Before heifer calves even are born, events that take place during their gestation may permanently change their ability to grow, process nutrients, resist disease, and produce milk. And they even may pass on those deficiencies to their own offspring.
Geoffrey Dahl, Professor of Animal Sciences at the University of Florida, discussed research performed by his own team and others in this arena at the 2020 Western Canadian Dairy Seminar. Included in the in utero factors that have been shown to impact fetal development and later-life performance are:
Nutrition – Compared to most beef cattle, dairy cows’ nutrition is generally highly specified, given the critical link between nutrition and milk yield. If gross nutritional deficiencies do occur, stunted calves with low birthweights likely will never catch up in growth and performance compared to normal herd mates. But Dahl said there are nutritional intricacies in even well-nourished dams that can affect fetal outcomes.
A most impactful one is choline. Research on the supplementation of pregnant cows with choline (for 3 weeks before until 3 weeks after calving) shows the dual benefit of both improved calf health and performance, and higher milk production by the dam.
In one recent study, calves from choline-supplemented dams had significantly higher survival rates at 24 days of age; reduced incidence of fever when challenged with disease; higher average daily gain through 300 days of life; and increased preweaning starter-grain intake.
Disease challenges -- When dams fall ill in late gestation, they may be passing immune system alterations on to their offspring. Dahl described two studies in which late-gestation cows were challenged at 50 days before calving with single dose of partial E. coli structures called lipopolysaccharide (LPS). This technique is commonly used to measure immune response.
The offspring of the LPS-challenged cows, and a control group of calves from non-challenged dams, were dosed with the same LPS at 240 days of age. The calves that had been challenged in uteroshowed longer periods of fever, and greater expression of clinical illness, compared to their non-challenged herd mates.
“This heightened immune response could cause disease-challenged heifers to partition growth away from growth and productivity, while not enhancing disease resistance,” concluded Dahl. “These results may indicate an increased risk for extended performance loss in calves.”
Heat stress – Dahl and his research team have studied the effects of in utero heat stress on fetal outcomes for several years. They have found that heat stress in late-gestation dams alters the ability of cows to exchange nutrients and oxygen with the fetus, resulting in shorter gestation lengths and lower-birthweight calves.
“We have found that this lower birthweight persists through weaning and puberty,” shared Dahl. “While these heifers do eventually catch up in body weight by the time they calve themselves, more of that second-year weight gain is likely due to fat deposition versus lean tissue growth.”
The result: shorter, fatter heifers that have higher insulin levels and lower ability to process insulin. They also process glucose more quickly. Both of these processes lead to diminished ability to convert nutrients to milk production. As a result, first-lactation milk yield has been shown to be negatively impacted for heat-stressed fetuses. That milk-production deficiency also persisted into the second and third lactations.
Furthermore, the University of Florida researchers have found that in utero heat stress calves have lower transfer of IgG from colostrum. They have determined this is not a factor of colostrum quality, but rather a faster closure of absorptive mechanisms in the digestive tract.
“This lower immune status translates into poorer health and greater death loss as these calves grow,” stated Dahl. Additionally, Dahl said there is evidence that the damage caused by in utero heat stress may initiate epigenetic programming that carries performance deficiencies into at least two future generations.
“Surprisingly, it appears most of the influence of the in utero environment takes place in the last three months of gestation, whereas we might have predicted greater impacts earlier in fetal development,” stated Dahl. “All of these results underscore the critical importance of attentive dry-cow management – not just to benefit the dam, but perhaps more importantly, to promote positive effects on the calf for its life and beyond.”