The great transition: Turning calves into functioning ruminants

Posted: August 27, 2019 | Written By: Dr. Anne Proctor, Form-A-Feed Nutrition and Production Specialist

transition

When you hear the word “transition,” do you automatically think of your pre- and post-fresh cows? Most dairymen do, but there’s another important transition group that requires your attention. That group is made up of calves transitioning off milk and onto a diet made up of dry feeds.

Not only are they going through a dietary change, they are also making a change in housing, going into a new pen, and some are moving into a group for the first time.

The three weeks before and after weaning are critical for the growth and health of that heifer. A calf that struggles at weaning loses those days of growth and does not get them back. The result is a heifer that takes longer to get to breeding size and costs more to feed and manage to calving. With the high cost to raise a heifer, we can’t afford a poor weaning transition.

The challenge at weaning time is often one of rumen development. In the young calf, all of her nutrients come from milk – and after weaning, all of her nutrients come from grains and forages. This dietary change requires a physiological change in the digestive system of the animal.

In the first eight weeks of the calf’s life, her digestive system changes from one of a functionally monogastric animal to that of the ruminant she will be for the rest of her life.

The change from a non-functional to functional rumen is a gradual one and requires changes in both the physical structure and physiology of the rumen. In an issue of Calf Notes, Jim Quigley, calf and heifer research and technical manager for Provimi, identifies five requirements for rumen development as:

  • Establishment of microbes in the rumen
  • Liquid in the rumen
  • Feed in the rumen
  • Ability of the rumen wall to absorb volatile fatty acids
  • Musculature to expel digesta from the rumen

When the calf is born, the rumen is sterile but quickly populates with microbes from the environment. Microbes need a wet environment, and the liquid in the rumen comes from the calf drinking water. This is one reason providing fresh water to calves is so important; it creates an environment for microbial growth.

Milk, on the other hand, goes into the abomasum and does not contribute water to the rumen.

The rumen microbes need a source of nutrients in order to grow. The dry feed the calf consumes serves this purpose. Microbial populations change depending on the sources of nutrients available. Those microbes produce volatile fatty acids, which are an energy source in a ruminant animal.

The presence of volatile fatty acids stimulate growth of finger-like projections on the wall of the rumen to increase surface area and maturation of the rumen tissue for greater absorption. The musculature of the rumen continually mixes the contents of the rumen and moves material further into the digestive tract. The muscles get stronger as more feed is consumed.

These functions are continually evolving, from the time the calf first starts to consume dry feed, and must be working well in order for the rumen to support the energy and protein needs of the calf on dry feed alone.

The focus in recent years has been on growth in the milk-fed calf, an important part of heifer development. The more milk we feed, the more nutrients we provide, and the better growth we see in the calf. However, at some point, we need to wean that dairy heifer, and she needs to be able to meet her nutritional needs from dry feed alone. Unfortunately, this transition is often overlooked.

We can have a beautiful calf at weaning, but if her rumen is not ready, growth can stall while the rumen catches up. Those days without growth are days in which you paid for the feed to maintain the heifer, but she did not gain weight.

In a worst-case scenario, the heifer loses weight in the first few weeks and, in the end, you have paid twice for those pounds of growth.

It is commonly thought it takes about three weeks from the time the calf starts consuming feed to the time when the rumen is mature enough to support the nutritional needs of the calf. That three-week process is independent of the age of the calf.

The earlier the calf begins to consume starter, the younger she is when the rumen can support her. If starter consumption starts when she’s 3 weeks old, she should be ready to wean after 6 weeks old. If starter consumption does not begin until some of the milk is removed from the diet, the calf may not be ready by weaning.

Achieving good growth rates and having a rumen ready for weaning is a balancing act and is different for every farm. How do you know if your calves are ready for weaning? Pay attention to the age the calves are when you can tell they are consuming starter. Weigh the amount of starter the calf will eat in a day. We’d like to see a calf eating at least 2 pounds of starter when the step-down weaning process begins or 3 pounds of starter for an abrupt weaning.

Evaluate body condition of heifers in the first three weeks after weaning. Calves should maintain body condition through and after weaning. If possible, check weights at weaning and again three to four weeks later. What is the average daily gain?

The Dairy Calf and Heifer Associations Gold Standards recommend calves gain 2.2 pounds per day from 61 to 120 days old. Monitor health of calves after weaning, as calves struggling with the transition are at higher risk of getting sick.

If you find your calves are struggling with the transition, re-evaluate your feeding program. Are you feeding so much milk calves are not looking for additional nutrients? Is the fat content of the milk or milk replacer inhibiting starter intake?

If they are not consuming starter before the weaning process begins, it may be beneficial to extend the weaning process to give the rumen time to catch up before taking milk totally out of the diet.

There are management factors that affect starter intake also. Is there starter available, and is it fresh? Rumen development does not begin until the calf consumes dry feed. Does the calf have water available, and can she reach it comfortably?

Remember: Milk goes to the abomasum, and we need water in the rumen for the microbes growing there. Are the buckets too high for the calf to eat comfortably from or are they too deep?

Being prey animals, calves can be hesitant to put their eyes below the rim of the bucket. Unfortunately, most calf buckets are deep, and the handful of feed we put in for the young calf requires she put her head all the way into the bucket.

Some farms have gone to shallow pans for young calves so they can reach the starter easily while still monitoring their environment. Is there enough bunk space in group pens? We think about bunk space for cows but sometimes forget bunk space matters to calves also. All of the calves should be able to eat at the same time.

Raising quality replacements is important to the profitability of the farm and requires careful management. While, as an industry, we have focused heavily on growth of pre-weaned calves, there are often opportunities when transitioning calves off milk and entirely onto dry feed.

Rumen development is essential for a good transition. Balancing the nutritional needs for growth while also developing a rumen ready to meet the calf’s nutritional needs results in calves that move easily into the next phase of the growing process.

Article originally written for and published by Progressive Dairyman.