Criteria for weaning

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 gt35 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