ENID, Okla. —
Many of us soon will be fighting the extra pounds that so often are the result of an abundance of holiday goodies.
But for beef cows going into winter, adequate fat cover is not only desirable, it is critical for future performance. As temperatures fall, grazing opportunities become restricted, and animal needs increase, the supplementation program must fill the nutritional gaps to ensure cows achieve or maintain adequate body condition.
Research studies abound showing the impact of nutritional status during pregnancy on subsequent reproductive performance. Condition score at calving, which is our practical measurement of how well animals are fed during the gestation period, is closely tied to both when and if cows breed back.
Some typical responses seen in an LSU study are shown in the table.
Calving 4 5 6 7
Preg. rate % 65 71 87 91
Days to Preg. 92 82 74 76
These figures obviously are important to the bottom line in any cowherd. For operations that produce breeding stock, whether for market or for internal replacements, there are additional incentives to manage winter nutrition. An in-depth review of the ties between nutrition and reproduction in ruminants (Roe et al., 2002) discussed the impact of gestation nutrition on the lifetime reproductive abilities of offspring. A bred cow’s plane of nutrition directly effects fetal development and heifers born to underfed cows may produce lower quality oocytes (eggs) throughout their life, due to altered ovary development in the womb.
With all the information available, it should not be hard to recognize the value and long-term payback of a balanced winter feeding program. But designing that program can be more complicated. Producers are faced with a wide range of feeding and supplementation options and multiple factors determine which strategy will most effectively and cost-effectively match a given situation.
In most cases, the primary practical and economic goal is to maximize utilization of available, low-cost forages. Since the cow is dependent on the microbes in the rumen to actually break down the roughages she consumes, the logical focus of a supplementation program is to first meet any needs these microorganisms might have. On a typical hay or crop residue-based diet, the first limiting requirement for the fiber-digesting bacteria is going to be rumen-degradable protein.
Energy supply also is important. Most dietary energy will come from the roughage portion of the diet, but much of that will be tied up in compounds that may take time to break down. Soluble energy sources in the supplement can help keep the ruminal energy supply more consistent. The trick is to provide energy in a form that will be used to promote activity of the fiber-digesting microbes.
Keep in mind there is a dynamic mix of bacteria and protozoa species in the rumen, and specific organisms have the ability to utilize specific substrates. Those that break down forages can benefit from sugar and soluble fiber supplementation. Supplemental starch (grain), on the other hand, encourages growth of different species.
The resulting shift in microbial populations, and fermentation end-products, can lead to reduced utilization of the base roughage. Supplemental fat does not contribute to rumen fermentation activity, and at levels above 5 percent of the diet, fat actually inhibits fiber digestion.
When a supplement delivers needed protein and energy to the rumen, microbial activity is increased. This leads to faster breakdown of the forage, allowing it to move through the system faster. That in turn makes room for increased levels of feed intake — on average, 40 percent more of a low-quality feed. Under these conditions greater populations of microbes are supported, and as their numbers turn over, the spent bacterial cells become a key supply of amino acid protein for the host animal.
Additionally, there can be more thorough breakdown of forage, which would be reflected in greater digestibility. This would be especially true if hay intake were limited.
The net result: A relatively small amount of the right supplement can result in a greatly increased supply of both energy and protein to the cow.
Nelson is Oklahoma Cooperative Extension Service ag educator for Garfield County.