The impact of trucking and handling stress on cow and heifer pregnancy rates
With calving season in full swing across the state, it’s worth considering what those embryos survived on their way to becoming newborn calves. South Dakota State University Beef Reproduction Specialist George Perry says producers should be aware of stresses that can impact embryo survival after fertilization, as they can have noticeable impacts on pregnancy rates.
“To know about this, you need to know a little about embryo development. If you look at that, day zero is day one of estrus. We know that 38 hours later that follicle will ovulate. If we get semen into that cow at the correct time, and she ovulates, we get fertilization about 90 percent of the time.
“But, when looking at AI conception rates, we’re talking about 60 to 70 percent. What’s happening to all those other pregnancies? What about when we’re down in the 40 percent conception area, considering everything else is being done right?” asks Perry.
He explains that the first cell division in an embryo occurs at day two, and between days five and six the embryo moves into the uterus. Days seven and eight are when the embryo enters the blastocyst stage, which is when cattle would be flushed.
“Day 15 is a big one. You bred her on day zero, and this is when she knows she’s pregnant. If we cause changes or problems to occur to that cow during those first two weeks, there isn’t even a signal for her to maintain that pregnancy,” notes Perry.
He continues, saying that the embryo attaches to the uterus on about day 19, and is definitively attached around day 42, after which it draws nutrients directly from the mother instead of relying on what’s secreted into the uterus. If all goes well, on approximately day 285, a calf is born.
“We need to think about what can affect those key points of time,” notes Perry. “First, there is the discussion of when to move cows after breeding, and some say as soon as your arm is out of her, and that’s a good move. Another part of that is to keep cattle calm while moving them,” says Perry, noting that early pregnancy stress is one thing that can have a potentially negative impact on pregnancy rates.
“There have been studies done at Miles City regarding shipping stress. There was a group of heifers that were synchronized and AI’d. Then they were trucked at either 1-4, 8-12, or 29-33 days post breeding. This was conducted by loading them on a truck and driving down the interstate, then driving back and unloading them at the same location – there was no change in environment or feed,” explains Perry.
The results compared pregnancy loss to that acquired in the heifers hauled between days one and four, and found a 12 percent reduction in pregnancy in those heifers hauled between days eight and 12, and a nine percent loss in those hauled between days 29 and 33.
“Then we did a follow-up study where we trucked heifers 45 to 60 days post-breeding. We ultrasounded every animal before it went on the truck to confirm they were pregnant, and they lost six percent, so we know trucking stress can be a real problem,” states Perry.
“If we’re putting time, effort and money into synchronizing and AIing, our biggest advantage are those AI pregnancies, so why give up as many as 10 percent of those?” asks Perry.
He adds that shipping stress causes the release of prostaglandin. A study in Tennessee infused small levels of prostaglandin into the uterus to determine if it had a negative effect on embryos in very small doses.
“Those small levels of prostaglandin were actually embryo toxic, and killed the embryo. So, even if we get small amounts leaking into the uterus during times of stress, we can kill that embryo,” notes Perry.
“But, if it’s prostaglandin killing embryos, we should be able to stop it, because we have prostaglandin inhibitors,” he continues.
To test this theory another study was conducted that included both cows and heifers.
“We AI’d these cows and heifers, then 14 days later we trucked one group, and gave another group a shot of flunicin meglumine (FM), a prostaglandin inhibitor, and trucked them,” explains Perry, adding there were also two control groups; one for the trucking group and one for the FM group.
“The cows and heifers that were trucked, and didn’t have an FM shot, had the lowest conception rates when compared with the control group,” says Perry.
In the group given an FM shot, the trucked cows were at the same conception rate as the non-trucked cows.
“There was about a nine percent reduction in pregnancy rate in the trucked group when compared to any of the other three groups,” says Perry.
Another study ran cows through the chute on day 14 of pregnancy, and compared them to cattle that were turned out to pasture and never touched.
“The group run through the chute had a decrease in conception rates of five to eight percent compared to those that were just turned out,” explains Perry.
“Think about these stress effects. We know there are factors that stress cattle, and we don’t have a good measure for stress. It’s also important to remember that heifers don’t have the experiences of older cows, and they get more stressed and high strung as a result. We need to think about these things as we’re handling animals, especially during those critical points of pregnancy,” concludes Perry.