Resumen Antecedentes: Las variables asociadas a mayor movilización de tejido corporal en vacas lecheras conducen a un mayor riesgo de falla reproductiva. Objetivo: Investigar la asociación entre los metabolitos sanguíneos y condición corporal (BCS) al comienzo de la lactancia y la eficiencia reproductiva y producción de leche de vacas Holstein en un ambiente caluroso. Métodos: En total, se seleccionaron 165 vacas Holstein de las cual se tomaron muestras de sangre para determinar la concentración de varios matabolitos sanguíneos, los cuales se asociaron con el desempeño reproductivo y producción de leche. Resultados: Las vacas con β-hidroxibutirato (BHBA) en suero ≤0,8 mmol/L una semana postparto tuvieron 3,3 veces más probabilidades de quedar preñadas en los primeros servicios, y 2,2 veces más probabilidades de quedar gestantes antes de los 80 días postparto que las vacas con mayores niveles séricos de BHBA. Las probabilidades (OR 2,7; IC 95% 1,3-5,4; p<0,01) de que una vaca se preñara en el primer servicio fueron mayores en vacas con niveles de creatinina en suero sanguíneo superiores a 2,0 mg/dL una semana postparto que las vacas con niveles más bajos de este metabolito en sangre. Una BCS de 3 a los 30 y 60 días postparto fue un buen predictor de la preñez al primer servicio y la gestación considerando todos los servicios. El nitrógeno ureico en sangre >15 mg/dL, la creatinina <1,8 mg/dL, la proteína total ≤5,0 mg/dL una semana después del parto y >0,40 unidades de pérdida de BCS durante los primeros 30 días postparto fueron los valores críticos para predecir una producción de leche a 305 días superior a 10.500 kg. Conclusiones: El BHBA y la creatinina en suero sanguíneo una semana postparto, así como la BCS 30 y 60 d después del parto, proporcionan valores razonablemente precisos para identificar las vacas que tendrán mejor desempeño reproductivo y mayor producción de leche a 305 días.

Abstract Background: Variables associated with body tissue mobilization place dairy cows at greater risk of reproductive failure. Objective: To investigate the association between blood metabolites and body condition score (BCS) at the beginning of lactation and the reproductive efficiency and milk yield of Holstein cows in a hot environment. Methods: In total, 165 Holstein cows were selected for the study from which blood samples were taken to determine the concentration of various blood metabolites and their association with the reproductive efficiency and milk yield. Results: Cows with serum β-hydroxybutyrate (BHBA) ≤0.8 mmol/L one week postpartum were 3.3 times more likely to become pregnant at first service, and 2.2 times more likely to become pregnant before 80 d postpartum than cows with higher serum BHBA levels. The odds (OR 2.7; 95% CI 1.3-5.4; p<0.01) of a cow getting pregnant at first service were higher in cows with serum creatinine levels higher than 2.0 mg/dL one week postpartum than cows with lower blood levels of this metabolite. The BCS at 30 and 60 d postpartum that predicted pregnancy at first service and pregnancy to all services was 3.0. Blood urea nitrogen >15 mg/dL, creatinine <1.8 mg/dL, total protein ≤5.0 mg/dL one week postpartum, and >0.40 units of BCS loss during the first 30 d postpartum were critical threshold that predicted the likelihood of 305-d milk yield higher than 10,500 kg. Conclusions: Serum BHBA and creatinine one wk after calving as well as BCS 30 and 60 d post-calving provided reasonably accurate cut-off screening values to discriminate cows with better reproductive performance and higher 305-d milk yield.

Resumo Antecedentes: A maior mobilização do tecido corporal das vacas leiteiras leva a um aumento do risco de falhas reprodutivas. Objetivo: Para investigar a relação entre os metabolitos sanguíneos e condição do corpo (BCS) para o início da lactação e eficiência reprodutiva e produção de leite de vacas Holstein num ambiente quente. Métodos: No total, foram selecionadas 165 vacas da raça Holandesa, das quais foram coletadas amostras de sangue para determinar a concentração de vários metabólitos sanguíneos, associados ao desempenho reprodutivo e à produção de leite das vacas. Resultados: As vacas com β-hidroxibutirato (BHBA) soro ≤0,8 mmol/L de uma semana após o nascimento foram 3,3 vezes mais probabilidade de engravidar nos primeiros serviços, e 2,2 vezes mais provável que seja grávida antes de 80 dias após o parto do que vacas com níveis séricos de BHBA mais elevados. As probabilidades (OR 2,7, IC de 95% 1,3-5,4, p<0,01) que uma vaca preñara primeiros serviços vacas foram maiores com níveis mais elevados de creatinina no soro do sangue >2,0 mg/dL, uma semana pós-parto do que vacas com níveis sanguíneos mais baixos deste metabolito. Um CC de 3 aos 30 e 60 dias pós-parto foi um bom predictor de gravidez no primeiro serviço e gestação, considerando todos os serviços. O azoto de ureia no sangue >15 mg/dL, creatinina <1,8 mg/dL e proteína total, ≤5,0 mg/dL uma semana após o parto e >0,40 unidades perda CC durante os primeiros 30 dias após o nascimento estavam valores críticos que previram produção de leite em 305 dias >10.500 kg. Conclusões: BHBA e creatinina sérica, uma semana após o parto, bem como CC 30 e 60 d após o parto, forneceram valores razoavelmente precisos para discriminar vacas com melhor desempenho reprodutivo e maior produção de leite em 305 dias.

Abstract The high temperatures recorded during the summer season in hot regions compromise the reproductive capacity of domestic animals. In rams, heat stress (HS) causes in the body a series of physiological, metabolic, endocrine and molecular adjustments in order to maintain normothermia and survive; however, several of these changes are negatively associated with their fertility, mainly endocrine ones. HS in rams causes a decrease in blood testosterone concentrations through different mechanisms, and this is negatively reflected on the process of spermatogenesis and sexual behavior. Consequently, heat-stressed rams exhibit low seminal quality and libido; at the sperm level, structural and DNA damage has been observed. Given this situation, the use of HS mitigation strategies during the summer in sheep farms in hot regions is recommended, such as the use of shades in pens, administration of antioxidants or modifications in the diet. Therefore, the objective of this document is to review the current knowledge regarding the effect of HS on the thermoregulation and reproductive capacity of rams, as well as the application of strategies for its mitigation.

Resumen Las temperaturas elevadas registradas durante la época de verano en las regiones cálidas comprometen la capacidad reproductiva de los animales domésticos. En carneros, el estrés por calor (EC) causa en el organismo una serie de ajustes fisiológicos, metabólicos, endocrinos y moleculares con el objeto de mantener normotermia y sobrevivir; sin embargo, varios de estos cambios se asocian negativamente con su fertilidad, principalmente los endocrinos. El EC en carneros provoca una disminución en las concentraciones sanguíneas de testosterona a través de diferentes mecanismos, y esto se refleja negativamente en el proceso de espermatogénesis y en la conducta sexual. En consecuencia, los carneros estresados por calor presentan baja calidad seminal y apetito sexual; a nivel de espermatozoides se ha observado daño estructural y en el ADN. Dada esta situación, se recomienda el uso de estrategias de mitigación del EC durante el verano en las explotaciones ovinas de regiones cálidas, tales como el uso de sombras en corrales, la administración de antioxidantes o modificaciones en la alimentación. Por lo tanto, el objetivo de este documento es revisar el conocimiento actual en relación al efecto del EC sobre la capacidad de termorregulación y reproductiva de los carneros, así como la aplicación de estrategias para su mitigación.

ABSTRACT Knowledge about vegetation patterns along topographic gradients is crucial for conservation and management of arid islands. The objective of this study was to identify environmental, soil, and topography variables affecting plant distribution in Monserrat Island. A floristic and environmental survey was undertaken on this island (25o 41’ 00” N, 111o 03’ 00” W; 19.9 km2) in the Gulf of California, Mexico. Seven geoform zones were distinguished. The vegetation is predominantly a sarcocaule xerophilous scrub which develops mainly in ravines and bottoms of streams. One hundred fourteen species were recorded, of which 33 plants (28.9%) are endemic belonging to 92 genera and 38 families of vascular plants. The most abundant families were: Asteraceae, Euphorbiaceae, Fabaceae, Poaceae, and Cactaceae. The Bursera trees are more abundant in areas with little steep slopes (less than 25o). On areas with steep slopes (greater than 45o), the development of vegetation is scarce. Northern exposure slopes had denser vegetation, with higher canopy cover values. Slope was far more reliably measure for describing vegetation distribution than altitude, although, the latter variable influences Olneya tesota. Euphorbia magdalenae was strongly associated with slope, and both Jouvea pilosa and Marina parryi was influenced by soil characteristics. Jatropha cuneata was found in almost all geoforms. It was concluded that Monserrat Island possesses a distinctive mix of xeric species making this island unique due to the high presence of endemic plants.

RESUMEN El conocimiento de los patrones de la vegetación en gradientes topográficos es crucial para la conservación y el manejo de islas en ecosistemas áridos. El objetivo de este estudio fue identificar variables ambientales, de suelo y topográficas que afectan la distribución de las plantas en la Isla Monserrat. Se realizó un estudio florístico y ambiental en esta isla (25o 41’ 00” N, 111o 03’ 00” O; 19.9 km2) en el Golfo de California, México. Se distinguieron siete geoformas. La vegetación es predominantemente un matorral sarcocaule xerófilo que se desarrolla principalmente en barrancos y fondo de arroyos. Se registraron 114 especies de plantas, de las cuales 33 (28.9%) son endémicas y pertenecen a 92 géneros y 38 familias de plantas vasculares. Las familias más abundantes fueron: Asteraceae, Euphorbiaceae, Fabaceae, Poaceae y Cactaceae. Los árboles de Bursera son más abundantes en áreas con pequeñas pendientes pronunciadas (menos de 25o). En áreas con pendientes pronunciadas (más de 45o), el desarrollo de la vegetación es escaso. Las pendientes de exposición norte tienen una vegetación más densa, con valores más altos de cobertura del dosel. La pendiente fue mucho más confiable para describir la distribución de la vegetación que la altitud, aunque esta última variable influye en Olneya tesota. Euphorbia magdalenae está fuertemente asociada con la pendiente, y tanto Jouvea pilosa como Marina parryi están influenciadas por las características del suelo. Jatropha cuneata se encontró en casi todas las geoformas. Se concluyó que la Isla Monserrat posee una mezcla distintiva de especies xéricas que hacen que esta isla sea única debido a la alta presencia de plantas endémicas.

Resumo: O objetivo deste trabalho foi identificar os metabólitos séricos e o escore de condição corporal (BCS) de vacas Holandesas associados à ocorrência de doenças periparturientes, quando sob estresse térmico. Amostras de sangue foram coletadas de 181 vacas uma semana após o parto, e o BCS foi determinado no parto. Vacas com concentração de β-hidroxibutirato (BHBA) ≥ 0,8 mmol L-1 tinham 2,2 vezes mais chances de desenvolver metrite e 4,4 vezes mais chances de desenvolver endometrite clínica (EC). Vacas com níveis séricos de creatinina ≥ 2,0 mg dL-1 apresentaram 2,2 e 4,5 vezes maior risco (p ≤ 0,05) de sofrer de metrite e EC, respectivamente, na lactação atual. As chances de metrite e EC foram 2,7 e 4,6 vezes maiores (p < 0,01) em vacas com proteína total sérica (TP) ≥ 5,0 mg dL-1. Vacas com níveis séricos de glicose ≤ 70 mg dL-1 e ácidos graxos não esterificados (NEFAs) ≥ 0,5 tiveram 9,4 e 8,8 vezes mais chances de desenvolver cetose clínica, respectivamente, que vacas com níveis mais baixos de glicose e NEFAs no sangue. O uso estratégico de testes metabólicos para monitorar vacas Holandesas em transição, para prevenir algumas doenças pós-parto devido ao estresse térmico, deve se concentrar em BHBA, NEFAs, glicose, creatinina e TP no sangue. Além disso, o BCS ≤ 3,2 deve ser evitado para prevenir a endometrite.

Abstract: The objective of this work was to identify the serum metabolites and the body condition score (BCS) of Holstein cows associated with the occurrence of periparturient diseases, when under heat stress. Blood samples were collected from 181 cows one week after calving, and the BCS was recorded at calving. Cows with β-hydroxybutyrate (BHBA) concentration ≥ 0.8 mmol L-1 were 2.2 times more likely to develop metritis and 4.4 times more likely to develop clinical endometritis (CE). Cows with serum creatinine levels ≥ 2.0 mg dL-1 showed 2.2 and 4.5 greater risk (p ≤ 0.05) of suffering from metritis and CE, respectively, during the current lactation. The odds of metritis and CE occurrence were 2.7 and 4.6 times greater (p < 0.01) in cows with serum total protein (TP) ≥ 5.0 mg dL-1. Cows with serum glucose levels ≤ 70 mg dL-1 and non-esterified fatty acids (NEFAs) ≥ 0.5 had 9.4 and 8.8 times greater odds of developing clinical ketosis, respectively, than cows with lower glucose and NEFA blood levels. The strategic use of metabolic tests to monitor transition Holstein cows, aiming to prevent some postpartum diseases due to heat stress, should focus on blood BHBA, NEFAs, glucose, creatinine, and TP. Additionally, the BCS ≤ 3.2 should be avoided to prevent endometritis.

Abstract The profitability of dairy farms is closely linked to reproductive performance. Identifying risk factors that compromise this performance is vital to implementing strategies to improve productivity. An analysis was done of the effects on reproductive performance of artificial insemination (AI) use, herd size and high seroprevalence of reproductive infectious diseases. Data on reproductive events were collected from 52 farms (10-100 cows; 959 lactations) over 18 mo (births 2011-2012). Neosporosis, bovine infectious rhinotracheitis (IBR) and bovine viral diarrhea (BVD) seroprevalences were documented at each farm. Multiple logistic regression analyses were applied to determine the degree of association (odds ratio, OR) between potential risk factors and reproductive variables. Herds of 33 or more cows (OR= 1.5) and high neosporosis seroprevalence (OR= 2.3) were risk factors for assisted calving. High IBR and BVD seroprevalences (OR= 1.3 and 1.9, respectively) were risk factors for days to first service over 70 d in milk (DFS>70). Artificial insemination was a common risk factor for DFS>70 (OR= 2.4) and days open over 110 days in milk (OR= 1.3). Herds of 33 or more cows was a risk factor for non- pregnant cows at first service (OR= 1.7). Artificial insemination, herds of 33 or more cows and high neosporosis, IBR and BVD seroprevalences are factors associated with reproductive performance in small-scale dairy farms in various geographical regions in Mexico.

Resumen La rentabilidad de los establos lecheros está fuertemente asociada con el desempeño reproductivo. Por lo tanto, la identificación de factores de riesgo que comprometen este desempeño es primordial para implementar estrategias que mejoren la productividad. En este estudio, se probaron los efectos del uso de inseminación artificial (IA), hatos grandes y seroprevalencia alta de enfermedades infecciosas reproductivas sobre el desempeño reproductivo. Se incluyeron al estudio 52 establos (10-100 vacas; 959 lactaciones) registrando eventos reproductivos durante 18 meses (partos 2011-2012). Las seroprevalencias de neosporosis, rinotraqueitis infecciosa bovina (IBR) y diarrea viral bovina (BVD) se registraron en cada establo. Se utilizaron análisis de regresión logística múltiples para determinar el grado de asociación (razón de momios, OR) entre factores potenciales de riesgo y variables reproductivas. Establos ≥33 vacas y seroprevalencia alta de neosporosis fueron factores de riesgo para Asistencia al Parto (OR 1.5 y 2.3, respectivamente). Seroprevalencias altas de IBR y BVD fueron factores de riesgo para Días a Primer Servicio>70 Días en Leche (DPS>70, OR 1.3 y 1.9, respectivamente). La IA fue un factor de riesgo común para DPS>70 y Días Abiertos>110 Días en Leche (OR 2.4 y 1.3, respectivamente). Establos ≥33 vacas fue un factor de riesgo para Vacas No Gestantes al Primer Servicio (OR 1.7). En conclusión, la IA, establos ≥33 vacas y seroprevalencias altas de neosporosis, IBR y BVD son factores asociados al desempeño reproductivo en establos de producción de leche a pequeña escala en varias regiones geográficas de México.

Abstract: Ten (10) multiparous hair ewes from white genotype, non-pregnant and non-lactating, were confined in order to determine diurnal variations of physiological variables and some blood metabolite concentrations through hot summer months (June to September) in an desert region of the northwest Mexico. While blood metabolite concentrations were measured at 6 and 18 h, physiological variables were evaluated at 0, 6, 12 and 18 h during 4-d in each month (weekly measurements). Temperature and temperature-humidity index monthly averages during the study were 33.6 oC and 78.6 units, respectively, being August the hottest month. Live weight and body condition did not change (P>0.05) across the summer months. Compared with other months, rectal temperatures in August were lower (P<0.05) between 0 and 12 h, and then increased (P<0.05) at 18 h. Respiration frequency decreased (P<0.05) at 6 h in all the months, but at 0 and 18 h this was higher in August than in other months. Higher (P<0.05) glucose concentration and lower (P<0.05) cholesterol and triglyceride concentration were observed in June and July than in August and September. In conclusion, under desert climatic conditions, hair ewes had the ability to maintain homeothermy during all summer warm months because they changed their diurnal rhythms of physiological and metabolic variables according to the intensity of the heat stress in each month.

Resumen: Se confinaron 10 ovejas multíparas Katahdin × Pelibuey, color blanco, no gestantes y no lactantes, para evaluar las variaciones diurnas de variables fisiológicas y concentración de algunos metabolitos sanguíneos a través de los meses calientes de verano (junio-septiembre), en una región desértica del noroeste de México. Las concentraciones de metabolitos se midieron a las 6 y 18 h y las variables fisiológicas a las 0, 6, 12 y 18 h durante cuatro días de cada mes (mediciones semanales). Los promedios para temperatura ambiental e índice de temperatura-humedad durante el verano fueron 33.6 ºC y 78.6 unidades, respectivamente, siendo agosto el mes más caliente. No cambió (P>0.05) el peso vivo y la condición corporal a través de los meses de verano. La temperatura rectal en agosto fue menor (P<0.05) entre 0 y 12 h, y mayor (P<0.05) a las 18 h comparado con los otros meses. La frecuencia respiratoria descendió (P<0.05) a las 6 h en todos los meses, pero a las 0 y 18 h fue mayor (P<0.05) en agosto que en los otros meses. Se observaron mayores (P<0.05) concentraciones de glucosa y menores (P<0.05) concentraciones de colesterol y triglicéridos en junio y julio con relación a agosto y septiembre. Se concluye que las ovejas de pelo mantienen homeotermia durante los meses de verano en regiones desérticas por cambiar el ritmo diurno de sus variables fisiológicas y metabolitos, de acuerdo con la intensidad del estrés calórico de cada mes.

ABSTRACT: The objective of this study was to analyse the reproductive performance of hybrid (Yorkshire x Landrace) gilts/ sows in relation to temperature-humidity index (THI) at artificial insemination (AI), season of AI, occurrence of estrus >8 d post- weaning, repeated estrus, insemination technique (cervical, CAI or post-cervical, PCAI) and parity. Data included 8851 reproductive records (1771 for gilts and 7080 for sows) from a pig farm in a sub-tropical zone (THI ranged from 72.9 in January to 81.8 in June). A decrease in pregnancy rate (PR, 89.8 vs 93.0%; P<0.01) and a tendency to decline farrowing rate (FR, 87.9 vs 90.3%; P=0.07) following AI during high THI (>82), compared to AI at <74 THI were observed. The spring and summer season were associated with decreased (P<0.01) PR compared with fall and winter (90.0% vs 93.0%). Likewise, FR decreased in spring and summer compared to fall and winter (88.5% vs. 90.9%). FR was higher (P<0.01) in non-repeat breeders compared with that of repeat-breeders (90.3% vs 76.2%). Litter size increased (P<0.01) from 10.8 ± 3.2 to 11.1 ± 3.1 pigs when the interval from weaning to estrus was >8 d. The insemination technique did not affect PR and FR but the litter size decreased (P<0.05) from 11.3 ± 3.0 to 11.1 ± 2.9 pigs when PCAI was used compared to CAI. This study reaffirms the negative effects of the hot season on reproductive performance of gilts/sows, although thermal stress at AI did not cause foetal losses. Also, there is no advantage in using the PCAI as compared to the CAI in gilts/sows with high numbers of sperm cells per AI.

ABSTRACT: The aim of this study was to determine the association among periparturient events such as mastitis, lameness (infectious and non-infectious) and ketosis and the reproductive performance of high producing Holstein cows in a hot environment. The health status and reproductive data variables were recorded from 6,566 completed lactations in a large dairy operation. A logistic regression model with the stepwise procedure was used, considering the occurrence of the health problems during the pre-breeding period as fixed effect risk factors and reproductive variables as dependent variables. Pregnancy rate of cows contracting clinical mastitis (CM) around the period of first inseminations was five percentage points lower than cows without this disease. Cows with CM shortly before or after the first service had twice the risk of requiring more than three services per pregnancy than cows with healthy udders. Cows experiencing abortion, laminitis or metritis were two times more likely to require >3 services per pregnancy than cows not experiencing these reproductive disorders. Cows experiencing lameness, mastitis and metritis presented a significantly longer interval between calving and pregnancy compared to healthy cows. Ketosis and lameness increased the odds of a cow of being inseminated for the first time after 70 days in milk. In conclusion, these results suggest that abortion, ketosis, CM, retained placenta (RP), metritis, and lameness are associated with decreased reproductive performance in high producing Holstein cows subjected to thermal stress.

Abstract: Milk production, kidding intervals and kid growth were evaluated in 20 multiparous indigenous goats of southern Mexico, grazing on a tropical forest. The association between milk production and kid growth rate was also assessed. The total average milk yield was 26.9 ± 9.3 kg, in lactations of 108 ± 13 d. Average daily weight gain of kids was 67 ± 27 g. Considering the entire lactation, daily milk yield accounted for less than 1 % of the known variation in kid weight gain. It was concluded that, due to the high energy investment in reproduction (mean kidding interval of these goats was 195 ± 8 d), low genetic merit for milk production, low adult body weight (28.7 ± 3.3 kg), and sub-optimum nutrition (6 h daily grazing), the lactation performance of the indigenous goats of southern Mexico was very poor, which forces kids to depend upon native forage at an early age.

Resumen: Se registró la producción de leche, el intervalo entre partos y el crecimiento de los cabritos de cabras criollas del sur de México en pastoreo en bosque tropical. La producción de leche por lactancia (108 d) fue de 26.9 ± 9.3 kg. La ganancia diaria de peso de los cabritos fue de 67 ± 27 g. La producción diaria de leche explicó que la variación de la ganancia de peso de los cabritos fuera menor a 1 %. Se concluyó que, debido a la alta inversion energética en la reproducción (intervalo entre partos de 195 ± 8 d), el bajo mérito genético para la producción de leche, su bajo peso corporal (28.7 ± 3.3 kg) y la sub-óptima nutrición (sólo 6 h diarias de pastoreo), la producción de leche de las cabras criollas del sur de México es muy pobre, lo cual obliga a sus cabritos a depender del forraje nativo a una edad muy temprana.

Resumen Antecedentes: la raza de ovejas Katahdin se ha difundido ampliamente en México. Esta raza y sus cruces han ganado recientemente la atención de los productores de ovinos; sin embargo, la investigación con cruces entre Katahdin y otras razas productoras de carne es limitada. Objetivo: evaluar factores genéticos y no genéticos que afectan las tasas de crecimiento y mortalidad de corderos hijos de ovejas Katahdin fecundadas con razas de carne. Métodos: corderos híbridos (n = 152) derivados de ovejas Katahdin fecundadas con machos Hampshire (KH; n = 43), Texel (KT; n = 53) y Charolais (KCH; n = 56) se evaluaron bajo condiciones intensivas de manejo. Se determinó el efecto del genotipo y factores no genéticos en el peso al nacer, peso al destete, ganancia de peso pre-destete, tasa de ganancia de peso pos-destete y mortalidad de los corderos. Resultados: no se detectaron diferencias entre grupos raciales para el peso al nacer (4 ± 1,1, 4,3 ± 0,9 y 4 ± 1,1 Kg para KCH, KH, KT, respectivamente) ni para el peso al destete realizado a los 60 días (20,2 ± 4,3, 20,9 ± 4,3, 18,2 ± 4,2 Kg para KCH, KH, KT, respectivamente). Los pesos de los corderos no difirieron significativamente entre sexos, pero disminuyeron (p<0,05) con el aumento del tamaño de la camada (el peso al destete a los 60 días para los corderos individuales, gemelos y trillizos fue 24,5 ± 2,6, 19,2 ± 3,5 y 14,3 ± 3,8 Kg, respectivamente). La tasa de mortalidad pre-destete de los corderos KH fue de 13,3% y fue significativamente más baja que la de los otros genotipos (24,5 y 39,3% para KT y KCH, respectivamente). Conclusión: el uso de sementales Charolais, Hampshire o Texel en rebaños de ovejas Katahdin genera resultados similares para peso de los corderos a los 60 días, pero la progenie de los moruecos Hampshire tiene mayor sobrevivencia hasta el destete.

Summary Background: Katahdin breed sheep is highly disseminated in Mexico. This breed and its crosses have recently gained attention among sheep producers. However, research with crosses between Katahdin and other meat breeds is limited. Objective: to evaluate the genetic and non-genetic factors affecting growth and mortality rate of crossbred lambs from Katahdin ewes fecundated with breeds specialized for meat production. Methods: crossbred lambs (n = 152) from Katahdin ewes sired with Hampshire (KH; n = 43), Texel (KT; n = 53) or Charolais (KCH; n = 56) were evaluated under intensive management conditions. The effects of genotype and non-genetic factors on birth weight, weaning weight, pre-weaning daily weight gain, and mortality rate were determined. Results: breed differences were not detected for birth weight (4 ± 1.1, 4.3 ± 0.9 and 4 ± 1.1 Kg for KCH, KH, KT, respectively), nor for the 60-d weaning weight (20.2 ± 4.3, 20.9 ± 4.3, 18.2 ± 4.2 Kg for KCH, KH, KT, respectively). Weight of lambs did not differ significantly between sexes, but it decreased (p<0.05) with increased litter size (weaning weight at 60 days for single, twins and triplets was 24.5 ± 2.6, 19.2 ± 3.5, and 14.3 ± 3.8 Kg, respectively). Pre-weaning mortality of KH lambs was 13.3% and it was significantly lower than that of the other genotypes (24.5 and 39.3% for KT and KCH, respectively). Conclusion: inclusion of Charolais, Hampshire or Texel rams in Katahdin flocks results in similar lamb weaning weight, but Hampshire-sired progeny excels regarding pre-weaning survival.

Resumo Antecedentes: Katahdin é uma raça de ovelhas altamente disseminada no México. Esta raça e seus cruzamentos têm recentemente ganhado atenção entre os produtores de ovinos. No entanto, a pesquisa com cordeiros híbridos entre Katahdin e outras raças de carne é ainda limitada. Objetivo: avaliar os fatores genéticos e não-genéticos que afetam a taxa de crescimento e a taxa de mortalidade de cordeiros híbridos de ovelhas Katahdin fecundadas com raças de carne. Métodos: cordeiros cruzados (n= 152) derivados de ovelhas Katahdin fecundados com carneiro Hampshire (KH; n = 43), Texel (KT; n = 53) e Charolais (KCH; n = 56) foram usadas neste estudo sob condições intensivas. Foi determinado o efeito do genótipo e dos fatores nãogenéticos sobre o peso ao nascimento, peso ao desmame, peso pré-desmame e percentagem de sobrevivência. Resultados: não foram detectadas diferenças raciais por peso ao nascimento (4 ± 1,1, 4,3 ± 0,9 e 4 ± 1,1 Kg para KCH, KH, KT, respectivamente), e peso ao desmame aos 60 dias (20,2 ± 4,3, 20,9 ± 4,3, 18,2 ± 4,2 Kg para KCH, KH, KT, respectivamente). Os pesos dos cordeiros não diferiram significativamente entre os sexos, mas o peso diminuiu (p<0,05) com o aumento do tamanho da leitegada (o peso ao desmame aos 60 dias de cordeiros individuais, gêmeos e trigêmeos foi de 24,5 ± 2,6, 19,2 ± 3,5 e 14,3 ± 3,8 Kg, respectivamente). A taxa de mortalidade pré-desmame dos cordeiros KH foi de 13.3% e este foi significativamente menor do que a taxa de mortalidade de cordeiros dos demais genótipos ( 24,5 e 39,3% para KT e KCH, respectivamente). Conclusão: o uso de carneiros Hampshire, Charolês ou carneiros Texel em ovelhas Katahdin pode ser implementado com resultados semelhantes para o peso do cordeiro ao desmame, mas a descendência Hampshire destacou-se por sua maior sobrevivência até o desmame.

Abstract: The objective of this study was to determine the non-genetic factors which affect growth traits in Dorper lambs under intensive conditions. Nine hundred and ninety birth weight records and 851 weaning weight data from a commercial sheep farm were used. A model containing the effects of year of birth, season of birth, litter size, dams' age and gender was used for identification of factors affecting growth traits. Birth weight was highest (p < 0.05) in summer and lowest in winter and spring. Male lambs excelled females in birth weight, weaning weight, and average daily gain. Young dams produced offspring with a lower (p < 0.05) birth weight and weaning weight than older ewes As a conclusion, important influences of environmental factors on growth traits were identified for Dorper lambs.

Resumen: Para determinar los factores no genéticos que influyen en las características de crecimiento de corderos Dorper en condiciones intensivas se registraron 990 pesos al nacimiento (PN) y 851 pesos al destete de una unidad de producción de ovejas entre 2006 y 2010. Se analizó el efecto del año, estación de nacimiento, tamaño de camada, edad de la madre y sexo de los corderos. El año de nacimiento afectó (p < 0.05) el peso al nacer pues fue más elevado en verano y más reducido en invierno y primavera. Los machos fueron más pesados (p < 0.05) al nacimiento y al destete y las tasas de crecimiento pre-destete fueron mayores que en las hembras (p < 0.05). Las ovejas primíparas produjeron crías más livianas (p < 0.05) al nacimiento y destete que las ovejas pluríparas. Se concluyó que diversos factores ambientales tuvieron un importante efecto en las características de crecimiento de corderos Dorper.

ABSTRACT The objective of the study was to evaluate the effect of zilpaterol hydrochloride (ZH) on the weight gain and carcass characteristics in lambs finished in alfalfa pasture and supplemented with concentrate in pen. A total of 24 Dorper x Pelibuey ram lambs initially weighting 25.0±0.24 kg were divided in two groups (n=12) and fed with 0 or 10 mg/ head/d of ZH for the last 30 d before slaughter. During the experimental period, all lambs were grazed in alfalfa during 8 h/d and supplemented with 450 g/d of concentrate. The ZH did not affect (P>0.05) the live weight. Daily and total weight gains were similar (P>0.05) between both groups. Carcass characteristics and wholesale cut yields were not affected (P>0.05) by ZH. In conclusion, growth and carcass characteristics were not improved by feeding zilpaterol (10 mg/head/d) in finished lambs on alfalfa grassland and supplemented with concentrate.

RESUMEN El objetivo del estudio fue evaluar el efecto de clorhidrato de zilpaterol (CZ) sobre la ganancia de peso y las características de la canal en corderos finalizados en pradera de alfalfa y suplementados con concentrado en corral. Un total de 24 corderos machos enteros Dorper x Pelibuey, con peso vivo inicial de 25.0 ± 0.24 kg, fueron divididos en dos grupos (n=12) y alimentados con 0 o 10 mg/cabeza/día de CZ los últimos 30 días antes del sacrificio. Durante el periodo experimental, todos los corderos pastorearon en alfalfa 8 h/día y se suplementaron con 450 g/d de concentrado. El CZ no afectó (P>0.05) el peso vivo. Las ganancias de peso diaria y total fueron similares (P>0.05) entre ambos grupos. Las características de canal y el rendimiento de cortes primarios no fueron afectados (P>0.05) por el CZ. En conclusión, el clorhidrato de zilpaterol a una dosis de 10 mg/cabeza/día no mejoró el crecimiento ni las características de canal en corderos finalizados en pradera de alfalfa y suplementados con concentrado.

O objetivo deste trabalho foi obter estimativas de prevalência de muco vaginal turvo durante o estro em vacas Holandesas criadas sob intenso calor, para avaliar o efeito das condições climáticas sobre sua ocorrência durante o estro e determinar seu efeito sobre a taxa de concepção. Em um primeiro estudo, foi estabelecida a associação entre a ocorrência de muco vaginal turvo durante o estro e a taxa de concepção de vacas inseminadas (18.620 serviços), criadas sob intenso calor (temperatura média anual de 22°C), em fazendas altamente tecnificadas, na região árida do norte do México. Em um segundo estudo, os dados desses grandes estábulos leiteiros foram utilizados para avaliar o efeito das condições climáticas, ao longo do ano, na ocorrência de muco vaginal turvo durante a inseminação artificial (76.899 cios). A taxa global de cios com muco vaginal turvo foi de 21,4% (16.470/76.899; intervalo de confiança de 95% = 21,1-21,7%). A taxa de concepção das vacas com muco vaginal límpido foi maior que a de vacas com muco anormal (30,6 vs. 22%). A prevalência de estros com muco vaginal turvo foi fortemente dependente de elevada temperatura ambiente, e significativamente maior em maio e junho. Taxas de concepção aceitáveis de vacas Holandesas com elevada produção de leite somente são obtidas em vacas que apresentem muco translúcido durante a inseminação artificial.

The objective of this work was to obtain prevalence estimates of cloudy vaginal mucus in artificially inseminated Holstein cows raised under intense heat, in order to assess the effect of meteorological conditions on its occurrence during estrus and to determine its effect on conception rate. In a first study, an association was established between the occurrence of cloudy vaginal mucus during estrus and the conception rate of inseminated cows (18,620 services), raised under intense heat (mean annual temperature of 22°C), at highly technified farms, in the arid region of northern Mexico. In a second study, data from these large dairy operations were used to assess the effect of meteorological conditions throughout the year on the occurrence of cloudy vaginal mucus during artificial insemination (76,899 estruses). The overall rate of estruses with cloudy vaginal mucus was 21.4% (16,470/76,899; 95% confidence interval = 21.1-21.7%). The conception rate of cows with clean vaginal mucus was higher than that of cows with abnormal mucus (30.6 vs. 22%). Prevalence of estruses with cloudy vaginal mucus was strongly dependent on high ambient temperature and markedly higher in May and June. Acceptable conception rates in high milk-yielding Holstein cows can only be obtained with cows showing clear and translucid mucus at artificial insemination.

In order to determine the circannual estrus behavior of Pelibuey ewes under arid conditions of Northwestern Mexico (32º NL), 22 adult ewes were maintained in confinement conditions with constant feeding during one year. Daily, morning and afternoon, the ewe group was exposed to one of three ram fitted with an apron to detect estrus behavior. Annual averages of temperature, relative humidity and temperature-humidity index were 25.3±8.1 °C, 33.1±10.7 % and 72.0±8.4 units, respectively. Monthly percentage of ewes in estrus was lower (P<0.05) from January to June than from July to December. The 100 % of ewes showed estrus signs in each month from July to December (P>0.05). Compared with others months, a higher (P<0.05) percentage of ewes showed shorter estrus (<24 h) in February and March, contrarily, the proportion of ewes with longer estrus (>36 and <48 h) was higher (P<0.05) in June and August. In conclusion, under arid-dry conditions of Northwestern Mexico, Pelibuey ewes decrease their estrus activity from January to June, and high environmental temperatures of summer are not a factor affecting the estrus presence in this sheep breed.

Con el objetivo de determinar la conducta estral circanual de ovejas Pelibuey bajo condiciones áridas del noroeste de México (32° LN), 22 ovejas adultas se mantuvieron en condiciones estabuladas con una alimentación constante durante un año. Diariamente, mañana y tarde, el grupo de ovejas fue expuesto a uno de tres machos provistos de mandil para detectar estro. El porcentaje de ovejas en estro y su duración se calcularon en forma mensual. Las medias anuales de temperatura, humedad relativa e índice de temperatura-humedad fueron de 25.8±8.4 °C, 33.1±11.2 % y 72.0±8.8 unidades, respectivamente. El porcentaje mensual de ovejas en estro fue menor (P<0.05) de enero a junio que de julio a diciembre. El 100 % de las ovejas presentaron estro en cada mes de julio a diciembre (P>0.05). Comparado con el resto de los meses; un mayor (P<0.05) porcentaje de ovejas mostraron estros cortos (<24h) en febrero y marzo, y contrariamente, la proporción de ovejas con estros largos (>36 y <48h) fue mayor (P<0.05) en junio y agosto. En conclusión, en condiciones áridas del noroeste de México, las ovejas Pelibuey disminuyen su actividad estral de enero a junio, y las elevadas temperaturas ambientales de verano no son un factor que afecte la presencia de estro en dicha raza.

Antecedentes: la asociación entre temperaturas ambientales elevadas y alta humedad conduce a fallas reproductivas, disminuyendo la fertilidad de hatos lecheros. Objetivo: determinar el efecto de temperaturas ambientales elevadas sobre el comportamiento reproductivo de vacas Holstein mantenidas en un ambiente árido y cálido y tratadas con hormona del crecimiento (rbST) durante toda la lactancia. Métodos: las variables reproductivas (n=18037 servicios) de una explotación comercial fueron evaluadas con respecto al máximo índice temperatura humedad (THI) antes, durante y después de la inseminación de las vacas. El procedimiento GENMOD de SAS se utilizó para determinar el efecto del THI y el mes de inseminación sobre las tasas de preñez (P/AI). Resultados: el incremento del THI de ≤ 70 a ≥ 95 unidades se asoció con una disminución en el P/AI de 47% a 26%. El P/AI para las vacas inseminadas en días con un ITH de 85 a 90, pero con temperaturas menos cálidas antes de la inseminación, fue de seis puntos porcentuales más altos (30% vs. 36%) que en las vacas expuestas a ITH más altos antes de la inseminación. El P/AI fue mayor (p<0,05) de enero a marzo (39% a 41%) comparado con el resto de los meses del año (27-35%). El número de servicios por preñez fue mayor (p<0,05) de mayo a julio (3,0 a 3,4) que en los otros meses del año (2,1 a 3,0). Conclusiones: en este ambiente extremadamente caliente (temperaturas máximas > 38 °C la mayor parte del año) y árido (promedio de precipitación anual de 230 mm), el estrés calórico poco antes o después de la inseminación disminuye drásticamente las probabilidades de establecer una gestación en vacas de alta producción de leche.

Background: high environmental temperature coupled with high humidity can result in reproductive failure in dairy cattle, with a drastic reduction in reproductive efficiency of dairy herds. Objective: to study the effect of high environmental temperature on reproduction performance of Holstein cows treated with recombinant bovine somatotropin (rbST) throughout lactation in an arid environment. Methods: reproductive variables (n=18,037 services) from a large dairy herd were evaluated with respect to the maximum temperaturehumidity index (THI) prior to breeding, on the breeding day, and after breeding. The GENMOD procedure of SAS was used to assess the effect of THI and month of breeding on pregnancy by artificial insemination (P/AI). Results: increased THI from ≤ 70 to ≥ 95 units was associated with a decrease in P/AI from 47% to 26%. P/AI for cows inseminated on extremely hot days (THI= 85 to 90) preceded by cooler temperatures was six percent points higher than cows subjected to high temperatures before breeding. P/AI was higher (p<0.05) from January to March (39% to 41%) compared with the rest of the year (27% to 35%). The average number of inseminations per pregnancy was higher (p<0.05) from May to July (3.0 to 3.4) compared to other months (2.1 to 3.0). Conclusions: in this particular hot-arid environment (maximum temperature >38 ºC most of the year, and 230 mm mean annual rainfall), heat stress shortly before or after breeding severely compromises the breeding success of high yielding Holstein cows.

Antecedentes: a associação entre alta temperatura e umidade no ambiente pode originar problemas reprodutivos, diminuindo o índice de fertilidade dos rebanhos leiteiros. Objetivo: avaliar o efeito da elevada temperatura ambiente sobre o desempenho reprodutivo de vacas da raça Holandês mantidas num ambiente quente e árido, as quais foram tratadas com somatotropina bovina recombinante (rBST) durante toda a lactação. Métodos: as variáveis reprodutivas (n = 18037 serviços) de um rebanho leiteiro foram avaliadas em relação ao máximo índice de temperatura-umidade (THI), antes, durante e depois da inseminação artificial das vacas. O procedimento GENMOD do SAS foi usado para avaliar o efeito do THI e do mês de reprodução sobre as taxas de gestação por inseminação artificial (P/AI). Resultados: o aumento do THI de ≤ 70 para ≥ 95 unidades foi associado com a diminuição no índice P/AI, de 47% a 26%. Em dias com THI de 85 - 90, mas com menor temperatura ambiental antes da inseminação, o índice P/AI foi 6% maior do que nas vacas expostas a superior THI. O índice P/AI foi maior (p<0,05) de janeiro a março (39% a 41%), em comparação aos outros meses do ano (27 a 35%). O número médio de inseminações por prenhez foi superior (p<0,05) de maio a julho (3,0 a 3,4) quando comparado aos outros meses do ano (2,1 a 3,0). Conclusões: em ambiente quente e seco (temperaturas máximas > 38°C a maior parte do ano, média de precipitação anual de 230 mm) o estresse térmico antes e depois da inseminação reduz drasticamente a possibilidade de estabelecer uma gestação em vacas de alta produção de leite.