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

1. Calf Nutrition Issues and Factors Affecting Rumen DevelopmentDr. Howard TylerDepartment of Animal ScienceIowa 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. 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 NOTstimulate mucosal growth Absorptive Ability of Rumen Tissue

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

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

20. Starter Without Hay Textured Commercial textured starter CP - 23.58% ADF - 6.39% Ground CP - 25.44% ADF - 6.44%

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 Hay of consistent particle size CP - 23.08% ADF - 6.47% Coarse + 15% Hay Hay of consistent particle size CP - 22.60% ADF - 7.43%

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