Lots of experience on this one.
First....There is only one correct answer to "What age should heifers freshen?" .......... and that is "It depends."
This is another area where there are many choices so having knowledge about YOUR operation and how your choices will effect it is critical. For any operation, profit is gross income minus expenses. Expenses are determined by input costs and the key inputs with heifers are feed, labor, and housing. The input that is shortest will be the factor that limits you heifer raising. Remember to include interest as an expense. If you are not borrowing you could be using the opportunity to invest your money elsewhere-- and interest you are not earning is a cost of keeping the money in feed, animals, etc. Look to what you could make on 2-5 year CDs for the rate to use.
In all cases you need to consider what the "best use" is for the inputs you have.
Maximizing income is different for selling heifers than it is for milking your own heifers. You are counting on only the value of the springer, not on the potential income from milk like we would.
We've played our heifer hands several different ways over the years, so the easiest way I can answer this is to tell what we've done and why.
When we were in the stall barn we had only 54 spots for cows and did not want to switch cows so maximizing income with stalls as the limiting factor meant bigger #/cow. To do this we wanted, within reason, for heifers to be well grown and ready to give big milk in the first lactation and we tended to average have 25-26 months to freshening. We had enough space to house 60-65 heifers (27 months worth) and had enough feed and enough labor too. On the down side, we found that mature-cow sized heifers-- those over 27 months-- were more likely to have calving problems. Our vet told us that heifers that were bigger and older when bred had the capacity to grow a bigger calf and that with age they had less flexibility in their pelvic area. That was a receipe for problems and occasionally we lost production (or lost the heifer) because of freshening issues.
When we hit some drought years, buying at high feed prices became the limiting factor and freshening older heifers showed to be more expensive than the gain, so we ratcheted the age down to a solid 24 months.
After our third (and last lol) baby, labor became the limiting factor. We decided that the best way for the two of us to manage was to freshen semi-seasonal-- trying for the bulk of the animals to freshen March-May and Sept-Nov. That had us holding off breeding to get them into our "windows" and put us back to the 25-26 month age. Using the "windows" let us stop freshening in the winter months when an injured heifer meant a culled heifer so we had a couple more springers to sell each year.
In '93 we went through our first phase of expansion. Our game plan changed-- we had surplus room for milkers and proportionally less room and labor for heifers. Using feed for milk returned the best money so getting the heifers in ASAP became a priority so we changed the "window" to exclude only Dec 20- March 1 and aggressively bred for less than 24 months freshening. Cheap corn and concentrates meant that we could push growth and get them in at 1250# early. We freshened animals as young as 21 months ith a minimal anount of trouble.
Like most freestall operations we are perpetually trying to grow milking numbers so we start breeding at 13 months. Freestalls offer the flexibility of having more than one animal per stall so we now look at # shipped/milking stall/year as one of our measurements. Young animals give a bit less milk but balance that with handling overcrowding well so the milk/stall stays high and freshening younger also gets them to that second laction where really big milk can kick in. Cost wise, if space for milkers is not limited, getting those girls milking early usually means more profit over the life of the animal. With solid rations heifers can grow while milking well and get into their second lactation by 36 months of age. and because cows produce more in the first 1/3 of their lactations, the more "first thirds" she has over a lifetime, the more milk she will produce. Waiting an extra 6 months to freshen at 28-30 months forfits 6 months of milking time (1/2 of a lactation) and what could be 1/2 of another calf in her lifetime. For our operation, I can't pencil out waiting on purpose.
Since '93 we have typically held repeats and bred some early to avoid the Dec 20-March 1 window so our average conception age tends to move over the course of the year.
This year the parlor will not be completed until September. We held off on breeding about 15 heifers (26 month freshening) and have bred about 20 heifers for 21-22 month freshening to maximize a Sept-Nov freshening window. So the "average" looks like 24 months... but the management getting there is strategic. We are now in our non-breeding window (except for the clean-up bull.)
For your operation: how much do you figure it will cost to raise your girls? How much per day is the feed for a 1200# animal? Remember that the bigger the animal the more expensive it becomes to add weight because you have more animal to maintain.
As for the sexing-- yes animals with heifers
could be worth more-- most likely to someone you know because they will trust your records. At smaller auctions, announcing that certain of your heifers carry females implies that those not announced carry bulls.... so you might want to consider that in choosing where or when you sell what. (Maybe send only known female embryos to one sale and unannounced (ie:male) to the next.)
Be sure to look at the costs carefully. Look at the marginal return for the increased number of female embryos. If sexed semen has a lower conception rate you will be selling older heifers on the average as you will have more repeats-- so you will have increased inout costs for semen,
feed and labor on each group. These costs should be allocated only to the female embryos above 50% because theoretcially you could get 50% without the increased costs that come with sexed semen.
Also remember that while sexed semen may have a 85-90% heifer rate as an average, averages are made up of random streaks of bulls and heifers over time so it is possible to get 50/50 or less even on sexed semen in small lots.Always look at worse case scenerios as real possibilities and only bet what you can afford to lose. (so what happens to profitability if you will get is 4 heifers and 7 conceptions from a rack of 10 --will you still break even or can you afford the loss?)
Vet expenses are big. Having 50 heifers to check at one time has alot less cost than 5 so the choice might be different at different numbers.Our vet has a $25 call charge and $80/hour so pg checking one heifer would cost at least $45 (assuming that she was caught up and cooperative-- 15 min including clean up and set up)
Our decisions might change again in time too. Last year when we were making the decision between expand and hold steady we looked at using fetal sexing in choosing which cows we or heifers we would sell to keep numbers down. We would then have moved the expansion to 2008 when all of those heifer embryos would freshen. I can forsee us doing this in the future. (Another reason to buy only whole herds lol. If they want to sell selectively I might get only bulls calves!!!)
You definitely have the right ideas for selling your heifers--- knowing who your potential buyers might be is very important as is the knowing which months will have the best demand. (November will demand higher prices than January so a 1200# Nov freshener might sell for as much and thus be more profitable than a Jan. 1300#.) If you have a reliable buyer who trusts your records you might want to use sexed semen for 1st service at 13-13.5 months and less expensive semen after that to keep your average age and thus average expense down. (female calves are smaller ie: easier calving & the knowledge of a heifer calf might make the size "penalty" less.) Be sure to look at all costs. Remember that records are only worth something if the buyer trusts them. And most importantly, keep reviewing your decisions because today's best options are not necessarily tomorrow's, next months, or next year's (so we have learned).
You've just completed Dairy Business 101 from the school of hard knocks lol.
Linda