Dois experimentos foram conduzidos com o objetivo de avaliar os efeitos do uso combinado de salinomicina e virginiamicina sobre o metabolismo ruminal, a digestibilidade, o comportamento ingestivo e as características sanguíneas de novilhos Nelore alimentados com dietas de alto concentrado. No experimento I, oito novilhos Nelore com 322 ± 26 kg de peso vivo (PV) inicial foram alocados no delineamento em quadrado latino 4 x 4 replicado, com quatro tratamentos em quatro períodos de 16 dias. Os tratamentos foram arranjados em esquema fatorial 2 x 2, com dois níveis de salinomicina (0 e 13 ppm) e dois níveis de virginiamicina (0 e 15 ppm) na matéria seca (MS) das dietas, que continham 80% de concentrado na MS. No experimento II, oito novilhos Nelore com 434 ± 35 kg de PV inicial foram alocados no mesmo delineamento, mas com períodos de 21 dias. Os tratamentos foram arranjados em esquema fatorial 2 x 2, com dois níveis de concentrado (70 e 90%) e dois níveis de virginiamicina (0 e 15 ppm) na MS das dietas. A salinomicina foi incluída em todas as dietas (13 ppm). Em ambos os experimentos, foram avaliados o consumo individual, a degradabilidade ruminal in situ, a digestibilidade aparente, a fermentação ruminal, o comportamento ingestivo, a população de protozoários ciliados ruminais e as características sanguíneas. As análises estatísticas foram realizadas pelo procedimento MIXED do SAS. No experimento I, houve efeito de nível de salinomicina e virginiamicina sobre as degradabilidades efetiva (DE) e potencial (DP) da fibra insolúvel em detergente neutro (FDN), sendo que os menores valores (P ≤ 0,05) foram observados para os animais tratados com os aditivos. A digestibilidade da proteína bruta (PB) foi maior (P = 0,01) para os novilhos que receberam salinomicina. Animais tratados com virginiamicina apresentaram maior (P = 0,01) concentração ruminal de propionato e menores (P ≤ 0,05) concentrações de acetato, butirato e lactato. Esses animais também apresentaram maior (P ≤ 0,03) tempo total de ruminação (TTR) e mastigação (TTM) e maior (P = 0,05) concentração de lactato no sangue. No experimento II, o aumento no teor de concentrado das dietas promoveu aumento (P = 0,01) no consumo de MS e nas digestibilidades aparentes da MS e PB, bem como redução (P < 0,01) na DE da FDN e PB. Animais tratados com ambos os aditivos apresentaram menor (P = 0,03) DE da FDN. As concentrações ruminais de acetato foram reduzidas (P < 0,01) com a inclusão de virginimicina, mas novilhos tratados com ambos os aditivos e alimentados com dieta contendo 90% de concentrado apresentaram aumento (P < 0,01) nas concentrações de propionato. O aumento no teor de concentrado promoveu redução (P < 0,01) no TTR e TTM dos animais, bem como na população de protozoários ciliados do rúmen e no pH sanguíneo. O uso combinado de salinomicina e virginiamicina apresentou efeitos positivos sobre a fermentação ruminal, especialmente quando a dieta com maior proporção de concentrado foi utilizada. / Two experiments were conducted to evaluate the effects of the combined use of salinomycin and virginiamycin on ruminal metabolism, digestibility, feeding behavior, and blood characteristics of Nellore steers fed high concentrate diets. In experiment I, eight Nellore steers with 322 ± 26 kg of initial body weight (BW) were allotted to a replicated 4 x 4 Latin square, with four treatments and four 16-day periods. Treatments were arranged in a 2 x 2 factorial design, with two salinomycin levels (0 and 13 ppm) and two virginiamycin levels (0 and 15 ppm) in the diet dry matter (DM), which contained 80% concentrate on a DM basis. In experiment II, eight Nellore steers with 434 ± 35 kg of initial BW were allotted to the same experimental design, but with 21-day periods, in a 2 x 2 factorial arrangement of treatments, with two concentrate levels (70 and 90%) and two virginiamycin levels (0 and 15 ppm) in the diet DM. Salinomycin was included in all diets (13 ppm). In both experiments, individual intake, in situ ruminal degradability, apparent digestibility, ruminal fermentation, feeding behavior, ciliated protozoa counts, and blood characteristics were evaluated. Statistical analyses were conducted using the MIXED procedure of SAS. In experiment I, there were effects of salinomycin and virginiamycin on effective and potential degradabilities (ED and PD, respectively) of the neutral detergent fiber (NDF), with lower values (P ≤ 0.05) observed for animals receiving the additives. Crude protein (CP) digestibility was higher (P = 0.01) for salinomycin-treated steers. Animals receiving virginiamycin showed higher (P = 0.01) ruminal concentrations of propionate and lower (P ≤ 0.05) ruminal concentrations of acetate, butyrate, and lactate. These animals also showed higher (P ≤ 0.03) total time spent ruminating (TTSR) and total time spent chewing (TTSC), as well as higher (P = 0.05) blood lactate concentrations. In experiment II, increasing concentrate levels increased (P = 0.01) DM intake and DM and CP digestibilities, but also decreased (P < 0.01) ED of the NDF and CP. Ruminal concentrations of acetate were reduced (P < 0.01) due to the inclusion of virginiamycin, but steers receiving both feed additives within the 90% concentrate group showed increased (P < 0.01) ruminal concentrations of propionate. Increasing concentrate levels decreased (P < 0.01) TTSR and TTSC, as well as ciliated protozoa counts and blood pH. The combined use of salinomycin and virginiamycin showed positive effects on ruminal fermentation, especially when animals were fed the higher concentrate diet.

Fetal programming is a relatively new and quickly growing field of research in the livestock industry. The concept of fetal programming is simply defined as the effects a change in maternal nutritional intake has on offspring, whether it be a genetic or physical change. The intention of this study was to specifically look at the effects of nutrient restriction of cows during the second trimester of gestation on the growth and performance of the resulting calves. In this study, thirty-two cows of predominantly angus influence from the Utah state university herd were chosen, naturally bred to a pure bred angus sire, and then allocated into two treatments: maintenance and restricted. These groups were treated uniformly for first and third trimesters of gestation, while in the second trimester, they were managed in a way that the maintenance group maintained a greater level of body condition and weight compared with the restricted group. Calf growth and performance was measured and compared for effects of fetal programming. Previous studies in beef found positive effects on carcass characteristics. However, little work has been done to ensure that fetal programming is not detrimental to calves early in life. Though this study did find that nutrient restriction resulted in more excitable cattle, no negative effects caused by programming were found in growth and performance of the offspring.

Graduation date: 1998

Bovine Spongiform Encephalopathy (BSE) belongs to a group of neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs) which affect many species. From 1986 more than 184,000 cattle in the UK have been confirmed to be infected with this disease, and in Canada total losses to the economy reached $6 billion. This study examines the gene expression in three major innate immunity components: complement system, toll-like receptors, interleukins, and selected proteins of their signaling pathways. Quantitative real time polymerase chain reaction analyses were performed on caudal medulla samples to identify differentially expressed genes between non-exposed and orally challenged animals. In general, immune genes were down-regulated in comparison to non-challenged animals during first 12 months of disease with a tendency to be up-regulated at terminal stage of BSE. The results from this study provide a basis for further research on the mechanisms modifying immune responses and altering progression of the disease. / Animal Science

Overwintering of cows is a major cost in a cow-calf production system on the prairies. Winter feeding hay and straw directly on pasture is a potentially more efficient and economical system compared to conventional drylot feeding in a yard. The objectives of the research described in this thesis were to compare winter feeding cattle directly on pasture to traditional drylot over-wintering of cattle and the associated mechanized spreading of manure on pasture. This trial compared the effects of winter feeding systems on pasture nutrient distribution, nutrient recovery in soil and forage, pasture forage response, cattle performance, and economics. <p>The experiment was conducted at Lanigan, SK, on an old russian wildrye grass pasture. Pasture nutrient levels and distribution were measured before and after winter feeding, as well as forage yield, and cattle weight and condition. Nutrient capture and cycling was assessed along with the economics of the different systems. In the pasture fed systems, cattle were fed by either bale processing or bale grazing methods over the winter of 2003-2004. Cattle concentration was 2080 cow-days ha-1, with the cattle in the field for 130 d. In the intensive system used for comparison, cattle were fed in a drylot and 67 tonnes ha-1 of raw manure or 22 tonnes ha-1 of compost was mechanically spread on the pasture in the fall of 2003.<p>Soil inorganic nitrogen (N) levels (0-15 cm) measured in the spring where the cattle were winter fed on pasture were 3 to 4 times the unfertilized, unmanured control treatment, with a mean gain of 117 kg N ha-1. Soil inorganic N was not significantly elevated where manure or compost had been spread by machine. Soil extractable potassium (K) was doubled on the winter feeding sites, with a mean gain of 1209 kg K ha-1. Soil extractable K did not increase where manure or compost had been spread mechanically. Soil distribution patterns of both nutrients were highly uneven following pasture feeding, with levels of inorganic soil N ranging from 12 to 626 kg ha-1 and extractable soil K ranging from 718 to 6326 kg ha-1. Additional nutrients in surface residue from uneaten feed, bedding, and manure were also heavy and variable following pasture feeding. Greater retention of N and K from urine added directly to the soil in the field in the bale grazing and bale processing systems compared to the drylot system is believed to be responsible for high soil available N and K levels compared to manure hauled from the drylot into the field.<p>Soil extractable phosphorus (P) levels (0-15 cm) were measured in the fall of 2005. The compost treatment had the largest increase at 2.6 times the control, an additional 46 kg ha-1. Mean soil P levels did not increase significantly where the cattle were wintered.<p> Over 18 months and 3 harvests, forage dry matter yields where the cattle were fed on pasture were 3 to 5 times the control where the cattle were fed on the pasture, and 1.4 to 1.7 times the control where raw manure or compost was mechanically spread. Also, protein content of the forage was increased to a greater extent in the in-field feeding compared to hauled raw manure or compost, reflecting a greater conservation of N.<p>The gain of N in the forage over 18 months on the winter feeding sites was 200 kg ha-1 of N, almost double what was measured in soil inorganic forms. Fourteen kg ha-1 of P was also recovered. This represented 34% of original feed N and 22% of original feed P that was imported into the field. Recovery of nutrients applied in the raw manure and compost sites was much lower, with only 7% recovery of N and 4% recovery of P in the forage. This was calculated to be 1% of original feed N and 3% of original feed P.<p>The system by which the cattle were overwintered had little influence on cattle weight and condition. All systems performed favorably in maintaining body weight and condition over the winter. Some slight advantages in cattle weight gain and condition were found on the winter feeding systems compared to the in-yard drylot that appeared to be related to slightly increased feed intake.<p>Economic calculations favored winter feeding directly on the pasture by 25% over the drylot systems when the feed value of additional pasture growth over 18 months was included and by 56% when the value of additional soil nutrients was factored in. Feed costs were similar between the systems but pasture feeding had savings in machinery use, fuel consumption and manure handling costs, and gains in pasture productivity.<p>Systems that winter fed cattle directly on pasture provided gains in nutrient cycling efficiencies, pasture growth, and economic savings compared to drylot feeding systems, while maintaining similar cattle growth and condition.

Overwintering of cows is a major cost in a cow-calf production system on the prairies. Winter feeding hay and straw directly on pasture is a potentially more efficient and economical system compared to conventional drylot feeding in a yard. The objectives of the research described in this thesis were to compare winter feeding cattle directly on pasture to traditional drylot over-wintering of cattle and the associated mechanized spreading of manure on pasture. This trial compared the effects of winter feeding systems on pasture nutrient distribution, nutrient recovery in soil and forage, pasture forage response, cattle performance, and economics. <p>The experiment was conducted at Lanigan, SK, on an old russian wildrye grass pasture. Pasture nutrient levels and distribution were measured before and after winter feeding, as well as forage yield, and cattle weight and condition. Nutrient capture and cycling was assessed along with the economics of the different systems. In the pasture fed systems, cattle were fed by either bale processing or bale grazing methods over the winter of 2003-2004. Cattle concentration was 2080 cow-days ha-1, with the cattle in the field for 130 d. In the intensive system used for comparison, cattle were fed in a drylot and 67 tonnes ha-1 of raw manure or 22 tonnes ha-1 of compost was mechanically spread on the pasture in the fall of 2003.<p>Soil inorganic nitrogen (N) levels (0-15 cm) measured in the spring where the cattle were winter fed on pasture were 3 to 4 times the unfertilized, unmanured control treatment, with a mean gain of 117 kg N ha-1. Soil inorganic N was not significantly elevated where manure or compost had been spread by machine. Soil extractable potassium (K) was doubled on the winter feeding sites, with a mean gain of 1209 kg K ha-1. Soil extractable K did not increase where manure or compost had been spread mechanically. Soil distribution patterns of both nutrients were highly uneven following pasture feeding, with levels of inorganic soil N ranging from 12 to 626 kg ha-1 and extractable soil K ranging from 718 to 6326 kg ha-1. Additional nutrients in surface residue from uneaten feed, bedding, and manure were also heavy and variable following pasture feeding. Greater retention of N and K from urine added directly to the soil in the field in the bale grazing and bale processing systems compared to the drylot system is believed to be responsible for high soil available N and K levels compared to manure hauled from the drylot into the field.<p>Soil extractable phosphorus (P) levels (0-15 cm) were measured in the fall of 2005. The compost treatment had the largest increase at 2.6 times the control, an additional 46 kg ha-1. Mean soil P levels did not increase significantly where the cattle were wintered.<p> Over 18 months and 3 harvests, forage dry matter yields where the cattle were fed on pasture were 3 to 5 times the control where the cattle were fed on the pasture, and 1.4 to 1.7 times the control where raw manure or compost was mechanically spread. Also, protein content of the forage was increased to a greater extent in the in-field feeding compared to hauled raw manure or compost, reflecting a greater conservation of N.<p>The gain of N in the forage over 18 months on the winter feeding sites was 200 kg ha-1 of N, almost double what was measured in soil inorganic forms. Fourteen kg ha-1 of P was also recovered. This represented 34% of original feed N and 22% of original feed P that was imported into the field. Recovery of nutrients applied in the raw manure and compost sites was much lower, with only 7% recovery of N and 4% recovery of P in the forage. This was calculated to be 1% of original feed N and 3% of original feed P.<p>The system by which the cattle were overwintered had little influence on cattle weight and condition. All systems performed favorably in maintaining body weight and condition over the winter. Some slight advantages in cattle weight gain and condition were found on the winter feeding systems compared to the in-yard drylot that appeared to be related to slightly increased feed intake.<p>Economic calculations favored winter feeding directly on the pasture by 25% over the drylot systems when the feed value of additional pasture growth over 18 months was included and by 56% when the value of additional soil nutrients was factored in. Feed costs were similar between the systems but pasture feeding had savings in machinery use, fuel consumption and manure handling costs, and gains in pasture productivity.<p>Systems that winter fed cattle directly on pasture provided gains in nutrient cycling efficiencies, pasture growth, and economic savings compared to drylot feeding systems, while maintaining similar cattle growth and condition.

Thesis (M.S.)--Mississippi State University. Department of Animal and Dairy Sciences. / Title from title screen. Includes bibliographical references.

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The cost of feed remains an important factor affecting the profitability of beef production, and the difficulty of recording feed intake is a major limitation in an industry-wide selection program. Novel genomics approaches offer opportunities to select for efficient cattle. Therefore, the main objective of this work was to identify genetic markers responsible for genetic variation in feed efficiency traits as well as to understand the molecular basis of feed efficiency traits. The candidate gene approach revealed new single nucleotide polymorphisms (SNPs) in the Cholecystokinin B receptor (CCKBR) and pancreatic anionic trypsinogen (TRYP8) genes that showed strong evidence of association with feed efficiency traits. An in silico approach was proposed as a cost-effective method for SNP discovery. SNPs within genes Pyruvate carboxylase, ATPaseH+, UBQEI, UCP2, and PTI showed evidence of association with carcass traits without negatively affecting feed efficiency traits. The polymorphisms within genes CCKBR and TRYP8 were associated with pancreas mass and pancreatic exocrine secretion. A fine-mapping study on 1,879 SNPs revealed 807 SNPs with significant associations corresponding to 1,012 genes. These 807 SNPs represented a genomic heritability of 0.32 and 89% of the genetic variance of residual feed intake (RFI). Genomic breeding values estimated from the SNP set (807) were highly correlated (0.96) to the breeding values estimated from a mixed animal model. The 10 most influential SNPs were located in chromosomes 16, 17, 9, 11, 12, 20, 15, and 19. Enrichment analysis for the identified genes (1,012) suggested 110 biological processes and 141 pathways contributed to variation in RFI. The 339 newly identified SNPs corresponding to 180 genes identified by fine-mapping were tested for association with feed efficiency, growth, and carcass traits. Strong evidence of associations for RFI was located on chromosomes 8, 15, 16, 18, 19, 21, and 28. Combing validated SNPs from fine-mapping and the candidate gene approach may help develop a DNA test panel for commercial use and increase our understanding of the biological basis of feed efficiency in beef cattle. / The Ministry of Higher Education of Egypt