Efficiency of energy utilisation and voluntary feed intake in ruminants

Abstract

Energy requirements of animals are most readily expressed in terms of net energy (NE), while the energy yield of feed is, at least initially, expressed in terms of metabolisable energy (ME). Energy evaluation systems 'translate' NE requirements into ME requirements (ME systems) or assign NE values to feeds (NE systems). Efficiency of ME utilisation is higher for maintenance than for production and the NE yield of a feed varies, therefore, with ME intake. In addition, energetic efficiency for maintenance and production is thought to be different for lactating and non-lactating animals and to be affected by diet quality. As a result, there are currently many national energy evaluation systems that are complex, differ in their approach and are, as a result, difficult to compare. As ruminants in most production systems are fed ad libitum, this is also the most appropriate intake level at which to estimate energetic efficiency. Analyses of older as well as more recent data suggest that ad libitum feeding (i) abolishes the effects of diet quality on energetic efficiency (almost) completely, (ii) abolishes the differences between lactating and non-lactating animals (almost) entirely and (iii) results in overall energetic efficiencies that are always close to 0.6. The paper argues that there is now sufficient information to develop an international energy evaluation system for ad libitum fed ruminants. Such a system should (i) unify ME and NE systems, (ii) avoid the systematic bias and large errors that can be associated with current systems (iii) be simpler than current systems and (iv) have as a starting point a constant efficiency of ME utilisation, with a value of around 0.6. The remarkably constant efficiency of ME utilisation in ad libitum fed ruminants could be the result of energetic efficiency as well as feed intake regulation being affected by the same variables or of a direct role of energetic efficiency in feed intake regulation. Models to predict intake on the basis of the latter hypothesis are already available for non-reproducing ruminants but remain to be developed for reproducing animals. Keywords: energy evaluation systems, energy requirements, efficiency of ME utilisation ImplicationsThere are currently many different national energy evaluation systems for ruminants, which makes comparisons across borders problematic. The paper suggests that these different systems could be unified by taking ad libitum feeding, that is, the dominant on-farm feeding system, as a starting point. The presented analyses of older as well as more recent data show that the overall efficiency of ME utilisation in ad libitum fed ruminants is (i) virtually independent of feed quality characteristics, (ii) not essentially different between lactating and non-lactating ruminants and (iii) close to a value of 0.6. Using a single value for overall energetic efficiency in ad libitum fed ruminants (i) considerably simplifies existing energy evaluation systems, (ii) avoids the use of different national energy evaluation systems and abo...

Requerimientos energéticos de ovinos de pelo en las regiones tropicales de Latinoamérica. Revisión

“…La eficiencia de la utilización de EMm (K m ) representa la fracción de EM que se puede convertir en energía neta (EN), para soportar los requerimientos de mantenimiento de los rumiantes. La fracción que no se puede convertir a EN se pierde como el incremento de calor incluyendo fermentación en el tracto gastrointestinal y reacciones fermentation in the gastrointestinal tract and biochemical reactions at the cellular level (29) . The efficiency of energy utilization of feedstuffs has an economic impact, and the best way to determine it is by means of feed conversion efficiency (27,30) .…”

“…Requerimientos energéticos para mantenimiento estimados en ovinos de pelo en condiciones tropicales de América Latina bioquímicas a nivel celular (29) . La eficiencia de utilización de la energía de los alimentos tiene un impacto económico, y la mejor manera de determinarla es por medio de la eficiencia de la conversión alimenticia (27,30) .…”

“…El valor medio de K m en la presente revisión fue de 0.66. En este respecto, cuando la EM de las dietas de calidad media (como los utilizados en los trópicos) se utiliza con una baja eficiencia para mantenimiento y ganancia, K m es relativamente mayor en comparación con K g (29) . Además, este autor reportó que K m podría considerarse en promedio como 0.60 independientemente de la dieta; esto se aproxima al valor promedio de este trabajo, que fue de 0.66 (Cuadro 4).…”

“…Por lo tanto, es necesario continuar con los trabajos que se centren en la determinación de las necesidades de nutrientes de ovinos de pelo y desarrollar un sistema de alimentación basado en las características de la ración, raza y condiciones ambientales que prevalecen en los mean value for k m in the present review was 0.66. In this respect, even when ME of diets of medium quality (such as those commonly used in the tropics) is utilized with a low efficiency for maintenance and gain, k m is relatively higher compared to k g (29) . Furthermore, this author reported that k m could be considered on average as 0.60 independently of the diet.…”

“…Tolkamp (29) reported that k g for rations of low to medium quality (such as those of tropical forages), is expected to be low. Tedeschi et al (35) mentioned that there are factors which may affect k g , pointing out that ration (energy density trópicos de América Latina.…”