Cholesterol Deficiency Mutation HCD Does Not Impact Milk Productivity and Blood Levels of Cholesterol and Triglycerides in Russian Holstein Black and White Cattle

Abstract

A b s t r a c tThe spread of lethal and semi-lethal mutations in cattle populations results in embryonic and postembryonic mortality of calves. The use of a limited number of sires creates the danger of wide spread of genetic abnormalities. Genetic markers identify carriers of a mutation in the absence of information about phenotypic manifestations of the disease. Cholesterol deficiency mutation (HCD, haplotype cholesterol deficiency), a recessive defect of Holstein cattle, is characterized by the death of calves in the first days or months of life. The extent of this genetic defect worldwide is currently very high, 6 to 17 %. In general, there is little information about the relationship of recessive mutations with dairy cattle productivity, and data on the effect of the HCD mutation, first described in 2015, on breeding traits are extremely limited. This paper is the first to report data on a genetic study of the APOB gene region on the BTA11 chromosome and milk production indices depending on the HCD status in a Russian dairy cow population. The obtained results indicate that in the studied population the HCD mutation does not reduce the pedigree value of animals in terms of milk production and milk quality (for fat and protein). The study was performed in a breeding farm of the Leningrad region in 2017. Random sample of Holstein black and white cattle include cows (n = 451) born in 2009-2015 and the calves (n = 7) with clinical signs of diarrhea and proven HCD carriers in pedigree (sires, sires of sires). Genotyping of animals was carried out by PCR using allele specific primers. The productivity of lactation 1 and 2 (milk, yield of milk fat and protein) was studied depending on the genotypes according to HCD. The ANOVA variance analysis and calculation of means were carried out with RStudio program on the basis of a single-effect model. Estimated breeding value of milk, fat and protein yields in kg was calculated using BLUP Animal Model. The concentration of triglycerides and cholesterol was determined with an automatic biochemical analyzer RX Daytona (Randox Laboratories, UK). According to the results of the study, 35 cows (7.76 %) of those tested are the HCD carriers. Among the calves, one calf was defined as a carrier and one heifer with homozygous HCD genotype for APOB gene had all symptoms of the disease. It is established that the HCD + cows are not inferior to their peers on milk productivity. The cows with the mutant allele of the APOB gene born in 2013 significantly exceeded healthy animals: during lactation 1 by 1219 kg (p  0.01) for milking, by 13.8 kg for milk fat yield, and by 19.9 kg for milk protein yield (p  0.05); during lactation 2 by 1392 kg (p  0.001) for milking, by 44 kg (p  0.05) for milk fat yield, and by 39.8 kg for milk protein yield (p  0.01). The average estimated breeding value (EBV) of HCD carriers is 6.8 % higher in milk yield, 8.1 % in fat and 4.8 % in protein compared to HCD  animals. Monitoring of progeny of HCD carriers using Illumina Bovine IBDv3 (50k) did not reveal...