A dairy producer’s reproductive program is one of the most important factors in a successful dairy operation.

However, many producers will admit that heifer reproduction is an area that can be improved upon. Heifers are the most fertile animals in a herd, and should posses the best genetics. To obtain the greatest profit from replacement heifers, dairy producers should work to get heifers bred sooner, use genetically superior A.I. bulls and actively monitor heifer reproductive performance.

Dave Fischer, University of Illinois extension dairy educator, says dairy producers should strive for three main goals:

  1. 1. Grow heifers to 60 percent mature bodyweight at first breeding.
  2. 2. Calve heifers at 23 to 25 months of age.
  3. 3. Strive for 60 percent heifer conception rate.

Knowing when to breed your heifers

The main goal of a replacement heifer program is to grow heifers to reach an optimal size and weight early to start puberty, establish pregnancy and calve easily at the lowest cost possible. Puberty in a dairy heifer is related more to body weight than age. Heifers, on average, reach puberty at 30 to 40 percent of their mature body weight. It is important that cycles prior to breeding be recorded to assure the heifer is cycling correctly and is ready for breeding. Heifers should reach proper weight and size for breeding by 14 to 16 months of age, allowing them to calve between 23 and 25 months of age.

Dairy heifers should be bred at 60 percent of their mature weight. Producers should monitor for weight and height to know when the criteria have been met and help establish ongoing goals if they have not already been set. Heifers that calve at an earlier age deliver many positive results for the dairy producer. It costs a producer on average $1,200 to raise a heifer from birth to calving. The later the heifer’s age at first calving, the more the producer’s costs will rise compared to a heifer that calves earlier, spends more of her lifetime producing milk and returns more profit to the farmer.


Research has also shown that extending the age at first calving results in a greater number of replacement heifers needed to maintain herd size. For example, a 100-cow dairy with an average age at first calving of 30 months and a 38 percent cull rate could decrease the number of replacement heifers needed by 21 head to maintain herd size if the average age at first calving was reduced to 24 months. By decreasing the number of heifers needed for replacement, the producer is also decreasing the associated input costs of feed and housing.

Using artificial insemination on your heifers

A survey asked producers why herd bulls are used instead of artificial insemination (A.I.). Many of their responses included ease, convenience, cost and efficiency. However, research shows that the opposite is true. A.I. programs offer the best genetics and long-term economic advantage compared to natural service bulls, especially on first calf heifers.

When producers use top A.I. bulls on all heifers, they are given an economical and efficient way to increase milk production and improve genetic value. Research has shown that heifers of A.I. sires have a more than 1,200-pound milk production advantage versus heifers sired by a natural service bull.

On many dairy farms first lactation cows represent the largest proportion of the herd, giving producers a direct opportunity to increase their herd’s genetics. Also, first calf heifers contribute proportionately greater numbers of healthy offspring available for herd replacements compared to cows in older age groups. Producers will realize lower semen costs with heifers compared to lactating cows because heifers traditionally have higher conception rates, resulting in fewer services per pregnancy.

While using natural service bulls may add convenience, producers lose income due to costs of feeding and housing the bull, while also losing future profits due to genetic inferiority. Dairy producers using natural service bulls have the risk of calving difficulties with heifers, as on-farm bulls do not possess calving ease records. In addition, keeping bulls on the farm may increase spread of venereal diseases and cause injury to employees.

The most effective way to accelerate genetic progress, increase milk yields, decrease health risks and maximize profits is to incorporate a strong A.I. breeding program.

Measuring reproductive performance

It takes good record keeping, determination and dedication to accurately track heifer reproduction performance rates. When monitoring heifer reproductive program performance, producers should focus on the following three areas:

  • Service rate – a measure of the proportion of eligible heifers serviced during a given 21-day period.

Each individual, nonpregnant heifer should exhibit estrus during a 21-day period. In ideal conditions producers should aim for more than 90 percent of heifers in estrus in a 45-day period.

  • Conception rate – in order to achieve a high conception rate, heifers will need to be at the proper body weight and adequate body condition at the time of breeding.

Producers should expect a high conception rate with a natural, standing heat compared to a timed A.I. program. Heifer raisers should aim towards a conception rate goal of 60 percent or greater.

  • Pregnancy Rate – is the rate at which heifers become pregnant after reaching puberty.

Pregnancy Rate = Service Rate x Conception Rate. Thus, maximizing the conception rate (as well as service rate) provides an opportunity for producers to take control of reproduction and overall profitability in their heifer reproduction program.

In the current state of the dairy industry, it is more important than ever for dairy producers to maximize profitability and increase herd genetics. The best way for a dairy producer to do this is to focus on the heifer reproduction program by breeding heifers earlier and at proper sizes, using a strong A.I. program and closely monitoring heifer reproductive performance. PD

References omitted due to space but are available upon request by emailing editor@progressivedairy.com.

Excerpts from Dairy Cattle Reproduction Council newsletter, Vol. 3, No. 3