Retrospective: Duration and efficiency of dairy cows productive lifespan depending on age at first calving and first lactation milk productivity
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The retrospective analysis involved 562 Holstein cows, 545 Ukrainian Black-and-White dairy cows and 100 Ukrainian Red-and-White dairy cows in Breeding Station Terezyne, Kyiv region. The influence of age at first calving and first lactation milk yield on the duration and efficiency of the productive lifespan of cows was studied. The results showed that with the increase of age at first calving from less than 22 to more than 34 months there was a steady tendency to reduction in the longevity and lifetime productivity of cows. There was found a statistically significant (P <0.001) inverse correlation between the age at first calving and indicators of duration and efficiency of productive lifespan (r = –0.177…–0.459). The age at first calving determines 3.0–21.2% of the phenotypic variability of the considered indicators of duration and efficiency of the productive lifespan of cows (P <0.001). According to the set of features, the most rational is the planning of age at first calving before 26 months, i.e. heifers need to be served before 15 months of age. With the first lactation milk yield increasing, the duration and efficiency of the productive lifespan of cows increase curvilinearly. Higher longevity is typical for cows with an average 305-d milk yield in the first lactation of 6 001–8 000 kg, and higher lifetime productivity – with the highest milk yield in the first lactation (over 9 000 kg). There was found a relatively low positive correlation between 305-d milk yield in the first lactation and the parity and lifespan (r = 0.087…0.164, P <0.001) and a moderately significant relationship – with lifetime productivity and lifetime daily milk yield (r = 0.327…0.504, P <0.001). The milk yield of primiparous cows has a relatively low impact on the variability of lifespan, productive lifetime and total lactation length (ηx 2 = 3.6–5.6%, P <0.001) and a higher impact on the indicators of lifetime milk productivity and milk productivity per one day of life, productive lifetime and lactation (ηx 2 = 12.5–35.6%, P <0.001). The productive lifespan of cows with first lactation milk yield over 6 000 kg can be considered quite effective.