Improving Reproduction Management, Part 1

John Grimes, OSU Extension Educator, Highland County

If you want to start a lively discussion with a group of cattle breeders, ask one of the following two questions: (1.) “What production traits are important to you?” and (2.) “What time of year do you prefer to calve?” We do not have adequate time or space in this article to address the merits of various production traits. However, I would like to make a case for reproduction rates being the most important trait for any cattle breeder to focus upon. Emphasis on any given production trait will be meaningless unless the female conceives and has a live calf every 12 months. Timing and length of the calving season will have a huge impact on eventual reproduction rates.

Results from the Ohio Beef Heifer Development Survey conducted in 2008 indicated that Ohio cow-calf producers are willing to calve during every month of the year. When asked the question “In what months do you calve on your farm?”, producers indicated some strong preferences. By a large margin, the most frequent month listed for calving was March at 74.6%. Following next were April (57.8%), February (51.1%), January (25.7%), and May (25.2%). A smaller group of producers indicated a preference for fall calving with September coming in at 18.8% and October at 17.8%. The remaining five months all had responses below 8.5%.

The decision of when to calve did not happen overnight. I believe much of these results can be attributed to tradition. Some operations have had the same calving season for generations and aren’t about to change. January through March are preferred calving times for those individuals looking for heavier calves to sell in the fall and by many seedstock or club calf producers. Others prefer to calve in warmer weather when the grass is growing (April, May, September, and October). I am struggling to find a sound rationale for calving in mid-summer!

What do our choices in regards to calving season mean in terms of reproductive performance and ultimately profitability? There are many factors to consider when choosing the proper calving season that will positively impact your operation’s profitability. Weather and the changes associated with seasonality have obvious impacts on conception and calving percentages. The species and amount of forages available to the cow herd play a large role in reproductive success. The owner’s labor availability (full-time farmer vs. off-farm employment) is a huge consideration in this process.

Let’s first discuss the impact of weather on reproductive performance. As we saw from the previously mentioned survey results, Ohio producers prefer to calve in the first five month’s of the year. Choosing when to concentrate your calving in this time frame is tough. Calving in February and March is challenging in Ohio because these months are typically wet and/or cold. Extra facilities for calving cows or young calves will help, but it is not unusual to see 5-10% calf death losses. Calf death losses are typically much lower with fall calving herds.

With the poor calving conditions in February and March, many producers choose to move their peak calving season to April and May. This would seem to be a logical choice as calf losses will likely be lower because of the greater odds of warmer weather, green grass, and less mud. However, calving later in the spring will move the breeding season in to the summer and result in lower pregnancy rates.

Dr. Les Anderson, Beef Extension Specialist, University of Kentucky, provides us with some interesting data from their Research Center at Princeton, Kentucky. They conducted a trial where cows were exposed to a 45-day natural breeding season. The breeding seasons were early (4/21-6/5), typical (5/21-7/6), or late (6/19-8/4). Pregnancy rates declined dramatically in cows that were bred later in the summer. Pregnancy rates were 89% for the cows bred early, 78% for the cows bred during the typical time, and only 59% for the cows bred to calve later. Why is pregnancy rate markedly lower for cows bred in mid- to late summer?

The primary factor that reduces pregnancy rates is heat stress. Heat stress occurs when the body temperature is elevated by more than two degrees above normal for more than 48 consecutive hours. Heat stress reduces pregnancy rates by increasing embryonic mortality. These losses typically can occur at two different times: before day 7 post-breeding (loss of the developing embryo) and from day 25-45 post-breeding (early fetal loss). Data from trials at the University of Kentucky illustrate that fetal death losses range from 5-25% depending upon the level of heat stress.

Heat stress problems are increased by the consumption of endophyte-infected fescue. Endophyte is a fungus that grows in fescue and it produces chemical compounds that reduce the ability of a cow to dissipate heat. These chemicals redirect blood flow in an animal’s body such that the blood supply pools in the interior regions of the body. Typically in the summer, an animal’s blood supply flows more to the exterior of the body so that it can be cooled. This redirection of the blood flow reduces the ability of an animal to cool itself during the night which results in tremendous heat stress on the body and lower pregnancy rates. This phenomenon explains why you see many cows on endophyte-infected fescue pastures frequenting wet, muddy areas and seeking shade for large portions of the day.

What can you do to reduce the impacts of heat stress? First, limit the access of your cows to endophyte-infected fescue during the heat stress periods (mid-June through August). Give them access to orchard grass, warm season grasses, endophyte-free fescue, annual forages, or pastures with higher legume content. Adding red clover to fescue pastures via frost seeding is a very economical way to diminish the effects of the endophyte fungus. Feeding supplemental feed higher in fat can also reduce heat stress.

So where do we go from here? It may be easier to calve your cows later in the spring but fewer of them will calve. Calving earlier will increase pregnancy rates but will likely increase calf death loss. However, a 5-10% death loss may be more financially sound than a 60-70% pregnancy rate. What other options do you have? I would suggest that you give fall calving strong consideration as a viable option.

While we do not have space in this article to discuss fall calving in great length, I will try to hit the major pros and cons. September and October provide excellent calving conditions with warmer temperatures and drier ground than the earlier months of the year. Calf birth weights are usually smaller in a fall season when compared to winter calving. Conception rates are typically better when breeding in November and December versus July and August. Another strong advantage for fall calving is that it gives you a feeder calf to market at a time (April-May) when prices are historically at their highest levels. On the negative side, cows nursing calves into the winter will have higher feed costs and they will require higher quality forages (harvested or stockpiled) or supplemental grain to maintain adequate body condition. Consider early weaning of the calves at 100-125 days of age to offset the increased feed requirements for the cows. The Ohio State University and other institutions have conducted a fair amount of research on the viability of early weaning as a sound management practice.

This article has focused largely on the differences in calving seasons facing Ohio cow-calf producers. There is no doubt that there are significant economic impacts resulting from the calving season that you choose. However, there are other reproductive improvements that can be made. Next week, we will follow-up with a discussion on shortening the length of the calving season that you choose and methods to utilize higher quality genetics and still maintain acceptable conception rates.