Efecto de la sustitución parcial del alimento concentrado por pastoreo con Leucaena leucocephala sobre la producción y características de la leche y variación de peso de vacas mestizas

At "La Esperanza" farm of the University of Zulia, located in Zulia state, Venezuela, 24 non-pregnant predominantly Holstein crossbred cows in the first 45 to 60 days of their third or fourth lactation were used to evaluate the effect of substituting 50 to 75% of concentrate feed (C) with 17% crude protein by grazing of a leucaena bank during 2 h/day (LB) on milk production and properties and liveweight (LW) gain. There were used 12 cows in the dry (DS) and wet (WS) season, respectively. The treatments during DS were: T1: 1 kg of C/cow/day + LB; T2: 2 kg of C/cow/day + LB, and T3: 4 kg of C/cow/day. An additional treatment T4, 2 kg of C/cow/day + LB during 2 h on alternate days, was evaluated during WS. A switch-back design was used in both seasons, with four (DS) and three (WS) cows per treatment and three 4-week periods. Basal diets were Brachiaria humidicola hay (DS) and grazing on Panicum maximum (WS) plus water and minerals ad libitum. Milk productions (kg/cow/d) for T2 (10.5 and 10.8) and T3 (10.8 and 11.1) were higher (P≤0.05) than those for T1 (9.9 and 9.7) in DS and WS, respectively. During WS, T4 (10.2 kg/cow/d) was higher than T1, but similar to T2 and T3. Treatments were similar (P>0.05) for LW gain (360 and 423 g/cow/d), milk fat (3.5 and 3.6%), and protein content (3.3 and 3.4%), acidity (16.5 and 16.6 mL NaOH 0.1N/100 mL) nor density (1.030 and 1.029 g/mL) during DS and WS, respectively.En la finca "La Esperanza" de La Universidad del Zulia, estado Zulia, Venezuela, se seleccionaron 24 vacas mestizas predominantes Holstein, no gestantes y en los primeros 45 a 60 días de su tercera o cuarta lactancia, para evaluar el efecto de sustituir el 50 a 75% de un alimento concentrado (C) con 17% de proteína cruda por pastoreo en bancos de leucaena durante dos horas diarias (BL) sobre la producción, características de la leche y variación de peso vivo. Se utilizaron 12 vacas en las épocas seca (S) y lluviosa (LL), respectivamente. Los tratamientos durante S fueron: T1: 1 kg de C/vaca/día + BL; T2: 2 kg de C/vaca/día + BL y T3: 4 kg de C/vaca/ día; durante LL, se evaluó también T4 : 2 kg de C/vaca/día + BL en días alternos. La alimentación base fue heno de Brachiaria humidicola (S) y pastoreo en Panicum maximum (LL) además de agua y minerales ad libitum. El diseño experimental de reversión doble, con tres periodos de cuatro semanas cada uno. La producción de leche (kg/vaca/día) para T2 (10,5 y 10,8) y T3 (10,7 y 11,1) fue mayor (P≤0,05) que para T1 (9,9 y 9,7) durante S y LL respectivamente, mientras T4 (10,2) resultó superior que T1 (P≤0,05) y similar a T2 y T3 en LL. Los tratamientos resultaron similares (P>0,05) para las variables ganancia de peso (360 y 423 g/animal/día), contenido de grasa (3,56 y 3,63%), proteína (3,3 y 3,4%), acidez (16,5 y 16,6 mL de NaOH 0,1N/100 mL) y densidad de la leche (1,030 y 1,029 g/mL) durante S y LL, respectivamente

Effects of stage of harvest on the protein value of fresh lucerne for ruminants

The ruminal degradation of dry matter (DM) and crude protein (CP) and the intestinal availability of CP of four fresh lucerne (Medicago sativa L.) samples, corresponding to a 3rd growing cycle and harvested at 2-week intervals, were determined. Rumen degradability, measured by the nylon bag technique, and rumen outflow rates were determined on three rumen-cannulated wethers. Intestinal digestibility was determined by the mobile bag technique on three duodenal fistulated wethers. Both groups of animals were fed a 2:1 lucerne hay to concentrate diet at an intake level of 40 g DM$\cdot$kg$^{-1}$ BW$^{0.75}$. The effective degradability (ED) of DM decreased with maturity in linear and quadratic form, as a consequence of a decrease in the soluble fraction and a similar increase in the undegradable materials. The resultant values were 0.795, 0.661, 0.600, and 0.576 for harvests at 2, 4, 6, and 8 weeks. The ED of CP showed the same trend. However, the variations (values of 0.896, 0.832, 0.791, and 0.817, respectively), were moderate and mainly due to the reduction of the proportion of soluble CP. The intestinal digestibility of CP of all samples showed a downward trend with the increase in the ruminal incubation time, as modelled according to a logistic function. The undegraded CP digested in the gut ($D_{\rm i}$) and therefore the effective intestinal digestibility (EID) were derived from this function according to the rumen outflow of undegraded CP. The effects of maturity on the mean values of $D_{\rm i}$, expressed as a proportion of the original CP content, were the opposite of those recorded for the ED of CP. These values were 0.067, 0.102, 0.115, and 0.089 for samples harvested at 2, 4, 6, and 8 weeks, respectively. Nevertheless, when $D_{\rm i}$ was expressed as g CP$\cdot$kg$^{-1}$ DM, these values (18.0, 17.4, 17.1, and 14.3, respectively) decreased in linear form. The same trend was observed for EID values, which represent 0.641, 0.609, 0.549, and 0.488, respectively. The change of the digestion site produced by the reduction of ED of CP was also associated with an increase in the undigested CP (values of 0.037, 0.066, 0.094, and 0.094, at the four harvesting times).Effets du stade de maturité sur la valeur protéique du fourrage vert de luzerne. La dégradation dans le rumen de la matière sèche (MS) et des matières azotées totales (MAT), ainsi que l'utilisation dans l'intestin des MAT de 4 fourrages de luzerne (Medicago sativa L.) recoltés en vert au 3e cycle à 2 semaines d'intervalle, ont été determinées. La dégradabilité effective (DE), mesurée en sachets de nylon, et le taux de sortie de particules du rumen ont été determinés sur 3 moutons fistulés dans le rumen, tandis que la digestibilité dans l'intestin a été mesurée, à l'aide des sachets mobiles, sur 3 moutons munis d'une canule du duodénum. Les deux groupes d'animaux ont été nourris avec une ration mixte de foin de luzerne et concentré (2:1 sur MS) distribuée à 40 g MS$\cdot$kg$^{-1}$ P$^{0,75}$. La DE de la MS a diminué de façon linéaire et quadratique avec l'âge du fourrage, par suite d'une diminution de la fraction soluble et d'une augmentation similaire de la fraction non dégradable. Les valeurs de DE ont été : 0,795, 0,661, 0,600 et 0,576 pour la fauche à 2, 4, 6 et 8 semaines. Une évolution similaire, mais plus modérée, a été observée pour la DE des MAT (valeurs de 0,896 ; 0,832 ; 0,791 et 0,817, respectivement). Ceci est principalement la conséquence de la réduction des proportions des MAT solubles. L'augmentation du temps de séjour dans le rumen a entraîné pour tous les échantillons une diminution de la digestibilité dans l'intestin, qui a pu être convenablement décrite par une fonction logistique. La proportion des MAT de l'aliment digérées dans l'intestin ($D_{\rm i}$) et la digestibilité intestinale effective (DIE) résultante ont été déduites de cette fonction et du flux de sortie du rumen des MAT non dégradées. L'évolution en fonction de l'âge, des valeurs de $D_{\rm i}$- exprimées comme proportion des MAT - a montré des effets inverses à ceux observés pour la DE des MAT. Ainsi, ces valeurs ont été : 0,067, 0,102, 0,115 et 0,089 pour les fourrages recoltés à 2, 4, 6 et 8 semaines, respectivement. Par contre, si $D_{\rm i}$ est exprimé en g MAT$\cdot$kg$^{-1}$ MS, les teneurs respectives (18,0, 17,4, 17,1 et 14,3) ont montré une diminution linéaire. Une évolution similaire a été observée pour les valeurs de DIE: 0,641, 0,609, 0,549 et 0,488, respectivement. Le déplacement du lieu de digestion, associé avec la réduction de la DE des MAT, donne lieu aussi à une augmentation des MAT non digérées. Ainsi, ces valeurs représentent 0,037, 0,066, 0,094 et 0,094, respectivement

In situ intestinal digestibility of dry matter and crude protein of cereal grains and rapeseed in sheep

The ruminal degradation and intestinal digestibility (ID) of dry matter (DM) and crude protein (CP) of different feed samples were measured in two trials by using nylon bag and rumen outflow rate techniques in three wethers cannulated in the rumen and in the duodenum. In trial 1, three samples of grains of wheat, barley, and corn treated by cooking (TW, TB, and TC, respectively) were studied together with a sample of untreated corn grains (CG) of different origin. In trial 2, these studies were carried out on a sample of rapeseed (RS) and on a mix of this same sample and rapeseed meal (in proportions 70: 30) treated by cooking (TR). In both trials, the animals were fed at the same intake level (40 g DM$\cdot$kg$^{-1}$ LW$^{0.75}$) with 2:1 (DM basis) forage to concentrate diets. Rumen degradation rates of DM were high in the treated cereals (between 11.0 and 14.2%$\cdot$h$^{-1}$) and low in the CG (6.35%$\cdot$h$^{-1}$), whereas for CP these rates were low in all cereals. For DM, in all cereals, ID decreased linearly as the ruminal incubation time increased. The values of intestinal effective digestibility (IED), calculated from these functions and from the rumen outflow, were respectively: 86.4, 62.1, 51.5, and 67.9%. For CP, ID was unaffected by the ruminal incubation time in corn samples, whereas in TW and TB a reduction of these values was only observed for the time of 48 h. The values of IED of CP for CG, TW, TB and TC were: 82.6, 88.9, 82.5, and 91.6%, respectively. Rumen degradation rates of the RS and TR samples were 8.35 and 8.23%$\cdot$h$^{-1}$ for DM and 12.0 and 9.59%$\cdot$h$^{-1}$ for CP. In RS, the ID of DM and CP showed a downward trend with an increase of the ruminal incubation time, as modelled according to an exponential function. This same trend was observed for TR after a lag period estimated at 7.53 and 6.51 h for DM and CP, respectively. The values of IED of RS and TR were respectively 56.5 and 50.8% for DM and 71.9 and 80.1% for CP. These same results were also determined by a simplified method using a sample pooled to be representative of the rumen outflow of undegraded feed. The respective values for RS and TR were 54.8 and 51.6 for DM and 65.8 and 78.9% for CP. This method seems to be a promising technique to estimate IED, although more studies are needed to improve its accuracy