Efficiency Of Cattle Production Research Articles

The genetic architecture of complete blood counts in lactating Holstein dairy cows.

Complete blood counts (CBCs) measure the abundance of individual immune cells, red blood cells, and related measures such as platelets in circulating blood. These measures can indicate the health status of an animal; thus, baseline circulating levels in a healthy animal may be related to the productive life, resilience, and production efficiency of cattle. The objective of this study is to determine the heritability of CBC traits and identify genomic regions that are associated with CBC measurements in lactating Holstein dairy cattle. The heritability of CBCs was estimated using a Bayes C0 model. The study population consisted of 388 cows with genotypes at roughly 75,000 markers and 16 different CBC phenotypes taken at one to three time points (n = 33, 131, and 224 for 1, 2, and 3 time points, respectively). Heritabilities ranged from 0.00 ± 0.00 (red cell distribution width) to 0.68 ± 0.06 (lymphocytes). A total of 96 different 1-Mb windows were identified that explained more than 1% of the genetic variance for at least one CBC trait, with 10 windows explaining more than 1% of the genetic variance for two or more traits. Multiple genes in the identified regions have functions related to immune response, cell differentiation, anemia, and disease. Positional candidate genes include RAD52 motif-containing protein 1 (RDM1), which is correlated with the degree of immune infiltration of immune cells, and C-X-C motif chemokine ligand 12 (CXCL12), which is critically involved in neutrophil bone marrow storage and release regulation and enhances neutrophil migration. Since animal health directly impacts feed intake, understanding the genetics of CBCs may be useful in identifying more disease-resilient and feed-efficient dairy cattle. Identification of genes responsible for variation in CBCs will also help identify the variability in how dairy cattle defend against illness and injury.

Circadian clocks and their integration with metabolic and reproductive systems: our current understanding and its application to the management of dairy cows.

The circadian system is an inbuilt timekeeping mechanism that tracks the 24-h day through the generation of circadian rhythms. Circadian rhythms enable animals to forecast and anticipate regular changes in their environment, and orchestrate biochemical, physiological and behavioral events so that the right process occurs at the right time. The 24 h rhythms generated by circadian clocks are integrated into homeostatic feedback loops and repair pathways. Metabolic and reproductive systems are highly integrated with the circadian timing system and demonstrate reciprocal regulation. Circadian clocks set the timing of circadian rhythms by gathering temporal information from external and internal signals to include light and nutrients. Exogenous and endogenous factors that function as inputs to the circadian clocks can disrupt their timing when applied at unusual and inappropriate times, and are referred to as chronodisruptors. Changes in the natural light-dark cycle perturb the circadian system. Other chronodisrupters include inappropriately timed food intake and physical activity and biological stress. Knowledge of the biology underlying circadian clock timing is critical to understanding how to maximize health and production efficiency of cattle. Here we review circadian clocks and their function in the regulation of metabolic and reproductive systems as well as the consequence of circadian disruption on mammary development and lactation with a particular focus on recent research findings from studies of dairy cows.

Deforestation, fires, and lack of governance are displacing thousands of jaguars in Brazilian Amazon

AbstractThe rate of deforestation and the number of large wildfires are increasing in the Amazon. Illegal loggers, miners, ranchers, and farmers all have contributed to this increase. Their activities have dramatic consequences for biodiversity, ecological services, and people. In this study, we estimated the number of jaguars affected by deforestation. We focused on the Brazilian Amazon from August 2016 to December 2019. Further, we analyzed the effects of socio‐geographic determinants of deforestation and state policies. To do so, we used deforestation data from DETER‐B satellite system. The number of jaguars within each deforested area was pulled from a previous study, which provided jaguar abundances for jaguar entire range. We assumed all jaguars within a deforested area were affected (displaced or killed). To determine the underlying causes of jaguar loss, we regressed the number of jaguars lost per state and year against the proportion of total forest area within reserves, distance to forest border, and monetary efficiency in cattle production. We estimate a total of 1,422 jaguars have been displaced/killed in recent years (2016: 488, 2017: 360, 2018: 268, 2019: 354). Only the proportion of protected area had an effect in reducing jaguar deforestation. We discuss how our work could result in near real‐time monitoring of jaguar displacement and how policies such as wood certification, more efficient cattle production, and centralizing governance may be solutions.

A Cow-Calf Farming System Fully Adapted to Elevation and Harsh Conditions in Andorra (Europe).

Simple SummaryOptimizing the use of natural resources in cattle production is a concern of the beef meat industry and consumers. Areas with scarce resources or adverse environmental conditions can efficiently take advantage of extensive systems with local breeds. These local breeds are adapted to the environment and can give optimal productive yields. The aim of this work is to explain the project of the Bruna d’Andorra, a local breed under an extensive cow–calf system in Andorra, as an example of local farming and marketing of its meat products. Andorra is a sovereign landlocked microstate in the eastern Pyrenees (Europe) that consists predominantly of rugged mountains and harsh weather conditions for livestock farming. This work describes the evolution of the Bruna d’Andorra population during the period of 2000–2020 focusing on the main meat productive and reproductive performance achievements. Finally, the plans for the future of the project are focused on optimizing a highly sustainable and environmentally friendly farming system.The use of natural resources is an important topic to optimize the efficiency of cattle production. The purpose of this work is to describe the project of the Bruna d’Andorra; a local cow breed under an extensive cow–calf system in Andorra (Europe), as an example of local farming and marketing of its meat products in an area with adverse environmental conditions. This breed is located in Andorra, a microstate that consists predominantly of rugged mountains and harsh weather conditions. The cow–calf Bruna d’Andorra extensive system is thoroughly described and productive and reproductive performance, compiled over 21 years (2000–2020), has been analyzed by years with the Chi-square test or ANOVA to compare proportions or means, respectively, and regression analysis was used to decipher evolution across years. The results show a population with a census large and stable enough to avoid inbreeding. Moreover, a sustained improvement of the productive performance and maternal fitness has been observed along the studied period for Bruna d’Andorra. The work concludes that local breeds can achieve sustainable animal production, especially when farmers, public administration and commercial circuits in the area agree to cooperate on such projects. The study also concludes that the Bruna d’Andorra cow breed can still improve in meat and reproductive performance.

Effect of different cryopreservation extenders added with antioxidants on semen quality and in vitro embryo production efficiency in cattle.

To evaluate the addition of antioxidants in extenders on post-thaw bovine semen quality and in vitro embryo production efficiency. Six semen samples were collected from five Holstein bulls. In the experiment I, the samples were diluted with AndroMed® and Bovimix® and added antioxidants glutathione (1.5 and 2.5 mM) and melatonin (0.5 and 1.0 mM). In the experiment II, the best treatments obtained in experiment I were used for in vitro fecundation. Glutathione did not improve sperm viability. Melatonin had a negative effect on semen characteristics. Andromed® showed better results in sperm kinetics parameters. Bovimix® was more efficient in maintaining cell integrity parameters. Significant correlation was found between sperm kinetics parameters and between cell integrity parameters. For in vitro embryo production, after oocyte selection, maturation, fertilization and cultivation were performed using the four treatments previously evaluated. Andromed® was more efficient in the cleavage rate, no effect of the addition of glutathione. However, the addition of 2.5 mM glutathione in the Bovimix® improved the cleavage rate. There was a significant moderate correlation between cleavage rate and sperm kinetic characteristics. Glutathione did not improve sperm viability. Melatonin reduced the maintenance of sperm characteristics. Andromed® was more efficient in in vitro embryo production and no effect of glutathione was found in this extender. Addition of 2.5 mM glutathione in the Bovimix® extender provided a higher cleavage rate.

Nitrogen recycling and feed efficiency of cattle fed protein-restricted diets

The ability of cattle to grow and reproduce when ingesting low-protein diets is a crucial attribute for productive beef cattle systems in the seasonally dry tropics and subtropics. Nitrogen (N) recycling to the rumen is an important and known physiological mechanism allowing ruminants to efficiently grow in low-protein diets, but is usually disregarded in the nutritional models. This review discusses the role and magnitude of N recycling to provide additional N as microbial substrate in the rumen and in determining the efficiency of ruminants ingesting low-protein diets, to better understand the major factors regulating N recycling to the rumen. In addition to a review of the literature, study-adjusted regressions were used to evaluate various aspects of crude protein (CP) intake and availability, N recycling and excretion. There is large variation in N excretion and N-use efficiency among diets and among individuals, illustrating the opportunity for improvement in overall efficiency of cattle production. These data indicated that N recycling to the entire gastrointestinal tract supplies from half to twice as much N available for microbial growth as does the diet. Addition of rumen-degradable protein can increase rumen efficiency in using the available energy, as, conversely, the addition of fermentable energy can increase rumen efficiency in using the available CP. The present review has demonstrated that both are possible because of greater N recycling. Also, the importance of preserving the available N for determining individual variation in feed efficiency and the implications for selection are discussed. Nitrogen recycling can be controlled at both the epithelial wall of compartments of the gastrointestinal tract and at the liver, where ureagenesis occurs. Addition of fermentable energy can increase N recycling to the rumen and to post-ruminal tract by acting at both sites, and the mechanisms for this are discussed in the text. Although the effect of altering CP concentration in the diet has been substantially investigated, other factors potentially modulating N recycling, such as total fermentable energy, sources of protein and energy, hormonal modulation, and genetic variance, remain poorly understood. The selection of more efficient animals and development of diets with a lower environmental impact inescapably means further elucidation of the N-recycling mechanism.

Efficiency of Resource Use in Dairy Enterprise in Karnataka

The study was under taken to analyze the resource use efficiency of dairy enterprise under stall-fed condition in Karnataka. A total sample size of 68 cattle farmers were selected from Vijayapura and Bagalakote districts of Karnataka for the present study. To estimate the resource use efficiency of cattle production, Cobb Douglas production function was used. The co-efficient of multiple determinations (R2) were 0.77 and 0.82 for Vijayapura and Bagalakote districts respectively, indicating that five variables selected for the analysis have explained 77 and 82 percent variation in the total cattle production. The results of Cobb-Douglas production function revealed that miscellaneous expenses in Vijayapura and concentrate in Bagalakote have positive and highly significant (r<0.001) influence on the gross output. The result of allocative efficiency of resource use in gross output of dairy revealed that labour, medical expenditure and miscellaneous expenses in Vijayapura whereas in case of Bagalakote labour, concentrate and miscellaneous expenses were underutilized and the variables like concentrate in Vijayapura and fodder and medical expenditure in Bagalakote were over utilized.

88 ENRICHMENT OF CULTURE MEDIUM WITH CROCETIN IMPROVES IN VITRO EMBRYO DEVELOPMENT IN CATTLE

The high incidence of developmental failure of bovine in vitro-produced embryos is due to suboptimal culture conditions that induce oxidative stress. Indeed, increased oxidative stress is one of the main factors affecting in vitro mammalian embryo development, decreasing the viability of IVP embryos. It is known that saffron has a powerful antioxidant capacity, mainly due to its active components crocin and crocetin. The aim of this study was to evaluate whether enriching the in vitro culture medium with crocetin improves in vitro embryo production efficiency in cattle. The range of concentrations of crocetin was chosen after a preliminary dose response trial (322 total presumptive zygotes were cultured with 0, 1, 10, and 50 μM, over 2 replicates) that showed beneficial and deleterious effects, respectively, with the lowest and highest concentration compared with the control (36.6 ± 5.6, 57.4 ± 4.5, 46.4 ± 4.4, and 6.8 ± 3.7% blastocyst rates, respectively, with 0, 1, 10, and 50 μM; P &lt; 0.01). Therefore, the range of concentrations to test was reduced. Abattoir-derived bovine oocytes (n = 832, over 4 replicates) were in vitro matured and fertilized according to standard procedures (Rubessa et al. 2011 Theriogenology 76, 1347–1355). Twenty hours after IVF, presumptive zygotes were cultured in SOF medium with 0 (control; n = 208), 1 μM (n = 208), 2.5 μM (n = 208), and 5 μM (n = 208), at 39°C under humidified air with 5% CO2, 7% O2, and 88% N2. The embryos obtained by the end of culture (i.e. on Day 7 post-IVF) were scored for quality, based on morphological criteria, and for developmental stage, as previously described (Robertson and Nelson 2010, Manual of the IETS, 86–105). The percentages of total transferable embryos and grade 1 and 2 blastocysts were recorded. As the chronology of development is a reliable parameter to assess quality, the percentage of fast-developing embryos (i.e. hatched and expanded blastocysts) was also compared among groups. Differences among groups were analysed by ANOVA, and Tukey method was used as a post-hoc test. Data are presented as means ± s.d. The supplementation of crocetin during culture did not affect cleavage rate (74.9 ± 6.3, 76.4 ± 8.4, 81.4 ± 4.3, and 76.4 ± 8.4%, respectively, with 0, 1, 2.5, and 5 μM). However, post-fertilization embryo development improved with 1 µM crocetin compared with the control, both in terms of total embryo output (43.8 ± 4.4, 61.1 ± 5.2, 50.4 ± 6.7, and 53.3 ± 7.3%, respectively, with 0, 1, 2.5, and 5 μM; P &lt; 0.01) and grade 1 and 2 blastocysts (41.0 ± 3.6, 54.3 ± 5.4, 46.2 ± 6.7, and 49.4 ± 6.5%, respectively, with 0, 1, 2.5, and 5 μM; P &lt; 0.05), whereas no differences were observed among the other groups. Moreover, the percentage of fast developing embryos increased with 1 µM (P &lt; 0.05) crocetin compared with the control, with no other differences recorded among groups (17.7 ± 5.8, 34.7 ± 5.7, 24.9 ± 5.1, and 28.7 ± 7.8%, respectively, with 0, 1, 2.5, and 5 μM). In conclusion, these results demonstrated a beneficial effect of low concentrations of crocetin (1 μM) during culture both on blastocyst yield and quality, as indicated by the improved chronology of embryo development.

Supplemental Zinc Oxide Does Not Interact With Zilmax in Feedlot Steers

Zilmax (Merck Animal Health; Summit, NJ) is in a class of feed additives known as beta agonists and is designed to improve production efficiency in cattle when fed 20 days prior to harvest. Zilmax works by altering deposition of body tissue to more lean muscle than fat. Zinc is an essential mineral necessary for normal growth and development of all mammals. Zinc functions largely in enzymes involved in protein synthesis and carbohydrate metabolism along with many other biological reactions. The purpose of this study was to assess changes in blood components and to evaluate the interactive effects of zinc and Zilmax supplementation on growth and carcass characteristics of finishing steers.

Grain feeding coordinately alters expression patterns of transcription factor and metabolic genes in subcutaneous adipose tissue of crossbred heifers1,2

The ability to improve meat quality and production efficiency in cattle is limited by an inability to enhance marbling and simultaneously limit undesirable adipose tissue accretion. The objective of this study was to examine expression of regulatory genes in subcutaneous (SCF) adipose tissue of heifers in response to increasing days on feed (DOF) and finishing strategy. Crossbred heifers (n = 24) were allotted as follows: Group 1 = 0 d, Group 2 = 99 d on winter annual ryegrass (grass; Lolium multiflorum Lam.), Group 3 = 218 g on grass, Group 4 = 99 d on grass followed by 119 d on grain. Adipose tissue samples were collected at time of harvest and frozen. Carcass characteristics were measured 24 h postharvest. As expected, HCW (P < 0.0001), ribeye area (REA; P < 0.0002), backfat (BF; P < 0.0001), KPH (P < 0.0001), and marbling score (P < 0.0009) increased with DOF though frame score was not different (P < 0.95). Average daily gain decreased with DOF (P < 0.0001). Yield grade increased (P < 0.0014) but cook loss percentage decreased (P < 0.001) with DOF without changes in 24-h pH (P < 0.31). Interestingly, Warner-Bratzler shear force (WBS) was decreased with DOF (P < 0.0089). Meanwhile, BF (P < 0.01) and KPH (P < 0.05) were greater, whereas marbling values trended greater in grain versus grass-finished heifers. Neither ADG (P < 0.89), HCW (P < 0.26), frame score (P < 0.85), nor REA (P < 0.38) were different between these groups. Grain finishing increased yield grade (P < 0.001) but did not affect 24-h pH (P < 0.88), cook loss percentage (P < 0.98), or WBS (P < 0.44) compared with grass-finished heifers. The expression of PPARγ, bone morphogenic protein 2 (BMP2), and SMAD family member 1 (SMAD1) mRNA was upregulated in response to DOF and grain finishing, whereas sterol regulatory element binding protein 1c (SREBP-1c), sonic hedgehog (SHH), chicken ovalbumin protein transcription factor 1 (COUP-TF1), chicken ovalbumin protein transcription factor 2 (COUP-TF2), and preadipocyte factor-1 (PREF-1) mRNA was decreased in response to DOF and grain finishing. These changes were associated with increased expression of lipoprotein lipase (LPL), stearoyl-coenzyme A desaturase (SCD), and fatty acid synthase (FAS) mRNA. In summary, increasing DOF was associated with improved meat quality whereas gene expression studies suggest several novel genes are associated with subcutaneous adipose tissue development in growing and finishing cattle.

Improved production efficiency in cattle to reduce their carbon footprint for beef production

The FAO publication, Livestock’s Long Shadow, indicated that livestock is responsible for 18% of the world’s greenhouse gas production thereby creating the perception that livestock is a major cause of global warming. Methane (CH4) makes up 16% of total world gas emissions and is the second most important greenhouse gas (GHG) after carbon dioxide (CO2). Ruminants are important to mankind since most of the world’s vegetation biomass is rich in fibre and only ruminants can convert this vegetation into high quality protein sources for human consumption. In spite of this important role of livestock, it is singled out as producing large quantities of GHG that contribute to climate change, since enteric fermentation is responsible for 28% of global CH4 emissions. However, the net effect from livestock is only a 4.5% contribution to GHG. The livestock industry should be aware of the effect of livestock on climate change and therefore it is important that mechanisms are put in place to mitigate this effect. The improvement of production efficiency through increased production per constant unit, crossbreeding and genetic improvement may be a cost effective and permanent way of reducing the carbon footprint of beef cattle.

Zilmax alters blood constituents of finishing cattle (2012)

The purpose of this experiment was to determine the effects of Zilmax (Merck Animal Health, Summit, NJ) on changes in blood metabolites. Zilmax is a feed additive designed to improve production efficiency in cattle when fed during the last phase at the feedlot. Zilmax works by redirecting the energy use in the body to form more lean muscle at the expense of fat deposition. The blood metabolites measured in our experiment were glucose and lactate, which are the energy sources for various body functions including muscle growth. Plasma urea nitrogen was measured as an indicator of protein catabolism. Non-esterified fatty acids also were measured as they were released into the bloodstream with the breakdown of adipose tissue.

Enrichment of Undifferentiated Spermatogonia and Germline Modification Using Lentiviral Vector in the Pre-Pubertal Bull Testis.

Gonocytes are long-lived primary germ cells in the lumen of seminiferous tubules, that gives rise to undifferentiated spermatogonia. During spermatogenesis, the undifferentiated spermatogonia give rise to spermatogonial stem cells (SCCs) that can self-renew and differentiate. Therefore, undifferentiated spermatogonia have become an attractive target for novel technology to enhance the quality and efficiency of cattle production. However, the rarity of bovine undifferentiated spermatogonia including SSCs has raised the need for an efficient selection method in order to culture and transplant them. The present research develops an efficient negative selection method to choose and enrich functionally viable bovine undifferentiated spermatogonial population using extracellular matrix (ECM), laminin, fibronectin, collagen type IV, and their derivative, gelatin. The result shows 8-fold increase in undifferentiated spermatogonia purity with combinatorial isolation method using laminin and gelatin. The transplanted PKH26-labeled bovine undifferentiated spermatogonial population were functionally active and proliferated and colonized in the recipient mouse testes. The transduction efficiency (TE) of lentiviral vector was 15.4% for the undifferentiated spermatogonial population including SSCs transduced with an enhanced green fluorescent protein (eGFP) transgene using a lentiviral vector. The selection and enrichment method proposed in this study can be applied to harvest a large number of functionally active bovine undifferentiated spermatogonia to aid in creating transgenic cattle with optimal reproductive rate. This research was supported by the Ministry of Education, Science and Technology/Stem Cell Research Center of the 21st Century Frontier Research Program (SC-5140) and the Technology Development Program for Agriculture and Forestry, Ministry for Food, Agriculture, Forestry and Fisheries, Republic of Korea (110025-03-1-HD110) and the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MEST) (2010-0023848). (poster)

In Vitro Embryo Production Efficiency in Cattle and Its Association with Oocyte Adenosine Triphosphate Content, Quantity of Mitochondrial DNA, and Mitochondrial DNA Haplogroup

Mitochondria have a broad range of functions that affect reproduction, and structural as well as quantitative variation in mtDNA has been associated with gamete quality and reproductive success. To investigate the mitochondria effect on in vitro embryo production, we collected oocytes by ultrasound-guided follicular aspiration from donor cows known to differ in the developmental capacity, measured by the blastocyst formation rate, of their oocytes. To evaluate the potential effects of mtDNA and mitochondrial function on oocyte quality, the donor cows' mtDNA control region was sequenced and, after pairwise comparisons of polymorphisms, animals were grouped into two major haplogroups. The number of mtDNA molecules per oocyte was quantified by real-time PCR, and the adenosine triphosphate (ATP) content was measured in each oocyte to identify variations between haplogroups. Overall, ATP stocks in oocytes of the two haplogroups differed significantly (P < 0.05; means +/- SEM) both at the germinal vesicle and metaphase II stages (2.8 +/- 0.06 pmol vs. 2.6 +/- 0.07 pmol and 2.9 +/- 0.1 pmol vs. 2.3 +/- 0.06 pmol, respectively). The proportion of development to blastocyst was significantly different between haplogroups (22.3 +/- 2.1 % vs. 36.7 +/- 2.9 %). The number of mtDNA molecules per oocyte was highly variable (377 327 +/- 14 104, ranging from 2.0 x 10(3) to 1.2 x 10(6)) but not significantly different between the two haplogroups; significant differences were observed between animals without any apparent relationship to blastocyst production. These data suggest that mitochondria and mtDNA haplogroup affect the developmental capacity of bovine oocytes in vitro.

Modeling growth of cattle for application within the structure of the Cornell Net Carbohydrate and Protein System.

We use cattle around the world to convert forages, feed grains, and food byproducts into human food under production conditions that vary in soil, climate, feed composition, and genotype of cattle. Our goal over the past 20 years has been to develop a model of cattle nutrition that can be used to balance diets, thus converting these nutrients into human food as efficiently as possible. Our analyses indicate that accurate prediction of nutrient balance in each situation depends on the ability to predict cattle requirements and the supply of ruminally degraded carbohydrates, protein, microbial growth, total digestible nutrients (TDN), metabolizable energy (ME), net energy (NE), heat increment (HI), metabolizable protein (MP), net protein (NP), and essential amino acids (EAA). Formulating rations for varying cattle requirements thus requires an accounting system for the variables known to influence requirements and the dietary supply of energy and absorbed amino acids. In case studies and field experiences, we have found that the efficiency of cattle production can be improved using models to account for performance variation by accurately predicting requirements and feed utilization in individual production settings. The O‘Cornell Net Carbohydrate and Protein SystemO’ (CNCPS), as described and validated by Fox et al. (1992), Russell et al. (1992), Sniffen et al. (1992), Ainslie et al. (1993), O’Connor et al. (1993), Tylutki et al. (1994), Fox et al. (1995), the National Research Council (NRC, 1996), Pitt et al. (1996), Fox et al. (2000a, b), and Tedeschi et al. (2000 a, b), was developed for that purpose. The CNCPS has been used as a teaching tool for students and consultants as well as to design and interpret experiments, apply research results, develop tables of nutrient requirements for any cattle type and production level, and evaluate and improve feeding programs on farms.

Ionophores for Dairy Cattle: Current Status and Future Outlook

Ionophores are used commercially throughout the world in the beef and poultry industries. Production efficiency of cattle is increased through alteration of rumen fermentation and control of protozoa that cause coccidiosis. Ionophores act by interrupting transmembrane movement and intracellular equilibrium of ions in certain classes of bacteria and protozoa that inhabit the gastrointestinal tract. The actions of ionophores provide a competitive advantage for certain microbes at the expense of others. In general, the metabolism of the selected microorganisms favors the host animal. Energy metabolism is enhanced through increased production of propionate among ruminal fatty acids with a concomitant reduction in methane. Ruminal degradation of peptides and amino acids is reduced, thereby increasing the flow of protein of dietary origin to the small intestine. Total flow of protein to the lower tract is often increased with ionophore feeding. Risk of digestive disorders such as bloat and acidosis that result from abnormal rumen fermentation is reduced, as are certain conditions caused by toxic products of fermentation, e.g., 3-methyl indole. Dry matter and nitrogen digestibilities are increased with ionophores, thereby providing environmental benefits. Monensin and lasalocid have been the most studied in research demonstrating benefits to the dairy cow. Ionophores enhance the glucose status of dairy cows through increased production of propionate. Many of the demonstrated benefits of ionophores are associated with enhancement of the energy status of the cow in the transition period and during early lactation. The benefits include less mobilization of body fat as evidenced by reduced blood nonesterified fatty acids and ketones and increased glucose. Animal manifestations include lower incidence of ketosis and displaced abomasum, reduced loss of body condition, increased milk production, and improved milk production efficiency.

Evaluation of growth curves of Brahman cattle of various frame sizes.

Partial stage and complete life-cycle growth curves of Brahman cattle were obtained for small, medium, and large frame sizes for a herd under grazing conditions in a subtropical environment. Data were grouped into three stages: birth to weaning (stage 1), weaning to 20 mo (males) or 32 mo (females) of age (stage 2), and 32 mo of age to maturity (females only; stage 3). Within each stage, multiplicative growth models were developed for each frame size and sex. Body weight growth on age t was represented as exp(a + bt + ct2) for stages 1 and 2, and as exp(A + B exp(kt)) for stage 3. The effects of sire and progeny within sire were considered in all models. For stages 2 and 3, the effect of season was also included. To obtain complete life-cycle curves, a growth stage-multiplicative model with stages 1 and 2 was defined; stage 3 was also included for females. Due to a 1-mo adaptation period after weaning, a transition stage between stages 1 and 2 was defined and represented by the model exp(a + bt). In stage 1, the shape of the growth curve differed (P < .05) among frame size groups; sex did not affect the shape of the growth curves, but bull calves had heavier (P < .05) weights than heifer calves. In stage 2, the shape of the growth curves did not differ among frame sizes, but BW differed among frame sizes (P < .05) and sex affected (P < .05) the shape of the growth curves. In stage 3, the shape of the growth curves differed (P < .05) among frame sizes. There were sire effects (P < .05) for stages 1 and 2, but sire effects were not significant for stage 3. Season effects were important (P < .05) for stages 1 and 2. These results suggest that variability in growth patterns provides an opportunity to use management and nutrition to improve production efficiency in cattle of different frame sizes.

The effect of body size on production efficiency in cattle. Breed comparisons and inter-breed relationships

The effect of body size on production efficiency in cattle. Breed comparisons and inter-breed relationships