Angus86- A couple of things came to mind. Guessing-Its not a terrible thing to guess weight of the heifers, but mostly Ive found people guess wrong. Don't believe me, get some cow poke friends together with the heifers and everybody guess their weights, then weigh them to see. I have done this. Some people can guess better than others, but verified scales don't lie.Key word:verified.
As mentioned earlier they need to adjust to the feed you chose.It may take them a little while to adjust to grain, as they were designed to consume and live off of forage. Knowing their weights, and using the 1-2% body weight rule will be a safe bet for you.You may have to start them out on 1/2% body weight and slowly move them up. I also have done this with both developing heifers, and bulls.
Types of feed-14% is general info. There are other things that can be additives to feed that can cause the heifers to eat less. I'm not saying you chose bad feed, just be aware of what does and doesn't work once you figure it out beyond the protein. High fat feed can work against you if the cattle are not acclimated to it or are not getting enough fiber in my experience. I liken it to eating a rich piece of cake or pie. Its real good to me and I like it a lot, but I can sure eat more quantity of vegetables or other foods than I can the rich desert. If I do eat a lot of the rich food, I feel bad and don't really want it much for a while. Kinda like when I eat a dozen Krispy Kreme doughnuts, I'm good for a while after that.
Also don't discount the hay quality. If you have exceptional hay, you may already be meeting their intake requirements. I found this out with some Alfalfa hay I tried to feed my bulls last year. They loved the hay, but didn't want the grain. Their growth was not so much as when they had less Alfalfa and more feed. I eventually cut the bulls to 2lbs/hd per day of the Alfalfa, 1.75% body weight in feed, and free choice middling hay(bermuda).
Worms-some types of worms infect the stomach and can make their stomachs hurt and subsequently eat less. I found this out the hard way too. A good oral drench was recommended to me by my 40+year veteran Vet. I did as he suggested and my gain increased, as well as consumption.
Genetics-they play a part too. Some calf's have the genetic base bred into them to grow faster at different times in their lives. Unfortunately, the general idea producers are encouraged to have is "more is better". If you have that as an ideal goal you may not want to keep on spending money on feed for the ones that wont come around. Some folks find the smaller ones make the more compact cows when grown that will still work and eat less of your inputs doing it. That can result in more profit, for you. Finished cow size, weaning weight preference are all up to you if you select for what you want.
Dont get discouraged- You have already gotten some good advise on CT before my post. Lots of cow pokes have had a group of yearlings make them scratch their heads at some time or another if they will admit it.The more you put into them the more you will get out of them as far as effort and care, but be cautious of that frame of mind when spending money on inputs.
Good Luck!!
Cotton1