Modifying the Lactation Curve in Dairy Goats: Effects of Milking Frequency, Dry Period, and Kidding Interval

Se utilizaron 79 cabras Murciano-Granadinas en 4 experimentos para estudiar los efectos de la frecuencia de ordeno, la omision del secado y el intervalo entre partos sobre la produccion de leche. En el Exp.1, 32 cabras se ordenaron una (1X, n=17) o dos veces diarias (2X). 1X redujo la leche un 18% respecto a 2X, siendo la reduccion mayor al principio de lactacion. Las cabras de 4 partos en 1X. La leche de las cabras 1X contuvo mas solidos totales, grasa y caseina que la leche de las cabras 2X, aunque el porcentaje de proteina y el RCS no vario. En el Exp. 2, se estudiaron los compartimentos de ubre (cisternal y alveolar) y el retorno de leche hacia los alveolos a diferentes intervalos entre ordenos (8, 16 y 24 h) en 14 cabras (1X, n = 7; 2X, n = 7). La leche alveolar aumento hasta las16 h, sin observarse cambios entre las 16 y las 24 h. La area cisternal y la leche cisternal aumentaron linealmente (R2=0.96 a 0.99) hasta las 24 h, indicando que el almacenamiento de leche en la cisterna es continuo, independientemente del grado de llenado del los alveolos. A pesar del intervalo extendido entre ordenos, las cisternas de las cabras 1X no fueron mas grandes que las cisternas de las 2X. No se observaron cambios en el area cisternal despues de una inyeccion de oxitocina, indicando la ausencia del fenomeno de retorno elastico de leche de la cisterna a los alveolos. En el Exp. 3, 17 cabras gestantes se dividieron en 2 grupos: cabras que se secaron 56 d antes del parto (D56; n=9), y cabras sin secado (D0; n=8). Cinco cabras del grupo D0 se secaron espontaneamente 27 d antes del parto (D27). Los cabritos de D0 nacieron con menos peso que los cabritos de D27 y D56. El calostro de las cabras D0 contuvo menos IgG que el de las cabras D27 y D56. En la lactacion siguiente, las cabras D0 produjeron menos leche que las cabras D27 y D56, sin diferencias entre estas ultimas. Los indices de apoptosis y proliferacion del tejido mamario aumentaron en las cabras D56 durante la involucion de la ubre. A la semana 7 de la siguiente lactacion, no se observaron diferencias entre grupos en la dinamica celular mamaria. En el Exp. 4, 30 cabras parieron anualmente (K12; n=16) o bianualmente (K24; n=16). La gestacion redujo la produccion de leche a partir de la semana 10 de gestacion. Entre las semanas 51 y 79, las cabras K12 produjeron 32% mas leche que las cabras K24, aunque su leche contuvo menos grasa y proteina que las cabras K24. Durante las 92 semanas experimentales, las cabras K12 y K24 produjeron cantidades similares de leche. En la semana 39, la grasa de la leche de K12 presento un mayor contenido en CLA con un mayor indice de desaturacion respecto que las cabras K24. En la semana 55, la leche de K12 contuvo mas C18:2 y C18:3, y menos C16:0, resultando en un menor indice de aterogenicidad que la de K24. La leche cisternal de las cabras K12 fue menor que la de las cabras K24 a la semana 39, mientras la leche alveolar no vario. La leche alveolar de las cabras K12 presento un mayor contenido en grasa que en la leche cisternal en la semana 55, lo que tambien se observo en las K24 en las semana 39 y 55. En conclusion, las cabras demostraron una buena adaptacion a 1X, la necesidad del secado y la posibilidad de realizar lactaciones extendidas. _________________________________________________ Seventy-nine Murciano-Granadina dairy goats were used in 4 experiments to study the effects of milking frequency, omitting dry period, and kidding interval on lactational performance and udder compartments. In Exp. 1, 32 goats were milked once- (1X, n=17) or twice-daily (2X, n=15). Once-daily milking reduced milk yield by 18% compared to 2X, with the reduction being greater in early lactation. Goats of < 4 parities lost more milk during 1X than older goats. Milk of 1X goats contained higher percentages of total solids, fat and casein than milk of 2X goats, but milk protein percentage and SCC did not differ. In Exp. 2, udder compartments (cisternal and alveolar) and cisternal recoil at different milking intervals (8, 16, and 24h) were studied in 14 of the goats used in experiment 1 and milked 1X (n=7) or 2X (n=7). Alveolar milk increased from 8 to 16 h after milking, but did not change thereafter. Cisternal area measured by ultrasonography and cisternal milk increased linearly (R2 = 0.96 to 0.99) up to 24 h, indicating continuous milk storage in the cistern at any alveoli filling degree. Despite extended milking intervals, cisterns of 1X goats did not become larger than 2X goats. Primiparous goats had smaller cisternal areas and less cisternal milk than multiparous goats. No changes in cisternal area were observed after oxytocin injection, indicating the absence of cisternal recoil in goats. In Exp. 3, 17 pregnant goats were assigned to 2 groups: goats that were dried off 56 d before expected kidding (D56; n=9), and goats without dry off (D0; n=8). Five goats in the D0 group dried off spontaneously at d 27 before kidding (D27). The D0 kids had lower birth weight than D27 and D56. Colostrum of D0 goats contained less IgG than D27 and D56 goats. In the subsequent lactation, D0 goats produced less milk than D27 and D56 goats, with no differences between D27 and D56. Apoptosis and proliferation indices increased during involution in D56 goats. At wk 7 of the subsequent lactation, mammary cell turnover did not vary between groups. In Exp. 4, 30 goats were divided to kid annually (K12; n=16) or biennially (K24; n=14). Over 92 wk, K12 goats had 2 lactations from wk 1 to 42 and from wk 51 to 92, whereas K24 goats had 1 extended lactation from wk 1 to 92. Pregnancy reduced milk yield in K12 goats from wk 10 of pregnancy. From wk 51 to 79, K12 goats produced 32% more milk than K24 goats, but their milk contained lower fat and protein than K24 goats. No changes were detected for milk lactose and SCC from wk 51 to 79. From wk 80 to 92, milk yield and milk composition did not vary between groups. Over the 92 wk, K12 (1192L) and K24 (1093L) produced similar total milk yield. At wk 39, milk fat of K12 goats contained greater conjugated C18:2 fatty acid and desaturase index than K24 goats. At wk 55, milk of K12 goats contained higher C18:2 and C18:3, and lower C16:0 fatty acids, resulting in a lower atherogenicity index compared to K24. Cisternal milk at wk 39 was lower for K12 than K24 goats, whereas alveolar milk did not differ. Fat content was greater for alveolar milk than cisternal milk for K12 goats at wk 55 and for K24 goats at wk 39 and 55. No differences in milk protein or lactose were detected between cisternal and alveolar milk. In conclusion, Murciano-Granadina dairy goats used in this work are adapted to once daily milking, need the dry period and can do extended lactations.