Late season grass and harvested hay quality effects on reproduction

Proper pasture management and having a good understanding of the herd grazing environment are two key components of successful cattle operations. Since cows are selective grazers, it is important to understand the type of grass species available and time of year to determine grass maturity and subsequent forage nutrient composition.

In many regions in the U.S., spring calving producers tend to align peak forage quality with peak milk production, thus allowing nutrient dense forages to provide much, if not all, of the nutrients required for milk production. However, for a variety of reasons many herds across the U.S. utilize different breeding and calving seasons that do not line up with optimum forage quality windows. Therefore, paying close attention to pasture forage quality and cow nutrient requirements is important to ensure optimal performance.

As pasture grasses mature in late summer to fall, nutritive value including crude protein and dry matter digestibility decline, but the rate at which grasses mature greatly depends on geographic location, environmental conditions, grass type and management. For example, dormant native pasture grasses in late summer to fall can average 5-7% crude protein and 55-59% total digestible nutrients. These values are considered deficient for even meeting cow maintenance requirements during gestation, thus supplementation is required to avoid loss of body condition in order maintain health and reproductive performance.

Following regional weather patterns and drought conditions in your area often is one recommendation that can help assess pasture conditions and subsequent forage nutritive value. As drought or grass maturity progresses, forage quality and cow condition can decline quickly. Staying ahead of pasture conditions and implementing a forage sampling program to monitor nutrient content can help effectively determine what to supplement, how much and when. 

Current conditions, according to the UNL Drought Monitor, indicate much of the high plains, west and south portion of the U.S. is currently experiencing moderate to exceptional drought conditions. Not only can these conditions be favorable to wildfires, they can also negatively affect vegetation, pasture conditions and forage availability. In these situations, cattle producers are forced to consider reducing stocking densities, dry-lot feeding which requires bringing in feed ingredients, or moving livestock to different regions are some effective strategies to cope with the challenging conditions.

On the contrary, the Midwest and eastern regions of the U.S. are mostly not considered to be in drought conditions where there has been an adequate amount rainfall; however, there are some abnormally dry and moderate drought pockets that do exist. In these areas, be sure to pay close attention to pasture conditions and consult with your nutritionist for recommendations for when to provide nutrient supplementation. 

Feed samples, whether it is pasture grasses, harvested hay, grain mixes or complete rations that are submitted for nutrient analysis can provide valuable insight on diet nutrient composition and help guide decisions on supplement formulation to meet cattle nutrient requirements to achieve optimal performance. For pasture grass, the sample should be representative of what the cattle are grazing, consisting of all species of grasses throughout the entire pasture, which can be difficult to capture in one sample. As more samples are collected over time, a better estimate of grass nutritive value can be obtained. 

Typically, feed samples are tested for macronutrients including crude protein, energy, phosphorus, and other nutrients. In some areas, molybdenum content should also be analyzed to determine if levels could lead to mineral antagonism, as this element can interfere with copper metabolism and potentially negatively affecting many bodily functions including immune function and reproductive performance. In many cases, source, level and ratios of copper, zinc, manganese and other trace elements should be formulated by a nutritionist to ensure cattle receive proper nutrient balance in environments with mineral antagonists.

Another type of analysis that is highly recommended for all feedstuffs, including pasture grasses and harvested hay samples, is to test for mycotoxin contamination. Mycotoxins are rarely the first factor considered when evaluating potential reasons for poor breed-back, weak calves, rough hair coats, or overall poor growth or reproductive performance in cattle grazing pastures throughout the U.S. According to reported U.S. mycotoxin surveys, there has been a variety of mycotoxins detected in grazing forages and harvested hay samples in all regions of the U.S. and although these fungal metabolites may not be the primary cause of health or performance issues on-farm, they can contribute to such challenges.

Some major mycotoxin-producing fungi that have been identified in forages grazed by cattle include endophytic species of fungi such as Epichloë and Neotyphodium which are associated with tall fescue toxicity as well as multiple Fusarium species, which have historically been associated with cereal contamination, but are also prevalent in forages.

Fusarium molds are known for producing several different mycotoxins including zearalenone (ZEN), fumonisins (FUM), type A trichothecenes (such as T-2 toxin and HT-2 toxin) and type B trichothecenes which include, deoxynivalenol (DON a.k.a. “vomitoxin”), nivalenol (NIV) and fusarenon X (FusX). Fusarium molds are believed to be produced after stress conditions followed by wet weather during flowering. Each Fusarium mycotoxin presents its own negative effects on cattle growth and reproductive performance and, unfortunately, these toxins have been identified in a broad-range of native grass species, legumes and perennial grasses.

Although cattle consuming the various Fusarium mycotoxins may display different outward clinical signs, type A & B trichothecenes are known to reduce gut integrity by inhibiting protein and nucleic acid synthesis, resulting in reduced nutrient absorption and altered immune function. Similar to DON, FUM contribute to the disruption of the intestinal barrier and act synergistically in the presence of DON and other mycotoxins, imposing greater negative effects when found in combination than when occurring alone.  Zearalenone is frequently found in the presence of DON and other type B trichothecenes and primarily has an estrogenic effect on animals, which can significantly impair heat cycles, embryo survival and cause abortions in cows as well as poor testicular development, sperm production, and semen quality in bulls.  

Mycotoxins have also been widely identified in harvested hays including meadow or prairie hay, brome, and others. More recently, there have been reports of a number of producers experiencing unexplained fertility issues in beef cow ranches in the high plains and southeast regions of the US. Pasture grass, hay, and ration samples on these ranches have indicated mycotoxin contamination, possibly contributing to the reproduction concerns. Regardless of the source of mycotoxin, it is important to be vigilant of a potential mycotoxin challenge by paying close attention to the growing conditions and routinely sampling and submitting feed samples to be evaluated for mycotoxins. 

Overall, some key nutrition strategies for managing cattle operations include paying close attention to pasture conditions, analyzing pasture grass, harvested hay, and other feedstuff ingredients for nutrient composition and be sure to work with your nutritionist to ensure an effective supplement program is in place to meet cattle nutrient requirements. Finally, being aware of other environmental factors, such as mineral antagonisms that can impair nutrient bioavailability, as well as, mycotoxin contamination that can cause poor fertility and production losses.

For more information, please contact a dsm-firmenich representative.


Published on

21 November 2022


  • Ruminants
  • Mycotoxins


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