Many areas have experienced their first frost of the season or will in the days ahead. For cows, these cooler temperatures are welcome following a summer with near-record heat across much of the Midwest. Despite the more ideal temperatures for cows, farmers find themselves disappointed with milk production this time of year.      
The fall milk slump is an age-old phenomenon. Although changes are less drastic than 10 years ago, the United States Department of Agriculture statistics consistently show the lowest milk production per cow takes place in the last quarter of the year as shown in the chart below. In fact, October and November are the lowest months for milk per cow across most Midwest states. Conversely, milk components (butterfat and protein) approach their seasonal highs during this time. Always look at production on an energy-corrected basis, particularly in the fall. Monitor combined pounds of fat and protein shipped rather than raw volume of milk.  
As with most production challenges on farms, this drop in production cannot be solved with a single quick fix.   
Heat stress has a prolonged effect on milk production. Summertime mid-lactation cows typically do not recover from summer heat stress, so they have depressed milk production during the fall. Early-lactation cows have reduced peak milk production during the fall season due to the negative impact of heat stress in the dry period. These cows also experience the stress of calving during heat stress, so it is common to see peak milk 5 to 10 pounds lower this time of year compared to previous months. Intuitively, cows that start lower in production will peak lower and shift the overall lactation curve downward.  
Photoperiod and day length have a clear impact on milk production. In 2002, while at the University of Illinois, Dr. Geoff Dahl summarized 10 research trials showing an average increase of 4 to 5 pounds with long-day lighting. Milk production is highest when cows are exposed to 16 to 18 hours of bright light each day. Conversely, dry cows exposed to short days of about eight hours of light milk better after freshening than those exposed to long day lengths of summer.  
Feed changes are often blamed for the fall milk production drop. In some cases, these changes are significant and abrupt. However, some farms that have complete or partial carryover of wet corn sources for several months still deal with lower fourth quarter milk production. If new corn silage and harvested wet corn are a factor on your dairy, incorporating rapidly digestible forms of carbohydrates may be the best short-term solution. Recognize that starch availability in wet corn changes significantly as fermentation progresses and needs to be monitored in the months ahead.  
Energy requirements go up in the fall as animals prepare for cold weather. Dry matter intakes are often high this time of year, resulting in reduced feed efficiency. Cows commonly appear nonresponsive to dietary changes in the fall. In our Midwestern climate, net energy for maintenance requirements dramatically rise for cattle in September and are greatest in late October and early November, not in the middle of winter like one might expect. Ruminants require as many or more maintenance calories to adapt to cold compared to surviving the cold. This preparation includes changing hair coats, placing fat under the skin for tissue insulation and raising basal metabolism. Most lactating dairy cattle are not housed outside in the winter, reducing the extent of these changes. However, they instinctively know it is going to get cold and will spend calories to prepare.
The extent to which these factors impact production is unique to each farm and management system. Evaluate which solutions are practical for your dairy. These may include controlled lighting, heat stress abatement, and efforts to manage reproduction and herd inventory variations. Work with your nutritionist and management team to evaluate and monitor feed changes. As always, let the cows tell you if you are making the right decisions.
    Barry Visser is a nutritionist for Vita Plus.