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Nonpuberal Estrus and Mature Cow Influences on Growth and Puberty in Heifers

U.S. Department of Agriculture¹, Miles City, MT 59301

Abstract

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>.10) affect rate of gain or yearling weight. Sire breed did (P<.01) influence weight on test and average daily gain during the test in both years and affected (P<.01) yearling weight during yr 2 but not (P>.10) during yr 1. A sire breed x treatment interaction effect on puberal traits was significant (P<.01) in yr 1 but not in yr 2. Twenty-two percent of the heifers in yr 1 and 13% of the heifers in yr 2 had at least one NPE. Sire breed influenced (P<.01) the occurrence of NPE in both years. Pregnancy rates were not different (P>.10) between those heifers that had NPE and those that did not. We concluded that NPE is not an abnormal event although its occurrence may be influenced by genotype, age and season of year or photoperiod.

¹ Fort Keogh Livestock and Range Research Station, USDA-ARS and Montana Agr. Exp. Sta., Miles City, MT 59301. Publication has been approved by the Director of the Montana Agr. Exp. Sta., Journal Series No. J-1499.