1. Nutrient Requirements of Horses Presentation Part 3: Protein #8895-C

2. Protein Amino acids - building blocks of protein Primary parts of muscles, enzymes, & many hormones – Enzymes - substances that increase the rate of a chemical reaction

3. Protein Requirement for protein is related to: – Horse ’ s dietary needs – Quality & digestibility of the protein

4. Requirements - Maintenance To estimate protein needs - look at digestible protein (DP) – Not crude protein (CP) Maintenance status - require 0.60 g /day DP per kg of body weight

5. Requirements - Maintenance For a 500 kg mare DP requirement will be: 500 kg x 0.60 g/day/kg = 300 g/day

6. Requirements - Maintenance To find how much CP is needed daily while eating forage diet of 46% digestibility, do the following: Divide DP requirement by the digestibility (in decimal form): 300 g/day ÷ 0.46 = 652.17 g/day or 652 g/day x 454 g/lb = 1.44 lbs of CP per day

7. Requirements - Maintenance If protein and lysine amino acid requirement met - other amino acids needs will be met – Lysine - first limiting amino acid in typical horse rations

8. Requirements - Maintenance If horses do not receive enough lysine, other amino acids will not be used effectively Normal diets contain 3.5% lysine

9. Requirements – Breeding and Gestation Mares not lactating during breeding season & early gestation have feed requirements similar to maintenance horses 60-65% of fetal development happens during last 90 days of gestation – Increases protein needs

10. Requirements – Breeding and Gestation Requirements of a 500 kg mare in gestation are: – 9th month - 127 g of DP/day over maintenance – 10th month - 130 g over maintenance – 11th month - 178 g over maintenance

11. Requirements – Breeding and Gestation DP for a mare in maintenance is 300 g For example in the 9th month: 127 g + 300 g = 427 g Feed ’ s digestibility must also be looked at

12. Requirements – Breeding and Gestation For example: If horse has 55% protein digestibility, divide DP needs of 427 g for a mare in the ninth month by 0.55, to get CP needs

13. Requirements - Lactation Protein content of milk - highest right after birth – Gradually diminishes Diet content does not affect milk production Production level relies upon intake of energy & protein

14. Requirements - Lactation To calculate CP needs for mares lactating assume the following: Milk consists of 2.1% in early & 1.8% in late lactation Efficiency of DP utilization for milk production - 65% Protein digestibility - 55%

15. Requirements - Lactation To calculate daily protein requirement of a 500 kg mare during early lactation: 500 kg x 0.03 kg of milk produced per kg of body weight x 2.1 % protein in milk 500 x 0.03 x 0.021 = 0.314 kg of protein secreted in milk

16. Requirements - Lactation 0.315 kg ÷ 0.65 (the efficiency of utilization coefficient) = 0.485 kg of protein for milk production 0.485 kg +.3 kg (maintenance requirement) = 0.785 kg of dietary DP needed 0.785 kg ÷ 0.55 (apparent protein digestibility coefficient) = 1.427 kg of dietary CP required

17. Requirements - Growth Primary nutritional factors that influence rate of growth for young, growing horses: – Protein – Energy consumption Growth rate restricted if either is limited

18. Requirements - Growth Weanlings: – 50 g/Mcal DE/day of protein – 2.1 g/Mcal of DE day of lysine Yearlings: – 45 g/Mcal DE/day of protein – 1.0 g/Mcal of DE day of lysine

19. Requirements - Work Mature horses - protein requirements increase only small amount with exercise Extra feed given to meet energy needs supplies sufficient protein

20. Requirements - Work Only concerns: – If hay being fed is very low in protein – If fed extra dietary fat to provide energy Provide higher protein amount in grain to compensate

21. Requirements - Work Feed 12% protein grain ration with 7-8% protein hay With lower quality hay, feed 14% protein grain ration

22. Use of Nonprotein Nitrogen Nonprotein nitrogen (NPN) available in the form of urea Does not benefit diet Mature horses can tolerate urea Should not receive more than 4% urea

23. Use of Nonprotein Nitrogen Ruminants, such a cattle and sheep, consume larger proportions of urea Growing horses cannot attain maximum growth, & lactating mares do not produce high milk volumes when urea supplies large portion of nitrogen requirement

24. Signs of Deficiency Young horses that receive insufficient protein or lysine have diminished growth & development Mature horses with inadequate protein or amino acid consumption results in: – Lower feed intake – Loss of body tissue – Poor hair coat – Decreased hoof growth

25. Signs of Excess Moderate excess of protein - no harmful effects Excess protein can change daily water needs