Nonpuberal estrus and mature cow influences on growth and puberty in heifers.

This experiment had two objectives. The first was to test a hypothesis that the presence of mature cows can influence the growth rate and physiological maturation rate of growing heifers. The second objective was to define a phenomenon termed nonpuberal estrus (NPE). Nonpuberal estrus in a prepuberal heifer is a behavioral estrus that is not followed by ovulation and formation of a corpus luteum. Two years of data were collected. All heifers were crossbred and were sired by Hereford, Charolais and Tarentaise bulls in yr 1 (n = 153) and by the same three breeds plus Jersey, Shorthorn, Brahman and Longhorn in yr 2 (n = 207). All heifers were born in the spring and weaned in October when approximately 180 d old. After weaning, heifers were assigned at random (within breed of sire) to control or mature cow (MC) treatment pens. Control pens contained 25 or 26 heifers and a sterile marker bull, while MC pens contained 25 or 26 heifers and a sterile marker bull plus four nonpregnant, mature cows. The presence of the mature cows did not (P greater than .10) affect rate of gain or yearling weight. Sire breed did (P less than .01) influence weight on test and average daily gain during the test in both years and affected (P less than .01) yearling weight during yr 2 but not (P greater than .10) during yr 1. A sire breed X treatment interaction effect on puberal traits was significant (P less than .01) in yr 1 but not in yr 2.(ABSTRACT TRUNCATED AT 250 WORDS)