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Although the beneficial effect of biostimulation on reproduction has been reported, the influence of selectivity and social factors on the response to biostimulation has not received sufficient research attention in both Bos indicus and Bos indicus influenced cattle. Furthermore, 'green and cheap' strategies to improve cattle reproduction are currently in demand while Bos indicus influenced cattle with inferior reproductive performance, and farmers with economic limitations are common in tropical zones. Hence, to assess the reproductive response of crossbred taurus × indicus cows to biostimulation by pre-pubertal (PPM) or pubertal (PM) teasers males, two trials of 2 years each were conducted. Trial 1 n = 187 cows (Year 1:85 cows exposed to PPM and Year 2:102 cows exposed to PM). Trial 2 n = 196 cows (Year 1:101 cows exposed to PPM and Year 2:95 cows exposed to PM). The effect of exposing cows to PPM and PM on the intervals calving to first service (ICFS), calving to conception (ICC) and economic cost of days open (ECDO) was analysed using Kruskal-Wallis ANOVA and the effect of exposing cows to PPM and to PM on reproductive status at 90 days (RS90) and proportion of cows requiring hormonal protocols (PRH) was compared using χ2 analysis. Both ICFS and ICC were shorter (p < .0001) for PM-exposed females (96.12 ± 4.1 and 110.93 ± 2.9 days; respectively) compared with those PPM-exposed (134.41 ± 3.3 and 135.64 ± 2.4 days; respectively). With RS90, more (p < .0001) PM-exposed cows (50.7%) were pregnant compared with PPM-exposed cows (16.1%). The PRH was greater (p < .0001) in PPM-exposed cows (79.0%) compared with PM-exposed (27.9%). The ECDO was less (p < .0001) in PM-exposed cows (US$ 142.9 ± 3.8) compared with PPM-exposed (US$ 176.3 ± 2.9). In conclusion, cows exposed to PM had shorter ICFS and ICC compared with cows exposed to PPM. More cows exposed to PM were pregnant after 90 days, and PRH was less than cows exposed to PPM. Cows exposed to PM had a reduced ECDO than those exposed to PPM.

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In order to determine whether seasonal variations may influence the estrous cycle length (ECL), corpus luteum size (CLS), maximum area of CL (MACL), day of cycle with maximum area of CL (DCMACL), and pre-ovulatory follicles size (PFS), ten Criollo Limonero heifers were subjected to daily ultrasound ovary scanning throughout their estrous cycles during three seasons: hot-dry (HD), hot-humid (HH), and wind-rain (WR). The effect of season on ECL, MACL, DCMACL, and PFS was analyzed with an ANOVA (PROC GLM, SAS), whereas, for the effect of season on CLS, an ANOVA with repeated measures (PROC MIXED, SAS) was used. Results showed no effect (P > 0.05) of season on ECL, MACL, and DCMACL. However, size of PFS was larger (P < 0.02) during the WR season and the CLS tended (P < 0.09) to be lower during the HH. In conclusion, the relative stability of ECL, MACL, DCMACL, PFS, and CLS measures suggests no major seasonal variations which could imply adaptation capability of Criollo Limonero cattle to the tropical environment.

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The objective of this study was to assess aspects of the social behavior of a mixed-breed herd of beef cows as a potential source for stress and economic losses. Angus (AN; N = 10), Brahman (BR; N = 10), and Senepol (SE; N = 10) cows were assigned to two groups (N = 15 each containing equal breed numbers) on separate pastures. Agonistic interactions (win/loss) during feeding were recorded daily for 45 days. Dominance values were estimated as the proportion of individuals dominated to total herdmates. From this, individuals were placed into social categories based upon linear ranking as follows: dominants (D), intermediate (I), and subordinates (S). Breed influenced (P < 0.01) social category, with SE cows being dominants (P < 0.05) over AN and BR cows. Interactions between AN and BR cows were less (P < 0.0005) than interactions between AN and SE (53 vs 140, respectively). Within breeds, BR (152) and SE (182) cows had more (P < 0.0005) agonistic interactions than AN (107) cows. Although apparently influenced by breed, agonistic interactions occurred more frequently (P < 0.005) between social categories than within social categories (814 vs 310, respectively). Dominant cows were involved in more agonistic interactions with cows from different social categories than were intermediate and subordinate cows (P < 0.0005). However, intermediate (100) and subordinate (157) cows generated more (P < 0.0005) agonistic interactions within their own social category than dominant cows (53). It was concluded that, in mixed-breed herds, breed influences both social organization and agonistic interactions which could be considered as potential sources of stress and economic losses.

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The variation in hair coat and skin histology traits of Criollo Limonero cattle was analyzed using 213 Criollo Limonero females. Skin biopsies were obtained from slick-haired (N=16) and normal-haired (N=14) animals. Measured traits included hair length (HL), color coat (CC), number of hair follicles per square centimeter (NHF), sweat glands per square centimeter (NSG), sweat glands size (SGS), sebaceous glands per square centimeter (NSBG), blood vessels per square centimeter (NBV), and thickness of epidermis (TE). Hair length differed (P<0.001) between slick- and normal-haired animals (4.9 ± 0.12 vs 10.9 ± 0.20, respectively). Differences (P<0.01) in CC (Bayo = 144/67.6% vs Red = 69/32.4%) and HL (slick-haired = 199/93.4% vs normal-haired = 14/6.5%) were found. Distribution of slick- and normal-haired animals differed (P<0.01) between bayo-coated and red-coated (139/62.2% vs 9/4.2%; respectively). Most (P<0.05) red-coated animals belonged to a single family. No differences (P>0.05) were found between slick-haired and normal-haired animals in NHF (637 ± 164 vs 587 ± 144, respectively), NSG (556 ± 134 vs 481 ± 118, respectively), NSBG (408 ± 87 vs 366 ± 77, respectively), NBV (1628 ± 393 vs 1541 ± 346, respectively), and TE (1.24 ± 0.14 vs 1.32 ± 0.12, respectively). However, SGS was greater (P<0.01) in slick-haired than normal-haired animals. In conclusion, Criollo Limonero cattle are predominantly bayo-coated, slick-haired, with a reduced number of hair follicles relative to Zebu cattle, sweat and sebaceous glands in proportion to hair follicle numbers, and with a high blood flow irrigating the skin. There is a sub-group of red-coated animals with yellow or cream skin, thicker epidermis, and with a higher frequency of normal-haired animals. It appears that the slick hair gene has been favored by natural selection in this breed.

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El presente estudio examinó el efecto de la bioestimulación por exposición al toro sobre el desempeño reproductivo durante el postparto temprano de vacas Angus bien alimentadas y sujetas a amamantamiento permanente. A una semana postparto, 90 vacas Angus sin historia de problemas al parto y sus becerros fueron distribuidos según el número de partos, peso y talla corporal en 3 grupos aislados de 30 vacas cada uno. Las vacas de los grupos A y B fueron expuestas permanentemente a toros maduros (BE), en tanto que las vacas del grupo C (NE) sirvieron como control. Las variables analizadas fueron: intervalos parto-reanudación de la actividad ovárica (ICR) y parto-primer celo expresado (ICE), longitud del primer ciclo estral (ECL), número de vacas mostrando celo por grupo y número de celos por vaca durante los 90 días previos a la época de monta (NEP). El ICR (38,1 ± 3,4 vs 51,0 ± 4,4; P<0,02) y el ICE (38,1 ± 3,4 vs 59,9 ± 2,5; P<0,001) fueron más cortos en BE que en NE, y no se hallaron diferencias entre grupos expuestos a toro. Más BE reanudaron la ciclicidad ovárica con ciclos normales en comparación con las NE (A=16/53 por ciento, B=16/53 por ciento, C=8/26,6 por ciento; P<0,01). Durante el experimento, más vacas BE mostraron celo que las NE (A: 29/30= 97 por ciento, B: 30/30 =100 por ciento, C: 24/30= 80 por ciento; P<0,002). Así mismo, el NEP observado en vacas BE fue mayor que en las vacas NE (A=70, B=68, y C=42; P<00,002). Más (P< 0,001) vacas BE tuvieron 3 celos durante el estudio. Se concluyó que, aun bajo condiciones de nutrición adecuada y amamantamiento permanente, hubo un efecto bioestimulatorio positivo sobre el desempeño reproductivo temprano de las vacas Angus postparto.

The present study tested the effect of biostimulation by bull exposure on the early postpartum reproductive performance of well fed and permanently suckled Angus cows. At 1 week postpartum, 90 Angus cows with no history of calving problems and their calves were allocated by parity, body weight, and body frame into 3 isolated groups of 30 cows each. Cows from groups A and B were permanently exposed to mature bulls (BE) while cows from Group C (NE) served as a control. Analyzed variables included; intervals from calving to resumption of ovarian activity (ICR), and first behavioral estrus (ICE), length of the first estrous cycle (ECL), number of cows showing estrus/group, and number of estrus periods (NEP) occurred per cow during the 90 days previous to the breeding season. The ICR (38.1 ± 3.4 vs 51.0 ± 4.4; P<0.02) and ICE (38.1 ± 3.4 vs 59.9 ± 2.5; P<0.001) were shorter in BE than in NE cows, and no differences between bull-exposed groups were found. More BE cows resumed reproductive cyclicity with normal ECL than NE cows (A= 16/53%, B=16/53%, C=8/26.6%; P<0.01). During trial, more BE cows showed behavioral estrus than NE cows (A: 29/30= 97%, B: 30/30 =100%, and C: 24/30 = 80%; P<0.002). Similarly, NEP recorded in BE cows was greater than that of NE cows (A=70, B=68, and C=42; P<0.0002). More BE cows (P< 0.001) had 3 estrous periods during trial. It was concluded that, even under conditions involving adequate nutrition and permanent suckling, there was a positive effect of biostimulation on early reproductive performance in postpartum Angus cows.

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Los objetivos de este estudio fueron determinar el número de dientes incisivos al nacer en becerros Criollo Limonero y las variables que lo influencian, así como, caracterizar la secuencia de desgaste en relación con la edad. Desde su nacimiento y hasta los 12 meses de edad, se observó mensualmente en la dentadura incisiva de 216 becerros Criollo Limonero el número de dientes al nacer, tipo de desgaste y magnitud del desgaste. Todos los becerros nacieron en la Estación Local Carrasquero-INIA, Zulia, Venezuela. El número de dientes al nacer fue analizado mediante distribución de frecuencias. Para analizar los factores que influencian el número de incisivos al nacer se practicó un ANAVA con un modelo estadístico que incluyó las variables sexo del becerro, familia de la madre y familia del padre, condición corporal pre-parto y el número de partos de la madre. 70,8% de los becerros nacieron con 6 dientes incisivos y un 2,3% con 4 dientes. Todos los becerros presentaron sus dientes por pares. Las hembras nacieron con más dientes (6 vs 5; P<0,02) que los machos, y los becerros nacidos de madres con ³ 6 partos presentaron más dientes (5,8 ± 0,3 vs 4,9 ± 0,2; P<0,04) que aquellos nacidos de hembras con £ 5 partos. La interacción sexo del becerro x número de partos de la madre tendió afectar el número de dientes al nacer (P>0,10). El desgaste dentario se inició con rasamiento leve a los 6 meses en pinzas, primeros y segundos medianos, este tipo de desgaste se acentuó a los 9 meses y se hizo marcado a los 12 meses de edad. Se concluyó que los becerros Criollo Limonero nacen predominantemente con 6 dientes, y que el número de dientes incisivos al nacer parece estar más influenciado por factores no genéticos como el sexo del becerro y el número de partos de la madre.

The objectives of this study were to determine the number of incisive teeth at birth in Criollo Limonero calves, factors influencing number of incisive teeth at birth and teeth waste until 12m age old. Incisive teeth from 216 Criollo Limonero calves owned by the Estación Local Carrasquero-INIA, Zulia, Venezuela were monthly observed from birth to 12 m age old. Likewise, type of teeth waste and its magnitude were monthly recorded. The number of incisive teeth at birth was analyzed by frequency distribution. In order to analyze the factors influencing the number of incisive teeth at birth, a statistical model that included the variables calf gender, dam and sire family, prepartum body condition score, and parity was built, and an ANOVA was performed. Most (70.8%) of calves were born with 6 incisive teeth, while 21.3% borh with 4 teeth. All calves had their teeth in pairs. Female calves were born with more (6 vs 5; P<0.02) teeth than male calves. Calves from dams with parity ³ 6 had more (5.8 ± 0.3 vs 4.9 ± 0.2; P<0.04) incisive teeth than those from dams with parity £ 5. The interaction calf gender x parity tended (P>0.10) to have an influence on number of incisive teeth at birth. Mild teeth waste started at 6m age old in front, first, and second lateral teeth. Mild teeth waste became more evident at 9m age old, and strong teeth waste was evident at 12m age old. It was concluded that Criollo Limonero calves are predominatly born with 6 incisive teeth and this number seems to be more influenced by non-genetic factors such as calf gender and parity.

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Records from ½ Criollo Limonero + ½ Holstein (F1) and backcrosses, ¾ Criollo Limonero + » Holstein (R) handled in a Venezuelan humid tropical forest zone were analyzed to compare their productive and reproductive performance. The analyzed variables were: age at first calving (AFC), interval from calving to conception (ICC), calving interval (CI), services per conception (SC), gestation length (GL), calf birth weight (CBW), lactation length (LL), milk at 90 d (M90), total milk yield (TMY), and milk adjusted to 305 d (M305). No statistical differences (P > 0.05) were found between F1 and R for AFC (3.4 ± 0.1 vs 3.2 ± 0.1 years), SC (1.6 ± 0.1 vs 1.7 ± 0.1), GL (both 280d), CBW (both 34 ± 0.6 kg), M90 (919 ± 99 vs 813 ± 105 kg), TMY (2093 ± 176 vs 1964 ± 176 kg) or for M305 (2424 ± 146 vs 2430 ± 151kg), respectively. However, the F1 cows had ICC (258 ± 18 vs 173 ± 22 d; P < 0.004) and CI (577 ± 21 vs 474 ± 25 d; P < 0.001) longer than R, respectively. Year of birth affected (P < 0.05) to AFC, (P < 0.03) to ICC, and (P < 0.01) to CI, M90, TMY, and M305. Environmental effects were found for GL, M90, TMY, M305, and LL. Although no differences between genotypes were found for milk yield, R cows had better reproductive performance than the F1 cows.

Con el objetivo de comparar el comportamiento productivo y reproductivo, se analizaron los registros de vacas ½ Criollo Limonero + ½ Holstein (F1) y retrocruces ¾ Criollo Limonero + » Holstein (R) manejadas en una zona de bosque húmedo tropical venezolana. Se analizaron las variables edad al primer parto (AFC), intervalo parto-concepción (ICC), intervalo entre partos (CI), servicios por concepción (SC), duración de la gestación (GL), peso al nacer de los becerros (CBW), longitud de lactancia (LL), producción de leche total (TMY), a los 90 días (M90) y ajustada a 305 días (M305). No se hallaron diferencias significativas (P > 0,05) entre F1 y R para AFC (3,4 ± 0,1 vs 3,2 ± 0,1 años), SC (1,6 ± 0,1 vs 1,7 ± 0,1), GL (ambos 280d), CBW (ambos 34 ± 0,6 kg), M90 (919 ± 99 vs 813 ± 105 kg), TMY (2093 ± 176 vs 1964 ± 176 kg) ni M305 (2424 ± 146 vs 2430 ± 151kg), respectivamente. No obstante, las F1 tuvieron ICC (258 ± 18 vs 173 ± 22 d; P < 0,004) e CI (577 ± 21 vs 474 ± 25 d; P < 0,001) más prolongados que las R, respectivamente. El año de nacimiento afectó (P < 0,05) a AFC, (P < 0,03) ICC, y (P < 0,01) a CI, M90, TMY, y M305. Se hallaron efectos climáticos sobre GL, M90, TMY, M305, y LL. Aunque sin diferencias en producción de leche, las R tuvieron mejor desempeño reproductivo.

RESUMO

El objetivo de éste estudio fue analizar factores asociados a características del crecimiento pre-destete y debilidad neonatal (NW) en becerros puros por cruce Brahman Rojos (RB, n=86) y Blancos (GB, n=33). Los parámetros observados fueron peso al nacer (BW), y a 210-d (W210), ganancia diaria de peso a 210-d (ADG), y varias medidas lineales. Al nacer los machos pesaron más que las hembras (31,6 ± 0,9 vs 28,5 ± 0,8 kg; P<0,002), hubo diferencias debidas al toro padre (P<0,001), y los becerros con NW tendieron a ser más livianos que los normales (29 ± 1,1 vs 31,2 ± 0,6kg; P<0,06). A los 210-d, los machos pesaron más que las hembras (124,7 ± 3,2 vs 111 ± 3,4 kg; p<0,007) y las vacas de segundo y cuarto parto tuvieron los becerros más pesados (P<0,001). Becerros nacidos durante la época seca tuvieron mayores W210-d (122,5 ± 3,4 vs 113 ± 3,1 kg P<0,01) y ADG (0,451 ± 0,01 vs 0,388 ± 0,01 kg/d; P<0,001) que los nacidos durante la época lluviosa. Becerros hijos de vacas en su segundo y cuarto parto tuvieron mayores ADG (P<0,01). AL nacer como a los 210-d, todas las medidas lineales y el peso corporal se hallaron correlacionados (P<0,001). A los 210-d, los becerros con NW fueron más livianos (113 ± 4 vs 122 ± 2,6 kg; P<0,05) y de menor talla en todas las mediciones (P<0,001) que los normales. La ocurrencia de NW fue mayor en RB que en GB (P<0,005) y se halló sociada a 3 toros (P<0,005)

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