Published online by Cambridge University Press: 02 September 2010
Lifetime productivity of 408 Aberdeen Angus cows from the Estacion Experimental Agropecuaria (EEA) of Balcarce, Argentina, was analysed during the 1972 to 1983 period according to their date of calving. Cows were allocated to two groups: one group of early first calving (Fl) when cows calved within the first 25 days of the calving period; the other, of late first calving (F2) when cows calved after that date. Independently using similar criteria, the effect of date of second calving on lifetime productivity was analysed in the same cows, groups SI and S2. Early first calving cows weaned more kg of calf when their first four calvings were considered than cows of late first calving (659 v. 628 kg). The same tendency was observed when cows were compared according to their second calving date (653 v. 634 kg). Differences in weaning weight between calves from early and late cows were only significant for the first calving (group Fl v. F2) and for first and second calving (group SI v. S2). This fact was a consequence of the shorter initial calving interval for late cows (F2 and S2) so that subsequent ages of their calves at weaning were similar to early cows (Fl and SI). Groups F2 and S2 cows had first and second calving intervals respectively of 351 and 356 days, while groups Fl and SI cows had intervals of 372 and 371 days. It is concluded that the date of the first calving and the high overall reproductive performance of the herd contributed to a high concentration of early calvings and a high productive efficiency.
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