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A mechanistic model of dairy cow metabolism is described. The model was constructed as part of a programme directed toward quantitative and dynamic analysis of concepts and data regarding factors which influence the partition of nutrients in lactating dairy cows. Sensitivity and behavioural analyses undertaken using the model indicate that concepts and data arising from tissue level experiments conducted in vitro can be used to structure and parameterize whole-animal models since the quantitative and dynamic behaviour of such a model is acceptable. These analyses indicate further that such models can be used to evaluate factors which influence patterns of nutrient utilization. By way of illustrating the model's utility regarding evaluation of concepts relating to the interpretation of energy balance experiments, results of a simulated energy balance experiment are presented. Apparent costs of milk synthesis are partitioned among biosynthetic costs, physiological costs, ion transport costs and the reductions in energy expenditures in synthesis of body components which accompany increasingly negative energy balances due to feed restriction.There is widespread interest among dairy scientists in identification and quantitative evaluation of genetic, metabolic, nutritional and physiological factors which govern the partition of nutrients in lactating dairy cows (Baldwin et al. 1980; Prior & Smith, 1982; Bauman et al., 1982). The model described herein was developed as a first step in a (modelling) research programme directed toward quantitative and dynamic evaluation of current concepts, hypotheses, and data for probable adequacy as explanations of variations in partition of nutrients in lactating cows. Specific objectives were: to evaluate the efficacy of using kinetic arguments and parameters derived from in vitro studies with tissue slices and dispersed cells in aggregated, largely mechanistic models of whole-animal metabolism; to aid in the design and interpretation of metabolic, energy balance and related experiments through simulation analyses of within-day patterns of nutrient use and overall energetic transactions ; and to provide a basis for formulation of a model of dairy cow metabolism with a 1-d integration interval and suitable for analysis of concepts and data regarding nutrient partition throughout the lactation cycle.

The effect of feeding quebracho tannin, a mixture of condensed tannins, on dietary nutrient utilisation and nitrogen (N) retention and its effects on the gastrointestinal (GI) tract was investigated in sheep and rats. Sheep (n = 24) were fed on a pelleted diet of dried grass alone (controls) or containing quebracho tannin at 50 g kg−1 diet dry matter (DM) (tannin‐fed animals) at a level sufficient to achieve a daily liveweight gain (DLWG) of 100 g day−1. Complete collections of faeces and urine were made for two seven‐day periods after two and six weeks of feeding these diets (n = 6 per group). Apparent digestibilities of dry matter, N and neutral detergent fibre (NDF) were significantly (P < 0.001) reduced in tannin‐fed animals at both measurement periods. No evidence was obtained to suggest that rumen micro‐organisms can adapt to the presence of dietary tannins with prolonged feeding. Tannin‐fed animals excreted significantly (P < 0.01) more N in faeces and less in urine than controls suggesting an alteration in N metabolism. Histological examination of samples of the GI tract obtained from pairs of sheep slaughtered after two, five and seven weeks of feeding the diets indicated ulceration and an increase in mucosal histiocytes, particularly in the jejunum and ileum of most tannin‐fed animals. In a subsequent experiment, rats were fed ad libitum a ground chow containing either cellulose or quebracho tannin at 40 g kg−1 DM. Tannin‐fed rats had significantly (P < 0.05) reduced feed intakes, DLWG, N retention and body fat deposition compared to controls. Protein synthesis rates in the duodenal mucosa were not increased in tannin‐fed rats suggesting that enterocyte proliferation was not stimulated in this region of the GI tract. These studies indicate that feeding quebracho tannin to ruminants has both ruminal and post‐ruminal effects that, together, result in reduced nutrient utilisation and impaired animal performance. © 1999 Society of Chemical Industry

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Data on individually recorded silage dry-matter intake (SDMI), concentrate dry-matter intake (CDMI) and live weight of steers and data on silage composition including toluene dry matter (TDM), pH, total nitrogen (N), ammonia nitrogen (NH3-N), volatile fatty acids (VFAs), digestible organic matter in the dry matter (DOMD) and neutral-detergent fibre (NDF) obtained from experiments conducted at three sites were used to obtain simple and multiple linear regressions of SDMI on other variables.Live weight accounted for a high proportion of the variation in intake but this effect could generally be removed by scaling intake by live weight raised to the power of 0·75 (M0·75). CDMI was the most important factor affecting scaled intake in mixed diets. TDM, NH,-N and VFAs all had important effects on SDMI. The relationship of SDMI with TDM was curvilinear suggesting that there is little to be gained in intake terms from wilting to TDM above 250 g/kg. The effect of NH3-N appeared to be related more to its correlation with VFAs than with any other nitrogenous constituent while the VFAs appeared to have a direct effect on SDMI. The effects of N and pH on SDMI were generally small. DOMD and NDF had relatively little effect on SDMI. Significant differences in intercepts between sites were found for most relationships although common slopes were often found.

This paper explores the environmental impacts of dietary changes consistent with the nutrition transition common in countries going through economic development, inferred from commodity supply data from FAOSTAT. Supply data for 1961 and 2011 from three case study countries which have undergone significant economic transition in recent decades (Brazil, China and India) were compared on a per-capita basis to avoid confounding issues of population growth. Brazil showed marked increases in beef and poultry meat supply (kcal) while in China poultry and pig meat showed marked increases, particularly for pig meat. Per-capita supply of fruit in Brazil and vegetables in China were higher than in Europe by 2011. Supply of vegetable oil increased in all three countries and this was the majority commodity traded, hence much of its impact would have been felt in country of origin. The increase in beef production in Brazil, attributed to changing diet (2001-2011), had the greatest impact on increased water use, although the increase in supply of pig meat in China and cereals in China and India (attributable to changing diets) also made major contributions. The increase in cereal supply in China and India had a major impact on phosphorus and nitrogen cycles, with beef having a major impact on greenhouse gas emissions (GHGs). The increase in vegetable oils had a major impact through increasing land use. These findings highlight differential environmental impacts of the nutrition transition in different countries and emphasise the need to measure environmental impacts beyond those on GHGs.

In an experiment designed to investigate the effects on the growth and voluntary food intake of grass silage by calves, the silage was supplemented with varying levels of fish meal and sucrose. The grass silage had a pH of 3·6, a lactic acid content of 90·0 g/kg dry matter (DM) and total nitrogen content of 15·5 g/kg DM. Supplements of 50, 75 and 100 g fish meal per kg silage DM and 50, 75, 100 and 150 g sucrose per kg silage DM were mixed with the silage just prior to feeding. The eight diets were offered to 32, 4-month-old British Friesian steers for 12, 7-day periods. Intake was recorded daily and live weight weekly.Digestibility of organic matter (P < 0·05) and N (P < 0·001) were increased by fish-meal supplementation but the effect of level of fish meal was not significant. Sucrose supplementation significantly decreased both N (P < 0·01) and cellulose (P < 0·05) digestibility. The effect on cellulose digestibility increased with level of sucrose (P < 0·01).The intake of silage DM increased in response to increasing level of fish-meal inclusion when intake was expressed in terms of kg/day (P < 0·01) but not when expressed in g/kg live weight. Total DM intake showed a significant (P < 0·001) linear response when expressed both in terms of kg/day and g/kg live weight. The intake of silage DM declined in response to increased level of sucrose supplementation both in absolute (P < 0·05) and live-weight terms (P < 0·001) but sucrose supplementation had no significant effect on total intake.Live-weight gain was significantly increased with increasing level of fish-meal supplementation (P < 0·001), but sucrose supplementation had a significant effect on live-weight gain relative to the control treatment at only the 75 g/kg level, where live-weight gain was increased.

A mathematical representation of the energy-requiring processes of protein turnover and Na+,K+-transport in the tissues of growing lambs is described. This model was then used to examine the relative contributions of these processes to ATP expenditure at two different growth rates (90-230 g/d). Protein turnover accounted for 19% of whole-body ATP expenditure at both growth rates examined, with the gastrointestinal tract (GIT), accounting for 25-27%, muscle for 21-26%, skin for 23-26% and liver for 13% of total protein turnover energy costs. The contribution of Na+,K+-transport increased from 18 to 23% of whole-body heat production as growth rate increased, with the GIT accounting for 39 and 50%, muscle for 17 and 10% and liver for 18 and 23% of total Na+,K+-transport costs at low and high nutrient inputs, respectively. Thus, protein turnover accounted for 19% of the increment in ATP expenditure due to the increased nutrient input at the higher rate of growth, while Na+,K+-transport accounted for 39%, and fat turnover and accretion accounted for 25%, leaving 17% of the ATP increment unaccounted for.