Consider this: 50 percent of lifetime height growth and 25 percent of lifetime weight gain occur in the first six months of a dairy calf’s life.¹
 
There’s no undo button or way to make up for lost growth during this time, yet many calves experience a post-weaning growth slump with life-long consequences.

Causes of growth slumps after weaning calves

Factors contributing to growth slumps include:

1. Abrupt diet changes: The transition from a milk-based diet to a grain and forage diet disrupts the microbes living in a dairy calf’s digestive tract. The result? A reduction in feed efficiency and growth.
2. Housing changes: Calves spend time learning where and how to eat when they’re moved to a new group housing environment. These activities can result in drops in feed intake.
3. Inadequate nutrition: Too often, the mindset when it comes to feeding heifers is “what’s available?” versus “what do these heifers need?” Just using what’s available can lead to a nutrient gap, affecting growth.
4. Post-weaning stress: Post-weaning stress can weaken calves’ immune systems, causing them to be more susceptible to scours, diarrhea and other digestive problems which impact feed intake.

What calves eat pre- and post-weaning can help them improve growth and successfully transition into life-long productive cows. A diet designed to develop the rumen and increase growth can help reduce age at first calving and save on costs by reducing days on feed and entering the milking herd earlier.^2,3

Pre-weaning calf rumen development

Post-weaning growth starts with calf rumen development in the pre-weaning phase. When a calf is born, her rumen isn’t fully developed. Nor are the papillae, the finger-like projections inside the rumen that absorb nutrients. The growth of papillae directly correlates with what the calf eats, even in the first few weeks of life.⁴ 

Feeding grain or calf starter pre-weaning sparks chemical reactions in the rumen that help it grow and develop. Introducing a high-quality calf starter feed on day 3 of life and feeding throughout the pre-weaned phase jumpstarts the rumen and prepares calves for the post-weaning transition.

Without a well-developed rumen, calves can’t effectively transition to an all-forage diet after weaning, which can lead to reduced feed intakes and growth slumps.

Feeding heifers after weaning

Most farms have a highly regimented pre-weaning nutrition plan. However, all bets are off when it comes to post-weaning nutrition. Some farms offer high forage diets and minimal grain, others offer a grower feed and supplement with forages, while still others offer newly weaned heifers a total mixed ration.

Rumen volume doubles five times from 8-24 weeks. But feeding a high fiber or fermented feed diet immediately after weaning calves can stall rumen development and impact long-term feed efficiency. Feeding calf starter ad-libitum through 12 weeks of age with free-choice hay will help smooth the transition and ensure continued growth. Research demonstrated that calves fed AMPLI-CALF^® 22% Starter showed 13.8 percent greater average daily gain through 12 weeks of age compared to calves fed a commercial 22% starter.⁵

Transition calves to a grower feed at 12 weeks of age to help prepare the calf’s rumen to absorb nutrients from a high-fiber diet. Research showed calves fed Purina^® AMPLI-CALF^® Grower 18% had over 50 percent more rumen surface area for absorbing nutrients (through papillae) and an improved feed-to-gain ratio of seven percent compared to calves fed a traditional grower.⁶

At 24 weeks the rumen is fully developed, and heifers are ready to transition to a fermented feed diet.
A nutrition plan focusing on rumen development in the pre- and post-weaning phase can help your calves avoid the post-weaning growth slump.
 
Still curious about calf rumen development? Check out this article on the science behind building a healthy rumen.