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I Don't think one day will make a difference. However, if breedings were stretched over, say 5 days, you could have some smaller pups from the last breedings. This is our theory so we like to space breedings over 3 days.
 

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According to vet books on reproduction spacing of breedings is irrelevant to age/size of pups. The eggs are only mature for 48 hours or so ( some books stretch it to 3 days) so no matter when sperm are inserted all fertilization takes place at essentially the same time, about a 48 hour period. We have had a number of experiences which demonsrate this but the science is what it is. As an aside ...we had a female ( no PT testing) in for breeding who allowed 4 breedings over a eight day period of time...if the other logic held true some pups would be 8 days older than others...give that some thought. There are many reasons why pups vary in size but timing/spacing of breedings is not one of them.
Bill Butikas
Blindfaith Retrievers
 

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According to vet books on reproduction spacing of breedings is irrelevant to age/size of pups. The eggs are only mature for 48 hours or so ( some books stretch it to 3 days) so no matter when sperm are inserted all fertilization takes place at essentially the same time, about a 48 hour period. We have had a number of experiences which demonsrate this but the science is what it is. As an aside ...we had a female ( no PT testing) in for breeding who allowed 4 breedings over a eight day period of time...if the other logic held true some pups would be 8 days older than others...give that some thought. There are many reasons why pups vary in size but timing/spacing of breedings is not one of them.
Bill Butikas
Blindfaith Retrievers
X2. Fertilization occurs when the eggs are ripe and the sperm gets there. The natural breeding gets a boost from stronger uterine contractions. The eggs are usually released at the same time over a 24 hour period. I have a male here that will breed early and I often breed him every other day 3 times, sometimes I do one with two days inbetween. I had 9 puppies all the same size from the second breeding. The smaller puppies are usually due to attachment in not as good places-down low, or as they said "There are many reasons why pups vary in size"
 
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X2. Fertilization occurs when the eggs are ripe and the sperm gets there. The natural breeding gets a boost from stronger uterine contractions. The eggs are usually released at the same time over a 24 hour period. I have a male here that will breed early and I often breed him every other day 3 times, sometimes I do one with two days inbetween. I had 9 puppies all the same size from the second breeding. The smaller puppies are usually due to attachment in not as good places-down low, or as they said "There are many reasons why pups vary in size"
Good points on the size. That can also be affected by where the pups are in the uterine horn. For example, pups at the "ends of the horseshoe" have more room to grow and can end up being larger at birth whereas the ones down where the two horns meet at the bottom of the "U" have less room because they can be more smooshed and yes that is a technical term. ;)
 
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