It’s not a new idea that cows’ nutritionally deficient diets during pregnancy can affect their calves. However, recent research has shone light on just what those adverse effects could be.
“Cows or heifers not getting enough energy or protein in their diet in late pregnancy can cause slowed or reduced growth and development of the fetus in utero, which can result in light weight calves at birth,” Dr. Allison Meyer, University of Missouri Assistant Professor of Ruminant Nutrition, said. “Although many producers may think low birth weight is a good thing, we want calves to reach the birth weight their genetics dictates. If calves do not grow enough prenatally, they can be less mature at birth, and have smaller organs.”
Meyer said these smaller calves also usually have less brown fat, which is important for early heat production, and have less cold tolerance due to their greater surface area to body mass ratios.
Meyer said the quality of the cow’s colostrum can also be hurt by nutrient restriction during late pregnancy.
“Thin cows also are weaker at calving, and prolonged calving is not good for calf survival,” she added. After birth, calves whose mothers have not been properly nourished in late pregnancy have demonstrated decreased growth, both preweaning and in the feedlot. Heifers have been less fertile, and carcasses from terminal progeny have been less likely to grade Choice. Calves from poorly fed cows can also have impaired immune systems, leading to more sickness and death.
The most obvious sign of dietary deficiency in a cow is a decline in the Body Condition Score (BCS), which is a measure of stored fat. The BCS declines as bones such as the backbone, ribs, hooks, pins, tailhead and shoulder become more apparent. Meyer also said it’s important during winter to take haircoat and fill into consideration.
“Often cows eat more hay or other feed when temperatures drop, and it can be easy to mistake fill for fat,” she said. “Poor haircoats can signal nutrient deficiencies.”
Mineral deficiencies can lead to other specific maladies, said Dr. Shane Gadberry, professor of animal nutrition with University of Arkansas Extension. “In situations like selenium, for example, we might be experiencing white muscle disease (nutritional myopathy) in newborn calves,” he said. “In cows, there could be a nutritional imbalance that’s associated with milk fever (postparturient hypocalcemia), or a magnesium deficiency with grass tetany. If we have an extreme phosphorus deficiency, our cattle will be less thrifty; it’s harder for them to maintain body condition, and our reproductive rates are very low.”
Gadberry said these deficiencies can also contribute to what he called “sub-acute” production losses, performance declines with no visible symptoms of illness. “Copper, zinc and selenium all affect the immune system,” he said. “Copper and selenium in particular can affect reproduction, so we may have subclinical deficiencies in trace minerals where we’re having modest reductions in reproduction rates.”
Behavioral signs are also indicators of poor nutrition. “If animals act very hungry soon after eating, are willing to eat moldy or otherwise undesirable feed, or eat strange things, they are likely missing nutrients,” she said. “Pica – eating non-food such as rocks, bones and sand – can mean mineral deficiencies.” The solution to all of these problems, she admitted, sounds more simple than it is – give the cows more, or better, feed. The producer could allocate hay supplies, feeding the lesser quality forage at mid-pregnancy, and then stepping up the quality in the final trimester.
