A.M - P.M. vs. Once-A-Day • Studies Have Found Cattle Can be Inseminated Over a 24 Hour Span With Acceptable Fertility – Fertility Was the Same for Cattle Inseminated Once-ADay or By the A.M.-P.M. Rule – Good Calving Rates Can be Obtained by Inseminating Cattle Over a 24 Hour Interval After First Heat Observation • Optimum Time for Insemination Was 16-24 Hours After Detection of Heat • Estrus is a random Event • 95% of Cows Ovulate Between 17 and 38 Hours After Standing Heat Starts Frequency and Time of Service Non Return Rates A.M - P.M. vs. Once-A-Day • Electronic Heat Devices – Provide Information of When Mounting Started – Offer Little Information on Cow Ovulation • Commercial Operation – Some Luck is Involved When Find Cattle in Heat • Cows are Mounted a Low Number of Times • Hard to Determine if First Mount or Last Dairy Management Issues • Important Considerations Include: – Extra Time Required in Lock-ups – Total Time Standing on Cement – Body Temperature of Cow During Summer Heat Stress – Inseminator Fatigue Beef Management Issues • Important Considerations Include: – Number of Cattle Handled – Inseminator Fatigue – Sorting Cattle After Observation of Heat When Using Synchronization Programs Summary • Cows and Heifers are Sexually Receptive for About 18 Hours During Estrous – This Time is Known as Heat – Standing to be Mounted is the Surest Sign of Heat • Observe Cattle for Heat For 30 Minutes Twice a Day – Early Morning and Late Evening are Best • Cows Should be Inseminated in Last 2/3rds of Standing Heat Summary • Studies Have Shown Once-a-Day Breeding is Comparable to Breeding Using the A.M.-P.M. Rule – Usually More Efficient for Commercial Operations • Determining Time of Heat Start is Difficult – Makes Precise Timing of Insemination Impossible – Inseminate 6 to 24 Hours After First Observation of Heat • Heat Detection Aids Help Many Producers Summary • Age and Weight of Heifers Determines When Cycling Begins – Most Will be Cycling by 13 to 14 Months • Cows Should be Given at Least 40 Days to Rest Before Rebreeding • Asking “Is the Cow Really in Heat?” is More Important Than Asking “What Time Should I Inseminate the Cow That is in Heat?”