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Use a step-down program to minimize the post-weaning slump

Kayla Aragona and Tana Dennis for Progressive Dairy Published on 30 April 2021

Over the last 10 years, the dairy industry has shown an increased interest in early life feeding programs for calves, spurred in part by several studies and meta-analyses illustrating the potential effect of greater pre-weaning average daily gain on future milk production.

This has resulted in dairy farmers feeding double and sometimes nearly triple the milk feeding rates that had been recommended for decades prior.

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Undoubtedly, growth rates are often excellent when milk feeding rates are high. However, much of the growth advantage gained in the first eight weeks of age is eventually lost due to poor growth rates in the weeks following the weaning transition. Several recent studies attribute the lost advantage, or “post-weaning slump,” to calves’ inability to consume enough energy from starter to match previous growth rates supported by high milk feeding. Some studies have pointed to reductions in starter digestibility during the weaning transition as being a major driver of performance post-weaning. Starter digestibility and the ability to utilize energy from starter is closely tied to the total amount of non-fiber carbohydrates (NFC, such as starches and sugars) consumed before weaning (Figure 1).

cumulative NFC intake

In nearly every published study comparing milk or milk replacer feeding rates, starter intake before weaning is reduced as milk allowance increases.

A few strategies employed to combat the post-weaning slump when high amounts of milk are fed are weaning calves more gradually, weaning calves later or a combination of both. Two recent trials performed at Provimi’s Nurture Research Center have tested some of these strategies relative to an abrupt weaning protocol. In the first trial, calves were fed one of four milk replacer programs:

  • 680 grams per day of milk replacer and weaned over three days (6 weeks old at weaning)

  • 1,130 grams per day of milk replacer and weaned over seven days (6 weeks old at weaning)

  • 1,130 grams per day of milk replacer and weaned over seven days (8 weeks old at weaning)

  • 1,130 grams per day of milk replacer and gradually weaned over 14 days (8 weeks old at weaning)

After weaning, calves were grouped by feeding program and fed a textured calf starter with 5% chopped grass hay until 4 months of age. Pre-weaning average daily gain was greater for calves fed 1,130 grams versus 680 grams of milk replacer. However, all four treatment groups had similar bodyweight and skeletal frame size at 4 months of age. Additionally, growth rates and starter digestibility were greatest post-weaning for calves fed 680 grams of milk replacer compared to calves fed more milk replacer. Calves fed 1,130 grams of milk replacer and gradually weaned over 14 days had greater starter digestibility up to four weeks post-weaning compared to calves fed 1,130 grams of milk replacer and weaned over seven days (Figure 2).

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Week of age

In the second trial, calves were fed one of four milk replacer programs and weaned at 7 weeks of age:

  • 680 grams per day of milk replacer and weaned in one step over seven days (abrupt)

  • 680 grams per day of milk replacer and weaned in two steps over 21 days (gradual step)

  • 1,130 grams per day of milk replacer and weaned in one step over seven days (abrupt)

  • 1,130 grams per day of milk replacer and weaned in two steps over 21 days (gradual step)

A few notable improvements with gradual weaning over 21 days when feeding 1,130 grams per day of milk replacer were initiating starter intake earlier (Figure 3), improved feed efficiency during the weaning transition, and improved fibre digestibility estimates around weaning and up to five weeks post-weaning compared to abrupt weaning over seven days.

Week of age

However, when calves were grouped by feeding program and fed to 4 months of age, there were no differences in final bodyweight. These results suggest gradual weaning is needed when feeding high amounts of milk replacer to maintain performance through the weaning transition.

Excellent starter intake pre-weaning is key to maintaining growth rates through the weaning transition. Defining excellent starter intake will depend on the NFC (starch and sugar) levels of the starter fed, as calves need to consume high levels of NFC before they are weaned. Consumption of these fermentable carbohydrates initiates rumen development and is a better predictor of changes in digestion than age. When calves are fed a high NFC starter, a cumulative intake of about 40 kilograms (Figure 1) of starter in the preweaning period would indicate sufficient ruminal development. If calves are fed a lower NFC starter, cumulative consumption of starter must be greater and closer to 68 or more kilograms. Based on this research, if calves are fed more than 680 grams of milk solids, the old rule of thumb that calves should be monitored to consume 680 to 900 grams of starter for three consecutive days prior to weaning is not valid. Calves need to begin consuming starter by 3 weeks of age and gradually increase intake through and after weaning to reach cumulative starter intakes of this magnitude; however, feeding more than 680 grams of milk solids reduces cumulative starter intake.

Calves with excellent starter intake before weaning are also usually fed less milk replacer or utilize a step-down weaning program to initiate earlier starter intake. When comparing on a cost-per-kilogram-of-weight-gain basis, it is often a smarter investment to focus on optimizing milk and starter intake compared to feeding higher amounts of milk for a longer period of time. Feed costs can be $20 to $76 more per calf as feeding rates increase from 680 to 1,130 grams of milk replacer and weaning is gradual or extended from 7 to 8 weeks of age (Table 1).

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Impact of milk replacer feeding and wearing program on intake, growth and feed costs to 4 months of age

With milk replacer costs being six to eight times more than the cost of starter, feeding more milk replacer increases the cost to raise a calf. With no improvements in bodyweight at 4 months of age, the feed cost per kilogram of bodyweight gain can increase 9% to 33% even with gradual weaning off of a high- milk-replacer feeding program. As the pre-weaned calf is the most expensive animal to feed and manage on the dairy, preserving growth rates through weaning should start with a milk feeding program that fosters more starter intake to ensure efficient starter utilization and growth post-weaning. end mark

Tana Dennis, Ph.D., is a dairy technology application lead at Provimi.

Kayla Aragona
  • Kayla Aragona

  • Dairy Calf and Heifer Specialist
  • Provimi
  • Email Kayla Aragona

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