REPRODUCTIVE EFFICIENCY TO GENERATE REPLACEMENT HEIFERS

I have heard it said that there are 2 kinds of people – those who think there are 2 kinds of people, and those who know that nothing is really quite that simple. In the 80’s and 90’s, there were 2 kinds of dairy producers – those who bought replacements to maintain herd size, and those who sold replacements to maintain herd size. Improvements in reproductive efficiency have made the former group smaller and the latter group larger. Most dairies produce enough replacements to maintain herd size, but they might purchase replacements to fill an expansion. Some dairies chose to focus all of their attention on the milking herd and plan to purchase all of their replacements.

Sexed semen gets a lot of credit for the increased supply of heifers. It certainly is a factor, but the beef semen used in managed breeding programs offsets some of the sexed semen.

Several other things come into play. Synchronization programs and activity monitoring systems have made it easier mange reproductive disorders, and breed cows in a timely manner. Better cow comfort and transition management have made it possible for cows to stay in the herd longer. Better calf management has meant that more of the animals born on a farm end up in the milking string. Faster heifer growth, and tighter heifer breeding protocols, bring heifers into the milking herd younger. All of these combined for a surplus of heifers. Eventually, dairy farmers realized it was expensive to raise heifers they didn’t plan to milk, and started producing crossbred beef calves. More recently, the beef herd has gotten smaller, the value of beef calves has skyrocketed, and we have come full circle, with dairy heifers in short supply again. Once again, reproductive efficiency is critical to maintaining a steady supply of replacements.

Pregnancy rate is the most popular measure of cow reproductive performance. It answers the question, how many of the cows that should have become pregnant actually did. It incorporates both the number of cows bred, and the conception rate. Top herds are over 40%. In essence it measures how quickly cows became pregnant after the voluntary waiting period. Synchronization programs are very effective tools to get cows pregnant soon after the voluntary waiting period. As activity systems gain popularity, the percent of cows pregnant by 150 days in milk becomes more relevant. If the voluntary waiting period is the starting line, 150 days in milk is the finish line. Cows that get pregnant after 150 days in milk are more likely to dry off early due to low production. So, the percent pregnant by 150 days in milk tells us how many cows were pregnant before the finish line. Top herds have over 85% of cows pregnant before 150 days in milk. Whichever measure fits your farm, higher reproductive performance means more calves are born – whether you choose to make replacements or market calves.

Heifer reproductive performance is measured a little differently. We can still use pregnancy rate, but we start counting according to age rather than days in milk, and goals for heifer pregnancy rate are much higher than goals for cow pregnancy rate. Age at calving is a more relevant number for most farms, and different farms will have different goals for age at first calving. 24 months is a common goal. Heifers need to be well grown when they enter the milking herd, so younger isn’t always better. On the other hand, heifers that are older when they calve require more space, and more feed, and produce fewer replacements. It goes without saying that the most important factor in determining age a calving is age at breeding. Heifers that calve younger enter the milking string earlier and provide replacements earlier.

Maintaining a high level of reproductive performance is critical for maintaining a consistent supply of replacements. So far, the focus has been on the total number of replacements. The final installment will cover strategies for maintaining a consistent number of milking cows from month to month.