It is noted in the article that two main (latent) factors that determine the shape of the lactation curve can be distinguished on the basis of the Analysis of the Main Component (PCA).
Data on the origin and indices of lactation activity (n = 526) during 1-9 lactations of 113 red red steppe cows that were descendants of 6 pedigree bulls and kept in the ST “Plemreproduktov” steppe (Mykolaiv region, Ukraine) during 2001-2014 pp. was used in the study. In addition, the total hopes for 305 days of lactation (Y305) were used to study the effects of the age and the month of calving of cows on the form of their lactation curves.
High correlations were found between the level of productivity during different months of lactation. The Analysis of the Main Component (PCA), performed on the basis of the correlation matrix of tastes for M1 … M10, proves the possibility of obtaining two new variables (PC1 and PC2) describing about 80% of the variability of the output data. The first main component (PC1) describes 53.0%, while the second (PC2) describes about 26.9% of the variability of the output data, respectively. PC1 had probable and positive correlations with M3 … M9 ranging from 0.658 to 0.938, while PC2 had probable and positive correlations with M2-M3 (0.695 … 0.717), but high and negative with M9-M19 (- 0.673 … -0.661). Thus, PC1 determines the potential level of dairy productivity, while PC2 characterizes the persistence of the lactation curve (the rate of reduction in milk productivity after reaching the peak).
The PC1 had a very high correlation with Y305 (0.958; p & lt; 0.001), while PC2 was uncorrelated with total lactation thirst for 305 days (0.007; p = 0.856). The absence of a correlation between PC2 and Y305 coincides with the suggestion by some authors of the possibility of using persistence as a measure that does not depend on the level of milk productivity.
It has been established that the calving number, age and month of calving of cows are also able to change the standard shape of the lactation curve. The first-breeders had the lowest milk productivity (Y305).
The obtained results indicate that the breeding work was mainly aimed at raising the level of milk productivity, rather than on the correction of the persistence of the lactation curve.
Keyword: lactation curve, persistency, Principle Component Analysis (PCA), dairy cattle.