Observations of Factors Controlling Daytime Calving

. ( FJ )

The following article was written by Brent Bunderson, a retired Utah State University county extension agent. Included are his observations of factors that may influence the occurrence of daytime or nighttime calving. Drovers submitted the article for review to two university animal science professors before agreeing to publish. While Bunderson’s observations may be accurate, the university professors cautioned that this is not peer-reviewed research, and that the observations have not been replicated in a controlled study. Drovers makes no claims regarding Bunderson’s observations, nor any claims that would refute the Konefal Method of managing for daytime calving. The observations are solely those of Brent Bunderson, and Drovers only publishes the article here as information to stimulate further thought and discussion. - Editor

An article recommending the Konefal Method of managing for daytime calving was published in a popular magazine recently. The Konefal Method prescribes feeding pregnant cows twice daily, midmorning and again in evening to promote daytime calving. The person credited with this method was Gus Konefal, a Manitoba purebred breeder.

Upon the advice of his vet, he began feeding straw in the evening with the idea that the heat of digestion would keep his cattle warmer during the cold Canadian winter nights, consequently, he reported that 80% of his calves were born between 6 am and 6 pm. The author of that article stated that it is not known why evening feeding is effective. The reason it is not understood is because the evening feeding is related only in time proximity to what actually is the trigger to daytime calving.

Unless one has an understanding of the underlying principles of the process, the desired outcome is left more to chance than management. There are a few important facts that must be understood in order to manage the timing of the birth of calves. First, the fetus initiates the onset of labor and unless one can manage the state of the fetus, birth time cannot be managed.  Another factor that affects the time of birth is the duration of labor, which is highly variable and influenced by several elements.

It is necessary to have an understanding of animal anatomy and physiology to begin to manage the state of the fetus. About ten days pre-partum, the blood cortisol levels begin to spike in the fetus indicating that it is experiencing some kind of stress. However, the cortisol level does not increase steadily but rather it spikes intermittently, indicating that the stress is a relatively short-term event.

These cortisol spikes increase in amplitude as pregnancy progresses. Cortisol is necessary in the development and maturation of several organs, notably the lungs. The lungs require about ten days under the influence of a high cortisol level to become fully mature. Cortisol also increases the metabolism of progesterone; the hormone responsible for pregnancy maintenance. Cortisol also causes the subsequent production of the hormone, PGF2a which causes uterine contractions. There is evidently a threshold level of cortisol which must be reached in order to initiate labor or the first spike would initiate labor but does not.

The source of the stress to the fetus is the complicating factor in managing the state of the fetus. It is a popular thought that it is either hypoxia or hypoglycemia or a combination of both that is the source of stress. It is difficult or impossible to determine because the procedure to monitor blood changes of the fetus would mask or influence the naturally occurring source of stress.

Once the hormonal threshold has been reached, it takes an average of thirteen and a half hours for birth to occur. Therefore, about thirteen and a half hours before birth, something affecting the fetus and causing fetal stress is the thing that the manager needs to understand. I will provide an understanding of those things. But first I will relate my own experience implementing the Konefal method.

I was calving out a bunch of pregnant heifers and was feeding in the afternoon to influence daytime calving. The practice was working well until an approaching winter storm prompted me to increase the amount of hay I was feeding. Every experienced rancher knows to expect more calves born during a storm than at other times.  And so it was in my case; the heart of the storm arrived during the night and as expected, many calves were born during that night.

Since a large portion of the cows had already calved, I decided to continue to feed the increased amount of hay. To my dismay, the afternoon feeding completely stopped working for me, and I got calves at totally random times. The only thing I could think of that was different was the extra hay I was feeding so I reduced the amount of hay to pre-storm levels. To my delight, the remaining calves were born during the daytime.

I concluded that in addition to feeding in the afternoon, the amount of feed was also a contributing factor in achieving daytime calving.  In hindsight the cows were returning to the feeding grounds to glean any stems etc., left from filling up at initial feeding. Shortly after this experience, I returned to the university to finish a bachelors degree in animal science and begin a concurrent masters degree in Livestock Management.

As a graduate student at the university, I conducted a trial to test the Konefal Method with some modifications. The motive for the modifications was my personal experience afore mentioned. In this trial, a herd of gravid cows was divided equally in to four groups. Groups 1 and 3 were fed in late afternoon; groups 2 and 4 were fed early morning.  Groups 1 and 2 were fed a diet which they totally consumed in a matter of about thirty minutes. It met all of the nutritional requirements but just barely met the dry matter intake requirements. Groups 3 and 4 were fed full feed; i.e., they essentially had feed before them all the time. However, both diets had equal total protein and calorie content; total dry matter was the only nutritional difference in the two diets.

The cows in this study were monitored every two hours; the temperature, bp [barometric pressure], and any births that may have occurred since the previous check were recorded. If feeding time was the trigger for labor induction then the expectation was that group 1 would calve during the day; group 2 would calve during the night. Groups 3 and 4 would calve at random times because they would, in essence, have, multiple feeding times.  

Group 1, as expected, calved primarily during the daytime. I was surprised to discover that group 2 also calved during the daytime. In fact, group 2 had a tighter grouping of calving time than group 1. The other two groups, 3 and 4, calved at random times as expected.  Groups 3 and 4 were observed at the feed bunk at random hours as they had feed present at all times. This short-interval feeding pattern was consistent with calving time distribution.

The similar calving time of groups 1 and 2 was not fully realized until mid-way through the trial at which time a partial analysis of the data was done. Subsequently, I began looking for something else that those two groups had in common besides diet. What I found was that 75-100%, depending on the day, of the cows in groups 1 and 2, were resting, i.e. lying down at least from 10:00 pm to 2:00 am.  Resting time at other hours did not prove to be effectual.

In the other two groups, only 50% of the cows were at rest in the corresponding time frame.  Had I known that resting time and duration could be a factor affecting calving time I would have included it in the complete data set. But I did record the percentage of cows at rest at each checking occasion for the duration of the trial. That resting time and duration phenomenon coincides with the thirteen-and-one- half-hour pre-birth event that would trigger labor. An understanding of the effect that this rest period would have on the fetus is critical.

The blood supply to the uterus is from the left and right iliac arteries that descend from the aorta down the interior walls of the birth canal. In a non-pregnant cow those arteries are turgid and a little smaller than a man’s little finger. In a gravid cow, the arteries are placid and are larger than a man’s thumb. When a gravid cow is at rest, i.e. lying down on her abdomen, it forces the fetus partially into the birth canal. The size and structure of the fetus’ head and fore feet press against the iliac arteries essentially restricting the blood flow to the uterus causing fetal hypoxia. Subsequent fetal stress and release of cortisol eventually trigger labor and, thirteen-and-one-half hours later on average, birth of the calf.

As previously mentioned, to collect data to prove that sequence of events is virtually impossible because as soon as the cow stands, gravity pulls the fetus from the birth canal and normal blood flow resumes. However, it is quite evident that it actually happens. One can observe that the vulva of a gravid cow in a resting position is quite protruded out from pelvic opening, evidence that the fetus is partially in the birth canal. This would explain the intermittent spike in fetal cortisol level.

I reviewed twelve studies that tested the Konefal method; six of them found it to be effective in promoting daytime calving and six found no effect. Statistically, when all reviewed studies were combined, one would conclude that afternoon feeding is not effective in promoting day time calving. I concluded from my trial that resting time and duration are the actual factors that promote daytime calving and is consistent with the hormonal process associated with labor rather that the common thought that somehow feeding time was the triggering factor. However, late afternoon feeding may create conditions conducive to daytime calving, i.e. after filling up on feed, cows might be more prone to resting.

The other factor previously mentioned affecting calving time is the duration of labor. I was aware, along with many other stockmen that a storm was associated with the time of births. Therefore, in my trial, I correlated the time of calving on a 24-hour clock to the relative change in bp [barometric pressure]. Plotted data points formed a perfect bell curve with >68% births occurred from 10:00 am to 2:00 pm; at the same time the change in the bp was near 0. That is, steady bp had no effect on birth time. The birth times to the right of the standard deviation were under the influence of a high and rising bp. Those on the left were under the influence of a low and falling bp. In other words, the greater the change in bp, the greater birth time deviated from the mean. When the bp was falling rapidly, births occurred as early 4-6:00 am. When the bp was high and rising, births occurred as late as midnight.

The interpretation of the cause and effect of the correlation of changing bp and birth time is left to speculation. However, based on the discussion of labor onset; there are at least three options to consider.  One, the metabolic rate of the dam could influence the speed/duration of labor. It is well documented that as a storm approaches, livestock feed consumption increases significantly and is associated with feedlot bloat. Also, grazing animals become opportunistic rather than selective grazers, i.e., they eat whatever is in front of them, as in the case of larkspur poisoning of cattle grazing high elevation rangeland. All of this is a function of metabolic rate. The conclusion is that once the hormone threshold level initiating labor is achieved, the rate of metabolism dictates the speed at which labor progresses.

The second option to consider is that the maternal cortisol level might contribute to the onset of labor. Stressful conditions that the cow experiences cause her cortisol level to increase. Stressful conditions include, but are not limited to, physical exertion, e.g., trailing cattle, etc.; anxiety caused by threatening environment; e.g., crowding/sorting, thunder and falling bp.  All of those conditions increase cortisol levels in the cow. Animals and humans are affected by falling bp; they become excitable and voracious.

The barometric pressure begins to fall twelve to fifteen hours preceding a storm; the average being thirteen-and-a-half hours; that is the exact length of time of the duration of the average labor. This is consistent with the observation that a relatively high number of births occur during the heart of a storm.

The third option is that the resting pattern of the cow during daytime when bp is very high is similar to night-time resting.  When the bp is very high cattle are prone to bask in the warm sun for lengthy periods which could cause them to calve during night-time. Considering the three mentioned options that cause the deviation of the time of birth from the norm, it is impossible to ignore the possibility that when the bp is falling, the elevated maternal cortisol level could contribute to the onset of labor. Conversely, under the influence of a high and rising bp, the maternal metabolic rate could be extending the duration of labor. These options need further research.

My Conclusion:

Feeding time has no direct effect on calving time. However, relative feed availability is a factor as it relates to feed consumption pattern. Cattle must have no reason to even search for feed at night, especially during critical resting time. Cattle are more likely to search for feed when there is a bright moon, potentially disrupting the desired resting period. Therefore, they must be conditioned not to expect any feed at night.  Cattle are very energy conservative in that regard.

Multiple feedings during the day might actually help daytime calving as it would encourage the cattle to remain on their feet during the day resulting in more resting time at night. However, if the act of feeding causes anxiety or undue excitement it may be counterproductive.

A roomy and dry resting environment is beneficial to promote the desired resting period. Do not disturb animals during the critical resting period (10:00 pm-2:00 am).

Be aware of impending storms predicted by rapidly falling bp. Expect calves 12-15 hours or sooner from a significant drop in bp; the faster the bp falls the sooner to expect calves. Unfortunately, there is little if anything one can do about that.

Lengthy daytime resting could cause night-time births, mimicking what happens at night that causes daytime births. Rousting the cows in a quiet manner frequently during the day at such times will increase metabolic rate and/or disrupt mimicry of mid night resting.