Impact of age at first calving on performance and economics in commercial dairy herds in Argentina

Dairy herd efficiency depends on an adequate replacement program, and one of the main management factors affecting the replacement cost is age at first calving (AFC). The primary objective of this study was to evaluate the impact of AFC on performance and economic results in commercial dairy herds in Argentina. A retrospective study was conducted to analyze data from a total of 26,614 first lactation cows from 290 argentinian dairy farms calved for the first time during the calendar year 2016. Milk yield for first lactation cows having at least 5 milk test days was used to analyze production (n=15,181). Records were stratified by AFC into 5 groups: 1) 18-21 mo (n= 202), 2) 22-25 mo (n= 5,569), 3) 26-29 mo (n= 5,579), 4) 30-33 mo (n=2,389), 5) 34-37 mo (n=1,442). The overall median of AFC was 27 mo. Although milk yield at the beginning of the lactation was lower for lower AFC categories, the differences between categories 2, 3, and 4 disappeared by the fourth WA day at approximately 113 days in milk. No effect of AFC category was detected for milk fat and protein content and for SCC. Considering AFC categories, cows calving for the first time at 22-25 mo of age needed the shortest period after calving to conceive. The lower income associated with the mild milk losses may be compensated by the cost of more than 80 extra d in the rearing period and the increment in days open estimated for the upper categories.