Part 8: Body Conditioning Score Series: Consequences of poor forage
Unfortunately, a lack of understanding of forage quality and beef cattle nutrient requirements by cow-calf producers often leads to poor body condition scores in their cattle, particularly in the early spring. The consequences of poor–quality forage fed over the winter without proper supplementation are readily seen in fall-calving cows that become very thin, don’t breed back easily, wean a lightweight calf, or suffer from preventable diseases that arise from malnutrition and suppression of the immune system. Poor calf health, low milk production, and rapid weight loss after calving are seen in spring–calving cows that have been fed poor quality forage through the winter.
What qualifies as low-quality forage? A common definition of low-quality forage is any forage that has less than 7% crude protein and is high in fiber (Paterson et al. 1996). The ratio of Total Digestible Nutrients (TDN) to crude protein (CP) can also be used to assess the quality of forages. When the TDN:CP ratio is greater than 7, the forage is poor quality (Moore et al., 1999). In poor quality forages, protein is the first limiting factor, because protein is needed by the microbes in the rumen to digest the forage and release the energy contained in the forage (Olson, 2015).
How much forage a cow ingests each day is related to the overall quality of the forage. As mentioned in a previous article, the Neutral Detergent Fiber (NDF) of a forage influences how much of the forage the cow will consume. Mature forages often have high NDF values, and take longer to break down in the rumen. This means the cow eats less, because she feels full longer. Poor quality forages are often deficient in protein as well, and protein also directly influences the daily dry matter intake of cattle. As the crude protein of a forage drops below 8%, dry matter intake also decreases. If cattle are consuming less of the forage each day, and are not supplemented with the appropriate amount of protein for the microbes in the rumen to break down the consumed forage, BCS will decline rapidly. This begins a vicious downward spiral of long-term nutrient deprivation as the cow is maintained on poor quality forage without proper supplementation throughout the winter.
Cow-calf and stocker producers who are faced with feeding a less than ideal quality forage as their only option should ensure that adequate protein is supplemented. A common form of protein supplement used by many producers are “lick tubs”. Although these tubs may be convenient for the producer, they rarely achieve their intended purpose, and often do not provide any additional protein to the animal, despite what the producer may believe. “Lick tubs” commonly contain urea as a non-protein nitrogen feed ingredient, and relying on urea to meet the protein needs of the cow is very risky for the producer. Grass hay-based diets often lack the energy (i.e. carbohydrates) needed for urea utilization, and as a result, cattle often receive no nutritional benefit from urea when on a primarily grass hay diet. Other forms of protein supplementation, such as feedstuffs high in protein (i.e. soybean meal) are preferable over urea. Further discussion on using “lick tubs” as a protein source can be found in later posts. Proper protein supplementation will increase dry matter intake, improve rumen microbe function, and improve forage digestion. However, not all protein supplements are created equal, making proper selection of supplement very important.
The information in this article as well as additional information on beef cattle rations can be found at the following sources:
Moore, J. E., M.H. Brant, W. E. Kunkle, and D.I. Hopkins. 1999. Effects of supplementation on voluntary forage intake, diet digestibility, and animal performance. J. Anim. Sci. 77(Suppl. 2):122-135
Olsen, K.C., Cow Supplementation: Getting the Best Bang For your Buck. Proceedings: The Range Beef Cow Symposium XXIV. 2015. https://beef.unl.edu/documents/2016-RBCSymposium/RBCS-2015-Cow-Supplementation.pdf
Paterson, J., R. Cochran, and T. Klopfenstein. 1996. Degradable and undegradable protein responses of cattle consuming forage-based diets. In: M.B. Judkins and F.T. McCollum III (eds.) Proc. 3rd Grazing Livestock Nutrition Conference. Proc. West. Sec. Amer. Soc. Anim. Sci. 47(Suppl. 1):94-103.
Parish, Jane A., Rhinehart, Justin D., Protein in Beef Cattle Diets. Mississippi State University Extension Service. Publication 2499. 2018. https://extension.msstate.edu/sites/default/files/publications/p2499.pdf