Urban expansion and the loss of prime agricultural lands in Puerto Rico.

In many countries where the economy has shifted from mainly agricultural to industrial, abandoned agricultural lands are lost to urbanization. For more than 4 centuries the Puerto Rican economy depended almost entirely on agriculture, but sociopolitical changes early in the 20th century resulted in a shift to industry. This shift in the economy, and an increase in population, has resulted in an increase in urban areas. This study describes the rate and distribution of urban growth on the island of Puerto Rico from 1977 to 1994 and the resulting influence on potential agricultural lands. Urban extent and growth were determined by interpreting aerial photographs and satellite imagery. The 1994 urban coverage was combined with a soil coverage based on agricultural potential to determine the distribution of urban areas relative to potential farmlands. Analyses showed that in 1977, 11.3% of Puerto Rico was classified as urban. After 17 years, urban areas had increased by 27.4% and urban growth on soils suitable for agriculture had increased by 41.6%. This represents a loss of 6% of potential agricultural lands. If this pattern of encroachment by urban growth into potential farmlands continues, Puerto Rico's potential for food production in the future could be greatly limited.

Dietary fibre in the diet of the growing pig: effects on apparent digestibility and resultant implications for its use in reducing the incidence of oesophagogastric parakeratosis.

The effects on apparent digestibility of increasing dietary fibre concentrations in barley-based diets by substituting for barley either bran, oatmeal by-product, guar gum or pectin were studied using 72 pigs. Increasing substitutions of bran up to a maximum of 300 g kg-1 gave progressive decreases in apparent digestibility of dry matter, ether extract and gross energy fractions and in digestible and metabolisable energy contents, progressive increases in apparent digestibility of modified acid detergent fibre but had no consistent effect on either nitrogen or extract free of nitrogen fractions. Increasing substitution of oatmeal by-product up to the same maximum gave significant linear decreases in apparent digestibility of dry matter, extract free of nitrogen and gross energy, significant depressions in apparent digestibility of modified acid detergent fibre and significant increases in ether extract. Guar gum and pectin, both substituted to a maximum of 50 g kg-1 had no significant effects on apparent digestibility. The results are discussed in the context of the concentrations of dietary fibre needed to reduce the incidence of oesophagogastric parakeratosis.

Effects of structural and non-structural polysaccharides in the diet of the growing pig on gastric emptying rate and rate of passage of digesta to the terminal ileum and through the total gastrointestinal tract.

Six experiments were made in growing pigs to investigate the effects of substituting bran, oatmeal byproduct, pectin and guar gum for barley on gastric emptying rate, pH and dry matter of digesta and on the dry matter content and rate of passage of digesta to the terminal ileum and overall. Twelve pigs with cannulas sited at the pyloric/fundic junction of the stomach were used to measure gastric emptying. Seventy-two pigs were kept in metabolism cages for the total collection of faeces and nine pigs were fitted with simple cannulas 150 mm cranial to the ileo-caecal junction. For the overall transit measurements the barley was ground through a 4.68 mm screen (C) and for the other studies either through this screen or a 1.56 mm screen (F). Gastric emptying rates were significantly faster for F diets than for C diets, but bran and oatmeal by-product substitutions were without significant effect on this variable or on rate of passage to the terminal ileum. Guar gum and pectin significantly speeded up gastric emptying and transit to the terminal ileum in C diets. Guar gum and pectin did not significantly affect overall transit time, but bran accelerated it. The results are discussed in relation to the depressive effects on nutrient utilization which have been recorded for the four polysaccharides: it is postulated that gastric emptying rate and transit time to the terminal ileum are likely to have a minimal effect on overall transit time.

Histopathology of oesophagogastric lesions in pigs.

The development of parakeratotic lesions and ulcers of the oesophagogastric epithelium was studied in pigs from a variety of sources and of ages ranging from 10 to 22 weeks. In general, the severity, as assessed by gross appearance, paralleled the depth to which parakeratotic change extended into the epithelium. However, some early degenerative change and erosion was observed in epithelium graded as macroscopically normal. Separation and erosion usually occurred beneath a band of epithelial cells with cytoplasmic pallor and nuclear degeneration underlying the parakeratotic layers. These findings are discussed in relation to the possible role of diet and gastric acidity in the pathogenesis of the lesions.

Rate of development of oesophagogastric parakeratosis in the growing pig: some effects of finely ground barley diets, genotype and previous husbandry.

The rate of development of parakeratotic lesions in the gastric pars oesophagea was investigated in three experiments using 360 pigs, initially aged 10 to 11 weeks and weighing about 30 kg, of differing genotype and with some differences in previous rearing method, given a diet based on finely ground barley which was known to predispose to lesion formation. Lesions were found in some pigs at 10 to 11 weeks old but the incidence and severity increased progressively indicating development as quickly as one month after first giving the finely ground diet. There were indications that different genotypes and different diets given previously in rearing may have influenced the results obtained. The possible influence of other environmental factors is discussed.

Oesophagogastric parakeratosis in the growing pig: effects of the physical form of barley-based diets and added fibre.

In four experiments a total of 288 individually fed pigs were given barley-based diets for about 100 days from about 20 kg liveweight. Fine grinding of barley increased the number and severity of oesophagogastric lesions. Pelleting a diet based on coarsely ground barley had a similar effect. Coarser grinding of the barley and substituting small proportions of oat husk, but not of bran, gave lower incidences and severities of lesions. The performance responses of the pigs differed and give a framework for deciding on the balance to be struck between optimal performance and the risk of lesion development.

Effects of exogenous amino acids on the multiplication of porcine Escherichia coli.

The multiplication rates of 70 porcine Escherichia coli strains were compared in minimal medium and in medium supplemented with aspartic acid, lysine, serine and threonine, which were the amino acids taken up during multiplication of porcine E. coli in a complex medium. The effects of these amino acids singly or in combinations and the amino acids norleucine and norvaline on the growth of porcine E. coli were studied. Together, aspartic acid, threonine, serine and lysine increased the multiplication rates of 42.9% of the strains, an effect traced to aspartic acid, but they had no effect on an equal number of strains. The rest were inhibited, and this effect was traced to serine. Cysteine, threonine, leucine and phenylalanine singly inhibited some or all of the strains tested. Norleucine and to a lesser extent, norvaline greatly prolonged the lag phase of culture in minimal medium. The inhibitory effect of norleucine was reversed by only methionine, although isoleucine, leucine and valine which were more effective in norvaline inhibition, also showed limited antagonism to norleucine inhibition.

Some factors influencing colicin activity between pathogenic and commensal Escherichia coli from the pig.

Commensal strains of Escherichia coli derived from pigs had a broad spectrum of in vitro colicin acitivity against pathogenic serotypes. Of eight pathogenic serotypes tested, only three were colicinogenic and were active against relatively few commensal strains. Colicin activity was influenced by temperature, pH and oxygen tension as well as by the availability of certain nutrients and the presence of trypsin. Lack of colicin activity in intestinal supernatant fluid was ascribed to the concentration of trypsin present. It was concluded that colicins are unlikely to influence the dominance of pathogenic Escherichia coli serotypes in the pig's intestine, except possibly in the colon and rectum where the concentration of trypsin is low.

Factors influencing occurrence of colibacillosis in calves.

This investigation describes some of the husbandry factors influencing the occurrence of colibacillosis in calves. Diarrhoea and mortality were usually associated with an increase in the proportion of "pathogenic" to total E coli to about 50 per cent in the faeces although there were occasions when the proportion of "pathogenic" E coli increased but no disease occurred. These increases often followed changes of diet which appeared to be more important than environmental conditions. The use of uncontaminated houses to break the cycle of infection appeared to have the greatest influence on the disease pattern.