Supplementing beef cows on foothill rangelands
Research aims to optimize cattle production while reducing reliance on harvested feeds
By Thomas Hamilton
Ruminant animals are unique and have co-evolved over millions of years with grasslands resulting in the ability to utilize low-quality feed to grow and survive. One of the most limited nutrients in these type of production systems is protein, which is comprised of amino acids linked by peptide bonds that, once digested, are used to produce metabolites that are critical for body function and growth [1].
Most organisms must consume adequate dietary protein daily to maintain these functions. Ruminants have the added advantage of also being able to utilize non-protein nitrogen (urea or biuret) and, via microbial protein synthesis, contribute to the whole animal protein status, [2]. Even with the ability to synthesize microbial protein from non-protein sources, numerous studies have illustrated that supplemental protein can be of great benefit to beef cattle production specifically for cattle in a pasture setting where diet quality may be less than the protein requirements of the animal [3-5].
Meeting the protein requirements of cattle in forage-based production settings has become a well-studied topic over the past decade with the use of supplemental products and the introduction of varying supplemental strategies. With these new technologies and supplemental strategies, producers have gained the ability to extend the grazing season into the late fall and winter months resulting in less reliance on harvested feeds such as hay which often account for over half of the total cost related to cow-calf production in the United States [6-8].
During these times of extended grazing we know that animals respond to the increased metabolic demand by increasing intake to meet thermoregulatory and metabolic needs [9, 10]. Intake on these dormant rangelands at northern latitudes is often limited by forage quality. Therefore, supplemental protein is provided to promote intake resulting in improved microbial fermentation and increased rate of fiber digestion [11, 12]. Crude protein levels >7% are required to maintain growth and maximize rumen fermentation in non-lactating ruminant animals [13].
Supplemental protein amount and frequency on an operation is variable depending on forage quality, available resources and production stage of cattle being supplemented. Common sources of supplemental protein on cattle operations would include alfalfa hay, distillers’ grains or “cake,” and manufactured products such as molasses-based tubs or pellets. Being able to implement these management tools without sacrificing cattle performance and wellbeing is critical in the cow calf production system in the western United States.
Recent and ongoing work at Montana State University has focused on evaluating the influence of increased levels of supplemental protein and interaction of winter environment on cow body weight and condition change during the winter grazing period, grazing behavior and resource utilization, and subsequent calf growth and performance from birth to weaning. The work we will discuss here was an 84-day winter grazing experiment that took place over two consecutive years (2021-2022) at the Red Bluff Research Ranch located near Norris, Montana. This ranch receives an average annual precipitation of 15.98 inches with bluebunch wheatgrass and Idaho fescue being the dominant herbaceous species.
Angus based bred cows were used for this work and were assigned to one of three treatments which included a control group receiving no supplement, a low supplement group (1.5 lbs of protein per head per day), and a high supplement group (3.0 lbs or protein per head per day). These cattle were fed the canola-based pellet supplement (30% crude protein) three days weekly on a replicated pen basis while grazing native rangeland. From day 84 of the study to day 112 all cattle were assigned to a common supplementation system as they were preparing to calve.
All cows were weighed, and body condition scored every 28 days to monitor weight change and assess body energy stores. Birthweights and weaning weights were also taken on all calves to measure the effect of cow supplementation on calf performance.
Results from this work will be discussed on a treatment by period, treatment by year, and year by period basis where period is represented by the weigh days within the study (28, 56, 84 and 112 days). Looking first at treatment by period responses we observed a linear response where increasing protein status resulted in modest weight gains relative to the control treatment (Figure. 1).
Cattle offered no supplementation lost weight throughout the duration of the study until they were introduced to the common supplementation system after day 84. During this same time period cattle offered the lower supplemental level were able to maintain their weight, while cattle on the high supplement were able to add both weight and body condition.
A year by period interaction was also detected where cows from year two exhibited less weight change on days 28, 56 and 84 of the study and had greater body condition than those from year one during these periods (Figure. 2). In addition, we observed a treatment by year interaction where cows from year two experienced less weight change and had greater body condition than cows from year one. These differences could be a result of several factors including the difference in weather and forage growth patterns between the two observed years.
While looking at subsequent calf performance no treatment by year interactions were detected for birth weight, average daily gain or adjusted 205-day weight in calves. A tendency was noted for cows offered high supplement level to have heavier calves at birth than their counterparts over both years (Table. 1).
A year effect was detected where calves born in year two had increased average daily gain and adjusted 205-day weights compared to those from year one. A tendency for the calves in year two of the study to have heavier weights at birth compared to those from year one was also noted. Data was also collected on the re-breeding efficiency of these cows after being AI bred and exposed to a clean-up bull for 42 days and it was found that cows had similar pregnancy rates for both AI pregnancy and natural pregnancy the following year regardless of supplement level offered during the winter months.
This research demonstrates that increasing levels of supplemental protein results in linear improvements of both body weight and body condition change in late gestation cows grazing native rangeland during the winter months. Non-supplemented cattle were still lighter at weaning time and even though no differences in pregnancy rates occurred in this study we believe that if cattle were left un-supplemented for consecutive years breeding efficiency could suffer as a result.
The supplemental protein offered to the dams tended to alter birth weights in calves, however, did not affect growth performance of the calves post-partum. On a similar note, optimal protein supplementation could potentially reduce the occurrence of weak calf syndrome or illness such as scours. The overall magnitude of response to supplemental protein level is influenced by both overall forage quality and winter environmental conditions. With this work and continued research, we can aim to optimize cattle production while reducing reliance on harvested feeds and maximizing use of native rangelands in the western United States. Remembering that supplemental level and frequency will fluctuate from year to year depending on environmental conditions, forage availability and quality, and stage of production of the animal being supplemented.
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Hamilton is a Ph.D. student in Animal and Range Sciences at Montana State University.
