At this time you are breeding cows who may be nursing your replacements. Your replacement heifers born last year are now fifteen months, old enough to breed. Are they big enough??
Probably they are. As a general rule, a heifer will be 55% of her expected mature weight at fifteen months of age. If your momma cows weigh 1200, that means their yearling heifers only need to weigh 660; if your cows are more like 1400 pounds, their yearlings will be 770.
The points I am leading to are these:
Creep feeding. This practice has been used for steers still on momma’s milk to grow as fast as possible and to transition faster after weaning. For intact bulls (as well as heifers) much of the weight gain from creep feeds is going to include fat, especially on smaller frame breeds. After puberty, with sex hormone production kicking in, animals start making fat from excess energy intake, and tend to store it both visibly (brisket) (neck) (tailset) and in the wrong places (inside body around kidneys) (inside pelvis around repro organs) (inside the mammary tissue) (inside testicles) – places where it will not metabolize at times when animals need to mobilize some stored energy. Internally stored fat is generally a negative to future health and reproductive performance. If you practice creep feeding, consider grouping cow-calf pairs so this is kept away from future replacements.
Conditioning for show. The growth planes of females are strongly influenced by breed. The traditional “English” breeds (Angus) (Red Angus) (Hereford) (Polled Hereford) (Shorthorn) (Red Poll) (British White) started with smaller frame size, reached puberty quicker, and were bred to finish on good grass, thus will “marble” based on age without supplemental feed. By contrast most of the “Continental” breeds (Charolais) (Simmental/Pie Rouge/Fleckveih) (Maine Anjou) (Limousin) (Gelbveih) (Chianina) which matured later, grew taller on heavier-boned frames and did not “marble” stored fat into the muscle typically needed supplemental feed to reach higher meat grades at slaughter.
Now that nearly all breeds known by “continental” names are actually crossed with Angus (to gain polled heads and black hair to compete in USA markets) the original “breed character” is no longer as predictable in the animals you are breeding. But the basic rule is that heifers of any breed, raised in any way other than grazing grass, should not be fed the same as steers and that means conditioning for showing must be very carefully done, with the body condition gain closely monitored to avoid heifers becoming too fat to breed and then have difficult calving.
Learn the differences in “type” between performance quality and maternal quality stock. It is as true in Beef as in Dairy genetics, too much emphasis on “performance” traits for females can lead to a staggier, bully-appearing, low fertility and hard calving cow herd of inefficient cow size. Such cows do not do well nursing calves on grass and have higher repro costs per calf.