birth weights (+/- 2.5 lbs per day)

[Okotoks]

Using the birth weight of the bull as a criteria for calving ease is pretty crazy - not only does it totally ignore the contribution of the dam (as well as all the ancestors on both sides)  to the calf's weight and calving  ease it implies that it is a meaningful number

I understand your points regarding both sides of the linage, but I don't see it being crazy.  What are you going to do to change your cows EPD's?  It is far easier to make adjustments in what bull you use and have a large impact (50% of all genetics tied up in 1 animal) vs having to sell your entire herd and start over.  In two generations you can change 75% of your genetics with 2 animals. 

After considering conformation, size should be considered.  Two long lanky bulls that sire similar calves and all else equal, but 1 avg 115 lbs and the other 85- which is more likely to result in a dystocia? 

I agree that there must be some relationship btwn gestation length and BW but I don't think itis linear - I would be interested in the relationship btwn gestation length and CE

If you increase the length of gestation, you will have increased time for growth in the period of exponential growth. You aren't going to see a downtrend. 

Since the birth canal isn't getting any larger with increased gestation, and the calf isn't getting any smaller.  My hypothesis has been made about CE.   

I agree with Commercialfarmer on this. I think it's really important to report the actual birth weights. I would be pretty annoyed to find out the BW was the adjusted weight based on length of gestation. The calf will probably sire longer gestations thus bigger BW's. If the calf is induced it's not really a relevant BW. Also if it's a twin that should be reported as again when it sires a single calf it's BW won't mean much.

 

[DL]

Using the birth weight of the bull as a criteria for calving ease is pretty crazy - not only does it totally ignore the contribution of the dam (as well as all the ancestors on both sides)  to the calf's weight and calving  ease it implies that it is a meaningful number

I understand your points regarding both sides of the linage, but I don't see it being crazy.  What are you going to do to change your cows EPD's?  It is far easier to make adjustments in what bull you use and have a large impact (50% of all genetics tied up in 1 animal) vs having to sell your entire herd and start over.  In two generations you can change 75% of your genetics with 2 animals. 

After considering conformation, size should be considered.  Two long lanky bulls that sire similar calves and all else equal, but 1 avg 115 lbs and the other 85- which is more likely to result in a dystocia? 

I agree that there must be some relationship btwn gestation length and BW but I don't think itis linear - I would be interested in the relationship btwn gestation length and CE

If you increase the length of gestation, you will have increased time for growth in the period of exponential growth. You aren't going to see a downtrend. 

Since the birth canal isn't getting any larger with increased gestation, and the calf isn't getting any smaller.  My hypothesis has been made about CE.   

I agree with Commercialfarmer on this. I think it's really important to report the actual birth weights. I would be pretty annoyed to find out the BW was the adjusted weight based on length of gestation. The calf will probably sire longer gestations thus bigger BW's. If the calf is induced it's not really a relevant BW. Also if it's a twin that should be reported as again when it sires a single calf it's BW won't mean much.

You guys have completely misinterpreted what I said - using the BW of the bull as a way to determine if you will have calving issues totally ignores the contribution of the dam - ie if the dam is big boned and weighed 110 at birth using a bull with an 80 pound birth weight does not guarantee that the calf will be small - the point is to understand and know your cows (not to sell half your herd) when picking a bull

Re gestation length and BW - I didn't say anything about a downward trend - I was asking what the relationshop was - I do not believe it is totally linear

okotoks - I didn't say anything about not reporting the actual BW

 

[DL]

this is kinda interesting - the study was on Holsteins but likely similar in other breeds

Factors effecting Gestation Length
Can. J. Anim. Sci. 69: 10$-1086 (Dec. 1989)

Parity, sex of calf, size of calf and
size of cow were found to have a significant
effect (P< 0.001) on gestation length. Gestation
length was found to increase with parity,
size of calf and size of cow. Anderson and
Plum (1965) also noticed that young cows
carry light calves for shorter periods than
older cows. Several studies cited in their
review paper have observed the gestation
length to increase by 1-2 d with each
successive calf. Most studies have found that
gestation length was influenced positively by
age of dam. The first parity cows had a
shorter gestation length by I day (P<0.001)
than the third parity cows. Gestation length
was about a day shorter (P< 0.001) for heifer
calves compared to bull calves. Size of the
calf was found to be the most important factor
(P<0.001) associated with gestation length.
Medium and large calves were associated with
extended gestation lengths of 1.7 and 3.6 d,
respectively.
Estimates of sire, maternal grand-sire and
residual variance components for ge^station
length were 2.868 d", 0.914 d' and
30.256 d', respectively, indicating that this
trait was more dependent on the service sire
through the fetus than on the dam through hersire.
The direct and maternal heritabilities for
gestation length calculated from service sire
and maternal grand-sire variance components
were 0.33 and 0.06 respectively. In a recent
study Azzam and Nielsen (1987) reported an
average heritability estimate of over 0.4 for
gestation length in beef cattle. Covariance
between sire and maternal grand-sire was
LII d2. which gave a sirJand maternal
grand-sire correlation of 0.68 for gestation
length^ In contrast, the genetic correlation
between direct and maternal effects for gestation
length was negative and low (-0.27).

A moderate to high heritability estimate for
gestation length indicates that selection for
shorter gestation length is possible. This
should reduce calf size and improve ease of
calving, which in turn would increase the lifetime
reproductive performance of cows.
Direct relationships between gestation length
and calving ease are, however, yet to be
investigated, as is the relationship between
calf mortality and gestation length. If shorter
gestation lengths are associated with easier
calving and not associated with increased calf
mortality, then it may be wise to record this
trait and select to reduce gestation lengths
slightly in breeds that experience significant
calving losses.

 

[Okotoks]

Using the birth weight of the bull as a criteria for calving ease is pretty crazy - not only does it totally ignore the contribution of the dam (as well as all the ancestors on both sides)  to the calf's weight and calving  ease it implies that it is a meaningful number

I understand your points regarding both sides of the linage, but I don't see it being crazy.  What are you going to do to change your cows EPD's?  It is far easier to make adjustments in what bull you use and have a large impact (50% of all genetics tied up in 1 animal) vs having to sell your entire herd and start over.  In two generations you can change 75% of your genetics with 2 animals. 

After considering conformation, size should be considered.  Two long lanky bulls that sire similar calves and all else equal, but 1 avg 115 lbs and the other 85- which is more likely to result in a dystocia? 

I agree that there must be some relationship btwn gestation length and BW but I don't think itis linear - I would be interested in the relationship btwn gestation length and CE

If you increase the length of gestation, you will have increased time for growth in the period of exponential growth. You aren't going to see a downtrend. 

Since the birth canal isn't getting any larger with increased gestation, and the calf isn't getting any smaller.  My hypothesis has been made about CE.   

I agree with Commercialfarmer on this. I think it's really important to report the actual birth weights. I would be pretty annoyed to find out the BW was the adjusted weight based on length of gestation. The calf will probably sire longer gestations thus bigger BW's. If the calf is induced it's not really a relevant BW. Also if it's a twin that should be reported as again when it sires a single calf it's BW won't mean much.

You guys have completely misinterpreted what I said - using the BW of the bull as a way to determine if you will have calving issues totally ignores the contribution of the dam - ie if the dam is big boned and weighed 110 at birth using a bull with an 80 pound birth weight does not guarantee that the calf will be small - the point is to understand and know your cows (not to sell half your herd) when picking a bull

Re gestation length and BW - I didn't say anything about a downward trend - I was asking what the relationshop was - I do not believe it is totally linear

okotoks - I didn't say anything about not reporting the actual BW

I was just commenting on the original question there, if there's any adjustment to be done let it happen with the EPD's, if the circumstances are unusal people should still report the actual birth weight.
I don't believe the correlation between BW and gestation is linear. If you look at the Australian EPD's where they have both gestation and calving ease you will find bulls with below average gestation lentgh and above average bw. Usually the shorter gestation lengths have beow average BW's but a person should probably be looking at both.

 

[DL]

okotoks - yeah I have noticed that with the EPDs from Oz - ain't nature wonderful?