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Freshening Date Changes of Cows in Iowa Dairy Herd Improvement Associations¹

Iowa State College

Abstract

Little change occurred from year to year in the percentages of cows in Iowa Dairy Herd Improvement Associations that calved in the different months and seasons. The average percentage distribution of freshening dates was found to be: winter, 30.0 per cent; spring, 19.8 per cent; summer, 14.1 per cent; and fall, 36.1 per cent.

The calculated average calving interval among Iowa D.H.I.A. cows was found to be 451 days which is similar to the calving interval of 446 days found in the Iowa State College herd over a 19-year period. Nearly one-half (48.3 percent) of the Iowa State College cows had calving intervals of less than 13 full months. The intervals of the other cows ranged up to over 2 years in length.

One hundred fifty-seven Iowa State College cows that calved for the first time in the fall season had subsequent calvings that were distributed as follows: winter, 28.7 per cent; spring, 20.0 per cent; summer, 12.2 per cent; and fall, 29.1 per cent. This distribution was similar to that found among Iowa D.H.I.A. cows.

When no apparent effort was made to freshen cows for the first time in any one season as appeared to be true in the College herd, the distribution of the freshening dates was noticeably different from that found with D.H.I.A. cows, the greatest differences being in the percentages that calved in the summer and fall seasons.

Iowa dairymen evidently have made an effort to freshen their cows in the fall but calving intervals longer than twelve months cause some calving dates to shift to other seasons. Economic factors other than high milk yields probably hinder any shifting of cows whose calving dates occur in other seasons back to fall calving.

¹ Journal Paper No. J-l044 of the Iowa Agricultural Experiment Station, Ames, Iowa. Project No. 31.