0.047 to 0.38 ± 0.04. These correlations and heritability values highlight the need for breeders to reassess and prioritise conformation traits within Holstein dairy cow breeding programs. By revising the traits scored and incorporating new ones during selection, breeders can indirectly improve milk production, reproduction, and longevity, enhancing the sustainability of milk production. This review paper aims to summarise current official type evaluation systems for Holstein cows, underscore the significance of various conformation traits in sustainable milk production, and propose potential enhancements to the scoring system.