CA7 - Beef from the Dairy Herd (Calves) 5

CA7 - Beef from the Dairy Herd (Calves) 5

1. 13. Economics asso. w/ milk substitute

   • Before weaning milk sub. comprises 2/3 of feed costs - hence strong economic incentive to get calves weaned as soon as is reasonable
     • Hence important to develop functioning rumen asap (see below)

2. 14. Developing a functioning rumen 1

   • 5 factors
     • 1. Establishment of bacteria in rumen
       • 2. Necessity to have liquid in rumen
         • 3. System for rumen to contract & relax - causes outflow of material
           • 4. Ability of rumen EPT to absorb microbial products
             • 5. Availability of substrate in rumen
   • Fresh clean water is required
     • Otherwise bacteria can't grow -> slows ruminal development
       • Milk can't replace fresh water!
   • Rumen bacteria in preruminal animal are different from those in mature animal
     • First born: Rumen is sterile - no bacteria.
       • 1 d.o.: Large [bacteria] (mostly aerobic) from swallowing bedding, saliva, etc. & inoculated by mother licking
         • No. & types of bacteria change as hay & feed intakae occurs & substrate available for fermentation changes
           • Decrease of aerobic bacteria when start to eat forage/grain
           • Before dry feed - bacteria exist by fermenting ingested hair, bedding & from milk from abomasum into rumen
           • Substrate ingested influences type of bacteria (e.g. hay vs grain)

3. 15. Developing a functioning rumen 2

   • Growth & development of ruminal absorptive SA (Papillae) - required for absorbing & utilising microbial digestion end products (esp. rumen VFA)
     • Won't happen on milk/milk sub alone -> Because its chemical composition & shunting by oesophageal groove limit milk's ability to stimulate rumen EPT metabolic activity & VFS production
   • Solid feed are directed to reticulo-rumen for digestion (unlike liquid)
     • stimulates rumen microbial proliferation & production of VFA
       • Chemical composition of feeds & resultant microbial digestion end products have greatest effect on EPT development
         • casein, starch, cellulosem, minerals & sodium butyrate - have the greatest influence
   • Conc. causes a change in microbial population (increased butyrate & propionate production at acetate's expense) & lowers pH
   • Forages maintain a higher ruminal pH due to bigger particle size & more fibre content
     • High pH supports microbial populations
   • Stimulants = Increased butyrate/propionate production OR Decreased ruminal pH concomitant w/ stronger ruminal acid production (OR a combination)
     • Concentrates have a greater effect on ruminal EPT development