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Potential benefits of growing heifers to reach puberty at a younger age

Noah Litherland and Pat Hoffman for Progressive Dairyman Published on 24 August 2017

Puberty in dairy heifers can be defined as a measurable increase in blood progesterone with the presence of a corpus luteum (CL) on an ovary, and heifers begin actively cycling. Dairy heifers reach puberty at a defined stage of maturity (45 to 50 percent of mature size) rather than a certain age.

The onset of puberty is not an acute event. Rather it is a chronic event and occurs over a few months as the heifer matures and reproductive hormone concentrations reach a threshold for cycle initiation.



Mature cow size is defined as the weight of third-lactation cows. For example, Holstein heifers should reach puberty by 600 to 700 pounds in herds with 1,400-pound mature cows or 700 to 800 pounds in herds with 1,600-pound mature cows.

Several factors impact age of puberty, including breed (Jerseys mature at a younger age than Holsteins), genetic maturity, nutrition, management and health. Stressors, such as thermal stress, impact the hormonal cascade that controls heifer development.

Many hormones influenced by nutrition also carry out important roles in reproduction. For example, leptin is a hormone produced by adipose tissue that links nutritional history, environmental stressors and physiology in mammals. Leptin is an essential hormone for puberty and reproduction.

Some farms already grow heifers at a rate to reach puberty earlier. This helps explain, at least in part, why these farms calve in heifers at 22 months without sacrificing milk yield. Their heifers reached puberty earlier because they grew to 45 to 50 percent of mature body size at a younger age.

Increased heifer growth rates do not mean a farm will produce a larger cow. Rather, they mean heifers will get to a productive size more quickly and efficiently, improving profitability for farmers and heifer growers. Although heifers can be fed and managed to reach maturity earlier, heifers should still be bred at 55 percent of mature size and calve in no earlier than 22 months of age.


Early and consistent heifer growth for an earlier start of puberty has several benefits. First, increasing efficiency to calve in more heifers at the targeted age range minimizes excessive days on feed. It also has benefits related to the increased number of estrus cycles heifers experience. Researchers reported up to a 21-percent increase in heifer fertility from pubertal estrus to the third estrus.

Increasing the number of full estrus cycles before breeding also has an impact on mammary gland parenchyma tissue development. This is a slow and highly coordinated process. At 30 days of age, parenchyma tissue is not readily visible. By 75 days of age, a walnut-sized mass of it is evident and, at 90 days, the parenchymal tissue weighs about one-third of an ounce, but has grown by 60-fold since birth.

A growing area of research aims to investigate links between calf nutrition, mammary development and age at puberty. This exciting work will help shed light on how we can unlock constraints to milk production through better youngstock husbandry.

Let’s look at a simple example demonstrating how growth rate in all three phases impacts the age heifers reach 550 pounds (Table 1).

Example growth of moderate or high performance heifers at eight months of age

In this example, the high-performance heifer grew to 550 pounds at 8 months, while the moderate-performance heifer reached 500 pounds at the same age.


The high-performance heifer is a whole month of growth ahead of the moderate-growth heifer and will likely have advantages of an extra estrus cycle before breeding time, greater mammary development at breeding and greater reproductive efficiency.

Now let’s focus on some strategies to keep heifers growing quickly, efficiently and consistently in all three growth phases.

Nursery phase

A successful nursery phase is a hallmark of programs that consistently produce quality replacement heifers. This success is greatly impacted by a high degree of competence in the maternity pen. Feed calves for a balanced nutrient supply from milk and starter grain, and maintain calf growth rate through the transition period. A reasonable goal for Holstein heifers is 190 pounds at 60 days or an average daily gain of 1.8 pounds per day.

Elite farms routinely exceed this growth rate. We grow calves from the inside out, and this growth does not occur overnight. Starter grain intake is critical for establishing a fast start to gastrointestinal tract maturity and, therefore, steady growth through weaning and transition.

A reasonable goal for Holstein heifers is an average starter intake of 1.6 to 2 pounds per day (100 to 120 pounds consumed in the first 60 days).

Adequate protein and energy intake from milk and starter early in the nursery phase is also key. Calves fed for greater gains (35-pound advantage versus control-fed calves) during the nursery phase reached puberty 23 days earlier (average age of puberty was 272 +/-27 days) than calves fed a low plane of nutrition from a low-protein and low-fat milk replacer.

Transition phase

The goal in the transition phase (three weeks after the nursery phase) is to maintain momentum from the nursery phase. Adequate calf size, a functioning and healthy rumen, a low-stress environment and adequate access to feed and water all impact success in the transition phase.

During this time, maintain feed intake and keep lungs healthy. Make sure feedbunks are designed to allow easy access to grain and that the feed’s starch and fiber concentrations are in balance.

Research showed that feeding for increased rates of gain from 200 to 400 pounds in Holsteins decreased time to puberty, and Holsteins reached puberty at an average of 553 pounds and Jerseys at 400 pounds.

Grower phase

During the grower phase, calves are sensitive to environmental and nutritional inconsistency. Some research has shed light onto the impacts of challenging environment and errors in nutrition on these heifers.

Socially dominant heifers achieved puberty earlier (314 days) than subordinate heifers (330 days). The authors concluded that, under continuously competitive situations, dominant heifers were more precocious than subordinate ones, achieving earlier puberty. Strive to maintain stocking density of heifer pens at or below 100 percent to minimize antagonistic social behaviors.

Feeding growing heifers corn contaminated with mycotoxins (aflatoxin and fumonisin) delayed puberty compared with heifers fed uncontaminated corn. Parasite infection (ostertagia, cooperia, haemonchus and trichostrongylus) during heifer development impaired normal growth and delayed onset of puberty through altered hormone profiles.

Studies demonstrated treatment for internal parasites effectively advanced the onset of puberty and increased IGF-1 (a primary hormone regulating growth) concentration.

Penn State researchers fed 4.5-month-old heifers to gain either 1.5 or 2.2 pounds per day and found higher growth rates decreased age of puberty by 32 days.


Work with your nutritionist, veterinarian and farm records to better understand the development of your heifers and consider how earlier puberty may affect your herd’s performance.

Take a close look at how age at puberty impacts age at breeding, age at calving, feed costs, number of nonproductive days, reproductive efficiency and first-lactation milk yield. You might be surprised by the opportunities you find.  end mark

Noah Litherland
  • Noah Litherland

  • Dairy Youngstock Technical Specialist
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