Ken Olson: Plan replacement heifer growth rates to increase values as cows
October 29, 2010
It is important to not under- or over-feed heifer calves from weaning until breeding as yearlings. Not only should they have reached puberty and be fertile before their first breeding starts, but they should not be overly fat because this can negatively influence fertility; calving ease (if they remain fat all the way through pregnancy); and a variety of other important production traits.
First, let’s talk about under-feeding. Based on substantial research from the 1970s and ’80s, the recommendation was established that yearling heifers should reach 65 percent of mature weight by the start of their first breeding season. This weight target increased the probability that most of the heifers would reach puberty by breeding. That has been a highly adopted goal in the beef cattle industry.
However, times and circumstances change, and it appears that we can lower this target. Research has shown that it can easily be lowered to 60 percent, and some evidence even suggests that it could be lowered to 50 percent of mature body weight. However, at 50 percent, not all cattle will reach puberty in time, so larger numbers would have to be retained because some heifers would not get pregnant. This is not all bad; because those heifers can be treated like they were backgrounded through the winter and sold as heavy feeders as soon as pregnancy checking identifies the open ones.
The major advantage of feeding to this lower level is reduced feed costs. Cow depreciation is the annual cost that each cow has to pay to eventually cover the cost of raising or purchasing her replacement. Typically, cow depreciation is the second highest cow cost, with only feed for the cow being higher. The major cost included in cow depreciation is the cost of the feed for the heifer from the time she is weaned until the birth of her first calf. Thus, feed costs are a huge part of beef cattle production costs.
As everyone knows, feed costs have escalated dramatically in the last few years and show no sign of decreasing. Opportunities to reduce feed inputs, such as feeding heifers to a lower target weight, can substantially reduce the feed component of cow depreciation.
A second advantage from lower target weights is that it creates additional options for wintering heifers. It is relatively easy to let heifers graze winter range with a reasonable supplementation program and have them achieve about 60 percent of mature body weight. We have research data from Kansas and South Dakota that supports this result. Winter grazing provides an excellent opportunity to cheapen winter feeding costs.
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Finally, a third advantage to lower target weights has been suggested by some recent research at the USDA-ARS Meat Animal Research Center (MARC) in Nebraska. Their results indicate that heifers that have been developed to lower yearling target weights have greater rebreeding success throughout their lives and stay in the herd longer. This is ongoing research, so pay attention for further evaluation of this situation.
An obvious question to ask is ‘why can heifers now reach puberty and perform at these lower target weights compared to 20 to 30 years ago?’ We don’t have a firm answer, but many beef cattle scientists suggest that genetic selection for cattle with improved reproductive performance, based on strict culling of heifers and cows that don’t breed or breed late, has selected for cattle that are capable of reaching puberty at lighter weights and younger ages. In other words, we have improved the overall genetic capability of the cattle population in the U.S. That is a real tribute to the effort of beef cattle producers.
Now, let’s look at overfeeding. In other words, that would be feeding weaned heifer calves to achieve a target weight in excess of 65 percent of mature body weight. In general, this typically promotes reaching puberty at an earlier age, but this does not necessarily lead to greater fertility.
Obesity, or excess fat, can have a negative influence on a variety of body functions that can reduce fertility. Primary among these is negative feedback on reproductive hormones that drive the processes of ovulation, pregnancy recognition and implantation. This means cattle don’t get pregnant. Unfortunately, it also dramatically increases cow depreciation costs, and leads to reduction of stayability in the herd. In other words, overfeeding is not a way to make a group of heifers’ lives better; it actually backfires.
The bottom line is that a beef cattle producer needs do a little planning at this time of year to ensure heifers reach an appropriate target.
First, determine the initial weight and target weight. Initial weight is easy if calves are being weighed at weaning. Target weight depends on knowledge of mature cow weight in a given herd. If a scale is not available to weigh cows, sale weights of cull cows can serve as a good estimate.
Next, calculate the number of days from weaning to breeding, and then calculate average daily gain (ADG) by dividing the weight difference by the number of days. Now, balance a ration for your heifers to achieve the desired ADG.
Help with ration balancing is available from your local Extension Educator. Monitor size and body condition of the heifers through the winter and adjust the diet if needed to reach the target without exceeding it.
A little planning of this nature can save feed money, while improving the likelihood that the heifers will develop into productive cows that have a long life in your herd.