Comparing dairy farm milk yield and components, somatic cell score, and reproductive performance among United States regions using summer to winter ratios

摘要

Heat stress abatement is a challenge for dairy producersin the United States, especially in the southernstates. Thus, managing heat stress is critical to maintaindairy cow performance in the summer. The abilityto employ a metric to measure heat stress and evaluateabatement strategies may benefit dairy producers byproviding meaningful feedback on the effectiveness ofcurrent and future management strategies with thegoal of improving heat stress management. Therefore,this study aimed to explore the use of the summer towinter performance ratio metric to quantify and comparefarm performance variables among regions of theUnited States. Monthly performance data recorded bythe Dairy Herd Improvement Association from 2007to 2016, for all US Dairy Herd Improvement Associationherds processing records through Dairy RecordsManagement Systems (Raleigh, NC), were obtained.Season dates were based on the astronomical definitionof the Northern Hemisphere with summer as June 21to September 21 and winter as December 21 to March19. States were grouped into regions based on climatezone classification. Performance records included a totalof 16,573 herds [Northeast (n = 7,955), Midwest (n= 6,555), Northern Plains (n = 305), Southeast (n =1,370), and Southern Plains (n = 388) regions]. Herdtest day performance variables energy-corrected milk,somatic cell score, milk fat and protein percentage, conceptionrate, heat detection rate, and pregnancy rate insummer and winter were used to calculate summer towinter ratios for each region. The MIXED procedureof SAS 9.4 (SAS Institute Inc., Cary, NC) was used tocompare test day performance variables. The effects ofyear, mean days in milk, mean 150-d milk, mean herdsize, and number of milkings per day were included ascovariates in the models. Dairy cattle performance inall climate regions was negatively affected by summerheat stress, but some regions greater than others. Adifference was also observed among regions when comparingsummer to winter ratios for each performanceparameter. This indicates that summer performancevaries by climate region identified by the summer towinter ratio and demonstrates usefulness of the metricto monitor degree of heat stress based on performance.