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Providing Extra Feed to Nutritionally Stressed Cows; Timing for Proper Calf Development

NDSU researchers examine how restricting nutrient delivery and subsequently feeding to nutrient requirements from early to midgestation can affect the development of placental blood vessels and the fetus.

Pasture quality and quantity in a given area is largely related to environmental conditions, which are variable from year to year. Poor-quality pastures can affect the nutritional and physiological status of not only the dam; they also can impact the development and lifetime productivity of the calf.

During early pregnancy, nutrient requirements for beef cows are low and appear trivial for calf growth. However, maternal nutrient intake at this point can influence early organ development of the fetus. More importantly, the calf’s placenta is growing rapidly and establishing itself as the organ essential for nutrient exchange between the calf and dam throughout the remainder of gestation. Factors that impair placental development early in pregnancy could, therefore, have major impacts on calf development during later pregnancy.

Two Cows at PastureThe specific objective of this study, funded by the U.S. Department of Agriculture, is to examine how restricting nutrient delivery and subsequently feeding to nutrient requirements from early to midgestation can affect the development of placental blood vessels and the fetus. Our hypothesis is that maternal nutrient restriction in beef cows during key developmental stages of the placenta will alter its function, resulting in stunted fetal growth and development. However, delivering diets of greater nutrient content later in the pregnancy may enhance placental function, allowing for adequate nutrients to be delivered to the fetus.

We also are determining how nutrition during pregnancy can influence the development of the mammary gland, the organ that replaces the placenta upon birth in delivering nutrients to the calf.

Forty-eight pregnant beef cows are housed in pens (five to six cows per pen) equipped with the Calan gate system at the NDSU Animal Nutrition and Physiology Center, which allows us to control individual feed intake. All cows are being fed a common diet (100 percent of National Research Council’s nutrient  requirements) until day 30 of pregnancy, at which time they are assigned to one of three treatments. In those treatments, the cows receive: 1) 100 percent of requirements throughout the study; 2) 60 percent of  requirements from days 30 to 85, thereafter 100 percent of requirements; or 3) 60 percent of requirements  from days 30 to 140 of pregnancy, thereafter 100 percent of requirements.

We can determine how maternal nutrition is impacting placental function by monitoring blow flow to the uterus and fetal umbilical cord. This is done by using a Doppler ultrasound, and measurements are obtained chuteside. Body weights are taken weekly to adjust rations for changes in body weight throughout the experiment. Refusals also are collected weekly, and body condition scoring and carcass ultrasounds are being performed throughout gestation. On days 85, 140 and 250, cows from each treatment are harvested at the NDSU Meat Laboratory.

Tissues from the dam, placenta and fetus are weighed and processed carefully. For us to further investigate placental function, we collect portions of the placenta and placental arteries. We are looking for factors associated with increasing placental vascularity and ability of the arteries to expand or dilate, allowing more blood to enter the placenta. We also are processing the mammary gland and will determine how maternal diet impacts its growth and potential capacity for milk production.

To maximize the amount of information learned, many scientists from the Department of Animal Sciences are involved in this research effort. We are making every attempt to harvest any organs and tissues from the dam and fetus that may give us insight into how diet during gestation impacts the cows and her developing fetus.

Several findings from this study will help expand our knowledge of maternal nutrition and calf development. They include:1) how maternal diet impacts uterine and umbilical blood flow (how nutrients are delivered to the calf); 2) how the timing of delivering extra nutrients can impact placental development, and thus nutrient delivery to the calf; and 3) how maternal nutrition during pregnancy impacts the development of the mammary gland, thus postnatal calf nutrition.

The information gathered from these experiments will be critical in developing future research efforts to focus on specific management strategies for producers to implement during times when pasture nutrient quality or quantity are inadequate for gestating beef cows. Specific strategies to explore may include the stage of pregnancy that has the most benefit from supplementation, the duration of supplementation and the specific nutrients that should be delivered in the supplement.

Ely Camacho, Graduate Student, and Kim Vonnahme, Associate Professor, NDSU Animal Sciences Department

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