Mature Cows Research Articles

Residual feed intake measured as replacement heifers is indicative of residual feed intake measured as mature cows

This study aimed to quantify the relationship between residual feed intake (RFI) measured in 500 heifers and subsequently as mid-gestation cows at the Roy Berg Kinsella Research Station (KIN; n=227) and Lacombe Research and Development Centre (LRDC; n=273). Heifers were initially tested for RFI adjusted for end of test rib fat (RFIfat) at 8-12 mo of age and then again as 3-yr old first-calf heifers at KIN and as 4-13 yr old cows at LRDC. Heifer RFIfat measured in drylot on a forage diet was associated (R2 >0.53; P < 0.001) with RFIfat measured again as older cows. Each 1 kg DM d-1 change in heifer RFIfat equaled 0.48±0.10 and 0.75±0.19 kg DM d-1 change in cow RFIfat for KIN and LRDC, respectively. Linear effects were also reported for RFIfat component traits, where DMI (P<0.001), ADG (P<0.060), mid-test metabolic weight (P<0.001) and end of test rib fat (P<0.001) measured as heifers were related when measured again as older cows. In addition, the linear effects of heifer RFIfat on cow RFIfat were constant across cow age groups from 4-10 yr of age. These results show that selection for RFI in heifers will result in cows that are also more feed efficient.

Assessing bull breeding soundness exam parameters following vaccination with modified-live or killed vaccine

Breeding bulls are often placed on a similar herd health plan and vaccinated for the same pathogens as the mature cow herd. The timing of the yearly vaccination is impacted by labor and time constraints with some bulls receiving vaccinations at the time of annual, complete breeding soundness exams or at the time of turnout prior to the breeding season. However, the potential impact of vaccination on spermatogenesis, if any, is unknown. Therefore, the study objective was to determine the impacts on normal sperm morphology through a complete spermatogenic cycle after vaccination of mature beef bulls against bovine herpesvirus 1 and bovine viral diarrhea virus using commercially available modified-live virus (MLV) or killed virus (KV) vaccine. Semen was collected from Bos taurus bulls (n = 11),which were randomly assigned prior to the first breeding soundness exam to vaccine treatment groups: 1) modified-live virus (MLVa); or 2) inactivated/killed virus (KVb). Breeding soundness exams were completed at days -7, 0, 5, 7, 17, 28, 61 following vaccination. No differences were found between vaccine treatment groups MLV and KV (P = 0.46) on the percentage of normal sperm over time (d = -7 through d = 61) as evaluated by two boarded theriogenologists. In conclusion, we found no detrimental effect of the administration of multivalent MLV or KV vaccines on percentage of normal sperm morphology of mature bulls over a 61 – day period.

PSLBII-5 Impacts of residual feed intake measured as a heifer in drylot on mature cows and calves grazing native pasture

Abstract Selection for feed efficiency is crucial for improving economic and environmental sustainability in beef cattle production. Residual feed intake (RFIfat) is a commonly used measure of feed efficiency and is determined in a drylot setting by calculating the difference between observed and expected dry matter intake (DMI), where expected feed intake is adjusted for metabolic body weight (BW), average daily gain (ADG) and body fatness. Lower RFIfat cattle are more efficient animals as they eat less than predicted for the same growth, body size and body fatness. Limited studies have been conducted evaluating the role of RFIfat on the subsequent performance of cow-calf pairs on native range. Kinsella Composite cows and calves (n = 120) grazed native pasture from July 11 to Sept 12 (summer) and from Sept 13 to Nov 2 (fall) of 2023 were included in this study. All dams had previously been evaluated for RFIfat as a heifer (8 to 12 mo of age) using the GrowSafe Feed Intake System (Vytelle, Canada). Cow and calf ADG were subjected to an analysis of covariance using lm function from stats R core package (R Core Team, 2024), with cow age (2 to 8 yr of age) as the fixed effect and RFIfat as the covariate, analyzing separately by season. An unbalanced Tukey HDS post-hoc were applied for age and p-values < 0.05 were considered significant. Weight gain was assessed on cows with an initial BW on pasture of 598.4 ± 68.4 kg, and 2 to 8 yr of age, and on calves having an initial on pasture BW of 106 ± 21.5 kg, and 65 ± 14 d of age. Cow age affected (P < 0.01) cow ADG during summer, with the youngest dams (2 yr old) gaining more weight than older animals (7 yr old; Figure 1A). No effect of RFIfat was found on cow weight gain during summer grazing. However, during fall grazing, RFIfat affected (P < 0.01) cow ADG (Figure 1B). Low-RFIfat cows (efficient) had increased weight gain during fall grazing as compared with high-RFIfat cows (inefficient: Figure 1B). Calf ADG was not affected (P > 0.1) by cow age, cow RFIfat and cow ADG during summer and fall. We conclude that cows with low RFIfat exhibited superior body weight gain, during fall grazing on native range when forage nutrient quality and quantity become limiting.

PSXI-2 Impact of flexible prepartum supplementation strategies on cow-calf and subsequent progeny feedlot performance

Abstract Implementation of minimal supplemental protein strategies during late gestation may have the potential to minimize any negative postweaning progeny performance while decreasing feed costs. A 3-yr study was conducted to evaluate the effects of mid- to late-gestation supplementation strategies on reproduction, cow body weight (BW), and calf performance in May-calving mature cows grazing upland native range. Cows received one of 3 supplementation strategies: 1) 0.227 kg/d of a 30% CP distillers-based supplement (HalfSupp), 2) 0.454 kg/d of a 30% CP distillers-based supplement (Supp), or 3) brief and intermittent supplementation of Supp at 0.454 kg/cow based on periods of acute environmental stress, such as snow cover, wet winter events, and is best described as flexible supplementation (Flex). Supplementation was initiated in December each year and terminated approximately 30-d prior to the start of the calving season in April. Across all 3 yr, average supplement feeding rate was 25.5, 50.9, and 5.4 kg/cow during the 112-d supplemental period, which resulted in average yearly prepartum supplemental costs of $27.30, 54.60, and 1.99 for HalfSupp, Supp, and Flex; respectively. After weaning, steers grazed sub-irrigated meadow with a dried distiller grain supplement until May. In May, all steers grazed sub-irrigated meadow without additional supplement until August/September when steers were shipped to West Central Research and Extension Center (WCREC). Steers were placed in a GrowSafe feeding system for the rest of the finishing feeding period. Each year, steers were slaughtered at a commercial facility (Tyson Fresh Meats, Lexington, NE) when estimated visually to have 1.3 cm fat thickness over the 12th rib as a group. Cow BW was not different (P = 0.86) at the initiation of supplementation in Jan. However, cows fed Half had a lighter (P < 0.01) BW at pre-calving and tended (P = 0.08) to have a lighter BW at pre-breeding than their counterparts. After a 45-d breeding season, pregnancy rates were not influenced (P = 0.91) by prepartum supplementation strategies. Prepartum supplementation strategies did not influence (P > 0.56) preweaning calf BW at birth, pre-breeding, and weaning. In addition, steer backgrounding BW was also not influenced (P > 0.63) by prepartum supplementation strategy of their dam. Upon entry into the feedlot, steer BW was not impacted (P > 0.84) by prepartum supplementation strategy of their dam. Feedlot performance (BW, average daily gain, and feed efficiency) was not influenced (P > 0.59) by prepartum supplementation strategy of their dam. After harvest, all carcass characteristics were not impacted (P > 0.11) by the prepartum supplementation strategy of the dam. Considering the cost for prepartum supplementation, feeding a protein supplement just during environmentally stressful periods during gestation appears to be a viable alternative to more conventional methods and reduces winter feed costs.

PSX-4 Exploring the impact of age and body condition score on the genetic analysis of mature cow weight in American Angus cattle

Abstract Selecting sires with optimal genetic merit for mature weight (MWT) is crucial for profitability of beef producers, ensuring cost-effective production and increased economic returns per animal. The main objective of this study was to determine how different statistical approaches [e.g., including the fixed effects (FE) of age and body condition score (BCS) in the statistical model and/or pre-adjusting the weights for these effects] affect variance components estimation and genetic parameters for MWT, and their impact in the posterior selection decisions. The dataset provided by the American Angus Association (AAA) comprised 80,296 MWT records from 37,934 cows aged 2 to 15 yr. Contemporary groups (CG) were defined by concatenating herd, year, and season of measurement. Model 1 analyzed unadjusted MWT with CG and BCS as categorical FE and age as a covariable (quadratic). Model 2 was model 1 without BCS, model 3 was model 1 without age, and model 4 considered CG as the only FE. In model 5, MWT was pre-adjusted for 6 yr of age and BCS of 6, and CG was the only FE included in the statistical model. Additive genetic and permanent environment (pe) random effects were included in all statistical models except model 5, which did not include pe (only one adjusted record per animal). Variance components were calculated using REML implemented in the BLUPf90+ family of programs. Sires with at least 10 offspring (n = 1,483) were ranked according to their breeding values (EBVs) predicted for MWT, and all and the top 10% sires were used to estimate the rank correlation across models. The heritability (± SE) estimated for MWT was 0.43 (± 0.011), 0.42 (± 0.011), 0.70 (± 0.008), 0.72 (± 0.082), and 0.37 (± 0.013) for models 1, 2, 3, 4, and 5, respectively. Repeatability values were 0.64, 0.67, 0.72, and 0.76 for models 1, 2, 3, and 4, respectively. The EBV ranks were highly correlated between models 1 and 2 (Top 10%: 0.96; All: 0.99), and models 3 and 4 (Top 10%: 0.99; All: 0.99). Inflated heritabilities in models 3 and 4 suggest that the effect of age is confounded with the additive genetic effect, which will not translate to greater genetic progress. Therefore, disregarding age in the genetic evaluation of MWT is not recommended. Similarities between models 1 and 2 suggest that BCS has a relatively small impact on MWT, probably related to the relatively low genetic correlation between these traits. Models 1 and 5 cannot be directly compared, as they use slightly different response variables (body weight vs. pre-adjusted weight) and may lead to slightly different selection decisions (correlation between Top 10%: 0.85; All: 0.95). Further investigations in this field are warranted.

262 Why are some cows skinny? An evaluation of stress and immune factors

Abstract For the mature cow with low body condition scores (BCS), being too thin can accompany health issues, reduced pregnancy rates, more days to rebreeding, and decreased milk production resulting in lighter calves at weaning. In addition, reduced fat insulation in low BCS cows during the winter equates to additional feed requirements for warmth. The hypothesis of this study was that stress and immune factors contribute to low BCS in mature cows. The objective of this study was to determine whether there were differences in hematology parameters, hair cortisol concentrations, and plasma cytokine concentrations among animals with low body condition (BCS ≤ 4). Over a 3 yr study, we collected 62 pairs of cows which included cows with a BCS ≤ 4, and a matched control animal born in the same year with the same or similar breed composition from the same population of animals with a BCS of 5 or higher. Hematology parameters, cytokine concentration, and cortisol concentrations were analyzed using a model with BCS classification and sample year as fixed effects and age in years as a covariate. Hemoglobin, hematocrit, red blood cell and mean platelet volume were all less among the low BCS cows, and neutrophil count was greater (P < 0.05). Platelet, monocyte counts, mean corpuscular volume, and mean corpuscular hemoglobin tended to be greater in low BCS cows (0.05 < P ≤ 0.1), and lymphocyte count tended to be less. Hair cortisol concentrations, a longer-term measure of cortisol, tended to be greater in low BCS cows (P = 0.09). None of the 15 cytokines tested differed with BCS. The combination of reduced RBC parameters with greater neutrophils suggests that low BCS cows were responding to or were the reflection of some type of chronic stressor, such as a subclinical disease state or a physiologic stressor. This was also supported by the tendency for greater cortisol concentrations in low BCS cows. USDA is an equal opportunity provider and employer.

347 Quantifying phenotypic and genetic variation for cow fertility phenotypes in American Simmentals using total herd reporting data

Abstract Inefficiencies in reproduction are the largest drivers of loss in United States beef production. Nearly all reproductive traits are at least modestly heritable, making genetic selection and improvement possible over the long term. Cow-centric reproductive traits present unique challenges, as they are not expressed in male animals and will not be observed until later in the productive life of a female, if at all. This makes cow-centric fertility traits ideal candidates for selection with Expected Progeny Differences (EPDs). We used a commercially generated dataset from the American Simmental Association (ASA) to explore the phenotypic and genetic variation in these traits. The dataset comprised Total Herd Enrollment (THE) records, which required unbiased reporting of enrollment, calving, and disposal for 303,158 females (132,403 cows and 170,755 heifers). Using the THE data, we calculated three continuous and two discrete traits that are indicators of heifer and cow fertility and rebreeding ability. These traits were: 1) calving date (calving date of the cow relative to the start of the calving season), 2) calving interval (days between calves), 3) first calving interval (calving interval observation between the first and second calving record for a female), 4) heifer pregnancy (did the animal calve as 2-yr-old?), and 5) discrete early calving (did animal calve in the first 30 d of the calving season?). We observed a significant difference in calving date in mature cows that calved in the first 30 d of the calving season of their contemporary group as heifers compared with those that calved later (Table 1). Early calving heifers averaged a nearly 10 d sooner calving date throughout their productive lives compared with those that calved after 30 d as heifers (29.9 d vs. 40.2 d, P-value < 0.01). We used a combined pedigree and genomic approach, implemented in GIBBSF90+, to estimate genetic, environmental, and permanent environmental variance components. We estimated heritabilities of 0.24 (± 0.037215) for heifer pregnancy, 0.06 (± 0.009265) for calving date, 0.07 (± 0.015451) for discrete early calving, 0.04 (± 0.003954) for calving interval, and 0.04 (± 0.009604) for first calving interval. We observed positive phenotypic and genetic correlations between these traits, ranging from 0.01 to 0.96 (Table 2). This work provides an extensive population survey of phenotypic trends in reproductive performance and management in a large seedstock population. The heritable nature of the inspected traits motivates further work in understanding their genetic architectures and how they are affected by heterosis in crossbreeding programs.

387 Impacts of rumen protected omega-6 fatty acid supplementation on cow reproduction and calf growth

Abstract Maternal nutrition during pregnancy is crucial for proper fetal development. Rumen protected omega-6 (ω-6) fatty acids (FA) may improve health and reproductive success in beef cattle. Previous research studied the effects of supplementing ω-6 on cow production either during late gestation or post-breeding but not during both stages. Our objective was to determine the effects of ω-6 supplementation during late gestation and post-breeding on cow reproduction and calf pre-weaning growth. Eighty cows were assigned to either a saturated FA control (C) or rumen protected ω-6 supplements for 40 d before parturition (PRE) and/or 35 d after artificial insemination (AI, POST) using a 2 × 2 factorial: PRE C-POST C(n = 19); PRE C-POST ω-6(n = 19); PRE ω-6-POST ω-6(n = 17); PRE ω-6-POST C(n = 18). Cows were fed ad libitum hay and water when on/off supplementation periods. Supplements were provided in low moisture tubs. Individual animal intake of supplement was measured by a GrowSafe system. Cow body weights and plasma FA concentrations were measured prior to and after supplementation during each period. Calves were weighed at birth, branding, 150 d old and weaning. Reproductive measurements included postpartum estrus activity, estrus response at fixed-time AI (FTAI), and pregnancy rates. Blood plasma for progesterone analysis was collected on d 7 post-AI on all cows. Corpus luteum (CL) area was measured on d 7 via transrectal ultrasonography on a subset of cows during the POST period (PRE ω-6-POST ω-6 n = 8; PRE C-POST C n = 8; PRE C-POST ω-6 n = 8; PRE ω-6-POST C n = 8). The relationship between supplement intake and plasma FA concentration was analyzed via linear regression, and all other variables were analyzed via ANOVA. Supplement intakes within treatments and between the PRE and POST supplemental periods were highly variable. Body weights remained similar for cows (P = 0.52), but POST ω-6 calves had larger weaning weights than POST C calves (P = 0.02). There was a positive linear relationship (r2 = 0.14, P < 0.03) between supplement intake and plasma FA for PRE ω-6 and POST ω-6. Positive linear relationships between intake and plasma ω-6 FA concentration were observed for PRE C (r2 = 0.11, P < 0.05), PRE ω-6 (r2 = 0.2, P < 0.007) and POST ω-6 (r2 = 0.31, P = 0.0005). Post-partum estrus activity was similar (P = 0.81) between PRE C and PRE ω-6 cows, and estrus response at FTAI was similar (P = 0.13) between POST C and POST ω-6 cows. POST ω-6 cows had larger CL areas than POST C cows (P = 0.03); however, blood progesterone concentrations at d 7 did not differ between treatments (P = 0.65). There was no difference in conception to FTAI between POST C and POST ω-6 (P = 0.08). These results indicate that free choice ω-6 FA supplementation during late gestation and post-AI result in large variation in intake between cows that influence plasma concentrations, but did not markedly alter reproductive measures in mature beef cows.

Beef cattle mating recommendation based on bioeconomic models

Recognizing the pivotal role of mating in animal breeding, this study strives to establish a robust strategy for recommending optimal matings among bovines. This strategy is built to maximize a single value derived from the economic selection index of full-cycle system in Brangus cattle. The study endeavors to apply computational methodologies to explore economically significant traits comprehensively, thereby leading to amplified financial gains for Brangus cattle breeders. Anchored within this overarching objective, a strategic deployment of a genetic algorithm is employed to formulate mating recommendations that precisely align with the priority traits designated by the genetic evaluation program of the Brazilian Brangus Association (BBA). The data set of the BBA for the simulations in this study encompass a range of selection criteria, including: i) birth weight; ii) mature cow weight; iii) ribeye area; iv) subcutaneous fat thickness; v) subcutaneous fat thickness at the rump; vi) escape speed; vii) nematode egg count per gram of feces; and viii) tick count. The research findings underscore that the recommendations provided by the computational strategy converge to increase the bioeconomic index while controlling the trade-off between this index and progeny inbreeding.

Evaluation of Hormonal and Biochemical Profile of Ladakhi Cow during Estrous Cycle: The Future Perspective of Reproductive Management of Ladakhi Cow

The Ladakhi cow is an indigenous breed from Ladakh, India, and has a unique genetic makeup to adapt to high-altitude hypobaric stress. Furthermore, little study is available on examining the Ladakhi cow’s blood biochemicals and reproductive hormonal status during various stages of the estrus cycle. Hence, the current study was conducted on eight reproductively mature Ladakhi cows at the experimental dairy cattle unit in Leh-Ladakh, India, to determine the changes in serum biochemical and hormonal levels during the estrus cycle. The estrus behaviour was initially observed before the blood sampling on days 0 (the day the cow exhibited heat symptoms), 2nd, 8th, 17th, and 21st days. The serum was isolated for biochemical and hormonal profiling as per standard procedures using commercially available kits. The results revealed that serum biochemicals, viz. Ca, Fe, ALT, AST, ALP, TG, TP, Albumin, Glucose, UA, Creatinine, and Urea levels were within the normal range of cows at high altitudes. However, reproductive hormones, e.g. GnRH, FSH, LH, progesterone, estrogen, PGF2α, IGF-1, and Insulin varied from the reference level at different stages of the estrus cycle. This study’s findings have provided new insights into the serum biochemical and hormonal profiling of Ladakhi cows during the estrus cycle and this information may help to develop a reference range and baseline value for the serum biochemicals and hormonal levels of Ladakhi cows for other breeding programs and health monitoring.

Evaluation of Body Measurements of Limousin Heifers in Some Western Hungarian Farms

Body weight and body measurements are important economic traits in beef cattle sector and can be used as selection factors. At young ages they give information on the maturity of the animals. Body measurements (withers height, tail height, width at shoulders, back length, width at hip bones, pin width) of Limousine heifers (n=313; age: 429.2 days) were taken on six Transdanubian farms in Hungary by skilled technicians with standardized equipment under appropriate conditions. Statistical analysis was made by SPSS 24.0. Normal distribution of data was confirmed by Shaphiro-Wilks test. The GLM model was focused on the intercept, the effect of herds (n=1 to 6) and covariant factors (age or live weight). The results showed that body measurement data of heifers in the same region can be evaluated by GLM which contains the effect of herd and age or weight as covariant. All components involved in the models were proven to have significant effects (P<0.001). Regarding their age, heifers of all herds were adequately developed both in live weight (69.6%) and height measurements (84-93%) compared to reference values of mature cows, ensuring a strong basis for successful breeding work in the future. The farm with the heaviest (505.7 kg) heifers had lower values for withers- (118.8 cm) and tail height (127.8 cm), and narrower shoulder (30.6 cm) which draws attention to the fact that large weight is not necessarily paired with a large frame.

The reproductive performance of phosphorus-deficient mature cows improved rapidly when given supplementary phosphorus in the Victoria River District of the Northern Territory

Context There is little published information on how long it takes for the performance of phosphorus (P)-deficient mature cows to improve once they start receiving P supplements, or whether their long-term performance is impaired by P deficiency early in life. Aims The performance of mature P-deficient and P-adequate Brahman cows was compared over 3 years to investigate the time it takes for the performance of P-deficient mature cows to improve once they are supplemented with P, and whether their long-term performance is compromised by P deficiency early in life. Methods Cows that had been a part of a P-supplementation trial at Victoria River Research Station from weaning until they were 5.5 years old were used for this study. One treatment group had received continuous P supplement (P+) since weaning and the other treatment had never received any P supplement (P−). At the conclusion of the original trial, 42 cows were randomly selected from each treatment and then grazed together in the same paddock for 3 years, during which time they were given P supplement continuously. Performance attributes were measured and compared. Key results This study found that P supplementation rapidly improved the liveweight, body condition, reproductive performance and survival rate of the P-deficient (P−) mature cows. Within a year of receiving P supplement, their performance improved to be similar to that of P+ cows. However, P deficiency early in life did have some residual stunting effects, resulting in lower mean hip height and liveweights of P− cows. Conclusions The performance of P-deficient mature cows improved rapidly once they were given P supplements and matched that of cows that had always been supplemented. However, P deficiency early in life caused stunting, resulting in mature cows being shorter and lighter. Implications Cattle producers in P-deficient country should see a rapid improvement in performance and return on investment once they start supplementing P-deficient cows. However, it is better to supplement cattle throughout their lives in P-deficient areas to avoid stunting.

The veterinarian’s role in reducing GHG emissions from beef and dairy production

The beef and dairy industries make significant contributions to sustainability objectives by providing our society with nutri­tious food, supporting farmers’ livelihoods, generating billions of dollars in economic activity, and contributing to healthy ecosystems. However, cattle production also generates negative environmental impacts, including greenhouse gas (GHG) emis­sions. Veterinarians have a unique opportunity to interface with beef and dairy farmers to assist with the implementation of products and practices that reduce GHG emissions, such that their clients can be more profitable and more sustainable. In general, the GHG intensity of beef and dairy production can be reduced by increasing output yields of beef and milk, while re­ducing inputs and maximizing efficiency. Some of the specific interventions include: early entry of feeder cattle to a feedlot, dry manure management, optimized inorganic nitrogen fertil­izer use, increased fat in the ration, use of anti-methane feed additives and ionophores, sourcing low-carbon corn, select­ing genetics for high feed efficiency, raising moderate/small mature beef cows and feed efficient dairy cows, improving pregnancy rate and reducing dystocia, conducting pregnancy checks, implementing artificial insemination, promoting herd health products and practices to reduce death loss, using growth-promoting implants, and utilizing SOP Lagoon®. As a trusted source of scientific information, veterinarians can be a conduit of information for producers and contribute to the ongoing effort to improve the resiliency of the beef and dairy industries.

PSIV-A-13 The relationship between breed-wide expected progeny differences, genomic predictors, and phenotypic values in mature Angus cows

Abstract For many years, selection for improved beef production centered on heavier weaning weights and more rapid post-weaning gain. More recently, measurement of post-weaning feed intake has facilitated direct improvement in feed efficiency in the feedlot. However, intake on a high concentrate diet is controlled by different biological mechanisms than intake on a high roughage diet. For this reason, the question remains whether an animal that efficiently converts calories from a high-quality concentrate-based ration similar to that of a feedlot diet where the expected progeny differences (EPDs) and genomic predictors (GPs) are developed would also be an efficient forage utilizer as a mature cow. To evaluate this relationship, we compared breed-wide EPDs and predictors to performance on a roughage diet and on a concentrate diet in mature cows. The objective of this study was to determine if EPDs and GPs developed and used in feedlots are applicable to commercial cow/calf producers utilizing forages and other roughages as the main diet ingredient. Data for this study were collected at Oklahoma State University from the fall of 2018 to the spring of 2021. Tissue samples from 64 mature Angus cows were submitted to Neogen for profiling according to genetic potential for 16 different traits. In each trial, retained energy (RE), dry matter intake (DMI), milk production (MILK), mature weight (MW), and average daily gain (ADG) were recorded and compared with the corresponding EPD and GP. Pearson correlations were determined between phenotypic values, GPs, and EPDs for both diets on each trial. No EPD or GP was significantly correlated to any measured trait on the forage diet. The DMI EPD was strongly correlated with DMI on a concentrate-based diet, however, did not predict DMI on a forage diet in mature cows. Based on the evaluations performed in this study, selecting for animals that perform well in the feedlot may be inadvertently selecting for mature cows that perform poorly on a typical mature cow diet of medium to low-quality forages.

92 Factors influencing bull selection in Illinois beef producers: Analysis of retained and non-retained ownership producers

Abstract The objective was to understand decision-making factors for bull selection of producers participating in the Illinois Performance Tested (IPT) bull sale. The IPT bull sale has served Illinois beef producers for the last 54 yr offering around 50 bulls annually. A comprehensive survey targeted a diverse group of beef producers that had previously attended the IPT bull sale. The survey was developed through Qualtrics and provided to producers via email. The survey consisted of 40 questions based on four categories: farm location, herd demographics, bull selection criteria, and feedback from previous experiences at the IPT bull sale. There were a variety of question types including multiple choice, select all that apply, open-ended, ranking of importance, and select on a scale from one to ten. Specific responses on bull selection criteria focused on expected progeny differences and functional traits. Survey results were grouped based on whether producers retained ownership of feedlot cattle; regularly retained ownership (RET; n = 12) and never retained ownership (NRET; n = 15). Data were analyzed with the MIXED and GLIMMIX procedures of SAS 9.4. For RET and NRET producers, there were no observed differences in mature cow body weight and herd size (P ≥ 0.42). Most producers responded that they calved in March and April. Producer groups did not differ (P = 0.99) in the percentage of respondents retaining replacement heifers, as 66% of RET and NRET producers retained replacements. However, RET producers tended to be more likely (P = 0.07) to regularly sell freezer beef. Specifically, 75% of RET producers regularly sell freezer beef compared with 13% of NRET producers. Additionally, RET producers tended to prioritize (P = 0.1) carcass trait expected progeny differences in bull selection more than NRET producers (66 vs 33%, respectively). There was no difference (P = 0.2) in the percentage of respondents that selected the weaning weight expected progeny difference in their top three traits. However, NRET producers were much more likely (P < 0.01) to prioritize yearling weight expected progeny difference in their bull selection decisions. Specifically, 66% of RET producers used yearling weight expected progeny difference in their bull selection compared with 0% of NRET producers. Lastly, there was no difference (P = 0.61) in the percentage of respondents who included docility in their top three functional traits. In conclusion, bull buyers at the IPT bull sale that regularly retain ownership of feedlot cattle were more likely to prioritize expected progeny differences for yearling weight and carcass traits while functional traits priorities were similar to producers that did not retain ownership of feedlot cattle.

Mechanisms by which feeding synthetic zeolite A and dietary cation-anion difference diets affect feed intake, energy metabolism, and milk performance: Part II

The objectives of this study were to assess the effects of feeding 2 different diets, a low dietary cation-anion difference (DCAD) or a diet with synthetic zeolite A to multiparous Holstein cows during the close-up period on DMI and energy metabolism, as well as evaluate colostrum and milk production. A hundred and 21 multiparous Holstein cows, blocked by lactation number and expected parturition date were enrolled at 254 d of gestation and randomly assigned to 1 of 3 dietary treatments: control (CON; +190 mEq/kg; n = 40), negative DCAD (DCAD, -65 mEq/kg; n = 41; Ultra Chlor; Vita Plus, Lake Mills, WI, USA), or a diet containing sodium aluminum silicate zeolite (XZ; +278 mEq/kg, fed at 3.3% DM, targeting 500 g/day; n = 40; X-Zelit, Protekta Inc., Lucknow, ON, Canada/Vilofoss, Graasten, Denmark). Prepartum DMI was measured daily using Insentec Roughage Intake Control (RIC) gates (RIC System, Holofarm Group, Netherlands). All cows received the same postpartum diet. Blood and urine samples were collected daily beginning 14 d before parturition (D-14) until parturition (D0), and on 1, 2, 3, 6, 9, 12, 15, 18, 21, 35, and 49 d postpartum. Colostrum collected within 6 h of parturition, weighed, and based on samples Brix value, IgG concentrations, and nutrient composition were analyzed. Prepartum, cows fed XZ diet had decreased DMI (11.70 ± 0.26, 13.88 ± 0.26, and 13.45 ± 0.25 kg/d for XZ, CON, and DCAD respectively) and lower rumination (487 ± 8.1, 531 ± 8.3, and 527 ± 8.5 min for XZ, CON, and DCAD respectively) compared with CON and DCAD fed cows. However, rumination was not different postpartum due to treatment. No prepartum or postpartum differences were observed for glucose or BHB concentrations in blood between dietary treatments. Colostrum collected from cows fed XZ had the highest IgG concentrations (91.10 ± 2.63, 78.00 ± 2.63, and 78.90 ± 2.63 mg/mL for XZ, CON, and DCAD, respectively), but yield did not differ between dietary treatments. Additionally, cows in their third or greater lactation fed XZ had the highest milk production (51.0 ± 1.1 kg) during the first 49 d in milk. This study demonstrates that despite a decrease in DMI and rumination in cows fed XZ prepartum, blood BHB concentrations were not altered. Additionally, cows fed XZ had higher colostral IgG concentrations and 3+ lactation cows fed XZ produced the most milk. These data suggest that feeding XZ prepartum may improve colostrum quality and improve milk yield in mature cows, and does not impact energy metabolism.

Genomic selection in dairy cattle: impact and contribution to the improvement of bovine fertility

Genomic selection has revolutionized the dairy cattle breeding industry, with ripple effects that have greatly impacted dairy herd management. Rate of genetic progress has increased markedly, especially in Holstein and Jersey breeds, for production, health, and fertility traits. Genomic testing of young bulls and heifers provides greater accuracy of selection decisions involving traditional fertility traits, such as daughter pregnancy rate, while creating the opportunity to improve novel traits, such as fetal loss. Cameras, wearable sensors, and other precision livestock farming technologies will allow selection for traits such as estrus duration and intensity that require high frequency phenotyping. At the same time, synergies between genomic testing and advanced reproductive technologies have led to rapid and widespread adoption of sexed semen, coupled with mating of females whose offspring are not needed as herd replacements to beef sires. This strategy produces added-value crossbred calves for the beef supply chain, while allowing genetically inferior mature cows that are still producing at a high level to remain in the herd for additional lactations.

3 Measuring feed intake in cows

Abstract In recent years, substantial progress has been made in understanding the sources of biological variation and genetic components of feed efficiency in growing animals consuming energy-dense mixed diets during the post-weaning phase. Much less is known about within-animal variation of feed efficiency for beef cows consuming moderate to low-quality forage diets common to most cow/calf production systems. Considerable evidence indicates the existence of a genetic by environment interaction for feed efficiency. Phenotype for feed intake and feed efficiency are most practically and cost effectively determined during the post-weaning growing stage. However, due to the additional nutrient sinks associated with gestation and lactation, and the cost, labor and technology required to measure economically relevant traits in mature cows, little is known about forage utilization efficiency in beef cows. The beef cow/calf segment of the industry represents, by far, the greatest opportunity to reduce beef production input costs and reduce the industry’s carbon footprint. We reason that selection tools for feed intake and feed efficiency developed over the last 20 years are effective for the post-weaning growing and finishing phases, although only marginally effective for beef cows consuming unprocessed, moderate to low-quality forage. In this session, we will discuss challenges, opportunities, and experiences associated with measuring forage intake and recovered energy in beef cows.

110 Effects of sire selection on puberty and reproduction of offspring selected as replacement heifers

Abstract Sire selection is important to maintain the desired genetic capability of any cattle herd; therefore, selection of economic production traits affect profitability by increasing pre- and post-weaning gain and carcass quality potential. Using heifers developed from sires selected for growth and milk traits may have long-term impact on sustainability of the cowherd by influencing mature cow size and milk production. Our objective was to determine the impacts of sires selected for high and moderate growth and high and low milk traits on growth and reproductive performance of replacement heifers. Therefore, we selected replacement heifers sired by bulls within the upper 5th and 50th percentiles of the Angus breed for yearling weight (YW) EPD as high growth (HG) moderate growth (MG), the upper 15th percentile of the Angus breed for milk EPD as high milk (HM), and the lower 15th percentile for low milk (LM) in a 2×2 factorial design resulting in 4 treatments: HG/HM, HG/LM, MG/HM, and MG/LM. Heifers (n = 46) from appropriate AI sires that were born and developed at Oklahoma State University – Range Cow Research Center – South Range Unit were selected as replacements. They were raised on a base diet of dry, dormant tall grass prairie and moderate quality grass hay following weaning and 2 kg/d of 16% crude protein concentrate supplement. Body weights and biometrics were recorded at weaning and approximately at 1-yr of age, and blood was collected at 11 and 0 d before synchronization for progesterone analysis to determine pubertal status pre-breeding. Estrus was synchronized using the 14-d CIDR-PG with timed AI method followed by a 45-d natural service breeding period. Pregnancy checks were conducted by serum collection 35-d following AI and via rectal palpation by an experienced veterinarian 112 d after removal of the bulls. Statistical analyses were performed using the mixed procedure of SAS (SAS 9.4, SAS INC., Carey, NC). Heifers from high growth sires were 28 kg heavier at weaning (P < 0.01) and 26 kg heavier as yearlings (P < 0.01) than those sired by moderate growth sires, while sire milk EPD affected neither (P ≥ 0.55). High growth and high milk sired heifers had greater hip heights, frame scores and thus greater (P ≤ 0.05) estimated mature body weight (EMBW). Despite this, sire selection had no impact on percentage of heifers pubertal before breeding, AI pregnancy, or the total pregnancy rates (P > 0.24) Based on these data, selection of sires for HG and HM leads to increased productivity of the offspring but gives rise to larger mature cows, which may pressure grazing resources in limited resource environments impacting the long-term sustainability of the cow-calf enterprise.

162 Nutritive value and dry matter yield of stockpiled tall fescue across plant hardiness zones 7 and 8

Abstract Pastures in Tennessee comprise mainly tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.], a cool-season perennial grass. Given that producers in Tennessee feed hay for an average of 143 d per year, there is interest in utilizing the practice of stockpiling to extend the grazing season. Although this practice has been proven to reduce hay needs (Freeman et al., 2019), it is vital to maintain up-to-date recommendations using data from across the southeastern US to inform grazing decisions. The objective of this study was to determine the nutritive value and dry matter yield of stockpiled tall fescue across plant hardiness zones 7 and 8. Fourteen farms across Tennessee and Alabama were identified as sampling sites. In September 2021, three exclusion cages (1.3 m × 1.3 m) were constructed at each site, forage was clipped to a 5-cm height, and plots were fertilized at a rate of 67 kg N/ha. During years 2021-2022 and 2022-2023, samples were clipped at a 5-cm height from a 0.1-m2 quadrat monthly from October through February. Samples were collected from a different location within the plot each month to ensure there was no overlap. Samples were dried and weighed to determine dry matter yield and then ground for NIRS analysis to determine nutritive value. Data were analyzed using PROC GLIMMIX for a completely randomized design. Independent variables were stockpile period length and plant hardiness zone. Results indicate that plant hardiness zone did not have a significant effect on forage yield (P = 0.2098). Dry matter yield increased over the length of the stockpiling period (P < 0.0001) from 2,637 to 4,922 kg DM/ha. Crude protein (CP) and total digestible nutrients (TDN) concentrations decreased (P < 0.0001 and P = 0.0358, respectively) throughout the stockpiling period; however, ranges were still within those needed to support the nutritional needs of a lactating cow with CP ranging from 15 to 17% and TDN ranging from 68 to 70%. As expected, neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations increased over the stockpiling period (P = 0.0029 and P = 0.0145, respectively) as plants matures. There were no significant changes in ash and fat concentrations due to stockpiling length. Results from this study conclude that stockpiled tall fescue in plant hardiness zones 7 and 8 can support the nutritional requirements of mature cows at all stages of production through the winter months. Results will be used to inform Extension recommendations to assist producers in making management decisions that increase grazing days and reduce supplemental feed input costs.