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 96
29.5 72 29 66
24.5 56 1
33.5
118 32 98
31.5 90
29.5 72 3
40.25
213
38.75
179 38
164
35.25
138 5 47
335
45.5
291
44.25
265
41.5
228 7
52.5
455
51.25
408
49.75
362
47.25
325 9 57
559 55
485
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
758
63.5
696
60.5
635 19
69.25
946
66.5
813
65.5
752
62.5
687 21
71.5
1025
68.5
885
67.5
816 64
740

5. OPEN HEIFERS Housing Health 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 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 h after
end of estrus
Pregnancy checked >35 d after breeding

7. Goals for heifer program
Body weight after calving: lb
Age at first calving: mo
Height at calving: in
Body condition score at calving: ~ 3.5
Average gain for heifer: 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 ~ 305 d or longer in dairy cows
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