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Criteria for weaning

Criteria for weaning. Dry feed consumption Size – ~ 150 lb General health Age – usually 6-8 wk. Heifer-raising industry. ~ __ million cows in US Average culling rate ___% Replacement heifers rank ___ in costs of milk production costs of the dairy enterprise. OPEN HEIFERS.

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Criteria for weaning

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  1. Criteria for weaning • Dry feed consumption • Size – ~ 150 lb • General health • Age – usually 6-8 wk

  2. Heifer-raising industry • ~ __ million cows in US • Average culling rate ___% • Replacement heifers rank ___ in costs of milk production costs of the dairy enterprise

  3. OPEN HEIFERS Open Heifer - Young female that has not been bred After weaning, calf should gain about 1.75 lb per day Reach puberty about 12 mos Heifers should be grouped by size and age Holstein heifers should weigh 800 – 850 lb by 15 mos of age

  4. Normal Heart-Girth Measurement and Weight of Calves and Heifers During Growing Period Holstein Ayrshire Guernsey Jersey Age in months Inches Pounds Inches Pounds Inches Pounds Inches Pounds At Birth 31 29.5 72 66 24.5 56 96 29 1 33.5 118 32 90 72 98 31.5 29.5 3 40.25 213 38.75 179 164 35.25 138 38 47 335 45.5 291 44.25 265 41.5 5 228 52.5 455 51.25 408 49.75 362 47.25 325 7 57 559 55 485 9 53.75 448 51.75 409 11 60.5 658 58 563 56.75 521 55 481 13 63.25 740 60.75 630 59.25 587 57.25 540 15 65.25 805 63 703 61.75 640 59 585 17 67.25 874 65.25 63.5 696 758 60.5 635 19 69.25 66.5 65.5 946 813 752 62.5 687 21 816 64 740 71.5 1025 68.5 885 67.5

  5. OPEN HEIFERS Housing Normally require protection from wind, wet weather, but adequate ventilation Health Vaccinations at 4 to 8 mos of age Stomach magnet Ionophores/Coccidiostats

  6. HEIFERS Breeding Estrous cycle -- 18-22 (21) d in length Estrus -- 16 h in length Restless, more alert Red and swollen vulva Increased mobility, tries to mount other cows Stands to be mounted by other cows Ovulation occurs 12 - 18 h after end of estrus Pregnancy checked >35 d after breeding

  7. Goals for heifer program Body weight after calving: 1200-1250 lb Age at first calving: 22-24 mo Height at calving: 55-57 in Body condition score at calving: ~ 3.5 Average gain for heifer: 1.8 - 2.0 lb/day

  8. Development of the mammary gland 10 mo. 3 mo. • The parenchymal tissue formed before puberty is the foundation for later growth. • Milk production is partly dictated by the number of parenchymal cells at puberty.

  9. Mammary glands • Number and location • Inguinal region--cows, goats, sheep, horses • Abdominal – sows • + correlation between # of glands, offspring

  10. Lifetime of the mammary gland • Periods of growth and regression related to reproductive cycle • Mammogenesis • Lactogenesis • Lactation • Involution

  11. MG Structure - external • Number of glands, teats • Cow – four glands, with four teats • Sheep, goats – two glands, with two teats • Horse – four glands, with two teats • Udder weight (cow) 30 – 80 lbs • Skin (protection, little support) • Teats – • exit for secretion • 25 – 50% cows have supernumerary teats

  12. MG structure - internal • Suspensory ligaments • Blood flow • Mammary tissue insensitive to heat or touch

  13. Structures of the Mammary Gland

  14. Lactation • Success determined by • Maintenance of cell #’s • Secretory activity • Milk removal • ~ 305 d or longer in dairy cows

  15. Milk production • Increases to peak ~ 8 weeks after calving • ~60% of milk produced by 2 rear quarters of dairy cow • Increased by administration of growth hormone, or bST

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