Research Progress Report 340 Project 1295 August, 1968

Estrus Synchronization Trials with a Commercial Beef Cow Herd
K.J. Drewry, K. Hawkins, C.J. Kaiser, L.A. Nelson and Randall Peterson, Jr.
Departments of Animal Sciences and Southern Indiana Forage Farm

Introduction
Estrus synchronization by use of hormones is one method of bringing all cows in the breeding herd into estrus at about the same time. Successful estrus synchronization should result in a shorter calving interval in the herd; and consequently, a more uniform set of calves at weaning because of age similarity.

The use of estrus synchronization dictates that the herd owner revise his cow herd management practices. Experimental results from herd management-reproductive performance studies have shown that cows must receive an adequate ration to obtain maximum reproductive performance. One of the successful methods of estrus synchronization is to incorporate a hormone at recommended levels in feed for a given number of days prior to the start of breeding period. Successful estrus synchronization, with hormone given in the feed, is dependent upon: (1) condition and nutrition levels of cows, and (2) adequate intake of feed by the cow to obtain recommended amounts of the drug.

All treated cows, regardless of method of drug application, will show estrus from 2 to 10 days following termination of hormone treatment. This dictates that the herd owner
must have extra bulls available or use artificial insemination. In most estrus synchronization studies personnel have chosen to use artificial insemination.

The trials described herein were conducted at the Southern Indiana Forage Farm. The trials were conducted with the following objectives: (1) comparing reproductive performance of control and medroxyprogesterone acetate (Repromix) treated cows, and (2) comparing breeding performance of control cows with Repromix treated cows bred on induced (first) estrus and Repromix treated cows bred on second estrus.

Experimental Procedure
Trials were conducted during fall and winter months of 1966 and 1967. The 1966 fall trial, conducted from September 28, 1966 to March 15, 1967, was preliminary trial involving 30 Herford cows. The objective of this trial was to compare reproductive performance of control cows and Repromix-treated cows. The 1967 fall trial was conducted from September 21, 1967 to March 19, 1968 and included 96 Herford cows. The objective of this trial was to compare the reproductive performance of control cows, Repromix-treated cows bred on first estrus, and Repromix-treated cows bred on second

PURDUE UNIVERSITY • Agricultural Experiment Station • Lafayette, Indiana