Target Weight for Beef Heifer at Calving
Heifers can exist developed to lighter target weights than the traditional 65% of mature weight past the commencement day of breeding season without sacrificing reproductive efficiency or longevity. Merely, it depends on the heifers, the surround and nutritional management during and afterward breeding flavour.
"If you lot have a crossbred herd comprised of early on-maturing breeds, moderate-framed cows and a big herd, you lot're able to pick from a lot of heifers for replacements — and if you alive in a limited-resource surround, and so managing heifers to attain 55% of their mature body weight by the commencement day of convenance season might be the way to go," says John Hall, Extension beef specialist at the University of Idaho. He's also superintendent of the Nancy G. Cummings Inquiry, Extension and Teaching Centre near Salmon.
On the other hand, Hall explains, "If you have a herd of limited numbers with larger-framed cows of later-maturing breeds, purebred or straightbred, then managing for 65% of mature body weight probably makes the most sense."
The weight fence
After all, the longstanding 65% target is based on sound science, feel and common sense.
Rather than selecting faster-growing, heavier heifers at weaning — indirectly selecting for larger mature size — or growing heifers faster and quicker with higher-energy rations — leading to precocious puberty — industry focus turned to using target weights every bit a percentage of expected mature weight as a guide.
"Across lightweight and heavyweight heifers, and beyond a wide range of breeds and a wide diversity of environments, 65% results in very positive pregnancy rates for heifers," Hall explains.
In some cases, the smaller size of heifers developed to lighter target weights, depending on how they're developed postbreeding, can outcome in calving issues. In the case of larger-framed heifers held to lighter target weights, Hall explains, "They can accept poor reproductive performance, because we aren't getting heifers large plenty for their mature size. If we severely restrict those kinds of heifers during the postweaning period, not only may we not get many heifers bred, but a greater pct of them can have problem maintaining pregnancy."
Developing heifers to the 65% target costs plenty, though, especially because the demand for supplementation in many instances, and the cost of delivering it effectively in extensively managed operations.
That's one reason why some producers and researchers began wondering if the target is excessive.
Rick Funston, a beef reproduction physiologist at the Academy of Nebraska'due south (UN) West Key Research and Extension Center at North Platte, and his team were among those asking the question. In research trials a decade or so ago, they began demonstrating that in commercial conditions, heifers can be managed to a target weight of 55% without sacrificing conception rates or longevity in the herd, and could be developed for significantly less price.
"Several studies [Un and others] have clearly shown that managing heifers to achieve 55% of mature weight by the beginning of the breeding season does not reduce the percentage of heifers becoming pregnant in the first 21 days of the breeding season, compared to heifers fed to a greater target weight," Hall explains. "However, to ensure acceptable pregnancy rates and proper size for calving, heifers still need to achieve ninety% of their mature weight before calving," he says.
"After the breeding flavor, heifers developed to a 55% target need to continue to gain weight at a more than rapid charge per unit than heifers adult to a 65% target," Hall says, and they need to go along to gain weight post-obit the breeding season.
Hall also points out a bulk of enquiry apropos the 55% target weight has been conducted with crossbred or blended cattle. Due to heterosis, he explains, these cattle attain puberty at a younger historic period than the purebred or straightbred breeds comprising them.
"Using the 55% target weight will exist fine for some operations, but non for others," Hall says.
Timing matters, as well
Whatsoever the target, Hall emphasizes, "A pregnant heifer is not the same as an early-significant heifer. Too often, we talk about getting 80% of the heifers pregnant, but that might be inside a 45-solar day or 60-twenty-four hour period breeding flavour. There are singled-out advantages to heifers that calve in the first 21 days of their initial calving season."
For one matter, various research shows that heifers calving in the first 21 days consistently wean heavier calves than those that don't. At least as important, heifers calving in the first 21 days are significantly more likely to remain in the moo-cow herd.
Hall uses inquiry from the U.S. Meat Fauna Research Middle equally an case. "When we become to nigh the fourth calving season, about 50% of the heifers bred in the kickoff 21 days of their initial breeding flavor are still in the herd," he explains. "At the same time, fewer than thirty% of the heifers bred after the kickoff 21 days of their initial breeding flavor are nevertheless in the herd."
Given the cost of developing a heifer into a productive cow, that'south no pocket-sized affair to consider as yous brand your 2016 management plans.
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Source: https://www.beefmagazine.com/nutrition/what-ideal-target-weight-heifers-it-depends
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