Evaluation of intensive vs extensive systems of beef production and the effect of level of beef cow milk production on postweaning performance

Charolais-sired calves from three groups of beef cows, similar in growth potential and mature size but different in genetic potential for milk production (5.6, 7.7, 9.0 kg/d; low, medium, and high, respectively), were allotted to two beef production systems each year for 3 yr. At weaning, calves in an intensive (Int) system went directly into the feedlot for finishing (236 d); calves in an extensive (Ext) system were wintered on corn residues (195 d), grazed pasture (115 d) and then were finished (122 d). Postweaning effects of increased weaning weight due to increased level of milk were small and not affected by growing-finishing system. Only the steer calves from the low milk-producing cows showed evidence (P less than .01) of compensatory growth postweaning in response to reduced levels of milk during the suckling phase. Cattle from the Ext system were heavier (P less than .01) before (388 vs 233 kg) and after (595 vs 531 kg) the finishing phase than Int system cattle. During finishing, cattle from the Ext system made more rapid gains (1.70 vs 1.36 kg/d) and consumed more feed (12.4 vs 8.5 kg/d, 2.52 vs 2.19% of average BW) but were less efficient (.137 vs .160, gain/feed) than cattle from the Int system (P less than .05). Extensive systems of beef production produced more total kilograms of beef per animal but they were 196 d older at slaughter.     

Feedlot efficiency implications on greenhouse gas emissions and sustainability

The term sustainable has many meanings, but in agriculture it generally refers to some balance between environmental, social, and economic goals. The objective of this project was to quantify inputs and outputs to assess the sustainability implications of 2 feedlot cattle management systems: Never Ever 3 (NE3) and a conventional (CON) system using metabolic modifiers. Angus-cross steers (n=104) were stratified by BW (337 kg ± 17) and randomly assigned to 4 pens per treatment group. The NE3 cattle received no feed additives or implants, whereas CON were implanted with 100 mg of trenbolone acetate and 14 mg of estradiol benzoate on d 1 and 70, and were additionally fed monensin [330 mg/(animal·d)] and tylosin phosphate [90 mg/(animal·d)] in their ration throughout the course of the study, and ractopamine hydrochloride at 254 mg/(animal·d) for the last 29 d on feed. Cattle were shipped on a constant average pen weight basis (596 kg ± 32 BW). The CON cattle had greater ADG (1.81 vs. 1.35 kg, P < 0.01) and were on feed fewer days (146 vs. 188 d, P < 0.01) than the NE3 cattle. No significant differences were observed in HCW (P = 0.072) or dressing percentage (P=0.62) between treatments (P > 0.05); however, CON carcasses averaged larger ribeye area (87 vs. 80 cm(2), P < 0.01), greater Warner-Bratzler shear force measurement (WBSF; 3.46 vs. 3.19 kg, P < 0.01), and smaller USDA marbling score (5.4 vs. 6.2, P < 0.01), and less backfat thickness (1.64 vs. 1.84 cm, P < 0.05) and yield grade (3.38 vs. 3.95, P < 0.01) than NE3 carcasses. Overall, CON cattle consumed 393 kg less DM in the feedlot (1,250 vs. 1,643 kg; P < 0.05). No treatment effects were observed for daily methane (CH(4); P=0.62) or nitrous oxide (N(2)O; P=0.7) emissions per steer. Assuming a constant emission rate on a DMI basis throughout the course of the feedlot trial, CON feedlot management resulted in a 31% decrease in emissions per finished steer compared with NE3 management. Expressing CH(4) emissions on a carbon dioxide equivalent (CO(2)-eq) basis revealed a 1.10-kg CO(2)-eq difference per kilogram BW gain (5.02 kg of NE3 vs. 3.92 kg of CON) between the 2 feedlot management systems. Although the metabolic modifiers resulted in additional costs for the CON treatment group, the cost per kilogram of feedlot BW gain was significantly less ($1.12/kg vs. $1.35/kg; P < 0.05) than NE3. Both production systems satisfied some sustainability criteria, although neither concurrently fulfilled all of the environmental, social, and economic goals of agricultural sustainability.     

Evaluation of mating systems involving five breeds for integrated beef production systems: II. Feedlot segment.

Computer models were used to simulate the feedlot segment of an integrated beef production system. Five breeds, Angus (A), Charolais (C), Hereford (H), Limousin (L), and Simmental (S), in three mating systems, pure-breeding and two- and three-breed rotational crossbreeding, were evaluated for feedlot and carcass performance. Breed data were taken from the literature. Feeder calves (steers and non-replacement heifers) entered the feedlot at 205 d of age. After a 35-d adjustment period, calves were custom-fed to four slaughter end points: 440 d, 457 d, 288-kg carcass weight, or low Choice. Cattle were fed to requirements (megacalories of ME). Input costs included feed and nonfeed expenses (purchase prices, transportation, yardage, and medicinal fees). Carcass values were $2.65 and $2.54/kg of carcass weight for steer and heifers, respectively, between 272 to 318 kg. Over- or underweight carcasses were discounted $.60/kg. At the 440-d end point, Select grade steer and heifer carcasses were discounted an additional $.22 and $17/kg, respectively. Biological efficiency was measured as megacalories of ME/kg of gain, and economic efficiencies were measured as input costs per kilogram of carcass weight, input costs per kilogram of lean weight, and input costs per carcass value. Continental breed combinations (C and S) were most efficient at age- and weight-constant end points for megacalories of ME per kilogram of gain and for input costs per carcass value and most efficient at all end points for input costs per kilogram of carcass weight and input costs per kilogram of lean weight. British breed combinations (A) were most efficient at a fat-constant end point for megacalories of ME per kilogram of gain and input costs per carcass value. Therefore, choosing breed combinations for feedlots depends on slaughter end point and measures of efficiency.     

Beef cattle feed intake and growth: empirical Bayes derivation of the Kalman filter applied to a nonlinear dynamic model

Feed intake and growth rate of a single group of growing-finishing feedlot beef cattle are difficult to predict. Subsequent performance can be projected more precisely from past performance of a group of cattle. Using an adaptation of the statistical procedure called the empirical Bayes (EB) derivation of the Kalman filter, estimates from any dynamic model (M) can be adjusted based on past performance. The model may be either linear or nonlinear. With this procedure, predictions of intake and body weight gain are periodically updated by multiplying the estimates from M by statistically weighted factors. These factors are derived from the ratio of performance in each period to the performance predicted by M. For comparison to the EB adjustment, weighting of factors by least-squares (LS) adjustment also was tested to predict subsequent feed intake and gain. The test data base consisted of periodic feed intake and gain observations (usually 28 d) for 200 pens of feedlot steers. Bias of prediction was lower for EB than for M or LS for feed intake and (usually) gain. Intake and gain prediction errors averaged for the whole feeding period were .42 kg/d for intake and .14 kg/d for gain by EB, being .84 and .18 kg/d more precise than M and .12 and .33 kg/d more precise than LS predictions. More than two observations were needed before LS produced accurate prediction but after about 80 d, LS and EB estimates converged. Accuracy of both estimates continued to improve as days on feed increased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of an inactivated Neospora caninum vaccine in beef feedlot steers

OBJECTIVE: To evaluate effects of vaccination of feedlot steers against bovine neosporosis on weight gain, feed intake and efficiency (feed intake per gain), and carcass characteristics. DESIGN: Longitudinal observational study. ANIMALS: 60 weaned Brangus steers seronegative for Neospora caninum. PROCEDURE: Steers were assigned to age-matched control and treatment groups. Steers in the treatment group received N. caninum vaccine on days 79 and 106, while control steers received 2 placebo injections. For each steer, serologic status for N. caninum was determined on days 0 (weaning), 51, 79, 106, 135, 163, 191, 219, and 247 by use of an ELISA; body weight was determined on the same days and at slaughter (day 259). Daily feed intake per steer was measured from days 79 to 259. RESULTS: Seroconversion occurred in 23 of 30 (76.7%) steers in the vaccinated group. Immediately after vaccination, average daily gain, average daily feed intake, and feed efficiency were significantly greater in the treatment group than in the control group, but these differences did not persist. No differences between groups were found in regard to live weight at slaughter, hot carcass weight, dressing percentage, or quality grade; however, steers in the vaccinated group had significantly lower yield grades than did control steers. CONCLUSIONS AND CLINICAL RELEVANCE: In feedlot steers, use of this vaccine against N. caninum was safe and did not affect overall feedlot performance or meat quality; effects on yield grade require further evaluation.     

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

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<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

Effect of age at feedlot entry on performance and carcass characteristics of bulls and steers

Seventy Angus x Simmental calves (BW = 166.3 +/- 4.2 kg) were used in a 3 x 2 factorial arrangement to determine the effect of age at feedlot entry and castration on growth, performance, and carcass characteristics. At 82 d of age, steers were castrated. Calves were placed in the feedlot at 111 (early-weaned), 202, or 371 (yearling) d of age. Steers were implanted with Synovex-S followed 93 d later with Revalor-S. Calves were harvested on an individual basis when fat thickness was estimated to be 1.27 cm. During the feedlot phase, yearlings gained faster (P < 0.01) than calves placed in the feedlot at 202 or 111 d of age (1.88, 1.68, and 1.62 kg/d, respectively); however, from 111 d of age until harvest, ADG was greatest for early-weaned calves, intermediate for cattle placed in the feedlot at 202 d of age, and lowest for yearlings (1.62, 1.47, and 1.21 kg/d, respectively; P < 0.01). Early-weaned calves spent the most days in the feedlot, followed by calves placed in the feedlot at 202 d of age; yearlings spent the fewest days in the feedlot (221, 190, and 163 d, respectively; P < 0.01). Total DMI when in the feedlot was similar (P = 0.22) among age groups; however, daily DMI was lowest for early-weaned calves, intermediate for calves placed in the feedlot at 202 d of age, and the highest for yearlings (7.1, 8.1, 10.5 kg/ d, respectively; P < 0.01). Early-weaned calves were the most efficient, followed by calves placed in the feedlot at 202 d of age; yearlings were the least efficient (227, 207, 180 g gain/kg feed, respectively; P < 0.01). Weight at harvest (682, 582, 517 kg, respectively; P < 0.01) and hot carcass weight (413, 358, 314 kg, respectively; P < 0.01) were greatest for yearlings, intermediate for cattle placed in the feedlot at 202 d of age, and lowest for early-weaned calves. Early-weaned calves had the smallest longissimus area, followed by calves placed in the feed-lot at 202 d of age; yearlings had the largest longissimus area (77, 86, 88 cm2, respectively; P < 0.01). Calves placed in the feedlot at 111 and 202 d of age had lower yield grades (3.2, 3.1, 3.5, respectively; P < 0.04), and produced fewer select carcasses than yearlings (25, 13, 48%, respectively; P < 0.01). Bulls and implanted steers both had an ADG of 1.7 kg/d when in the feedlot; however, bulls had a greater (P < 0.09) hot carcass weight (370 vs 354 kg) and a larger (P < 0.01) longissimus area (85.8 vs 81.3 cm2) than steers. Earlier feedlot placement resulted in greater quality grades but lower carcass weights.     

Influence of monensin on the performance of cattle

Performance data on nearly 16,000 head of cattle that were used in trials to document effects of monensin on feedlot cattle were summarized. Cattle fed monensin-containing diets gained 1.6% faster, consumed 6.4% less feed and required 7.5% less feed/100 kg gain than cattle fed control diets. Monensin resulted in the greatest improvement in feed/gain at 2.9 Mcal metabolizable energy (ME)/kg diet dry matter (DM). Within the range of monensin concentrations used in the trials that were summarized (31.8 +/- 7.5 mg/kg DM), high monensin concentrations did not improve feed/gain over that obtained with lower concentrations. Carcass characteristics were not significantly influenced by monensin. Responses of cattle to monensin and implants were additive. Energy metabolism data suggested that monensin improved digestibility of DM, reduced fasting heat production and increased dietary net energy maintenance (NEm) values more than it increased net energy gain (NEg) values. Data showing the response of cattle to monensin when fed various dietary protein concentrations or sources of supplemental N suggested that monensin had a protein sparing effect. Monensin has also been shown to reduce lactic acid production, aid in the control of coccidia and bloat and to be toxic to face and horn fly larva in feces of monensin-fed cattle. In pasture trials, monensin improved daily gains. When fed to beef cows, monensin reduced amounts of feed required to maintain cow weight.     

Effects of ractopamine hydrochloride on performance, rate and variation in feed intake, and acid-base balance in feedlot cattle

Two experiments evaluated effects of ractopamine hydrochloride (RAC) on performance, intake patterns, and acid-base balance of feedlot cattle. In Exp. 1, 360 crossbred steers (Brangus, British, and British x Continental breeding; initial BW = 545 kg) were used in a study with a 3 x 3 factorial design to study the effects of dose [0, 100, or 200 mg/(steer x d) of RAC] and duration (28, 35, or 42 d) of feeding of RAC in a randomized complete block design (9 treatments, 8 pens/treatment). No dose x duration interactions were detected (P > 0.10). As RAC dose increased, final BW (FBW; P = 0.01), ADG (P < 0.01), and G:F (P < 0.01) increased linearly. As duration of feeding increased, ADG increased quadratically (P = 0.04), with tendencies for quadratic effects for FBW (P = 0.06), DMI (P = 0.07), and G:F (P = 0.09). Hot carcass weight increased linearly (P = 0.02) as dose of RAC increased. Thus, increasing the dose of RAC from 0 to 200 mg/(steer x d) and the duration of feeding from 28 to 42 d improved feedlot performance, although quadratic responses for duration of feeding indicated little improvement as the duration was extended from 35 to 42 d. In Exp. 2, 12 crossbred beef steers (BW = 593 kg) were used in a completely random design to evaluate the effects of RAC [0 or 200 mg/(steer x d) for 30 d; 6 steers/treatment] on rate of intake, daily variation in intake patterns, and acid-base balance. To assess intake patterns, absolute values of daily deviations in feed delivered to each steer relative to the total quantity of feed delivered were analyzed as repeated measures. There were no differences (P > 0.10) in feedlot performance, urine pH, blood gas measurements, or variation in intake patterns between RAC and control cattle, but steers fed RAC had increased (P = 0.04) LM area, decreased (P = 0.03) yield grade, and increased (P < 0.10) time to consume 50 and 75% of daily intake relative to control steers. Our results suggest that feeding RAC for 35 d at 200 mg/(steer x d) provided optimal performance, and no effects on acid-base balance or variation in intake patterns of finishing steers were noted with RAC fed at 200 mg/(steer x d) over a 30-d period.     

Effects of phase-feeding of crude protein on performance, carcass characteristics, serum urea nitrogen concentrations, and manure nitrogen of finishing beef steers

As cattle mature, the dietary protein requirement, as a percentage of the diet, decreases. Thus, decreasing the dietary CP concentration during the latter part of the finishing period might decrease feed costs and N losses to the environment. Three hundred eighteen medium-framed crossbred steers (315 +/- 5 kg) fed 90% (DM basis) concentrate, steam-flaked, corn-based diets were used to evaluate the effect of phase-feeding of CP on performance and carcass characteristics, serum urea N concentrations, and manure characteristics. Steers were blocked by BW and assigned randomly to 36 feedlot pens (8 to 10 steers per pen). After a 21-d step-up period, the following dietary treatments (DM basis) were assigned randomly to pens within a weight block: 1) 11.5% CP diet fed throughout; 2) 13% CP diet fed throughout; 3) switched from an 11.5 to a 10% CP diet when approximately 56 d remained in the feeding period; 4) switched from a 13 to an 11.5% CP diet when 56 d remained; 5) switched from a 13 to a 10% CP diet when 56 d remained; and 6) switched from a 13 to an 11.5% CP diet when 28 d remained. Blocks of cattle were slaughtered when approximately 60% of the cattle within the weight block were visually estimated to grade USDA Choice (average days on feed = 182). Nitrogen volatilization losses were estimated by the change in the N:P ratio of the diet and pen surface manure. Cattle switched from 13 to 10% CP diets with 56 d remaining on feed or from 13 to 11.5% CP with only 28 d remaining on feed had lower (P < 0.05) ADG, DMI, and G:F than steers fed a 13% CP diet throughout. Steers on the phase-feeding regimens had lower (P = 0.05) ADG and DMI during the last 56 d on feed than steers fed 13.0% CP diet throughout. Carcass characteristics were not affected by dietary regimen. Performance by cattle fed a constant 11.5% CP diet did not differ from those fed a 13% CP diet. Serum urea N concentrations increased (P < 0.05) with increasing dietary CP concentrations. Phase-feeding decreased estimated N excretion by 1.5 to 3.8 kg/steer and nitrogen volatilization losses by 3 to 5 kg/steer. The results suggest that modest changes in dietary CP concentration in the latter portion of the feeding period may have relatively small effects on overall beef cattle performance, but that decreasing dietary CP to 10% of DM would adversely affect performance of cattle fed high-concentrate, steam-flaked, corn-based diets.     

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

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 × 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<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

Effect of feed delivery fluctuations and feeding time on ruminal acidosis, growth performance, and feeding behavior of feedlot cattle

Research was conducted to determine whether fluctuations in the amount of feed delivered and timing of feeding affect ruminal pH and growth of feedlot cattle. In Exp. 1, the effects of constant (C) vs. fluctuating (F) daily feed delivery on ruminal pH were assessed in a crossover experiment (two 28-d periods) involving six mature, ruminally cannulated steers. The diet consisted of 86.8% barley grain, 4.9% supplement, and 8.3% barley silage (DM basis) and was offered ad libitum for 2 wk to estimate DMI by individual steers. Steers in group C were offered a constant amount of feed daily equal to their predetermined DMI, whereas steers in group F were offered 10% more or less than their predetermined DMI on a rotating 3-d schedule. Ruminal pH of each steer was measured continuously via an indwelling electrode placed in the rumen during the last 6 d of each period. Mean pH tended to be lower (0.10 units) for F than C (5.63 vs. 5.73; P = 0.15), and ruminal pH of steers in group F tended to remain below 5.8 (P = 0.03) or 5.5 (P = 0.14) for greater proportions of the day than steers in group C. Inconsistent delivery of feed lowered ruminal pH, suggesting increased risk of subclinical acidosis. In Exp. 2, a 2 x 2 factorial was used to study the effects of pattern (C vs. F) and feeding time (morning [0900] vs. evening [2100]) on the feeding behavior and performance of 234 (310 +/- 23 kg) Charolais x Hereford beef steers during backgrounding and finishing phases over 209 d. One pen per treatment was equipped with a radio frequency identification (GrowSafe Systems Ltd., Airdrie, Canada) system that monitored bunk attendance by each steer throughout the trial. Pattern of feed delivery did not affect (P = 0.16) DMI (7.36 kg/d), ADG (1.23 kg/d), G:F (0.17), or time spent at the bunk (141 min/d), nor were pattern of feed delivery x time of feeding interactions observed (P = 0.18). Late feeding increased (P < 0.05) daily DMI (7.48 vs. 7.26 kg), ADG (1.28 vs. 1.00 kg/d), and G:F (0.21 vs. 0.15). These studies indicate that the risk of subclinical acidosis was increased with fluctuating delivery of feed, but the greater risk of acidosis did not impair growth performance by feedlot cattle. Consequently, daily intake fluctuations of 10% DMI or less that do not alter overall intake by feedlot cattle are unlikely to have any negative consequences on growth performance.     

Effects of water sulfate concentration on performance, water intake, and carcass characteristics of feedlot steers.

Two hundred forty single-source, cross-bred steers (304 kg) were used to evaluate the effects of various water sulfate concentrations on performance, water intake, and carcass characteristics of feedlot steers. Cattle were stratified by weight and assigned within weight blocks to five water treatments. Averaged over time, actual water sulfate concentrations (+/- SEM) were 136.1 (+/- 6.3), 291.2 (+/- 15.3), 582.6 (+/- 16.9), 1,219.2 (+/- 23.7), and 2,360.4 (+/- 68.2) mg/L, respectively. Weather-related data were recorded. Increasing water sulfate concentration resulted in linear decreases in ADG (P < 0.01) and gain:feed ratio (P < 0.01) and a quadratic effect on water intake (P = 0.02) and tended to quadratically increase then decrease DMI (P = 0.13). Sulfate x period interactions were evident for DMI (P = 0.01), ADG (P < 0.01), and feed efficiency (P < 0.01). Time had quadratic effects on DMI, water intake, ADG, and feed efficiency (P < 0.01 for all models). Increasing water sulfate concentration resulted in linear decreases in final weight, hot carcass weight, and dressing percentage, a linear increase in longissimus muscle area, and a quadratic effect on fat thickness over the 12th rib and predicted yield grade (P < 0.05 for all dependent variables). Mean daily temperature explained 25.7% of the observed variation in water intake. Other factors that explained a significant (P < 0.01) amount of variation in water intake were BW, DMI, water sulfate concentration, barometric pressure, wind speed, and humidity. High water sulfate concentrations had a significant and deleterious effect on performance and carcass characteristics of feedlot steers. Increasing the sulfate concentration in water may have resulted in a functional water restriction early in the trial when ambient temperatures were greatest. However, toward the latter stages of the trial, cattle supplied higher-sulfate water had higher ADG and FE. These improvements later in the trial may represent compensatory gain associated with decreased ambient temperature and water requirements. Averaged over time, a water sulfate concentration of greater than 583 mg/L, equivalent to 0.22% of the diet, decreased feedlot performance.     

The effects of active immunization against gnRH on testicular development, feedlot performance, and carcass characteristics of beef bulls

The objective was to determine the effects of a recombinant fusion protein anti-GnRH vaccine on testicular development, feedlot performance, and carcass quality of beef bulls. Crossbred beef bulls (n = 58, average weight 306 kg, 9 mo of age), were randomly allocated to two groups and received either an anti-GnRH vaccine (GnRH) or placebo (Control) by intramuscular injection on d 0, 56, and 112. There were group effects (P < 0.01; as a percentage of Control) on testicular weight (53%), daily sperm production (40%), and epididymal sperm reserves (16%). There were group x time interactions (P < 0.0001) for scrotal circumference and serum testosterone concentrations; at slaughter, bulls in the GnRH group had a smaller (P < 0.05) scrotal circumference (28.3 vs 33.9 cm) and lower (P < 0.05) serum testosterone concentrations (2.2 vs 8.6 ng/mL) than those in the Control group. Average daily gain, feed intake, and feed efficiency were not different between treatments during the backgrounding phase (d 0 to 84). During the finishing phase (d 98 to 182), ADG was greater (P < 0.05) for bulls in the Control group (1.69 vs 1.42 kg/d), as was carcass weight (6.9%; P < 0.01). However, GnRH bulls had numerically better feed efficiency (6.12 vs 7.08 kg DMI/kg gain; P < 0.23) and shear force values for ribeye that were 16% lower (P < 0.14) than Control bulls, warranting further investigation. Vaccinating bulls against GnRH suppressed testicular function, with growth and carcass characteristics similar to that expected with steers.     

Phosphorus requirement of finishing feedlot calves

Dietary P supplied to feedlot cattle is important because an inadequate supply will compromise performance, whereas excess P may harm the environment. However, P requirements of feedlot cattle are not well documented. Therefore, 45 steer calves (265.2+/-16.6 kg) were individually fed to determine the P required for gain and bone integrity over a 204-d finishing period. The basal diet consisted of 33.5% high-moisture corn, 30% brewers grits, 20% corn bran, 7.5% cottonseed hulls, 3% tallow, and 6% supplement. Treatments consisted of 0.16 (no supplemental inorganic P), 0.22, 0.28, 0.34, and 0.40% P (DM basis). Supplemental P was provided by monosodium phosphate top-dressed to the daily feed allotment. Blood was sampled every 56 d to assess P status. At slaughter, phalanx and metacarpal bones were collected from the front leg to determine bone ash and assess P resorption from bone. Dry matter intake and ADG did not change linearly (P > 0.86) or quadratically (P > 0.28) due to P treatment. Feed efficiency was not influenced (P > 0.30) by P treatment and averaged 0.169. Plasma inorganic P averaged across d 56 to 204 responded quadratically, with calves fed 0.16% P having the lowest concentration of plasma inorganic P. However, plasma inorganic P concentration (5.7 mg/dL) for steers fed 0.16% P is generally considered adequate. Total bone ash weight was not influenced by dietary P for phalanx (P = 0.19) or metacarpal bones (P = 0.37). Total P intake ranged from 14.2 to 35.5 g/d. The NRC (1996) recommendation for these calves was 18.7 g/d, assuming 68% absorption. Based on performance results, P requirements for finishing calves is < 0.16% of diet DM or 14.2 g/d. Based on these observations, we suggest that typical grain-based feedlot cattle diets do not require supplementation of inorganic mineral P to meet P requirements.     

Comparative cost-effectiveness of ivermectin versus topical organophosphate in feedlot calves

A study was conducted in a commercial feedlot in western Canada to evaluate the impact of treatment with ivermectin versus a topical organophosphate on growth rate and feed efficiency in calves entering a feedlot at an average 275 kg liveweight.

A total of 9527 head of cattle was used. Variables measured included average daily gain, average days occupation, and feed conversion.

Ivermectin treated animals gained an average 0.08 kg per day more than those treated with topical organophosphate. In addition, they required an average 0.23 kg less feed/kg gain. Based on an average 227 kg of gain, this would result in 11 fewer days occupation and 52.3 kg less feed for ivermectin treated animals. This equaled a net benefit of $7.04 per head over treatment costs for ivermectin treatment versus topical organophosphate.

     

Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism

A winter grazing/feedlot performance experiment repeated over 2 yr (Exp. 1) and a metabolism experiment (Exp. 2) were conducted to evaluate effects of grazing dormant native range or irrigated winter wheat pasture on subsequent intake, feedlot performance, carcass characteristics, total-tract digestion of nutrients, and ruminal digesta kinetics in beef cattle. In Exp. 1, 30 (yr 1) or 67 (yr 2) English crossbred steers that had previously grazed native range (n = 38) or winter wheat (n = 59) for approximately 180 d were allotted randomly within previous treatment to feedlot pens (yr 1 native range = three pens [seven steers/pen], winter wheat = two pens [eight steers/pen]; yr 2 native range = three pens [eight steers/pen], winter wheat = four pens [10 or 11 steers/pen]). As expected, winter wheat steers had greater (P < 0.01) ADG while grazing than did native range steers. In contrast, feedlot ADG and gain efficiency were greater (P < 0.02) for native range steers than for winter wheat steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for winter wheat steers than for native range steers. In contrast, 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ among treatments. In Exp. 2, eight ruminally cannulated steers that had previously grazed winter wheat (n = 4; initial BW = 407 +/- 12 kg) or native range (n = 4; initial BW = 293 +/- 23 kg) were used to determine intake, digesta kinetics, and total-tract digestion while being adapted to a 90% concentrate diet. The adaptation and diets used in Exp. 2 were consistent with those used in Exp. 1 and consisted of 70, 75, 80, and 85% concentrate diets, each fed for 5 d. As was similar for intact steers, restricted growth of cannulated native range steers during the winter grazing phase resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) compared with winter wheat steers. In addition, ruminal fill (P < 0.01) and total-tract OM digestibility (P < 0.02) were greater for native range than for winter wheat steers across the adaptation period. Greater digestibility by native range steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by native range steers in the feedlot, grazing winter wheat before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit.     

Effects of prenatal testosterone treatment and postnatal steroid implantation on growth performance and carcass traits of heifers and steers

Two experiments were conducted to evaluate the effect of prenatal testosterone treatment in combination with postnatal steroid implantation (Exp. 1) and to assess the effect of time of prenatal testosterone treatment in conjunction with postnatal steroid implantation (Exp. 2) on animal performance and carcass characteristics. In Exp. 1, seventy-six pregnant cows were assigned randomly to a control group or implanted with testosterone propionate (TP) silastic implants between d 40 and 80 of gestation. Half the heifer calves were selected randomly to be implanted with 200 mg TP plus 20 mg estradiol benzoate (EB); the other half of the steer calves were implanted with 200 mg progesterone plus 20 mg EB on d 1 and 85 of the feedlot trial. Daily gain of heifers was increased 10.4% (P less than .08) due to prenatal testosterone treatment (P) and 16.4% (P less than .05) by postnatal steroid implantation (I). Feed efficiency was 12.9% greater (P less than .05) due to P and 9.5% greater (P less than .05) due to I. Prenatal testosterone treatment decreased (P less than .05) kidney, pelvic and heart fat and final yield grade but increased (P less than .05) ribeye area of heifers. Heifers had greater (P less than .07) liver weights per unit of carcass weight due to P. In Exp. 2, one hundred seventy-four pregnant cows were assigned randomly to a control group or implanted with TP silastic implants on d 42, 63, 84 or 105 of gestation. Half the heifer and steer calves were selected randomly to be implanted on d 1 and 112 of the feedlot trial. Time of P caused a quadratic effect (P less than .08) on birth weight of heifers. There was a quadratic effect (P less than .05) of time of P on daily gain and final weight per day of age of heifers. Feed efficiency of heifers was improved (P less than .05) due to P. Postnatal steroid implantation increased (P less than .05) daily gain and feed efficiency of heifers by 9.6% and 8.6%, respectively. No changes were observed in growth performance of steers due to P. Results from these two trials suggest that the combination of prenatal testosterone treatment and postnatal testosterone and estradiol implantation produced an additive improvement of daily gain, feed efficiency and carcass merit of heifers.     

Effects of different grazing and feeding periods on performance and carcass traits of beef steers

Over three consecutive years, 180 (60/yr) fall-born steer calves were weaned in May (average initial BW = 238 kg, SD = 36.2 kg) and allocated to one of three groups: 1) calf-fed steers that entered the feedlot at weaning; 2) short yearlings that grazed irrigated pasture for another 4 mo and entered the feedlot in September; and 3) long yearlings that grazed with short yearlings during the summer, remained on annual California foothills range through the fall, winter, and spring, and entered the feedlot the following May. All steers were fed until the average group backfat (BF), determined by ultrasound, reached 11 to 12 mm. On pasture, short- and long-yearling steers gained weight in the summer; long yearlings then slightly lost weight in the fall and winter, and then gained weight again the following spring. Average days in the feedlot were 188, 158, and 94 (P < 0.10) for calves, short yearlings, and long yearlings, respectively. Feedlot DMI increased with age (and weight) at feedlot entry, with no difference among groups in gain:feed ratio. The gain of BF was nil on pasture, even when animals were gaining weight, and then increased rapidly when animals were placed on a high-energy diet. Final body weights were heaviest (P < 0.10) in long yearlings, followed by short yearlings and then calves, indicating that a prolonged growing period increases the apparent mature size of the animal. Moreover, total carcass fat contents and percentage of Choice or above were all lower (P < 0.10) in cattle that were older at feedlot entry (i.e., long yearlings) compared with the other groups. In conclusion, increasing the backgrounding period decreased time and total concentrate requirements in the feedlot of Angus-Hereford steers. Older cattle reached 10 mm of BF at heavier weights. Grazing animals gained weight without increasing BF; however, BF increased rapidly in the feedlot. Prolonged grazing may decrease quality grade, either by impairing the ability of the animal to deposit intramuscular fat or by decreasing the time during which dietary energy supply is adequate for intramuscular fat deposition to occur.