Managing pregnant females for optimal offspring productivity
Published on Jan. 25, 2020
“During pregnancy, a fetus depends completely on the mother to support metabolic processes required for growth. Consequently, the nutritional management of pregnant cows during gestation can have an impact on calf development in utero and calf performance after it is born,” says Reinaldo Fernandes Cooke of the Department of Animal Science at Texas A&M.
This process, known as fetal programming, has been proven in human medicine.
Cooke and his colleagues set out to understand if the same is true in beef cattle and what producers can do in terms of management and nutrition to ensure the calf is efficient after it is born.
A look at human medicine
“The Institute of Medicine for the National Academies suggest women with normal weights prior to pregnancy should gain about 30 to 35 pounds during gestation,” says Cooke. “This is about three pounds a month on average.”
He continues, “They also state women should be more concerned with their second and third trimesters and should be gaining around four pounds a month during this period.”
Cooke notes the reason for this is to ensure the mother has plenty of nutrients for herself and the growing baby.
In addition, women may also supplement certain nutrients during pregnancy even if they are not deficient, Cooke notes.
“Two of the most common supplemented nutrients recommended for pregnant women are trace minerals from organic sources, mainly zinc, copper, omega-six and omega-three fatty acids,” he says.
Static BCS versus increased BCS
Alongside his colleagues, Cooke conducted research to understand the effect of a static body condition score (BCS) versus a changing BCS on calves after birth.
The study looked at five groups of cows – one with a static BCS of four, one with a BCS four growing to a six in the first trimester, one with a BCS of four growing to a six in the second trimester, one with a BCS of four growing to a six in the third trimester and one with a static BCS of six.
“In the study we were not only trying to understand if it is important for cows to gain weight during gestation, but when it is the most beneficial,” states Cooke.
“In order to gain one BCS in the first trimester, we have to provide four extra megacalories per cow per day,” he explains. “If we do this during the second trimester, the requirements drop significantly to 2.8 megacalories per cow per day and then rises again when moving to the third trimester to 3.7 megacalories per cow per day.”
He continues,” Therefore, it is more efficient to supplement cows in the second trimester.”
When analyzing the results of their study, calf birth weights and cow milk yield weren’t affected by a change in BCS.
However, calf weaning weights were higher in the groups of cows who gained a single BCS compared to those whose BCS remained static, according to Cooke. He also states these weaning weights were the highest in cows who gained a BCS during the second trimester.
“Because of this increase in weaning weights, there was also an increase in calf value at weaning. In fact, we had about an $80 increase from calves born of cows who changed BCS during pregnancy,” Cooke explains.
“The studies show it is important for us to ensure we provide good nutrition to pregnant cows during gestation, so they are able to gain BCS and wean heavier calves,” he adds.
The affect of supplementing trace minerals
While little is known about the importance of trace minerals, including zinc, colbalt, manganese and copper, in terms of physiology, Cooke notes they have a significant impact on fetal development and offspring health and performance after birth.
Because of this, Cooke and his colleagues conducted a second study testing the importance of trace mineral supplementation to pregnant cows at the end of their second trimester.
The study analyzed three groups of cows – the first group received a control diet of alfalfa, grass, seed straw, cracked corn and a macro-mineral mix, the second group received the same base diet in addition to an inorganic source of copper, cobalt, manganese and zinc, while the third groups received the base diet with an organic source of these nutrients.
“These three diets had the same crude protein content and total digestible nutrients (TDN),” states Cooke.
He also mentions although the control diet had half of the amount of the copper, cobalt and zinc and 75 percent of the manganese the supplemented diets had, it still had necessary requirements for the trace minerals.
“The results from our study were not related to deficiency of trace nutrients because the control diet was meeting the minimum needs of these minerals,” Cooke says.
After the cows calved, researchers collected liver samples from both the cows and calves as well as the placentas. Calves were weaned at seven months of age, preconditioned for 45 days and then shipped to Beef Northwest until slaughter.
“When we looked at the cows’ liver mineral status, we found the pre-calving cobalt content increased on both groups receiving supplements but was higher in those supplemented with an organic source. Copper concentrations increased in both groups receiving supplements but was higher in those supplemented with an inorganic source. Zinc increased in the groups receiving supplements although there wasn’t much of a difference between organic or inorganic sources and manganese didn’t change much,” says Cooke.
“These trace minerals didn’t have much of an effect on birth weights,” he states. “However, organic sources increased weaned calf value by nearly $70 compared to the control group with an extra feeding cost of $3.10 per cow. Inorganic sources increased weaned calf value by $32 compared to the control group with an extra feeding cost of $2 per cow.”
The researchers tracked calves through slaughter.
“Zinc and copper have an important impact on immune system development during gestation, which may be why the animals supplemented with organic trace minerals had a significant decrease in the percentage treated for Bovine Respiratory Disease (BRD) compared to both the control and inorganic groups,” Cooke says.
“Body weight at the end of the growing lot period was higher in both groups receiving supplementation and highest in those receiving organic supplementation,” he states. “The same was true for body weight at the end of the finishing lot period and for hot carcass weight (HCW).”
He continues, “In the end, we had a 20 pound increase in HCW from the group receiving inorganic supplementation and a 42 pound increase in HCW from the group receiving organic supplementation.”
EFA supplementation
A second part of the supplementation study was conducted to understand the effect of supplementing essential fatty acids (EFA) to beef cows at the end of their second trimester.
The control group received a diet of grass/alfalfa hay, soybean meal and a saturated fatty acid source, while the treated group received the same base diet alongside omega-six and omega-three fatty acids.
Similar to the first study, calves were weaned at seven months of age, preconditioned for 45 days and shipped to Beef Northwest until slaughter.
“Cow plasma of fatty acids at calving increased in the treated group compared to the control group,” Cooke states. “Birth weight and weaning weights were similar between both groups.”
He continues, “However, as soon as those animals went to the feed yard, we saw a 0.2 pound increase on average daily gain (ADG) in the growing lot and in the finishing lot in the group supplemented with EFAs. This resulted in hot carcass weights that were 35 pounds heavier. They also had better marbling.”
Hannah Bugas is the assistant editor for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
