Ideal answer: Springing heifers ready to calve, walk into the milking herd and work.
Sounds simple, but what does that really mean? Looking at a couple factors, we can start putting some numbers to “springing heifers ready to walk into the milking herd.”
Growth. We need to grow the heifer from somewhere around 90 pounds to what? A weight that makes her competitive in the lactating herd.
But not a fully mature weight. It is not economical to wait till a heifer is 3 or 4 years old for her to calve for the first time.
Research.A nice piece of work by Lormore and Meyer compared lifetime income over feed costs of animals with an age at first calving (AFC) of 23, 26 and 30 months.
The 23 and 26 month AFC animals had a clear and continuous advantage over the 30 month AFC heifers.
At 5 years of age, the 23 month AFC cow had a net income over fed costs of $3,445; the 26 month AFC cow, $3,251; and the 30 month AFC cow $2,749.
Even if the 30 month AFC cow produced one year longer than the 23 month AFC cow, her income at $3,316 is barely equal to that of the 23 AFC cow at $3,445.
The calculated net incomes were adjusted to account for the time value of money. In other words, a dollar in your hand today is worth more than a dollar in your hand a year or two years from now.
The heifers that calved at 23 months were generating income for 7 months before the heifers that calved at 30 months.
Even though the older heifer would enter the herd at a larger size, and theoretically be better able to compete, she never catches up to the heifers that calved earlier.
Bred. To calve at 23 or 24 months, a heifer has to be pregnant by 13 to 14 months of age, at the latest.
Heifers have to reach puberty before they can become pregnant. Holstein folks think this has to do with reaching about half of a mature size.
Anyone who raises Jerseys knows that they start showing signs of heat at about 3 months. This is just a Jersey behavioral thing. They are not ready to breed!
Charts say that target breeding weights are 750 to 800 pounds for Holsteins and 525 to 575 pounds for Jerseys.
Consider weight. We must also consider what weight we want the heifers to be as they enter the milking herd.
Charts again will tell us that target post-calving weights are 1,260 pounds for Holsteins and 810 pounds for Jerseys. These are fine as guidelines, but for established herds, set goals based on the herd’s genetics and management.
What is mature cow weight? This weight is not determined by looking back at cull cow weights. Cull cows are usually over- or underweight compared to the rest of the herd.
Use a weigh tape or scale on cows 4 years old and older. Their average post calving body weight should establish your target heifer weight.
Post-calf. By post-calving body weight, we are looking at body weight a week or so after calving.
For heifers, we would like to see that post-calving body weight at 85 percent of the mature cows’ body weight.
A herd with 1,500-pound cows would be looking for post-calving weights averaging 1,275 pounds for their 2-year-olds. Pretty close to the chart.
So pre-calving weights would be higher, in the 1,450-pound range as she is carrying a calf, placenta and fluids.
However, a herd with 1,600-pound cows should aim for post calving weights averaging 1,360 pounds, considerably higher than the charts. For this herd, pre-calving weights would be closer to 1,540 pounds.
Charts are a help when establishing goals for growing heifers, especially when animals are from unknown origins.
But for herds with history, records and good management, better growth targets can be calculated for heifers that can walk into the milking herd and get down to business.