Cows need higher-quality feed, and more of it, as pregnancy progresses. Nutrient requirements in early gestation are not much different from maintenance requirements, but as the fetus grows larger the cow’s nutrient needs increase.
After calving, when a cow is lactating, she needs a much higher level of protein and energy than when she is pregnant. Young cows’ requirements are highest because they are still growing. A heifer should be about 85 per cent of her projected mature body weight at breeding, says Barry Yaremcio, an Alberta Agriculture beef and forage specialist.
During her first pregnancy, the heifer needs to grow a calf and herself at the same time. For the average 1,100 to 1,600-pound beef cow the protein requirements in mid-, late -and after-calving rations would be a minimum of seven, nine and 11 per cent protein respectively, on a dry-matter basis.
“The energy requirements, as a percent of TDN, should be 55, 60 and 65 per cent respectively, for those same stages,” says Yaremcio. There is a change from the last trimester of pregnancy to after calving (lactation). The cow’s nutrient requirements jump by about 25 per cent from late pregnancy to after calving to maintain lactation.
Watch body condition
During winter, cattle also need an increase in feed just to maintain body heat in cold weather. It helps if they go into the winter in good body condition, since fat acts as insulation against the cold; the cow won’t need as much feed to keep warm. Fat can also be mobilized for heat energy if needed.
“Ranchers need to watch for thin cows going into winter. Pastures in many regions are running out and some cows are losing condition. A cow that is one body condition score lower than what it should be will be about 200 pounds lower in weight. It is difficult for her to regain weight during winter without grain supplement,” Yaremcio says,
“In order for the thinner cow to stay warm, she will require an extra 1,400 pounds of hay compared to a cow in proper body condition. She needs that much extra hay just to stay warm and hold her own, without gaining weight. That’s one extra big round bale per cow through winter, and with hay prices at $150 a bale or more, that’s a major expense,” Yaremcio says.
Milking off their backs
It pays to keep cows from losing weight in late fall. “If a cow is thin, and doesn’t produce the quantity and quality of colostrum needed by her calf, there is a greater risk for the calf to get sick. Passive immunity from cows to their calves will be compromised and the ability of the calf to resist diseases will be reduced,” Yaremcio says.
The thin cow won’t be able to milk adequately. Peak lactation occurs during the first eight weeks of lactation. Maximum feed intake does not occur until 12 weeks after calving. During early lactation, it’s very difficult to meet the energy requirements of the cow.
If energy needs aren’t met she will take the fat off her back, and lose more weight. If she’s thin it will affect reproduction and breed-back. For every pound of fat that the cow mobilizes off her back, there’s enough energy in that fat to produce seven pounds of milk. For a newborn calf, seven pounds of milk is what’s required to gain one pound of weight per day.
“So basically the cow and the calf are trading weight, pound for pound, at that point in time,” Yaremcio says. If you don’t have some fat on the back of the cow to produce that extra energy, the calf is not going to grow as well. You need to pay special attention to the first-calf heifer because the amount of feed she is able to consume is less than the larger cow.”
Yaremcio says you have to feed the cow to produce milk to grow the calf. Feeding extra grain to this group, compared to the mature cows, can be beneficial.
“The goal for after-calving nutrition is to have the cow on an increasing plane of nutrition and have her maintain or gain a small amount of weight each day. If a cow is in good condition and she loses a pound of fat per day for one or two weeks it’s not a big deal. But if the cow or first calf heifer is thin and loses more weight, it will negatively affect reproduction.”
The long-term effect of having a thin cow or one that is losing weight after calving is it will take between 30 and 60 days longer (than a cow that’s in good condition) to be physically prepared to have her first heat cycle, says Yaremcio. She will either be late calving or open the next year, in a 45- to 63-day breeding season.
“First service conception rate on thin cows is roughly 20 to 25 per cent lower than a cow in good condition,” he says. “If the rancher doesn’t take care of the problem there could be a large number of open cows the next calving season. The long-term ramifications of being short of protein and energy in the ration and having thin cows this fall is not going to stop at Christmastime. It will carry over for a year or even two years, until reproductive efficiency is back to normal.”
If feed quality is too low, cows will need some kind of supplement through the winter, during pregnancy.