Early gestation provides important development
During the early stages of gestation, the fetus of the calf is very small, with minimal nutrient requirements, but Jana Block of North Dakota State University’s Hettinger Research Center says there are a number of things that happen during early gestation that ranchers should be aware of.
“We don’t really think a lot about early gestation,” Block says, noting implantation of the egg, organ development and follicle development are all important during that period. “How our different nutritional management programs impact these processes can really impact our calves.”
Maternal recognition
After the egg is fertilized, Block explains the next step is recognition of the egg and implantation in the uterus. The uterus must recognize the egg and implant to maintain the pregnancy.
“Shortly after, we have the placenta implanting into the uterine wall and beginning to grow,” she says. “Around the same time, fetal organs are starting to develop. That starts as early as 20 days of gestation.”
The heart, liver, brain, lungs and other important organs begin developing between 15 and 16 days of gestation.
“During this process of organ development, the survival organs – such as the brain and heart – have higher nutrient priority for the nutrients that are received,” Block explains. “There are other tissues being developed at the same time. If we have a nutrient restriction during this time, those tissues will be more susceptible to those deficiencies.”
Development
In early gestation, the follicle is also being developed. The fluid-filled sack supports the egg as it grows and can be impacted in early gestation if nutrients are restricted.
Block also cautions placental growth and development are critical during that stage, as well.
“The placenta is critical to meeting the demands of the fetus throughout gestation,” she says. “In early gestation, we see the development of the attachment sites to both the dam and the fetus.”
As the placenta attaches, a plasmatome is created. The plasmatome is the area where gases, nutrients and waste are exchanged between the dam and fetus.
“The majority of placenta growth happens during the first half to two-thirds of gestation,” Block explains. “We see a huge increase in fetal and placenta blood flow through gestation, which is designed to keep up with the increasing nutrient requirements of the rapidly growing calf.”
“Circulation must be established early in gestation,” she continues. “During that time, we have to have nutrients available to the placenta.”
Nutrient restriction
If nutrients are restricted or environmental stress is felt during placenta development, the consequence is possibly reduced nutrient availability to the fetus and reduced ability of the umbilical vein to carry oxygen and growth factors that contribute to development of the future.
“We also know the majority of fetal losses occur in early gestation,” Block comments.
In one study at the University of Wyoming, Block explains pregnant cows were fed 68 percent of their maintenance energy requirements and 87 percent of metabolizable protein requirements, then evaluated for fetal and placental growth.
On day 125 of gestation, a portion of cows were necropsied to measure and weigh fetuses and placenta. Another segment was necropsied at 245 days of gestation.
“On day 125, they saw 40 percent of nutrient restricted fetuses has reduced fetal weight and increased organ weights,” Block comments. “This happens because these tissues have higher nutrient priority.”
Further, the impact of lighter calves was more pronounced for cows that averaged 3.5 years of age compared to cows that were five years old or older.
“This points back to the fact that younger cows are unable to buffer nutrient restriction as well as older cows,” she says. “This study didn’t use a very extreme restriction, but it played a big role in fetal weights.”
Block presented during the 26th Annual Cattlemen’s College, held during the 2019 National Cattlemen’s Beef Association Cattle Convention and Trade Show. In next week’s Roundup, learn about impacts of nutrient restriction in mid-gestation.
Saige Albert is managing editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
