Growing Cattle Grazing Research Articles

PSXIII-4 Evaluation of an in-pasture weighing system to measure body weight change of growing cattle grazing wheat pasture

Abstract In winter 2023-2024, 65 stocker cattle grazed wheat pasture at the Southern Plains Experimental Range near Fort Supply, Oklahoma. Cattle had access to two in-pasture weighing system (IpWS, SmartScale, C-Lock) units placed at the water trough. Except for occasional standing water following precipitation, the only accessible water source was through the IpWS. Initial squeeze chute body weights (SCBW) were collected following ~16 h fast without feed or water. Full SCBW were collected without overnight fast every 28 d thereafter. Animals place their front feet onto the IpWS platform to drink water (ad libitum) and the front of the animal is weighed with an adjustment factor to convert the value to whole body weight (BW). The objective was to compare the two cattle weighing methods for growing cattle grazing wheat (Triticum aestivum) pasture. There were two cattle types and initial SCBW was 6 beef steers (BS, BW = 249.6 ± 14.4 kg), 6 beef heifers (BH, BW = 252.7 ± 7.3 kg), 26 beef-dairy cross steers (BDS, BW = 129.4.2 ± 18.7 kg), and 27 beef-dairy cross heifers (BDH, BW = 131.0 ± 10.3 kg). We fit a linear model to IpWS weight data as a function of day-of-study, sex, and type with a random animal effect. We estimated BW on the SCW d from the model and compared the IpWS and SCBW values. We used limits-of-agreement analysis to compare methods by date. A positive bias indicates IpWS BW are greater than SCBW and negative bias means IpWS BW < SCBW. In general, IpWS BW overestimated SCBW with biases of 5.2 ± 1.0 kg, 13.4 ± 0.8 kg, 17.2 ± 1.0 kg, and 10.2 ± 1.1 kg on d 0, 28, 56, and 84, respectively. The biases were occasionally affected by cattle type or sex. On d 0, bias was greater for larger beef cattle than for smaller beef-dairy cross cattle (13.7 vs. 3.3 kg, respectively, P = 0.004). On d 56, bias depended on sex with a 22.3 kg bias for steers vs. a 16.2 kg bias for heifers (P = 0.049). On d 28 and 84, biases did not depend on sex or type. Over the 84-d period, BW gain was biased (5.03 ± 1.27 kg). Similarly, average daily BW gain was biased (0.06 ± 0.12 kg/d). The cattle type affected bias for BW gain (beef type = -2.13 kg and beef-dairy cross type = 6.69 kg) and average daily BW gain (beef type = 0.03 and beef-dairy cross type = 0.08 kg/d, P = 0.005). These results indicate that adjustments are likely needed to convert front BW from an IpWS to whole BW and to remove BW bias.

Beef Cattle Grazing Native Grasslands May Follow Three Different Supplement Response Patterns

Previous studies on winter supplementation of growing cattle grazing stockpiled native Campos grasslands suggest that forage allowance (FA), herbage mass, and weather conditions before and during the supplementation period could all affect supplement feed efficiency (SFE)—that is, the difference or change in average daily gain (ADG) between supplemented (S) and control (C) animals (ADGchng, kg) per unit (kg) of supplement dry matter (DM) intake. In this study, we analyse data from fifteen collated winter supplementation trials carried out in Uruguay between 2004 and 2018. The working hypotheses of this research paper were: (i) that average substitution rates are positive, and (ii) that ADGchng is not constant throughout the supplementation period and that its variation may be attributed to sward, animal or weather variables. There were two main objectives: (i) to estimate the average supplement substitution rate (sSbR, kg forage, f, dry matter, DM intake reduction: kg supplement DM intake) and potential herbage intake substitution rate (hSbR, kg fDM intake reduction: kg fDM intake of control animals), and its association with SFE, and, (ii) to assess the existence of different phases and supplementation response patterns and its association with other relevant variables. Estimated substitution rates were always positive (sSbR = 0.3–1.1 kg/kg; hSbR = 0.1–0.3 kg/kg) and were negatively and moderately associated with SFE. Supplementation proved to be a dynamic process where three possible supplementation responses over the supplementation period were identified (linear, quadratic and Weibull). While linear patterns did not appear distinctly associated with any particular set of variables, quadratic models were mostly associated with herbage biomass and substitution rates, whereas Weibull models were the clearest in their association with frosts. Regardless of the response pattern, at the beginning of the trials it was the animals’ body weight and supplement quality that most influenced supplement response, whereas towards the end, supplementation intake, supplemented animals’ ADG and forage quality played a more relevant role. The estimated parameters and response patterns are expected to be used as inputs in decision support systems for livestock farmers in the future.

Supplement feed efficiency of growing beef cattle grazing native Campos grasslands during winter: a collated analysis.

Supplementing growing cattle grazing native subtropical Campos grasslands during winter improves the low, even negative, average daily weight gain (ADG) typical of extensive animal production systems in Uruguay. Nonetheless, to render the practice profitable, it is crucial to control supplement feed efficiency (SFE), that is, the difference in ADG between supplemented and control animals (ADGchng) per unit of supplement dry matter (DM) intake. Little has been studied specifically on how SFE varies in these systems. The objective of this study was to quantify the magnitude and variation in SFE of growing beef cattle grazing stockpiled native Campos grasslands during winter and assess putative associations with herbage, animals, supplements, and climatic variables. We compiled data from supplementation trials carried out in Uruguay between 1993 and 2018, each evaluating between one and six supplementation treatments. The average ADG of unsupplemented and supplemented animals were 0.13 ± 0.174 and 0.49 ± 0.220 kg/animal/day, respectively. In both cases, ADG decreased linearly as the proportion of green herbage in the grazed grassland was lower, but the ADG of unsupplemented animals was further reduced when winter frosts were numerous. Estimated SFE were moderately high, with an average of 0.21 ± 0.076 ADGchng/kg DM, resulting from average ADGchng of 0.38 ± 0.180 kg/animal/day in response to an average supplementation rate of 1.84 ± 0.68 kg supplement DM intake/animal/day (0.86% ± 0.27% body weight). No association was found between SFE and supplementation rate or type (protein vs. energy-based; P > 0.05), but forage allowance negatively affected it, and herbage mass positively affected it, yet in a smaller magnitude, suggesting that a balance is needed between the two to maximize SFE. Weather conditions during trials affected SFE (P < 0.05), with greater SFE in winters with lower temperatures and more frosts. Daytime grazing time was consistently lower in supplemented animals compared to their unsupplemented counterparts, whereas ruminating time during the day was similar, increasing as the proportion of green herbage decreased. Herbage intake estimated from energy balance suggested the existence of some substitution effect. This agrees with the moderately high SFE and with the total digestible nutrients-to-protein ratio of these subtropical humid grasslands being higher than in semi-arid rangelands and dry-season tropical pastures but lower than in sown pastures.

Configuration of daily grazing and searching of growing beef cattle in grassland: observational study

Many of the studies in Campos grasslands focus on management aspects such as the control of herbage allowance, and application of nutrients and/or overseeding with legumes. However, there is little literature on how the Campos grassland resource is utilised, especially regarding the grazing pattern and the relationship between pasture quantity and quality on daily grazing activities. The study of the ingestive behaviour in species-rich and heterogeneous native grasslands during daylight hours, and understanding how animals prioritise quality or quantity of intake in relation to pasture attributes, are important to comprehend the ingestive-digestive processes modulating the energy intake of animals and to achieve a better grazing management. Therefore, the objective was to describe and quantify the daily grazing behaviour of growing cattle grazing native pasture with different structures as a result of different management practices, and study the relationship of pasture attributes and intake through multivariate analysis. The study was carried out at the Faculty of Agronomy, Paysandú, Uruguay. Treatments were native grassland, overseeding with Trifolium pratense and Lotus tenuis + phosphorus, and native pasture + nitrogen-phosphorus. Grazing activities were discriminated into grazing, searching (defined when animals take 1–2 bites in one feeding station and then change to another feeding station and so on), ruminating and idling. The probability of time allocated to each activity was continuously measured during daylight hours (0700–1930) and was related to pasture structure and forage quality using regression tree models, while the bite rate was determined every 2 h. The diurnal pattern of growing cattle showed grazing and searching sessions, followed by ruminating and idling sessions. The length of sessions (as the probability of time allocated to each activity) varied throughout the day. The grazing probability was greater during afternoon than morning and midday (0.74 vs 0.45 vs 0.46, respectively), and it was associated with higher bite rate (34.2 bites/min). Regression tree models showed different grazing, searching and ruminating strategies according to pasture attributes. During the morning, animals modified grazing, searching, ruminating and idling strategies according to bite rate, crude protein in diet and herbage allowance. At midday, they only adjusted ruminating and idling, while during afternoon sessions, grazing activities were modified by pasture quantity attributes such as herbage mass and herbage allowance. By controlling the herbage allowance, herbage mass and pasture height, animals prioritise quality in the morning and quantity in the afternoon, integrating and modifying the grazing-searching and ruminating-idling pattern.

A Comparison of Pearl Millet and Sorghum–Sudangrass Pastures during the Frost-Prone Autumn for Growing Beef Cattle in Semiarid Region

Sorghum–sudangrass (Sorghum bicolor × S. sudanense (Piper) Stapf.) and pearl millet (Pennisetum glaucum (L.) R. Br.) provide adequate nutritive value for growing beef cattle; however, unlike pearl millet, sorghum–sudangrass produces hydrocyanic acid (which is toxic to livestock) when frosted. Forage yield, nutritive value, and weight gain of growing cattle grazing sorghum–sudangrass and pearl millet were compared during the frost-prone autumns of 2013 and 2014, at New Mexico State University’s Rex E. Kirksey Agricultural Science Center in Tucumcari, NM USA, in randomized complete block designs each year with two replicates. No differences existed between pearl millet and sorghum–sudangrass forage yield, although there was a year–forage interaction for fiber-based nutritive value components because of maturity differences across years between the forages when freeze-killed. Pearl millet allowed for extending grazing of available forage for an additional 14 and 24 d in 2013 and 2014, respectively, compared to sorghum–sudangrass during the frost-prone autumn periods. During that period, when sorghum forages produce potentially toxic levels of hydrocyanic acid, animals grazing pearl millet accumulated an additional average of 94.9 kg live-weight gain ha−1 (p &lt; 0.001). These factors afford producers an opportunity to increase returns on the similar investments of establishing and managing warm-season annual forage crops each year, and allow more time to stockpile cool-season perennial and annual forages for winter and early spring grazing, or to reduce hay feeding.

Relative value of field pea supplementation compared with distillers grains for growing cattle grazing crested wheatgrass

The objective was to determine a salvage value for field peas (FP) relative to dried distillers grains plus solubles (DDGS) and establish a pricing system for FP as a supplement for growing cattle in regions where FP are grown and DDGS has limited availability. In a 2-yr study, 114 heifers each year (294 ± 34.6 kg, yr 1; 306 ± 16.3 kg, yr 2) grazed crested wheatgrass pastures (n = 12). Treatments were arranged in a 2 × 2 factorial arrangement with the main factors being supplement type (FP or DDGS) and level (0.4 or 0.8% of BW). Pasture was the experimental unit, and cattle were blocked by BW. The experimental design was a randomized complete block design. There were no interactions between supplement type and level ( P > 0.22). Level of supplement was not different ( P > 0.15) for ADG (1.00 vs. 1.06 kg/d) or BW (416 vs. 421 kg) for 0.4 versus 0.8% BW, respectively. Heifers supplemented DDGS had greater gain ( P = 0.02) than those supplemented FP (1.09 vs. 0.98 kg/d, respectively). Final BW was greater for heifers supplemented with DDGS (425 kg) compared with FP (411 kg; P = 0.04). Field pea–supplemented heifers had 10% lower ADG and 9% greater cost of gain compared with DDGS-supplemented heifers. Field peas are an acceptable grazing supplement but result in ADG 10% less than DDGS, with a supplement cost of gain 9% greater than DDGS, warranting approximately 10% price reduction before transportation.

Efficacy of mineral supplementation to growing cattle grazing winter-wheat pasture in northwestern Oklahoma.

Two experiments were conducted to evaluate the efficacy of mineral supplementation to cattle grazing winter-wheat pasture. In experiment 1 (fall), 120 steers and heifers (body weight [BW] = 232 ± 11.4 kg) were assigned randomly to four blocks of replicated pastures during the second week of November in 2008 and 2009 and all herds (6 animals/pasture; 4.9 ha/pasture) were allowed to graze for 84 d. In experiment 2 (spring), 216 steers (BW = 248 ± 7.9 kg) were assigned randomly to five blocks of replicated pastures during the second week of February in 2009 and 2010 and all herds (12 or 6 animals/pasture; 4.9 ha/pasture) were allowed to graze for 84 d. Half the pastures in both experiments received a free-choice mineral mixture (Wheat Pasture Pro; Land O'Lakes Purina Feed, LLC; St. Paul, MN; Ca, 16% and P, 4%); mineral feeders were weighed weekly to determine mineral intake. All pastures were planted in early September of each year (67 kg of seed/ha) and fertilized with 50 kg of urea-N/ha. Standing herbage dry matter was determined midway between weigh dates by clipping wheat forage to the ground along 122 cm of drill rows at 10 locations/pasture. Data were analyzed by ANOVA, with treatment as the fixed effect and pasture, animal sex (experiment 1), and block as random effects. In experiment 1, cattle offered minerals had a 43% faster average daily gain (ADG; P = 0.02, 0.73 kg) than cattle not offered minerals (0.51 kg); hence, supplemented cattle weighed 6% more (P = 0.04; 286 kg) after 84 d than nonsupplemented cattle (271 kg). In experiment 2, cattle offered the mineral supplement had a faster ADG (20% increase; P = 0.04; 1.00 kg) than cattle not offered minerals (0.83 kg). Further, supplemented cattle weighed 4% more (P = 0.03; 326 kg) after 84 d than nonsupplemented cattle (312 kg). In both experiments, daily standing herbage dry matter averaged 1,381 kg/animal and never differed (P ≥ 0.47) between treatments. Mineral intakes averaged 135 (experiment 1) and 124 (experiment 2) g/d, resulting in a cost of supplement to kilogram of added BW gain of $0.53 and $0.64, respectively (assuming a mineral cost of $0.88/kg). Overall, supplementing an appropriate mineral mixture to cattle grazing winter-wheat pasture increased ADG in a cost-effective manner.

Performance of growing cattle grazing stockpiled Jesup tall fescue with varying endophyte status1

The objective of this study was to evaluate the performance of growing cattle when intensively grazing stockpiled endophyte-infected (E+), endophyte-free (E-), and nontoxic endophyte-infected (EN) tall fescue during the winter. The experiment was conducted over 5 consecutive winters. In each year, plots (1 ha each, 4 per treatment) were harvested for hay in August, fertilized in September, and forage was allowed to accumulate until grazing was initiated in early December. Each year, 48 Angus-cross tester cattle (4 per plot) were given a daily allotment of forage, under strip-grazing (frontal grazing) management, with a target residual height of 5 cm. Steers were used the first year, and heifers were used in subsequent years. The grazing periods for determination of pasture ADG were 86 d (yr 1), 70 d (yr 2), 86 d (yr 3), 72 d (yr 4), and 56 d (yr 5). Pasture ADG of cattle did not differ among treatments (P = 0.13) and were 0.51, 0.59, and 0.56 kg/d (SEM 0.03) for E+, E-, and EN, respectively. Serum prolactin concentrations of heifers grazing E+ were less (P < 0.05) than those grazing E- and EN during all years except yr 2. In yr 2, E+ and E- did not differ (P = 0.11). Serum prolactin of heifers grazing E- and EN did not differ (P > 0.20) except in yr 4. During yr 4, serum prolactin of heifers grazing E- was greater (P = 0.05) than that of heifers grazing EN. Serum urea-N concentrations (SUN) tended to differ among treatments (P = 0.10) and there was a treatment x year interaction (P = 0.05). During yr 1 through 3, SUN did not differ (P > 0.15) among treatments. However, as the stands aged, E- had a greater invasion of other plant species, which increased the CP content of the sward, thus causing heifers grazing E- during yr 5 to have greater (P < 0.01) SUN than heifers grazing E+ and EN, which did not differ (P = 0.89). Forage disappearance (DM basis) did not differ (P = 0.75) among treatments and was 4.7, 4.7, and 5.0 kg/animal daily (SEM 0.27) for E+, E-, and EN, respectively. Body weight gain per hectare was greater (P = 0.04) for E+ (257 kg) than for E- (220 kg) or EN (228 kg). In most years, animal grazing days on E+ were greater than those on E- or EN. However, in yr 5, animal grazing days did not differ (P > 0.20) among treatments. The use of stockpiled E+ as a source of low-cost winter feed is a viable option for producers, whereas grazing of EN may be more beneficial during the spring and fall, when more severe negative effects of ergot alkaloids have been observed.

Evaluation of Supplementation Programs for Growing Cattle Grazing Tall Fescue

AbstractEighty steers and heifers were used to determine the effects of supplemental energy or undegradable intake protein (UIP) on the performance of growing cattle grazing tall fescue. Treatments included 1) no supplemental feed offered (control), 2) 0.91 kg/d of supplemental corn supplying 26g UIP/d, 3) low-escape protein—0.91 kg/d of a 22% CP supplement supplying 117g UIP/d, or 4) high-escape protein—0.91 kg/d of a 42% CP supplement supplying 239g UIP/d. Effective N degradabilities of the supplements were 63.6, 43.8, and 37.5%, respectively. All supplements also supplied 224mg of lasalocid/ kg. Calf ADG was increased by an average of 0.11kg by supplementation (control vs supplement, P = 0.02), and supplement type did not affect ADG (linear and quadratic responses of UIP, P > 0.36). The ratio of in-situ ruminallydegraded OM to ruminally-degraded CP (RDOM:RDCP) can be an effective predictor of the balance of ruminally available N and energy for designing supplementation programs for grazing cattle. Thus, the ratio of forage RDOM:RDCP was determined at 0, 8, 16, 24, 36, and 48h of in situ incubation. The ratio of RDOM:RDCP of the forage samples remained essentially unchanged after 24h of incubation, indicating that a single point in situ analysis can be used to determine this ratio. In conclusion, calves grazing tall fescue with 24-h in situ RDOM:RDCP ratios of 4.32 or less benefited equally from grain-based energy supplements or supplements supplying 117 and 239g of UIP daily.

Performance of growing cattle grazing moderate quality legume - grass temperate pastures when offered varying forage allowance with or without grain supplementation

This research evaluated the effect of supplementation with cracked corn grain (0 or 1% of liveweight) on the performance of Hereford steers grazing a mixed pasture of legume and grass at 3 forage allowances (3, 6 or 9 kg DM/100 kg liveweight). The experiments were conducted in West Uruguay over 2 consecutive summers, with 72 Hereford steers (282 ± 15.3 kg; n = 36/year) randomly allocated to 1 of the 6 treatments in a factorial arrangement. Cattle were supplemented in individual pens and weighed every 14 days. Grain intake did not differ (P&gt;0.05) between forage allowances. Both supplementing and increasing forage allowance reduced (P&lt;0.01) forage utilisation. Year effect was significant (P&lt;0.01) for liveweight gain and grain intake, but neither the 2- nor the 3-way interaction of year with forage allowance or supplementation was significant (P&gt;0.05). Increasing forage allowance only improved (P&lt;0.01) liveweight gain of non-supplemented cattle (0.299, 0.483, 0.667 kg/day for forage allowance of 3, 6 or 9%, respectively). Hence, response to supplementation decreased with forage allowance, increasing the grain (kg)/gain (kg) conversion ratio. These results provide a quantitative basis on which to decide upon the best feeding management option for summer.

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture11Approved for publication by the director, Arkansas Agric. Exp. Stn., manuscript no. 00097.22This project was conducted with funding from the Univ. of Arkansas Agric. Exp. Stn., Hatch Project No. ARK1735. This project was also partially supported by product donations from Ivy Laboratories, Inc. (Overland Park, KS).

Abstract Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 x 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P

Absence of a weight gain response to Vitamin B12 supplementation in weaned dairy heifers grazing pastures of marginal cobalt content

Aim. To obtain information on serum and liver vitamin B12 and urinary methylmalonic acid concentrations as diagnostic tests to predict a weight gain response to supplementation with vitamin B12 in young dairy cattle when grazing pasture of low cobalt content. Methodology. Forty dairy cattle (12 Friesian, 14 Friesian × Jersey and 14 Jersey) were allocated to two equal sized groups, treated and untreated, based on liveweight. At monthly intervals for 14 months, all animals were weighed, their serum and urine sampled, their liver biopsied and the pasture sampled from the paddocks they were grazing and going to graze. Serum and liver were assayed for Vitamin B12 concentrations. For the first 5 months of the trial, urine was assayed for methylmalonic acid concentrations. Both washed and unwashed pasture samples were assayed for cobalt concentrations. Results. No weight gain response occurred to Vitamin B12 supplementation in young growing cattle grazing pasture with a cobalt concentration of 0.04-0.06 mg/kg DM. For 5 months of the trial, liver Vitamin B12 concentrations from untreated calves were in the range 75-220 nmol/kg and serum vitamin B12 concentrations were as low as 72 pmol/1. There was no associated growth response to supplementation. Conclusion. Further trials involving young cattle grazing pastures with cobalt concentrations less than 0.04 mg/kg DM are required to reliably determine liver and serum Vitamin B12 concentrations at which growth responses to Vitamin B12 or cobalt supplementation are likely under New Zealand pastoral grazing conditions.

Seasonal nutrient intake and phosphorus kinetics of grazing steers in northern Australia

The growth of Bos indicus cross-steers grazing native grass and native grass-legume (Stylosanthes scabra cv. Seca) pastures was monitored for 392 days in five unreplicated experimental paddocks, each grazed by three steers. Two phosphorus (P) fertilizer rates: F1, 4-5 kgP/ha every 2 years and F2, 9.0 kgP/ha annually, together with an unfertilized control, FO, were studied. P supplement was supplied to cattle in two additional paddocks (FOS and F1S) at the rate of 5 gP/ha/day-l. In the dry, wet and late wet seasons, pasture yield and pasture component yield were measured. At the same time, the nutrient intake and P kinetics of resident steers were measured using chromic oxide capsules and intravenous injections of 32P . Additional non-resident steers, fistulated at the oesophagus, grazed the pastures intermittently to provide estimates of dry matter digestibility, fibre, nitrogen (N) and P content of the selected diet. Phosphorus fertilizer increased legume and native grass growth which resulted in more dry matter containing higher concentrations of P and N than unfertilized pastures. Both P fertilizer and supplement increased dry matter intake and liveweight gain of cattle. During the experimental period of 13 months, steers which grazed pastures that received the (F2) fertilizer treatment gained on average 0.43 kg/day compared with 0.19 kg/day for those which grazed unfertilized FO pastures. Supplementation increased wet season liveweight gain from 0.45 to 0.59 kg/day and 0.46 to 0.73 kg/day for FO and F1 treatments respectively. Only cattle which grazed pastures that received the F1S and F2 treatments gained weight in the dry season. Nitrogen was the primary nutrient limiting cattle growth from unfertilized pastures in the dry season, but when pastures were fertilized (4.5 kgP/ha every 2 years) and legumes established, P was the primary limiting nutrient. Intakes of P ranged from 7 to 35 mg/kg LW and were lower than those recommended by recognized authorities for the steer growth rates we recorded. Both the absorption and faecal excretion of dietary P were closely related to P intake. Endogenous faecal P values varied with P intake in the range 9-22 mg/kg liveweight. Endogenous faecal P was also related to dry matter intake and plasma inorganic P. The coefficient of P absorption was lowest (0.65) for steers grazing unfertilized native pasture (FO), but increased with P intake to 0.85 for steers grazing the F1S treatment. We conclude that the P requirements of growing cattle grazing native grass and native grass-legume pastures in northern Australia are about half those recommended by most authorities.

Digestion, feed intake, and live weight gain by cattle consuming bermudagrass and supplemented with different grains.

The objectives of this study were to determine whether type of supplemental cereal grain, with a relatively high level of supplementation, affects feed intake, characteristics of digestion, and live weight gain by cattle consuming bermudagrass (BER). In Exp. 1, five beef steers (423 +/- 22 kg average BW) with cannulas in the rumen and duodenum were used in a Latin square design experiment. Steers consumed BER hay (1.5% BW; 10.1% CP, 75% NDF, and 6% ADL) alone (Control) or with approximately .7% BW (DM) of ground corn (GC), whole corn (WC), ground sorghum grain (SG), or ground wheat (W). At 8 h after supplementation, ruminal pH was lower for W than for Control, WC, and SG (P < .05). True ruminal OM digestion was lowest for SG and highest for W (P < .05; 49.4, 50.7, 51.0, 42.0, and 57.3% for Control, GC, WC, SG, and W, respectively). In Exp. 2, five Holstein steer calves (187 +/- 9 kg average BW) were used in a Latin square design. Bermudagrass hay (9.7% CP, 72% NDF, and 6% ADL) was consumed ad libitum alone (Control) or with approximately 1% BW of grain (same as in Exp. 1). Digestible OM intake was similar among grain treatments. In Exp. 3, 96 crossbred beef steers (256 +/- 2 kg initial BW) grazed BER (clipped forage samples: 13 to 16% CP, 68 to 73% NDF, and 4 to 5% ADL) for 85 d and received the same grain treatments as in Exp. 2 plus a barley (B) treatment. Live weight gain was .47, .84, .80, .68, .81, and .51 kg/d for Control, GC, WC, B, SG, and W, respectively (SE = .028). In conclusion, when growing cattle grazing BER were supplemented once daily with grain at approximately 1.0% BW, grain that degraded in the rumen slowly (GC, WC, and SG) resulted in live weight gain greater than that resulting from grain that degraded rapidly (B and W).

Diet composition and gains of escape protein-supplemented growing cattle grazing corn residues

Effect of level and method of escape protein (EP) supplementation on weekly steer performance and their diet composition were evaluated in two corn residue grazing trials. In Trial 1, 60 steers (average weight 239 kg) received .8 kg.animal-1.d-1 of a 50% CP supplement to provide one of six levels of EP (60, 88, 116, 144, 172, or 200 g.animal-1.d-1). Steers grazed (2.2 animals/ha) nonirrigated fields (NIF) for 63 d. In Trial 2, 59 steers (average weight 219 kg) grazed either NIF (1.97 animals/ha) or irrigated fields (IF, 3.96 animals/ha) and were supplemented with 60, 95, 130, 165, or 200 g of EP.animal-1.d-1. In a 2 X 5 X 2 factorial arrangement, treatments were IF vs NIF, level of protein, and two supplementation methods: 1) feeding the lowest level of EP (60 g) for 21 d then for the remaining 42 d feeding one of the five EP levels or 2) feeding each EP level continuously. Weekly diet composition was evaluated using four esophageally fistulated steers. In Trial 1, no EP effect (P greater than .05) was found up to 20 d, but EP affected (P less than .05) ADG from d 20 to 34, resulting in 3.35 g of ADG/g of EP. In Trial 2, steers grazing NIF had higher (P less than .01) ADG than those grazing IF (644 vs 414 g/animal). Steer daily gains were increased (P less than .05) by level of EP but were not affected (P greater than .05) by the method of supplementation, indicating that EP supplementation was not needed during the first 21 d.(ABSTRACT TRUNCATED AT 250 WORDS)

A simulation model of forage yield, quality and intake and growth of growing cattle grazing cornstalks.

A simulation model was developed to predict corn crop residue yield and quality and intake and performance of growing cattle grazing cornstalks. The model is wholly deterministic and integrates the effects of weather, residue supply and animal components. Low temperatures increase animal energy requirements, whereas snow cover decreases residue available. Residual grain and leaf are calculated from grain yield. Residue quantity and quality are reduced daily by environmental losses and animal consumption. Daily performance is predicted based on the nutrients obtained from residue and supplemental feed. Under unlimited roughage supply, leaf, husk and grain are primary diet components. Grain consumption decreases as the supply diminishes and forage quality decreases with time. Intake is calculated based on digestibility and fecal output = .0365 W.75. Forage availability affects intake in a curvilinear fashion. Energy gain is predicted by NRC equations and protein gain from metabolizable protein supply. The model underestimated intake of calves measured with chromic oxide and in vitro DM disappearance. Simulated daily gain (y, kg) of calves grazing at several stocking rates was related to observed daily gain (x, kg) by the equation y = .012 + .853 x (R2 = .71, Sy.x = .077). The model overestimated response to protein supplementation. Severe cold weather was predicted to reduce gains or cause weight loss due to increased energy requirements for maintenance. The model can be used as an aid in both research planning and cattle management.

Diet composition and daily gain of growing cattle grazing dryland and irrigated cornstalks at several stocking rates.

Diet composition and the relationships between daily gain of calves grazing cornstalks and certain characteristics of the available residue and diets selected by esophageally fistulated cattle were studied in two trials during November and December of 1984 (Trial 1) and of 1986 (Trial 2). Eight adult steers and four esophageally fistulated calves were used in Trials 1 and 2, respectively, to collect extrusa samples from dryland and irrigated fields grazed at several stocking rates. Steers grazing irrigated cornstalks selected a diet with more (P less than .05) starch and less (P less than .05) CP than those grazing dryland fields. As grazing continued, extrusa starch content decreased (P less than .05). In vitro DM disappearance (IVDMD) of both diet and the roughage fraction of the diet decreased (P less than .05) with days of grazing; this decrease was greater (P less than .05) at higher stocking rates. Calves grazing dryland fields gained faster (P less than .05) than calves grazing irrigated fields. With a low level of protein supplementation (213 g CP/d, Trial 1), daily gain was positively correlated with CP of both diet (extrusa) or available leaf plus husk but not with grain available per animal or with extrusa IVDMD, suggesting that protein was first limiting. With a higher level of protein supplementation (458 g CP/d, Trial 2), daily gain was correlated positively with residue available per animal and IVDMD of extrusa at the end of the grazing season. The energy value of feed consumed by cattle grazing cornstalks decreases with time, and complex interactions between protein needs and energy intake may occur.

Growth response to escape protein and forage intake by growing cattle grazing cornstalks.

Two trials were conducted to study the protein requirements of growing cattle grazing cornstalks. Diet composition and forage intake were determined at different periods during the grazing season. Residue intake and dietary CP content decreased (P less than .05) .079 kg and .044 percentage units per day of grazing, respectively. In vitro DM disappearance of the roughage fraction of the diet remained high early in the grazing period when husk availability was high, then declined in a curvilinear pattern. Calves required time to learn to find and consume the residual grain. During 54 d of grazing in Trial 1, calves supplemented with 409 g CP gained .105 kg/d more than those supplemented with 213 g CP. Maximal daily gain (.308 kg) in Trial 2 was obtained with 163 g/d of ruminal escape protein. Growing cattle grazing cornstalks responded to protein supplementation at levels above current National Research Council recommendations for 250-kg calves gaining .3 kg/d.

EFFECTS OF SUPPLEMENTATION WITH SILAGE ON FORAGE INTAKE AND KINETICS OF DIGESTA FLOW OF CATTLE ON PASTURE

Effects of increasing silage intakes by growing cattle grazing wheat and bermudagrass pastures on forage intake, flow, turnover, fill and fecal output were studied. Increasing intakes of silage increased flow of wheat forage and appeared to have associative effects on wheat forage intake, whereas intake of bermudagrass decreased linearly as silage intake increased. Key words: Forage intake, grazing cattle, silage