Study shows nighttime is right time for calving
By DONALD STOTTS
Oklahoma State University
STILLWATER, Okla. -- It is generally accepted that adequate supervision at calving has a significant positive effect on reducing calf mortality, which has been of in-creasing importance with the use of larger beef breeds and cattle with larger birth weights.
"On most ranching operations, supervision of first-calf heifers and more mature cows will be best accomplished in daylight hours while the poorest observation typically will take place in the middle of the night," said Glenn Selk, Oklahoma State University Cooperative Ex-tension emeritus cattle specialist.
The easiest and most practical method of inhibiting nighttime calving at present is by feeding the expectant mothers at night; the physiological mechanism is un-known, but some hormonal effect may be involved.
Selk said rumen motility studies indicate the frequency of rumen contractions falls a few hours before parturition. Intraruminal pressure begins to fall in the last two weeks of gestation, with a more rapid decline during calving.
"It has been suggested that nighttime feeding causes intraruminal pressures to rise at night and decline in the daytime," he said.
In a Canadian study of 104 Hereford cows, 38.4 percent were fed at 8 a.m. and again at 3 p.m. and delivered calves during the day.
A British study utilizing 162 cattle on four farms compared the percentages of calves born from 5 a.m. and 10 p.m. to cows fed at different times. When the cows were fed at 9 a.m., 57 percent of the calves were born during the day, compared to 79 percent for cows fed at 10 p.m.
"There are field trials by cattle producers utilizing nighttime feeding when 35 cows and heifers were fed once daily between 5 p.m. and 7 p.m.; 74.5 percent of the calves were born between 5 a.m. and 5 p.m.," Selk said.
In perhaps the most convincing study to date, more than 1,330 cows on 15 farms in Iowa were fed once daily at dusk, with 85 percent of the calves being born between 6 a.m. and 6 p.m.
"Whether cows were started on nighttime feeding the week before calving, started in the herd or started two weeks to three weeks earlier made no apparent difference in calving time," Selk said.
Various means have been employed to reduce effectively animal loss at calving time, and skilled personnel should be available to render obstetric assistance and neonatal care.
"Currently, evening feeding of cattle seems to be the most effective method of scheduling parturition so assistance can be available during daylight hours," Selk said.
Though it is always a sound management practice to observe all the females in a herd, typically the percentage of adult mature cows that need assistance at calvng is extremely low compared to the percentage of first-calf heifers.
"That's good news on a number of fronts, particularly because -- on ranches with larger herds -- it is pretty much physically impossible to feed all of the expectant mothers after 5 p.m.," Selk said. "In those instances, the ranch manager should plan to feed the mature cows earlier in the day, and then feed the first-calf heifers at dusk."
What about the situation where large round bales of hay are being fed to the cows and heifers? If the cows have unrestricted access to the hay around the clock, then the best method of influencing the time of calving is via the time of day that the supplement is being fed.
According to an Oklahoma State University animal science study, the switch from supplement feeding in daytime to late afternoon or early evening feeding encouraged 72 percent of the cows to calve between 6 a.m. and 6 p.m. The cows had 24-hour, seven-days-a-week access to large round bales of grass hay. Before the change was made, when supplement was fed during the morning hours, the ratio of nighttime versus daytime calving was nearly even, with half of the calves born at night and half during the day.
Selk said some ranchers with small herds have reported success controlling access to the large round bales.
"The hay is fed within a small enclosed pasture or lot near a larger pasture where the cows graze during the day," he said. "In the evening, the gate to the area where the hay is placed is opened and the cows are allowed to enter and consume hay during the night. The next morning, they are moved back to the daytime pasture to graze until the following evening. In this manner, the nighttime feeding is accomplished with hay or silage only."
Selk recommends cow-calf producers do whatever best fits their specific operation.
"During winter months, baby calves born in the warmer part of the day have radiant heat from the sun to help reduce cold stress," he said. "These calves have a better chance for early colos-trum consumption and therefore survival. Let's not overlook that advantage."