Metabolic and reproductive characteristics of replacement beef heifers subjected to an early-weaning regimen involving high-concentrate feeding.

In an effort to better understand the consequences of early weaning (EW) for replacement beef heifers, a two-phase experiment was conducted investigating the impact on metabolic function and documenting reproductive characteristics. In phase 1, Angus×Simmental heifers (n=35) were stratified by BW and sire, and randomly assigned to either a normal weaning (NW, n=18) or EW (n=17) treatment. EW heifers were weaned at 107±3 days of age and provided access to a concentrate-based ration ad libitum with limit-fed mixed grass hay. NW heifers remained with their dams until 232±3 days of age, at which point heifers from both treatments were comingled and grazed on mixed summer pasture. Following NW, weekly blood samples were collected from all heifers for progesterone analyses used to determine the onset of puberty. Pelvic and ovarian size was measured before breeding. All heifers were subjected to an estrous synchronization protocol with timed artificial insemination (AI) at 437±4 days of age. During phase 2 of the experiment, a subset of pregnant heifers (n=16) were divided into two replicates and subjected to a glucose tolerance test, epinephrine challenge and progesterone clearance analysis. Neither age nor BW at puberty differed between EW and NW heifers. Likewise, no differences in pelvic area or ovarian size were observed. Thus, it appears that the reproductive maturity of EW and NW heifers was similar. Heifers studied during phase 2 of the experiment were restricted to those that had become pregnant to their first AI. Within this cohort, EW heifers tended to have lower overall circulating progesterone concentrations than those that were NW (P=0.14). Aspects of glucose and insulin dynamics were also altered, as EW heifers tended to have lower baseline glucose concentrations (P=0.10) despite similar baseline insulin concentrations. Compared with NW heifers, EW heifers had lower insulin area under the curve (P<0.05), which was partly the result of a tendency for lower peak insulin concentrations (P=0.11). Results of the glucose tolerance test indicate that a lesser insulin response was necessary to properly clear the glucose in the EW heifers, suggesting enhanced insulin sensitivity. Collectively, these results indicate that EW is not detrimental for the growth or reproductive development of replacement beef heifers, although some differences in glucose and insulin dynamics persist into adulthood.

Effect of early grain feeding of beef steers on postabsorptive metabolism.

The objective of this study was to determine the effect of early weaning followed by a period of high-grain feeding on plasma acetate kinetics and signaling protein phosphorylation in LM tissue of growing steers. We hypothesized that early grain feeding would result in altered cell signaling and acetate use to support observed improvements in carcass gain and marbling. Fall-born Angus × Simmental steers were weaned at 106 ± 4 d of age (early weaned [EW]; n = 6) and fed a high-grain diet for 148 d or remained with their dams (normal weaned [NW]; n = 6) on pasture until weaning at 251 ± 5 d of age. Both treatments were subsequently combined and grazed on mixed summer pasture to 394 ± 5 d of age followed by a feedlot ration until harvest at 513 ± 5 d of age. Longissimus muscle tissue biopsies were collected at 253 ± 5 and 394 ± 5 d of age and at harvest. Total and phosphorylated forms of 5' adenosine monophosphate-activated protein kinase (AMPK) and downstream proteins of the mammalian target of rapamycin signaling pathway were determined by western blotting. Eight steers were used to assess acetate clearance at different age points via a bolus infusion of acetate (4 mmol/kg of BW). Early weaned steers had greater (P < 0.05) ADG than NW steers during the early grain feeding period. Phosphorylated to total ratios of ribosomal protein S6 (rpS6) and ribosomal protein S6 kinase 1 (S6K1) were significantly different during the early grain feeding period. Phosphorylated to total ratios of S6K1, rpS6, acetyl-CoA carboxylase, and 4E binding protein 1 and the absolute amount of phosphorylated AMPK were correlated with ADG, explaining 46% of the variance. Acetate clearance rates were less (P < 0.05) and synthesis rates were greater (P = 0.06) in EW steers during early grain feeding. Acetate synthesis rates were also greater (P < 0.05) in NW steers at harvest, suggesting a permanent shift in the gut microflora or gut function in response to the treatment. Neither treatment nor acetate infusion significantly affected plasma glucose or insulin concentrations. Plasma ß-hydroxybutyric acid concentrations increased with acetate infusion (P < 0.05). Based on these results, altered cell signaling during the early grain feeding period likely mediated increased protein deposition, leading to increased carcass weights, but observed changes in acetate appearance and clearance rates do not appear to explain the observed differences in intramuscular fat deposition during the terminal feeding period.

Acetate and glucose incorporation into subcutaneous, intramuscular, and visceral fat of finishing steers.

The objectives of this study were to assess the effects of early grain feeding on acetate and glucose turnover rates and acetate and glucose preference for palmitate synthesis by subcutaneous fat (SCF), intramuscular fat (IMF), and visceral fat (VF) in finishing steers. Sixteen Angus × Simmental steers were used in the study; 8 were early weaned (EW) and fed a high-grain diet immediately after weaning for 100 or 148 d, and 8 remained with their dams on pasture until weaning at 202 ± 5 or 253 ± 5 d of age. Normal weaned (NW) and EW animals were combined and grazed to 374 ± 5 or 393 ± 5 d of age, when they were placed on a corn silage-based finishing ration until they achieved a SCF thickness of 1.0 to 1.2 cm (494 ± 17 d of age for EW steers and 502 ± 12 d of age for NW steers). Immediately before harvest, steers were continuously infused for 12 h with [2H3] acetate (1.63 mmol/min; n = 8) or [U-13C6] glucose (0.07 mmol/min; n = 8). Blood samples were collected before initiation of infusions and at the end of the infusion from 8 animals or at 1-h intervals for the first 11 h and at 15-min intervals for the last hour of infusion for the other 8 animals. Adipose tissue samples from SCF, IMF, and VF depots were collected at harvest, and lipids were extracted. Plasma enrichments of acetate and glucose and palmitate enrichment in each depot were used to calculate plasma turnover rates and fractional synthesis rates (FSR; % per h) of palmitate from each isotope. Early weaned steers had greater marbling scores compared to NW steers ( P< 0.05). Plasma turnover rates and FSR for EW and NW steers were similar except for SCF, where a greater FSR from acetate was observed for EW steers. It is possible the greater FSR for SCF was due to harvesting the animals at a slightly more advanced stage of conditioning as evidenced by the trend for greater 12th rib fat (P = 0.07). Plasma acetate turnover and palmitate FSR from acetate were much greater (P < 0.05) than the corresponding rates from glucose, supporting the primary role of acetate as an energy source and the primary substrate for lipid synthesis across fat depots. However, FSR from acetate and glucose were not different among depots, suggesting that any potential effects of dietary starch on differential deposition of energy in SCF and IMF are not substrate driven.

Effects of calf weaning age and subsequent management systems on growth performance and carcass characteristics of beef steers.

Brahman × British crossbred steers (n = 40 and 38 in yr 1 and 2, respectively) were used to evaluate the effects of calf management systems following early weaning (EW) on growth performance, muscle gene expression, and carcass characteristics. On the day of EW (d 0), steers were stratified by BW and age (95 ± 14 kg; 74 ± 14 d) and randomly assigned to a control treatment that was normally weaned (NW) on d 180 (n = 10 steers/yr) or to 1 of 3 EW treatments: 1) EW and limit fed a high-concentrate diet at 3.5% of BW (as-fed basis) in drylot until d 180 (EW180; n = 10 steers/yr), 2) EW and limit fed a high-concentrate diet at 3.5% of BW (as-fed basis) in drylot until d 90 and then grazed on bahiagrass pastures until d 180 (EW90; n = 10 steers/yr), or 3) EW and grazed on annual ryegrass pastures until d 60 (yr 1; n = 10 steers) or 90 (yr 2; n = 8 steers) and then on bahiagrass pastures until d 180 (EWRG). Early-weaned steers on ryegrass and bahiagrass pastures were supplemented with high-concentrate diet at 1.0% of BW (as-fed basis) until d 180. From d 180 to 270 (yr 1), all EW steers remained in their respective treatments, whereas NW steers were provided high-concentrate diet at 1.0% of BW (as-fed basis) on bahiagrass pastures. In yr 1, feedlot finishing period began on d 270. In yr 2, the study was terminated on d 180. In both years, EW180 steers were heaviest (P < 0.0001) on d 180. On d 180 of yr 1, EWRG steers were lightest (P < 0.0001) and EW90 steers were heavier (P = 0.05) than NW steers, whereas EW90, EWRG, and NW steers had similar BW on d 180 of yr 2 (P ≥ 0.14). On d 90, muscle PPARγ mRNA expression tended (P = 0.07) to be greater for EW180 steers and was greater (P = 0.008) for EW90 vs. EWRG steers but similar (P = 0.25) between EW180 and NW steers. On d 180, PPARγ mRNA was greater (P ≤ 0.06) for EW180 vs. NW, EW90, and EWRG steers. From d 274 to 302, EW180 steers had the least ADG (P ≤ 0.09), whereas EW90 steers had similar (P = 0.19) ADG compared with EWRG steers but greater (P = 0.03) ADG than NW steers. At slaughter, carcass characteristics did not differ (P ≥ 0.22) among treatments. In summary, EW steers provided a high-concentrate diet in drylot for at least 90 d were heavier at the time of normal weaning than NW steers and EW steers grazed on ryegrass pastures for 60 to 90 d and supplemented with concentrate at 1.0% of BW. Feeding a high-concentrate diet immediately after EW enhanced the muscle PPARγ expression but did not enhance marbling at slaughter.

Early metabolic imprinting events increase marbling scores in fed cattle.

Early weaning of calves to a high concentrate diet results in greater fat deposition and suggests early postnatal metabolic imprinting events may be exploited as a management tool to improve cattle value. Our objective was to implement a short, high energy dietary intervention before a typical grazing period to manipulate intramuscular fat deposition in finishing cattle. Fall-born, Angus-sired steer calves (n = 24) were stratified by sire and randomly assigned to normal weaned (NW) or metabolic-imprinted (MIP) treatments. At 105 ± 6d (135kg), MIP calves were transitioned to a diet containing 20% CP and 1.26 Mcal/kg NEg. Metabolic-imprinted calves were fed ad libitum as a group. Normal weaned calves remained on their dam until 253 ± 6 d of age. At this time, treatment groups were combined and grazed for 156 d on a mixed summer pasture. Following the grazing phase, steers were adapted to a corn silage-based feedlot diet and performance was monitored on 28-d intervals. Calves were staged for harvest based on backfat endpoint (target 1.0 to 1.2 cm). Metabolic-imprinted calves were heavier (P < 0.05) than NW calves (341 vs. 265 ± 4.2 kg) at normal weaning age. During the grazing phase, NW steers gained more weight than (P < 0.05) MIP steers (0.69 vs. 0.35 ± 0.03 kg/d). Feedlot performance and USDA yield grade were similar (P > 0.20) between treatments. However, MIP steers produced heavier (P < 0.05) carcasses (564 vs. 524 ± 5.6 kg) with higher (P < 0.001) marbling scores (645 vs. 517 ± 23). Therefore, calves consuming a high concentrate diet for 148 d after early weaning produced higher quality carcasses. This suggests early weaning and feeding a high concentrate before grazing is a viable strategy to increase marbling deposition compared with a traditional production system.

Impact of water troughs on cattle use of riparian zones in the Georgia Piedmont in the United States.

Cattle use of riparian areas may lead to stream water contamination with nutrients, pathogens, and sediments. Providing alternative water away from the stream may reduce the amount of time cattle spend near streams and therefore reduce contamination. We conducted this study to 1) evaluate the effect of providing water troughs outside of the riparian zones on the amount of time cattle spend in riparian zones, and 2) evaluate if environmental factors such as temperature and humidity affect the impact of water trough availability on the amount of time cattle spend within riparian and nonriparian locations. Global positioning system (GPS) collars were used to document cow locations every 5 min in 2 mixed tall fescue/common bermuda-grass pastures of the Georgia Piedmont in the United States. We found that when the temperature and humidity index (THI) ranged between 62 and 72, providing cattle with water troughs outside of riparian zones tended to decrease time cattle spent in riparian zones by 63% (52 min x d(-1); P = 0.11). When THI ranged between 72 and 84, nonriparian water availability did not have a significant impact on the amount of time cattle spent in the riparian zone or in riparian shade. These results suggest that water troughs placed away from unfenced streams may improve water quality by reducing the amount of time cattle spend in riparian zones when environmental conditions as evaluated by THI are not stressful.

Phosphorus, sediment, and Escherichia coli loads in unfenced streams of the Georgia Piedmont, USA.

Contamination of unfenced streams with P, sediments, and pathogenic bacteria from cattle (Bos taurus) activity may be affected by the availability of shade and alternative water sources. The objectives of this study were to evaluate water quality in two streams draining tall fescue (Festuca arundinacea Schreb.)-common bermudagrass (Cynodon dactylon L.) pastures with different shade distribution, and to quantify the effects of alternative water sources on stream water quality. For 3 yr, loads of dissolved reactive phosphorus (DRP), total phosphorus (TP), and total suspended solids (TSS) were measured during storm flow, and loads of DRP, TP, TSS, and Escherichia coli were measured every 14 d during base flow. We also used GPS collars to determine amount of time cattle spent in riparian areas. Our results showed that cattle-grazed pastures with unfenced streams contributed significant loads of DRP, TP, TSS, and E. coli to surface waters (p < 0.01). Time spent by cattle in riparian areas as well as storm flow loads of DRP, TP, and TSS were larger (p < 0.08) in the pasture with the smaller amount of nonriparian shade. Water trough availability decreased base flow loads of TSS and E. coli in both streams, and decreased time cattle spent in riparian areas in the pasture with the smaller amount of nonriparian shade (p < 0.08). Our results indicate that possible BMPs to reduce contamination from cattle-grazed pastures would be to develop or encourage nonriparian shade and to provide cattle with alternative water sources away from the stream.

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.

Use of nonergot alkaloid-producing endophytes for alleviating tall fescue toxicosis in stocker cattle.

Grazing studies were conducted to determine cattle growth performance, evaluate toxicosis, and compare grazing behavior in stocker cattle grazing nonergot alkaloid-producing endophyte-infected (AR542 or AR502), endophyte-free (E-), or wild-type toxic endophyte-infected (E+) Jesup, Georgia-5, and Kentucky-31 tall fescue. Replicated 0.81-ha tall fescue paddocks were established at the Central Georgia Branch Station at Eatonton and the Northwest Georgia Branch Station at Calhoun during October 1998 and were stocked with beef cattle for autumn and spring periods from fall 1999 through spring 2002. Mean ergot alkaloid concentrations were higher (P < 0.01) on E+ pastures than the other treatments at both locations. At Calhoun and Eatonton, post-treatment serum prolactin concentrations were decreased (P < 0.01) on E+ compared with AR542, AR502, and E- tall fescue. Cattle on AR542, AR502, and E- pastures had lower (P < 0.05) post-treatment rectal temperatures than cattle grazing E+ tall fescue during spring at Eatonton and Calhoun. Calf ADG was higher (P < 0.05) on AR542, AR502, and E- as compared with E+ tall fescue during autumn and spring grazing at Eatonton, and at Calhoun, cattle on E+ pastures had lower (P < 0.05) ADG in both autumn and spring. Gain/hectare was higher (P < 0.05) on AR542, AR502, and E- than on E+ during autumn at Eatonton and during spring at both locations. In autumn at Calhoun, gain/hectare was greater (P < 0.05) on AR502 and E- compared with E+ tall fescue. During April, May, and June, cattle grazing E+ pastures at Eatonton spent more (P < 0.01) time idling, more (P < 0.01) time standing, and used more (P < 0.01) water than cattle on AR542 and E- tall fescue. Daily prehensions and biting rate were each higher (P < 0.01) on AR542 and E- tall fescue than E+ tall fescue in both grazing seasons. There were no differences among pasture treatments for bite size in either spring (P = 0.50) or autumn (P = 0.34). Steers grazing E+ pastures had lower DMI than steers grazing AR542 and E- pastures during spring (P < 0.10) and lower DMI than steers grazing E- pastures during autumn (P < 0.05). Daily steer water usage was decreased (P < 0.10) in E+ pastures compared with AR542 and E- pastures during late fall. These results indicate that nonergot alkaloid-producing endophyte technology is a promising option for alleviating tall fescue toxicosis in stocker cattle.

Use of nonergot alkaloid-producing endophytes for alleviating tall fescue toxicosis in sheep.

Nonergot alkaloid-producing endophytes from New Zealand were inserted into tall fescue (Festuca arundinacea) cultivars in an attempt to address the problem of fescue toxicosis in grazing sheep. A 3-yr grazing study was conducted to determine lamb performance and to evaluate toxicosis in lambs grazing nonergot alkaloid-producing endophyte-infected (AR542 or AR502), endophyte-free (E-), or wild-type toxic endophyte-infected (E+) Jesup tall fescue or nonergot alkaloid-producing endophyte-infected (AR542) Georgia-5 tall fescue. Replicated 0.11-ha tall fescue paddocks were established at the central Georgia Branch Station during September 1997 and stocked with lambs from spring 1998 through autumn 2000. Mean ergot alkaloid concentrations were higher (P < 0.01) in E+ forage than in AR542, AR502, and E- tall fescue, and ergot alkaloid concentrations in E- plants and plants infected with AR542 and AR502 were low. Forage availability did not differ (P = 0.92) across treatments during autumn and was higher (P < 0.05) in Georgia-5 AR542 than in Jesup AR502 and E+ pastures. Initial serum prolactin (PRL) concentrations did not differ (P = 0.58) across treatments during autumn, but were higher on Jesup AR542 than E+ during spring. Post-treatment serum PRL concentrations were depressed (P < 0.01) on E+ compared with AR542, AR502, and E- in both spring and autumn. Signs of heat stress were observed in E+ lambs during periods of high ambient temperatures. Mean post-treatment rectal temperature and mean stocking rate exhibited treatment x year interactions (P < 0.05). Lamb ADG was higher (P < 0.05) on AR542, AR502, and E- than on E+ tall fescue. Similarly, gain/hectare was higher (P < 0.015) on AR542, AR502, and E- than on E+. Tall fescue pastures containing AR542 and AR502 endophytes yielded lamb performance that did not differ from that on E- tall fescue and which was superior to performance on E+ tall fescue. Depressed PRL concentrations and elevated rectal temperatures as indicators of toxicosis were evident only in lambs grazing E+ tall fescue, suggesting that nonergot alkaloid-producing endophyte-infected tall fescue is a viable alternative for alleviating tall fescue toxicosis.

Phosphorus and ammonium concentrations in surface runoff from grasslands fertilized with broiler litter.

Application of broiler (Gallus gallus domesticus) litter to grasslands can increase ammonium (NH4-N) and dissolved reactive phosphorus (DRP) concentrations in surface runoff, but it is not known for how long after a broiler litter application that these concentrations remain elevated. This long-term study was conducted to measure NH4-N and DRP in surface runoff from grasslands fertilized with broiler litter. Six 0.75-ha, fescue (Festuca arundinacea Schreb.-)bermudagrass [Cynodon dactylon (L.) Pers.] paddocks received broiler litter applications in the spring and fall of 1995-1996 and only inorganic fertilizer N in the spring of 1997-1998. Surface runoff from each paddock was measured and analyzed for NH4-N and DRP. Broiler litter increased flow-weighted NH4-N and DRP concentrations from background values of 0.5 and 0.4 mg L(-1), respectively, to values > 18 mg L(-1) in a runoff event that took place immediately after the third application. Ammonium concentrations decreased rapidly after an application and were not strongly related to time after application or runoff volume. In contrast, DRP concentrations tended to decrease more slowly, reaching values near 1 mg L(-1) by 19 mo after the last application. Dissolved reactive P concentrations decreased linearly with the natural logarithm of days after application (p<0.03), and increased linearly with the natural logarithm of runoff volume (p<0.0001).

Phosphorus losses from grasslands fertilized with broiler litter: EPIC simulations.

Broiler litter, a mixture of poultry excreta and bedding material, is commonly used to fertilize grasslands in the southeastern USA. Previous work has shown that under certain situations, application of broiler (Gallus gallus domesticus) litter to grasslands may lead to elevated levels of phosphorus (P) in surface runoff. The EPIC simulation model may be a useful tool to identify those situations. This work was conducted to evaluate EPIC's ability to simulate event and annual runoff volume and losses of dissolved reactive phosphorus (DRP) from tall fescue (Festuca arundinacea Schreb.)-bermudagrass [Cynodon dactylon (L.) Pers.] paddocks fertilized with broiler litter. The EPIC simulations of event runoff volume showed a trend toward underestimation, particularly for runoff events >30 mm. On an annual basis, EPIC also tended to underestimate runoff, especially at runoff volumes > 100 mm. Both event and annual runoff estimations were strongly associated with observed values, indicating that model calibration could improve the simulation of surface runoff volume. The relationship between simulated and observed values of DRP loss was relatively poor on an event basis (r=0.65), but was stronger (r=0.75) on an annual basis. In general, EPIC tended to underestimate annual DRP losses. This underestimation was apparently caused by the lack of an explicit mechanism to model broiler litter on the soil surface. These results suggested that additional work on the EPIC P submodel would be warranted to improve its simulation of surface application of broiler litter to grasslands.

Nitrogen metabolism and hormonal responses of steers fed wheat silage and infused with amino acids or casein.

Four Holstein steers (159 kg) surgically fitted with abomasal-infusion cannulas were used in a 4 x 4 Latin square study to test amino acid (AA) and casein (CAS) infusions on nitrogen balance and hormonal status of steers consuming vegetative wheat (Triticum aestivum L.) silage (12.3% CP). Treatments were 5-d infusions of 1) water (CONT), 2) arginine (ARG; 13.69 g/d), 3) limiting amino acids (LAA, 13.69 g/d arginine + 10.92 g/d histidine + 28.97 g/d lysine + 10.88 g/d methionine + 16.96 g/d threonine, and 4) Na-CAS (300 g/d). Whole blood was collected for plasma AA, growth hormone (GH), insulin, and IGF-I concentrations. Data were analyzed by ANOVA, and the following orthogonal contrasts were used to separate treatment means: CONT vs ARG; ARG vs LAA; and LAA vs CAS. Urinary N increased (P < .02) for CAS vs LAA. Arginine increased N retention, as did CAS, compared to LAA. Total plasma essential AA were decreased by arginine. Mean plasma insulin concentrations were increased by CAS (P < .034). Arginine increased mean plasma GH levels, but not IGF-I. The CAS treatment increased (P < .015) IGF-I levels, but not GH. These data suggest that performance of steers fed wheat silage was limited by duodenal AA flow and that arginine was the first-limiting AA. Casein infusion increased plasma insulin and IGF-I, which would explain the improved growth noted in calves and lambs fed forages supplemented with ruminally undegraded protein.

Effects of selection for scrotal circumference in Limousin bulls on reproductive and growth traits of progeny.

Nine pairs of Limousin bulls from nine contemporary groups were acquired, with each pair consisting of one large scrotal circumference (SC) bull and one small SC bull. Average adjusted yearling scrotal circumferences were 36.3 cm (SD 1.6 cm) and 28.5 cm (SD .9 cm) for large SC (LP) and small SC (SP) bulls, respectively. In addition to the phenotypic grouping, non-parent SC EPD were used to group bulls into high (HE, > .53 cm), average (AE), and low (LE, < -.61 cm) lines. Each bull was mated to a randomly assigned group of 15 to 20 Brangus x Hereford cows each yr for 1 to 3 yr. Birth weights, weaning and yearling weights and heights, and ultrasound measurements for backfat and ribeye measurements were taken on 407 progeny. Blood samples were collected on 210 heifer progeny when they averaged 11, 13, and 15 mo of age to determine whether they had reached puberty. When subjected to a breeding soundness exam (BSE), LP bulls scored higher (P < .01) for motility as well as total BSE score. The LP calves had heavier birth weights (P < .05) and greater testicular mass at weaning (P < .01) than SP calves. The HE and AE bull calves had greater (P < .02) testicular mass than did the LE bull calves. A greater (P < .05) percentage of HE heifers had reached puberty by the 11- and 13-mo measurements than either the AE or LE heifers. The HE heifers reached puberty at a younger age than AE (P < .01) or LE (P < .001) heifers. Selection using SC EPD was more effective than phenotypic selection in reducing age at puberty in daughters.

Market value and managerial decisions: implications from a decade of feeder cattle teleauctions.

Data from feeder cattle teleauction sales in Georgia from 1977 to 1988 were analyzed using least squares analysis of variance to detect significant (P less than .05) influential factors on price. The sample was divided into two periods, 1977 to 1982 and 1983 to 1988, to test whether the influence of factors had changed over the time periods. The test of equality was rejected (P less than .01) using a Chow test, thus suggesting a change had occurred. Hereford breeds were discounted in the latter period whereas Angus breeds generated a premium in the earlier period. Treatment for specific diseases resulted in premium prices, as did preconditioning, during the 1983 to 1988 period. The effect of seasonality on prices decreased over the two time periods. The optimal lot size increased from 228 to 280 cattle during the time periods.

Effect of hot-fat trimming on factors associated with the subprimal yield of beef carcasses.

Thirty-two crossbred cattle (steers = 17; heifers = 15) exhibiting an ultrasound fat thickness at the 12 to 13th rib region of at least 10 mm were selected from a slaughter shift at a commercial packing plant. After splitting, alternating sides of each carcass were trimmed of 1) subcutaneous fat in excess of 6.4 mm; 2) all kidney, pelvic, and heart fat; and 3) all cod or udder fat and fat in the flank region. Both sides of each carcass were fabricated into subprimals (final trim level of 6.4 mm) according to normal industry procedures. Effect of hot-fat trimming, yield grade (3, 4, and 5), and gender on hot-fat trim, fabrication fat trim, major subprimal, and total subprimal yield of untrimmed and trimmed carcasses were determined. Higher numerical yield grade (YG) corresponded with higher (P less than .05) percentages of hot-fat trim. Hot-fat trimming increased (P less than .05) the difference in fabrication fat trim between steers and heifers and between YG 3 and YG 5. Steers and heifers differed (P less than .05) in percentage of major subprimals and total subprimals when processed conventionally, whereas hot-fat trimming eliminated this difference (P less than .05). Untrimmed YG 3 carcasses had 3.1 and 5.0% higher major subprimal yield (P less than .05) than untrimmed YG 4 and YG 5 carcasses, respectively, whereas hot-fat trimming reduced this difference to 2.5% for YG 4 and to 3.7% for YG 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Ruminal escape protein supplementation and zeranol implantation effects on performance of steers grazing winter annuals.

Fifty-four crossbred steers (275 kg) were assigned randomly to one of three isoenergetic but not isonitrogenous ruminal escape protein (EP) supplements: high ruminal escape protein (HEP), low ruminal escape protein (LEP), or corn. The supplements contained corn, distillers' dried grains with solubles (DDGS), and fish meal. Supplements were fed at approximately 1.5 kg/d; the HEP and LEP supplements provided .25 and .12 kg more EP per day than corn, respectively. These supplements also supplied .20 and .10 kg more CP per day than corn. Fish meal and DDGS provided 66.7 and 33.3% of the supplemental EP, respectively. One-half of the steers in each supplement treatment were implanted once with 36 mg of zeranol. Steers grazed wheat (Triticum aestivum L.)-annual ryegrass (Lolium multiflorum Lam.) pastures for 73 d (March 1 to May 12). Daily gains (kg/d) increased linearly (P less than .07) as EP increased (HEP, 1.61; LEP, 1.54; corn, 1.47); responses were apparent only during the later periods as forage quality declined. Zeranol implants increased (P less than .02) ADG (kg/d) by 9.7% (1.58 vs 1.44). After grazing, all cattle were fed a finishing ration for 76 d. Pre-feedlot EP level produced a negative linear (P less than .04) response on feedlot ADG (kg/d) (HEP, 1.44; LEP, 1.50; corn, 1.59). Zeranol implantation during the grazing phase did not affect (P greater than .2) performance during the feedlot phase or carcass characteristics other than increased ribeye area (P less than .08). Compensatory feedlot performance negated all weight gain advantages elicited by EP supplementation during the grazing period.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein and fiber digestion by steers grazing winter annuals and supplemented with ruminal escape protein.

Six abomasally cannulated Hereford steers (12 mo of age, 300 +/- 10 kg) grazing annual ryegrass (Lolium multiflorum Lam.) paddocks were used in a replicated 3 x 3 Latin square design to determine effects of ruminal escape protein (EP) supplementation on forage intake, fiber digestion, and protein flow to the intestine. Steers were fed one of three isoenergetic supplements: high ruminal escape protein (HEP), low ruminal escape protein (LEP), or corn, which supplied an estimated .25, .125, or 0 kg of EP/d in addition to EP supplied by corn. Fish meal (FM) and distiller's dried grains with solubles (DDGS) were sources of EP; FM provided 66.7% and DDGS provided 33.3% of estimated EP. Steers were adjusted to each supplement for 7 d before a 4-d collection period. Both total and forage DMI responded quadratically (P less than .03 and P less than .07, respectively) to EP supplementation. Total tract DM digestion tended (P less than .13) to increase linearly with EP supplementation. Abomasal total CP flow increased linearly (P less than .10) as supplemental EP increased. Crude protein flow in steers receiving HEP, LEP, and corn was 1,137, 1,027, and 844 g/d, respectively. Likewise, abomasal nonammonia N (NAN) tended to be greater (P less than .15, linear) for steers receiving HEP. Nonammonia N flows were 1,044, 955, and 771 g/d for steers receiving HEP, LEP, and corn, respectively. Abomasal ammonia flow did not differ (P less than .20) among treatments, nor did reticuloruminal fiber digestion (P less than .20). These data indicate that EP can increase postruminal protein flow and will not negatively affect fiber digestion in steers grazing annual ryegrass pastures.

Digestibility of cotton plant by-product diets for sheep at two levels of intake.

Crossbred wethers (n = 48) were assigned randomly to 1 of 12 experimental diets, arranged in a 3 X 2 X 2 split plot to evaluate three levels of cotton plant by-product (25, 50 and 75% CPB), two levels of NaOH treatment of CPB (0 and 4%) and two levels of monensin supplementation (0 and 30 ppm, DM basis) at two intake levels (70 and 90% of ad libitum). Intake was a within-lamb variable. Ad libitum intake was established over an initial 17-d adjustment period. Feed intake and fecal output were recorded during collection periods with aliquots retained for laboratory analysis. Intake was affected by a linear CPB X monensin interaction (P less than .06) with monensin depressing intake more at higher CPB levels. Neutral detergent fiber (NDF) digestibility decreased linearly (P less than .001) as the dietary level of CPB increased. NaOH treatment of CPB improved (P less than .001) the digestibility of organic matter (OM) and NDF. The supplementation of 30 ppm monensin resulted in greater (P less than .004) apparent digestibilities of NDF and hemicellulose (HC). Increasing daily feed intake from 70 to 90% of ad libitum decreased (P less than .004) digestibility of NDF, HC and ADF.

Effects of rapid weight gain to puberty on reproduction, mammary development and lactation in ewe lambs.

The effects of rapid weight gain to puberty on reproduction, mammary development and milk production in ewes lambing at 13 mo of age were investigated on three trials. A total of 64 Dorset and 93 Suffolk ewe lambs were weaned at 42 d of age and their mean weight was 16 kg. These ewes were assigned, within breed groups, to either a finishing diet or a growing diet. Onset of puberty was determined by daily checks for estrus and ewes were bred beginning at 7 mo of age. In Trial 2, mammary gland development was determined in eight Suffolk ewes from each diet. Ewes on the finishing diet were younger at puberty than those on the growing diet (199 vs 206 d, P<0.05) but required more services per conception (1.3 vs 1.1, P<0.05). Dietary conception rate and lambing rate means were similar. Mean 4-h milk yield was lower (P<0.10) for ewes on the finishing diet (283 g) than for those on the growing diet (310 g). Mammary gland fat pad area was higher (P<0.05) for ewes on the finishing diet compared with those fed for growth. Gross and adjusted duct areas were higher in ewes on the growing diet, but differences were not significant. At puberty, negative correlation coefficients for milk yield with performance traits were as follows: daily weight gain, -0.184 (P<0.08); weight-to-height ratio -0.262 (P<0.01); body condition score, -0.189 (P<0.07); and body weight, -0.212 (P<0.05). Results of this study indicate that rapid weight gain to puberty impairs mammary gland development and milk production in ewe lambs.