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Freshening Ages of Purebred Cows in Iowa Cow Testing Associations^*

Iowa State College, Ames, Iowa

ABSTRACT

1. The mean age at which 570 registered heifers in Iowa Cow Testing Associations first freshened was found to be 27.1 months but the distribution was decidedly skew with the mode at 24 months. More than half of them freshened before they were
   months old. These ages were computed as the last full month attained before the freshening day and therefore are about 15 days less than the actual ages.
   
2. Some significant differences were found among the different breeds studied. Nearly 73 per cent of the data concern Holsteins.
   
3. Differences found from herd to herd were large enough to show a variation in management policy in this respect or an effective difference in herd environment.
   
4. Heifers fed liberally enough to approach advanced registry conditions and heifers fed poorly calved later than those which received about average feeding, but this relation is too slight to be practically important and even its statistical significance is doubtful.
   
5. The numbers of cows calving at various ages show a distinct cycle, the peaks being twelve months apart and beginning at 24 months. This cyclical distribution should be taken into account in studying the relation of other variables to age at calving.
   
6. This study is a survey of actual breeding practice among Iowa breeders of purebred dairy cattle. Whether breeding for such early freshening has more desirable than undesirable consequences, everything considered, is something we hope to investigate at an early date.
   

^* Journal Paper No. J 168 of the Iowa Agricultural Experiment Station Project 317.