You might assume that you want a heavier heifer to ensure that she reaches puberty as soon as possible. Ensuring puberty then leads to a higher birthing rate in the herd in year but also greater efficiency as it allows for the greater possibility of more calves born within a 21-day period. (Why is that important? Read that here.)
As described in the research summary from the Western Beef Development Centre, mature cow body weight from cows 5 years and older is 1410 lbs.
In this trial, which allocated cattle in two different years and studied them both over the course of 3 years, heifers were bale-grazed bromegrass-alfalfa round bales and supplemented with barley grain. Trials were completed in a drylot pen and in a field paddock, but no notable differences were found between the two feeding areas. These heifers were also split into two other categories: those who were fed to reach 55 percent of their mature weight, (770 lbs), and those who were fed to reach 62 percent of their mature weight (870 lbs). It should also be stressed that both of these groups were well fed – their rations were designed to reach the recommended protein and energy requirements for pregnant beef heifers.
As expected, during the winter development period, heifers fed to gain only 55 percent of their mature weight had a lower average daily gain. This resulted in lower feed costs for these replacement heifers compared to the heifers provided with more food to reach 62 percent of their mature weight within the winter development period.
But did it affect their birth rate? Pregnancy rates were very similar for both groups. The replacement heifers fed to reach 55 percent of their mature weight had a pregnancy rate of 86 percent, while the replacement heifers fed to reach 62 percent of their mature weight had a pregnancy rate of 88 percent. The pregnancy rates between the two groups leveled off even more within the next two years, with rates between 94 and 96 percent for both subsequent years.
So, if there’s wasn’t a big difference in pregnancy rates, which group had a greater benefit for the producer? The group that was only fed to gain 55 percent of their mature weight had a significantly lower cost. Without a loss in reproductive performance, the smaller replacement heifers reduced their development cost by $58 per animal.
As you keep in mind the number of replacement heifers you’ll need this fall, which are likely just calves now, also keep in mind the costs you could reduce in this coming year as well. How much feed will you have available, and how much is necessary? Did you have healthy replacement heifers? Could you have reduced your feed costs this past year? Answering these questions could improve your herd and your costs next year. Talk to your nutritionist to determine a ration that will lower your costs, but still provide the necessary nutrients for your replacement heifers. (In Saskatchewan, contact your Agricultural Knowledge Centre at (306) 694-3727 for more assistance with your feed rations)
Would you like another point of view? Check out this article from the Beef Magazine.