Many factors blamed for open cows, heifers this fall

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            Producers and veterinarians in some parts of eastern Montana and the Dakotas say they are seeing more open cows than usual this fall. Veterinarians are blaming flies, washy grass and grasshoppers including other possible causes.

MONTANA – Dr. Liam Robbins, a veterinarian based in central Montana just north of Lewistown near the town of Roy, pregnancy tests for ranchers all over the state. He says pregnancy rates seem to be worse for his clients in eastern Montana.  “In central Montana where I am, the breed-up has actually been pretty good.  Some areas in eastern Montana and parts of North and South Dakota had a lot of rain a year ago and again this year, and also had grasshoppers. There was an influx of stable flies this year and cows bunched up in corners trying to get away from them.” Flies disrupted their normal grazing patterns.

            “I think the biggest impact was washy green grass that was low in protein for the past year and a half.  Some ranchers put up record amounts of hay a year ago, but a lot of that hay was really low in protein,” says Dr. Robbins. “Some producers are checking their hay now, and its only 9 to 11 percent protein.”

            Yearling heifers on many ranches where Dr. Robbins tested had poor pregnancy rates. “The trend I saw was that most of the heifers that were kept at home on hay and pasture were lightweight for their age—maybe 100 to 150 pounds lighter than normal. They were probably slow to reach puberty and I think that was a lot of the reason many of them weren’t pregnant this fall,” he says.

            “Low protein levels probably had an effect on cows, as well,” he said, pointing out that the problem probably wasn’t a single issue, but the combination of washy grass, flies and grasshoppers. “In Baker, Montana, they had 26 inches of rain this year. They usually have about 13 inches,” he said. 

On a year like this, Dr. Robbins says that a supplement might have been helpful.  “People didn’t think about it during winter, however, because they had so much hay, not realizing how short it was on protein.  Some ranches in eastern Montana had decent breed-up in yearlings that were in feedlots over winter, getting a full ration that was probably a better balanced diet.  Those heifers developed normally, but the ones that were just on hay and then grass in the spring didn’t do as well.” Weather is a little different each year, and sometimes the extremes can have an adverse effect. 

“Here in central Montana, we had grasshoppers, lots of moisture, and our calves were light, but breed-ups have been good.  A lot of it was probably due to what the cows carried through.” Dr. Robbins surmises that they had higher protein feed over the winter and  probably went into breeding season more ready to conceive.

“A cow’s rumen is like a box and there is only so much room in the box to put food in.  If the feed doesn’t have adequate nutrients, even though the cow tries to eat more, you can’t put enough in there,” he says.

SOUTH DAKOTA – Dr. Dave Barz, Northwest Veterinary and Supply, Parkston, South Dakota, says his area was in a drought, with intense heat.  “This hurt us, and this year a lot of folks are trying to find answers since they are seeing a higher number of open cows.  I inspect cattle at Mitchell Livestock Auction in Mitchell, South Dakota, and cows are sold every Wednesday.  We’re seeing a lot more of cows coming to market right now in southeastern South Dakota.  It seems strange that people are selling so many cows, with the lowest population of cows in the country right now.  Most people want to rebuild their herds, but we’re selling more slaughter cows,” says Dr. Barz.

            “We’ve run diagnostics on some of the open cows, finding some Neospora,” he said. Raccoons and other animals eat on the silage and hay piles, shedding the protozoa into those piles, he said. 

“In our area, the coyote population has boomed, and they can also spread this parasite,” he said.

Hemorrhagic disease transmitted from deer could also be contributing to the situation. “This is caused by a virus and spreads readily in warm, dry weather. After sending blood samples from some open cows to diagnostic labs, we are finding this virus, and this may explain why they are open.  Some cows have antibodies in their blood, which means they’ve been exposed,” says Dr. Barz.

This summer there was also an outbreak of anaplasmosis in South Dakota.  “It’s become common here because we are no longer isolated,” he says.  That disease can travel thousands of miles with carrier cows or in ticks on cows coming from regions where this disease is endemic.  Some of these diseases could play a role in increased incidence of open cows in some herds, he believes.

NORTH DAKOTA – Dr. Bleaux Johnson serves cattle producers in southwestern North Dakota and northwestern South Dakota from West River Veterinary Clinic in Hettinger, North Dakota.

He has seen an increased number of open cows and heifers in some of the herds he’s checked.

            “Our open rates are typically about 6 to 8 percent but this year the numbers have almost doubled in some herds; we’re seeing 13 to 14 percent open on average.  I had one group this week that had 30 percent open, and in the past month some herds were pushing 50 percent, though most have been between 13 and 20 percent” he says.

            “As to why, that’s a good question.  Though we had a lot of moisture this year, many people had lighter calves.  In pastures where producers had lighter calves, they generally had poor breed-up. It might be a micronutrient deficiency. We also saw more fly burden in many areas, and that may have been a factor. Some producers felt that increase in grasshoppers played a role,” says Dr. Johnson.

            “There may have been something lacking in the grass,” he said, citing situations where some heifer mates were fed in a feedlot prior to breeding and others were out on pasture, and feedlot cattle bred better. “The feedlot group probably had a more balanced diet right up until breeding, and better micronutrient levels,” he believes.

            “Some cows, and heifer development in many herds may have been impacted by last year’s extreme winter.  Most producers had a lot of hay, but perhaps the extreme cold was a factor.  The cows looked ok coming out of winter, and we assumed they were ok but they may have been lacking in something,” he says.

            The puzzling thing was that some differences seemed random. “Some pastures just had more open cows.  We might have 20 percent open at one place, and only 7 percent open in the adjacent pasture.  We had adequate water this year—good runoff from a lot of snow—and plenty of rain later, so I don’t think our surface water sources were bad.  I wish I had an answer because people are wondering what the reasons might be,” says Johnson.

            “As we get later into preg-check season we’re now doing more of the later-calving cows and it seems like pregnancy rates are a little better, if body condition scores are good,” he said.