Protein utilization during energy undernutrition in sheep sustained by intragastric infusion: effects of protein infusion level, with or without sub-maintenance amounts of energy from volatile fatty acids, on energy and protein metabolism

Abstract

Utilization of endogenous and exogenous energy for protein accretion during energy undernutrition has been studied. Nine lambs nourished by intragastric infusion were given either progressively increasing or decreasing amounts of casein-N up to 2550 mg/kg metabolic weight (W@ "), with or without 250 k J k g W@" of volatile fatty acids daily. Energy balance (respiration calorimetry) and N balance were measured. While all experimental animals were in negative energy balance, N balance increased curve-linearly with the increase in casein-N infusion and attained positive N balance.Endogenous energy (presumably body fat) was found to meet the energy needs for protein accretion during energy undernutrition. It is concluded that body fat can be effectively utilized to support lean-tissue growth during energy undernutrition, so that the classical nutritional concept of dietary energy:protein ratio is only meaningful when both endogenous and exogenous energy are considered.Intragastric infusion: Energy undernutrition: Protein utilization: Fat mobilization Due to the interdependence of fermentable energy intake and microbial protein production (Agricultural Research Council, 1980), the depositions of body fat and protein are normally found to be positively correlated in fed animals (Leat, 1983). The technique of intragastric infusion, in which all nutrients are infused (volatile fatty acids (VFA) into the m e n , and protein, minerals and vitamins into the abomasum; 0rskov et al. 1979), has enabled the supplies of energy (VFA) and protein to be varied independently. Thus, 0rskov et al. (1983) and Hovell et al. (1983) were able to test whether otherwise fasted animals would metabolize infused protein as a source of energy or utilize it to meet the estimated protein requirement for tissue maintenance. They showed that dairy cows, steers and lambs did not oxidize the supplied protein as a source of maintenance energy but rather retained it to achieve N equilibrium. This was made possible by the mobilization of endogenous energy (presumably body fat) to fuel protein accretion (0rskov & Hovell, 1986). Using the intragastric infusion technique, steers were given protein ranging h m zero to four times that of maintenance requirement with no other source of energy; the animals not only attained positive N balance at the expense of body fat, but showed rapid body-weight gain (Chowdhury et al. 1990). This implies that with normally-fed animals the effect of dietary

Interaction between protein and energy supply on protein utilization in growing cattle: A review

“…These results suggest the existence of protein-and energy-dependent phases of growth. In contrast to those results, other studies with lambs and steers (Chowdhury et al, 1990) demonstrated that N retention increased due to increases in N supply, even when sub-maintenance levels of energy were supplied. Those results supported the earlier studies (see earlier) with fish meal supplementation (Fattet et al, 1984;Vipond et al, 1989), suggesting that endogenous fuel (fat mobilization) can be used to maintain protein deposition in situations in which energy (but not protein) supply is limiting.…”

Protein utilization during energy undernutrition in sheep sustained by intragastric infusion

“…The technique of intragastric infusion, the composition of infusates and the control of infusion were as described previously (Chowdhury et al 1997). In addition to the standard VFA mixture (acetate-propionate-butyrate 65 : 25 : 10, molar proportions) infused previously, a glucogenic VFA mixture (acetate-propionate-butyrate 16 : 79 : 5, molar proportions) was also used.…”

“…It has been shown, using intragastrically-nourished sheep, that infusion of volatile fatty acids (VFA) to provide additional exogenous energy (250 kJ/kg metabolic body weight (W0'75) daily) had little effect on the N balance when protein was infused in progressively increasing amounts (Chowdhury et al 1997). Even when not given any VFA, and in negative energy balance, the sheep were able to retain N. It was concluded that endogenous energy reserves (body fat) were mobilized to provide the energy required for protein retention.…”

An experimental approach for studying the genetic and physiological background of nutrient transformation in cattle with respect to nutrient secretion and accretion type

“…As a second factor, interactions between the nutrients are probably of importance as well. Animals which are able to mobilise body fat as an energy source for protein synthesis could be more efficient in protein utilisation (CHOWDHURY et al, 1997).…”