Fooling Mother Nature
Dr. Elizabeth Homerosky, DVM, recalls learning as a 4-H’er that young heifers should be developed to as much as 80% of their mature body weight at breeding. The result was heifers that looked good, but the program was too aggressive and not financially worthwhile.
“Research out of the U.S. and Canada consistently says we can develop heifers to 50% to 55% of mature body weight without negatively impacting health, without increasing dystocia rate, and it’s economical,” said Homerosky. “But when and how heifers get there is important.”
Heifers raised in a system similar to backgrounding are referred to as “late gain.” Intake is reduced while heifers maintain low but efficient gain. Late gain strategies, also referred to as extensive systems (or “rough it” systems) are effective because heifers are challenged early and producers can determine which animals are the most efficient and fertile. Heifers develop better grazing habits.
“We’re treating heifers more like they’re cows,” said Homerosky. “The more you treat her like a cow, the better cow she’s going to be. The worst thing to do is what my dad and I did: pour feed to them, pamper them and subsidize inefficient animals so much that they still became pregnant in spring. Because heifers inherently aren’t that fertile or efficient, they come up open as a lactating two-year-old, and that’s where depreciation costs can creep up.”
The late gain/extensive system allows Mother Nature to help select the most efficient and fertile heifers.
Homerosky said the extensive system encourages heifers to develop good grazing habits. “They’re feeding on stockpiled forage or swath grazing and having to seek feed rather than the feed coming to them,” she said. “The last thing I want is cows waiting for the tractor or feed truck to arrive.”
Extensive systems take advantage of compensatory gain. Homerosky prefers seeing a slightly thin heifer in gaining condition at breeding time rather than an overconditioned heifer.
“Whatever body condition score (BCS) a heifer was in the first year, she wouldn’t start cycling in subsequent years until she reached the same BCS,” she said. “If she was overconditioned her first year, there’s a chance she isn’t going to cycle in time to be bred for her second calf.”
This system works well for spring-calving herds that calve in April, May and June. Calving in January, February and March doesn’t align with pasture growth that provides grass for flushing.
It’s important to maintain a short breeding season. If heifers are exposed for three cycles, the hard work doesn’t pay off. The ideal maximum breeding season is 42 days or fewer; however, 30 days is ideal.
“Maintain a positive energy balance and continued growth through calving,” said Homerosky. “The first year you do this, you might want to keep back more heifers. After doing this for several years, many heifers are likely to conceive in the first cycle.”
Homerosky likes to assess heifers about six weeks prior to bull turnout, which allows time to assess the percentage of heifers cycling. If not enough are cycling or BCSs are lower than ideal, there’s still ample time to create a flushing effect and improve BCS. It’s also a good time to vaccinate. Homerosky advised producers to work with their veterinarian to determine the ideal vaccination program.
“A common recommendation is to use modified live vaccine with an ‘FP’ (fetal protection) label claim to protect the fetus from becoming persistently infected with BVD,” said Homerosky. “This means if a heifer or cow comes in contact with the BVD virus, the gestating fetus is protected from becoming persistently infected with BVD.”
Six weeks before breeding is the ideal time to administer this vaccine. The first time the heifer “sees” the vaccine, the IBR fragment can cause temporary inflammation in the ovaries and reduce fertility for one cycle, but that isn’t a problem in subsequent years.
A 21-year research project by the U.S. Meat Animal Research Center followed more than 16,000 heifers and showed that on average, heifers that conceived and calved in the first cycle had an advantage and remained in the herd at least one year longer and weaned one more calf before coming up open as an aged cow. The research project also showed that first cycle pregnancies always weaned a heavier calf.
While a 30-day breeding period seems harsh, Homerosky explained it’s possible to get two cycles of pregnancies in 30 days. One is an estrous synchronization, which requires several handling events and shots and may not be practical for many producers due to labor requirements and costs of hormones and semen. However, short cycling is an effective way to accomplish a similar outcome.
“Bulls go in as they normally would, and they’re allowed to breed on natural heats for the first five days of the breeding season,” said Homerosky. “About 20% to 25% of heifers will come into heat and be bred. At the end of day five, every heifer gets a shot of prostaglandin. Heifers bred in the first five days are unaffected by the shot, but those not bred in the first five days are likely at a point in the cycle where there’s a corpus luteum (CL) on the ovary. Prostaglandin causes the CL to break down, which sets off the cascade that results in ovulation of another follicle. Any heifers that weren’t bred in the first natural heat will come into heat in the next four days.”
By day nine, all heifers have had one chance to conceive, which is the equivalent conception rate of one full cycle. The bull remains with heifers for an additional 21 days. This takes the cycle to day 30, and by this time, 85% should be pregnant. Heifers should be ready for pregnancy checks 30 to 45 days after bulls are removed from the group.
“This is a great way to set heifers up and build momentum in the herd,” said Homerosky. “It gives them more time to rebreed for the next season and promotes longevity. Let Mother Nature help you find fertile and highly efficient cows.”
by Sally Colby
