Factors influencing the structure and function of the small intestine in the weaned pig: a review

Rates of clearance, ingestion, ammonia excretion, respiration and egg production were measured in food-acclimated (0 to 1700 W C 1-l) planktonic copepods Acartia tonsa in relation to food concentration. Carbon and nitrogen budgets were constructed. Clearance peaked at a food concentration of 150 W C 1-l, and decreased at both higher and lower concentrations. Ingestion and egg production rates increased sigmoidally with food concentration approaching plateaus equivalent to 180 and 64 % body C d-l, respectively. Rates of ammonia excretion and respiration increased with algal concentration in a decelerating manner. Respiration and excretion rates of copepods fed at saturation food concentration were more than 4 times higher than those for starved individuals. The causality of the increased respiration rate in association with feeding (specific dynamic action, SDA) is discussed by considering the physiology and biochemistry of the processes that potentially contribute to SDA. The theoretical biochemical minimum costs of biosynthesis accounted for between 50 and 116 % of observed SDA, while assimilation costs equalled 18 to 28 %. Costs of feeding, digestion and excretion (-1 % of SDA), and the mechanical work required to transport food down the gut, contributed insignificantly to SDA. It is concluded that the increment in metabolic rate of feeding A. tonsa largely relates to biosynthesis ('growth') and transport, and that the efficiency of egg production in this species is near its theoretical maximum.

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Bioenergetics of the planktonic copepod Acartia tonsa: relation between feeding, egg production and respiration, and composition of specific dynamic action

I N T R O D U C T I O N . . 278 C H A R A C T E R I Z A T I O N OF LOW-QUALITY F O R A G E S . . . 278 C H E M I C A L C O M P O S I T I O N O F LOW-QUALITY F O R A G E S . . 279 BASIC C O N C E P T S F O R E N S U R I N G A B A L A N C E D N U T R I T I O N F O R R U M I N A N T S O N F O R A G E B A S E D D I E T S . . 279 O P T I M I Z I N G M I C R O B I A L G R O W T H I N T H E R U M E N . . 280 MINERAL REQUIREMENTS OF RUMEN MICROBES . . 280 Requirements for sulphur . . 280 Requirements for phosphorus . . 280 Requirements for magnesium . . 281 Requirements for ammonia . . 281 Timing of urea supplements and the ratio of sugars and starches to fibre in a diet . . 281 REQUIREMENTS FOR AMINO A C I D S / P E P T I D E S BY RUMEN ORGANISMS . 283 M A N I P U L A T I N G T H E E F F I C I E N C Y O F F E R M E N T A T I V E D I G E S T I O N . 285

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Factors Affecting the Utilization of ‘Poor-Quality’ Forages by Ruminants Particularly Under Tropical Conditions

Residual feed intake (RFI) is the difference between the actual and expected feed intake of an animal based on its BW and growth rate over a specified period. The biological mechanisms underlying the variation in feed efficiency in animals with similar BW and growth rate are not well understood. This study determined the relationship of feedlot feed efficiency, performance, and feeding behavior with digestion and energy partitioning of 27 steers. The steers were selected from a total of 306 animals based on their RFI following feedlot tests at the University of Alberta Kinsella Research Station. Selected steers were ranked into high RFI (RFI >0.5 SD above the mean, n = 11), medium RFI (RFI ± 0.5 SD above and below the mean, n = 8), and low RFI (RFI 0.10). Residual feed intake was correlated with daily methane production and energy lost as methane (r = 0.44; P < 0.05). Methane production was 28 and 24% less in low-RFI animals compared with high- and medium-RFI animals, respectively. Residual feed intake tended to be associated (P < 0.10) with apparent digestibilities of DM (r = -0.33) and CP (r = -0.34). The RFI of steers was correlated with DE (r = -0.41; P < 0.05), ME (r = -0.44; P < 0.05), heat production (HP; r = 0.68; P < 0.001), and retained energy (RE; r = -0.67; P < 0.001; energy values are expressed in kcal/kg of BW). Feedlot partial efficiency of growth was correlated (P < 0.01) with methane production (r = -0.55), DE (r = 0.46), ME (r = 0.49), HP (r = -0.50), and RE (r = 0.62). With the exception of HP (r = 0.37; P < 0.05), feed conversion ratio was unrelated to the traits considered in the study. Feeding duration was correlated (P < 0.01) with apparent digestibility of DM (r = -0.55), CP (r = -0.47), methane production (r = 0.51), DE (r = -0.52), ME (r = -0.55), and RE (r = -0.60). These results have practical implications for the selection of animals that eat less at a similar BW and growth rate and for the environmental sustainability of beef production.

Relationships of feedlot feed efficiency, performance, and feeding behavior with metabolic rate, methane production, and energy partitioning in beef cattle

Contributors. Preface. Units and Conversion Factors Contents. Avian Energetics, Ecology, and Evolution-- R E Ricklefs Nutrition and Metabolism-- M Murphy Digestive Plasticity in Avian Energetics and Feeding Ecology-- W H Karasov Energetic Features of Avian Thermoregulatory Responses-- W R Dawson and T.P. O'Connor Physiological and Ecological Aspects of Hypothermia-- R E Reinertsen Energetics and Nutrition of Molt-- M E Murphy Energetics of Flight-- U M Norberg Energetics of Avian Foraging-- B A Mauer Energetics of Migratory and Winter Fattening-- H Biebach Female Reproductive Energetics -- C Carey Energetics of Avian Incubation-- J Williams Embryonic energetics-- C M Vleck and D. Vleck Energetics of Post-natal Growth-- W Weathers Populational and Community Energetics-- J A Wiens and A H Farmer.

Avian Energetics and Nutritional Ecology

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The energetic efficiency of metabolism.

The energetic efficiency of growth

The effects of conventional and novel methods for the manipulation of growth in meat animals are reviewed within the context of the fundamental laws that determine the biological efficiency of energy conversion. Interspecies comparisons reveal large differences in the energetic efficiency of growth between mammals and birds. The similarity between mammals of different sizes is remarkable, both between and within species, which suggests that manipulation of growth rate per se has little effect on efficiency. The best way to improve the efficiency of growth is to maximize the conversion of metabolizable energy (ME) to lean tissue at all stages of maturation. The principal destination of ME is heat, however thermogenesis linked to essential metabolic functions is resistant to manipulation. It is more profitable to manipulate the partition of retained energy between protein and fat. Whether this is achieved by nutrition, conventional breeding or bioengineering, it is necessary to ensure that it does not compromise the normal health and vigour of the growing animal.

Bioenergetics, bioengineering and growth

The behaviour of two groups offour pigs in concentrations of ammonia gas that are frequently recorded in piggeries (0, 10, 20 and 40 p.p.m.), was continuously observed for 14 days each in a choice test. An octagonally shaped (annular), eight compartment preference chamber was built to house the pigs. Each compartment supplied the pigs with ample food, water and bedding material but differed in the level of atmospheric contamination. Adjacent compartments were separated by plastic curtains, allowing the pigs free access to neighbouring compartments while reducing cross-contamination of the pollutant. The position of the contamination was changed weekly to eliminate positional preferences. The location of the pigs was scan sampled every 15 min and their behaviour at this time was instantaneously recorded. A significantly greater proportion of their time was spent in the unpolluted compartments (53·4%) than in the 10 p.p.m. (26·9%), 20 p.p.m. (7·1%) or 40 p.p.m. (5·1%) compartments (P 0·05). The occupancy pattern was resumed following the rotation of the ammonia concentrations and/or following cleaning (P > 0·05). Higher concentrations of ammonia were visited less often (P = 0·005) and once there, the pigs stayed for a comparatively shorter time (P = 0·003) for approximately 35 min. As the aversion was not immediate, it is suggested that aversion was not due to the odour of ammonia initially experienced on entry. Instead the insidious aversion may be due to a sense of malaise that may develop while a pig is in a polluted atmosphere. The pigs chose to rest (P = 0·002), sit (P = 0·007), feed (P = 0·007) and forage (P = 0·013) more in the unpolluted compartments. Overall more feeding behaviour was observed in the fresh air and more food was consumed in these compartments of the chamber (P = 0·002).

Behavioural responses of pigs to atmospheric ammonia in a chronic choice test

This chapter is concerned with the factors that determine the utilization of food energy for the maintenance of life and the efficiency with which food energy surplus to that required for maintenance can be used to promote growth. The subject, of course, dates back to Lavoisier and de la Place (1784) and many of the basic concepts that I shall use in this chapter are the same now as then. There have been a number of classic treatises on energy metabolism of which the most famous five must be, in chronological order, Kellner (1900), Rubner (1902), Brody (1945), Kleiber (1961) and Blaxter (1962). All these contain both information and ideas which are still valuable to the modern student of energy metabolism. Indeed, most of the controversies in energy metabolism, such as that concerning diet-induced thermogenesis, have arisen several times during its history and each time have been resolved reasonably satisfactorily in the light of the information available at the time. Bernard Shaw said, ‘Every good scientific discovery should be made once every ten years,’ which is fair comment since each time a theory is repeated it is usually in the light of new evidence. It should not, however, be necessary each time to start from square one. There are giants in the field of energy metabolism. We should have the humility and good sense to stand on their shoulders.

A. J. F. Webster

Papers

The energetic efficiency of metabolism.

The energetic efficiency of growth

Bioenergetics, bioengineering and growth

Behavioural responses of pigs to atmospheric ammonia in a chronic choice test

Energetics of Maintenance and Growth