Missouri Forage and Grassland Council 2000 Annual Meeting October 30-31, 2000 Lake Ozark Holiday Inn, Lake Ozark, Missouri

1. Time of calving.
   
2. The cow’s ability to store and relinquish energy in the form of body fat.
   
3. A balanced supplement that accounts for forage deficiencies relative to animal requirements - no more/no less.
   

Rancher - Manager - Naturalist
There is a time to breed and a time to calve. There is a time to wean. There is a time to build energy reserves as body fat and a time to utilize the stored energy. As with the seasons of the year, the annual reproduction cycle of the cow is similarly ordered. As ranchers, do we allow the cycle to flow with nature or do we apply expensive fossil fuel technology to force the cycle to fit our desires?

Visualize for a moment that neither you nor anyone else are involved in any way with the management of your cow herd. Assume that the bulls are with the cows at all times. Further, all fences and structures that could impede cattle movement are removed. The cattle are free to roam. Now, picture yourself leaving the country for several decades. When you return to inspect your herd, when will the cows be calving? Will it be at a different time than the one you have established for them at present?

Assume that your ranch is quite isolated. It is necessary to drive the cattle several miles to weigh and load them onto trucks. It would be quite impossible to bring in a load of supplement. Since the only item of equipment you have is a wheelbarrow, you are not going to be in the hay business. Given this scenario, would you change the date that your cows calve?

We ponder situations such as these because of the performance of wild ungulates. Game biologists say that when you see that new fawn, elk calf or bison calf, somewhere in the brush nearby is a yearling offspring from 65% of the dams.

One cannot help but wonder - How many more yearlings would there be if it were possible to remove the sterile breeding males? It will be something more that 65%, I am certain. How much more I don’t know. There are a lot of barren females out there, taking up space and consuming feed. What if they were culled from the herd? Would the percentage of yearlings increase? I believe it would, but how much? I don’t know.

How well do we manage our cow herds? Over the years, we’ve learned about “Bioenergetics and Growth” from Missouri. The Texans taught us about scrotal circumference and normal sperm count. From Oklahoma, we gleaned information about body condition at calving and conception rates. California taught us the Net Energy system. Now our computers are full of nutritional equations from New York. The ranch is stocked with expensive bulls. The cows are synchronized. We go out to the pasture with syringes filled with vaccines, dewormers and antimicrobials. The better ranchers are spending more than $100.00 per cow/calf for hay and other supplemental feeds. It is also the better ranchers who wean an 80% calf crop (from females exposed to the bull).

Listen to the Land
In the deserts of Eastern Oregon and Western Idaho the rainfall is about 10 inches. With irrigation, high-quality alfalfa is grown. When harvested pre-bloom, there are four cuttings per year. The annual yield per acre is 10 tons. In the south-central desert of Arizona, the rainfall is about 10 inches. High-quality alfalfa hay is produced with irrigation. When harvested just prior to flowering, there are eight cuttings per year. The annual yield is 10 tons per acre.

With computers, Range Scientists simulate situations in which rainfall, soil type, elevation, etc., are made similar. With season of the year from north to south the only variable, annual forage production would be the same. This similarity is viewed most clearly when forage energy is measured rather than forage quantity.

A hunter looking for a trophy white tailed deer (Odocoileus virginianus) in South Texas will be pleased if his kill weighs 150 lb. Similarly, a hunter searching for the same species of deer in Alberta expects to bag a buck weighing 300 lb.

Is the land speaking to us? - Are we refusing to listen? Is there a proper size of cattle for the land? Will the land support the level of lactation we’ve chosen? Are we most profitable when fossil fuel technology is applied to surmount the limitations of the land?

The gestation periods of wild ungulates vary considerably.
     DEER = 201 days
     ELK = 250 days
     NORTH AMERICAN BISON = 278 days
All give birth at about the same time.

A ranch located in the Willowa Mountains in northeastern Oregon (45^o N latitude, elevation 5,000 to 6,000 ft) commenced calving about March 15. New management changed the program from scheduled breeding to a system where the bulls were left with the cows year-round. In just 15 years, calving started the last week of May and lasted for about five weeks.

Dr. Jan Bonsma¹, the noted South African animal scientist, observed that sexual activity of cattle was greatest at or near the times of the vernal and autumnal equinoxes, i.e., around March 21 and September 22. Since he was in the Southern hemisphere, he recommended that breeding take place around the time of the vernal equinox. In the Northern hemisphere, the autumnal equinox would be considered. If a cow is bred September 22 and she has a 280 day gestation period, she will calve June 29 of the following year.

Photoperiod also impacts the anestrus period (postpartum interval to first estrus). The cow that calves during the longest day of the year has a much shorter anestrus period than does the cow that calves on the shortest day of the year. Be mindful that the cow must breed by 85 days postcalving to remain on a calf per year schedule.

British investigators² found that the average acyclic period of suckling cows calving between November and April was more than 70 days. Cows that calved between May and October were acyclic for only 36 days. Those cows that experienced first estrus 70 days post-calving will have to breed at first estrus. The 36-day group cycled for the first time 45 days prior to the 85-day deadline. They would have experienced two normal heat periods before visiting the bull. They should be recovered fully from the calving experience and be very fertile.

A similar response to season was observed with Angus cows in New Zealand³. Cows calved early (January 22 to March 19) or late (March 13 to May 3). (Dates from the original publication were altered by 180 days to match Northern Hemisphere photoperiods). Cows that calved early commenced cycling at 83 days post-calving, while those that calved later experienced first estrus at 62 days. The conclusion was that the interval to first estrus was shortened by 0.404 days for each day later in the season that the cow calved. Almost the same value was found in a Canadian study⁴. The post-calving interval to first estrus was reduced by 0.43 days for each day later that cows calved.

With data from only 32 suckled Angus cows⁵, the equation expressed by Figure 2 was proposed. The curve indicates that cows calving from June through August will commence cycling within 60 days of calving. Those calving in the winter, however, may not cycle for 90 days or more after calving. The body condition of the cows at calving was not considered in this study.

Heifer calves are 20% more fertile during their third heat period than during their pubertal estrus. Since the heifer must calve by her second birthday, it is important that she achieve puberty at a reasonably young age.

Age at calving	730 days
Gestation	-280 days
Age at breeding	450 days
Allowance for 2.5 cycles	-50 days
Age at puberty	400 days

Hereford heifers born between January and June in Wisconsin⁷ exhibited pubertal estrus one day of age less for each day later that they were born. A calf born April 15 would experience pubertal estrus⁶ three months younger than one born January 15. In a following study⁸ with Angus and Angus crossbred heifers, a similar relationship between birth date and age of puberty was observed. When supplemental lighting was introduced, age at puberty was reduced even more.

When data from these studies are massaged into an equation⁹, they can be pictured as in Figure 3. This curve reflects daily photoperiods at 40^o N latitude. Heifers born from about the middle of March through late September will experience pubertal estrus prior to 400 days of age. At more Northern latitudes, the range of acceptable birth dates shortens.

Body condition score is a means of placing a numeric value on the amount of body weight that is fat. Figure 4 shows this relationship¹². Body condition score has considerable utility in the management of a Cow/Calf operation. Its first application is conception. The higher the BCS (within reason) at the time of calving, the higher the conception rate within 85 days post-calving. The foraging cow that has just calved utilizes stored body fat for energy to recover from pregnancy. Energy, over and above feed energy, appears to function primarily in the normalization of the ovary and the initiation of follicular activity. However the stored energy may function, the end result is an early return to cyclicality after calving. The probability for conception is highest with the cow that has experienced more than one normal cycle post-calving.

A classic study at Oklahoma State University¹³ even proffered an equation to predict percentage pregnancy from body condition at calving. Figure 5 reflects this equation¹⁴, although extrapolated beyond actual observations. The research facility maintaining this herd is situated at about 35^o N latitude. Furthermore, the cows calved in late winter.

While a cow with a BCS of 5 is certainly not thin, the likelihood of her conceiving within 85 days postcalving is less than 60%. A cow with a BCS of 6.5 to 7 has better than an 80% chance of getting bred. That is a large difference when the economic success or failure of a ranching operation is on the line.

How are these high BCS(s) attained? Animals deposit fat when the dietary energy consumed is in excess of that required for other physiological functions. It can come from forage that already has been paid for or it can be purchased in the form of hay or an energy-containing supplement.

Nutritionists say that brood animals require energy for maintenance, gestation and lactation. Body weight maintenance requires the greatest, followed by lactation and then gestation. With a female that produces a large quantity of milk, energy requirement for lactation can be as much as or more than that required for maintenance. When the two functions are taken together, there is an enormous requirement for energy. This is depicted in Figure 6.

In order to satisfy this requirement for both milk and maintenance, ranchers breed their females to give birth just prior to the onset of lush forage. Thus it is common for cows to calve during the late winter months. Spring and summer forage production goes toward milk production and calf growth. The program is directed to achieve the heaviest weaning weights possible. If the primary goal of such operations is verbalized, it would have to describe the cow’s milk production capabilities as measured by the calf’s performance. Conception and calving rates are secondary goals to these producers.

This scenario, in which cows require energy only for maintenance, gestation and lactation, is true if body weight and body condition are maintained. If the animal loses weight and body condition, however, there is an additional energy requirement for body weight gain.

The mature female ruminant has considerable capacity to store fat. This energy reserve, in the form of fat, can be mobilized to provide for life’s necessary functions. Stored energy can be used to maintain the animal. Survivors of the World War II holocaust can attest to this. The dam can manufacture and give milk from stored energy. Energy for the growth and development of the fetus can be derived from body stores of energy.

Energy that is to be stored (fat deposits) can come only from feed. If the purchase of supplemental energy is to be avoided and there is to be full reliance upon the forage, the rancher must consider the following:

1. For the twelve-month reproductive cycle of the cow, during what period does she have the least requirement for energy?
   
2. During what period is the forage most likely to be at its best year after year?

Only the rancher can answer the second question. He/she knows better than anyone else about his/her forage production. The best forage production, however, probably occurs during the period presently used for milk production.

If the cow/calf producer is to allow the cow to harvest and store plant energy, as opposed to hay stacks and granaries, she must consume a considerable quantity in a relatively short period of time. The actual allowable time depends upon the length of the period in which there is likely to be abundant forage. The time needed by the cow to regain her weight depends upon her condition going into the recovery period. Her condition, for the most part, can be controlled by the timeliness of weaning.

Figure 7 indicates the quantity of energy required by the cow if the recovery period is limited to the final month and a half of the production year.

In total, more energy is required when the cow is allowed to cycle in body weight and BCS. This may be termed as biologically expensive. The weight gain, however, comes from the land (that in one form or another has been or is being paid for). Large quantities of supplement do not have to be purchased. The hay can be grazed standing or harvested and sold.

Simply by knowing the weight of a cow that maintains that weight for a given period, we know the quantity of energy consumed. Likewise, if she maintains her weight and the calf gains (xx) pounds, we know the energy consumed for maintenance plus that for lactation. Tabled or easily calculated values are available for weight gain or loss, gestation, etc., at the school.

Energy consumption varies with the energy content of the forage. Young, growing forage (elongation stage) is high in energy, low in fiber and free of lignin. Consumption is high. Conversely, mature forage is relatively low in energy, high in fiber and contains considerable lignin. The indigestible portion of the forage waits in the rumen for regurgitation and grinding before moving along the gut, destined for excretion.

The relationship of forage quality and energy consumption is shown in Figure 8.

The establishment of this relationship renders the determination of other nutrient requirements quite straightforward. It becomes a matter of factoring a given constant (different for each nutrient) by energy required and/or consumed.

One example of this relationship with energy is the requirement for degradable protein. All feedstuffs contain two kinds of protein - degradable and escape (bypass). The rumen microorganisms require nitrogen, together with energy, to manufacture amino acids (building blocks of protein) and eventually microbial protein. Just as it sounds, degradable protein is degraded to nitrogen (ammonia) by the rumen microorganisms. In order to maximize forage utilization and its conversion to usable energy, the microorganisms’ requirement for degradable protein must be satisfied. The requirement is related directly to forage energy consumption as indicated in Figure 9.

Simply multiply energy consumed by the constant 0.10. Thus, the daily requirement for degradable protein is known. Requirements of the other nutrients can be determined by similar relationships.