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Will fetal programming reprogram the future of your dairy herd?

Amanda Kerr for Progressive Dairy Published on 30 April 2020

What is fetal programming? Fetal programming occurs during pregnancy where changes in the intrauterine environment impact the development and subsequent phenotype (physical, biological, metabolic traits) of the fetus.

The constraint of uterine space in a young heifer, lack of nutrients supplied to the fetal calf during high milk production or long lactation lengths, reduced blood flow to the placenta during heat stress, elevated or depressed levels of growth factors circulating in the dam’s blood (due to age or stage of lactation) can all be influencers of fetal programming.

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If fetal programming influencers occur at key moments in embryonic development, or are harsh enough, it can have lasting multigenerational effects. During embryonic development, organs, tissues and metabolic pathways are established, with key points of differentiation occurring at different stages of pregnancy.

For example, the cells and tissues destined to become part of the mammary system develop within the first half of gestation. Thus, if a challenge such as nutrient restriction to the fetal calf due to high demands of peak lactation occurs during early embryonic development, there could be deleterious effects on the future performance of the calf. The effects of lactation during gestation were shown to be significant in that heifers born to mature cows produced significantly less milk (52 kilograms) than heifers born to heifers. Similar effects of lactation during pregnancy yielded reduced survivability to second lactation and increased somatic cell count (SCC) in daughter calves.

Calf bodyweight differences

Fetal programming can begin early. Research in 2014 showed that at 18 days after breeding, embryos of lactating cows had impaired gene expression related to metabolism compared to growing heifer embryos. In this example, the demands of peak lactation (approximate time of re-breeding for cows) coincides with early pregnancy, establishment and growth of the placenta, and survivability of the embryo.

How insults during embryonic development alter future milk production could be linked to differences in early calf metabolism. For instance, research in 2017 showed calves born in the summer (under heat stress conditions) were more insulin-sensitive, which was later correlated to increased milk yield during their first lactation. However, other research has shown negative effects of heat stress during late gestation, such as less effective passive transfer of immunoglobulins from colostrum and impaired immune function in the calf. These two examples, therefore, show the impact of duration and severity of insults during gestation can have.

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Moreover, growth restriction during pregnancy will lead to a compensatory growth pattern once the calf is born due to what is termed as the “thrifty phenotype hypothesis.” When embryonic growth is restricted, the metabolic pathways of the calf are expecting to enter a world where there is a shortage of feed. When the calf is born and feed is not restricted, compensatory growth occurs but at an expense to future reproductive efficiency and possible metabolic disease as a mature cow. In a field study conducted by Grober Nutrition, results illustrated the different growth rates of heifer calves born to a first-calf heifer versus a mature cow. Initial weight and growth rate in the first month were lower for calves born to a first-calf heifer than to those born to a mature cow; however, by compensatory growth, both groups of calves had similar weaning weights.

Moreover, overnutrition and overconditioned cows during gestation can impart negative effects on the calf. This is less understood in dairy cattle, but we know the effects of overnutrition in beef cattle such that calves born to fat cows have greater concentration of fat cells and collagen in their muscle, thus impacting future carcass characteristics. Likewise, in humans and rats, obese mothers are linked to diabetes, high blood pressure and increased body fat in their offspring.

Beyond maternal nutrition, transitioning from the dry period into lactation causes stress to both the cow and calf. The transition period causes an inflammatory response in the cow and, if severe enough, leads to transition cow diseases. However, dysregulation of inflammation can also impact the calf. Low birthweight, slower growth in the first month and even alterations to a calf’s immune markers can be attributed to maternal inflammation. How this occurs is not yet known, but increased levels at birth of one immune marker, haptoglobin, increases the risk of disease and mortality during the first 4 months of a calf’s life.

Calf growth rate differences

During gestation, adaptations to the placenta may help to protect against challenges. The dam provides nutrients to the fetal calf via cotyledons in the placenta. The surface area and numbers of cotyledons present are modified according to when a challenge occurs during gestation. Despite this strategy, the efficiency of the placenta to transfer nutrients from dam to calf is still reduced.

However, means of reducing the negative effects of stressors during embryonic development are under review by researchers. Future practical means of reducing negative effects during embryonic development and, conversely, increasing positive fetal programming could include maternal diet manipulation such as precision ration changes to coincide with stages of embryonic development.

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Calf growth

Other strategies can be implemented in practice by making changes to animal husbandry on-farm with the overarching goal to keep mom happy for a healthy calf. For instance, grouping pregnant cows and heifers according to social dominance to prevent competition for feed, ensuring adequate feedbunk space, providing sources of heat abatement during heat stress such as additional fans or sprinklers and considering the economic balance of calving intervals and reduction of genetic potential in offspring due to demands of lactation during key stages of pregnancy.

Ultimately, early life programming can create results we can see right away, such as low birthweights, but can also lead to far-off future reductions in performance.  end mark

References omitted but are available upon request. Click here to email an editor.

Amanda Kerr is a senior nutritionist at Grober Nutrition

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