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Are your heifers all grown up?

Al Kertz for Progressive Dairy Published on 07 May 2021

When are heifers “all grown up?” Not really until at least the end of their first lactation. And cows are not considered mature until around their third lactation. Look at the data in Table 1 from a herd database.

Lactation number

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These numbers would vary somewhat in herds dependent on genetics and other factors, but the patterns would be similar. Mature weight and height peaks at around the third lactation.

All cows or first-calf heifers lose 11% of their bodyweight from calving due to the weight of the calf and other tissues and fluids lost. Calves weigh more after the first lactation of their dam. And male calves weigh about 7% more than female calves. These factors impact some first-calving issues like greater calving difficulty incidence of first-calf versus older cows and greater calving difficulty with male than female calves.

Let’s step back now and look at later heifer growth and what happens in the first lactation. Heifers should be averaging about 1.8 to 2 pounds daily gain as noted in a previous article “Heifer growth issue and parameters.” We want to be especially careful that undue fattening does not occur during the last 60 to 90 days before first-calving, as that will most likely increase calving difficulty and then “fat cow syndrome” issues post-calving. Since during the last 60 days before calving about two-thirds of the fetal calf’s weight is deposited, the dam’s bodyweight can be confounded by this, so body condition scoring is more appropriate.

There are a few differences for first-calf heifers versus older cows. A Michigan State study evaluated differences between older cows and first-lactation heifers to a prepartum dietary cation-anion difference diet (DCAD). Milk production was increased by treatments with cows but was the same with heifers. Dry matter intake (DMI) decreased for heifer treatments, but only for one diet for cows. Treatments for heifers increased liver fat content, while they decreased liver fat content for cows – similar for nonesterified fatty acids (NEFAs). In general, heifers are less susceptible to lower plasma calcium, but DCAD can lower DMI and milk production and lead to fatty liver problems.

Differences in DMI, milk production, bodyweight change, and growth and energy balance between first-calf heifers and older cows are shown in this series of graphs (Figure 1, 2, and 3). Key points are:

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Milk production by lactation number

Intake and weight change

Energy deflicit by laction number

  • Milk production is greater overall, increases more rapidly after calving, but declines more rapidly (8% to 10% per month) after peak for older cows versus first-calf heifers (4% to 6% per month).

  • Energy deficit is greater and more extended for older cows versus first-calf heifers because heifers are growing another 10% during their first lactation and give some priority using some nutrients for that growth rather than just for milk production.

  • DMI is less for first-calf heifers versus older cows, and weight loss, like energy balance, is not as great for these first-calf heifers, which are still growing.

The other major area of difference with first-calf heifers versus older cows is in social order and dominance. Since first-calf heifers are smaller and inexperienced, older cows will most likely push them to the bottom of the social order. When grouped after calving, that means they will not likely be able to compete very well with older cows. For that reason, first-calf heifer should be grouped separately after calving, at least for the first third or half of lactation. This will help them eat more, produce more milk and grow that additional 10% bodyweight until they have their next calf.

In many herds, first-calf heifers make up from a third to as much as half of all cows in the herd. And since they also usually have the higher genetics in a herd (increasing about 200 pounds or more each year), it simply makes sense to recognize the differences laid out in this article and manage for first-calf heifers to do better in your herd.  end mark

PHOTO: Staff photo.

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References omitted but are available upon request. Click here to email an editor.

A.F. Kertz
  • A.F. Kertz

  • Nutritionist
  • Andhil LLC
  • Email A.F. Kertz

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