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Milk replacer feeding rate impacts nutrient digestion as calves age

Tana Dennis for Progressive Dairyman Published on 31 March 2016

Over the last decade, research has consistently shown average daily gain (ADG) improves when milk or milk replacer is fed at rates providing more than 1.0 pounds of solids per day. Liquid feeding programs encouraging intakes greater than 2.0 pounds of solids per day have been promoted by several university research groups and feed companies in order to provide more “biologically appropriate” nutrition.

While ADG is certainly increased by feeding more milk, several studies have shown calves consuming more than 1.5 pounds of solids per day often experience a “slump” in ADG immediately after weaning. Some have suggested reduced starter intake at weaning explains reduced performance after weaning; however, not all trials feeding more milk resulted in reduced daily starter intake at weaning or immediately post-weaning.

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There are a few digestibility estimates for calves fed large amounts of milk, although lower organic matter and fiber digestibility immediately post-weaning have been reported when more than 1.5 pounds of solids are fed in the liquid diet.

Much of the focus has been on digestibility around weaning, although an understanding of the evolution of nutrient digestibility in calves learning to consume solid feed is lacking and may help explain variability in intake and performance after weaning for calves fed large amounts of milk.

Several trials have been conducted at the Nurture Research Center to determine nutrient digestibility as calves age under different feeding regimens pre- and post-weaning. Milk replacer feeding rates were classified as either “moderate” (1.0 to 1.5 pounds per day of powder) or “aggressive” (greater than 1.5 to 2.5 pounds per day of powder) for analysis.

Calf starter and grower grain offered to calves pre- and post-weaning ranged in chemical composition from 17 to 21 percent protein (CP), 11 to 43 percent starch and 13 to 43 percent fiber (NDF) on a dry matter basis. Weaning was completed by 6 or 7 weeks of age and chopped, low-quality grass hay was provided after 8 weeks of age at a rate of 5 percent of the total mixed diet.

Using digestibility estimates from calves from 3 to 16 weeks of age, we observed distinct patterns in solid feed intake and nutrient digestion. Starter intake was depressed for calves fed aggressive milk replacer rates pre-weaning, but not post-weaning (Figure 1).

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Starter intake of calves fed moderate (MOD) or aggressive (AGG) milk replacer

Digestion of organic matter (OM) was greatest at 3 weeks of age for calves fed more milk (89 vs. 82 percent), but was reduced about nine percent compared to calves fed moderate feeding rates from 8 to 11 weeks of age when milk was no longer in the diet (Figure 2).

Organic matter digestibility of calves fed moderate or aggressive milk replacer

NDF digestibility was roughly 51 percent greater, on average, for calves fed moderate amounts of milk replacer from 3 to 11 weeks of age (Figure 3).

Fiber digestibility of calves fed moderate or aggressive milk replacer

Starch digestibility was 17 to 22 percent greater for calves on moderate compared to aggressive feeding programs when milk was still in the diet (3 and 6 weeks of age; Figure 4), but was similar once starter or grower diets were the sole source of nutrients to 16 weeks of age.

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Starch digestibility of calves fed moderate or aggressive milk replacerAs digestibility estimates for NDF and starch would be directly related to solid feed intake in these calves, it appears delayed starter intake in calves offered more than 1.5 pounds of milk replacer powder negatively affected digestion throughout the pre- and immediate post-weaning period.

This may also reflect delayed rumen development despite similar starter intakes immediately post-weaning (8 weeks of age).

Much of the promotion of feeding rates in excess of 1.5 pounds of solids per day has been to provide “biologically appropriate nutrition” to young calves with the expectation of increased first-lactation milk yield.

While improving early life nutrition compared to how we have raised calves in the past undoubtedly increases growth potential and lifetime milk production, sacrificing growth around weaning due to reduced digestion seems counterproductive to achieve high growth rates prior to weaning.

Balance between maximizing growth from milk or milk replacer feeding and encouraging early starter intake to develop the rumen would likely result in similar or improved growth rates from birth to 16 weeks of age due to enhanced nutrient digestion earlier in life. PD

Tana Dennis
  • Tana Dennis

  • Calf and Heifer Nutritionist
  • Provimi North America
  • Email Tana Dennis

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