Effects of Stress Factors on the Estrous Cycles of Beef Heifers

Publisher Website
Google Scholar
Abstract
Similar groups of ungentled range weaner beef heifers were reared separate from other cattle at the University's Davis campus and Range Field Station. When 15 months of age they were observed twice daily (period 1) for estrus. Twice daily observations continued (period 2) after inducing stresses by placing one subgroup with strange mature cows, transporting another to the opposite location, while a third were non-stressed controls. While there were considerable differences in the abilities of the observers to detect estrus it was shown that it was possible for a skilled observer, with the aid of a marker animal, to detect a very high percentage of the heats with twice daily observations. There was no evidence of stress effects on the means of the established normal class of 15- to 25-day cycle lengths, which varied from 19.4 to 19.8 days, between the four treatments. The relative frequency of short cycles was higher under stress conditions at both locations, but did not approach the 5% level of statistical significance. However, when the non-stressed and stressed data were combined at each location the relative frequency of short cycles was significantly less at Davis. Supporting this evidence of possible greater stress conditions at the Field Station there were a significantly greater number of short cycles observed in the groups trucked from Davis to the Field Station than in the reciprocal movement. Similarly, the within-heifer variance of cycle lengths did not differ significantly between the non-stressed and stressed groups at either location, but when the data were combined at each location, it was significantly smaller at Davis. Copyright © 1972. American Society of Animal Science. Copyright 1972 by American Society of Animal Science.

This publication has 0 references indexed in Scilit: