Effects of weaning age and diet on growth and carcass characteristics in steers

Two experiments were conducted to determine the effects of diet on growth of steers weaned at approximately 100 vs 205 d of age. In Exp. 1, a 2 x 2 x 2 factorial experiment was conducted using 78 Angus crossbred cow-calf pairs. The factors examined were age at weaning (early, at 103+/-3 d [EW] vs normal, at 203+/-3 d [NW]), feeding strategy (ad libitum vs postweaning programmed intake), and dietary CP concentration (100 vs 120% of NRC [1984] recommended levels). Early-weaned calves had a greater (P < .001) ADG than NW calves from 103 to 203 d and reached market weight at 385 d vs 418 d for NW calves (P < .001). Likewise, steers offered feed for ad libitum consumption reached market weight at 394 d, compared with 409 d for programmed-intake steers (P < .05). In Exp. 2, 64 Angus crossbred steers were either weaned at 93+/-3 d and fed one of four diets, weaned at 210+/-3 d without access to creep feed, or weaned at 210+/-3 d with access to creep feed for 60 d prior to weaning. Early-weaned calves were heavier (P < .01) than NW calves at 210 d if fed either 100 or 90% concentrate diets, and they had greater (P < .001) backfat thickness at 210 d but no difference (P > .10) in longissimus muscle area compared to EW calves fed a 60% concentrate diet. At slaughter, 80 to 100% of steers on all treatments graded low Choice or higher. Feeding high-concentrate diets to EW beef calves accelerated growth rate and fat deposition early in the feeding period and may be a way to provide young cattle for a high-quality beef market.     

Effect of early weaning on the performance of three-year-old,first-calf beef heifers and calves reared in the subtropics

The objective of this study was to investigate the effectiveness of early weaning fall-born calves on heifer and calf performance in Florida. Over two consecutive years, 3-yr-old Braford and Brahman x Angus first-calf heifers were assigned randomly to one of two treatments; early-weaned (EW, n = 20 and 30 for yr 1 and 2, respectively) and normal-weaned (NW, n = 20 and 38 for yr 1 and 2, respectively). Calves were EW on January 23 and 3 for yr 1 and 2, respectively. Following EW, all first-calf heifers were returned to bahiagrass (Paspalum notatum) pastures with the mature cowherd. Early-weaned calves were maintained on annual ryegrass (Lolium multiflorum) pastures at 8.2 and 10.7 calves/ha for yr 1 and 2, respectively, and were provided supplemental grain mixture (14% CP) at 1.0% of BW daily. Normal-weaned calves remained with their dams in the mature cowherd on bahiagrass. Final calf BW was collected on April 17 (d 84) and April 24 (d 111) for yr 1 and 2, respectively. Early-weaned calves had a greater (P < 0.001) ADG (0.17 kg/d) in yr 1, but a lower (P < 0.001) ADG (-0.24 kg/d) in yr 2 compared with NW calves. Early weaning resulted in heavier first-calf heifers with greater BCS at the time of normal weaning (August 1; 491 vs. 452 kg, with BCS = 6.34 vs. 4.75 for EW and NW heifers, respectively; SEM = 5.0 and 0.07). Heifers with EW calves had a higher (P < 0.07) pregnancy rate during both years than normal-weaned heifers (89.5 vs. 50.0 and 96.7 vs. 80.0% pregnant during yr 1 and 2, respectively). Early-weaned, first-calf heifers also had a lower (P < 0.05) calving interval in yr 2 (384 vs. 404 d; SEM = 6.0). These data suggest that EW will improve body condition of first-calf heifers resulting in an increased pregnancy rate. Early-weaned calves maintained on winter ryegrass provide producers with the ability to optimize early-weaned calf performance, while capitalizing on low cost of gain and favorable spring markets.     

The effect of early weaning on feedlot performance and measures of stress in beef calves

Forty crossbred steers (Brahman x English) were categorized into two groups: 1) early weaned (EW; n = 20); and 2) normal weaned (NW; n = 20). Calves were 89 and 300 d of age at the time of EW and NW, respectively; SEM = 4.4. Early-weaned calves were kept on-site (University of Florida, Ona), provided supplement (1% of BW), and grazed on annual and perennial pastures until NW. At the time of normal weaning, all calves were loaded on a commercial livestock trailer and transported to the North Carolina State University Research Feedlot in Butner (approximately 1,200 km). Upon arrival, calves were stratified by BW and randomly allotted to four pens per weaning age treatment. Individual calf BW and blood samples were collected at the time of normal weaning, on arrival at the feedlot (d 1; 24 h following weaning), and on d 3, 7, 14, 21, and 28 of the receiving period. Individual BW was collected at the start and end of the growing and finishing periods, and feed intake by pen was measured daily. As an estimate of stress during the receiving period, plasma was collected and analyzed for the acute-phase proteins, haptoglobin and ceruloplasmin. Early-weaned calves were lighter (P = 0.03) at normal weaning than NW calves (221 vs. 269 kg; SEM = 10.6). By d 28, EW calves tended (P = 0.12) to be lighter than NW calves (242 vs. 282 kg, respectively). Gain:feed was improved for EW compared with NW calves during both the receiving (G:F = 0.157 vs. 0.081) and growing (0.159 vs. 0.136) periods. There tended (P < 0.10) to be weaning age x day interactions for each acute-phase protein. Ceruloplasmin concentrations increased in NW, but not EW calves, and peaked on d 7 (27.6 and 34.2 mg/100 mL for EW and NW calves, respectively; P < 0.05). Haptoglobin concentrations increased in both groups and were greatest (P < 0.05) in NW calves on d 3 (7.63 vs. 14.86 mg of haptoglobin/hemoglobin complexing/100 mL). No differences in ADG or G:F were detected during the finishing phase; however, overall G:F was improved (P = 0.03) for EW vs. NW calves (0.155 vs. 0.136). Carcass measures, including backfat thickness, USDA yield grade, marbling score, and LM area, did not differ between treatments. These data imply that EW calves, which are maintained onsite before shipping, may be more tolerant to the stressors associated with transportation and feed yard entry. Early weaned calves, managed within the system described in this study, may have improved G:F.     

Production systems comparing early weaning to normal weaning with or without creep feeding for beef steers

A 2-yr study was conducted to determine the effects of three weaning management systems on cow and steer performance. Cow-calf pairs were randomly assigned to one of three treatments, in which the steer calves were 1) early-weaned (yr 1, 177 +/- 9 d; yr 2, 158 +/- 21 d of age) and placed on a finishing diet (EW), 2) supplemented with grain for 55 d on pasture (yr 1, 177 to 231 d; yr 2, 158 to 213 d of age) while nursing their dams and then placed on a finishing diet (NWC), and 3) on pasture for 55 d while nursing their dams (yr 1, 177 to 231 d; yr 2, 158 to 213 d of age) and then placed on a finishing diet (NW). In yr 2, potential breed differences were evaluated using steers of three breed types: 1) Angus x Hereford (BRI); 2) Angus x Simmental (CON); and 3) Angus x Wagyu (WAG). In yr 1, EW steers gained 100% faster (P = .0001) than the average of NWC and NW steers, and NWC steers gained 32% faster (P = .02) than NW steers before weaning. In the feedlot, EW steers had lower intakes (7.70 vs 8.16 kg/d, P = .008) and better feed conversions (.170 vs .153, P = .002) than the average of NWC and NW steers. Marbling score was improved for EW steers compared with the average of NWC and NW steers (P = .003). In yr 2, EW steers had higher gains (P = .0006) during the entire study than the average of NWC and NW steers, and NWC steers had higher gains (P = .003) than NW steers. The EW steers had lower intakes (7.29 vs 7.68 kg/d, P = .0008) and better feed conversions (.160 vs .141, P = .0001) than the average of NWC and NW steers. The CON steers were heavier at slaughter than BRI steers (P = .01), and BRI steers were heavier than WAG steers (P =.0004). Early weaning improved the percentage of steers grading Average Choice or higher by 40%. The percentage of BRI steers grading Choice or greater was 21% higher and percentage of steers grading Average Choice or greater was 33% higher than CON. Cows with EW steers had higher ADG than cows with NW steers (.38 vs -.17 kg/d, P = .0001) before weaning. Cows with EW steers gained in body condition score (.23 vs .00, P = .04), and cows with NW steers did not change. Early weaning improved feed efficiency and quality grades of beef steers.     

Comparison of crossbred cows containing various proportions of Brahman in spring or fall calving systems: III. Productivity as three-, four-, and five-year olds

Productivity of 3-, 4-, and 5-yr-old crossbred cows containing various proportions (0, 1/4, or 1/2) of Brahman breeding out of Angus or Hereford dams was evaluated using 489 spring-calving and 427 fall-calving records collected over a 4-yr period. Cows were bred to Limousin sires for the first 3 yr and to Limousin and Salers sires the 4th yr. Interactions between crossbred cow group and season of calving were not significant. Percentage of cows exposed to breeding that weaned a calf increased (P less than .01) as proportion Brahman breeding increased, was higher (P less than .01) for cows out of Angus dams than for cows out of Hereford dams, and was higher (P less than .01) for spring-calving cows. As the proportion Brahman increased, the percentage requiring assistance at birth decreased, and cows out of Angus dams required less (P less than .05) assistance than those out of Hereford dams. Preweaning ADG, adjusted weaning weight, weaning conformation, weaning condition, and adjusted weaning hip height increased a proportion Brahman breeding increased. Spring-born calves gained .12 kg/d faster (P less than .01) than fall-born calves. However, weight at weaning was similar for the two groups; spring-born calves were weaned at an average age of 205 d, and fall-born calves were weaned at an average age of 240 d. Fall-calving cows were heavier (P less than .05) than spring-calving cows, and 0 and 1/2 Brahman cows were heavier (P less than .01) than 1/4 Brahman cows. These data indicate that Brahman-cross dams can be used to improve reproductive rate and increase preweaning growth rate, and thus weaning weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Productivity of cow-calf pairs grazing tall fescue pastures infected with either the wild-type endophyte or a nonergot alkaloid-producing endophyte strain, AR542

The nonergot alkaloid-producing endo-phyte, AR542, has been shown to improve the persistence and yield of tall fescue pastures without causing the animal disorders commonly associated with tall fescue toxicosis. A 3-yr grazing study was conducted to compare effects of AR542-infected tall fescue pastures with wild type endophyte-infected (E+) tall fescue pastures on cow-calf performance. Replicated 7.3-ha pastures of each treatment were grazed by cow-calf pairs (16 pairs per pasture replication) each year from March to weaning in September. The cows were exposed to breeding on their respective pasture treatments from April 1 through June 15. The treatment groups were compared for reproductive performance, ADG, BCS, calf growth rate, and weaning weight. Blood samples were also collected for serum prolactin (PRL) analysis. There were no significant differences in calving rate (P = 0.98) or calving interval (P = 0.62) between pasture treatments. Cows that grazed the AR542 pastures subsequently gave birth to calves that were heavier (P < 0.05) than calves from cows that had grazed the E+ pastures. Cows grazing the AR542 pastures had higher (P < 0.05) BCS at the end of the grazing period, and had higher ADG during the grazing period. Calves raised on the AR542 pasture had higher (P < 0.05) ADG and weaning weights than calves of the same sex raised on the E+ pastures. Serum PRL concentrations were decreased (P < 0.05) in both cows and calves on the E+ pastures compared with serum PRL concentrations in cows and calves grazing the AR542 pastures. The results indicate that grazing tall fescue pastures infected with the AR542 endophyte may give significant advantages in cow-calf growth rates and BCS over grazing E+ pastures. However, there did not seem to be any benefit in reproductive performance in this trial. There was a small, but significant increase in birth weight in cows grazing AR542 pasture.     

Growth rate, body composition, and meat tenderness in early vs. traditionally weaned beef calves

One hundred forty spring-born Angus x Gelbvieh and purebred Angus steers were selected for study as early weaned (EW; average age at weaning = 90 +/- 30 d) or traditionally weaned (TW; average age at weaning = 174 +/- 37 d) steers that were non-implanted or implanted (Synovex-S, Fort Dodge Animal Health, Overland Park, KS). Initially, steers were sorted by age, sire, and farm, and then allotted randomly in a 2 x 2 factorial arrangement of treatments of EW implanted (EWI), EW nonimplanted (EWN), TW implanted (TWI), or TW nonimplanted (TWN). Ultrasound measurements (US) of LM area (LMA), 12th rib fat thickness (US-BF), and marbling (US-M) were collected every 28 d during the time that steers were on feed. At 202 d of age, EW calves had larger US-LMA, US-BF, and BW than TW calves (37.9 vs. 32.3 cm2, 0.38 vs. 0.26 cm, and 271.6 vs. 218.9 kg, respectively; P < 0.001). At slaughter, EW calves had heavier HCW (290.4 vs. 279.7 kg, respectively; P < 0.05) and greater USDA marbling scores (51.25 vs. 46.26, respectively; P < 0.05) than TW calves; more EW steers graded USDA Choice or greater (P = 0.05). However, no differences were detected in BW (P = 0.15), LMA (P = 0.39), BF (P = 0.45), or liver abscess scores (P = 0.41). Twenty-four implanted steers were selected from the original group of 140 and sorted into two slaughter groups of 12. Twelve implanted steers from each weaning group, matched in slaughter BW but differing in age, were subsampled at slaughter to assess the effect of weaning age and chronological age on muscle tenderness. Younger animals had lower Warner-Bratzler shear force values (P < 0.001) than older calves after 14 d of postmortem aging; however, no differences were found in tenderness after 21 d of aging. Furthermore, there was greater variance (P < 0.001) in Warner-Bratzler shear force values among younger, EW steers vs. older, TW steers. These data provide evidence that early weaning of beef calves may be used as a tool to more effectively manage the cow-calf production system without compromising the quality of the offspring.     

Effect of early weaning on performance, carcass and meat quality of spring-born bull calves raised in dry mountain areas

Sixteen bull calves were born in the Spanish Central Pyrenees in spring. They were either early (EW, 90 days of age) or normal weaned (NW, 180 days of age). At day 90, EW calves were placed on an intensive diet while NW calves were turned out with their dams to high mountain pastures. After summer, at day 180, NW calves were weaned and placed with EW calves on a common finishing diet until slaughter at the fixed age of 1 year. From birth to early weaning date, no performance differences appeared. However, EW calves gained faster (1.549 kg/day) than their unweaned counterparts (0.783 kg/day) from early to normal weaning date (P < 0.001). During the finishing period, NW calves showed compensatory growth, with a 44% higher ADG than EW calves (P < 0.001), with a similar feed intake and a better feed conversion ratio. Early weaned calves had a longer fattening phase than NW calves (264 vs. 158 days, respectively; P < 0.001) and thus total feed intake and feed costs were greater. When slaughtered at 1 year of age, EW and NW calves attained similar weight (489 vs. 510 kg, respectively; P > 0.05), but dressing percentage was higher for EW calves (56.9%) than for NW calves (55.2%) (P < 0.01), which led EW calves to have heavier carcasses, without differences in fat score or conformation. The different growth paths, the result of weaning management, did not affect meat tenderness, chemical composition and fatty acid profile, but affected meat lightness, with higher values for compensating calves (NW) than calves in continuous growth (EW). In conclusion, advancing weaning age modified calf performance without affecting substantially carcass characteristics, except for an improvement in dressing percentage, or meat quality.     

Epidemiology and effects of nematode infections on beef cow-calf systems of Argentina's western pampas.

The epidemiology and the effects of nematode infections on cow-calf systems were followed from 3 weeks before calving to 7 months afterwards. Two groups, each of 15 cow-calf pairs grazed on separate lucerne pastures. Group I (GI) were treated monthly with oxfendazole (4.5 mg kg-1), cows being dosed from calving and calves starting 45 days later. Animals in Group II (GII) were not treated. The egg output of the cows was very low. An increase was recorded 2 months after parturition, consisting mainly of Ostertagia spp. The egg output and worm burdens of calves remained low until late summer and reached a peak in autumn. Ostertagia, Cooperia and Haemonchus were the main genera recovered from slaughtered calves. The pasture contamination and tracer calf worm counts remained consistently low until autumn when they began to increase. Inhibited early fourth stage larvae of Ostertagia were recovered during spring. After calving, the live-weight gains (LWG) of treated GI cows were significantly higher (P less than 0.004) than those of GII cows, whereas the LWG of GI calves were significantly higher during December (P less than 0.037) and March (P less than 0.029) than those of GII calves. There were significant (P less than 0.04) cumulative LWG responses between GI and GII calves with no differences in cow cumulative LWG at the end of the trial. For spring-born calves, these results suggest that strategic deworming programs in cow-calf systems may produce benefits.     

Effect of rotation frequency and weaning date on forage measurements and growth performance by cows and calves grazing endophyte-infected tall fescue pastures overseeded with crabgrass and legumes

A grazing study was initiated in April 2000 and continued through three calving and weaning cycles (ending July 2003) to investigate the effects of rotational grazing management (twice monthly [2M] vs. twice weekly [2W]) and weaning date (mid-April [EARLY] vs. early June [LATE]) on production of fall-calving cow-calf pairs (495 +/- 9.6 kg initial BW) grazing Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.) overseeded with legumes and crabgrass. Secondary objectives of the experiment were to monitor differences in quantity and quality of available forage and to evaluate changes in forage species composition. Pastures were dominated by tall fescue throughout the study, and the proportion of basal cover was greater (P < 0.05) in 2M than in 2W pastures. The percentage of legumes was very low across all treatment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadratically across years for both summer and fall sampling periods, regardless of rotation or weaning program. In vitro DM disappearance and mineral concentrations varied minimally because of rotation frequency or weaning date. Rotation frequency did not substantially affect (P = 0.11 to 0.97) cow BW, hay offered, milk production, calving interval, calf birth weight, or actual or adjusted weaning weights; however, 2M cows had 0.3 units higher (P < 0.05) BCS at the time of breeding than 2W cows. Calves weaned late had greater (P < 0.05) actual weaning weight and weighed more (P < 0.05) on the LATE weaning date than on the EARLY weaning date, but 205-d adjusted weaning weights did not differ (P = 0.74) across weaning dates. Therefore, rotation frequency and/or weaning date had little effect on forage species composition or forage quality. In addition, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall-born calves grazing endophyte-infected tall fescue pastures at approximately 189 d of age seemed to be detrimental to calf performance compared with delaying weaning until 243 d of age.     

Calving system and weaning age effects on cow and preweaning calf performance in the Northern Great Plains

A 3-yr study evaluated late winter (Feb), early spring (Apr), and late spring (Jun) calving systems in conjunction with varied weaning strategies on beef cow and calf performance from Northern Great Plains rangelands. Crossbred cows were randomly assigned to one of three calving systems (on average n= 168.calving system(-1).yr(-1)) and one of two weaning times (Wean 1, 2) within each calving system. The Feb and Apr calves were weaned at 190 and 240 d of age, whereas Jun calves were weaned at 140 and 190 d of age. Breeding by natural service occurred in a 32-d period that included estrous synchronization. Cows were managed throughout the year as appropriate for their calving season. Quantity and quality of hay and supplements were provided based on forage and weather conditions, physiological state of the cows, and available harvested feed resources within a year. After weaning, two-thirds of the early weaned steers were fed in confinement in Montana, and one-third were shipped to Oklahoma and were grazed or fed forage. One-half of the early weaned heifers grazed seeded pastures, and the other half was fed in confinement. Early weaned calves were weighed on approximately the same day as late-weaned calves. Birth weight and overall rate of gain from birth to weaning did not differ for calves from the three calving systems. Calf weaning weight differed by weaning age within calving system (P = 0.001), and calves from the Jun calving system that were weaned at 190 d of age tended (P = 0.06) to be lighter than calves of the same age from the Feb or Apr calving systems. Cow BW change and BCS dynamics were affected by calving system, but the proportion of cows pregnant in the fall was not. Cows suckled until later dates gained less or lost more BW during the 50 d between the first and second weaning than dry cows during this period. The previous year's weaning assignment did not affect production in the following year. Estimated harvested feed inputs were less for the Jun cows than for the Feb and Apr cows. We conclude that season of calving and weaning age affect outputs from rangeland-based beef cattle operations.     

Creep grazing and early weaning effects on cow and calf productivity

One hundred fifty Simmental-Hereford cows and calves were used in a 3-yr study to evaluate three creep grazing treatments and an early weaning treatment on cow and calf performance during midsummer (July to September). Calves were approximately 150 d of age and averaged 178.6 kg when treatments were initiated. Tifleaf pearl millet (Pennisetum Americanum L. Leeke) was used as the forage for two of the creep treatments, representing two cow stocking intensities of .466 (TLM1) and .239 (TLM2) ha of base hill land pasture/cow, and as pasture for early weaned calves. A red clover (Trifolium pratense L.)-Kentucky bluegrass (Poa pratensis L.) mixture was used as the other creep forage. Hill land pastures were similar for the mature cow units in all creep treatments. Calf average daily gains ranged from .93 to 1.10 kg and were not influenced (P greater than .05) by treatment. Calf gains per hectare were similar for the control, red clover and TLM1 treatments. The TLM2 and early weaning treatments resulted in increases of 105.4 and 39.1 kg of calf gain/ha (P less than .05) compared with the control. When calves were allowed to creep graze millet, decreasing the forage area from .466 to .239 ha per cow-calf unit resulted in an increase of 97.7 kg of calf gain/ha with no reduction in calf gain. Cows on the more intensively grazed millet creep treatment (TLM2) lost more weight (P less than .05) during midsummer than those on the TLM1 treatment, but they gained 18.5 kg more (P less than .10) weight than TLM1 cows between weaning and the start of winter feeding.     

Allocating forage to fall-calving cow-calf pairs strip-grazing stockpiled tall fescue

In a 2-yr study, we evaluated the effect of different forage allocations on the performance of lactating beef cows and their calves grazing stockpiled tall fescue. Allocations of stockpiled tall fescue at 2.25, 3.00, 3.75, and 4.50% of cow-calf pair BW/d were set as experimental treatments. Conventional hay-feeding was also evaluated as a comparison to grazing stockpiled tall fescue. The experiment had a randomized complete block design with 3 replications and was divided into 3 phases each year. From early December to late February (phase 1) of each year, cows and calves grazed stockpiled tall fescue or were fed hay in the treatments described above. Immediately after phase 1, cows and calves were commingled and managed as a single group until weaning in April (phase 2) so that residual effects could be documented. Residual effects on cows were measured after the calves were weaned in April until mid-July (phase 3). During phase 1 of both years, apparent DMI of cow-calf pairs allocated stockpiled tall fescue at 4.50% of BW/d was 31% greater (P < 0.01) than those allocated 2.25% of BW/d. As allocation of stockpiled tall fescue increased from 2.25 to 4.50% of cow-calf BW/d, pasture utilization fell (P < 0.01) from 84 +/- 7% to 59 +/- 7%. During phase 1 of both years, cow BW losses increased linearly (P < 0.02) as forage allocations decreased, although the losses in yr 1 were almost double (P < 0.01) those in yr 2. During phases 2 and 3, few differences were noted across treatment groups, such that by the end of phase 3, cow BW in all treatments did not differ either year (P > 0.40). Calf ADG in phase 1 increased linearly (P < 0.01) with forage allocation (y = 0.063x + 0.513; R(2) = 0.91). However, calf gain per hectare decreased linearly (P < 0.01) as stockpiled tall fescue allocations increased (y = -26.5x + 212; R(2) = 0.97) such that gain per hectare for cow-calf pairs allocated stockpiled tall fescue at 4.50% BW/d was nearly 40% less (P < 0.01) than for those allocated 2.25% of BW/d. Allocating cow-calf pairs stockpiled tall fescue at 2.25% of BW/d likely optimizes its use; because cow body condition is easily regained in the subsequent spring and summer months, less forage is used during winter, and calf gain per hectare is maximized.     

Factors affecting animal performance during the grazing season in a mountain cattle production system

The factors influencing weight changes during the grazing season of Brown Swiss autumn-calving cows and Brown Swiss and Pirenaica spring-calving cows and their calves were studied over an 8-yr period in Spanish mountain conditions. The data set comprised 552 annual production cycles of cows that calved in two consecutive years. The animals grazed on alpine ranges during the summer and on forest pastures in the spring and autumn. They were housed during the winter and fed at different feeding levels (83 to 117% of their energy requirements) throughout the years of study. Weights were recorded every 3 mo and corrected to account for changes of digestive content and fetal growth, using theoretical relationships. Cow weight gains both on forest pastures and high mountain ranges were higher in autumn- than in spring-calving Brown Swiss cows, and therefore also during the whole grazing season (52.1 vs 7.7 kg, respectively, P < 0.001). Therefore, weight at calving and thereafter was significantly higher in autumn- than in spring-calving cows, which was associated with better reproductive performance (35.5 vs 49.1 d from calving to first ovulation, P < 0.01). In the spring-calving herd, Pirenaica cows had slightly higher gains than Brown Swiss cows during the grazing period (18.5 vs 7.7 kg, P < 0.001), mainly due to their higher gains on forest pastures, but their reproductive performance was similar (44.5 vs 49.1 d from calving to first ovulation, respectively, not statistically significant). Gains were higher in multiparous than in primiparous cows (31.1 vs 14.1 kg, respectively, P < 0.001), especially in the case of Brown Swiss cows, which were younger at first calving. Gains were affected by year of study (P < 0.001) and previous weight changes during the housing period (r = -0.35 and r = -0.21 in autumn- and spring-calving cows respectively, P < 0.001). In the case of autumn-calving cows, performance on pasture was also affected by the stage of pregnancy at housing (r = -0.51, P < 0.001). Growth rates through lactation were higher in autumn- than in spring-born calves (P < 0.001), although the shorter lactation period resulted in lower weight at weaning of the former (P < 0.001). Breed was a significant source of variation in the performance of spring-born calves, weights and gains being higher in Brown Swiss than in Pirenaica calves (P < 0.001).     

Comparison of crossbred cows containing various proportions of Brahman in spring or fall calving systems. I. Productivity as two-year-olds

Productivity of 2-yr-old crossbred cows containing various proportions (0, 1/4 or 1/2) of Brahman breeding was evaluated using 203 spring-calving and 171 fall-calving heifers over a 3-yr period. All heifers were mated to Limousin sires. Percentage of cows exposed to breeding that weaned a calf was the only trait for which a significant crossbred cow group x season of calving interaction was found. Preweaning ADG and age-adjusted weaning weight increased as proportion Brahman breeding increased. Age-adjusted weaning weight was similar for the two groups because spring-born calves were weaned at an average age of 205 d and fall-born calves were weaned at an average age of 240 d. For weaning condition scores, an interaction between dam breed and proportion Brahman was detected; scores tended to be greater for calves out of 1/2 Hereford dams than for those out of 1/2 Angus dams, and this difference increased as proportion Brahman increased. Weaning conformation scores were similar for all calves. Age-adjusted weaning hip height increased as proportion Brahman breeding increased. Based on numbers of weaned calves, spring calving was more advantageous than fall calving. Averaged across both calving seasons, weaning weight tended to increase as proportion Brahman increased.     

Nursing enhances the negative effect of estrogen on LH release in the cow

Twenty-three crossbred beef cows between 4 and 5 yr of age were assigned at random to one of six treatments: (1) ovariectomized 4 d postpartum (OVX) with early weaning of calves 21 d postpartum (OVX-EW; n = 4), (2) OVX-EW and 17 beta-estradiol implants (OVX-E2-EW; n = 4), (3) OVX and normal nursing by calves throughout the experiment (OVX-NN; n = 3), (4) OVX-NN and 17 beta-estradiol implants (OVX-E2-NN; n = 4), (5) intact cows and early weaning of calves 21 d postpartum (EW), (6) intact cows and normal nursed (NN). Blood was collected at 15-min intervals over a 4-h period once weekly during the 12-wk postpartum period in the OVX cows. Early weaned intact cows exhibited estrus 23 d sooner (P less than .05) than normally nursed cows. A hormone level for each cow at each week was determined from the mean of the 17 samples collected over the 4 h period each week. There were no significant changes due to E2 treatment, for concentrations of LH, FSH or number of pulses during wk 1 through 3. However, during wk 4 through 12 the linear and quadratic contrasts of wk X estrogen X nursing were significant for serum LH, indicating there was no difference between the treatments for EW and NN without E2 but there was a large difference in the presence of E2. During nursing E2 suppressed serum LH below that of nonestrogen-treated cows while after weaning E2 stimulated LH release above that of nonestrogen-treated cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Grazing and feedlot performance of yearling stocker cattle integrated with spring- and fall-calving beef cows in a year-round grazing system

Effects of calving season and finishing system on forage and concentrate consumption and carcass characteristics of calves were compared. In each of 3 yr, two replicates of three growing and finishing systems were compared including 1) spring calves finished on a high-grain diet in a feedlot immediately post-weaning (WF); 2) spring calves backgrounded on a hay-corn gluten diet over winter for 179 +/- 18 d after weaning, grazed for 98 +/- 9 d in cool-season grass-legume pastures, and finished on a high-grain diet in a feedlot (SGF); and 3) fall calves backgrounded on a hay-corn gluten feed diet over winter for 69 +/- 31 d after weaning, grazed for 98 +/- 9 d in cool-season grass-legume pastures, and finished on a high-grain diet in a feedlot (FGF). During the grazing phase, calves on the SGF and FGF treatments were equally stocked with spring-calving cow-calf pairs before grazing by pregnant fall-calving cows in a first-last rotational stocking system at a rate of 1.9 standard livestock units/ha. As designed, retained calves in the FGF system spent 110 fewer days in the drylot during backgrounding than retained calves in the SGF system (P = 0.01), resulting in less feed provided during winter. A greater (P < 0.01) quantity of hay was fed to SGF calves after weaning over winter (1,305 kg of DM per calf) than the quantity fed to FGF calves (305 kg of DM per calf). Quantity of grain (including commercial starter) fed to SGF calves after weaning did not differ (P = 0.28) from that fed to FGF calves (126 vs. 55 kg of DM per calf); however, calves in the FGF system required 80 and 71 kg of DM per calf more concentrate to finish to an equivalent external fat thickness compared with SGF and WF calves, respectively (P = 0.02). Average daily gains in the feedlot were greater (P < 0.01) for SGF and FGF calves than for WF calves during all 3 yr. There were no differences (P = 0.69) in carcass quality grades among calves in all groups, but SGF calves had greater (P < 0.01) hot carcass weight and LM area measurements at slaughter than FGF or WF calves. Although calves in the FGF system were 25 kg lighter than calves in the WF system at slaughter (P = 0.03), and had a lower dressing percent (P = 0.03), other carcass characteristics did not differ between these two groups. Lower stored-feed requirements and similar carcass quality characteristics made retention of a fall calf crop advantageous over retention of a spring calf crop for use as stocker animals before finishing.     

Influence of Urea Alone or Combined with Fish Meal and Solubles in Liquid Supplements on Performance of Grazing Cow-Calf Pairs

Experiments were conducted for 84 d, beginning on July 1, with cow-calf pairs grazing summer grass to determine the effects of feeding molasses containing urea or urea, fish solubles, and fish meal on BW gains, milk production, and blood metabolites. The four treatments based on a 16% CP urea-molasses mixture were no supplement, 97.8% base mixture plus 2.2% urea for cows and calves, 80% base mixture plus 10% fish solubles and 10% fish meal for cows and calves, and the supplement with fish solubles and fish meal as a creep feed for calves. The mixture contained 23% CP as fed. In Exp. 1, 60 crossbred cows with Angus-sired calves were allotted according to sex and birth date to 12, 2-ha pastures. Three pastures each with five cow-calf pairs were assigned to each treatment. In Exp. 2, 48 Hereford X Brahman F₁ cows with Angus- or Belgian Blue-sired calves were allotted as in Exp. 1 to 24, 1-ha Alicia bermudagrass pastures. Three pastures with two cow-calf pairs were assigned to each treatment for each sire breed of calf. Cows were machine-milked, and jugular blood samples were collected initially and on d 28 and 56. Cows and calves were weighed, and cows were condition-scored after a 16-h shrink at the beginning and end of both experiments. Both supplements were consumed at similar levels (1.75 kg/d) by cow-calf pairs in both experiments. Cows in Exp. 1 and calves in both experiments gained more (P<0.05) BW when cow-calf pairs had access to the supplement containing fish solubles and fish meal. Milk yield was numerically higher on d 28 (P<0.18) and d 56 (P<0.11) when cows received fish solubles and fish meal in the supplement. The decline in milk yield from initial milking tended to be less (P<0.10) on d 28 and was less (P<0.05) on d 56 when cows received this supplement. Plasma ammonia N concentrations were higher (P<0.05) when cows were fed supplement containing only urea, and both supplements increased (P<0.05) plasma urea N when compared with no supplement. Supplements containing molasses, urea, fish solubles, and fish meal appear beneficial for cow-calf pairs grazing summer forage.     

Influence of calving season and stocking rate on birth weight and weaning weight of Simmental-sired calves from Brahman-Hereford F1 dams.

Braham-Hereford F1 dams have been used to evaluate the influence of grazing pressure on forage attributes and animal performance at the Texas A&M University Agricultural Research Center at Overton. Data for this study were compiled from 1,909 records of Simmental-sired calves born to Braham-Hereford F1 cows from 1975 to 1990. Birth weight and weaning weight were analyzed independently to estimate the influence of year, season of birth, dam age, weaning age, and sex of calf. The effect of stocking rate as represented by levels of forage availability on weaning weights and subsequent birth weights was measured. Within the fall and winter calving seasons, lactating dams grazing at a high stocking rate produced calves with the lowest subsequent birth weights. Lactating dams assigned to creep-fed treatments had calves with the heaviest subsequent birth weights. Although dams that were less than 3.5 yr of age had calves with the lightest birth weights, there was no apparent decline in birth weight of calves from dams 12 to 17 yr old. Year, sex of calf, age of dam, stocking rate, season of birth, age at weaning, and birth weight were significant factors affecting weaning weight (P less than .01). Fall-born calves grazing cool-season annual pastures were heavier at weaning (267.6 kg) than either winter- (252.0 kg) or spring-born calves (240.9 kg). A stocking rate x season-of-birth interaction was observed for birth weight and weaning weight (P less than .05). Differences in weaning weight from low- vs high-stocked pastures were greater for fall-born calves (61.6 kg) than for winter-born calves (48.7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cow and calf performance on Coastal or Tifton 85 Bermudagrass pastures with aeschynomene creep-grazing paddocks

Cow and calf performance was determined in a 2-yr, 2 x 2 factorial, grazing experiment using Coastal or Tifton 85 (T85) replicated Bermudagrass pastures (4 pastures each; each pasture 4.86 ha), without or with aeschynomene creep-grazing paddocks (n = 4, 0.202 ha each, planted in May of each year, 13.44 kg/ha). On June 10, 2004, and June 8, 2005, 96 winter-calving beef "tester" cows and their calves were grouped by cow breed (9 Angus and 3 Polled Hereford/group), initial cow BW (592.9 +/- 70.1 kg, 2-yr mean), age of dam, calf breed (Angus, Polled Hereford, or Angus x Polled Hereford), calf sex, initial calf age (117 +/- 20.1 d, 2-yr mean), and initial calf BW (161.3 +/- 30.4 kg) and were randomly assigned to pastures. Additional cow-calf pairs and open cows were added as the forage increased during the season. Forage mass was similar for all treatment pastures (P > 0.70; 2-yr mean, 6,939 vs. 6,628 kg/ha, Coastal vs. T85; 6,664 vs. 6,896 kg/ha, no creep grazing vs. creep grazing). Main effect interactions did not occur for performance variables (P > 0.10; 2-yr means), and year affected only the initial and final BW of the calves and cows. The 91-d tester calf ADG was greater for calves grazing T85 than Coastal (0.94 vs. 0.79 kg; P < 0.01), and for calves creep grazing aeschynomene compared with calves without creep grazing (0.90 vs. 0.82 kg; P < 0.03). Calf 205-d adjusted weaning weights were increased for calves grazing T85 compared with Coastal (252.9 vs. 240.3 kg; P < 0.01) and for calves with access to creep grazing (249.9 vs. 243.3 kg; P < 0.05). The IVDMD of esophageal masticate from pastures had a forage x creep grazing interaction (P < 0.05; Coastal, no creep grazing = 57.4%; Coastal, creep grazing = 52.1%; T85, no creep grazing = 59.1%; T85, creep grazing = 60.0%), and IVDMD was greater (P < 0.05) for T85 than for Coastal pastures. Cows were milked in August 2004, and in June and August 2005, with variable milk yields on treatments, but increased milk protein (P < 0.05) for cows grazing T85 compared with Coastal pastures in August each year, contributing to increased calf gains on T85 pastures. These results complement previous research with T85 and indicate increased forage quality and performance of cattle grazing T85 pastures. Calf gains on T85 pastures and for calves on creep-grazed aeschynomene paddocks were high enough to influence the efficiency of cow-calf operations.