Maturity Index used to reduce dystocia in first-calf heifers
Calving first-calf heifers can be time consuming and costly when problems occur. Research indicates that more mature heifers have fewer calving problems. When selecting what age to breed heifers, ranchers often use the animal’s weight. According to a University of Nebraska Beef Report, utilizing a more in-depth maturity index (MI) can provide higher quality results.
One current weight estimate option is described as the percentage of average herd weight (PAHW). The heifers actual mature body weight won’t be known until she reaches four or five years of age. However, knowing the average weight of all cows in the herd provides an estimate of what she will weigh as an adult.
The effectiveness of PAHW is rough at best. If ranchers are genetically selecting for larger or smaller females, average herd weights won’t accurately represent a current heifer’s mature weight. Most commercial herds also contain animals at a variety of weights. Age, weather and a variety of other factors can affect cow weight and result in a less accurate PAHW.
In an effort to improve a rancher’s ability to measure maturity, the heifer (MI) was developed using data collected at the Gudmundsen Sandhills Laboratory. It is based on individual animal characteristics and uses availably technology.
Two studies were conducted in Nebraska using an initial group of 500 heifers. Individual animal data was collected. The data set included pre-breeding weight, birth weight, dam mature body weight, pre-breeding age and nutrition level. This data was entered into an equation to determine MI. Positive or negative coefficients were multiplied by each respective piece of data based on the magnitude and nature of the relationship each has to the MI. The higher a heifer’s MI, the better.
This method does require more time and data collection on each animal. The equation is long and more complex than what is used for PAHW. Ranchers with an even herd who aren’t attempting to change the average size of mature cows may find the PAHW method easier and sufficient for maturity estimates.
But for producers who experience calving problems, or dystocia, an additional University of Nebraska Beef Report found that MI levels correlate with dystocia problems. A higher MI rate in heifers results in fewer instances of dystocia.
During two experiments several hundred heifers were developed to different MI levels and bred. Data was collected, noting heifers that required calving assistance, and statistical equations were designed. Only those females that were retained through the fall of their second pregnancy were included in the data set.
Results showed that as MI increased, dystocia levels continued to drop, until they reached a consistent base of around 13 percent at an MI of 70. This is significantly lower than 50 MI heifers, of which over 40 percent experienced some form of dystocia. All other factors were kept as consistent as possible throughout the experiments.
The report states it isn’t economically viable for most producers to raise heifers to an MI of 70 before breeding them. But, after taking into the consideration the increased time and costs related to calving problems, producers may find it beneficial to breed heifers at a higher maturity level. Figuring MI levels on heifers and comparing them to dystocia levels at that MI will give ranchers the necessary tools to determine what is most economically viable for their operation.
“This research demonstrates that dystocia of the female leads to reduced second pregnancy rates and increased costs. This reduction in pregnancy indicates that breeding smaller MI heifers comes at some additional cost to future production as well as added labor and vet expenses and leads to the conclusion that an economic analysis needs to be completed to illustrate the degree to which the physical relationships affect profitability,” stated the report.
For producers experiencing high levels of dystocia this is a management option that can potentially reduce the problem. Several other factors, such as the influence of the bull’s genetics and nutritional history can cause dystocia. However, maturity of the female has long been considered a top priority when breeding yearling heifers. MI’s give ranchers more accurate information about the maturity of females in the herd and have the potential to solve some calving related issues on the ranch.