Invited review: Role of livestock in human nutrition and health for poverty reduction in developing countries.

Livestock keeping is critical for many of the poor in the developing world, often contributing to multiple livelihood objectives and offering pathways out of poverty. Livestock keeping also affects an indispensable asset of the poor, their human capital, through its impact on their own nutrition and health. This paper outlines the linkages between livestock keeping and the physical well-being of the poor, and examines a number of commonly held beliefs that misrepresent livestock development issues related to these linkages. These beliefs limit the scope of intervention programs to promote livestock and limit their potential contribution to poverty reduction. Recognition of the complexity of the role livestock play in household decision-making and of the opportunities foregone due to these misconceptions can enhance the ability of livestock to contribute to human well-being in the developing world.

Responses of pocket gophers (Thomomys bottae) to changes in diet quality.

We examined digestibility of dry matter, nutrients, and fiber, and food intake, metabolic fecal losses, weight change, and gut size of pocket gophers (Thomomys bottae) in relation to diet quality in the laboratory. Pocket gophers were maintained for 15-20 days on one of seven diets which contained from 18% to 56% neutral detergent fiber (NDF). NDF content of the diet was an excellent predictor of diet quality. Digestibility of dry matter, NDF, and nitrogen all decreased with increasing NDF content of the diet. In general, pocket gophers compensated for low diet quality by increasing dry matter intake, but those given high quality forage before the lowest quality diet reduced their intake. Thus, the response of pocket gophers to low quality diets may depend on their body condition. Because increased food intake resulted in increased total metabolic fecal losses and metabolic fecal nitrogen losses, decreasing food intake on low-quality diets may be advantageous. A further response of pocket gophers to decreased food quality was an increase in size of cecum and large intestine, suggesting that fermentation of cell walls became increasingly important as diet quality decreased.

Factors determining the digestive efficiency of the domesticated donkey (Equus asinus asinus).

Factors determining the digestive efficiency of donkeys were studied in animals fed either a low quality roughage (wheat straw: 77.1% neutral detergent fibre, 2.8% crude protein) or a high quality forage (alfalfa hay: 47.5% neutral detergent fibre, 22.7% crude protein). The neutral detergent fibre (NDF) intake when fed wheat straw was 1693 +/- 268 g animal-1 day-1, 10% higher than when fed alfalfa hay. Digestive coefficient of NDF and acid detergent fibre (ADF) when fed wheat straw amounted to 50.9 +/- 4.9 and 42.0 +/- 4.1% respectively. NDF and ADF apparent digestibilities and mean retention times (37.7 +/- 1.7 and 36.4 +/- 3.2 h respectively) were not significantly different (P greater than 0.05) between the two diets. The donkey appears to digest cell wall constituents as efficiently as the Bedouin goat when on low quality roughage, but less efficiently when fed alfalfa hay. Its energy digestibility is, however, as high as that reported for the Bedouin goat. The donkey's high energy digestibility is related to its capacity to digest soluble food components more efficiently than the ruminant. The mean retention time in the donkey is shorter than in the Bedouin goat and is consistent with its capacity to compensate for a lower quality diet by increasing its intake rate. Recycling of urea in donkeys maintained on wheat straw amounted to 75.5 +/- 13.0% of the entry rate. A decrease in the rate of renal urea filtration, coupled with an increase in the fraction reabsorbed, increased the retention of nitrogenous waste and permitted recycling of nitrogen into the gut.

Forage ingestion: effects of sward characteristics and body size.

A model of a grazing ruminant in a range environment integrates ingestive behaviors (bite size, chewing rate, movement rate) and processing behaviors (mastication and rumination requirements) with rumen function to predict the combination of behaviors that produces the highest rate of energy digestion per unit of time (DE/T). Ingestive and processing behaviors compensate to maintain DE/T as the environment changes. Compensation for a change in forage density is more complete than for a change in forage quality. Ingestive behaviors alone have limited ability to offset environment changes, and control of passage rate through processing behaviors is an important additional compensatory mechanism. Optimal solutions of the model maintain a high intake by sacrificing diet quality and maintain a high rate of passage by increasing mastication and rumination effort when eating low-quality diets. When the model is scaled to body size, decreases in body size lead to higher selectivity and more pronounced processing behaviors. In no case are optimal solutions characterized by less than maximum rumen fill. The model predicts that the small ruminant derives an increasing proportion of its energy from the cell contents. The model suggests that selection for production has produced plastic ingestive and processing behaviors and has increased body size.

Digestion and passage kinetics of chimpanzees fed high and low fiber diets and comparison with human data.

To investigate the digestive kinetics and fiber digestion of great apes, we conducted digestion trials on chimpanzees (Pan troglodytes) with diets of two fiber levels, one containing 34% neutral detergent fiber (NDF) and the other 14% NDF. Chimpanzees exhibited a response to fiber similar to that of humans. First, increases in the fiber concentration of the diet decreased mean transit time (MTT), hindgut turnover time (T) and the digestibility of fiber. Second, differences in MTT and T between the treatments and animals explained most of the variability in the digestibility of fiber components. Third, consistent with human data, the fiber marker passed more slowly than the liquid marker only when the high fiber diet was consumed. Fourth, individual variability, as in humans, was a significant factor affecting digestion and passage. Fifth, the MTT of chimpanzees was longer than that of humans. This result may be due to the apes' larger hindgut. In comparison with other hominoids, humans have smaller volumes in the gastrointestinal tract and hindgut. The gut proportions of modern humans, in combination with evidence from the fossil record, indicate that during its evolution the human lineage was able to overcome nutritional constraints imposed on body size increases in the great apes. We suggest that this advance was achieved through technological and social innovations that permitted early humans to achieve larger body size without lowering dietary quality.