Managing replacement heifers starts at conception
Developing replacement heifers can start as early as conception, according to a South Dakota State University extension cow/calf field specialist. Taylor Grussing told producers the point when heifer development starts can vary by a producer’s goals and if they are raising or buying replacements.
“For some producers, it starts at birth when we notice that she’s a nice heifer and will hopefully make a good replacement,” she said. For other producers, it is careful genetic selection at breeding to produce heifer replacement prospects. “If you buy replacements, it could start at weaning or when you are buying bred heifers,” she said.
“What is important to realize is that you develop heifers with a system that matches your environment, your goals, and your wallet,” Grussing said. “When talking about maximum versus optimum heifer development, it comes down to economics. We want to get as many heifers in the herd bred as possible, but it comes down to doing that in the most economical way,” she said.
In a maximum development scenario, Grussing said the heifers would be fed ad Librium, consuming as many nutrients as they want, and growing to their optimum potential. Every heifer in the pen would be bred, the bulls would be left in for 60 or more days, pregnancy checking would be later, and open heifers would be rolled into a fall program, to give them another opportunity to breed.
In an optimum scenario, replacement heifers would be limit fed to reach a targeted weight while providing them with a supply of feed so they could grow efficiently. Only the oldest heifers would be bred, and the breeding season would be limited to 30-45 days. “It is one of the best ways to put selection pressure on fertility, and it gives the females that breed early a competitive and economic advantage. Producers would also have the option of pregnancy checking the females early, and marketing the ones that are open,” she said.
“Which scenario a producer chooses depends upon their goals,” she said. “If you sell replacement heifers, your goal is to get as many bred as possible. If you want to raise your own replacements, you will want to select ones that will stay in the herd longest because of development costs,” she said.
With either option, Grussing said it is important to recognize the importance of selecting the right heifers to meet those goals. She recommends keeping the oldest heifers and culling the late born ones. She doesn’t recommend selecting the largest size for replacements. “Larger frame heifers may be the hard-doing ones later on. It could also increase the cow size of your herd. I would eliminate the small ones, the tall ones, the poor doers or heifers born to cows that have bad udders and feet,” she said.
Many producers select replacement heifers from dams with proven performance. “A fertile heifer will be a fertile cow,” she said. “Age is directly correlated to puberty. Puberty is a factor you can try and select for by physically monitoring the heifers to see which ones are mounting or riding one another.”
Most likely, producers should notice activity about 30-60 days prior to breeding. “If you aren’t seeing estrus activity at that point, you may want to consult a veterinarian,” Grussing said.
Size at puberty can be influenced by age, preweaning growth and expected mature weight. “It is an interaction of growth genetics, mothering ability, forage availability and milk production,” she said. “Heifers given high-energy rations will reach puberty at an earlier age.”
Some heifers fed a high-energy ration too early in life may stall when it comes to puberty. Precocious puberty, which means they stop showing puberty, can occur at four to eight months. “It can also be caused by underdeveloped frame and pelvic area, and they may stop cycling. These heifers may need help to start resuming their cycle later” she said.
Grussing recommended contacting a veterinarian to help analyze heifers prior to breeding. A reproductive soundness exam can help producers get an idea of how successful the heifer will be in terms of growth 35-45 days prebreeding. During this exam, the veterinarian pelvic measures the heifer, and also calculates a reproductive tract score. Producers can also calculate a body condition score, which is a great indicator of energy reserves the heifer has available. If a scale is available, they may also want to calculate body weight, evaluate frame score and make a functional soundness exam.
When the veterinarian calculates a reproductive tract score, it is scored from one to five, with four and five being the best scores. Grussing recommended culling any heifers that score one or two. Heifers that score a three may need more development time. “It gives you an idea on fertility, which has life-long impacts,” she said.
Heifers scoring below 145 cm pelvic measurement should also be culled. “The veterinarian is measuring the width and height of the pelvis to see how big of a calf the heifer can have,” she said.
When developing heifers, Grussing said it is important to cull the right ones. “Any with a small pelvic area, infantile reproductive tract, disposition, hard fleshing, and soundness issues should all be culled. If you are custom developing heifers and selling them, you may also want to select heifers that are all uniform in color, and cull any with short ears or tails. Also, I would consider hybrid vigor. Research shows that heifers conceiving within the first 21 days of the breeding season stay in the herd the longest, and raise the equivalent of an extra calf in their lifetime,” she said. If the earliest born heifers calve early, 90 percent of them will calve within 15-20 days on either side of that when they are a cow, research shows. ❖
— Clark is a freelance livestock journalist from western Nebraska. She can be reached by email at firstname.lastname@example.org.