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Don’t Cut Corners on Cow Diets

What a cow eats during pregnancy influences the performance of her calf.

Cutting corners on cow nutrition may save on feed costs in the short term, but the long-range consequences could be more costly and more far reaching than expected.

Research has shown that calves born to cows whose diets were nutritionally restricted during gestation experience long-term losses in performance, as compared with progeny born to cows receiving 100% of their nutritional requirements throughout gestation.

“Studies reported instances of compromised maternal nutrition during gestation resulting in increased neonatal mortality, intestinal and respiratory dysfunction, metabolic disorders, decreased postnatal growth rates, and reduced meat quality,” says Rick Funston, University of Nebraska reproductive physiologist.

nutrition is important at every stage

Identifying the stage of gestation most nutritionally critical for the fullest development of the fetus is more elusive than nutritionists earlier thought. “Different systems develop at different times in the fetus, so there’s the potential for these different systems to be affected by the dam’s nutrition at different times during gestation,” says Funston.

Limb development, for instance, begins as early as day 25. Sequential development of other organs soon follows, including the pancreas, liver, lungs, thyroid, spleen, brain, and kidneys.

“Testicle development begins by day 45 in male calves, and ovarian development begins in female calves between day 50 and 60,” he says. “Another important event in female gonadal development occurs about day 80 of gestation, when follicles are formed that after puberty affect what’s known as the ovarian reserve. This can influence a heifer’s reproductive lifespan.”

If the cow experiences a nutritional deficiency at any point in the gestational period, the fetus receives a metabolic signal through blood flow to the placenta. Fetal programming causes the fetus to adjust to the nutritional restriction. The developmental process under way in the fetus at the time of the restriction may affect the ability of the fetus to reach its full genetic potential.

“Because muscle fiber numbers do not increase after birth, the fetal stage is crucial for skeletal muscle development,” says Funston. “Because skeletal muscle is a lower priority in nutrient partitioning compared with the brain, heart, or other organ systems, it’s vulnerable to nutrient deficiency.”

As a result, the calf may be born with reduced muscle mass, thus, expressing reduced performance in growth and carcass development. The accumulation of intramuscular fat can be reduced, as well.

The fetal stage most nutritionally important to the development of muscle mass is the second to seventh months of gestation. The third trimester is the most critical for the development of marbling in the offspring.

One study compared the performance of calves born to cows grazing native range during the fourth to sixth months of gestation with the performance of calves from cows grazing improved pasture during the same period.

Calves born to the cows grazing native range had a weaning weight of 534 pounds, a hot carcass weight (HCW) of 726 pounds, and a marbling score of 420. Calves born to cows on improved pasture had a weaning weight of 564 pounds, a HCW of 768 pounds, and a marbling score of 455.

Like steer performance, the conception rate of heifers suffered, too, from nutritional restriction of dams, according to another study. The pregnancy rate of heifers born to cows grazing dormant range during the last third of gestation was only 80%. Conversely, heifers born to cows supplemented with protein under the same conditions had a pregnancy rate of 93%.

Cows appear to meet the nutritional needs of the fetus when they are maintained in a body condition score of 5, says Funsto

LEARN MORE

Rick Funston

308/696-6703

rfunston2@unl.edu

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