Ruminal metabolism in nonlactating cows fed whole cottonseed or extruded soybeans.

Five nonlactating Holstein cows (average weight 574 kg) with cannulas in the rumen and duodenum were fed five total mixed diets at 2.14% (DM) of BW for seven 2-wk periods to estimate the ruminal degradation of protein and fatty acids in whole cottonseed (WCS) and extruded soybeans (ESB). Lanthanum was used as an indigestible marker. Ruminal propionic acid (molar proportion) was larger and butyric acid was smaller for WCS diets than for control or ESB diets. Total VFA (mM) and acetic acid (molar proportion) were similar for all diets. Duodenal flow of nonammonia nitrogen (N) was 13% higher for ESB diets than for WCS diets, but was similar for the control and diets with WCS. The percentage of intake protein that was undegraded was 19% higher for ESB diets than for WCS diets. Ruminal and total apparent digestibilities of ADF were not reduced by the addition of oil seed. In conclusion, the protein from ESB was less degraded in the rumen of cows than protein from WCS. The addition of ESB at 12.7% (DM) or WCS at 25.3% of the diet did not reduce the apparent digestibility of fiber. The unsaturated fatty acids in WCS were not protected from ruminal biohydrogenation, presumably due to mastication of the seed coat.

Effect of dietary level of barley-based supplements and ruminal buffer on digestion and growth by beef cattle.

Six ruminally cannulated beef steers were used in a 6 x 6 Latin square experiment with a 3 x 2 factorial arrangement of treatments to evaluate the effects of barley supplementation (BS; 10, 30 or 50% of diet DM) and ruminal buffer (RB; Na sesquicarbonate at 0 or 4% of BS DM) addition to bromegrass hay-based diets on digestion. When early- (boot) and late- (full maturity) havested bromegrass and wheat straw substrates were incubated in situ, no interactions (P greater than .10) involving substrate with dietary BS or RB were observed, indicating that forages differing in fermentability responded similarly to different ruminal environments. Averaged across substrates, RB had no effect with 10% BS and a positive effect with 30% BS, but a negative effect with 50% BS diets (BS x RB, quadratic; P less than .05) for in situ DM and NDF disappearance for 18 and 24 h of incubation and for rate of disappearance of potentially degraded DM and NDF. Intakes of DM and digested DM were greater (P less than .01) for RB diets; however, RB had no effect (P greater than .10) on total tract DM and NDF digestibility. Intake and digestibility of DM increased linearly (P less than .01), whereas NDF digestibility decreased linearly (P less than .01) as BS percentage was increased in the diet. Sixty beef steers (avg initial wt 302 kg) were fed the same dietary treatments in a growth experiment. A numerical improvement in DM intake (P = .20) and ADG (P = .06) was observed when RB was provided with the 50% BS diet. Results of these experiments indicate that RB may moderate negative effects occurring on ruminal fiber digestion when grains are used to supplement forage-based diets; however, improvements in ruminal digestion were not translated effectively to improved animal productivity.

Influence of reducing dietary crude protein from 17 to 13.5 percent on early lactation.

A total of 117 Holstein cows were in two trials to determine how reduction in concentration of dietary protein influences early lactation. Treatments were feeding 17% crude protein for 3 mo or reducing dietary crude protein from 17 to 13.5% after 1st or 2nd mo postpartum. Results were similar in both trials. Reducing concentration of dietary crude protein to 13.5% at 1 mo postpartum tended to decrease intake of dry matter during the 2nd and 3rd mo of lactation. Milk production of multiparous, but not primiparous cows, was decreased. Dry matter intake and milk production did not decrease following a drop in concentration of dietary protein at 2 mo postpartum. Returns over feed costs were reduced by feeding the diet with 17% crude protein to primiparous cows longer than 1 mo or to multiparous cows longer than 2 mo postpartum. Milk composition, body weight change, and reproductive performance were not affected by treatment.

Nitrogen requirement and utilization in dairy cattle.

Formulation of dairy cow rations should consider the following points regarding nitrogen utilization by lactating cows. (a) Maintenance of ruminal ammonia nitrogen in excess of 5 mg/100 ml rumen fluid has no effect on microbial protein production. (b)Supplemental nonprotein nitrogen is not utilized in typical dairy and feedlot beef rations containing more than 12 to 13% crude protein(dry matter basis). (c)Nonprotein nitrogen is approximately equal to true protein as a source of nitrogen in typical dairy and feedlot rations containing not more than 12 to 13% crude protein. (d)A scheme based upon metabolizable protein (absorbable protein) for calculating requirements and comparing protein sources is superior to crude or digestible protein designations. Ultimate expression of the requirement may be in terms of crude protein for the sake of simplicity. (e)One kilogram of crude protein, regardless of nitrogen source, equals about .75kg metabolizable protein in typical dairy and feedlot beef rations containing not more than 12 to 13% crude protein. One kilogram of plant protein (true protein) fed in excess of an amount equivalent to 12 to 13% dietary protein equals about .3 kg metabolizable protein. (f)Protein supplementation of lactating cows might be related more to stage of lactation than to milk production. (g)Lactating cows having above average lactational ability may benefit from dietary protein as high as 16 to 17% (dry matter basis) during the first third of lactation. (h)Cows in the latter two-thirds of lactation appear to require 12.5% dietary protein or less. (i)Plant protein (true protein) should be the supplemental sources of nitrogen during the first third of lactation, with NPN providing most, if not all, the supplemental nitrogen during the last two-thirds of lactation.

Relationship between ruminal ammonia and nonprotein nitrogen utilization by ruminants. I. Development of a model for predicting nonprotein nitrogen utilization by cattle.

The influence of ration composition on mean ruminal ammonia concentration was studied by collecting samples of ruminal ingesta from cattle fed rations varying in crude protein and total digestible nutrient content. A minimum of four sampling times distributed throughout the day permitted calculation of mean ruminal ammonia concentrations. Mean ruminal ammonia concentration was positively related to dietary crude protein concentration and negatively related to total digestible nutrient concentration. It is postulated that mean ruminal ammonia concentration may be a useful criterion for predicting efficacy of nonprotein nitrogen supplementation. A quantitative approach for evaluating nonprotein nitrogen supplementation based upon determination of the point at which ruminal ammonia exceeds the requirement (5 mg ammonia nitrogen/100 ml rumen fluid) of the ammonia-utilizing bacteria is proposed. Dietary conditions expected to result in excessive concentrations of ruminal ammonia are defined and recommended upper limits for nonprotein nitrogen supplementation are presented. Theoretical relationships between composition of the unsupplemented ration, amount of nonprotein nitrogen added, and efficiency of nonprotein nitrogen utilization are discussed. The practice of adding nonprotein nitrogen so as to exceed 12 to 13% crude protein in typical dairy or feedlot rations needs to be reevaluated.

Relationship between ruminal ammonia and nonprotein nitrogen utilization by ruminants. II. Application of published evidence to the development of theoretical model for predicting nonprotein nitrogen utilization.

Results from published experiments dealing with several aspects of nitrogen utilization by ruminants were used to test the concept of zero utilization of nonprotein nitrogen under conditions where more ammonia (greater than 5 mg ammonia nitrogen/100 ml) is in the rumen than can be converted to microbial protein. Results from experiments where the flow of non-ammonia nitrogen to the abomasum of sheep was measured indicate that when urea was the source of supplemental nitrogen, a constant quantity of amino acids reached the abomasum for all rations ranging from 10 to 23% crude protein. From growth studies, addition of nonprotein nitrogen to low protein, high energy rations caused an improved rate of gain. Additions of nonprotein nitrogen to rations resulting in predicted ruminal ammonia concentrations greater than 5 mg ammonia nitrogen/100 ml rumen fluid were without benefit. From lactation studies, nonprotein nitrogen supplementation did not improve milk production if the ration contained more than 12.5% crude protein prior to supplementation or if the predicted ruminal ammonia concentration was greater than 4 mg ammonia nitrogen/100 ml rumen fluid. The importance of the amino acid requirement of the animal as well as the composition of the ration in designing and evaluating nitrogen supplementation studies is discussed.

Early lactational response to supplemental protein by dairy cows fed grass-legume forage.

A total of 24 primiparous and 46 multiparous Holstein cows were in two trials to determine the influence of concentration of dietary protein on performance during early lactation. Treatments were 13.5 or 16.5% dietary crude protein for the first 12 wk of lactation. Complete mixed diets of grass-legume forage and concentrates were fed for ad libitum consumption. Treatment patterns repeated across trials. Yields of milk and 3.5% fat-corrected milk, intake of dry matter, and returns over feed costs were improved by feeding the diet with 16.5% crude protein. Percent milk fat, body weight change, and reproductive performance were unaffected by treatment. The results demonstrate benefit, during early lactation, from supplementing protein to grass-legume based diets containing 13.5% crude protein. Performance responses to increased concentrations of dietary crude protein during early lactation appear greater for multiparous than primiparous cows.

Production responses in early lactation to additions of soybean meal to diets containing predominantly corn silage.

Responses in yield of milk and intake of dry matter to increased concentrations of dietary crude protein by cows in early lactation were modeled from published data. The data base was 625 Holstein cows in second or later lactation fed diets primarily composed of corn grain and a combination of corn silage and alfalfa. Dietary crude protein as a percent of dry matter ranged from 9.5 to 20.2% and was varied with soybean meal. Exponential models were developed to predict changes in milk yield and dry matter intake per unit change in dietary crude protein. The consequence of changes in concentration of dietary crude protein on performance can be predicted with the models. The dose-response relationships can be used with relevant price information to estimate the concentration of crude protein that maximizes returns over feed costs. Profitability is improved by adjusting concentration of dietary crude protein for changes in the price of soybean meal. Present feeding standards could be enhanced by incorporation of information on dose-response and economics.

Responses of dairy cows to additions of distillers dried grains with solubles in alfalfa-based diets.

Twenty-four Holstein cows in wk 3 through 12 of lactation were used to evaluate distillers dried grains with solubles as a protein source for alfalfa-based diets. Diets were formulated containing 0, 10.1, 20.8, or 31.5% distillers dried grains with solubles. Crude protein in these diets was 13.9, 16.0, 18.1, and 20.3%. Milk yield increased linearly with increasing dietary CP, whereas DMI was not affected. Dry matter intake averaged over 4% of BW for all treatments. Intake of undegraded intake protein was .93, 1.27, 1.63, and 1.97 kg/d. Yields of milk protein, casein, and lactose all increased linearly with increasing dietary CP. The proportion of milk N as whey N decreased, whereas N as NPN increased, with increasing dietary CP. Plasma urea N and essential and branched-chain AA increased linearly, and nonessential AA decreased linearly, with increasing dietary CP. Increasing the concentration of CP in the diet from 13.9 to 18.1% by the addition of distillers dried grains with solubles was beneficial to cows fed alfalfa-based diets in early lactation. Little additional benefit was observed by feeding greater than 18.1% dietary CP.

Relationship between ruminal ammonia and nonprotein nitrogen utilization by ruminants. III. Influence of intraruminal urea infusion on ruminal ammonia concentration.

In three trials, we studied the effect of incremental amounts of intraruminally infused urea on mean ruminal ammonia concentration of steer fed at 2-h intervals. Basal rations contained these percentages of crude protein and total digestible nutrients (dry matter basis); Trial I, 11.1 and 81; Trial II, 6.0 and 54; Trial III, 6.5 and 58. Mean ruminal ammonia concentration reached 5 mg ammonia nitrogen/100 ml rumen fluid at crude protein equivalents of 12.0, 9.3, and 9.4% in I, II, and III. Once ruminal ammonia began to accumulate, there was a linear relationship between intake of urea and mean concentration of amino acids of plasma, serving as an indirect measure of amino acid absorption from the intestine, was not increased by increased intake of urea in III. Results of this experiment support the concept from in vitro data that microbial protein synthesis is unaffected by ruminal ammonia concentration in excess of 5 mg ammonia nitrogen/100 ml rumen fluid.

Response of dairy cows in early lactation to additions of cottonseed meal in alfalfa-based diets.

The effect of increasing CP levels by additions of cottonseed meal to diets for early lactation was studied in 24 multiparous Holstein cows. Diets containing 13.8, 17.5, 20.4, and 23.9% CP were fed during three 3-wk periods beginning at wk 4 postpartum. Each cow received three of the four dietary treatments giving 18 observations per treatment in a randomized complete block design. Undegraded intake protein as a fraction of total protein for the diets was .25, .32, .36, and .39. Dry matter intake increased linearly with increasing dietary CP concentrations. Daily milk yield increased as dietary CP increased from 13.8 to 17.5%. Increased milk yield was accompanied by increased daily yields of milk fat and protein, but the concentration of these components in milk was not altered. The proportion of total milk N that was NPN increased linearly with increasing dietary CP level. Plasma amino acids and urea N were increased by increasing the dietary CP level. The conclusions of the study were that increasing dietary CP levels from 13.8 to 17.5% by the use of cottonseed meal was beneficial to cows consuming alfalfa-based diets in early lactation. Increasing dietary CP above 17.5% showed little benefit in milk yield. Increasing dietary protein caused an increase in blood urea N and milk NPN, indicating N wastage by the animal.

Influence of dietary protein concentration on milk production by dairy cattle during early lactation.

In a 3 X 2 factorial experiment 75 Holstein cows in first, second, or third lactation were fed rations containing either 12.2% or 16.2% crude protein in total ration dry matter. On the average, 26% of dry matter intake was from corn silage, 22% from alfalfa-grass hay, and 52% from a grain mix. Protein was controlled by feeding a 13.7% crude protein grain mix with 1.4% urea for the 12% ration and a 19.8% crude protein grain mix with natural protein for the 16% ration. Average daily milk production (kg/day) for wk 2 through 12 of lactation for 12% and 16% rations by lactations were: first, 21.6 and 21.9; second, 25.7 and 31.5; and third, 27.5 and 34.0. Dry matter intakes by lactations were .42, 1.18, and 2.05 kg/day higher for cows fed the high protein compared to low protein rations. Milk composition was not influenced by protein treatment. The markedly different response to protein supplementation in milk production between heifers in first lactation and more mature cows is unexplained.