North Dakota State University * Dickinson Research Extension Center
1089 State Avenue, Dickinson, ND 58601-4642 Voice: (701) 483-2348 FAX: (701) 483-2005


Greg Lardy, Ph.D., Extension Beef Cattle Specialist, Department of Animal and Range Sciences


Protein nutrition of grazing ruminants has been intensively studied for years. For beef cattle receiving low quality forage based diets, urea alone does not appear to be an effective protein supplement. Provision of natural protein appears to have a stimulatory effect on rumen microbes. When natural protein supplements are provided to grazing beef cattle, forage intake and/or forage digestibility are usually increased, but responses are variable. Natural protein supplement may provide rumen microbes with branched chain volatile fatty acids which are required by fiber digesting bacteria. During lactation, the need for escape protein (protein not digested in the rumen) increases. Provision of natural protein supplements generally increases milk production and, consequently, calf weight gain. Energy supplementation of forages is complex. Provision of starch-based (cereal grain) supplements generally decreases digestibility of low quality forages, while providing these supplements with high quality forages generally does not decrease digestibility. Use of fiber based supplements (soyhulls, beet pulp, etc.) may alleviate the negative effects of starch on fiber digestion. Degradable intake protein appears to be the first limiting nutrient for cattle grazing dormant native range.


Cow-calf producers in southwest North Dakota have access to dormant grasses during fall and winter months when lack of snow cover permits grazing. Stockpiled forages (native range) represent a low-cost forage resource for these producers since it requires no haying or feeding operation to deliver it to cattle. Cattle do the harvesting themselves. To make any extensive dormant grazing program successful, strategic, accurate supplementation is necessary. Degradable intake protein (DIP), which is protein available to the rumen microbes, is the first limiting nutrient in dormant native range. Strategic supplementation will improve cattle performance on dormant grasses and improve forage utilization. This review will discuss protein supplementation of grazing cattle.

Non-protein nitrogen supplements

If a source of ammonia is all that is necessary to improve digestion and intake of low quality forages, non-protein nitrogen (NPN) should provide adequate ammonia levels for this purpose. Clanton (1978) summarized several experiments conducted on native sandhills range using NPN in protein supplements and found that NPN was not as effective as all natural protein supplements as a source of protein for growing calves wintered on native range. Possibly the metabolizable protein requirement of these calves was high enough that they responded to the additional escape protein. Calves supplemented with biuret had similar rates of gain compared with calves supplemented with urea (Clanton 1978), indicating that biuret provided no additional benefit over and above urea.

When urea replaced soybean meal in supplements fed to cannulated steers fed low quality range forage, digestion of dry matter (DM) and organic matter (OM) decreased, but the synthesis of microbial protein was relatively unchanged (Kropp et al. 1977). In this study, soybean meal was replaced isocalorically and isonitrogenously with urea and ground sorghum. It is possible that the sorghum in the supplements influenced DM and OM digestibility due to negative associative effects of starch digestion on fiber utilization (Chase and Hibberd 1987, Mertens and Loften 1980). Ground sorghum levels ranged from 9.5 to 19.6% of the diet and dry matter intake averaged 4.6 kg/head/day. Starch content of the sorghum and starch intake was not reported.

The effectiveness of biuret or urea in dry or liquid supplements compared with all natural protein supplements for cows grazing dormant winter range was investigated by Rush and Totusek (1976). They found that cows fed the all natural protein supplement had less weight loss than isonitrogenous blends of molasses and urea when cows were wintered on native range. However, weight losses between supplements were similar if cows were provided prairie hay in addition to grazing native range. No advantage was noted with feeding either biuret in a dry supplement or urea in a liquid supplement compared with feeding urea in a dry supplement. These studies were conducted with gestating cows which calved during the trials, which makes interpretation difficult, because protein requirements change dramatically from gestation to lactation. Urea and biuret supply degradable protein needed by the ruminal microorganisms, but do not supply metabolizable protein.

The use of 15% urea/85% corn, 100% soybean meal, 10% corn/40% soybean meal/50% urea, or 14% corn/36% blood meal/50% urea as supplements for low quality native forage was investigated by Petersen et al. (1985). They found that digestibility of organic matter, bacterial nitrogen flow to the abomasum, feed nitrogen flow to the abomasum, and microbial efficiency were not different among these supplements. In a companion nitrogen balance study (Peterson et al. 1985), no supplement, soybean meal, soybean meal and urea, and urea and blood meal were fed with low quality native forage. Supplementation increased digestibility of DM and NDF, and nitrogen retention was greater for steers fed soybean meal or blood meal/urea. They concluded that a blend of blood meal and urea was an effective supplement for cattle consuming low quality native grass.

Urea and other forms of NPN do not appear to be adequate sources of degraded intake protein for cattle consuming low quality forage diets. The stimulatory effect of natural protein, peptides, and/or amino acids in vitro indicate that rumen microbes require natural protein and/or amino acids for optimum growth. The results of supplementation trials comparing NPN to natural protein supplements indicate that urea is not an effective N supplement unless a portion of the N is supplied by protein or peptides.

Effects of feeding natural protein supplements

Several broad categories of effects are reported when supplementing low quality forages with natural protein based supplements. These include increases in forage intake, increased digestibility, and increased rate of passage. Variation in responses is common and not all effects are observed in each trial.

Most responses to protein supplements are observed when forage crude protein levels were reported below 7% crude protein (Paterson et al. 1994). In most studies reported, protein supplements were based on oilseed meals which contain both rumen degradable and escape protein which makes ascertaining the biological mechanism responsible for eliciting responses difficult. In addition, protein deficiency has not always been demonstrated. Because of differential responses between urea based supplements and natural protein, a factor other than rumen ammonia provided by natural protein supplements may be responsible for the effects observed when natural protein supplements are fed. These factors could include 1) provision of nitrogen in a form other than ammonia, i.e. amino acids or peptides which are possibly stimulatory toward the rumen microbial population, 2) provision of some other growth factor required by the ruminal bacteria, which could include branched chain volatile fatty acids, 3) provision of escape protein which helps to meet the metabolizable protein needs of the animal, or 4) stimulation of ruminal kinetics allowing increased flow of non-nitrogen and nitrogen containing compounds is increased (Petersen 1987).

A review of literature pertaining to supplemental protein for ruminants grazing dormant native range indicates that responses to supplemental protein have been highly variable and year dependent. Factors contributing to or influencing this variation include weather conditions, which includes temperature and snow cover (Kartchner 1980), animal factors such as cow age (Adams et al. 1986), and differences in forage quality from year to year (Kartchner 1980, Soder et al. 1995).

Protein supplementation of forages, which are low in crude protein, increases intake (Kartchner 1980, Hennessy et al. 1983, McCollum and Galyean 1985, Krysl et al. 1987, Fleck et al. 1988, Guthrie and Wagner 1988, Stokes et al. 1988, DelCurto et al. 1990a, DelCurto et al. 1990b, Hannah et al. 1991, Nunez-Hernandez et al. 1991, Ovenell et al. 1991, Marston and Lusby 1995, Horney et al. 1996, Köster et al. 1996, Stafford et al. 1996). Forage crude protein levels in these trials ranged from 1.9 to 8.1% CP.

Other workers have not reported increases in intake when protein supplements were offered to cattle consuming low quality forages (Kartchner 1980, Krysl et al. 1989, Villalobos 1993, Forcherio et al. 1995, Hollingsworth-Jenkins et al. 1996). Forage crude protein levels in these trials ranged from 4.8% to 11.3%. Reasons why intake did not increase in the work of Villalobos (1993) and Hollingsworth-Jenkins et al. (1996) are not readily apparent. However, intake of control cows in these studies was approaching 2.0% of body weight, while intake of control animals in studies which have reported responses are sometimes considerably lower, 0.49 (DelCurto et al. 1990b) and 0.87% of body weight (DelCurto et al. 1990a).

Responses in digestibility to protein supplements are also variable. Some workers have reported increased digestibility when protein supplements were fed (Fleck et al. 1988, Guthrie and Wagner 1988, Stokes et al. 1988, Krysl et al. 1989, DelCurto et al. 1990a, Nunez-Hernandez et al. 1991, Ovenell et al. 1991, Sunvold et al. 1991, Hollingsworth-Jenkins et al. 1996, Horney et al. 1996); while others have reported no differences in digestibility with supplementation (Kartchner 1980, Petersen et al. 1985, Köster et al. 1996). Villalobos (1993) reported increases in digestibility with protein supplementation when measured in metabolism studies but was unable to show differences in digestibility with grazing cows fed similar supplements. Some of these differences are attributable to methods used to determine digestibility in the various studies (Galyean et al. 1986, Cochran et al. 1987).

Effects of feeding supplemental protein are variable. Factors which affect this variation include environmental influences such as temperature and snow cover, forage quality, and physiological status of the animal.

Provision of Microbial Growth Factors

The effect mediated by natural protein supplements may be due, in part, to the provision of branched chain fatty acids through the fermentation of leucine, isoleucine, and valine. These branched chain fatty acids are either required or highly stimulatory to cellulolytic bacteria (Mackie and White 1990). No differences in intake, digestibility, or microbial crude protein production were found in steers given branched chain fatty acids, indicating that the supply of branched chain fatty acids were not limiting or had no effect on microbial fermentation with the diets tested (McCollum et al. 1987).

Natural protein supplements may also supply amino acids which are limiting. Blends of urea and DL-methionine, urea and ammonium sulfate, or soybean meal as supplements for ruminally cannulated crossbred beef cows fed a 75:25 blend of grass hay and barley straw were investigated by Clark and Peterson (1988). In situ rate of fermentation was increased with the methionine treatment. Similar treatments were imposed on weaned heifer calves, no differences were found between the soybean meal and urea-methionine supplements.

The use of a blend of sugar beet pulp and DL-methionine or soybean meal as a supplement for gestating beef cows grazing native range was investigated by Lodman et al. (1990). The methionine treatment did not support the same level of performance that the soybean meal treatment did. Momont et al. (1993), in a similar trial, compared soybean meal to a blend of urea, corn, and methionine for cows grazing dormant winter range. They found that the urea, corn, and methionine treatment did not support the same level of cow performance that the soybean meal did.

Supplementing the lactating beef cow

Lactating cows grazing smooth bromegrass pastures and fed increasing levels of escape protein supplementation had increased milk production and increased calf weight gain (Blasi et al. 1991). No response was noted when cows grazed big bluestem, however. In situ analysis of forage samples suggested that escape protein content of smooth bromegrass was lower than that of big bluestem.

The effect of time of initiation of protein supplementation on cow performance was examined by Sowell et al. (1992) using spring calving cows. Protein supplementation began either pre-calving or post-calving. Cows which were supplemented pre-calving had less spring weight loss and higher prebreeding body condition scores than cows which did not receive supplement until after calving. However, no differences were noted in reproductive performance.

Ovenell et al. (1991) found no interactions between lactational status and supplement type (soybean meal, wheat middlings, or corn-soybean meal) in hay intake, digestibility, or particulate passage rate. Differences in intake were detected, 2.1% and 1.9% of body weight, respectively for lactating and pregnant cows. No differences were found in dry matter digestibility or particulate passage rate.

Hunter and Magner (1989) supplemented lactating primiparous cows with formaldehyde-treated casein. They found no differences in milk production during the first eight weeks of lactation; however during the second half of lactation, supplemented heifers produced less milk than unsupplemented heifers. Longer periods of anestrus were noted for unsupplemented heifers. No differences were detected in dry matter intake, possibly because the basal diet was 8.75% CP.

Supplements varying in ruminal degradability (25 or 50% undegraded intake protein as a % of CP) were fed to 2 groups of lactating spring calving cows (Dhuyvetter et al. 1992). Cows were split into groups based on calving date. Early calving cows grazed native range and were fed 5.4 kg of a medium quality grass hay (10.5% crude protein), late calving cows grazed native range only. Late calving cows had similar weight losses no matter which supplement was fed. Early calving cows fed the 50% undegraded intake protein supplement lost 39 kg less weight than cows fed the 25% undegraded intake protein supplement. They concluded that the late calving cows did not respond to escape protein in the same manner as the early calving cows because rumen degradable protein may have been limiting.

Response to escape protein was dependent on inclusion level in the diet with lactating ewes (Loerch et al. 1985). When blood meal was fed at 3.3% of diet dry matter, milk production was increased from 2.5 to 3.2 kg/day, compared to a diet supplemented with soybean meal. In a second study, when the blood meal was included at 6.8% of the diet, feed intake and milk production tended to be lower as compared to the diet supplemented with soybean meal. The authors attributed this to the poor palatability of the diet which contained high levels of blood meal. Dry matter intake was 3.0 kg when soybean meal was used as the supplement and 2.7 kg when 6.8% blood meal was included in the diet.

Milk production increased with increasing level [0 to 21 g supplement/kg body weight0.75] of protein supplementation in Hereford cows fed a low quality tropical grass hay (2.7% CP; Lee et al. 1985). They used a protein supplement which was made up of a blend of cottonseed meal, fishmeal, meat meal, and mineral mix at 75.5%, 9.45%, 9.45%, and 5.6% of the supplement dry matter, respectively. The authors stated that 53% of the nitrogen in the sample remained after a 15-hour in situ incubation. Nonsupplemented cows lost 2.56 kg/day while cows on the highest level of supplementation gained 0.15 kg/day. Growth rates of calves which nursed cows receiving increasing level of supplement were also higher.

The most consistent response from supplementing natural protein to the lactating beef cow was increased milk production. Consequently, calf gain usually increases when lactating cows are supplemented with natural protein.

Energy supplementation

Numerous authors have evaluated the use of grains for supplements to forage based diets. When grain or starch is fed as a supplement to low quality forages, results have been poor, because energy, in most cases, is not the first limiting nutrient (Klopfenstein 1996). Forage intake and/or digestibility often decreases when high levels (greater than 0.2% of body weight) of grain or starch based supplements are fed (Chase and Hibberd 1987, Sanson and Clanton 1989, Sanson et al. 1990, Adams 1991, Pordomingo et al. 1991). When highly digestible fiber sources are used in energy supplements rather than grain for supplement to low quality forages, digestibility and intake are not decreased (Martin and Hibberd 1990, Grigsby et al. 1992, Grigsby et al. 1993).

Forage quality seems to interact with grain supplementation. Matejovsky and Sanson (1995) reported that when corn supplements were fed with high quality hay (14.2% crude protein) no effects on NDF or ADF digestibility or digestible dry matter intake were noted. When corn was fed as a supplement to low quality grass hay, NDF digestibility and hay intake decreased.

When energy supplements do not adversely affect dry matter intake or forage digestibility, increased production usually results. However, practices such as supplementing low quality forages with starch generally have a negative impact on animal productivity since forage intake and/or digestibility are negatively impacted.


Degradable intake protein is limiting on low quality dormant forages and native range. Use of supplements high in protein degradability (sunflower meal, canola meal) should be considered in these situations. Urea or other NPN sources generally do not produce satisfactory results when used as the sole source of degradable intake protein. They may be used in combination with natural protein sources with a higher degree of success. Lactating beef cows may need supplemental escape protein when forage quality is low and/or when milk production is high. Use of starch-based energy supplements with low quality forages is generally not successful since intake and digestibility of the forage will be reduced. Producers should first provide adequate degradable intake protein and then supply additional energy as needed. Strategic supplementation will improve beef cattle performance and allow utilization of dormant native range with minimal cost.

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