# Impact of apolipoprotein B-associated cholesterol deficiency genotype on milk composition, somatic cell count, and parity effects in Lithuanian Holstein cows

## TL;DR

This study examines how a cholesterol deficiency gene affects milk composition and cell count in Lithuanian Holstein cows, finding minor impacts on fat content and some lactation-related differences.

## Contribution

The study identifies the presence and effects of a cholesterol deficiency genotype in Lithuanian Holstein cows, focusing on milk traits and parity effects.

## Key findings

- Non-carriers showed marginally higher milk fat, protein, and cholesterol levels, with significant differences in fat content.
- Significant differences in milk fat, somatic cell count, and protein content were observed in specific lactation groups.
- Milk cholesterol concentration did not vary significantly across genotype groups in any lactation stage.

## Abstract

Cholesterol deficiency (CD) in Holstein cattle, caused by a loss-of-function mutation in the apolipoprotein B (APOB) gene, is a heritable autosomal recessive condition with known implications for fat metabolism and cholesterol transport. This study aimed to investigate the effect of the CD genotype on milk yield components, cholesterol concentration, and somatic cell count (SCC) in Lithuanian Holstein cows, and to determine whether lactation number modulates these relationships.

A total of 188 cows were classified by lactation: 1st (n = 44), 2nd (n = 50), 3rd and 4th (n = 60), and ≥5th (n = 34). Genotyping for the APOB mutation was conducted using allele-specific polymerase chain reaction. Milk fat, protein, lactose, and SCC were determined using LactoScope Fourier-transform infrared spectroscopy and Somascope methods, while cholesterol concentration was measured by high-performance liquid chromatography. Statistical analysis involved the Kruskal–Wallis H test due to non-normal data distribution.

The heterozygous CD genotype was identified in 17.02% of the population, with wild-type and mutant allele frequencies of 0.91 and 0.09, respectively. Non-carriers showed marginally higher fat, protein, and cholesterol levels, with a statistically significant difference in fat content (p = 0.04). When stratified by lactation, significant differences were observed for fat content in the 1st lactation group (p = 0.026), SCC in the 2nd (p = 0.038), and protein content in the 3rd (p = 0.030). No significant variation in milk cholesterol concentration was detected across genotype groups in any lactation group.

This study confirms the presence of the CD-associated APOB allele in the Lithuanian Holstein population. While CD status significantly influenced milk fat percentage, its effect on other milk composition traits and SCC was limited. Parity exhibited specific but non-consistent modulating effects. Further large-scale, longitudinal studies are warranted to elucidate the physiological underpinnings of these findings.