Technical note: Digital quantification of eye pigmentation of cattle with white faces.

Cancer of the eye in cattle with white faces occurs less frequently in cattle with pigmented eyelids. Corneoscleral pigmentation is related to eyelid pigmentation and occurrence of lesions that may precede cancer. Objectives of this study were to assess 1) variation in the proportion of eyelid and corneoscleral pigmentation in Hereford, Bos taurus, and Bos indicus crossbreds and 2) the occurrence of lesions with the presence of pigmentation in those areas. Hereford and Bos indicus crosses (Brahman or Nellore with Angus and Hereford and straightbred Brafords) and Bos taurus crosses (Angus-Hereford) were included in the study (n = 1,083). Eyelid pigmentation proportions were estimated by pixel quantification and were evaluated as total proportions and for upper and lower eyelids distinctly for each eye. Fixed effects included breed type, age categories, and sex of the animal. Lesion presence (1) or absence (0) was obtained by visual appraisal of image and was assumed to be binomially distributed. Eyelid pigmentation proportions (overall, upper, and lower eyelids) for Hereford ranged from 0.65 ± 0.03 to 0.68 ± 0.03 and were significantly lower than Bos indicus (range from 0.93 ± 0.02 to 0.95 ± 0.02) or Bos taurus (ranged from 0.88 ± 0.02 to 0.92 ± 0.02) crosses. Corneoscleral pigmentation in Hereford cows (0.17 ± 0.06) did not differ (P = 0.91) from Hereford calves and yearlings (0.16 ± 0.07). Bos indicus and Bos taurus crossbred cows had larger corneoscleral pigmentation (0.38 ± 0.05 and 0.48 ± 0.04 for left eyes and 0.37 ± 0.05 and 0.53 ± 0.04 for right eyes, respectively) than all calves (P < 0.001), and their corneoscleral pigmentations were greater than that of Hereford cows (P < 0.003). Bos indicus and Bos taurus cows had greater proportions of left eye corneoscleral pigmentation (0.38 ± 0.05 and 0.48 ± 0.04, respectively) than Hereford cows (0.17 ± 0.06) and all young animal breed types (P < 0.05). Right eye proportions differed for all cow groups (P < 0.05; 0.53 ± 0.04, 0.37 ± 0.05, and 0.17 ± 0.06). Among calves and yearlings, Hereford had a lower right eye corneoscleral pigmentation proportion (0.16 ± 0.07) than Bos taurus (P = 0.02). The lesion proportion for Hereford (0.08 ± 0.03) was significantly greater than that of either Bos indicus (0.01 ± 0.005) or Bos taurus (0.01 ± 0.003). Crossbreeding with Bos taurus or Bos indicus animals appears to increase eye pigmentation, which may help reduce the occurrence of cancer in eyes of cattle with white faces.

The effectiveness of vasopressin as an ACTH secretagogue in cattle differs with temperament.

By using the temperament selection criterion of exit velocity (EV), cattle typically exhibiting hypercortisolism and a blunted response to exogenous corticotrophin-releasing hormone (CRH) can be identified via individual behavioral responses to handling. To further characterize hypothalamic-pituitary-adrenal (HPA) axis dysfunction associated with bovine temperament, the present study compared pituitary and adrenal activity, following stimulation with exogenous vasopressin (VP), in steers with an excitable or calm temperament. Serial blood samples were collected via indwelling jugular cannula for 6h preceding and 6h following administration of a VP bolus. Plasma concentrations of adrenocorticotropic hormone (ACTH) and cortisol were quantified by RIA to determine pituitary and adrenal responsiveness within temperament groups. Cortisol concentrations in excitable steers during the pre-challenge period revealed an increased initial adrenal reactivity to interactions with humans. Subsequent acclimation to the experimental surroundings yielded greater baseline cortisol concentrations in the cattle with an excitable temperament. Pituitary stimulation with VP resulted in a greater ACTH output from the excitable compared to the calm animals. The data presented herein provide additional evidence that HPA axis function in cattle of an excitable temperament may be akin to a state of chronic stress. The bovine temperament model may be of further use to both decipher mechanisms associated with HPA dysfunction and to elucidate physiological phenotypes or pathologies that have parallels in other species.

Phenotypic and genetic relationships of residual feed intake with performance and ultrasound carcass traits in Brangus heifers.

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DMI, with predicted DMI determined by linear regression of DMI on mid-test BW(0.75) (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DMI, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R(2) (0.578 vs. 0.534) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DMI and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition.

ASAS Centennial Paper: Future needs of research and extension in forage utilization.

Forage-animal production agriculture is implementing infrastructure changes and management strategies to adjust to increased energy-related costs of fuel, feed grains, fertilizers, and seeds. The primary objectives of this position paper are to assess future research and extension scientific needs in forage utilization, financial support for the discipline, and changing status and number of scientists. A survey questionnaire returned from 25 land-grant universities in the eastern half of the United States rated the top 4 research needs as 1) pasture systems and efficiency of production; 2) interfacing with energy concerns; 3) forage cultivar evaluations and persistence; and 4) environment impacts. Plant-animal future research needs at 11 USDA-ARS regional locations are targeted at sustainable management and improved livestock performance, ecophysiology and ecology of grasslands, environment impacts, and improved technologies for nutritive value assessments. Extension scientists from 17 southern and northeastern states listed the top 3 needs as forage persistence, soil fertility and nutrient management, and pasture systems and efficiency of production. Grant funds currently provide more than 40% of land-grant university research and extension efforts in forage utilization, and scientists estimate that this support base will increase to 55 to 60% of the funding total by 2013. Reduced allocation of state and federal funding has contributed to a reduction in the number of full-time equivalent (FTE) scientists engaged in forage utilization research and extension activities. The current 25 state FTE conducting research number about 2.8 per state. This includes 10 states with >3, 11 states with <2, and 3 states with <1 FTE. Increased interest in cellulosic energy, climate change, and environmental impact may offer new opportunities for these FTE to participate in integrated cross-discipline research Extension programming, and technology transfer methods will change to accommodate reduced funding but with increasing numbers of novice, recreation-oriented landowners.

Relationship of temperament, growth, carcass characteristics and tenderness in beef steers.

Relationships of temperament evaluated at different production stages with growth, carcass characteristics and beef tenderness were determined in Bonsmara crossbred steers managed under commercial managent. Temperament was evaluated at weaning and at initiation of the finishing phase. Steers from a Roswell, NM ranch (n=156) and a Cline, TX ranch (n=21) were stratified at fall weaning by weight and source and randomly allotted to winter ryegrass at Uvalde or Overton, TX followed by feeding in a commercial feedlot near Batesville, TX. Cattle were observed for temperament (escape velocity, EV, m/s; pen and chute temperament score, PTS and CTS) at weaning and upon entry to the feedlot. Cattle were harvested at approximately 7 mm 12th rib fat. Carcass data was taken approximately 36 hrs post-mortem and 2.5cm thick steaks were removed from the 13th rib for Warner-Bratzler shear force (WBS) determination. The only measures of temperament significantly related to performance were EV and PTS. Weaning EV appeared to be more related to feedlot ADG (r=-0.26, P<0.003), ribeye area (r=-0.37, P<0.0008), yield grade (r=0.29, P<0.01) and WBS, r=0.27, P<0.005) than did the later measures of temperament. However, in-feedlot EV was associated with feedlot weights (r=-0.28, P<0.0004). Results of this research suggest temperament, particularly at weaning, is related to feedlot performance, carcass merit, and beef tenderness at a low to moderate level and evaluation of this trait may be a helpful management tool.

Fate of phosphorus in dairy wastewater and poultry litter applied on grassland.

Large and repeated manure applications can exceed the P sorption capacity of soil and increase P leaching and losses through subsurface drainage. The objective of this study was to evaluate the fate of P applied with increasing N rates in dairy wastewater or poultry litter on grassland during a 4-yr period. In addition to P recovery in forage, soil-test phosphorus (STP) was monitored at depths to 180 cm in a Darco loamy sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudults) twice annually. A split-plot arrangement of a randomized complete block design comprised four annual N rates (0, 250, 500, and 1000 kg ha(-1)) for each nutrient source on coastal bermudagrass [Cynodon dactylon (L.) Pers.] over-seeded with ryegrass (Lolium multiflorum L. cv. TAM90). Increasing annual rates of N and P in wastewater and poultry litter increased P removal in forage (P = 0.001). At the highest N rate of each nutrient source, less than 13% of applied P was recovered in forage. The highest N rates delivered 8 times more P in wastewater or 15 times more P in poultry litter than was removed in forage harvests during an average year. Compared with controls, annual P rates up to 188 kg ha(-1) in dairy wastewater did not increase STP concentrations at depths below 30 cm. In contrast, the highest annual P rate (590 kg ha(-1)) in poultry litter increased STP above that of controls at depth intervals to 120 cm during the first year of sampling. Increases in STP at depths below 30 cm in the Darco soil were indicative of excessive P rates that could contribute to nonpoint-source pollution in outflows from subsoil through subsurface drainage.

Comparisons among Tuli-, Brahman-, and Angus-sired heifers: intake, digesta kinetics, and grazing behavior.

As part of an evaluation of Tuli crossbred cattle, forage intake, digesta kinetics, and grazing behavior were estimated in two Texas environments. In humid east Texas, Tuli x Brahman heifers were compared with purebred Angus and Brahman and Angus x Brahman heifers. Fecal output, forage intake, compartmental mass, and compartmental residence time did not differ among breeds. Angus and Brahman heifers had different (P < . 02) gastrointestinal residence times (51.1+/-1.56 vs 43.1+/-1.56 h, respectively), but values for the purebreds did not differ from those for Tuli x Brahman or Angus x Brahman heifers. Angus heifers had shorter (P < .05) 24-h grazing times (398+/-15.4 min/d) and fewer (P < .05) grazing periods (7+/-.4) than Tuli x Brahman (552+/-16.8 min/d and 10+/-.4), Angus x Brahman (507+/-18.4 min/d and 9+/-.5), and Brahman (560-/+ 16.8 min/d and 9+/-.4, respectively) heifers. In semiarid southwest Texas, Tuli x Angus heifers were compared with purebred Angus and Brahman and Brahman x Angus heifers. Fecal output and forage intake were similar in Tuli x Angus and Brahman x Angus heifers (14.2+/-.69 and 14.9+/-.91 g fecal DM/ [d.kg BW] and 24.5+/-1.33 and 25.6+/-1.75 g/d of forage DMI, respectively) but higher (P < .05) than those of purebred Brahman heifers (12.2+/-.64 and 20.3+/-1.23 g/[d.kg BW] of fecal DM and forage DMI, respectively). Grazing times did not differ among breeds. We conclude that Tuli-sired heifers are likely to be as productive as Brahman crossbred heifers in Texas, based on the similarities in intake, digesta dynamics, and grazing behavior.

First Report of Pythium ultimum, P. irregulare, Rhizoctonia solani AG4, and Fusarium proliferatum from Arrowleaf Clover (Trifolium vesiculosum): A Disease Complex.

Poor stand establishment, failure to recover after grazing, and premature plant death have reduced the utilization of arrowleaf clover (Trifolium vesiculosum Savi) as a forage crop in the southeastern United States in recent years. Clover plants collected from poor stands in east Texas pastures during the 1995 to 1996 and 1996 to 1997 seasons first exhibited root disease symptoms as young seedlings in the fall. Symptoms consisted of one or more of the following: tan discoloration of lateral roots and taproot; root pruning; and small, tan, sunken lesions on the taproot and crown. Many Rhizobium nodules were brown and dead. Toward spring, symptoms increased in severity. Root lesions became larger and darker, and internal crown discoloration was observed. Disease incidence reached 100% in both growing seasons. Premature death of plants also was observed, especially in pastures where plants had been grazed. Most of the fungi isolated from diseased roots were Pythium, multi- and binucleate Rhizoctonia, and Fusarium spp. Many plants were infected with two or three pathogens simultaneously. Two Rhizoctonia isolates (AR96-17 and -26) were identified as R. solani anastomosis group 4 (AG4; D. R. Sumner, University of Georgia). AR96-8 was identified as Fusarium proliferatum (T. Matsushima) Nirenberg (Fusarium Research Center, Penn State University; deposited as isolate M-8382). Three Pythium isolates (AR96-7, -11 and -39) were identified as P. irregulare Buisman, based on oogonial and sporangial characteristics. Eight other Pythium isolates were not identified. Pythium isolate AR97-1, found in 1997, was identified as P. ultimum Trow. Greenhouse studies to confirm pathogenicity of these isolates were conducted by sowing cv. Yuchi arrowleaf clover seed into artificially infested soilless medium. In pathogenicity tests for P. ultimum, seedling emergence for controls was 69% after 8 days, but no seedlings emerged from P. ultimum-infested media. Several seeds showed imbibition and emerging radicles but were symptomatic. The pathogen was reisolated from necrotic radicles. After 19 weeks, survival and root disease symptoms were recorded for plants infected by the other isolates. Pathogens were reisolated from diseased plants. Disease symptoms were similar to those observed on plants collected in the field, and differed among pathogens. The Pythium isolates and P. irregulare caused tan discoloration and pruning of the entire root system, sometimes leaving only stubs along the taproot. Survival of clover plants infected by Pythium spp. and P. irregulare isolates averaged 79 and 83%, respectively. R. solani AG4 isolates caused internal crown discoloration, root lesions, and severe root rot, and plant survival was only 31%. F. proliferatum caused hyperelongation of the hypocotyl and stem, mild chlorosis, tan discoloration of roots, and 94% plant survival. Survival was 86% for control plants. P. ultimum, P. irregulare, R. solani AG4, and F. proliferatum are part of a larger disease complex occurring on arrowleaf clover in east Texas that also includes bean yellow mosaic virus (1) and possibly other root and crown rot diseases. This report is the first to identify some of the components of this disease complex impacting arrowleaf clover in Texas, and to demonstrate pathogenicity of each fungal pathogen individually. There are no arrowleaf clover cultivars currently known to have resistance to any of these pathogens. Reference: (1) I. J. Pemberton et al. Phytopathology 81:1001, 1991.

Herbage allowance x yearling heifer phenotype interactions for preweaning calf growth on humid pasture and semiarid rangeland.

Preweaning growth data were obtained during 4 yr on 349 Braford-sired calves from Brahman-Hereford F1 first-calf females. These females were allotted to either semiarid rangeland (Uvalde) or humid improved pasture (Overton) as weanlings and to one of four herbage allowance levels at each location as yearlings. Females were wintered on systems in local industry practice and maintained on various allotted herbage levels both as yearlings and during first lactation. The desired range in herbage allowance (400 to 2,800 kg of DM per 100 kg of BW at Uvalde and 80 to 460 kg of DM per 100 kg of BW at Overton) was accomplished by adjusting stocking rate monthly from April to weaning (October). Herbage allowance and yearling heifer characteristics (hook height, condition score, or weight) were treated as continuous, independent variables in regression analyses. Preweaning daily gain responded to increased herbage allowance differently for the two locations. Generally, at Overton, herbage allowance influenced suckling calf growth to a greater extent than for the F1 yearling variables, but at Uvalde this trend was reversed. Heifers with larger yearling heights had first calves that grew faster to weaning for both locations and all herbage allowances, although the relationship was stronger for greater herbage allowances at Overton (herbage allowance x yearling weight interaction, P < .07). This interaction was not detected (P > .15) at Uvalde. Interactions between herbage allowance and yearling condition score were detected (P < .05) at both Overton and Uvalde, but these interactions were different (P < .15) at the two locations.(ABSTRACT TRUNCATED AT 250 WORDS)

Herbage allowance x yearling heifer phenotype interactions for the growth of Brahman-Hereford F1 first-calf females grazing humid pasture and semiarid rangeland.

Growth data were collected over 4 yr from 349 Brahman-Hereford F1, first-calf, lactating females that had been allotted as weanlings to either semiarid extensive rangeland (Uvalde) or humid improved Bermudagrass pasture (Overton) and to one of four herbage allowance levels at each location as yearlings. Heifers were wintered according to systems in local practice and maintained on allotted forage levels both as yearlings and during their first lactation. Heifers were bred to Braford bulls to calve as 2-yr-olds in January to March. Herbage allowance (400 to 2,800 kg of DM/100 kg BW at Uvalde and 80 to 460 kg of DM/100 kg BW at Overton) was maintained by adjusting stocking density monthly from April to weaning (October). Herbage allowance and yearling heifer hook height, condition score, or weight (taken on April 15) were continuous independent variables in regression analyses. Final heifer weight, height, and condition responses to increased herbage allowances were related to yearling phenotypes differently (P < .01) for the two locations. At Uvalde, yearling condition score interactions were especially important in that heifers that had more condition (especially those > 5 for 1 to 10 with 10 = fattest) as yearlings retained more (P < .05) weight and condition and grew more (P < .05) in height than did those of lower yearling condition. These females also responded to increased herbage allowance by gaining advantage (P < .05) in these variables, whereas those of lower yearling condition made smaller advances. At Overton, yearling condition played little role in subsequent growth. The yearling variable that had the greatest interactive effect was height. Shorter yearling heifers (< 123 cm) responded (P < .07) to increased herbage allowance so that they had greater final condition and grew more rapidly in height than those taller as yearlings.

Forage availability x heifer phenotype interactions for Brahman-Hereford F1 yearling heifers grazing humid pasture and semiarid rangeland.

Yearling heifer growth data were obtained during 4 yr for 524 heifers allotted to either humid bermuda grass pastures (Overton) or semiarid rangeland (Uvalde). Each year, heifers were allotted on April 15 to four forage availability levels (400 to 2,800 kg of DM per 100 kg of BW at Uvalde and 80 to 260 kg of DM per 100 kg of BW at Overton) maintained by varying the stocking rate monthly until mid-October of each year. Forage availability and yearling heifer characteristics (weight, condition score, and height at hooks, taken on April 15) were treated as continuous variables in regression analyses. Final heifer weight, height, and condition responses to increased forage allowance were related to yearling phenotypes differently for the two locations. Generally, at Overton, forage availability influenced final characteristics to a greater extent than did yearling variables, whereas the trend was the opposite at Uvalde. At Uvalde, the yearling characteristic that had the largest effect on performance was height at hooks. Yearlings with large frames benefited from increased forage allowance by accumulating body fat at a faster rate than those with small frames. In contrast, at Overton, the yearling characteristic that had the largest effect on performance was condition. Fat heifers responded to increased forage availability to gain even greater advantages in fatness at the expense of potential growth in height and, thus, achieved early maturation. Yearling phenotypes were more broadly adapted to arrays of forage availability for humid, improved pastures than for semiarid rangeland.

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)

Inhibition of DNA synthesis and decreased reproductive capacity in cattle maintained on semi-arid rangeland with Acacia species as a major component of available browse.

The ability of bovine lymphocytes to initiate in vitro blastogenesis in response to mitogen stimulation or to initiate DNA excision repair after treatment with a mutagen was evaluated as a function of the differing environmental conditions under which donor animals were maintained. Crossbred Brahman-Hereford F1 females were held on either a humid, coastal bermudagrass, improved pasture at Overton, TX, or in low or high grazing pressure herds on a semi-arid rangeland (Acacia-dominated shrubland) at Uvalde, Tx. Peripheral blood lymphocytes (PBL) from these animals were examined to determine their in vitro ability to engage in phytohemagglutinin (PHA)-stimulated blastogenesis and to initiate excision repair of DNA damage after exposure of the cells to the model polynuclear hydrocarbon carcinogen 7,8-dihydrodiol-9, 10-epoxy-benzo(a) pyrene (BPDE). PBL from cattle at both locations were compared, with significantly decreased blastogenesis and DNA excision repair observed in PBL from Uvalde high grazing pressure cattle. Cattle in the Uvalde high grazing pressure herd also exhibited significantly decreased reproductive efficiency. The data indicate that ingestion of sufficient quantities of palatable, but toxic, forage species available at the Uvalde test site is sufficient to decrease DNA synthesis associated with either mitogen-stimulated blastogenesis or DNA excision repair in bovine PBL, and suggest that the reduction in PBL DNA synthesis may be correlated with the changed reproductive efficiency in animals ingesting an increased ratio of forage from Acacia species.

Effect of zeranol on sexual development of crossbred bulls.

Three groups of 1/2 Simmental X 1/4 Brahman X 1/4 Hereford bull calves were used during two different years to study effects of zeranol on sexual development. At 154 d of age, half the calves were implanted with 36 mg zeranol and half, not implanted, served as controls. Implanted calves were reimplanted at 90-d intervals throughout the trial (9 mo) each year. Trial 1 was conducted with 24 calves and Trial 2 was conducted the following year with 10 bulls. Twenty-four days after weaning (200 d of age) and at 28-d intervals thereafter, bulls in drylot in Trial 1 were weighted, scrotal circumference (SC) was measured and an ejaculate of semen was collected by electroejaculation to determine puberty. At these times, bulls were given 200 micrograms of GnRH i.m. and blood was collected at 0, 1, 2, 3, 4 and 5 h after GnRH. Serum concentrations of LH and testosterone (TEST) were determined. At slaughter, testis weight, length and circumference and pubertal status were recorded. Bulls implanted with zeranol had smaller SC than control bulls during the entire 9-mo period (P less than .0001). More control bulls reached puberty than did implanted bulls (82.4 vs 23.5%, respectively; P less than .001). Control bulls had larger testis measurements at slaughter (P less than .0001). Implants did not alter total weight gain or ADG (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)

Simulated effect of calving season and winter hay feeding level on cow herd productivity.

The Texas A & M Cattle Production Systems Model was used to study herd productivity under several management plans open to cow-calf producers in the southeastern United States. An east Texas farm herd was simulated as a self-contained unit where all hay fed in the winter months was harvested from hay pastures or as surplus forage from grazed pastures. Management options examined involved (1) variation in the amount of forage fed as hay, and (2) spring vs fall calving. All forage was produced on well fertilized, intensively managed Coastal bermudagrass pastures. The winter feed options consisted of hay fed (1) ad libitum, and at (2) 80, (3) 60 and (4) 40% of the ad libitum level. The hay feeding period was November 15 through April 15. Overall herd productivity decreased as level of winter feeding decreased. Higher levels of hay feeding resulted in fewer cattle/unit land area but higher production/breeding cow. Herd size increased by 2.9, 11.9 and 32.5% as winter hay levels were reduced from ad libitum to 80, 60 and 40% of ad libitum, respectively, under spring calving management, whereas herd productivity measured as total live weight sold/herd (fixed land area) declined by 2.2, 9.4 and 10.3% with the respective feed levels. Spring-calving herds were approximately 3.2% larger in number than corresponding fall-calving herds on the same land area, but fall-calving herds produced an average of 3.6% more live weight sales.

Effect of monensin on gain and forage utilization by calves grazing bermudagrass.

Two trials were conducted to determine the influence of monensin on live weight gain and efficiency of forage utilization of calves grazing Bermudagrass. In trial 1, 32 calves, weaned at an average age of 238 days and 250 kg, were grazed on "Coastcross I" Bermudagrass from July 20 to October 13. Eight steers and eight heifers were randomly assigned to one of two treatments: 200 mg monensin/head/day or 0 mg monensin/head/day fed in a .01 kg/head/day diet of pelletized 14% protein feed. Both groups were stocked at 15.3 head/ha. Monensin-fed calves gained .52 kg/head/day, while the control-fed calves gained .42 kg/head/day (P < .10). Average daily gains (ADG) of steers (.54 kg) were greater (P < .05) than those of heifers (.40 kg). Forage to gain ratio estimates were 15:1 and 19:1 for calves on monensin and control paddocks, respectively. In trial 2, 48 steer calves, averaging 265 days of age and 260 kg, were randomly assigned to each of two replicates of the following grazing treatments: common Bermudagrass only (P), Bermudagrass + .91 kg/head/day 14% protein feed (PF) or Bermudagrass + .91 kg/head/day feed + 200 mg monensin/head/day (PFM). ADG were .45, .47 and .68 kg for steers fed P, PF and PFM, respectively. The monensin-fed calves showed a 45% improvement in ADG (P < .05). Estimated forage to gain ratios for calves fed P, PF and PFM were 20:5:1, 19:1 and 13:1, respectively. The use of 200 mg monensin/head/day improved calf gains by 23 to 45% and increased estimated feed efficiencies by 21 to 36% on Bermudagrass pastures. The improvement in gain for heifers fed monensin was 28.6%, while steers gained 18.4% more when fed monensin.