Feeding Strategies for Dairy Cattle

1. Feeding Strategies for Dairy Cattle

2. Rumen Function • Rumen functions as flow-through fermentation chamber • Microbes (starch and fiber digesters) • Feed mixing (rumen contractions mix feed, water, microbes and saliva) • 1-3 rumen cycles per minute) • Eructation (remove gases) • 30-50 liters per hour • Eructated at 200 cm/second (bloat)

3. Rumen Microbes • Microbes as a feed source • about 50% protein • Over 80% digestibility • Closer to amino acid profile of milk than any other protein source • For cow producing 100 lbs milk, 80% of protein needs CAN be met by microbial protein (~5 lbs/day) • Depends on quality of feeding program (large range) • DIRECTLY DETERMINES PROFITABILITY OF FEEDING PROGRAM

4. Microbial Requirements for Maximal Growth • Fluid-based media (water source) • Proper temperature (104-106 in rumen) • Constant source of substrate (determined by feeding program) • Proper pH (6.0 target for rumen) • Above 6.2 for fiber digesters • Below 5.8 for starch digesters

5. Rumen Environment • Depends on feeding program • Water availability and quality (and temp) • Maintains fluid-based media • Feed availability and quality • Maintains substrate availability • Rumen temperature increases with increased forage • pH varies dependent on two factors • Rate of acid production and rate of removal from rumen • Rate of buffer production

6. Rumen pH • Acid production • Primarily VFA’s • Acetateprimarily from fiber digesters (fat synthesis in cow) • Propionatefrom all microbes (glucose synthesis in cow – lactose in mammary gland) • Butyrate from starch digesters (rumen epithelium energy source and some fat synthesis) • Also lactate from specific starch digesters • strong acid (high dissociation constant) with slow absorption rate from rumen

7. Rumen pH • Dilution and flushing effects • Water intake flushes acids through digestive system • Absorption rate • The surface area of the rumen (papillae length and integrity) and blood flow to the rumen wall determine the rate at which acids leave the rumen • Buffer production • Buffer provided primarily from saliva (sodium is primary buffer in saliva) • High-producing cows can produce up to 50 gallons a day of saliva • Cannot replace with feed sources (palatability issues)

8. Saliva Production • Directly determined by feed intake and cud-chewing activity • More remastication, more saliva • Level of remastication determined by amount of feed ingested and particle size of feed ingested • Balance between slow rate of digestion (excessive particle size) and rumen acidosis (inadequate particle size)

9. Feeding Order • Feeding forage before feeding concentrates (in component-fed herds where forages and concentrates are fed separately) will buffer rumen before large amounts of acids are produced • More stable rumen environment • Better forage digestibility, faster rate of passage, and increased cow performance compared to feeding forages after concentrates

10. Rumen Acidosis Inadequate particle size Decreased remastication Decreased saliva production Decreased pH in rumen Forage digesters Starch Digesters Decreased Digestibility and Rate of Passage

11. Rate of Passage • Directly affects level of feed intake • Decreased gut motility decreases rate of passage • The reverse is not necessarily true • Increased forage intake increases rumen contractions but decreases rate of passage • Decreased digestibility of feeds decreases rate of passage • Can be feed quality issue or microbe issue • Rumen environment affects feedstuff digestibility!!!

12. Microbes and Digestibility • Each class functions at optimal pH and temperature • Forage digesters above 6.2 • Starch digesters below 5.8 • Above or below optimal environment, digestion slows, microbial growth and reproduction slow • Dead microbes don’t digest anything • Also don’t grow or reproduce!

13. Feed Quality and Digestibility • NDF = cell wall material • Inversely related to intake • 1% increase drops feed intake, milk production • ADF = cellulose, lignin, ash • Inversely related to energy content and digestibility • Both ADF and NDF positively related to remastication and saliva production • Must balance needs of cow with needs of rumen • Relative Feed Value (RFV) – incorporates ADF and NDF values to estimate potential intake value • Does not include protein in this “value” • Forage value increases ~$1/ton per unit of RFV • PEAQ – estimates RFV prior to harvest

14. Fiber Requirements • ADF = 19% of ration • NDF = 28% of ration • 27% in TMR • 29% if particle size inadequate • Particle size • Top box (> 0.75”) about 8-10% of ration • Bottom box (< 0.3”) less than 50% of ration • Middle box (0.3” – 0.75”) the rest of the ration

15. Forage for Dairy Rations • Forage is the foundation of any ration • Most variable component • Greatest possibility of having negative impact on performance • Greatest single factor limiting success of ration balancing

16. Forage Harvest Issues • Weather fluctuations influence harvest date • Harvest date affects forage quality • Digestibility decreases 0.5% each day cutting is delayed • Intake decreases 0.5% each day cutting is delayed • Effects are additive – feeding value decreases 1% each day cutting is delayed

17. Fig 17-8. Purchased hay is delivered to an Iowa dairy farm (Courtesy of Mark Kirkpatrick)

18. Fig 20-5. This extended pile of silage is covered with plastic that is held in place with half-tires until it is ready to be fed out (Courtesy of Howard Tyler)

19. Fig 20-6. Under adverse conditions, plastic coverings protecting silage can be damaged or lost, resulting in spoiled or moldy silage (Courtesy of Howard Tyler)

20. Forage Digestibility • Increase rate of digestion by increasing surface area • Too small of particles does not allow remastication • Long-stem forage enhances saliva production and stabilizes rumen environment • Too large of particles slows down digestion and decreases rate of passage • Decreases feed intake and milk production • Must balance particle size needs of rumen with intake effects on cow

21. Regulating Feed Intake • Physical capacity of rumen • Neural control • NDF fraction • Intake decreases when passage of feedstuffs slows • Acidosis • Unstable rumen

22. Non-structural Carbohydrates (NSC) • Sugars and starches • Produce VFA’s • Rapidly digested • Can change rumen pH quickly!! • Meet energy needs of microbes • Require about 38-40% in ration for this need • Can be a challenge in high-fat diets • On paper, energy needs of cow are met, but ration is actually energy deficient for optimal rumen microbial synthesis

23. Fats • Increase energy density in ration • Do not supply energy to microbes!!!!! • Unpalatable, tend to decrease feed intake • Over 3% in ration will suppress feed intake • Can supplement with “rumen protected” fats • Suppress microbial function • Form “soaps” in rumen • PUFA’s greater negative effect than SFA’s • Decrease fiber digestibility, slow rate of passage • Oilseeds are “slow-release” form of fat, less negative effects in rumen

24. Protein Fractions • Dietary proteins classified based on solubility in the rumen • A • NPN, instantly solubilized/degraded • B1 B2 B3 • Potentially degradable • C • Insoluble, recovered in ADF, undegradable

25. Rumen Degradable Protein (RDP) • About 60% of protein in the ration should be rumen degradable (RDP) to meet needs of microbes • 30% of the protein should be rumen soluble for component-fed herds • 45% should be rumen soluble in TMR-fed herds • Soybean meal is rumen soluble • Corn gluten is an insoluble protein source

26. Rumen Ammonia • Formed from the breakdown of rumen degradable protein • RDP broken down to ammonia and carbon and then re-formed into higher quality microbial proteins • Should be between 2 and 5 mg/dl • High ammonia reflects problem with formation of microbial proteins

27. Microbial Crude Protein (MCP) • Protein produced by microbial synthesis in the rumen • Primary source of protein to the ruminant animal • Microbes combine ammonia nitrogen and carbohydrate carbon skeleton to make microbial crude protein • Diet affects the amount of nitrogen entering the small intestine as microbial crude protein

28. Factors Limiting Microbial Protein Synthesis • Amount of energy • ATP • Available nitrogen • NPN • Degraded feed intake protein nitrogen (RDP) • Available carbohydrates • Carbon residues for backbone of new amino acid Microbial crude protein synthesis relies on synchronization of carbohydrate (for carbon backbones) and nitrogen availability (for amino group)

29. VFA (CHO fermentation) Concentration Blood NH3 Rumen NH3 Time post-feeding Adapted from Van Soest, 1994 Microbial Protein Synthesis • Synchronization of carbohydrate and N availability • NPN supplementation • Carbohydrates used for carbon skeleton of amino acids Carbon backbone (from CHO fermentation)

30. Microbial Protein Formation Dietary Starch Sugar Dietary Cellulose Hemicellulose rapid slow Dietary NPN Carbon Skeletons Sulfur Other Co-factors rapid MicrobialProteins NH3 ATP Amino Acids slower very slow Dietary Insoluble RDP Dietary Soluble RDP

31. Synchronous Feeding Challenges • Soluble protein sources (SBM) are rapidly broken down to ammonia which is primarily used by fiber digesters (cellulolytic bacteria) • Insoluble protein sources (corn gluten meal) are slowly broken down to peptides which are more effectively used by starch digesters (amylolytic bacteria) • For example, feeding NPN in a ration high in structural carbohydrates (high forage diet) results in ammonia moving to blood rather than forming microbial protein

32. Nitrogen Recycling • Excess NH3 is absorbed through the rumen wall to the blood • Quickly converted to urea in the liver • Excess NH3 may elevate blood pH • Ammonia toxicity • Costs energy • Urea (two ammonia molecules linked together) • Relatively non-toxic • Excreted in urine • Returned to rumen via saliva (rumination important) • Efficiency of nitrogen recycling decreases with increasing nitrogen intake

33. Nitrogen Recycling • Nitrogen is continually recycled to rumen for reutilization • Ability to survive on low nitrogen diets • Up to 90% of plasma urea CAN be recycled to rumen on low protein diet • Over 75% of plasma urea will be excreted on high protein diet • Plasma urea enters rumen • Saliva • Diffuses through rumen wall from blood Urease Urea Ammonia + CO2

34. Feed Protein, NPN and CHO RUP Feed Protein AA Feed Protein RDP NH3/NH4 NH3 SMALL INTESTINE Feed NPN Bacterial N MCP MCP AA NH4+ loss RUMEN Salivary N Liver ATP Blood Urea

35. Ruminant Digestion and Absorption • Post-ruminal digestion and absorption closely resembles the processes of monogastric animals • However, amino acid profile entering small intestine different from dietary profile

36. Recycled urea Salivary Urea NH3 UREA LIVER NPN Non-utilized Ammonia Dietary Nitrogen PEPTIDES NH3 AMINO ACIDS LEVEL TO PROVIDE FOR MAXIMUM MICROBIAL GROWTH POOL AMINO ACIDS 65% OF PROTEIN AMINO ACIDS RDP PROTEIN MICROBIAL PROTEIN SMALL INTESTINE 35% OF PROTEIN RUP Reticulo-rumen

37. Milk Urea Nitrogen (MUN) • Rumen ammonia that is absorbed into the bloodstream is converted to urea by the liver and ends up in milk and urine (some in saliva) • Optimal MUN levels between 12 and 14 mg/dl • High crude protein or a low NSC:CP ratio increases MUN • High MUN (>20 mg/dl) reflects rations with excess protein or inadequate NSC • MUN also increases with excessive body condition losses (more muscle protein breakdown) as occurs in early lactation • Must interpret MUN carefully in early lactation cows

38. Microbial Protein Synthesis Summary • Requires that ammonia (from breakdown of RDP) is present at the same time as carbon skeletons (from the breakdown of either complex or simple carbohydrates) • “Nutrient synchrony” • Most crucial when meal feeding, less of a problem when rumen is always full of all feeds (TMR fed with 24-hour feed availability)

39. Rumen Undegradable Protein (RUP) • Protein that “by-passes” rumen degradation to meet the needs of the cow that are not met by microbial protein production • Should be about 40% of total nitrogen fed • Sources include heat-treated soybeans, fish or meat meal, distillers grains • Optimal LYS:MET ratio is 3:1 • Typically requires overfeeding protein to meet methionine needs of cow • Can meet needs with lower RUP and supplemental rumen-stable methionine supplements ($$$)

40. Overview of Protein Feeding Issues in Ruminants • Rumen degradable protein (RDP) • Low protein quality in feed  very good quality microbial proteins • Great protein quality in feed  very good quality microbial proteins • Feed the cheapest RDP source that is practical regardless of quality • Rumen undegradable protein (RUP) • Not modified in rumen, so should be higher quality protein as fed to animal • May cost more initially, but may be worth cost if performance boosted enough

41. Ionophores • Change metabolism within rumen by altering microflora to favor propionic acid production • Bovatec and Rumensin • Fed to heifers to improve live weight gains and efficiency of feed utilization • Fed to cows to improve feed efficiency • Change rumen retention time? • May change % RDP, RUP, amount of nutrients bypassing rumen • Ration composition affects profitability of ionophore inclusion

42. Water • Most overlooked nutrient on many farms • 4-5 lbs water required for every lb milk • Intake varies by: • Weather (temperature, humidity) • Size of cow • Milk production • DM consumed • DM content of feed • Water temperature (effect on rumen function) • Water quality

43. Water • Necessary for maintaining body fluids and proper ion balance, digesting, absorbing, and metabolizing nutrients, etc. • Cows drink 100 to 200 lbs water per day • Heavy producers drink up to 400 lbs • Fresh clean water is crucial • Clean troughs routinely • Intensity of production dramatically affects water requirements

45. Fig 14-18. Lactating cows may require over 50 gallons of fresh water daily to maintain high levels of milk production (Courtesy of Iowa State University)

46. Fig 14-19. Water quality is as crucial as water availability (Courtesy of Howard Tyler)

47. Feeding Systems • Dictated or limited by facility design • Individual feeding systems • Component-fed herds

48. Individual Feeding Systems • Advantage • Ability to feed each cow to her individual needs • Disadvantage • Labor cost • Requirements for specialized housing or specialized feeding equipments

49. Component-fed Herds • Tie stall barns: fed both roughage and concentrate feeds • Many dairy producers modify this version • Concentrates fed at milking time • Roughage portion fed at a feed bunk • Primary challenge is managing the feed order • Provide forage prior to concentrate • Frequent feedings are best

50. Fig 15-2. Concentrate is top-dressed on forage for this component fed herd, allowing cows to selectively consume ration components (Courtesy of Iowa State University)