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Dynamics of forage ingestion, oral processing and digesta outflow from the rumen: a development in a mechanistic model of a grazing ruminant, MINDY
- P. Gregorini, F. D. Provenza, J. J. Villalba, P. C. Beukes, M. J. Forbes
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- Journal:
- The Journal of Agricultural Science / Volume 156 / Issue 8 / October 2018
- Published online by Cambridge University Press:
- 19 November 2018, pp. 980-995
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Detailed representation of ingesta inflow to and digesta outflow from the rumen is critical for improving the modelling of rumen function and herbage intake of grazing ruminants. The objective of the current work was to extend a mechanistic model of a grazing ruminant, MINDY, to simulate the dynamic links between ingestive and digestive processes as affected by forage and sward features (e.g. sward structure, herbage chemical composition) as well as the internal state of the animal. The work integrates existing aspects of forage ingestion, oral physiology and rumen digestion that influence ingesta characteristics and digesta outflows from the rumen, respectively. The paper describes the structure and function of the new development, assessing the new model in terms of dynamic changes of oral processing of ingesta and rumen dilution rate under different grazing contexts. MINDY reproduces characteristics of ingesta inflow to and digesta outflow from the rumen of grazing ruminants, achieving temporal patterns of occurrence within and between meals, similar to those for grazing animals reported in the literature. The model realistically simulates changes in particle size distribution of the ingestive bolus, bolus weight and rumen dilution rate in response to contrasting grazing management regimes. The new concepts encoded in MINDY capture the underlying biological mechanisms that drive the dynamic link between ingestion and digestion patterns. This development advances in the understanding and modelling of grazing and digestive behaviour patterns of free-ranging ruminants.
The physiological and metabolic impacts on sheep and cattle of feed and water deprivation before and during transport
- James P. Hogan, J. Carol Petherick, Clive J. C. Phillips
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- Journal:
- Nutrition Research Reviews / Volume 20 / Issue 1 / June 2007
- Published online by Cambridge University Press:
- 01 June 2007, pp. 17-28
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Sheep and cattle are frequently subjected to feed and water deprivation (FWD) for about 12 h before, and then during, transport to reduce digesta load in the gastrointestinal tract. This FWD is marked by weight loss as urine and faeces mainly in the first 24 h but continuing at a reduced rate subsequently. The weight of rumen contents falls although water loss is to some extent masked by saliva inflow. FWD is associated with some stress, particularly when transportation is added. This is indicated by increased levels of plasma cortisol that may be partly responsible for an observed increase in the output of water and N in urine and faeces. Loss of body water induces dehydration that may induce feelings of thirst by effects on the hypothalamus structures through the renin–angiotensin–aldosterone system. There are suggestions that elevated cortisol levels depress angiotensin activity and prevent sensations of thirst in dehydrated animals, but further research in this area is needed. Dehydration coupled with the discharge of Na in urine challenges the maintenance of homeostasis. In FWD, Na excretion in urine is reduced and, with the reduction in digesta load, Na is gradually returned from the digestive tract to the extracellular fluid space. Control of enteropathogenic bacteria by normal rumen microbes is weakened by FWD and resulting infections may threaten animal health and meat safety. Recovery time is required after transport to restore full feed intake and to ensure that adequate glycogen is present in muscle pre-slaughter to maintain meat quality.
Comparison of voluntary food intake, apparent digestibility, digesta kinetics and digestive tract content in Manchega and Lacaune dairy sheep in late pregnancy and early and mid lactation
- E. Molina, A. Ferret, G. Caja, S. Calsamiglia, X. Such, J. Gasa
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- Journal:
- Animal Science / Volume 72 / Issue 1 / February 2001
- Published online by Cambridge University Press:
- 18 August 2016, pp. 209-221
- Print publication:
- February 2001
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Two experiments were carried out with pregnant (experiment 1) and lactating ewes (experiment 2), to compare dry-matter (DM) intake, and total tract apparent digestibility, digesta kinetics and weight of digestive tract contents of Lacaune and Manchega sheep, with the aim of explaining possible differences between the breeds in voluntary food intake. In experiment 1, 20 3-year-old single-bearing pregnant ewes, 10 Manchega and 10 Lacaune, were permanently housed for the last 10 weeks of pregnancy. The diet used consisted of lucerne hay, offered ad libitum, supplemented with 0·3 kg/day of concentrate. DM and digestible DM intake per kg M0·75 were higher (P < 0·01) in Lacaune than in Manchega sheep. Breed did not affect total tract apparent digestibility, fractional rates of passage, transit time, total mean retention time, or weight of digestive tract contents. Changes in body weight and body condition score were similar between breeds. In contrast, Lacaune lambs tended (P = 0·09) to weigh less than Manchega lambs, suggesting genetic differences in the energy utilization between breeds in late pregnancy. Higher DM intake observed in Lacaune sheep may have been related to a higher energy demand for mammary development. In experiment 2, 32 3-year-old lactating multiparous ewes, 16 Manchega and 16 Lacaune, were permanently housed during the first 12 weeks of lactation. The experimental diet used was based on a mixture of maize silage and dehydrated lucerne (10: 1, fresh weight basis), offered ad libitum, and supplemented with 0·8 kg/day of concentrate. Milk, fat and protein yield as well as DM and digestible DM intake in Lacaune ewes was higher (P < 0·01) than in Manchega ewes. DM intake was constant in Lacaune sheep with advancing lactation, while in Manchega sheep DM intake decreased. Throughout this period Lacaune ewes lost 0·5 kg of body weight while Manchega gained 4·4 kg. Breed did not affect either apparent digestibility of DM, organic matter and neutral-detergent fibre, or fractional rates of passage, transit time and total mean retention time. The weight of total tract digestive contents was greater (P < 0·05) in Lacaune than in Manchega sheep, particularly in the reticulo-rumen. Results suggest that the scheme of selection in Lacaune dairy sheep has increased milk yield together with voluntary food intake, the latter being associated with an increase in the rumen fill capacity. The higher milk yield of Lacaune ewes cannot be attributed to the higher DM intake only; other factors, i.e. mobilization of fat reserves, are required to support this higher milk output.
Diurnal patterns in rumen volume and composition of digesta flowing into the duodenum
- M. Gill, P. H. Robinson, J. J. Kennelly
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- Journal:
- Animal Science / Volume 69 / Issue 1 / August 1999
- Published online by Cambridge University Press:
- 18 August 2016, pp. 237-249
- Print publication:
- August 1999
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Rate of passage of digesta out of the rumen is generally assumed to follow first order kinetics but this assumption may not hold within 24-h feeding cycles. Four lactating cows offered a mixed forage/concentrate diet ad libitum from 08.00 h to 00.00 h and a protein-rich meal at either 08.30 or 00.30 h were used to investigate diurnal patterns in rumen volume and composition of digesta flowing into the duodenum. Cows were fitted with large rumen cannulae to permit complete emptying of rumen digesta and T-piece duodenal cannulae with inserts to enable collection of representative samples of digesta. Chromium-mordanted lucerne hay manually dosed to the rumen at 2-h intervals and a continuous infusion of cobalt-EDTA were used as digesta flow markers. Duodenal digesta was sampled over three alternate days to obtain samples representing every hour of the 24-h day, which were analysed individually. Use of either of the two markers gave similar results for mean daily flow but not for hourly flow and thus hourly flow data were not considered reliable. The content of crude protein in duodenal digesta varied within one feeding cycle from 200 to 320 g/kg in cows offered protein at 08.30 (‘day’) and from 240 to 300 in cows offered protein at 00.30 h (‘night’). On a daily basis, fractional passage rates (calculated from duodenal flow divided by rumen pool size) were significantly (P = 0·016) lower for protein for ‘night’ (0·0750 per h) versus ‘day’ (0·0824 per h) cows. The observation that marked diurnal patterns in the composition of protein flowing into the duodenum can apparently be ‘smoothed’ simply by altering feeding sequence, which was correlated with an increased milk fat yield, suggests there is potential for improving production through manipulating the way in which dietary components are offered within a day.
Rate of passage of digesta out of the rumen is generally assumed to follow first order kinetics but this assumption may not hold within 24-h feeding cycles. Four lactating cows offered a mixed forage/concentrate diet ad libitum from 08.00 h to 00.00 h and a protein-rich meal at either 08.30 or 00.30 h were used to investigate diurnal patterns in rumen volume and composition of digesta flowing into the duodenum. Cows were fitted with large rumen cannulae to permit complete emptying of rumen digesta and T-piece duodenal cannulae with inserts to enable collection of representative samples of digesta. Chromium-mordanted lucerne hay manually dosed to the rumen at 2-h intervals and a continuous infusion of cobalt-EDTA were used as digesta flow markers. Duodenal digesta was sampled over three alternate days to obtain samples representing every hour of the 24-h day, which were analysed individually. Use of either of the two markers gave similar results for mean daily flow but not f or hourly flow and thus hourly flow data were not considered reliable. The content of crude protein in duodenal digesta varied within one feeding cycle from 200 to 320 glkg in cows offered protein at 08.30 day’) and from 240 to 300 in cows offered protein at 00.30 h (‘night’). On a daily basis, fractional passage rates (calculated from duodenal flow divided by rumen pool size) were significantly (? = 0·016) lower for protein for ‘night’ (0·0750 per h) versus ‘day’ (0·0824 per h) cows. The observation that marked diurnal patterns in the composition of protein flowing into the duodenum can apparently be ‘smoothed’ simply by altering feeding sequence, which was correlated with an increased milk fat yield, suggests there is potential for improving production through manipulating the way in which dietary components are offered within a day.
Contribution of dietary nitrogen and purine bases to the duodenal digesta: comparison of duodenal and polyester-bag measurements
- J. F. Pérez, J. Balcells, J. A. Guada, C. Castrillo
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- Journal:
- Animal Science / Volume 65 / Issue 2 / October 1997
- Published online by Cambridge University Press:
- 02 September 2010, pp. 237-245
- Print publication:
- October 1997
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Four ewes fitted with ruminal and duodenalT-piece cannulas were given fourdietsin a 4 × 4 factorial design. Diets consisted of 700 (HF) or 400 (LF) g/day of ammonia-treated barley straw supplemented respectively with 150 or 600 g/day of concentrate made up with barley plus either soya-bean meal (SBM) or fishmeal (FM) as the protein source, offered at 2-h intervals. Duodenal flowsof digestawere estimated by the dual-phasetechniqueusing CoEDTAand Yb-acetate as markers and (15NH4)2SO4 was infusedinto the rumento label microbial N. Bacteria were isolated from the liquid (LAB) or solid (SAB) rumendigesta. Purinebases (PB) were isolated by precipitationin an acid solution of AgN03, and microbial contribution either to the duodenalnitrogen(N) or PB were determinedby 15N measurements induodenaldigesta and bacteria.Simultaneously, therumen degradation of Nand PB contained in SBM and FM was studiedby incubating supplements in polyesterbags in the rumen.PBcontent (mmol/g dry matter)and guanine: adenine(G/A) ratio of barley strawwas 2·89 and 5·23; barley grain,7·91 and 111;SBM, 18·8 and 1·26; and FM, 58·9 and 6·96, respectively. Duodenal flow ofPB(mmol/day)was significantly higher than PB intake on all diets and G/A ratio showed a meanvalue of 0·97, similarto the ratios determined in SAB(0·80) and LAB (1·04) and muchlower than diets(1·31 to 4·32). Microbial contribution to duodenal Nflow ranged from43·3% to 61·0%, beinghigherin SBM(59·0%)thanin FM(46·7%)diets. However, microbial contribution to duodenal PB was not affected by the experimentaltreatment, accounting for proportionately 0·77 of total PB at the duodenum. Rumen degradability of PB was much higher than that of total N and in both cases degradability was higher in SBM than FM. Direct measurements of non-microbialN were significantly higher than values determined by the polyester-bagmeasurements. However, once corrected forthe endogenousN (52 mgN per kg live weight)contribution, results show edan acceptable agreement. Duodenal flow of PB non-attributable to microbes (unlabelled PB) showed a mean value of 3·25 mmol/daywithouta significanteffect of dietary treatment. However, undegradablePBsupply determinedfor0·02, 0·05 and 0·08 per h fractional out flow rates were proportionately lower than 0·025 with SBM and 0·100 with FM diets of the estimated duodenalPB flow. Despite the magnitudeof the unlabelledduodenalPB, the close agreement between G/A ratios in duodenaldigesta and bacteria suggests thatthe contribution of dietary PB to the duodenalflow was low and seemsto confirm the reliability of values obtained from polyester-bag measurements.