-The effect of supplementation with corn oil (CO) and its mixture with palm kernel oil (CO:PKO 75:25) to grazing cows on ruminal fermentation, milk yield, and its fatty acid (FA) profile was evaluated. The treatments were: one control treatment (C) without oil and two treatments with 720 g d −1 /cow of CO or CO:PKO (ether extract: 22.7 g kg −1 for control treatment, 66 g kg −1 for CO, and 65 g kg −1 for CO:PKO). Six multiparous Holstein cows (6.3±1.8 yr, 597±11.5 kg body weight (BW), 160±29 d in milk; mean ± standard deviation) were assigned to a double 3 × 3 × 3 Latin square design. Cows grazed (3 kg DM/100 kg BW) a Cenchrus clandestinus (previously Pennisetum clandestinum) pasture and were supplemented with 0.9 kg d −1 DM corn silage, 4.2 kg d −1 DM concentrate, and 9 g Cr 2 O 3 . The mixture of concentrate and oils was offered twice a day. The addition of oils increased milk yield (kg d −1 ) (C: 21.4, CO: 23.6, CO:PKO: 23.9) and milk fat concentration (g kg milk −1 ) (C: 31.5, CO: 34.0, CO:PKO: 34.0). Compared with control, conjugated linoleic acid (18:2 c9 t11 CLA) proportion (g 100 g −1 FA) in milk fat was higher for oil treatments (C: 0.68, CO: 1.56, CO:PKO: 1.01). Voluntary intake and digestibility were not different among treatments. The molar ratio of acetate, propionate, and butyrate was not different among treatments, but the molar concentration of volatile fatty acids (VFA) was lower for CO and CO:PKO, resulting in a lower estimated methane (CH 4 ) production (mL/100 mol VFA) for CO and CO:PKO treatments. Supplementing CO and CO:PKO to grazing dairy cows increases milk yield without affecting voluntary intake or diet digestibility. The proportion of conjugated linoleic acid increases more for CO than for CO:PKO.

This study aimed at determining the nutritional efficiency of Kikuyu grass, when it is cultivated at different altitudes and defoliated with a different number of leaves per tiller. Four farms, with Kikuyu crops (Cenchrus clandestinus), were selected, two in an average altitude of 2,552 m.a.s.l. and two in average altitude of 2,914 m.a.s.l. In each farm, there were established eight plots of 4 m2 each (four treatments, two replicates). For 10 months, the pastures were defoliated when they presented 4, 5, 6, and 7 leaves per tiller (treatments) at 5 cm above ground when 90% of the tillers reached the number of leaves corresponding to each treatment. Data were analyzed as serial experiments using a completely randomized block (farms) design with an analysis of variance. The leaf appearance interval was higher for the highest altitude (8 vs. 10 days) but vary among treatments at a lower altitude (P<0.05). Pastures at higher altitudes were shorter (8.9 vs. 13.5 cm), but its height varied among treatments depending on the altitude (P<0.001). The quality of the pastures was similar, except for the ones with seven leaves per tiller at 2,552 m.a.s.l. that had less protein and in vitro dry matter digestibility (P<0.01). The nutrient yield was higher for the pastures cultivated at 2,552 m.a.s.l. (P<0.001), and, at this altitude, pastures defoliated with five leaves had the largest nutrient yield. The Kikuyu cultivated at higher altitudes grows slowly and yield fewer nutrients independently of the number of leaves per tiller.

Introducción. Se ha sugerido que el perfil lipídico en la leche bovina afecta la salud humana y se ha identificado que el ácido linoleico conjugado (ALC c9 t11) podría tener efectos anticarcinogénicos. En trópico alto se ha investigado el efecto de la alimentación sobre el perfil lipídico de la leche, pero pocos estudios se han hecho en trópico bajo. Objetivo. El objetivo fue evaluar el efecto de tres intensidades de pastoreo (1, 2 y 3 animales ha-1) en pasto Guinea cv. Tanzania (Megathyrsus maximus) sobre la producción, composición y perfil lipídico en la leche de vacas mestizas en diferentes tercios de lactancia. Materiales y métodos. De septiembre a octubre de 2013, se seleccionaron dos grupos de nueve animales (tres vacas en cada tercio de lactancia) y se asignó una vaca por tercio de lactancia a cada intensidad de pastoreo (tratamiento), durante 42 días de evaluación, en un diseño de cuadrado latino 3 x 3 replicado. Resultados. La producción de leche fue similar (p>0,05) entre tratamientos y fue mayor (p<0,05) en vacas en inicio de lactancia. Los tratamientos no afectaron (p>0,05) la composición de la leche, pero el tercio de lactancia tendió (p<0,10) a incrementar la concentración de sólidos totales y grasa. La grasa de la leche bovina en el pasto manejado con intensidad de pastoreo de 2,0 y 3,0 animales ha-1 tuvo una concentración mayor (p<0,05) de ALC c9 t11 y de ácidos grasos poliinsaturados (AGPI), que cuando el pasto fue manejado con 1,0 animal ha-1. El tercio de lactancia no afectó (p>0,05) la concentración de ALC y AGPI. Conclusión. El manejo del cultivar Tanzania con intensidades de pastoreo de 2,0 y 3,0 animales ha-1, resultó en las concentraciones más altas de ALC (c9 t11) y AGPI en la grasa de la leche, lo cual podría tener efectos positivos en salud humana.

To determine the optimum harvest time of kikuyu grass (Cenchrus clandestinus (Hochst. ex Chiov.) Morrone), according to the number of leaves per tiller and nitrogen fertilization level, an experiment was carried out under greenhouse conditions using a 4×4 factorial design. The factors were the number of leaves per tiller (3, 4, 5, 6 leaves) and level of nitrogen (N) fertilization (0, 50, 100,150 kg of Nitrogen ha-1 year-1). Dry matter (DM) yield and nutritional quality were determined. Additionally, the independent effect of nitrogen fertilization on undisturbed height, tiller density, and the phyllochron were evaluated. When the number of leaves per tiller increased (3 to 6), the leaf yield and dead forage also increased (P<0.05). The leaf-stem ratio (L:S) remained constant (P>0.05) among the number of leaves. Green forage-dead forage ratio (GF:DF) decreased (P<0.05) with a higher number of leaves per tiller. The concentration of crude protein (CP) decreased while the concentration of neutral detergent fiber (NDF) increased with an increment of the number of leaves per tiller (P<0.05). Nitrogen fertilization increased the undisturbed height, the density of tillers, DM yield from leaves, stems and green forage, GF:DF, and CP (P<0.05) while NDF decreased (P<0.05). The phyllochron was higher without N fertilization. The effects of the number of leaves per tiller and N fertilization on the most variables measured were independent of each other. However, due to an increment in DM yield caused by N fertilization, the pasture can be defoliated with fewer leaves per tiller, increasing defoliation frequency and improving forage quality

In order to estimate the base temperature (Bt) of growth through the appearance of leaves and calculate the phyllochron for kikuyu grass, three plots were established on three farms in the Provincia of Ubaté (Cundinamarca, Colombia) located at different altitudes (2560, 2640, 3143 m. a. s. l.). Measurements were made in four cycles in a period of eight months. The Bt was estimated by the least coefficient of variation method using a second order regression model and the model obtained was validated by the cross-validation method. The Bt values for the first, second, third and fourth leaf were 4.02, 3.68, 3.93, and 3.62 ° C, respectively. For the appearance of the first leaf, the kikuyu required more thermal time (TT) (97.5 accumulated growing degree days (AGDD)) than for the second (74.2 AGDD), third (73.8 AGDD) and fourth leaf (76.0 AGDD) (p<0.05). There were no differences in TT among farms (p> 0.05). There was a tendency to a greater number of days required to reach each leaf stage in the farm located at higher altitude and with lower mean temperature. The validation showed an adequate adjustment (r2 = 0.94) and a substantial concordance (CCC = 0.97) between the observed values and the predicted values for the estimated TT with the Bt value obtained for each leaf stage. The results of Bt for kikuyu grass obtained, will allow to make more precise predictions about the phyllochron and generate growth models close to reality.