First report of a perforated abomasal ulcer in a beef heifer calf in Argentina

Abomasal ulcers are local processes of autodigestion of the mucosa caused by the disturbance of the balance between protective and aggressive mechanisms at the abomasal mucosa. Several causes have been suggested and a multifactorial origin has been proposed. Signs are mostly non-specific and vary among the different ulcer types. This report describes for the first time in Argentina the clinical case of a perforated abomasal ulcer that induced sudden death in a heifer calf at foot dairy. At necropsy, digestive content in the abdominal cavity and two ulcers in the abomasum mucosa were evident. One ulcer had a well-defined 3 cm diameter perforation. Its leading cause has not been determined. To minimize the risk of developing perforated abomasal ulcers, stressful management practices should be avoided.Fil: Pérez, Denisa Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigación Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigación Veterinaria de Tandil. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Centro de Investigación Veterinaria de Tandil; ArgentinaFil: Pérez, Flavio. No especifíca;Fil: Bretschneider, Gustavo. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Buenos Aires Sur. Estacion Experimental Agropecuaria Balcarce. Agencia de Extension Rural Necochea.; Argentin

Comparative evaluation of udder and body conformation traits of first lactation ¾ Holstein x ¼ Jersey versus Holstein cows = Comparación de las características de conformación de la ubre y el cuerpo de vacas de primera lactancia ¾ Holstein x ¼ Jersey versus Holstein

To facilitate the process of decision-making in selecting specific breeds for crossbreeding, this study aimed to determine the conformation traits of ¾ Holstein (HO) x ¼ Jersey (JE) crossbreds, relative to their pure HO contemporaries during the first lactation. All measurements were objectively recorded on first-calf heifers between 40 and 100 days in milk. Crossbreds had smaller stature (-9.62 cm; P = 0.0001), narrower rump width (-1.55 cm; P = 0.005), shallower body depth (-6.45 cm; P = 0.04), smaller heart girth (-10.43 cm; P = 0.0001), narrower chest width (-2.18 cm; P = 0.006), and lower foot angle (-4.61°; P = 0.02) than HO first-calf heifers. Among udder traits, HO x JE crossbreds had deeper (+3.80 cm; P = 0.006) and narrower (-2.32 cm; P = 0.001) udders with longer front teats (+0.54 cm; P = 0.04) compared with HO. It is suggested that certain aspects of the mammary conformation of ¾ HO x ¼ JE crossbreds, as identified in this study, may be animal-associated risk factors of concern for cow culling, mainly in high input production systems.Con el objetivo de facilitar la selección de razas para cruzamiento se realizó una evaluación comparativa de las características de conformación de vacas cruza ¾ Holstein (HO) x ¼ Jersey (JE) versus vacas HO. Todas las mediciones fueron registradas en vaquillonas de primer parto de 40 a 100 días en lactancia. En relación con la raza HO, para la cruza se registró una menor estatura (-9,62 cm; P = 0,0001), ancho de grupa (-1,55 cm; P = 0,005) y ancho de pecho (-2,18 cm; P = 0,006), más estrechos, profundidad corporal (-6,45 cm; P = 0,04) y perímetro torácico (-10,43 cm; P = 0,0001) menores y menor ángulo de pezuña (-4,61°; P = 0,02). Entre las características de la glándula mamaria, la cruza presentó ubres más profundas (+3,80 cm; P = 0,006) y estrechas (-2,32 cm; P = 0,001), con pezones anteriores más largos (+0,54 cm; P = 0,04) que la raza HO. Se sugiere que ciertos aspectos de la conformación de la glándula mamaria de la cruza ¾ HO x ¼ JE podrían ser factores de riesgo asociados al animal de importancia en el descarte de vacas, principalmente en sistemas lecheros intensificados.EEA RafaelaFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Arias, Dario Raul. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentin

Estimation of body weight by an indirect measurement method in developing replacement Holstein heifers raised on pasture = Estimación del peso corporal mediante un método indirecto en vaquillonas Holstein de reposición criadas sobre pasturas

Scale is the most accurate means of measuring the actual body weight (BW) in developing heifers. However, when it is not available, indirect tools to estimate BW are needed. The objective of this study was to evaluate the distance between the left and right coxal tuberosity (DLRCT) as potential estimator of shrunk BW (SBW) of developing Holstein heifers as compared with the actual weight measured by an electronic scale. The study included pre-breeding Argentinean Holstein females from 3 to 21 months of age. A dataset comprising 496 observations was used to quantify the relationship between the DLRCT (cm) and the SBW (kg) by the least squared method. The power function Y = 0.131X2.0758, where X = DLRCT provided the best fit (P < 0.0001) for predicting SBW. A dataset comprising 194 observations was used to assess the strength of agreement of the power function. The Lin correlation coefficient value was 0.97 and the computed 95% CI was 0.965-0.979. The mean difference between observed and estimated SBW was -0.99 kg. There was no significant difference (t = -0.83; P = 0.41) in the mean SBW between observed and estimated data. As a predictor of SBW, particularly in heifers ≥ 5 months of age and ≤ 350 kg BW (i.e. ≤ 45 cm), the DLRCT demonstrated to be a useful alternative that can be easily applied during any practice usually performed on replacement heifers, without requiring a squeeze chute.El método más preciso para medir el peso corporal (BW) es la balanza. Sin embargo, cuando la misma no está disponible son necesarios métodos indirectos para estimar el BW. El objetivo de este estudio fue evaluar la distancia entre la tuberosidad coxal izquierda y derecha (DLRCT) como potencial estimador del BW desbastado (SBW) de vaquillonas Holstein en desarrollo, las que fueron pesadas simultáneamente con una balanza electrónica. El estudio incluyó hembras Holstein Argentino preservicio de 3 a 21 meses de edad. Se usaron 496 observaciones para cuantificar la relación entre la DLRCT (cm) y el SBW (kg) por el método de los cuadrados mínimos. La función exponencial Y = 0,131X2,0758, donde X = DLRCT tuvo el mejor ajuste (P < 0,0001) para predecir el SBW. Se emplearon 194 observaciones para validar la función. El coeficiente de correlación de Lin fue 0,97 y el IC 95% fue 0,965-0,979. La diferencia media entre el valor observado y estimado del SBW fue -0,99 kg. No hubo diferencias significativas (t = -0,83; P = 0,41) entre la media observada y estimada del SBW. Como un estimador del SBW, particularmente en vaquillonas ≥ 5 meses de edad y ≤ 350 kg BW (i.e. ≤ 45 cm), la DLRCT demostró ser una alternativa útil que puede ser usada fácilmente durante cualquier práctica habitual realizada sobre las vaquillonas en desarrollo, sin necesidad de instalaciones especiales para la sujeción ni el manipuleo del ganado.EEA RafaelaFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Arias, Dario Raul. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Vottero, Dante Alberto. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentin

Enterohemorrhagic <i>E. coli</i>: virulence factors and infection in cattle

Las cepas de E. coli enterohemorrágica (EHEC) constituyen un subgrupo de las E. coli verotoxigénicas (VTEC) o E. coli productoras de toxinas Shiga (Stx) (STEC). Dentro de este grupo, E. coli O157:H7 es el serotipo productor de Stx más conocido. Las cepas de EHEC producen colitis hemorrágica y el síndrome urémico hemolítico en humanos. Al igual que las cepas enteropatogénicas de E. coli (EPEC), estas cepas median su patogénesis a través de lesiones de "adherencia y destrucción" (lesión A/E). El ganado bovino es el principal reservorio de E. coli O157:H7 y se lo asocia directamente a la mayoría de los brotes en humanos. En esta revisión se analizan los factores de virulencia involucrados en la patogénesis de las cepas EHEC, especialmente aquellos que participan en la colonización de la mucosa intestinal de los bovinos.Enterohemorrhagic E. coli (EHEC) strains constitute a subset of the verotoxigenic E. coli (VTEC) or Shiga toxin (Stx)-producing E. coli (STEC). Within this group, E. coli O157:H7 is the most well-known Stx-producing serotype. EHEC strains produce hemorrhagic colitis and hemolytic uremic syndrome in humans. Like enteropathogenic E. coli (EPEC) strains, they mediate their pathogenesis through "attaching and effacing" (A/E) lesions. Cattle are the main reservoir of E. coli O157:H7 and they are directly linked to most of the human outbreaks. In this review, the virulence factors involved in the pathogenesis of EHEC strains, especially those participating in the colonization of the bovine intestinal mucosa, are analyzed.Facultad de Ciencias Veterinaria

Productive Response of Dairy Cows Fed with Different Levels of Totally Mixed Ration and Pasture

Forty multiparous Holstein cows in early lactation (66 ± 19 days) were assigned to one of four treatments that consisted in different ratios of total mixed rations (TMR) and pasture at 100% TMR (T0), 75:25 (T1) 50:50 (T2) and 25:75 (T3) over 9 weeks in autumn-winter. Measures of rumen parameters and digestion were performed on 4 additional Holstein cows in late lactation (287 days postpartum) fitted with permanent ruminal fistulae and producing 22.6 (±5.4) kg milk in a 4 × 4 Latin Square design. In T1 to T3 cows were taken to the grazing plot once they finished the pre-planned TMR intake and pasture was offered at 2 times the expected forage DM intake. Milk was analyzed for chemical composition, milk fatty acid (FA) profile and antioxidant compounds. The cows were individually weighed and body condition score (BCS) was determined. After the morning milking, blood samples were taken every 2 weeks and plasma was analyzed for glucose, urea, non-esterified fatty acids (NEFA), insulin, growth hormone (GH) and insulin-like growth factor (IGF-I). Herbage mass in pre grazing strips of pasture averaged 2540 ± 343 kg DM/ha. As TMR intake increased, production variables increased linearly excepting milk fat (3.88 g/100g) and milk protein (3.43 g/100g) contents that were not affected. Milk yield (kg/cow/d) resulted maximal in T0 (34.2) and linearly decreased (p < 0.01) with pasture intake averaging 32.1 (T1), 28.4 (T2) and 26.8 (T3) as a higher energy intake and a lower energy cost associated with grazing activity. Milk fat output (kg/cow/d) resulted higher in T0 (1.35) and T1 (1.25) compared to T2 (1.10) and T3 (1.04). Milk protein yield (kg/cow/d) was also higher in T0 (1.18) and T1 (1.11) compared to T2 (0.96) and T3 (0.92). Total DM (24.09 kg/cow/d) and energy (41.95 Mcal NEL/cow/d)) intakes resulted maximal in T0 decreasing as pasture replaced TMR without effects on conversion efficiency (1.48 kg milk/kg DM). Plasma concentration of glucose, insulin and IGF-I were not affected but GH and NEFA increased as pasture replaced TMR in T3. Ruminal pH (5.91) and total or VFA proportions did not differ but NH3-N concentration resulted higher in treatments with higher proportion of pasture. Kinetic parameters of DM and NDF digestion from pasture or corn silage were not affected. Milk FA profile and milk antioxidant quality showed unfavorably changes as TMR increased by a decrease in rumenic and linolenic acids and content of antioxidant vitamins, without effect on the atherogenicity index. Results suggested a depressing effect of the pasture on total DM and energy intake probably explained by qualitative deficiencies chemical composition of the forage and/or factors that affect animal behavior that may induce losses in body condition of high yielding dairy cows.EEA RafaelaFil: Salado, Eloy Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela. Area de Investigación en Producción Animal; ArgentinaFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Agencia De Extensión Rural Necochea; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela. Area de Investigación en Producción Animal; ArgentinaFil: Descalzo, Adriana Maria. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Tecnología de Alimentos; ArgentinaFil: Gagliostro, Gerardo Antonio. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Area de Investigación en Producción Animal; Argentin

Milk Yield and Composition and Pasture Ruminal Digestion in Grazing Dairy Cows Receiving Three Levels of Energy Concentrate Supplementation

The objective of the experiment was to determine the effect of feeding three levels (T3.5, T7.0 and T10.5) of energy concentrate (3.5, 7.0 and 10.5 kg cow-1 day-1) on total dry matter (DM) and energy intakes, milk yield and composition, nutritional value of milk and rumen pasture neutral detergent fiber (NDF) digestion in grazing dairy cows. Twenty-one multiparous Holstein cows in early lactation (70.2 ± 13 days postpartum) producing 37.1 (±4.7) kg of milk were assigned to a 3 treatments (7 cows/treatment) × 3 periods Latin square design. Parameters of ruminal environment and pasture NDF degradation were obtained using 3 additional cows of the same breed fitted with rumen cannulae. On a wet basis, concentrate was composed by corn grain (68%), soybean meal (22%), wheat bran (8%) and a vitamin-mineral nucleus with monensin. Pasture (Medicago sativa, sp) was used in a rotational grazing system with an herbage allowance of 30 kg DM cow-1 d-1. Yield (kg cow-1 d-1) of fat corrected milk (4% FCM) resulted higher (p < 0.05) in T7.0 (29.0) compared to T3.5 (26.8) but similar to T10.5 (30.2). Milk and protein yields were linearly increased (p < 0.01) by concentrate intake. Milk fat (3.13 g/100g) and total solid contents (11.79 g/100g) did not differ whereas milk protein (p < 0.03) and casein (p < 0.01) levels (g/100g) increased linearly from 3.05 to 3.10 (protein) and from 2.42 to 2.47 (casein). Pasture intake decreased but total DM and energy consumption were enhanced showing addition effects after concentrate feeding. Body weight (BW) loss and plasmatic levels of non esterified fatty acids (NEFA) decreased with concentrate intake. Circulating levels of insulin-like growth factor-I (IGF-I) were higher (p < 0.05) in T10.5 while those of glucose, plasma urea nitrogen, insulin and somatotrophin were not affected. Ruminal pH and acetate concentration resulted lower (p < 0.05) in T10.5 when compared to T3.5. The acetate:propionate ratio decreased (p < 0.01) from 4.25 in T3.5 to 3.08 in T10.5 and ruminal ammonia nitrogen levels tended (p < 0.07) to be lower as concentrate intake increased. Kinetics parameters of NDF degradation remained unchanged. The potential hypercholesterolemic fatty acids (FA) of milk (C12:0 to C16:0.) remained unchanged as concentrate intake increased. Milk content of linolenic acid decreased and the n-6:n-3 ratio increased with concentrate intake from 1.56 (T3.5) to 2.57 (T10.5) remaining below the recommended values for human health (<4:1). Milk content of antioxidant vitamins was not significantly altered even when pasture DM intake fall in T10.5 compared to T3.5. Increased consumption of a starch-rich concentrate up to 40% of DM intake of cows showed additive effects on total DM and energy intakes improving milk yield, milk protein and casein contents without negative effects on milk fat concentration or yield. Pasture fiber digestion and nutritional parameters linked to healthy value of milk fat were not affectedEEA RafaelaFil: Salado, Eloy Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela. Area de Investigación en Producción Animal; ArgentinaFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Agencia De Extensión Rural Necochea; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela. Area de Investigación en Producción Animal; ArgentinaFil: Descalzo, Adriana Maria. INTA-LABINTEX-Centre de Coopération Internationale en Recherche Agronomique pour le Déeveloppement (CIRAD), Déepartement PERSYST, UMR Qualisud; FranciaFil: Gagliostro, Gerardo Antonio. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Area de Investigación en Producción Animal; Argentin

Effect of ensiling a total mixed ration on feed quality for cattle in smallholder dairy farms = Efecto de ensilar una ración totalmente mezclada sobre la calidad nutritional para el ganado en pequeñas explotaciones lecheras

The aim of this study was to assess the impact of ensiling a total mixed ration (TMR) on chemical composition, fermentation and sensory characteristics. Whole-plant corn (WPC) was ensiled alone, as a control, or in combination with other available local feeds. Ensiled feedstuffs were manually mixed and packed into mini-silos. Thereafter, they were stored and allowed to ferment for 75 days. Mould growth was not observed. Color was scored as good for both silage treatments, whereas odor was scored as moderate for TMR silage and good for WPC silage. The pattern and rate of decrease of pH during the storage was not different between silage treatments. However, mean pH values were different (P < 0.01; 3.81 vs. 4.38) between WPC- and TMR-silages, respectively. Relative to WPC silage, the concentration of dry matter (DM) (36.58 vs. 64.25 %; P = 0.001), crude protein (9.89 vs. 18.15 %; P = 0.005) and metabolizable energy (P = 0.03; 2.51 vs. 2.80 Mcal/kg DM) was higher for TMR silage, as expected. Furthermore, the neutral detergent fibre content decreased along the storage but at a different rate (P = 0.04) for each silage treatment. The rate of decrease, expressed as percentage/day, was -0.16 and -0.05 for WPC- and TMR- silage, respectively. Overall, TMR silage had adequate attributes to cope with dairy cow requirements. It is suggested that the ensiling of TMR, composed by locally available feedstuffs, is a simple and low cost technology that could aid smallholder dairy to improve their net daily income.El objetivo de este estudio fue determinar el impacto del ensilado sobre la composición química y las características fermentativas y sensoriales de una ración totalmente mezclada (TMR). La planta entera de maíz (WPC) fue ensilada sola, como control, o combinada con otros alimentos disponibles en la región. Los alimentos ensilados se almacenaron en minisilos durante 75 días. No se observó desarrollo de moho. La variable de color se calificó como buena para ambos tratamientos, mientras que el olor se calificó como moderado para el ensilaje de TMR y bueno para el ensilaje de WPC. No hubo diferencias en el patrón y la tasa de disminución del pH entre los tratamientos. Sin embargo, los valores promedios de pH difirieron (P < 0,01; 3.81 vs. 4.38) entre los ensilajes de TMR y de WPC, respectivamente. La concentración de materia seca (MS) (36,58 vs. 64,25 %; P = 0,001), proteína bruta (9,89 vs. 18,15%; P = 0,005) y energía metabolizable (P = 0,03; 2,51 vs. 2,80 Mcal/kg MS) resultó, como era esperado, mayor para el ensilaje de TMR. El contenido de fibra detergente neutro disminuyó durante el almacenamiento, aunque a una velocidad diferente (P = 0,04) para cada tratamiento. Expresada como porcentaje/día, la tasa de disminución fue -0,16 y -0,05 para los ensilajes de WPC y de TMR, respectivamente. Se sugiere que el ensilado de TMR es una tecnología simple y de bajo costo que podría ayudar a mejorar, mediante una mejor alimentación del ganado lechero, los ingresos económicos de los pequeños productores lecheros.EEA RafaelaFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Mattera, Juan. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Arias, Dario Raul. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Wanzenried Zamora, Rosana Andrea. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentin

Productive response to two concentrate allocation strategies in dairy cows grazing with restricted pasture allowance

The objective of this study was to compare the effects of two concentrate allotment strategies on the performance of dairy cows grazing on restricted pasture and supplemented with conserved forage. Dairy cows fed equal amounts of concentrate (fixed daily rate: 5.5 kg DM/cow) were compared to cows supplemented with concentrate according to their lactation stage as follows: 10.0, 5.0, and 1.5 kg DM/cow daily during early, mid, and late lactation, respectively (average daily dose: 5.5 kg DM/cow). There was a supplementation strategy × lactation stage interaction (P < 0.05) for energy-corrected milk (ECM). For early lactation cows, supplementation at a variable rate increased ECM yield by 14.61% (P < 0.05). There was a supplementation strategy × lactation stage interaction (P < 0.05) for body weight change. At late lactation stage, cows supplemented at a fixed rate gained weight (+ 0.16 kg/day), whereas those supplemented at a variable rate lost weight (– 0.08 kg/day; P < 0.05). No significant effect was found for body condition score. The prioritization of milk production rather than the attenuation of body reserve mobilization suggests that concentrate allowance based on lactation stage may be unsuitable for minimizing the negative energy balance in early lactation cows.EEA PergaminoFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Agencia de Extensión Rural Necochea; ArgentinaFil: Salado, Eloy Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Mattera, Juan. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino. Forrajeras; ArgentinaFil: Pece, Mariela. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Arias, Dario. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Cuffia, Maira. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Dieguez, Virginia. Actividad Privada; Argentin

Sistemas de alimentación combinando pastura y ración totalmente mezclada : respuesta productiva y comportamiento reproductivo de vacas lecheras

La competencia de la agricultura por el uso de la tierra y su consecuente aumento de valor ha generado interrogantes sobre la continuidad de los sistemas ganaderos con alternativas de dedicarse a la actividad agrícola, convertirse a sistemas mixtos o implementar estrategias que permitan aumentar la producción y ser más eficientes en el uso de la tierra. Este contexto generó una demanda creciente de información sobre sistemas de alimentación intensificados, que incluyan estrategias de confinamiento parcial o completo en reemplazo del pastoreo.En el presente artículo se presentan resultados obtenidos a partir de un ensayo realizado en el tambo experimental de la EEA Rafaela del INTA, cuyo objetivo fue evaluar los efectos de dos sistemas de alimentación (confinado vs. pastoril con suplementación) sobre la respuesta productiva y el desempeño reproductivo de vacas lecheras en un ensayo de larga duración. Adicionalmente, se evaluó la viabilidad económica de los 2 sistemas utilizando indicadores simples.EEA RafaelaFil: Salado, Eloy Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Maciel, Nicolás. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Bretschneider, Gustavo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Cuatrin, Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Castignani, Horacio. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentin

Escherichia coli O157:H7 infection and associated immune responses in adult cattle

Escherichia coli O157:H7 is an important zoonotic pathogen, and one in which cattle are a major reservoir. E. coli O157:H7 type III secreted proteins are thought to contribute to rectal colonization and fecal shedding in cattle, but studies have not been conducted in slaughter-age animals, nor addressed the immune responses to these proteins in response to infection. This study addressed the significance of the translocated intimin receptor (Tir) in this regard. Adult cattle were orally challenged (C1) with a Tir+ or Tir- E. coli O157:H7 strain and 42 days later rechallenged (C2) with the nalidixic acid (Nal) R parent organism. The Δtir, Tir complemented mutant, and Δtir vector control strains inadvertently did not express flagellin nor effectively colonize the intestine. Prior to C1 inoculation, cattle (n=30) had serum antibody titers to EspB and O157 lipopolysaccharide (LPS) that were higher (P\u3c0.05) than those to Tir, intimin and EspA. After C1, those cattle inoculated with the wild type strain became colonized as evidenced by the magnitude and duration of fecal shedding, and developed significant increases in their serum antibody titers to the Tir, EspA, EspB, intimin and O157 LPS (P\u3c0.05). However, as fecal shedding decreased, titers to all, except EspB, also decreased. In contrast, IgG and IgA antibodies to these same antigens were not detected in the feces, but were detected at low levels in the rectocolonic mucosal secretions. Hence, adult cattle respond serologically and mucosally to E. coli O157:H7 type III secreted proteins, intimin and O157 LPS during the course of infection and the response is correlated with the extent of fecal shedding. Due to the loss of flagellin expression by the Tir -stains, we were unable to determine whether Tir exposure had any effect on protection, and the cause of the loss of expression of flagellin was not addressed. However, we interpret these results as suggesting that either the flagellum or a factor that regulates both its production and that of some other effector has an important function in colonization. This information should aid in the understanding of factors involved in colonization and protection of cattle against E. coli O157:H7 infection