Alternative parameterizations of relatedness in whole genome association analysis of pre-weaning traits of Nelore-Angus calves.

Gestation length, birth weight, and weaning weight of F2 Nelore-Angus calves (n = 737) with designed extensive full-sibling and half-sibling relatedness were evaluated for association with 34,957 SNP markers. In analyses of birth weight, random relatedness was modeled three ways: 1) none, 2) random animal, pedigree-based relationship matrix, or 3) random animal, genomic relationship matrix. Detected birth weight-SNP associations were 1,200, 735, and 31 for those parameterizations respectively; each additional model refinement removed associations that apparently were a result of the built-in stratification by relatedness. Subsequent analyses of gestation length and weaning weight modeled genomic relatedness; there were 40 and 26 trait-marker associations detected for those traits, respectively. Birth weight associations were on BTA14 except for a single marker on BTA5. Gestation length associations included 37 SNP on BTA21, 2 on BTA27 and one on BTA3. Weaning weight associations were on BTA14 except for a single marker on BTA10. Twenty-one SNP markers on BTA14 were detected in both birth and weaning weight analyses.

Longitudinal Evaluation of Salmonella in Environmental Components and Peripheral Lymph Nodes of Fed Cattle From Weaning to Finish in Three Distinct Feeding Locations.

Salmonella prevalence in bovine lymph nodes (LNs) varies due to seasonality, geographic location, and feedyard environment. The objectives of this study were to (1) establish prevalence rates of Salmonella in environmental components (trough water, pen soil, individual feed ingredients, prepared rations, and fecal samples) and LNs from weaning to finish in three feeding locations, and (2) characterize recovered salmonellae. Calves (n = 120) were raised at the Texas A&M University McGregor Research Center; in lieu of beginning the backgrounding/stocker phase, thirty weanling calves were harvested. Of the remaining ninety calves, thirty were retained at McGregor and sixty were transported to commercial feeding operations (Location A or B; thirty calves each). Locations A and B have historically produced cattle with relatively "low" and "high" rates of Salmonella-positive LNs, respectively. Ten calves per location were harvested at the conclusion of (1) the backgrounding/stocker phase, (2) 60 d on feed, and (3) 165 d on feed. On each harvest day, peripheral LNs were excised. Environmental samples were obtained from each location before and after each phase, and every 30 d during the feeding period. In line with previous work, no Salmonella-positive LNs were recovered from cattle managed at Location A. Salmonella-positive LNs (30%) and environmental components (41%) were most commonly recovered from Location B. Of 7 and 36 total serovars recovered from Salmonella-positive LN and environmental samples, respectively, Anatum was identified most frequently. Data from this study provide insight into Salmonella prevalence differences among feeding locations and the possible influence of environmental and/or management practices at each. Such information can be used to shape industry best practices to reduce Salmonella prevalence in cattle feeding operations, resulting in a decreased prevalence of Salmonella in LNs, and thus, minimizing risks to human health.

Consider the Source: The Impact of Social Mixing on Drylot Housed Steer Behavior and Productivity.

Cattle are a social species in which social mixing can induce physical and psychosocial stress; however, the impact of social mixing on cattle welfare is unknown. Two different sources of genetically similar Angus crossbred steers were transported to the same feedlot and assigned to a pen where they were either socially mixed or housed with individuals from their source herds. Social mixing did not impact average daily gains in pens, feed intake, or feed efficiency; pens of socially mixed steers were more active. Sources differed in their responses to social mixing. One source was unaffected, whereas social mixing negatively impacted productivity for the other source. Irrespective of social mixing, the sources differed in the amount of time per day they spent ruminating and drinking. Group analyses indicated that socially mixing two sources of feedlot steers did not negatively impact group productivity, yet the impacts that were observed at the individual level suggest that prior experiences may influence their ability to cope with social stress, emphasizing the importance of early-life experiences to long-term welfare and productivity. Social mixing was not universally detrimental to cattle welfare, and the source of cattle may have the greatest affect on their performance regardless of whether a social mixing event has occurred.

Systems Assessment of Beef Sustainability.

Assessment of sustainability of a system is largely a forecasting problem, in which the likelihood of system persistence must be evaluated. The use of systems thinking and systems analysis provides useful mechanisms for assessing sustainability in complex food animal production systems. Importantly, evaluation of the system also aids in the identification of variables highly correlated to persistence and ratios among stocks and outputs that can be useful for management. The complexity of the systems makes linear assessment of sustainability from gross resource use indicators tenuous, and likely to lead to false inference. Development of a framework for indicator development and assessment is critical to avoid unintended consequences of inadequate forecasts.

Effects of Tylosin, a Direct-Fed Microbial and Feedlot Pen Environment on Phenotypic Resistance among Enterococci Isolated from Beef Cattle Feces.

In two sequential replicates (n = 90 and n = 96 feedlot finisher cattle, respectively) we measured the impact of an Enterococcus faecium-based probiotic (DFM) and an altered feedlot pen environment on antimicrobial resistance among fecal enterococci in cattle fed (or, not fed) the macrolide tylosin. Diluted fecal samples were spiral-plated on plain and antibiotic-supplemented m-Enterococcus agar. In the first replicate, tylosin significantly (p < 0.05) increased the relative quantity of erythromycin-resistant enterococci. This effect was diminished in cattle fed the DFM in conjunction with tylosin, indicating a macrolide susceptible probiotic may help mitigate resistance. A similar observed effect was not statistically significant (p > 0.05) in the second replicate. Isolates were speciated and resistance phenotypes were obtained for E. faecium and E. hirae. Susceptible strains of bacteria fed as DFM may prove useful for mitigating the selective effects of antibiotic use; however, the longer-term sustainability of such an approach remains unclear.

Evaluation of Autogenous Vaccine Use in Mitigating Salmonella in Lymph Nodes from Feedlot Cattle in Texas.

ABSTRACT: Managing the presence of Salmonella in ground beef has been an ongoing challenge for the beef industry. Salmonella prevalence can vary regionally, seasonally, and within the animal, making the development of interventions difficult. The objective of this study was to assess the efficacy of an autogenous Salmonella vaccine in mitigating Salmonella in lymph nodes (LNs) of feedlot cattle. An autogenous vaccine was developed using the most common Salmonella enterica serovars (Salmonella Kentucky, Salmonella Anatum, Salmonella Muenchen, Salmonella Montevideo, and Salmonella Mbandaka) identified from cattle managed at a South Texas feedlot with historically high Salmonella prevalence. Fifty-five heifers were selected for even distribution across five groups: (i) BASE, which received no autogenous vaccinations and were harvested after the stocker stage, (ii) CNTRL, which received no autogenous vaccinations, (iii) FARM, which received autogenous vaccinations at the ranch only, (iv) SPLIT, which received autogenous vaccinations at both the ranch and feedlot, and (v) YARD, which received vaccinations at the feedlot only. One heifer each from the BASE and CNTRL groups did not complete the study. All treatment groups except BASE were harvested after reaching market weight. Left and right superficial cervical and subiliac LNs from each carcass were collected and analyzed for Salmonella presence, and positive samples were serotyped. No salmonellae were recovered from LNs derived from BASE, FARM, SPLIT, or YARD groups. Cattle in the BASE group were expected to have a low occurrence of Salmonella based on previous research. However, the percentage of Salmonella-positive animals in the CNTRL group was 20.0% (2 of 10), which is lower than expected based on historical data from the same feeding location. There could be several causes of decreased Salmonella presence in the LNs of control cattle, creating an opportunity for future investigation into the development of preharvest interventions to combat Salmonella in feedlots.

Maternal nutrient restriction in late pregnancy programs postnatal metabolism and pituitary development in beef heifers.

Maternal undernutrition during pregnancy followed by ad libitum access to nutrients during postnatal life induces postnatal metabolic disruptions in multiple species. Therefore, an experiment was conducted to evaluate postnatal growth, metabolism, and development of beef heifers exposed to late gestation maternal nutrient restriction. Pregnancies were generated via transfer of in vitro embryos produced using X-bearing sperm from a single Angus sire. Pregnant dams were randomly assigned to receive either 100% (control; n = 9) or 70% (restricted; n = 9) of their total energy requirements from gestational day 158 to parturition. From post-natal day (PND) 301 until slaughter (PND485), heifers were individually fed ad libitum in a Calan gate facility. Calves from restricted dams were lighter than controls at birth (P<0.05) through PND70 (P<0.05) with no difference in body weight from PND105 through PND485 (P>0.10). To assess pancreatic function, glucose tolerance tests were performed on PND315 and PND482 and a diet effect was seen with glucose area under the curve being greater (P<0.05) in calves born to restricted dams compared to controls. At slaughter, total internal fat was greater (P<0.05) in heifers born to restricted dams, while whole pituitary weight was lighter (P<0.05). Heifers from restricted dams had fewer growth hormone-positive cells (somatotrophs) compared to controls (P<0.05). Results demonstrate an impaired ability to clear peripheral glucose in heifers born to restricted dams leading to increased deposition of internal fat. A reduction in the number of somatotrophs may contribute to the adipogenic phenotype of heifers born to restricted dams due to growth hormone's known anabolic roles in growth, lipolysis, and pancreatic islet function.

Effects of monensin inclusion and level of intake in limit-feeding strategies for beef cows.

A study was conducted to evaluate the effects of intake management and ionophore inclusion on diet utilization under managed intake conditions in beef cattle. Two experiments utilized common diets fed at 120% (H) or 80% (L) of maintenance with either 0 or 200 mg/d monensin in a factorial arrangement. Forty cows were fed for 56 d (Exp. 1) to evaluate effects on diet utilization and energy retention; diets were fed to 16 ruminally cannulated steers (Exp. 2) to determine effects on digestion, energy value, and ruminal fermentation. Cows fed H had greater body weight (BW) gain (P < 0.01) and retained energy (RE; P < 0.01), although estimated heat production was also greater (P < 0.01). Monensin had limited effects on overall BW gain (P = 0.97). Monensin had no effect on RE (P = 0.94) or calculated heat energy (HE; P = 0.53) despite effects on diet utilization observed in steers. In steers, L increased (P < 0.01) digestion of dry matter, organic matter, acid detergent fiber, and gross energy (GE) and reduced (P < 0.01) passage rate; monensin did not affect digestion (P > 0.15) but did reduce passage rate (P < 0.03). Monensin lowered (P < 0.01) acetate:propionate ratio and increased (P < 0.05) ruminal pH. Monensin did not alter feed required for maintenance; however, limit-feeding reduced apparent daily maintenance requirement to 62.85 kcal/kg BW0.75, a 26% reduction from model-predicted values.

The effects of the forage-to-concentrate ratio on the conversion of digestible energy to metabolizable energy in growing beef steers.

Metabolizable energy (ME) is calculated from digestible energy (DE) using a constant conversion factor of 0.82. Methane and urine energy losses vary across diets and dry matter intake (DMI), suggesting that a static conversion factor fails to describe the biology. To quantify the effects of the forage-to-concentrate ratio (F:C) on the efficiency of conversion of DE to ME, 10 Angus steers were used in a 5 × 5 replicated Latin square. Dry-rolled corn was included in experimental diets at 0%, 22.5%, 45.0%, 67.5%, and 83.8% on a dry matter (DM) basis, resulting in a high F:C (HF:C), intermediate F:C (IF:C), equal F:C (EF:C), low F:C (LF:C), and a very low F:C (VLF:C), respectively. Each experimental period consisted of a 23-d diet adaption followed by 5 d of total fecal and urine collections and a 24-h gas exchange collection. Contrasts were used to test the linear and quadratic effects of the F:C. There was a tendency (P = 0.06) for DMI to increase linearly as F:C decreased. As a result, gross energy intake (GEI) increased linearly (P = 0.04) as F:C decreased. Fecal energy loss expressed as Mcal/d (P = 0.02) or as a proportion of GEI (P < 0.01) decreased as F:C decreased, such that DE (Mcal/d and Mcal/kg) increased linearly (P < 0.01) as F:C decreased. As a proportion of GEI, urine energy decreased linearly (P = 0.03) as F:C decreased. Methane energy loss as a proportion of GEI responded quadratically (P < 0.01), increasing from HF:C to IF:C then decreasing thereafter. The efficiency of DE to ME conversion increased quadratically (P < 0.01) as F:C decreased, ranging from 0.86 to 0.92. Heat production (Mcal) increased linearly (P < 0.04) as F:C decreased but was not different as a proportion of GEI (P ≥ 0.22). As a proportion of GEI, retained energy responded quadratically (P = 0.03), decreasing from HF:C to IF:C and increasing thereafter. DM, organic matter, and neutral detergent fiber digestibility increased linearly (P < 0.01) and starch digestibility decreased linearly (P < 0.01) as the F:C decreased. Total N retained tended to increase linearly as the proportion of concentrate increased in the diet (P = 0.09). In conclusion, the efficiency of conversion of DE to ME increased with decreasing F:C due to decreasing methane and urine energy loss. The relationship between DE and ME is not static, especially when differing F:C.

Technical note: Relationship between placentome location and gene expression in bovine pregnancy.

A novel, non-terminal surgical procedure to remove a single placentome from the pregnant ewe for gene expression and histological analyses was recently developed in our laboratory. This technique allows for evaluation of nutritional insults on placental development at more than one stage of gestation using a single animal. Early attempts to develop a similar technique in cattle were met with complications due to inaccessibility of the gravid uterine horn because of its location and mass. One alternative is to collect a placentome from the contralateral uterine horn; however, the question remains as to whether gene expression varies among placentomes based on location relative to the fetus. Pregnant heifers were maintained on forage during early gestation and later moved into pens with a Calan gate system (American Calan, Northwood, NH). On gestational day (GD) 158, five heifers were assigned to receive a hay-based diet formulated to meet 100% of NRC requirements, and five heifers were fed 70% of NRC requirements until necropsy on GD244. At necropsy, a single representative placentome was selected for analysis from the antimesometrial side: (1) of the gravid uterine horn central to the amnion, (2) over the allantois immediately adjacent to the amnion, (3) in the tip of the gravid uterine horn, and (4) in the tip of the contralateral uterine horn. Mean placentome weight was greater (P < 0.05) for locations central to the amnion and allantois compared to locations within the tips of the ipsilateral and contralateral horns, respectively. Gene expression for angiogenic factors (FGF2, ODC1, VEGFA, and FLT1), nutrient transporters (SLC7A1 and SLC2A1), and factors associated with hormone action (ESR1, IGF1, IGFBP3, CSH1, and PAG1) were unaffected (P > 0.05) by dietary treatment or location of the placentome. Results indicate that location of the placentome in relation to the fetus does not impact gene expression, enhancing the efficacy of nonterminal methodologies for sampling gene expression in placentomes.

Effects of diet type on nutrient utilization and energy balance in drylot heifers1.

Feeding cattle in intensified settings allows cow-calf producers to decrease their reliance on grazed forage and utilize alternative feedstuffs. During times of intense management, diet type may alter energy utilization. Fourteen pregnant MARC III heifers (405 ± 44 kg BW) were used in a 180 d experiment to determine effects of diet type on nutrient and energy utilization. Heifers were randomly assigned to one of two treatments, a forage diet (FOR; 2.10 Mcal metabolizable energy [ME]/kg; 95.75% forage) or a concentrate diet (CONC; 2.94 Mcal ME/kg; 71% concentrate), and individually fed to meet maintenance energy requirements (0.135 Mcal ME/kg BW0.75). The CONC diet contained dry-rolled corn, corn stalks (10.16 cm grind size), soybean meal, corn silage (approximately 45% corn grain; stored in a plastic bag), dicalcium phosphate, urea, and a premix pellet; FOR contained alfalfa hay (harvested at mid-bloom), corn silage, dicalcium phosphate, and a premix pellet. Measurements of energy intake and digestibility were measured over a 4-d period on days 116, 172, and 235 of gestation. Using portable headbox calorimeters, measurements of O2, CO2, and CH4 gases were collected over a period of 24 h. Data were analyzed in a completely randomized design with diet as fixed effect. Dry matter and organic matter digestibility were greater for CONC than FOR (P < 0.01). Intake of gross energy (GE) and digestible energy (DE) were greater for FOR (P < 0.01), but by design, ME intake was not different between treatments (P = 0.26). Energy lost as methane (% of GE intake) was not different between treatments (P = 0.49). The ratio of ME to DE was greater for CONC (86.8 vs. 82.8; P = 0.01) than FOR. Heat production relative to ME was not different between treatments (P = 0.85). Maternal tissue energy did not differ and was 1.2 Mcal/d for CONC and 0.9 Mcal/d for FOR (P = 0.73). Greater nitrogen (N) consumption was observed for FOR (192.2 g/d) than CONC (134.0 g/d; P < 0.01), and retained N was greater for FOR than CONC (P < 0.01) on days 116 and 235 of gestation. Neither concentrate-based or forage-based diets affected body condition score (P = 0.26). Heifers fed concentrate-based diets retained more energy in part because they had larger calves, but this energy was not recovered in maternal tissue.

Evaluation of net protein contribution, methane production, and net returns from beef production as duration of confinement increases in the cow-calf sector1.

Intensification of cow-calf production may provide a sustainable solution for meeting increasing beef demand in the face of diminishing resources. However, intensification with its greater reliance on cereal grains potentially decreases the upcycling of human-inedible protein into beef. A previously described model was used to evaluate cow-calf intensification on beef's ability to meet human protein requirements. Four scenarios were compared, based on a 1,000 cow herd: 1) Conventional cow-calf production system (0CON), 2) cows limit-fed in confinement for 4 mo after weaning (4CON), 3) cows limit-fed in confinement for 8 mo after breeding (8CON), or 4) cows limit-fed in confinement year-round (12CON). Changes were not made to either the stocker or feedlot segments of the beef value chain. Net protein contribution (NPC) was calculated by multiplying the ratio of human-edible protein (HeP) in beef produced to HeP in feed by the protein quality ratio. A NPC >1 indicates that the production system is positively contributing to meeting human requirements, whereas a NPC <1 indicates the sector or value chain is competing with humans for HeP. Methane was estimated based on proportion of forage in diet and total methane production was reported per kg HeP. In the cow-calf sector, HeP conversion efficiency (HePCE) decreased from 2,640.83 to 0.37 while methane production decreased from 4.53 to 1.82 kg/kg HeP produced as the length of intensification increased from 0CON to 12CON. Decreased HePCE resulted in NPC values for cow-calf sector of 8,036.80, 4.93, 2.19, and 1.28 for 0CON, 4CON, 8CON, and 12CON, respectively. Protein quality ratio of the entire beef value chain increased from 3.15 to 3.33, while HePCE decreased from 0.99 to 0.39 as length of intensification increased from 0CON to 12CON. For the beef value chain, NPC was 3.11, 2.30, 1.73, and 1.31 for 0CON, 4CON, 8CON, and 12CON, respectively. Across the value chain, confinement of cows for 12 mo decreased enteric methane from 3.05 to 1.53 kg/kg HeP (0CON and 12CON, respectfully). Additionally, profitability of the cow-calf operation decreased from $249.34 to $102.16 per cow as intensification increased. Of confinement scenarios, probability of loss to an operation was least (4%) for 4CON. Feed costs increased by $260.79 per cow for 0CON when drought conditions existed (0COND). Total methane production was reduced by intensification and none of the scenarios evaluated competed with humans for HeP.

Limit feeding as a strategy to increase energy efficiency in intensified cow-calf production systems.

Two experiments were conducted to measure efficiency of energy use in limit-fed cows. In Exp. 1, 32 pregnant, crossbred cows were used to examine the effects of dietary energy concentration and intake level on energy utilization and digestion. In a 2 × 2 factorial treatment arrangement, cows received diets formulated at either 1.54 Mcal NEm/kg high energy (H) or 1.08 Mcal NEm/kg low energy (L); amounts of each diet were fed at amounts to achieve either 80% (80) or 120% (120) of maintenance energy requirements. Fecal grab samples were collected on days 14, 28, 42, and 56 for determination of energy digestion and metabolizable energy (ME) intake. Acid detergent insoluble ash and bomb calorimetry were used to estimate fecal energy production. Cow body weight and 12th rib fat thickness were used to estimate body energy, using 8 different methods, at the beginning and end of a 56-d feeding period. Energy retention (RE) was calculated as the difference in body energy on days 0 and 56. Heat energy (HE) was calculated as the difference in ME intake and RE. Energy digestion increased (P = 0.04) with intake restriction. Cows consuming H tended to have greater (P = 0.08) empty body weight (EBW) gain than cows consuming L, but no difference was observed (P = 0.12) between cows fed 120 compared with cows fed 80. Estimates of HE were greater for L than H (P < 0.01) and greater for 120 than 80 (P < 0.01), such that estimated fasting heat production of H (57.2 kcal/kg EBW0.75) was lower than that of L (73.3 kcal/kg EBW0.75). In Exp. 2, 16 ruminally cannulated, crossbred steers were used to examine the effects of dietary energy concentration and intake level on energy digestion. Treatment arrangement and laboratory methods were replicated from Exp. 1. Following a 14-d adaptation period, fecal samples were collected, such that samples were represented in 2-h intervals post-feeding across 24 h. Diet × intake interactions were observed for nutrient digestibility. Energy digestibility was greater in steers fed H than in steers fed L (P < 0.01); however, digestibility of each nutrient increased by approximately 10% in steers fed H80 vs. those fed H120 (P ≤ 0.03); nutrient digestibility was similar among levels of intake in steers fed L (P = 0.54). These results suggest that intake restriction may increase diet utilization and that the magnitude of change may be related to diet energy density.

Net protein contribution of beef feedlots from 2006 to 2017.

Feedlot efficiency increases as technologies are adopted and new feed ingredients, especially byproducts, become available and incorporated into diets. Byproduct availability increased in response to the renewable fuels standard of 2005, creating substantial amounts of feedstuffs best used by ruminants. Cereal grains have been partially replaced with human-inedible byproducts, as they provide comparable levels of energy in cattle diets. To evaluate the effects of changes in diet and feedlot production practices on net protein contribution (NPC) and human-edible protein conversion efficiency (HePCE) across time, a deterministic NPC model was used. NPC was assessed for the feedlot industry using lot level production data from 2006 to 2017 for eight commercial feedlots. Ingredient and nutrient composition was collected for a representative starter and finisher diet fed for each year from each feedlot. NPC was calculated by multiplying human-edible protein (HeP) in beef produced per unit of HeP in feed by the protein quality ratio (PQR). Systems with NPC >1 positively contribute to meeting human protein requirements; NPC < 1 indicates competition with humans for HeP. NPC was regressed on year to evaluate temporal change in NPC. Feedlots were categorized as increasing NPC (INC; slope > 0) or constant NPC (CON; slope = 0) according to regression parameter estimates. Four feedlots were categorized as INC and four were CON. The rate of change in PQR was similar for CON and INC (P ≥ 0.79), although rates of change among INC and CON differed for byproduct and cereal grain inclusion (P ≤ 0.01) across years evaluated. Feedlots categorized as INC reduced HeP consumed by 2.39% per year, but CON feedlots did not reduce HeP consumed each year (0.28%). Cattle received and shipped by INC were lighter than those in CON feedlots (P < 0.01). Across years, INC produced more HeP (20.9 vs. 19.2 kg/hd) than CON (P < 0.01), and both feedlot types tended to improve HeP gained over time (0.1 kg per year; P = 0.10). Differences in slope over time for INC and CON were observed for conversion efficiency of HeP (P < 0.01). NPC increased 0.027 units per year for INC (P < 0.01) and was 0.94 in 2017. NPC by the feedlot sector improved from 2006 to 2017, decreasing the amount of human-edible feeds required to produce more high-quality protein from beef.

Evaluation of active dried yeast in the diets of feedlot steers. II. Effects on rumen pH and liver health of feedlot steers1.

The objective of this trial was to determine the benefits of supplementing active dried yeast (ADY; 3 × 1010 CFU/d of Saccharomyces cerevisiae) in diets of growing and finishing steers on ruminal pH and liver health, and evaluate the relationship of these variables with performance traits. Growing beef steers (n = 120) were blocked by weight (i.e., heavy and light) and allocated to 1 of 4 pens in an automated feed intake monitoring system. Steers were fed either control (CON; no ADY) or ADY supplemented in 4 sequential diets: grower diet from days 0 to 70, 2 step up diets (STEP1 and STEP2) for 7 d each, and finishing diet from days 85 to 164. Indwelling rumen boli were administered to monitor rumen pH during days 56 to 106 during the dietary transition. An exchange of pen assignment, within block, occurred on day 70 resulting in 4 final treatment (TRT) assignments: steers fed CON before and after the exchange (CC; n = 30), steers fed CON before and ADY after the exchange (CY; n = 30), steers fed ADY before and CON after the exchange (YC; n = 30), and steers fed ADY (YY; n = 30). Ruminal parameters were analyzed as a randomized complete block design with repeated measures of day, diet and TRT as fixed effects, and block as random effects, using 2 approaches: preliminary analysis of the means or drift analysis (DA; units change from basal values over time). Ruminal pH duration (DUR) below 6.0 (P = 0.05) and 5.8 (P = 0.05) was greater for CY steers than CC steers. Acidosis bout prevalence (pH < 5.6 for 180 consecutive minutes; P < 0.01) and bout DUR (P = 0.05) were greater for CY than other TRT groups. The DA indicated that the ruminal pH variables range, variance, and amplitude of steers in the YC group drifted further from basal pH values than CY and YY steers during the dietary transition (P ≤ 0.02), indicating that removing ADY during the dietary transition was not favorable, but including ADY may reduce ruminal fluctuation. Steers with fewer days experiencing bouts (DEB) had numerically greater ADG (P = 0.11) and tended to have greater G:F (P = 0.06). Liver abscess severity negatively affected ADG (P = 0.04). However, liver abscess severity was not affected by DEB (P = 0.90). There is evidence to suggest that the addition of the specific ADY strain in the diets of beef cattle during the dietary transition may aid in ruminal stabilization, but our study did not find evidence that acidosis bouts were related to abscess prevalence or severity.

Evaluation of active dried yeast in the diets of feedlot steers-I: Effects on feeding performance traits, the composition of growth, and carcass characteristics1.

The use of active dried yeast (ADY) in the diets of feedlot steers may improve feed efficiency, growth performance, and reduce days on feed. Strategic timing of ADY inclusion in the diet may increase feed conversion or aid in the dietary transition from growing to finishing diets. One hundred twenty steers, blocked by weight, were fed four diets for 164 d: grower (70 d), first transition diet (7 d), second transition diet for (7 d), and finisher (80 d) in a GrowSafe System. Four treatment sequences of ADY inclusion were evaluated in a Balaam's design where steers were fed a control diet before and after the grower phase (CC), control before and ADY after the grower phase (CY), ADY before and control after the grower phase (YC), and ADY before and after the grower phase (YY). A random coefficients model was used to evaluate the following variables of interest: feeding performance and growth traits, including biometric measurements and carcass ultrasound measurements, and carcass characteristics. Treatment was a fixed effect and block was a random effect. Treatment did not affect feeding performance or behavior (P ≥ 0.14). The rate of change of biometric measurements were not different (P ≥ 0.16) across treatment groups except for rib girth circumference, which was greater for the YY and CY groups intermediate for the CC group and least for the YC group (0.828 and 0.809 vs. 0.751 vs. 0.666 cm/d, respectively; P < 0.01). Faster growth rates of rib girth circumference resulted in larger final measurements for steers that were finished on ADY (P < 0.01). Ultrasound measurements (backfat, LM area, intra-muscular fat, and rump fat) were not different across treatments (P ≥ 0.15). However, there was a tendency for the YC group to have a slower rate of back fat deposition than other treatment groups (P = 0.09). Steers' final shrunk BWs did not differ (P = 0.61), but shrink percentage was greater for CC than for YY groups (3.7% vs. 2.7%, respectively; P = 0.05). Carcass characteristics were not different across treatments (P ≥ 0.20). Crude fat, CP, ash and moisture analyses of the 9th to 11th rib section were not different across treatments, and there was no difference in adjusted final shrunk BW (P ≥ 0.45). Feeding the ADY strain used in this study to growing and finishing feedlot steers increased rib girth circumference development rate and reduced shrink loss without affecting feeding behavior, feeding performance, or carcass characteristics.

Estimation of human-edible protein conversion efficiency, net protein contribution, and enteric methane production from beef production in the United States.

A model was developed to estimate beef's contribution toward meeting human protein requirements using a summative model of net protein contribution (NPC) and methane production. NPC was calculated by multiplying the ratio of human-edible protein (HeP) in beef to the HeP in feedstuffs by the protein quality ratio (PQR). PQR describes the change in biological value of HeP that occurs when plant-derived HeP is converted to beef. An NPC > 1 indicates that the production system is positively contributing to meeting human requirements; systems with NPC < 1 reduce the net protein available to meet human requirements. Scenarios were arranged as a 2 × 2 factorial with two sets of dietary inputs and two sets of production parameters. Dietary inputs represented either inputs used in a previous report estimating HeP (previous diet; PD) or inputs more representative of conventional beef production systems (current diet; CD). Production parameters were either drawn from previous reports (previous parameters; PP) or chosen to characterize current industry standards (current parameters; CP). The HeP conversion efficiency (HePCE) for current industry diets and production parameters (CDCP) (kg HeP yield/kg HeP input) was greatest in the cow-calf sector (2,640.83) compared with stocker (5.22) and feedlot (0.34), and other scenarios followed a similar trend. In addition, the entire production system had an HePCE of 0.99 for CDCP; the previous model diets and production parameters (PDPP) scenario estimated HePCE to be 0.46, and other scenarios were in between. For the CDCP scenario, 56%, 10%, and 34% of the HeP were produced in the cow-calf, stocker, and feedlot sectors; PDPP was similar (59%, 13%, and 28%, respectively). PQR averaged 3.04, 3.04, and 2.64 for cow-calf, stocker, and feedlot sectors, respectively, indicating each sector enhances the biological value of the HeP fed. The NPC was greatest for the cow-calf sector (8,794), followed by the stocker and feedlot sectors (8.85 and 0.23, respectively). The entire beef value chain had a PQR of 2.68 and NPC ranged from 1.01 to 3.11, which correspond to PDPP and CDCP, respectively. Overall, 3.05 kg of CH4 were produced per kilogram HeP for CDCP and 2.58 for PDPP, with the cow-calf sector being greater than the feedlot sector (4.53 vs. 0.94 kg CH4/kg HeP, CDCP). Our results suggest that each individual beef sector and the entire value chain produce more high-quality HeP than is consumed in production. Accordingly, beef is a net contributor to meeting human protein requirements.

Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance.

The objective of this study was to determine if feeding monensin would improve diet digestion, energy and nitrogen balance in bred heifers receiving a limit-fed corn stalk-based diet. Sixteen pregnant Meat Animal Research Center (MARC) III composite heifers were used in a 161-d completely randomized design. Heifers were randomly assigned to one of two treatments, no monensin (CON) or 150 mg/d monensin (MON), with eight heifers in each treatment group. Heifers were limit-fed a corn stalk-based diet at 100% of MEm requirements. Effects of monensin on energy and nitrogen balance were determined via total fecal and urine collections and open-circuit respiration calorimetry. Total fecal and urine collection occurred on d 14, 42, and 161 of monensin feeding, and calorimetry measurements were made on d 0, 3, 14, 28, 42, and 161 of monensin feeding. DMI was not different (P = 0.94) for CON and MON heifers and, by design, increased (P < 0.01) from d 14 to d 161 of the trial to account for increasing fetal growth requirements. No differences (P = 0.91) in GE intake were observed between CON and MON heifers, and DE and ME intakes did not differ (P > 0.58) with monensin inclusion. DM, OM, NDF, and ADF digestion did not differ (P > 0.52) between treatments. Fecal, methane, urinary, and heat energy losses were not different (P > 0.16) for MON and CON heifers. Methane production was not different between treatments when expressed as daily liters of methane (P = 0.40); however, MON heifers produced 7% less (P = 0.03) methane per day than CON heifers when expressed as liters of methane produced on a metabolic body weight (MBW) basis. Furthermore, monensin had no effect (P = 0.36) on overall retained energy (RE). Nitrogen intake and excretion was not different (P > 0.13) between treatment groups. Results of this experiment indicate that adding monensin to limit-fed, corn stalk-based diets may not have a large effect on the energy and nitrogen balance of confined heifers.

Evaluation of F1 cows sired by Brahman, Boran, and Tuli bulls for reproductive, maternal, and cow longevity traits.

This study evaluated reproductive, maternal performance, and longevity traits of 143 F1 cows sired by Brahman (Br), Boran (Bo), or Tuli (T) bulls from Angus or Hereford cows from 1994 to 2011. Cow traits were measured at 7 yr of age in 1999 and 2000 for 1992- and 1993-born cows, respectively. From 2004 to 2010, excluding 2008, incisor condition (solid, broken, smooth) scores were assigned to cows remaining in production; scores were evaluated with two models. Broken and solid mouths were each assigned a score of "1" and smooth assigned "0"; Br-sired (0.76) and Bo-sired cows (0.71) had higher scores (P < 0.05) than T-sired cows (0.54). When solid mouths were scored 1 and smooth and broken scored 0, Br-sired cows (0.34) were higher than T-sired (0.01) (P < 0.05), and Bo-sired (0.23) cows were not different from either (P > 0.05). Age level of the cow within birth year was important for all modeled calf traits (P < 0.05). Birth weights were not different among cow inheritance (P > 0.05). Cow type influenced (P < 0.05) 205-d adjusted weaning weight of calves; Br-sired dams (228.1 ± 2.37 kg) produced the greatest weaning weight, followed by Bo-sired (213.7 ± 3.10 kg), and T-sired (201.6 ± 2.69 kg) dams (P < 0.05). Adjusted means for calving rate for Bo-sired (0.92 ± 0.02) cows were higher (P < 0.05) than Br-sired (0.86 ± 0.02) and T-sired (0.86 ± 0.02) cows. Adjusted mean weaning rate was greater (P < 0.05) for Bo-sired cows (0.86 ± 0.02) than for cows sired by Br (0.77 ± 0.02) bulls, but weaning rate for T-sired cows (0.80 ± 0.02) were similar (P > 0.05). Cow weight was greater (P < 0.05) for Br-sired cows (590.5 ± 8.35 kg) than for Bo-sired (505.8 ± 10.46 kg) or T-sired cows (508.5 ± 9.37 kg). BCS at weaning for 7-yr-old cows was similar (P = 0.08) for Br-sired and Bo-sired cows and lower for T-sired cows (P = 0.0005, condition scores 6.0, 6.3, and 5.8, respectively). Boran-sired cows were older when they were removed from the herd, on average (12.7 ± 0.74 y, P = 0.03) than T-sired (10.6 ± 0.61 y); Br-sired cow persistence was intermediate and not different (11.05 ± 0.60 y, P > 0.06) from the others. Boran-sired cows had higher calving and weaning rates and better mouth scores than the other groups; consequently, they had greater longevity as well. Boran-sired and T-sired cows were moderate in size and weighed less than Br-sired cows throughout the study. Tuli-sired cows weaned the lightest calves and had the most tooth deterioration as they aged.

Genome-wide association study for stayability measures in Nellore-Angus crossbred cows.

Beef cow stayability is a complex, economically important trait often used as an indicator of a cow's potential lifetime productivity. Stayability is defined as capability of a cow to maintain a perfect record up to 6 yr of age. This age is commonly cited as a financial break-even point, where initial costs of cow development and maintenance are recovered by her cumulative net income from yearly calf receipts. Later-maturing Bos indicus-Bos taurus crossbred cows may experience reproductive difficulty early in life but have a high potential for a long reproductive life span. It was the objective of this study to identify genetic variants associated with measures of beef cow stayability. A population of B. indicus-B. taurus crossbred cows (n = 305) from central Texas was used. Phenotypes for various measures of stayability to 6 yr of age were produced by artificially imposing five different culling criteria on data from the population. Cows were scored either as a 1 (indicating a perfect record through 6 yr) or a 0 (indicating failure at or before 6 yr), under each criterion. Genome-wide association studies (GWAS) were conducted for each criterion using univariate procedures and prefitting the fixed effect of cow contemporary group. SNP associations for two criteria surpassed the false discovery threshold of 0.15, when a cow was scored as 0 upon her first failure to wean a calf, regardless of reason, through 6 yr (criterion 2), and when a cow was scored as 0 upon her first failure to give birth to a calf, through 6 yr (criterion 3). Associated SNP were found on bovine chromosomes (BTA) 1, 2, 5, 9, 18, and 21 for criterion 2 and on BTA 1, 5, 11, 15, and 24 for criterion 3. A critical region on BTA 5: 43-50 Mb was identified for each criterion. Due to the similarities to prior work, the tendency for B. indicus cattle to experience reproductive difficulties early in life, and due to the large proportion of cows that left the herd at an early age under these criteria, these results suggest that the associations are likely driven by an early life trait such as age at puberty or rate of heifer development.