N. Torrentera

Effects of preslaughter withdrawal period on response of feedlot heifers to zilpaterol hydrochloride supplementation: growth performance and carcass characteristics.

Sixty-four crossbred heifers (451 +/- 23 kg) were used in a 42-d feeding trial (4 pens per treatment in a randomized complete block design) to evaluate the influence of preslaughter zilpaterol hydrochloride withdrawal period on growth performance and carcass characteristics. Heifers were fed a diet based on steam-flaked corn (2.13 Mcal of NE(m)/kg). Treatments were 1) control, no zilpaterol supplementation; 2) zilpaterol supplementation for 30 d, drug withdrawn from the diet 3 d preslaughter (ZIL-3); 3) zilpaterol supplementation for 30 d, drug withdrawn 6 d preslaughter (ZIL-6), and 4) zilpaterol supplementation for 30 d, drug withdrawn 12 d preslaughter (ZIL-12). Zilpaterol was supplemented at the rate of 0.15 mg/kg of BW daily. Intake of DM averaged 9.2 +/- 0.26 kg/d and was not affected (P > or = 0.36) by treatment. Compared with control heifers, ZIL-3 increased (P < 0.01) carcass-adjusted ADG (59%), G:F (57%), apparent dietary NE(m) (31%), and decreased observed/expected DMI (25%). Treatment with ZIL-3 did not affect marbling score (P = 0.49) or backfat thickness (P = 0.17), but compared with the control group, increased HCW (3.6%, P = 0.03), carcass dressing percentage (3.2%, P = 0.02), LM area (6.3%, P = 0.05), and reduced trimmed fat (31%, P = 0.03). Prolonging the period of zilpaterol withdrawal preslaughter tended to decrease carcass-adjusted ADG (linear, P = 0.11), G:F (linear, P = 0.08), apparent dietary NE(m) (linear, P = 0.11), and carcass dressing percentage (linear, P = 0.11). We conclude that growth performance and carcass yield responses to zilpaterol supplementation are negatively affected by prolonging the period of zilpaterol withdrawal beyond 3 d (the required minimum withdrawal period according to label). Drug withdrawal period may be a relevant factor in explaining variation in performance response to zilpaterol supplementation in commercial feedlots.

Influence of processing method on comparative digestion of white corn versus conventional steam-flaked yellow dent corn in finishing diets for feedlot cattle

Four Holstein steers (137 ± 2 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square design to evaluate the influence of processing method on comparative digestion of white corn. Treatments consisted of a basal finishing diet containing 80% corn grain (DM basis) as 1) dry-rolled white corn (DRWC), 2) steam-flaked white corn (SFWC) with 0.36 kg/L flake density (SFWC36), 3) SFWC, 0.31 kg/L flake density (SFWC31), and 4) steam-flaked yellow corn (SFYC) with 0.31 kg/L flake density (SFYC31). Characteristics of ruminal, postruminal, and apparent total tract digestion of OM, starch, and N were similar (P ≥ 0.08) for SFYC31 and SFWC31 treatments. Decreasing flake density of white corn (from 0.36 to 0.31 kg/L) did not affect (P = 0.22) ruminal OM digestion, but increased (1.9%, P = 0.07) apparent total tract OM digestion. Compared with dry rolling, steam flaking white corn increased ruminal (9.4%, P = 0.05), postruminal (14.4%, P < 0.01), and apparent total tract OM digestion (8.2%, P < 0.01), reflecting corresponding increases in ruminal (13.3%, P < 0.01), postruminal (43%, P < 0.01), and apparent total tract (12.3%, P < 0.01) starch digestion. Apparent postruminal and apparent total-tract N digestion also were greater (6.5 and 5.6%, respectively, P = 0.04) for SFWC than for DRWC. The DE value of SFWC and SFYC diets was similar, averaging 3.39 Mcal/kg. The DE value of SFWC was greater (8.1%, P < 0.01) than that of DRWC. Ruminal pH (4 h postprandial) averaged 5.74 and was not affected (P ≥ 0.48) by dietary treatments. Compared with dry rolling, steam flaking markedly enhances the feeding value of white corn, with optimal flake density being less than 0.36 kg/L. Although white corn has greater vitreous endosperm content, characteristics of ruminal starch digestion and undegradable intake protein are similar to conventional yellow dent corn when processed to a similar flake density (0.31 kg/L). However, postruminal and apparent total tract starch digestion tends to be slightly less for flaked white corn than for yellow corn.

Effect of level and source of supplemental tannin on growth performance of steers during the late finishing phase

ABSTRACT Two trials were conducted to evaluate the effect of tannin supplementation of steers during the feedlot finishing phase. In Trial 1, 96 Holstein steers (478 ± 6.5 kg) were used to evaluate the effects of level of supplemental condensed tannin (0%, 0.2%, 0.4%, and 0.6% of dry matter basis) on growth performance. Supplemental tannin increased (6.5%, P = 0.05) weight gain, gain efficiency (5.5%, P = 0.04), and tended to increase dietary net energy (3.2%, P = 0.06). In Trial 2, 96 Holstein steers (392 ± 4 kg) were used to evaluate the effect of tannin sources on growth performance. Treatments consisted of a steam-flaked corn diet supplemented with (1) no supplemental tannin, (2) 0.6% condensed tannin, (3) 0.6% hydrolysable tannin, and (4) a blend of 0.3% condensed and 0.3% hydrolysable tannin. Tannin supplementation tended to increase average daily gain (ADG, 6.8%, P = 0.08) and dry matter intake (DMI, 4%, P = 0.04). It is concluded that tannin supplementation promotes greater DMI, and hence, ADG of steers during the finishing feedlot phase. The basis for this effect on feed intake is not certain, but is apparently independent of potential tannin effects on metabolizable protein supply. Source of supplemental tannin (condensed vs. hydrolysable) have minimal effects on overall growth performance response to supplementation.

Effects of monensin and virginiamycin supplementation in finishing diets with distiller dried grains plus solubles on growth performance and digestive function of steers

Two trials were conducted to evaluate the influence of virginiamycin (26 mg/kg) and monensin (34 mg/kg) supplementation of a steam-flaked corn-based finishing diet containing 15% distiller dried grains plus solubles (DDGS) on growth performance and digestive function. In Trial 1, 135 steers (257 ± 21 kg) were used to evaluate treatment effects on 145-d growth performance. There were no treatment effects (P > 0.20) on dry matter intake (DMI). Antibiotic supplementation tended to increase average daily gain (ADG; 7%, P = 0.07); increased gain efficiency (11%, P < 0.01) and estimated dietary net energy (NE; 10%, P < 0.01). Carcass marbling score was greater (12%, P = 0.04) for virginiamycin vs. monensin. In Trial 2, three Holstein steers (300 ± 7 kg) were used in a 3 × 3 Latin square to evaluate treatment effects on digestion. Both monensin and virginiamycin depressed ruminal digestion of organic matter (OM; 6%, P < 0.01) and feed nitrogen (N, 15%, P = 0.03) and microbial protein synthesis (15%, P = 0.03). There were no treatment effects of total tract OM and N digestion. Antibiotic supplementation increased (2.3%, P = 0.02) ruminal pH, associated with decreased (7%, P = 0.04) ruminal volatile fatty acids (VFA) concentrations. It is concluded that monensin and virginiamycin supplementation of growing-finishing diets for feedlot cattle may enhance daily weight gain, gain efficiency and dietary energetics. These effects are associated with a shift towards great intestinal OM digestion and decreased ruminal degradation of feed N and microbial protein synthesis.

Influence of protein nutrition and virginiamycin supplementation on feedlot growth performance and digestive function of calf-fed Holstein steers

Two experiments were conducted to examine the influence of protein and virginiamycin (VM) supplementation on feedlot growth performance, digestion, and metabolizable AA (MAA) supply of calf-fed Holstein steers. Growth performance and dietary energetics were evaluated in 120 Holstein steers (127 ± 9 kg). During the initial 112-d feeding period, a steam-flaked corn-based diet was balanced to meet either 100% (MAB) or 87% (UREA) of MAA requirements. Diets were supplemented with or without 22.5 mg/kg VM in a 2 × 2 factorial arrangement. Subsequently (d 112 to 308), all steers received the UREA diet with or without VM. During the initial 112-d, MAB increased ADG, G:F, and dietary NE ( < 0.01). Thereafter, when all steers received the UREA diet, ADG, G:F, and dietary NE were not different ( > 0.10) across initial supplementation treatments. Overall (d 1 to 308), MAB did not affect ADG ( > 0.10) but enhanced G:F efficiency ( = 0.03) and dietary NE ( = 0.05). During the initial 112-d period and through the remainder of the experiment, VM increased G:F ( < 0.01) and dietary NE ( < 0.01). Four Holstein steers (146 ± 4 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square design to evaluate initial 112-d treatment effects on digestive function. There were no treatment effects ( > 0.10) on ruminal digestion of OM, NDF, starch, microbial efficiency, or total tract digestion of OM and NDF. The MAB increased indispensable AA flow to the small intestine ( < 0.01) and total tract digestion of N ( < 0.01) and starch ( = 0.04). Observed AA supply to small intestine was in agreement with expected supply ( = 0.96). Virginiamycin decreased ( = 0.04) nonammonia N flow to the small intestine and did not affect ( > 0.10) total tract N digestion. Extrapolating from AA supplies in the metabolism study, MAB satisfied indispensable AA requirements during the initial 112-d period, whereas the UREA diet met 73.5% and 79.2% of methionine and lysine requirements, respectively. During the subsequent periods (d 112 to 308) indispensable AA supplies exceeded theoretical requirements. We conclude that enhancements in energy utilization when diets are balanced to meet MAA requirements of calf-fed Holstein steers during the initial 112-d feedlot period remain appreciable throughout time on feed. Virginiamycin enhanced efficiency of energy utilization throughout the feedlot growing-finishing period.

Influence of Ionophore Supplementation on Growth Performance, Dietary Energetics and Carcass Characteristics in Finishing Cattle during Period of Heat Stress

Forty-eight crossbred heifers (378.1±18 kg) were used in a 56-d feeding trial (four pens per treatment in a randomised complete block design) to evaluate the influence of ionophore supplementation on growth performance, dietary energetics and carcass characteristics in finishing cattle during a period of heat stress. Heifers were fed a diet based on steam-flaked corn (2.22 Mcal NEm/kg) with and without an ionophore. Treatments were: i) control, no ionophore; ii) 30 mg/kg monensin sodium (RUM30); iii) 20 mg/kg lasalocid sodium (BOV20), and iv) 30 mg/kg lasalocid sodium (BOV30). Both dry matter intake (DMI) and climatic variables were measured daily and the temperature humidity index (THI) was estimated. The maximum THI during the study averaged 93, while the minimum was 70 (THI average = 79.2±2.3). Compared to controls, monensin supplementation did not influence average daily gain, the estimated NE value of the diet, or observed-to-expected DMI, but tended (p = 0.07) to increase (4.8%) gain to feed. Compared to controls, the group fed BOV30 increased (p≤0.03) daily gain (11.8%), gain to feed (8.3%), net energy of the diet (5%), and observed-to-expected DMI (5.2%). Daily weight gain was greater (7.6%, p = 0.05) for heifers fed BOV30 than for heifers fed MON30. Otherwise, differences between the two treatments in DMI, gain to feed, and dietary NE were not statistically significant (p>0.11). Plotting weekly intakes versus THI, observed intake of controls was greater (p<0.05) at THI values ≤77 than ionophore groups. When THI values were greater than 79, DMI of control and MON30 were not different (p = 0.42), although less than that of groups fed lasalocid (p = 0.04). Variation in energy intake was lower (p>0.05) in the ionophores group (CV = 1.7%) than in the control group (CV = 4.5%). Inclusion of ionophores in the diet resulted in relatively minor changes in carcass characteristics. It is concluded that ionophore supplementation did not exacerbate the decline of DM intake in heat-stressed cattle fed a high-energy finishing diet; on the contrary, it stabilised feed intake and favoured feed efficiency. Ionophore supplementation reduced estimated maintenance coefficients around 10% in finishing cattle during a period of heat stress. This effect was greatest for heifers supplemented with 30 mg lasalocid/kg of diet.

Influence of feeding chromium-enriched enzymatically hydrolyzed yeast on growth performance, dietary energetics and carcass characteristics in feedlot cattle under conditions of high ambient temperature

Forty crossbred steers (245 ± 0.95 kg) were used in a 222-day feeding trial to assess the effects of a supplementation of chelated chromium-enhanced extract of enzymatically hydrolyzed yeast (Cr-EHY) on growth performance, dietary energetics and carcass characteristics in feedlot cattle finishing during high ambient temperatures. Treatments consisted of a steam-flaked corn-based diets supplemented with 0 or 0.4 g/kg of diet with Cr-EHY (0.3 g/kg of TruMax plus 0.1 g/kg of chelated Cr). Both dry matter intake (DMI) and climatic variables were measured weekly and the temperature humidity index (THI) was estimated. Daily maximal THI that exceeding a THI value of 72 was reached in 213 of the 222-day study (avg. THI = 75.24). During the initial 112-day period (including the receiving and diet transition phases), Cr-EHY increased average daily gain (ADG) (7%, P = 0.03). This effect was due to a tendency (P = 0.07) for increased DMI. There were no treatment effects on gain efficiency and dietary net energy (NE). Overall, however, there were no treatment effects on growth performance or dietary NE. Nevertheless, Cr-EHY supplementation had a modulating effect on carcass quality, decreasing carcass fat thickness (10%, P = 0.09, and increasing longissimus muscle area (7%, P < 0.01) and retail yield of boneless closely trimmed primal cuts (2%, P = 0.07). Results indicate that supplementation with a chelated chromium-enhanced extract of enzymatically hydrolyzed yeast can have beneficial effects on feed intake and daily weight gain, particularly during the initial receiving growing phase. It also appears to have a modulating effect on carcass quality, enhancing muscularity and reducing external fat. These results indicate that Cr supplementation has a modulating effect on carcass quality and may enhance DMI and corresponding ADG of feedlot cattle during periods of high ambient temperature.

Influence of ruminal degradable intake protein restriction on characteristics of digestion and growth performance of feedlot cattle during the late finishing phase

Two trials were conducted to evaluate the influence of supplemental urea withdrawal on characteristics of digestion (Trial 1) and growth performance (Trial 2) of feedlot cattle during the last 40 days on feed. Treatments consisted of a steam-flaked corn-based finishing diet supplemented with urea to provide urea fermentation potential (UFP) of 0, 0.6, and 1.2%. In Trial 1, six Holstein steers (160 ± 10 kg) with cannulas in the rumen and proximal duodenum were used in a replicated 3 × 3 Latin square experiment. Decreasing supplemental urea decreased (linear effect, P ≤ 0.05) ruminal OM digestion. This effect was mediated by decreases (linear effect, P ≤ 0.05) in ruminal digestibility of NDF and N. Passage of non-ammonia and microbial N (MN) to the small intestine decreased (linear effect, P = 0.04) with decreasing dietary urea level. Total tract digestion of OM (linear effect, P = 0.06), NDF (linear effect, P = 0.07), N (linear effect, P = 0.04) and dietary DE (linear effect, P = 0.05) decreased with decreasing urea level. Treatment effects on total tract starch digestion, although numerically small, likewise tended (linear effect, P = 0.11) to decrease with decreasing urea level. Decreased fiber digestion accounted for 51% of the variation in OM digestion. Ruminal pH was not affected by treatments averaging 5.82. Decreasing urea level decreased (linear effect, P ≤ 0.05) ruminal N-NH and blood urea nitrogen. In Trial 2, 90 crossbred steers (468 kg ± 8), were used in a 40 d feeding trial (5 steers/pen, 6 pens/ treatment) to evaluate treatment effects on final-phase growth performance. Decreasing urea level did not affect DMI, but decreased (linear effect, P ≤ 0.03) ADG, gain efficiency, and dietary NE. It is concluded that in addition to effects on metabolizable amino acid flow to the small intestine, depriving cattle of otherwise ruminally degradable N (RDP) during the late finishing phase may negatively impact site and extent of digestion of OM, depressing ADG, gain efficiency, and dietary NE.

Delay implant strategy in calf-fed Holstein steers: growth performance and carcass characteristics

ABSTRACT The influence of live weight (LW) at first implanting on growth performance and carcass characteristics was evaluated in calf-fed Holstein fed a steam-flaked corn-based diet. Treatments were: (1) control (not implanted); (2) first implanted at 267 kg LW; (3) first implanted at 291 kg LW, and (4) first implanted at 321 kg LW. All implanted cattle were re-implanted on d-112 of trial. Both the initial and final implants contained 120 mg of trenbolone acetate and 24 mg of oestradiol. Compared with non-implanted controls, implanting increased (P < .01) overall dry matter intake (DMI, 5.9%), average daily gain (ADG,16.7%), gain efficiency (ADG:DMI; 9.4%), and estimated dietary net energy for maintenance (NEm, 8.6%) and gain (NEg, 9.7%). Increasing LW at first implanting decreased overall DMI (linear effect; P = .01), but did not affect overall ADG (P = .17) or gain efficiency (P = .32). Within the range of 267–321 kg, weight at first implanting did not affect growth-performance or carcass characteristics. Interval growth performance of implanted and non-implanted calves was a predictable function of LW.

Effect of energy density and virginiamycin supplementation in diets on growth performance and digestive function of finishing steers

Objective This study was determined the influence of virginiamycin supplementation on growth-performance and characteristics of digestion of cattle with decreasing dietary net energy value of the diet for maintenance (NEm) from 2.22 to 2.10 Mcal/kg. Methods Eighty crossbred beef steers (298.2±6.3 kg) were used in a 152-d performance evaluation consisting of a 28-d adaptation period followed by a 124-d growing-finishing period. During the 124-d period steers were fed either a lesser energy dense (LED, 2.10 Mcal/kg NEm) or higher energy dense (HED, 2.22 Mcal/kg NEm) diet. Diets were fed with or without 28 mg/kg (dry matter [DM] basis) virginiamycin in a 2×2 factorial arrangement. Four Holstein steers (170.4±5.6 kg) with cannulas in the rumen (3.8 cm internal diameter) and proximal duodenum were used in 4×4 Latin square experiment to study treatment effects on characteristics of digestion. Results Neither diet energy density nor virginiamycin affected average daily gain (p>0.10). As expected, dry matter intake and gain efficiency were greater (p<0.01) for LED- than for HED-fed steers. Virginiamycin did not affect estimated net energy value of the LED diet. Virginiamycin increased estimated NE of the HED diet. During daylight hours when the temperature humidity index averaged 81.3±2.7, virginiamycin decreased (p<0.05) ruminal temperature. Virginiamycin did not influence (p>0.10) ruminal or total tract digestion. Ruminal (p = 0.02) and total tract digestion (p<0.01) of organic matter, and digestible energy (p<0.01) were greater for HED vs LED. Ruminal microbial efficiency was lower (p<0.01) for HED vs LED diets. Conclusion The positive effect of virginiamycin on growth performance of cattle is due to increased efficiency of energy utilization, as effects of virginiamycin on characteristics of digestion were not appreciable. Under conditions of high ambient temperature virginiamycin may reduce body temperature.