diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteCalendarAction.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteCalendarAction.java
index ffc05485547..d4cdb48dd5a 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteCalendarAction.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteCalendarAction.java
@@ -14,6 +14,7 @@ import org.elasticsearch.client.Client;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.DeleteByQueryAction;
 import org.elasticsearch.index.reindex.DeleteByQueryRequest;
 import org.elasticsearch.tasks.Task;
@@ -77,7 +78,7 @@ public class TransportDeleteCalendarAction extends HandledTransportAction<Delete
 
     private DeleteByQueryRequest buildDeleteByQuery(String calendarId) {
         DeleteByQueryRequest request = new DeleteByQueryRequest(MlMetaIndex.INDEX_NAME);
-        request.setSlices(5);
+        request.setSlices(AbstractBulkByScrollRequest.AUTO_SLICES);
         request.setRefresh(true);
 
         QueryBuilder query = QueryBuilders.termsQuery(Calendar.ID.getPreferredName(), calendarId);
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteForecastAction.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteForecastAction.java
index c0783ac8d3c..1e5659bd233 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteForecastAction.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteForecastAction.java
@@ -29,6 +29,7 @@ import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.query.BoolQueryBuilder;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.BulkByScrollResponse;
 import org.elasticsearch.index.reindex.DeleteByQueryAction;
 import org.elasticsearch.index.reindex.DeleteByQueryRequest;
@@ -198,7 +199,7 @@ public class TransportDeleteForecastAction extends HandledTransportAction<Delete
         DeleteByQueryRequest request = new DeleteByQueryRequest()
             .setAbortOnVersionConflict(false) //since these documents are not updated, a conflict just means it was deleted previously
             .setMaxDocs(MAX_FORECAST_TO_SEARCH)
-            .setSlices(5);
+            .setSlices(AbstractBulkByScrollRequest.AUTO_SLICES);
 
         request.indices(AnomalyDetectorsIndex.jobResultsAliasedName(jobId));
         BoolQueryBuilder innerBoolQuery = QueryBuilders.boolQuery();
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteJobAction.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteJobAction.java
index 3f8321fa4b1..98275a294d1 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteJobAction.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteJobAction.java
@@ -38,6 +38,7 @@ import org.elasticsearch.index.query.ConstantScoreQueryBuilder;
 import org.elasticsearch.index.query.IdsQueryBuilder;
 import org.elasticsearch.index.query.QueryBuilders;
 import org.elasticsearch.index.query.TermQueryBuilder;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.BulkByScrollResponse;
 import org.elasticsearch.index.reindex.DeleteByQueryAction;
 import org.elasticsearch.index.reindex.DeleteByQueryRequest;
@@ -305,7 +306,7 @@ public class TransportDeleteJobAction extends TransportMasterNodeAction<DeleteJo
                                 new ConstantScoreQueryBuilder(new TermQueryBuilder(Job.ID.getPreferredName(), jobId));
                         request.setQuery(query);
                         request.setIndicesOptions(MlIndicesUtils.addIgnoreUnavailable(IndicesOptions.lenientExpandOpen()));
-                        request.setSlices(5);
+                        request.setSlices(AbstractBulkByScrollRequest.AUTO_SLICES);
                         request.setAbortOnVersionConflict(false);
                         request.setRefresh(true);
 
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/persistence/JobDataDeleter.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/persistence/JobDataDeleter.java
index 9380be0c15b..f48dcb977e5 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/persistence/JobDataDeleter.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/persistence/JobDataDeleter.java
@@ -16,6 +16,7 @@ import org.elasticsearch.index.query.ConstantScoreQueryBuilder;
 import org.elasticsearch.index.query.IdsQueryBuilder;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.BulkByScrollResponse;
 import org.elasticsearch.index.reindex.BulkByScrollTask;
 import org.elasticsearch.index.reindex.DeleteByQueryAction;
@@ -129,7 +130,7 @@ public class JobDataDeleter {
         private DeleteByQueryHolder(String index) {
             dbqRequest = new DeleteByQueryRequest();
             dbqRequest.indices(index);
-            dbqRequest.setSlices(5);
+            dbqRequest.setSlices(AbstractBulkByScrollRequest.AUTO_SLICES);
             dbqRequest.setAbortOnVersionConflict(false);
         }
     }
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredForecastsRemover.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredForecastsRemover.java
index 3225a7eb921..3556a3bc9a9 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredForecastsRemover.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredForecastsRemover.java
@@ -22,6 +22,7 @@ import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.query.BoolQueryBuilder;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.BulkByScrollResponse;
 import org.elasticsearch.index.reindex.DeleteByQueryAction;
 import org.elasticsearch.index.reindex.DeleteByQueryRequest;
@@ -143,7 +144,7 @@ public class ExpiredForecastsRemover implements MlDataRemover {
 
     private DeleteByQueryRequest buildDeleteByQuery(List<ForecastRequestStats> forecastsToDelete) {
         DeleteByQueryRequest request = new DeleteByQueryRequest();
-        request.setSlices(5);
+        request.setSlices(AbstractBulkByScrollRequest.AUTO_SLICES);
 
         request.indices(RESULTS_INDEX_PATTERN);
         BoolQueryBuilder boolQuery = QueryBuilders.boolQuery().minimumShouldMatch(1);
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredResultsRemover.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredResultsRemover.java
index d7b16ef8c46..e24ecfbe8b0 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredResultsRemover.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/retention/ExpiredResultsRemover.java
@@ -12,6 +12,7 @@ import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.BulkByScrollResponse;
 import org.elasticsearch.index.reindex.DeleteByQueryAction;
 import org.elasticsearch.index.reindex.DeleteByQueryRequest;
@@ -85,7 +86,7 @@ public class ExpiredResultsRemover extends AbstractExpiredJobDataRemover {
 
     private DeleteByQueryRequest createDBQRequest(Job job, long cutoffEpochMs) {
         DeleteByQueryRequest request = new DeleteByQueryRequest();
-        request.setSlices(5);
+        request.setSlices(AbstractBulkByScrollRequest.AUTO_SLICES);
 
         request.indices(AnomalyDetectorsIndex.jobResultsAliasedName(job.getId()));
         QueryBuilder excludeFilter = QueryBuilders.termsQuery(Result.RESULT_TYPE.getPreferredName(),