by
Susan Schoenian
Date of last revision:
29-Sep-2006 18:16
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In
order to make fair comparisons, records need to be adjusted to a common
basis.
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To be used properly in selection, all records need to be adjusted to a common basis. Growth measures such as weaning weight need to be adjusted for sex of lamb, type of birth/rearing, lamb age, and age of dam.
Calculating Age-Corrected Weaning Weights
The first step is to adjust weaning weights to a common day of age. For lambs that are weaned at less than 75 days of age (on-average), 60-day weaning weights should be calculated. For lambs weaned over 75 days of age, 90-day weaning weights should be calculated. To do this, you need to determine the lamb's pre-weaning average daily gain (ADG).
If birth
weights are not known, pre-weaning weight per day of age (WDA) can be used instead
of pre-weaning ADG
Adjusting Age-Corrected Weaning Weights for lamb sex, ewe age, and type of birth/rearing
Once you determine the age-corrected weaning weight, you need to adjust it for the sex of the lamb, age of its dam, and type of birth and rearing. The table below gives the appropriate adjustment factors.
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ADJUSTMENT
FACTORS
Multiplicative adjustment factors to correct for effects of sex, age of dam, and type of birth and rearing on lamb weaning weights |
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Sex
of Lamb
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Age
of Dam
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Type
of birth and rearing
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1,
1
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1,
2
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2,
1
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2,
2
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3+,
1
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3+,
2
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3+,
3
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Ewe
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1
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1.14
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1.30
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1.27
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1.37
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1.36
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1.46
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1.56
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2
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1.06
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1.21
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1.18
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1.27
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1.26
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1.36
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1.45
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3-6
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1.00
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1.14
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1.11
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1.20
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1.19
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1.28
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1.37
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>
6
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1.04
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1.19
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1.15
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1.25
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1.24
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1.33
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1.42
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Ram
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1
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1.04
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1.18
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1.15
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1.24
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1.23
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1.33
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1.42
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2
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0.96
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1.10
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1.07
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1.16
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1.15
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1.23
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1.32
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3-6
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0.91
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1.04
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1.01
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1.09
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1.08
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1.16
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1.25
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>
6
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0.95
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1.08
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1.05
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1.14
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1.13
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1.21
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1.30
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Wether
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1
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1.11
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1.26
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1.23
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1.33
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1.32
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1.42
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1.51
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2
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1.03
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1.21
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1.14
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1.23
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1.22
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1.32
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1.41
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3-6
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0.97
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1.11
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1.08
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1.16
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1.15
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1.24
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1.33
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>
6
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1.01
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1.15
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1.12
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1.21
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1.20
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1.29
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1.38
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Here are some examples:
Example
#1
Let's determine the 60-day adjusted weaning weight of a ewe lamb with a birth
weight of 8 lbs. and a weaning weight of 68 lbs. at 70 days of age. She was
born and raised as a twin. Her dam is 2 years old.
1. Pre-weaning
ADG = (68 - 8) / 70 = 0.857 lbs./day
2. Age-corrected weaning weight = (0.857 x 60
d) + 8 = 59.4 lbs
3. Adjustment factor for a ewe lamb, born and reared as a twin, out of
a 2 year old dam is 1.27 (see table)
4. Adjusted 60-day weaning weight = 59.4 x 1.27
= 75.5 lbs.
Example #2
Now, let's determine the 60-day adjusted weaning weight of a ewe lamb with a
birth weight of 12 lbs. and a weaning weight of 85 lbs. at 75 days of age. She
was born and raised as a single. Her dam is 5 years old.
1. Pre-weaning
ADG = (85 - 12) / 75 = 1.04 lbs/day
2. Age Corrected weaning weight = (0.97 x 60 d)
+ 12 = 70.4 lbs
3. Adjustment factor for a ewe lamb, born and reared as a twin, out of
a 2 year old dam is 1.00 (see table)
4. Adjusted 60-day weaning weight = 70.4 x 1.00
= 70.4 lbs.
If you had only looked at actual weaning weights, you would have favored the second ewe lamb in your selection program. However, the first ewe lamb has superior performance and is the genetically superior choice.
