O pacu (Piaractus mesopotamicus) é um peixe neotropical de água doce. É uma das espécies mais importantes cultivadas em áreas de bacias dos rios Paraná e Paraguay. Foi analisado o efeito da duração da larvicultura intensiva no crescimento, sobrevivência e incidência de malformações ósseas em pacu. Os tratamentos consistiram de uma larvicultura semi-intensiva (LS) em viveiros, larvicultura intensiva no laboratório até 60 dias de idade (LIn), ou misto, com 20 dias de larvicultura semi-intensiva após 14 (L1), 21 (L2), 33 (L3) e 40 (L4) dias de larvicultura no laboratório. No final da experiência, as larvas do tratamento LS apresentaram maior crescimento, com valores de peso médios (2,28g) e comprimento total (CT-48,20mm) estatisticamente superior ao resto (P<0,05). Os tratamentos L1 a L4apresentaram valores de crescimento intermediários, sem diferença estatística entre eles (P>0,05), enquanto LIn apresentaram os menores valores de crescimento estimados (P<0,05). A sobrevivência foi estimada em torno de 75% em todos os grupos, com exceção do LS, o qual apresentou um valor mais baixo (17,5%, P<0,05). Em todos os tratamentos experimentais, foram detectadas alterações esqueléticas, mas em nenhum caso foi encontrado alteração morfológica visível. O presente estudo mostra que a retenção prolongada de larvas de pacu em alta densidade melhora a disponibilidade temporal e sobrevivência dos juvenis, sem afetar o crescimento ou desenvolvimento osteológico posterior destes.

The pacu (Piaractus mesopotamicus) is a neotropical freshwater fish. It is one of the most important species farmed in areas of the Parana and Paraguay Rivers basins. The effects of different rearing protocols on growth, survival and incidence of skeletal malformations in pacu larvae were analyzed. A total of six experimental treatments were considered, consisting of: a semi-intensive larviculture (LS) in ponds; intensive larviculture (LIn) in laboratory (both LS and LIn until 60 days of life); and mixed larviculture, with 20 days of semi-intensive larviculture into cages in ponds after 14 (L1), 21 (L2), 33 (L3) or 40 (L4) days of laboratory larviculture. At the end of the experimental period, LSlarvae showed higher growth rate, with average weight values (2.28g) and total length (TL-48.20mm) statistically higher than the rest (P<0.05). L1 to L4 treatments showed intermediate growth values, without differences between them (P>0.05), while LIn presented the lowest growth (P<0.05). Survival was around 75% in all experimental groups, except LS, that presented a significantly lower value (17.5%, P<0.05). Skeletal abnormalities were detected in all experimental treatments, but LIn and L1 presented the lowest incidence. In no case, visible morphological alterations were found. This study shows that prolonging pacu rearing under laboratory conditions at high densities improves temporal availability and survival of juvenile without affecting growth or subsequent osteological development of fish.

The objective of the present work was to test a new mathematical expression destined to improve the interpretation of somatic cell counts and milk production levels. A multiple model of the lactation curve it was compared to the classical Wood model separately for each of the cell ranges (RC). A refined data base was used taken from a control system of five dairy herds, which represent a total of 1200 Holstein-Friesian dairy cows. The milk production curve was adjusted, separately for adult cows (AC) and first lactation cows (FLC), via the equation y(t) = a t b e-c t. The multiple model proposed was based in the previous equation incorporating the variable RC in the form of y(t, RC) = a t b e-c t + d RC + f RC2, where y (t, RC) = milk production in the t th week for an AC or FLC with a cell range RC. The goodness of fit for individual models varied between 0.36 and 0.74 for FLC and 0.77 and 0.93 for AC. The multiple model with coefficients of determination of 0.59 and 0.89, for AC and FLC respectively, was found simpler and applicable. With respect to total estimated milk production, this multiple model permitted the inference that in both animal groups the difference between the lowest and the highest range is in the order of 25-28%. It is concluded that the multiple model proposed, seems to be simpler to understand and apply than the traditional Wood model.

El objetivo del presente trabajo fue probar una nueva expresión matemática destinada a mejorar la interpretación de los recuentos de células somáticas y niveles de producción de leche. Un modelo múltiple de curva de lactancia se comparó con el modelo clásico de Wood, separadamente para cada uno de los rangos celulares (RC). Se trabajó con una base de datos depurada proveniente del control sistemático de cinco rebaños lecheros que representan una masa de 1200 vacas Holstein Friesian. Se ajustó una curva de producción de leche, separadamente para vaquillas y vacas, mediante la expresión y(t) = a t b e- c t. El modelo múltiple propuesto estuvo basado en la ecuación anterior, incorporando la variable RC en la forma y (t, RC = a t b e- c t e d RC + f RC2. El grado de ajuste para los modelos individuales varió entre 0,36 y 0,74 en vaquillas y 0,77 y 0,93 en vacas. El modelo múltiple, con coeficientes de determinación de 0,59 y 0,89 en vaquillas, y vacas respectivamente, resultó más simple y aplicable. Respecto a la producción total estimada, el modelo múltiple permitió inferir que en ambos tipos de animales la diferencia entre el rango más bajo y el rango más alto es del orden del 25-28%. Se concluyó que el modelo múltiple propuesto, parece ser de más simple comprensión y aplicabilidad que el modelo tradicional de Wood.

A study was carried out in five herds from central and southern Chile in order to establish the effect of increasing somatic cell counts on the production and composition of milk. Information coming from a monthly control system for each of the animals belonging to the experimental dairy herds was managed in a computer database designed for said purpose. Starting from the records registered in two years of data collection, the relations existing among the somatic cell count and the production and composition of milk were studied. A general adjustment model was established allowing an adequate explanation of this phenomenon (y = a + bx + cx² +, where a, b, and c are parameters; y = Total Solids, % (ST); Butterfat, % (MG) and Non Fat Solids, % (SNG); and x = level of mastitis (assessed in ranges 0 to 9)). The main results were the following: a one unit increment in somatic cell count represented a decrease in milk production of 0.760 and 0.790 kg d-1, for range 1 vs. 0.530 and 0.810 (P<0.05) for range 9, for heifers and dairy cows respectively. The values found for the composition parameters, in the same order, were as follows: 0.095 and 0.092 for range 1 vs. 0.024 and 0.092 for range 9 for ST; 0.021 and 0.031 vs. 0.010 and 0.015 for MG; 0.068 and 0.065 vs. - 0.025 and 0.068 for SNG. These results confirm that losses due to sub-clinical mastitis have an important and detrimental effect on milk production and composition.

Se realizó un estudio en cinco lecherías de la Zona Central y Sur de Chile, destinado a establecer el efecto de concentraciones crecientes de células somáticas sobre la producción y composición de leche de vacas. Se utilizó la información proveniente de controles sistemáticos mensuales, de cada uno de los animales pertenecientes a los rebaños experimentales, siendo manejada en una base computacional específicamente diseñada para dicho fin. A partir de los antecedentes registrados en dos años de recopilación, se estudiaron las relaciones existentes entre el recuento de células somáticas y la producción y composición de la leche, lográndose establecer un modelo general de ajuste (y = a + bx + cx², donde a, b, c son parámetros, y = Sólidos totales (ST), Materia Grasa (MG), Sólidos no granos (SNG), x = score o rango de mastitis (0 a 9)), herramienta que permite dar adecuada explicación al fenómeno. Los principales resultados fueron: el incremento de una unidad en el recuento de células representó en el volumen diario de producción de leche, una tasa de disminución expresada en kg d-1 de 0,760 y 0,790 para el nivel o rango 1 vs 0,530 y 0,810 (P < 0,05) en el rango 9, para vaquillas y vacas, respectivamente. En igual secuencia los valores encontrados en los parámetros composicionales fueron: 0,095 y 0,092 en el rango 1 vs 0,024 y 0,092 en el rango 9 para ST; 0,021 y 0,031 vs 0,010 y 0,015 para MG; 0,068 y 0,065 vs 0,025 y 0,068 en SNG. Estos resultados permiten concluir que las pérdidas registradas como consecuencia de la mastitis subclínica, constituyen un importante factor detrimental de la producción y composición de leche.