Effects of high-starch or high-fat diets formulated to be isoenergetic on energy and nitrogen partitioning and utilization in lactating Jersey cows.

The objective of this study was to determine the effects of high-starch or high-fat diets formulated to be isoenergetic on energy and N partitioning and utilization of energy. Twelve multiparous Jersey cows (mean ± standard deviation; 192 ± 11 d in milk; 467 ± 47 kg) in a crossover design with 28-d periods (24-d adaptation and 4-d collection) were used to compare 2 treatment diets. Treatments were high starch (HS; 30.8% starch, 31.8% neutral detergent fiber, and 1.9% fatty acids) or high fat (HF; 16.8% starch, 41.7% neutral detergent fiber, and 4.1% fatty acids). Diets were formulated to have net energy for lactation (NEL) content of 1.55 Mcal/kg of dry matter according to the National Research Council (2001) dairy model. Nutrient composition was varied primarily by replacing corn grain in HS with a rumen-inert fat source and cottonseed hulls in HF. Gross energy content was lower for HS (4.43 vs. 4.54 ± 0.01 Mcal/kg of dry matter), whereas digestible (2.93 vs. 2.74 ± 0.035 Mcal/kg of dry matter) and metabolizable energy (2.60 vs. 2.41 ± 0.030 Mcal/kg of dry matter), and NEL (1.83 vs. 1.67 ± 0.036 Mcal/kg of dry matter) content were all greater than for HF. Tissue energy deposited as body fat tended to be greater for HS (4.70 vs. 2.14 ± 1.01 Mcal/d). For N partitioning, HS increased milk N secretion (141 vs. 131 ± 10.5 g/d) and decreased urinary N excretion (123 vs. 150 ± 6.4 g/d). Compared with HF, HS increased apparent total-tract digestibility of dry matter (66.7 vs. 61.7 ± 1.06%), organic matter (68.5 vs. 63.2 ± 0.98%), energy (66.0 vs. 60.4 ± 0.92%), and 18-carbon fatty acids (67.9 vs. 61.2 ± 1.60%). However, apparent total-tract digestibility of starch decreased for HS from 97.0 to 94.5 ± 0.48%. Compared with HF, HS tended to increase milk yield (19.7 vs. 18.9 ± 1.38 kg/d), milk protein content (4.03 vs. 3.93 ± 0.10%), milk protein yield (0.791 vs. 0.740 ± 0.050 kg/d), and milk lactose yield (0.897 vs. 0.864 ± 0.067 kg/d). In addition, HS decreased milk fat content (5.93 vs. 6.37 ± 0.15%) but did not affect milk fat yield (average of 1.19 ± 0.09 kg/d) or energy-corrected milk yield (average of 27.2 ± 1.99 kg/d). Results of the current study suggest that the HS diet had a greater metabolizable energy and NEL content, increased partitioning of N toward milk secretion and away from urinary excretion, and may have increased partitioning of energy toward tissue energy deposited as fat.

Increasing the concentration of linolenic acid in diets fed to Jersey cows in late lactation does not affect methane production.

Although the inclusion of fat has reduced methane production in ruminants, relatively little research has been conducted comparing the effects of source and profile of fatty acids on methane production in lactating dairy cows. A study using 8 multiparous (325 ± 17 DIM; mean ± SD) lactating Jersey cows was conducted to determine effects of feeding canola meal and lard versus extruded byproduct containing flaxseed as a high-C18:3 fat source on methane production and diet digestibility in late-lactation dairy cows. A crossover design with 32-d periods (28-d adaptation and 4-d collections) was used to compare 2 different fat sources. Diets contained approximately 50% forage mixture of corn silage, alfalfa hay, and brome hay; the concentrate mixture changed between diets to include either (1) a conventional diet of corn, soybean meal, and canola meal with lard (control) or (2) a conventional diet of corn and soybean meal with an extruded byproduct containing flaxseed (EXF) as the fat source. Diets were balanced to decrease corn, lard, and canola meal and replace them with soybean mean and EXF to increase the concentration of C18:3 (0.14 vs. 1.20% of DM). Methane production was measured using headbox-style indirect calorimeters. Cattle were restricted to 95% ad libitum feed intake during collections. Milk production (17.4 ± 1.04 kg/d) and dry matter intake (15.4 ± 0.71 kg/d) were similar among treatments. Milk fat (5.88 ± 0.25%) and protein (4.08 ± 0.14%) were not affected by treatment. For methane production, no difference was observed for total production (352.0 vs. 349.8 ± 16.43 L/d for control vs. EXF, respectively). Methane production per unit of dry matter intake was not affected and averaged 23.1 ± 0.57 L/kg. Similarly, methane production per unit of energy-corrected milk was not affected by fat source and averaged 15.5 ± 0.68 L/kg. Heat production was similar, averaging 21.1 ± 1.02 Mcal/d. Digestibility of organic matter, neutral detergent fiber, and crude protein was not affected by diet and averaged 69.9, 53.6, and 73.3%, respectively. Results indicated that increasing C18:3 may not affect methane production or digestibility of the diet in lactating dairy cows.

Reducing methane production with corn oil and calcium sulfate: Responses on whole-animal energy and nitrogen balance in dairy cattle.

The addition of fat and calcium sulfate to diets fed to ruminants has resulted in a reduction in methane production, but the effects on energy balance have not been studied. A study using indirect calorimetry and 16 multiparous (8 Holstein and 8 Jersey; 78 ± 15 d in milk; mean ± standard deviation) lactating dairy cows was conducted to determine how mitigating methane production by adding corn oil or calcium sulfate to diets containing reduced-fat distillers grains affects energy and nitrogen balance. A replicated 4 × 4 Latin square design with 35-d periods (28 d of adaption and 4 d of collections) was used to compare 4 different dietary treatments. Treatments were composed of a control (CON) diet, which did not contain reduced-fat distillers grain and solubles (DDGS), and treatment diets containing 20% (dry matter basis) DDGS (DG), 20% DDGS with 1.38% (dry matter basis) added corn oil (CO), and 20% DDGS with 0.93% (dry matter basis) added calcium sulfate (CaS). Compared with CON, dry matter intake was not affected by treatment, averaging 29.6 ± 0.67 kg/d. Milk production was increased for diets containing DDGS compared with CON (26.3 vs. 27.8 ± 0.47 kg/d for CON vs. DDGS, respectively), likely supported by increased energy intake. Compared with CON, energy-corrected milk was greater in DG and CO (30.1 vs. 31.4, 31.7, and 31.0 ± 0.67 kg/d for CON, DG, CO, and CaS, respectively). Compared with CON, the addition of calcium sulfate and corn oil to diets containing DDGS reduced methane production per kg of dry matter intake (22.3, 19.9, and 19.6 ± 0.75 L/kg per d for CON, CO, and CaS, respectively). Similarly, methane production per kilogram of energy-corrected milk was reduced with the addition of calcium sulfate and corn oil to diets containing DDGS (14.2, 12.5, and 12.4 ± 0.50 L/kg per d for CON, CO, and CaS, respectively). Compared with CON and CaS, the intake of digestible energy was greater for DG and CO treatments (57.7, 62.1, 62.0, and 59.0 ± 1.38 Mcal/d for CON, DG, CO, and CaS, respectively). Intake of metabolizable energy was greater in all treatments containing DDGS compared with CON (50.5 vs. 54.0 ± 1.08 Mcal/d for CON vs. DDGS, respectively). Net balance (milk plus tissue energy) per unit of dry matter was greater in CO (containing DDGS and oil) than CON (1.55 vs. 1.35 ± 0.06 Mcal/kg for CO vs. CON, respectively). Tissue energy was greater in DG and CO compared with CON (6.08, 7.04, and 3.16 ± 0.99 Mcal/d for DG, CO, and CON, respectively. Results of this study suggest that the addition of oil and calcium sulfate to diets containing DDGS may be a viable option to reduce methane production and in the case of oil also improve net energy balance in lactating dairy cows.

Use of indirect calorimetry to evaluate utilization of energy in lactating Jersey dairy cattle consuming common coproducts.

The use of coproducts as an alternative feed source is a common practice when formulating dairy rations. A study using 12 multiparous (79 ± 16 d in milk; mean ± standard deviation) lactating Jersey cows was conducted over 5 mo to evaluate the effects of dried distillers grains with solubles (DDGS) or canola meal on milk and gas production. A replicated 4 × 4 Latin square design was used to compare 4 dietary treatments. Treatments comprised a control (CON) containing no coproducts, a treatment diet containing 10% (dry matter basis) low-fat DDGS (LFDG), a treatment diet containing 10% high-fat DDGS (HFDG), and a 10% canola meal (CM) treatment. The crude fat content of the LFDG, HFDG, and CM treatments was 6.05 ± 0.379, 10.0 ± 0.134, and 3.46 ± 0.085%, respectively. Coproducts were included in partial replacement for corn and soybean meal. Indirect headbox-style calorimeters were used to estimate heat production. Dry matter intake and milk yield were similar between all treatments, averaging 17.4 ± 0.56 kg/d and 24.0 ± 0.80 kg, respectively. Milk urea N was affected by treatment and was highest in CON (20.6 mg/dL; 18.0, 19.9, and 18.1 ± 0.62 mg/dL in LFDG, CM, and HFDG, respectively). Heat production per unit of metabolic body weight tended to be affected by treatment and was lowest for CON, and diets containing coproducts were not different (192, 200, 215, and 204 ± 5.91 kcal/kg of metabolic body weight for CON, LFDG, CM, and HFDG, respectively). The concentration of metabolizable energy was affected by dietary treatment; specifically, HFDG did not differ from CON but was greater than LFDG and CM (2.58, 2.46, 2.29, and 2.27 ± 0.09 Mcal/kg for HFDG, CON, LFDG, and CM, respectively). The concentration of net energy balance (milk plus tissue) tended to be affected by dietary treatment; HFDG did not differ from either CON or LFDG, but it was higher than CM (1.38, 1.36, 1.14, and 1.06 ± 0.11 Mcal/kg for HFDG, CON, LFDG, and CM, respectively). Results of this study indicate that milk production and dry matter intake were not affected by feeding common coproducts and that differences may result in whole-animal energy use; fat content of DDGS is a major factor affecting this.

Energy balance and diurnal variation in methane production as affected by feeding frequency in Jersey cows in late lactation.

Methane (CH4) production of ruminants typically increases with increased dry matter intake (DMI). However, few studies have observed the effects of feeding multiple times a day and its effects on diurnal variation in CH4 production and energy balance in late-lactation dairy cattle. A study using headbox-style indirect calorimetry and 12 multiparous (225 ± 16.2 d in milk; mean ± SD) lactating Jersey cows was conducted to determine the effects of feeding twice daily on diurnal variation in CH4 production and total energy balance. A crossover design with 14-d periods (10 d of adaption and 4 d of collection) was used to compare 2 treatments. Treatments consisted of either once a day feeding (1×; 100% of feed given at 1000 h) or twice a day feeding (2×; 50% of feed given at 1000 h and the final 50% at 2000 h) with a common diet fed in both treatments. Dry matter intake was not different between treatments, with a mean of 16.9 ± 0.88 kg/d. Once a day feeding tended to have greater milk yield compared with twice a day feeding (21.2 vs. 20.4 ± 1.59 kg/d, respectively). Milk fat and milk protein percentage were not different, with means of 6.18 ± 0.20% and 3.98 ± 0.08%, respectively. Total CH4 production did not differ between treatments, with a mean of 402.1 ± 20.8 L/d. Similarly, CH4 per unit of milk yield and DMI was not different between treatments, with means of 20.5 ± 1.81 and 23.8 ± 1.21 L/kg, respectively. Feeding frequency did not affect diurnal variation of hourly CH4 production, with a mean of 17.1 ± 0.74 L/h. A trend was observed for a treatment × hour interaction. Methane production per hour increased after the second feeding for cattle fed twice versus once daily. Gross energy, digestible energy, metabolizable energy, and balance (milk plus tissue) per kilogram of DMI did not differ by feeding frequency, with means of 4.41 ± 0.01, 3.05 ± 0.03, 2.63 ± 0.03, and 1.32 ± 0.08 Mcal/kg of DM, respectively. Metabolizable energy for maintenance was 146 kcal/kg of metabolic body weight, with an efficiency of converting metabolizable energy to net energy balance (milk plus tissue) of 76%. Nitrogen balance did not differ among treatments, with a mean balance of 17.3 ± 13.0 g/d. Therefore, total CH4 production and energy maintenance were not affected by feeding frequency. However, CH4 was variable throughout the day, and caution should be exercised when collecting CH4 samples at a limited number of time points because this may under- or overestimate total production.

The influence of fat and hemicellulose on methane production and energy utilization in lactating Jersey cattle.

Feeding fat to lactating dairy cows may reduce methane production. Relative to cellulose, fermentation of hemicellulose is believed to result in less methane; however, these factors have not been studied simultaneously. Eight multiparous, lactating Jersey cows averaging (±SD) 98 ± 30.8 d in milk and body weight of 439.3 ± 56.7 kg were used in a twice-replicated 4 × 4 Latin square to determine the effects of fat and hemicellulose on energy utilization and methane production using a headbox-type indirect calorimetry method. To manipulate the concentration of fat, porcine tallow was included at either 0 or 2% of the diet dry matter. The concentration of hemicellulose was adjusted by manipulating the inclusion rate of corn silage, alfalfa hay, and soybean hulls resulting in either 11.3 or 12.7% hemicellulose (dry matter basis). The resulting factorial arrangement of treatments were low fat low hemicellulose (LFLH), low fat high hemicellulose (LFHH), high fat low hemicellulose (HFLH), and high fat high hemicellulose (HFHH). Neither fat nor hemicellulose affected dry matter intake, averaging 16.2 ± 1.18 kg/d across treatments. Likewise, treatments did not affect milk production, averaging 23.0 ± 1.72 kg/d, or energy-corrected milk, averaging 30.1 ± 2.41 kg/d. The inclusion of fat tended to reduce methane produced per kilogram of dry matter intake from 24.9 to 23.1 ± 1.59 L/kg, whereas hemicellulose had no effect. Increasing hemicellulose increased neutral detergent fiber (NDF) digestibility from 43.0 to 51.1 ± 2.35%. Similarly, increasing hemicellulose concentration increased total intake of digestible NDF from 6.62 to 8.42 ± 0.89 kg/d, whereas fat had no effect. Methane per unit of digested NDF tended to decrease from 64.8 to 49.2 ± 9.60 L/kg with increasing hemicellulose, whereas fat had no effect. An interaction between hemicellulose and fat content on net energy balance (milk plus tissue energy) was observed. Specifically, increasing hemicellulose in low-fat diets tended to increase net energy balance, but this was not observed in high-fat diets. These results confirm that methane production may be reduced with the inclusion of fat, whereas energy utilization of lactating dairy cows is improved by increasing hemicellulose in low-fat diets.

Microarray analysis of subcutaneous adipose tissue from mature cows with divergent body weight gain after feed restriction and realimentation.

Body weight response to periods of feed restriction and realimentation is critical and relevant to the agricultural industry. The purpose of this study was to evaluate differentially expressed genes identified in subcutaneous adipose tissue collected from cows divergent in body weight (BW) gain after feed restriction and realimentation. We compared adipose samples from cows with greater gain based on average daily gain (ADG) during realimentation with samples from cows with lesser gain. Specifically, there were four comparisons including two comparing the high and low gain animals across each feeding period (feed restriction and realimentation) and two that compared differences in feed restriction and realimentation across high or low gain classifications. Using microarray analysis, we provide a set of differentially expressed genes identified between the high and low gain at both periods of nutrient restriction and realimentation. These data identify multiple differentially expressed genes between these two phenotypes across both nutritional environments.

The effects of monensin in diets fed to finishing beef steers and heifers on growth performance and fecal shedding of Escherichia coli O157:H7.

Two experiments were conducted to study the effects of monensin dose on growth performance and O157:H7 shedding in finishing beef cattle. In Exp. 1, 198 heifers (298 ± 1.1 kg BW) were allocated to 1 of 2 treatments consisting of 1) 200 mg/heifer daily of monensin and 2) 400 mg/heifer daily of monensin and fed for 151 d. In Exp. 2, 199 steers (430 ± 1.9 kg BW) were stratified by BW and allocated to 1 of 2 treatments consisting of 1) 0 mg/steer daily of monensin and 2) 400 mg/steer daily of monensin and fed for 128 d. For both experiments, there were 4 pen replicates per treatment. For Exp. 1 and Exp. 2, the model included the fixed effect of treatment for growth performance measures and the fixed effects of treatment, time, and treatment × time interaction, respectively, for O157:H7 shedding. In Exp. 1, final BW was 1.9% greater for heifers fed 400 mg/d monensin than for heifers fed 200 mg/d monensin ( = 0.05). Furthermore, ADG was 4.9% greater ( = 0.05) and G:F was 3.1% greater ( = 0.04) when the heifers were fed 400 mg/d monensin vs. 200 mg/d monensin. Pen prevalence for O157:H7 ( = 0.96) and the percentage of animals in the pen shedding O157:H7 at enumerable levels ( = 0.82) did not differ between heifers fed 200 mg/d monensin and heifers fed 400 mg/d monensin over the 4 sampling periods. For Exp. 2, steers fed the supplement containing monensin had a 1.9% greater final BW ( = 0.04) and a 5.2% greater ADG ( = 0.02) than steers fed a control supplement without monensin. No differences in DMI or G:F were noted across the treatments ( ≥ 0.14). O157:H7 percentage of enumerable cattle within the pen was greater for the steers fed monensin than the control steers not fed monensin than the control steers not fed monensin ( = 0.02) over the 4 sampling periods. However, the percentage of animals in the pen shedding O157:H7 (prevalence positive) did not differ between treatments ( = 0.18), nor did the average fecal counts ( = 0.45). In conclusion, feeding a higher dose (400 mg/d) of monensin improved final BW and ADG compared with a low dose of monensin or a no-monensin control in steers and heifers across multiple years. The percentage of animals shedding O157:H7 at enumerable levels was greater for steers fed the monensin supplement than for steers fed the control supplement, yet the presence of monensin, irrespective of the dose, did not affect the percentage of animals in the pen shedding O157:H7.

Hourly methane production in finishing steers fed at different levels of dry matter intake.

Methane (CH) loss from finishing cattle is important as it represents an energy loss that could be used for maintenance and growth, and CH is a greenhouse gas with a global warming potential 21 to 25 times that of CO. Our objectives were to determine hourly CH production from growing cattle fed diets differing in corn processing method (dry rolling or steam flaking) and wet distillers grains with solubles (WDGS) inclusion rate. Eight steers (195 kg ± 2.3 in Exp. 1 and 322 kg ± 3.7 in Exp. 2) were fed the following diets: 1) steam-flaked corn (SFC)-based diet with 0% WDGS (SFC-0); 2) SFC-based diet with 15% WDGS (SFC-15); 3) SFC-based diet with 30% WDGS (SFC-30); 4) SFC-based diet with 45% WDGS (SFC-45); 5) Dry-rolled corn DRC)-based diet with 0% WDGS (DRC-0); and 6) DRC-based diet with 30% WDGS (DRC-30). All hourly CH data were analyzed using the MIXED procedure of SAS. Individual animal was the experimental unit. The model included the fixed effect of h, diet, and the h × diet interaction. Hourly differences in CH were analyzed using repeated measures. There were numerous h × diet interactions and thus simple-effect means are presented. In steers fed DRC-0 or DRC-30 at 2-times maintenance, the greatest hourly CH emissions occur 6 h after feeding ( < 0.01) with a secondary peak between 10 and 11 h after feeding ( < 0.01). For cattle fed SFC-0, SFC-15, SFC-30, and SFC-45 at 2-times maintenance, all diets had peak CH emissions 5 and 6 h after feeding ( < 0.01), with a secondary CH peak for SFC-45 nine to 11 h after feeding ( < 0.01). Cattle fed all diets at a maintenance level of intake exhibited 1 peak in hourly CH production between 3 and 6 h after feeding ( < 0.01). All steers fed SFC-30 and SFC-45 had sustained CH production over several hours, irrespective of intake level. Steers fed SFC-45 produced more CH beginning 4 h after feeding ( < 0.01) and produced a greater amount of CH than any other treatment ( < 0.01). Methane production generally peaked 6 h after feeding irrespective of intake level or diet type. Additionally, when fed above a maintenance level of intake, a secondary peak in CH production was observed 9 to 11 h after feeding, and steers fed at a maintenance level of intake had only 1 peak in CH production in a 23-h period.

Effects of zilpaterol hydrochloride on methane production, total body oxygen consumption, and blood metabolites in finishing beef steers.

An indirect calorimetry experiment was conducted to determine the effects of feeding zilpaterol hydrochloride (ZH) for 20 d on total body oxygen consumption, respiratory quotient, methane production, and blood metabolites in finishing beef steers. Sixteen Angus steers (initial BW = 555 ± 12.7 kg) were individually fed at ad libitum intake and used in a completely randomized design. The model included the fixed effects of dietary treatment, day, and treatment × day. Dry matter intake did not differ between the treatments ( = 0.89), but was greater on d 0 than any other day ( < 0.01). Oxygen consumption was not different between treatments ( = 0.79), but was different across day ( < 0.01) on d 7, 14, 21, and 28. Respiratory quotient was less for cattle fed ZH than control ( < 0.01), and also different across day ( < 0.01), being greater on d 7, 21, and 28 than d 3 or 21. Methane production (L/kg of DMI) was greater for steers fed the control vs. the ZH diet ( < 0.01), and it also differed by day ( < 0.01), being greater on d 21 and 28 than d 0, 3, 7, and 14. Nonesterified fatty acids were not different across treatments ( = 0.82), and there was no effect of treatment on ß-hydroxybutyrate concentration ( = 0.45). Whole blood glucose concentrations were not affected by feeding ZH in this experiment ( = 0.76); however, lactate concentrations were reduced by feeding ZH ( = 0.03). Additionally, there was no treatment effect on ɑ-amino-N, blood glutamate, or glutamine ( ≥ 0.16). Plasma NH was not affected by ZH ( = 0.07), but plasma urea nitrogen was reduced by ZH ( < 0.01). Urinary creatinine was increased by steers receiving ZH ( = 0.01), and urine 3-methylhistidine (3-MH) concentrations were normalized to creatinine, the 3-MH:creatinine ratio decreased from d 0 to d 3 in steers fed ZH, and remained less than control steers until d 28. These data provide insight into how ß-agonists alter nutrient partitioning and improve the efficiency of tissue accretion, mainly through decreased muscle protein turnover and altering the catabolic fuel for peripheral tissues.

Genetic variance and covariance and breed differences for feed intake and average daily gain to improve feed efficiency in growing cattle.

Feed costs are a major economic expense in finishing and developing cattle; however, collection of feed intake data is costly. Examining relationships among measures of growth and intake, including breed differences, could facilitate selection for efficient cattle. Objectives of this study were to estimate genetic parameters for growth and intake traits and compare indices for feed efficiency to accelerate selection response. On-test ADFI and on-test ADG (TESTADG) and postweaning ADG (PWADG) records for 5,606 finishing steers and growing heifers were collected at the U.S. Meat Animal Research Center in Clay Center, NE. On-test ADFI and ADG data were recorded over testing periods that ranged from 62 to 148 d. Individual quadratic regressions were fitted for BW on time, and TESTADG was predicted from the resulting equations. We included PWADG in the model to improve estimates of growth and intake parameters; PWADG was derived by dividing gain from weaning weight to yearling weight by the number of days between the weights. Genetic parameters were estimated using multiple-trait REML animal models with TESTADG, ADFI, and PWADG for both sexes as dependent variables. Fixed contemporary groups were cohorts of calves simultaneously tested, and covariates included age on test, age of dam, direct and maternal heterosis, and breed composition. Genetic correlations (SE) between steer TESTADG and ADFI, PWADG and ADFI, and TESTADG and PWADG were 0.33 (0.10), 0.59 (0.06), and 0.50 (0.09), respectively, and corresponding estimates for heifers were 0.66 (0.073), 0.77 (0.05), and 0.88 (0.05), respectively. Indices combining EBV for ADFI with EBV for ADG were developed and evaluated. Greater improvement in feed efficiency can be expected using an unrestricted index versus a restricted index. Heterosis significantly affected each trait contributing to greater ADFI and TESTADG. Breed additive effects were estimated for ADFI, TESTADG, and the efficiency indices.

The effects of feeding increasing concentrations of corn oil on energy metabolism and nutrient balance in finishing beef steers.

The use of an added lipid is common in high-concentrate finishing diets. The objective of our experiment was to determine if feeding increasing concentrations of added dietary corn oil would decrease enteric methane production, increase the ME:DE ratio, and improve recovered energy (RE) in finishing beef steers. Four treatments were used in a replicated 4 × 4 Latin square ( = 8; initial BW = 397 kg ± 3.8). Data were analyzed using a Mixed model with the fixed effects of period and dietary treatment and random effects of square and steer within square. Treatments consisted of: (1) 0% added corn oil (Fat-0); (2) 2% added corn oil (Fat-2); (3) 4% added corn oil (Fat-4); (4) 6% added corn oil (Fat-6). Dry matter intake or GE intake did not differ across diets ( ≥ 0.39). As a proportion of GE intake, fecal energy loss, DE, and urinary energy loss did not differ by treatment ( ≥ 0.27). Additionally, methane energy produced decreased linearly as corn oil increased in the diet ( < 0.01). No differences were detected in ME loss as a proportion of GE intake ( ≥ 0.98). However, the ME:DE ratio increased linearly ( < 0.01; 93.06, 94.10, 94.64, and 95.20 for Fat-0, Fat-2, Fat-4, and Fat-6, respectively) as corn oil inclusion increased in the diet. No differences in RE or heat production as a proportion of GE intake were noted ( ≥ 0.59) and dry matter digestibility did not differ across diets ( ≥ 0.36). Digestibility of NDF as a proportion of intake responded quadratically increasing from 0% corn to 4% corn oil and decreasing thereafter ( = 0.02). Furthermore, ether extract digestibility as a proportion of intake responded quadratically, increasing from 0% to 4% corn oil inclusion before reaching a plateau ( < 0.01). As a proportion of GE intake, RE as protein decreased linearly as corn oil was increased in the diet ( < 0.01). As a proportion of total energy retained, RE as protein decreased when corn oil increased from 0% to 6% of diet DM ( < 0.01). Similarly, RE as fat and carbohydrate as a proportion of GE intake increased linearly as corn oil increased in the diet ( = 0.05). From these data, we interpret that adding dietary fat decreases enteric methane production and increases the ME:DE ratio, in addition to increasing the amount of energy retained as fat and carbohydrate.

The effects of backgrounding system on growing and finishing performance and carcass characteristics of beef steers.

The objective of this 2-yr study was to evaluate growing and finishing performance as well as carcass characteristics of spring-born steers backgrounded on 3 different systems, using feedstuffs readily available in the Midwest: 1) grazing corn residue and being supplemented with dried distillers plus solubles at 2.68 kg DM/steer 6 d/wk (RESIDUE), 2) grazing a late summer-planted oat-brassica forage mix (CCROP), or 3) being fed a corn silage-based diet in a drylot (DRYLOT). Steers ( = 715) were stratified by BW (278 kg ± 23 in yr 1 and 291 kg ± 91 in yr 2) and assigned to treatment and replicate (4 replications per treatment per yr). Steers assigned to DRYLOT were fed a corn silage-based diet for 54 d in yr 1 and 52 d in yr 2 before being transitioned to the finishing diet. Steers assigned to RESIDUE and those assigned to CCROP grazed 65 d in yr 1 and 66 d in yr 2 and then were fed a corn silage-based diet for 21 d in yr 1 and 33 d in yr 2 before being transitioned to the finishing diet. During backgrounding, the ADG (SEM 0.022) of steers assigned to DRYLOT (1.48 kg/d) was greater ( < 0.01) than that of steers assigned to both CCROP (1.05 kg/d) and RESIDUE (0.87 kg/d) and ADG of steers assigned to CCROP was greater ( < 0.01) than that of steers assigned to RESIDUE. At the start of the finishing period, BW of steers assigned to CCROP (381 kg) was greater ( < 0.01, SEM 2.5) than that of steers assigned to DRYLOT (361 kg) and RESIDUE (366 kg). The finishing period lasted 160 d for all treatments. Both 12th-rib fat ( = 0.89) and calculated yield grade ( = 0.39) did not differ among treatments. Finishing G:F of steers assigned to DRYLOT (0.162 kg/kg) was greater ( < 0.01, SEM 0.0015) than that of steers assigned to RESIDUE (0.153 kg/kg) and CCROP (0.153 kg/kg), which did not differ ( = 0.79). In yr 1, HCW of steers assigned to CCROP (402 kg) was greater ( < 0.01, SEM 2.1) than that of steers assigned to both RESIDUE (389 kg) and DRYLOT (391 kg), which did not differ ( = 0.40). This difference in HCW is most likely a result of differences in BW at the start of the finishing phase in yr 1. However in yr 2, HCW of steers assigned to CCROP (400 kg) and RESIDUE (397 kg) did not differ ( = 0.26, SEM 2.1) but were greater ( < 0.01) than that of steers assigned to DRYLOT (367 kg), despite the fact that steers assigned to RESIDUE entered the finishing phase at a lighter BW than steers assigned to CCROP. Marbling was greater ( = 0.01, SEM 3.9) for steers assigned to DRYLOT (429) than for steers assigned to RESIDUE (414), although steers assigned to CCROP (424) were not different ( ≥ 0.10) from steers assigned to DRYLOT or RESIDUE. When cost and price scenarios from the last 5 yr were conducted, no treatment appeared to be consistently superior in terms of cost of gain or net return. Therefore, all 3 systems appear to be viable options for producers.

The effects of zilpaterol hydrochloride and shade on blood metabolites of finishing beef steers.

The effects of feeding zilpaterol hydrochloride (ZH) and shade were evaluated on blood metabolites in finishing beef steers ( = 480). Cattle were fed 0 or 8.33 mg/kg of diet DM ZH for 21 d with a 3- or 4-d withdrawal before harvest and were housed in open or shaded pens. Blood samples were collected the day before ZH was fed and on the day the cattle were shipped to the commercial abattoir. Lactate concentration was not different between cattle fed ZH in open or shaded pens ( = 0.12). Nonetheless, a tendency for a diet × time interaction was detected for lactate concentration ( = 0.09), in which it was greater in cattle fed the control diet in open pens before being fed ZH. Cortisol concentration was less before and after ZH was fed ( = 0.01). Glucose was greater for cattle fed the control diet than cattle fed ZH for 21 d ( = 0.03). Cattle fed in open vs. shaded pens did not differ in glucose concentration ( = 0.12), whereas glucose concentrations were greater before ZH was fed than after ( = 0.02). In contrast, plasma urea nitrogen (PUN) concentration was not different in response to diet ( = 0.24), housing type ( = 0.65), or before vs. after being fed ZH ( = 0.60). Lactate concentrations were not different across diet or shade treatments before ZH was fed, whereas after ZH, lactate concentrations were greater in control cattle than cattle fed ZH. Additionally, cortisol was less after feeding ZH. Glucose was greater before than after feeding ZH.

Changes in acyl and total ghrelin concentrations and their association with dry matter intake, average daily gain, and feed efficiency of finishing beef steers and heifers.

Ghrelin is a peptide hormone produced in the gut that is implicated in signaling appetite and regulating dry matter intake (DMI). The objective of this experiment was to determine the change in acyl ghrelin, total ghrelin, and the ghrelin ratio (acyl ghrelin/total ghrelin) over an 84-d DMI and average daily BW gain (ADG) measurement period and to determine the association of those ghrelin measurements with DMI, ADG, ADG:DMI ratio (G:F), and residual feed intake in finishing beef steers and heifers. Blood samples were collected on day 0 and day 83 before feeding and between 0730 h and 1130 h. Samples were analyzed for acyl and total ghrelin using commercially available RIA. DMI in steers was greater during the last 35-d period of the experiment compared with the first 35 d (P < 0.01) and was greater than heifers regardless of period (P < 0.01). Steers had greater acyl ghrelin concentrations on day 0 than heifers, but concentrations decreased by day 83 to equal concentrations in heifers (P < 0.01). Total ghrelin concentrations were lower on day 0 in heifers but increased by day 83 and did not differ from steers on day 83 (P < 0.01). A mixed model analysis was used to determine the association of ghrelin concentrations and ratio with production traits, independent of breed and sire effects. There was an interaction of day 0 acyl ghrelin concentrations with time of sample collection for 84-d DMI (P < 0.01), ADG (P < 0.01), and G:F (P = 0.09), indicating a general positive association of acyl ghrelin with production traits, but the association weakened as time of sample collection increased. The mean ghrelin ratio tended (P = 0.08) to be positively associated with DMI in the last 35-d period. The ghrelin ratio on day 0 interacted with time of sample collection for ADG and G:F (P < 0.05), indicating an overall positive association of the ghrelin ratio with ADG and G:F. Results indicate that ghrelin is associated with DMI, ADG, and feed efficiency of finishing beef cattle, and data lend more evidence that ghrelin is involved in appetite regulation of ad libitum fed cattle.

Effects of dietary protein concentration and ractopamine hydrochloride on performance and carcass characteristics of finishing beef steers.

Ractopamine hydrochloride (RAC) is used in the feedlot industry to increase daily gain, improve feed efficiency, and increase HCW. However, little work has been done to determine whether additional protein is needed in the diet to maximize the benefit of RAC in beef cattle. Objectives of our experiment were to determine if feeding additional CP in conjunction with RAC would improve animal performance and carcass characteristics. Therefore, an experiment was conducted using finishing diets containing 13.5 or 17.5% CP with 0 or 300 mg of RAC for 30 to 33 d at the end of the finishing period. Beef steers ( = 438; 387.8 ± 1.9 kg initial BW) were randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement (16 pens total, 4 pens/treatment). No interactions between feeding RAC and CP level were detected ( > 0.19) for animal performance or carcass traits. Final BW did not differ among treatment ( = 0.37); however, final BW had a tendency to be 2% greater ( = 0.07) when the 13.5% CP diet was fed. Dry matter intake was not different between steers fed 0 or 300 mg/d of RAC ( = 0.20), yet DMI was 12% greater for cattle fed the 13.5% CP compared with steers fed the 17.5% CP diet ( < 0.01). Daily gain did not differ for cattle fed different levels of RAC or CP ( > 0.16). The G:F was 3.6% greater for cattle fed 300 vs. 0 mg/d of RAC ( = 0.04). The G:F was 8.7% greater for cattle fed the 17.5% diet vs. the 13.5% CP diet ( < 0.01), which can be attributed to the decreased DMI for cattle fed the 17.5% CP diet. Hot carcass weight was not different for steers fed 0 or 300 mg/d of RAC ( = 0.36) or for steers fed the 13.5% diet vs. 17.5% CP diet ( = 0.93). Dressing percentage was 1.5% greater for cattle fed 300 vs. 0 mg/d of RAC ( = 0.05) but was not different between cattle fed the different CP levels in the diet ( = 0.16). Longissimus area, adjusted 12th-rib fat, and marbling score did not differ across RAC or CP treatments ( > 0.26). Additionally, no differences in USDA yield grade or percentage of cattle grading USDA Choice were detected for RAC or CP treatments ( > 0.26), which also supports the idea that quality grade of cattle fed RAC at the same level of fatness is not impacted. Our data indicate excess protein did not enhance the response to RAC, and furthermore, the improved performance from RAC reported by others was not observed other than a small increase in G:F.

Differential gene expression in the duodenum, jejunum and ileum among crossbred beef steers with divergent gain and feed intake phenotypes.

Small intestine mass and cellularity were previously associated with cattle feed efficiency. The small intestine is responsible for the digestion of nutrients and absorption of fatty acids, amino acids and carbohydrates, and it contributes to the overall feed efficiency of cattle. The objective of this study was to evaluate transcriptome differences among the small intestine from cattle with divergent gain and feed intake. Animals most divergent from the bivariate mean in each of the four phenotypic Cartesian quadrants for gain × intake were selected, and the transcriptomes of duodenum, jejunum and ileum were evaluated. Gene expression analyses were performed comparing high gain vs. low gain animals, high intake vs. low intake animals and each of the phenotypic quadrants to all other groups. Genes differentially expressed within the high gain-low intake and low gain-high intake groups of animals included those involved in immune function and inflammation in all small intestine sections. The high gain-high intake group differed from the high gain-low intake group by immune response genes in all sections of the small intestine. In all sections of small intestine, animals with low gain-low intake displayed greater abundance of heat-shock genes compared to other groups. Several over-represented pathways were identified. These include the antigen-processing/presentation pathway in high gain animals and PPAR signaling, starch/sucrose metabolism, retinol metabolism and melatonin degradation pathways in the high intake animals. Genes with functions in immune response, inflammation, stress response, influenza pathogenesis and melatonin degradation pathways may have a relationship with gain and intake in beef steers.

Leptin concentrations in finishing beef steers and heifers and their association with dry matter intake, average daily gain, feed efficiency, and body composition.

The objective of this experiment was to determine the association of circulating plasma leptin concentrations with production and body composition measures of finishing beef steers and heifers and to determine if multiple sampling time points improve the associations of plasma leptin concentrations with production and body composition traits. Individual dry matter intake (DMI) and ADG were determined for 84 d using steers and heifers (n = 127 steers and n = 109 heifers). Blood was collected on day 0, day 42, and day 83 for determination of plasma leptin concentrations. Leptin concentrations were greater in heifers than those in steers on day 0 (P < 0.001 for sex by day interaction), and leptin concentrations increased in both sexes but were not different from each other on day 83. Leptin concentrations at all 3 time points and the mean were shown to be positively associated with DMI (P ≤ 0.006), whereas the mean leptin concentration explaining 8.3% of the variance of DMI. Concentrations of leptin at day 42, day 83, and the mean of all 3 time points were positively associated with ADG (P ≤ 0.011). Mean leptin concentration was negatively associated with gain:feed ratio and positively associated with residual feed intake (RFI), indicating that more efficient cattle had lower leptin concentrations. However, leptin concentrations explained very little of the variation in residual feed intake (≤ 3.2% of the variance). Leptin concentrations were positively associated with body fat measured by ultrasonography at the 12th rib and over the rump (P < 0.001), with the mean leptin concentration explaining 21.9% and 12.7% of the variance in 12th rib and rump fat thickness, respectively. The same trend was observed with carcass composition where leptin concentrations were positively associated with 12th rib fat thickness, USDA-calculated yield grade (YG), and marbling score (P ≤ 0.006) and mean leptin concentration explained 16.8, 18.2, and 4.6% of the variance for 12th rib fat thickness, yield grade, and marbling score, respectively. Given these and previous results, it appears that leptin physiology could be a candidate for mechanisms that contribute to feed intake and feed efficiency variation in beef cattle.

Relationship of glucocorticoids and hematological measures with feed intake, growth, and efficiency of finishing beef cattle.

The objective of this experiment was to determine the association of glucocorticoids and markers for immune status in finishing beef steers and heifers with DMI, growth, and efficiency. Steers ( = 127) and heifers ( = 109) were individually fed a finishing ration for 84 d with BW measured every 21 d. Blood samples were collected via jugular venipuncture for metabolite (glucose and lactate) and cortisol analysis and rectal grab samples of feces were collected for corticosterone analysis on d 83 of the experiment. Plasma cortisol was not correlated to DMI ( = -0.08, > 0.05) or fractional DMI (g DMI/kg BW; = -0.03, > 0.05) but was negatively correlated with ADG ( = -0.17, < 0.01) and G:F ( = -0.20, < 0.01) and positively correlated to residual feed intake (RFI; = 0.14, < 0.05). Fecal corticosterone was positively correlated to fractional DMI ( = 0.15, < 0.05) and RFI ( = 0.23, < 0.01) and negatively correlated to G:F ( = -0.18, < 0.01). Using a mixed model analysis, none of the metabolites or hormones were associated with DMI ( > 0.05) but fecal corticosterone was positively associated with fractional DMI only in heifers ( = 0.04). Plasma lactate ( < 0.01) was and plasma cortisol ( < 0.10) tended to be negatively associated with ADG. Plasma cortisol ( < 0.05) and fecal corticosterone tended ( < 0.10) to be negatively associated with G:F. Fecal corticosterone was positively associated with RFI in heifers ( < 0.04). In a mixed model analysis, total leukocyte count was positively associated with ADG ( < 0.04) and tended to be positively associated with G:F ( < 0.06). Among leukocyte subtypes, neutrophil count was positively associated with ADG in steers ( < 0.02) and monocytes were positively associated with ADG in heifers ( < 0.03). Lymphocyte counts (LY) in steers were negatively associated with DMI ( = 0.03) and fractional DMI ( < 0.03). In heifers, LY tended to be positively associated with DMI ( < 0.09) and fractional DMI ( < 0.06). Lymphocyte count was also positively associated with ADG ( < 0.01) and G:F ( = 0.05) in heifers. The association of production traits with immune status seems to be different between steers and heifers. There was a stronger relationship of cortisol than fecal corticosterone to feed efficiency measures, suggesting that cortisol concentrations could be a better marker for feed efficiency traits than fecal corticosterone concentrations.