Growth data of some bones (shank, tibia, and keel) and the digestive tract in White Leghorn pullets, which consumed ad libitum and restricted diets, were analyzed by mono- and diphasic allometric functions. Fat-free plucked empty body mass (FFEBM) or a functional entity was used as the independent variable in the equations. Pullets had been fed a low-lysine diet or a daily restricted amount of an adequate diet, from 0 to 6 or 7 to 18 wk of age. An additional group of pullets consumed ad libitum a control starter and grower diet. Relative growth of the skeletal bones and parts of the digestive tract, vs FFEBM, was described most accurately by a diphasic model. For each constituent, allometric slopes of the first growth phase (beta1) vs FFEBM were smaller than 1 (beta1 varied from 0.39 to 0.43 for shank and tibia, from 0.48 to 0.73 for the keel, from 0.89 to 0.98 for the total digestive tract, and from 0.80 to 0.84 for the gizzard, separately). These results suggest that each of the assessed organs matured earlier than the FFEBM. Except for the keel, which grew relatively faster than FFEBM if an early nutrient restriction had been applied, beta1 of all other assessed structures was similar for all treatments. If the allometric slope of the second growth phase (beta2) was estimated to be not different from zero, then the breakpoint between both phases was defined as the moment of attainment of maturity for the respective constituent. The attainment of maturity of the different body structures confirmed the classical growth sequence studies of the Hammond School. No differences in mature weights for the assessed organs between the feeding regimens were observed. The results indicated that in studies in which a nutritional deficiency had been applied, the weights of several body structures, most often expressed in terms of weight per 100 g BW, are strongly related to the decrease in growth rate of the fat-free body. It was concluded that most of the reported effects on growth retardation as a result of nutrient restrictions are primarily a consequence of the mobilization of fat per se.

The effects of pressure toasting of whole and broken peas, lupins and faba beans on in situ degradability of protein and starch and intestinal digestibility of protein were studied. To test for associative effects on rumen degradability and intestinal digestibility after toasting, a mixture of peas, lupins and faba beans was examined and results were compared with weighted averages of separately processed feedstuffs. Pressure toasting for 3min at 132°C decreased in situ protein degradability of peas, lupins and faba beans and in situ starch degradability of peas and faba beans, especially when broken versus whole seeds were processed. Undegraded intake protein (%UIP) increased after toasting whole or broken seeds from 25% to 44% and 52% for peas, from 22% to 47% and 51% for lupins and from 20% to 48% and 57% for faba beans, respectively. Undegraded intake starch (%UISTA) increased from 39% to 50% and 53% after toasting whole and broken peas and from 33% to 53% and 60% for toasted whole and broken faba beans, respectively. Total tract protein digestibility, measured after 12h rumen and subsequent intestinal incubation, remained unchanged for peas and faba beans, but decreased from 99% to 98% for toasted whole lupins and to 97% for toasted broken lupins. For toasted whole and broken faba beans, pressure toasting increased %UISTA from 33% to 53% and 60%, respectively. After pressure toasting, washable fractions (W) of all legume seeds decreased for both constituents, the fractional rate of degradation (kd) of protein decreased, while the kd of starch increased. It was concluded that protein degradability decreased after pressure toasting, without seriously affecting its total tract protein digestibility. Toasting a mixture of peas, faba beans and lupins resulted in higher starch degradabilities than expected, based on the separately treated feedstuffs. The kd's of the mixtures were higher than expected: 5.49 versus 4.29%h−1 for whole seeds and 5.01 versus 4.18%h−1 for broken seeds, respectively. Consequently, %UISTA was lower than expected (47% vs. 51% for whole seeds and 50% vs. 57% for broken seeds).

The increase in number and production of livestock also introduced a considerable nutrient surplus in livestock systems. Because of the negative effects on the environment, the sustainability of the system on national, regional, or farm levels has becom e one of the key item s in anim al produ ction. The co ncept of s ustainability is not well d efined. Usually th e oppo site, lack of su stainability, is use d to illustrate the aim of sustaina bility. The m ain indicator of the imbalance in a system is the nutrient balance. Therefore, the monitoring of nutrient flow on farm and at animal levels has been given much attention, especially that of nitrogen, phosphorus and potassium.

In the rumen, unnecessary N-losses occur because the availability of energy and N in the rumen is usually unbalanced. Because N is more rapidly available than energy, decreasing the protein degradability optimizes fermentation and decreases N-losses. Heat treatment can be used to decrease protein degradability. Therefore, heat treatment of legume seeds, such as lupins, peas and faba beans, may result in a more efficient use of these seeds in ruminant diets. When whole seeds are treated by heat, the presence of the covering hull may affect the result. Not only the protein degradability, but also the degradability of starch present in peas and faba beans, may be altered due to the heat treatment.

The relationship between protein nutrition and milk urea N was investigated in three experiments with a total of 125 cows. After 4 wk of pretreatment, cows received 1 of 13 diets with different ratios of protein to energy for 16 wk. Milk was sampled individually for urea analyses during pretreatment and during wk 1, 5, 10, and 15 of treatment. Results were compared with N losses estimated from rumen fermentation and with N losses of metabolic origin. The mean milk urea N concentration was 12.6 mg/100 ml of milk (range, 9.0 to 18.3 mg). For bulk samples especially, the rumen efflux of crude protein intake was the main determinant of the variation in milk urea N (r2 = 0.81; residual SD = 1.1). However, N losses from the rumen explained only about 50% of the variation in the milk urea N content of samples from individual cows. The N losses of metabolic origin, which, in these experiments, were responsible for 47 to 100% of urinary N losses, were not related to milk urea N. Results showed that regular measurement of milk urea N in bulk samples can be used to monitor N losses from rumen fermentation. However, the value does not give an indication of the efficiency with which the absorbed protein is utilized.