1. Calf Nutrition Issues and Factors Affecting Rumen Development Dr
Calf Nutrition Issues and Factors Affecting Rumen Development Dr. Howard Tyler Department of Animal Science Iowa State University

2. Meeting The Nutrient Requirements of the Calf
A nutritionist’s nightmare
Entire pre-weaning period is transition period from non-ruminant to ruminant
proportions of nutrients provided by liquid vs. solid feeds in constant flux
physical capacity of rumen increases
potential for dry matter intake also increases
fermentative capacity of rumen increases
absorptive capacity of rumen increases
therefore, digestibility of solid feeds also changes as rumen develops

3. Energy Requirements
Approximately 20 kcal/pound of body weight in a thermoneutral environment for maintenance
Eighty pound calf requires 1500 kcal maintenance and 850 kcal for 0.5 lb of gain (2350 kcal/day total)
Requirements increase 1% for every degree below 500 F
High surface area:body mass ratio
Require 450 kcal more at 200 F (2800 kcal/day total)
Difference between ruminating calves and non-ruminating calves
Difference between small and large calves

4. Body Size and Growth Rate Affects Protein Requirements
The size of the calf affects the protein requirements at any given level of intake
For 95 lb calf receiving 10 ounces of milk replacer twice daily, a 20:20 milk replacer meets the protein needs
An 85 lb calf receiving the same amount of milk replacer needs 22.5% protein, and a 75 lb calf needs 25% protein
Less energy needed from maintenance in lighter calves, so more energy available for growth
Therefore, more protein required to support lean growth
Required protein:energy ratio needed changes with rate of gain targeted and size of animal being fed

5. Factors Affecting Protein Requirements
Rate of gain determines amount of protein required
If facilities, genetics, and calf source/management permit rapid gain, then high levels of protein and energy required in diet
If facilities, genetics or calf source/management LIMIT rate of gain, then protein and energy must be reduced accordingly
The size of the animal affects the protein requirements at any given level of intake
Less energy needed from maintenance in lighter animals, so more energy available for growth
Therefore, more protein required to support lean growth
Frequency of feeding affects digestive efficiency
Natural suckling frequency allows greater intake than most “hand-feeding” systems can achieve
Required protein:energy ratio changes accordingly

6. Imbalanced Protein:Energy Ratios
If energy diverted to immune function (poor facilities), then it is NOT available for growth
Excess protein must be de-aminated and ammonia detoxified and excreted
Energy required (3 ATP per molecule of urea) and therefore even LESS energy available for growth and immunity
Overfeeding protein (in this case by underfeeding energy) impairs growth and may impair immunity

7. Is Mortality Rate an Issue? (Summary)
Under excellent management conditions, there is no evidence that calves fed higher levels of protein (appropriate for maximal growth rates) are at more risk or less risk for dying
Under marginal conditions, calves fed higher levels of protein may be at higher risk
Under highly challenging conditions, calves fed higher protein levels are at higher risk of dying than calves fed conventionally
This begs the question – do calves on
a higher plan of nutrition have a stronger
immune system or a weaker immune system?

8. Does Higher Plane of Nutrition = Higher Functioning Immune System?

9. Does Higher Plane of Nutrition = Higher Functioning Immune System?

10. Does Higher Plane of Nutrition = Higher Functioning Immune System?

11. Does Higher Plane of Nutrition = Higher Functioning Immune System?

12. Challenges with Liquid Feeding Strategies
High energy intake from liquid feed delays initiation of starter intake and suppresses appetite for starter
high fat inclusions during cold weather
higher solids in the same volume
of milk replacer
higher volume intakes
Must balance accelerated growth with accelerated rumen development

13. Establish Microbial Populations
After birth aerobic bacteria colonize
Anaerobic bacteria soon dominate
cellulolytic and methanogenic first
lactate-fermenting exceed adult values then decline
protozoa introduction requires contact with mature ruminants
Influenced by access to solid feed and the composition of the ration

14. Water Water availability may limit starter intake
free water necessary for development of rumen fermentative capacity
water in milk replacer bypasses rumen

15. The Rumen at Birth
At birth, the rumen and reticulum are under developed, sterile, and non-functional
Milk bypasses the reticulorumen by the esophageal groove
The reticulorumen comprises less than 1/3 of the entire stomach volume

16. The Rumen at Weaning
The rumen is the primary compartment (over ½ of stomach volume)
Size, metabolic activity, and blood flow have increased markedly
The rumen modifies both energy and protein prior to digestion by the calf

17. Absorptive Ability of Rumen Tissue
The rumen wall consists of two distinct layers:
musculature
absorptive epithelium (mucosa)
The mucosa is responsible for absorbing VFA
Muscle is develops in response to material in the rumen
Development of the mucosa depends on the production of VFA
Roughage does NOT stimulate mucosal growth

18. Rumens of 4-Week-Old Calves
Milk and Hay
Milk, Grain, and Hay

19. What is the Right Balance?
Concentrates
VFA production
butyrate
High in energy
fermentable carbohydrates
Palatable
Forages
Low in energy
structural carbohydrates
Ruminal abrasion value (RAV)
Bulk
Rumination

20. Starter Without Hay Textured Ground Commercial textured starter
CP % ADF %
Ground
CP % ADF %

21. Importance of Particle Size
Particle size of the diet influences
Palatability
Speed of digestion
Rate of acid production
Rumen retention time for digesta
Rumen pH via saliva production
Integrity of rumen papillae (RAV)

22. Starter With Grass Hay Coarse + 7.5% Hay Coarse + 15% Hay
Hay of consistent particle size
CP % ADF %
Coarse + 15% Hay
Hay of consistent particle size
CP % ADF %

23. Calf Starter with 7.5% Grass Hay
Increased body weight
Increased feed efficiency
Alters rumen VFA production
increased acetate:propionate
Creates a more stable rumen environment
Decreased starter costs
significantly improved feeding profitability
4 lbs chopped hay per 50 lb bag of starter

24. Changes in Nutrients Utilized by Calves After Rumen Development
VFA are produced in the rumen and become an important source of energy
Blood glucose declines
Ruminal bacteria increase in population and become a primary source of protein
50% protein
80% digestible
High biological value

25. Weaning Strategies
Level of calf starter intake correlates with maturity of rumen fermentative function as well as physical development of rumen
Weaning should be intake-based
Weaning reduces labor costs by 50% and costs of gain by 3 to 5-fold
earlier weaning of healthy calves is most profitable

26. Can A Ruminant Survive Without A Rumen???
Rumenectomies (early removal of the rumen) or prolonged milk feeding used to answer this question
Young ruminants will survive for a time without rumen fermentation
Animal viability decreases and sudden death occurs between 6 and 8 months of age
Can be reversed almost immediately by providing food to the rumen!!!
Ruminant animals “hard-wired” metabolically to function as ruminants
Must utilize the end-products of microbial fermentation

27. On raising calves
The first four weeks of its life the calf must receive the whole of its mother’s milk, because in this period the nutrition contained in the milk in so small volume can be replaced by no other equally nutritious and as easily digestible means of food.
After four weeks the milk may be replaced by that means of fodder which nutritious substance next to it in equal weight of dry volume, in the greatest possible amount.
USDA, 1847