The results of the research on the influence of genetic factors on milk productivity and quality composition of milk in the cows at the state farm “Hontarivka” of the Institute of Animal Science, NAAS, Kharkiv region have been given in the article.
According to the analysis of variance the factor “line” significantly influenced all indicators of daily milk yields (р < 0,001). However, the degree of the influence of this factor was not high. The factor “line” had the greatest effect on the content of protein in milk – 2.41% and it had the least influence on the somatic cell count in milk.
When studying the average physical and chemical values of milk, it was found that the highest average daily milk yield was in the cows of the Hanover line (20.4 kg) and the lowest – in the cows of the Cavaler and Chiff lines (19.6 kg). The cows of Bella line had the best performance as for the content of fat in milk – 4.31%, while the percentage of fat in the milk of Chiff line cows was only 3.98%. The cows of Elevation line had the maximum protein content in milk (3.28%), while the cows of Hanover line had a minimum content of protein in milk – 2.96%. The milk of the animals differed by the somatic cell count, the average content of which varied from 314 000/ cm3 in the milk of cows of the Bell line to 530 000/ cm3 in the animals of the Hanover line.
Negative values of the coefficients of the correlation of daily milk yields with the content of fat (–0.225), protein (–0.305), the somatic cell count in milk (–0.134) were obtained. The positive relationship was revealed between the content of fat and protein in milk (+0.282). The low positive connection was also detected between the somatic cell count and the content of protein (+0.061) and the connection with the percentage of fat in milk was lower (+0.021). The revealed dependencies have indicated that the selection aimed at the increase in milk yield should take into consideration the content of fat and protein in milk. However, it does not exert a negative influence on such an indicator of milk quality as the somatic cell count.
By the results of the analysis of variance, it has been found that the factor “sire’ significantly influenced the daily milk yield, the content of fat and protein, the number of somatic cells in the milk of their daughters (р < 0.001). Due to the effect of this factor on the daily milk yields the following results were obtained: milk yield – 2.11%, content of fat – 4.21%, the content of protein – 8.2%, somatic cell count – 1.14%.
When comparing the average values of the parameters under investigation it has been found that the daily milk yields of some bulls ‘daughters varied from 18.9 kg to 21.2 kg of milk. The daughters of the bull K. Stallion 50750432 were the most productive by the milk yields (p < 0.001), they exceeded by 6.5 – 12.2% the daughters of the bull Chapman 0347903595, Eldorado 579136891, Dante 580024972 and Besson 393035302. As for the content of fat in milk the differences between the best and the worst parameters of the daughters of the bulls under investigation were 0.39%. In this case, the daughters of the sire Benjamin 7866444 significantly exceeded (p < 0.001) the daughters of the sires Besson 393035302 and Eldorado 579136891 by the above parameter. The daughters of the bulls B. R. Harmoni 9498163 and Prento 1402472395 were the best by the content of protein.in milk, they exceeded the daughters of the bulls Belissar 365235897 and Chapman 0347903595 by 0.27–0.35% (р < 0,001). The milk of the daughters of the above bulls was different by the somatic cell count. The average value of this parameter varied from 288 000/ cm3 in the milk of the daughters of Chapman 0347903595 to 530 000/ cm3 in the daughters of Belissar 365235897. The difference between all minimum and maximum average parameters was highly probable (P < 0.001).
If we consider the number of cases of diagnosis of mastitis in the daughters of different bulls, then it was proportional to the average values of the somatic cell count in the milk. The incidence of mastitis among the cows ranged from 11.6 ± 2.71% in the daughters of the bull Chapman 0347903595 to 22 ± 4.16% in the daughters of Belissar 365235897.
It should be noted that in accordance with the above data the difference between the parameters of the physical and chemical properties of milk and the incidence of mastitis obtained in the cows of different lines was less than that in the daughters of different sires. Therefore, it is advisable to make the assessment and selection by some sires rather than by their lineage.
Estimates of genetic trends for daily milk yield and somatic cell score of primiparous Holstein cattle in Iran
