Improving Forage Utilization

In cattle production, profit depends on achieving a marketable calf per cow bred as well as increasing production efficiency on existing forage sources. Not all land set aside for cattle ranching contains optimal forage sources. Most cattle operations exist on land that cannot sustain agricultural crops and that cannot produce high quality forage on a year-round basis. Profit therefore depends upon managing forage and feeding programs efficiently to yield maximum cattle crops.

A cow’s forage intake is crucial to obtaining optimal forage utilization. Two factors that influence forage intake are rumen fill (or rumen capacity) and the rate of passage of forage types through the cow’s digestive system. The rumen is like a bucket with limited capacity. When it is full, the cow will stop eating until the rumen empties enough for her to consume more forage.

The rate of passage of the forage through the rumen depends upon the quality of the forage, the health and populations of the microbes that inhabit the rumen and aid in digestion, the rumen environment (whether or not it supplies the nutrients and energy the microbes need to work), and the total feeding program. The higher quality the forage, the easier it is for the “bugs” to digest, the faster the rate of passage, and the higher the intake. Rumen microbes play an important role in the cow’s digestive process by helping the cow’s body break down and utilize the nutritional components of forage. These microbes are living microscopic organisms and need certain elements to be present in the total diet in order for them to function efficiently.

Poor quality forage contains less nutrients to feed the microbes and is more difficult for them to break down. Its rate of passage is slower and when the rumen is full, the cow will stop eating even though her nutritional needs are not met. Forage utilization decreases; production efficiency is negatively affected. For dormant winter pasture, daily intake can range from 1.3% to 1.8% of body weight. Winter forage is also often fibrous, lignified (more difficult to digest) and low in nutrients.

Feeding supplement when forage is fair to poor quality is often viewed by cattle producers as an expense but in fact should be looked at as an investment that will bring higher returns. Supplementing provides the nutrients lacking in poor quality forage enabling the rumen microbes to perform more efficiently in digesting poor quality forage, thereby increasing forage intake and the nutrients available to the cow. The results are more efficient use of available forage sources and enhanced forage digestibility. Cattlemen make a profit by getting as much use of their land and forage as they can. Supplementing poorer quality forage sources gets more of the rancher’s grass into the cattle, improving forage utilization and production efficiency.

Increased Forage Utilization by Supplementing

Non-Supplemented Supplemented*
Forage Intake** 18 21
% Dry Matter Digestibility 40.6 50.6
Lbs. of Digestible Forage 7.3 10.6

*4 lbs. of a Purina 20% balanced protein/energy range supplement

** Grass/hay quality of 5.5% crude protein and 42% TDN

The above study looks at how the concept of forage utilization translates on a per cow basis. The study represents a 1,000-pound cow in late gestation to early lactation on a typical winter feeding program of dormant grass pasture, hay or both. The forage has a crude protein value of 5.5% and a TDN of 42%. The cow was fed 4 pounds of Purina 20% balanced protein/energy supplement according to feeding directions, daily. Forage intake increased from 18 pounds/head/day to 21 pounds/head/day. The cow was being stimulated to consume more dormant grass because her rumen microbe population had the nutrients needed to efficiently digest the poorer quality forage. Digestible forage intake increased from 7.3 pounds to 10.6 pounds.

The cow on supplemented forage is receiving 45% more nutrients from the available grass to help her meet increasing nutritional needs during late gestation and lactation. Let’s look at an example of the true value of feeding poor quality grass or hay to lactating cows.

This study demonstrates that lactating cows without supplement on poor quality grass/hay receive only 1.0 pounds of protein and 7.6 pounds of TDN when they need 1.9 pounds of protein and 10.8 pounds of TDN for optimum production. Losses show up in the areas of reduced body condition at calving and during rebreeding, prolonged returns to estrus, lower herd conception rates, decreased milk production for calves and less than optimum weaning weights for calves of malnourished dams. With effective supplementing, additional forage intake alone provides 1.2 pounds of protein and 8.8 pounds of TDN.

Nutrient Value To the Lactating Cow When Dormant Grass Is Supplemented

Nutrients Supplied by Forage
No Supplement
Supplement Nutrients Supplied By Forage + Supplement Lactating Cow Nutrient Requirement
Lbs Protein Intake 1.0 1.2 2.0 1.9
Lbs. TDN Intake 7.6 8.8 11.4 10.8

A supplemented cow gets 63% of the protein she needs and 81.5% of the energy she needs just by increasing her intake of low quality forage. However, she can’t do this without a supplement. The nutritional value of a Purina range product combined with her increased capacity for forage gives her 100% of her nutritional requirements for optimum production.

Nutrient Value To the Cow When Dormant Grass Is Supplemented

Nutrients Supplied by Forage
No Supplement
Supplement Nutrients Supplied By Forage + Supplement
Lbs Protein Requirement 53% 63% 100%
Lbs. TDN Requirement 70% 81.5% 100%

We have briefly touched on the necessity of meeting microbial population needs in order to stimulate forage digestibility, rate of forage passage, and increased intake. Why does this occur in the rumen and what are the needs of the microbial population?

Rumen microbes need a specific environment in order to operate efficiently. They must receive proper levels of minerals, ammonia and energy. Minerals act as catalysts in some digestive reactions, ammonia provides the protein form that microbes need to reproduce and grow, and energy supplies the microbes with the fuel needed to effectively withdraw and synthesize nutrients from the forage for the cow. When forage quality is poor, feed intake decreases because the forage cannot supply: the minerals needed to aid in the transport and synthesis of nutrients; the energy needed to increase the numbers and viability of the rumen microbes; and the energy to fuel digestive reactions.

Examples of limiting minerals in poor quality forages include calcium, phosphorus, potassium, magnesium, salts, copper and zinc. Purina range products are formulated to provide the balance of these nutrients necessary to meet production requirements and keep cows in good condition.

Ammonia. The amount of ammonia available in a cow’s total diet, provided by natural protein or by urea, is critical to the health and population of rumen microbes. Research has shown that ammonia requirements for maximum microbe synthesis to be 3 to 5 mg/100 ml of rumen fluid. A study done at New Mexico State shows that unsupplemented steers had rumen ammonia levels substantially below this level.

Ruminal Ammonia Concentration As Influenced By Protein Supplementation In Steers Grazing Dormant Blue Grama Rangeland

Time After Supplementation (hrs.) Ammonia (NH3) Unsupplemented Mg/100 ml Supplemented
-3 1.6 3.6
0 1.8 4.6
1 1.3 7.1
4 1.5 5.4
8 2.2 5.1

New Mexico Data

Ammonia levels below 3 to 5 mg/100 ml of rumen fluid reduce maximum microbial synthesis.

Organic Matter Intake As Influenced By Protein Supplementation in Steers Grazing Dormant Blue Grama Rangeland

Unsupplemented Supplemented
Forage DM Intake
G/Kg BW-1, d-1
9.3 11.6*

* 25% Increased forage intake for the supplemented animals

Forage intake in an unsupplemented steer is limited as ammonia was limited to meet microbial needs thus decreasing rate of passage and resulting in rumen fill. Contrast this limitation to forage intake in a supplemented steer. Proper supplementation directly translates to an increased forage intake of 25%. The rumen empties faster because the microbes are more efficient and the cow can eat more forage to meet her needs.

Energy supplementation versus protein supplementation alone

Is supplementing with additional protein enough or is energy equally important? Following are results from a study at the Purina Research Center.

The Need For Energy

Cottonseed Meal (41% CP) Cottonseed Meal (41% CP) Cube 2 (20%)
Feeding Rate (lbs/head/day) 2 4 4
Lbs protein provided/day 0.8 1.6 0.8
Cow Weight Lossa -71.1 -28.8 -31.9
Calf Weight Gainb 102.1 105.6 110.3

a January — May weight change
b Calf weight difference between calving (March-April) and weight taken in May.

This study involved feeding cows 2 pounds of cottonseed meal, 4 pounds of cottonseed meal or 4 pounds of a Purina cube. The amount of protein available was the same in the 2 pounds of cottonseed meal and the 4 pounds of Purina cube (0.8 pounds per head per day of protein). The 4 pounds of cottonseed meal provided twice that amount; 1.6 pounds per head per day of protein.

Cows lost 40 pounds more on cottonseed meal than on the Purina cube. Even doubling the amount of cottonseed meal did not bring its quality as a supplement up to the performance rate of the Purina cube. Why? The primary difference between the two was the level of energy. Purina’s cube contained the proper balance of energy necessary to utilize the forage to its fullest potential. This resulted in improved performance.

This means that, though protein provided to the cow was equal with 2 pounds of cottonseed meal or 4 pounds of Purina Cube 2N, there was not enough energy delivered to the cow from the 2 pounds of cottonseed meal to limit cow weight loss and maintain milk production for the calf. Even doubling the amount of cottonseed meal to 4 pounds per head per day did not bring its quality as a supplement up to the performance rate of 4 pounds of a 20% Purina Cube 2N.

Purina Research Center trials summarize the real benefit of correct protein and energy supplementation and its impact on grass/hay utilization and animal performance.

The trials were conducted January through May. Two groups of cows were used in the trials and both groups were late gestation or early lactation. Calving began in early March. One group was fed free choice hay or pasture and the other group was fed free choice hay or pasture supplemented with 4 pounds of 20% protein Purina cattle supplement. The crude protein for the free choice forage available to both groups was 6.5%.

Purina 20% Supplement Versus No Supplement

Cows on Forage Only Cows on Forage + Purina 20% Supplement
Forage Intake Only (lbs) 21.3 25.3
Initial Cow Weight (lbs) 1192 1197
Ending Cow Weight (lbs) 1049 1159
Cow Weight Loss During Trial (lbs) -143 -38
Average Daily Gain/Loss During Trial (lbs) -1.34 -.36
Fat Thickness Change Between the 10th and 11th Rib -.36 -.08
Calf Birth Weight (lbs) 77.2 79.2
Calf Weight at End of Trial (lbs) 179 190
Calf Gain During Trial (lbs) 102 111

Forage intake increased by 18.8% in the supplemented cows. More total nutrients were obtained form the available forage source, than when that forage was not supplemented. Cow weight loss was about 100 pounds less when cows were supplemented. The feed conversion on the Purina product equaled 4:1.

This research also demonstrates that cows that are not supplemented and are on nutritionally inadequate forage do not perform to their potential production capability. Nutrient deficiencies in the forage that are not corrected by the proper supplementation extended the time to first estrus, delayed rebreeding and reduced weight gains in calves. Supplementing nutritionally deficient forage produced an average of 9 pounds more calf per cow/calf pair in the study.

The bottom line in supplementing is that the balanced mineral, protein and energy contained in a quality Purina supplement improve forage utilization enabling cattlemen to receive more value and profit potential from their operation. Production efficiency is improved as supplemented cows improve body condition, return to estrus more quickly, increase conception rates and deliver more pounds of marketable calves at weaning.

Cattle give land its economic value. It is good business sense for cattlemen to ensure that their land is able to yield its full potential to produce cattle. With proper supplementing and management practices, it is possible to do this even when cattle are grazing dormant winter grass.

Feeding a quality Purina range supplement improves the utilization of forage and increases a cow’s daily intake of low quality forage making more efficient use of resources. Feeding to achieve more marketable pounds of beef per acre represents a strategic business decision and the best possible return on investment.

Dr. Lee Dickerson, Jr.

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