Modeling the flow of digesta through the ruminant reticulorumen

Abstract only availableRuminants possess a specialized gastrointestinal (GI) tract that enables them to efficiently digest fibrous feeds. The first stomach compartment of the ruminant GI tract, the reticulorumen (RR), is the site of most fiber digestion due to the presence of cellulolytic microorganisms in conjunction with selective retention of feed particles; undigested fibrous feed particles are selectively retained and fermented by cellulolytic microorganisms in the RR until certain digestive processes are completed, enabling the particles to pass. Selective retention and the overall process of digesta flow in the RR affect feed digestibility, feed intake, and microbial efficiency—all important animal performance parameters in ruminant production. It is imperative to model digesta flow in the RR to better predict these animal performance parameters for use in ruminant production systems. Mathematical models have indeed been developed to describe the flow of digesta in the RR, typically with the RR represented as one or more mathematical compartments with flow between compartments defined by kinetic rate variables or constants. Mathematical models developed to the present use either fractional rate constants or rate variables based on the gamma distribution. The Yule distribution has also been suggested for modeling RR digesta flow kinetics, but its development has been cursory. It remains unseen what, if any, benefits may arise from applying the Yule distribution to describe the kinetics of RR digesta. In this study, a model incorporating the Yule distribution is fully developed. Physiological justification for using the Yule distribution is also provided on the basis of selective retention. A comparison between the model developed herein and a previously published model using the gamma distribution reveals that both models give similar mathematical results under certain cases. Still, it is suggested that the physiological relevance of the model treated here may make it superior. Animal feeding trials are currently being conducted to validate the structure of model. Additionally, mathematical models are being developed to describe small and large intestinal flow in ruminant and non-ruminant species, thereby expanding this modeling effort to include most of the GI tract.Life Sciences Undergraduate Research Opportunity Progra

Total mixed dairy rations on your farm? (1991)

Total mixed dairy rations (TMR) offer an opportunity to improve business profits through improved animal performance and health, decreased feed wastage, improved labor efficiency and improved butterfat. The installation of a TMR system normally requires added investments in feed mixing and distribution equipment. The purpose of this publication is to provide a format for evaluating the economic consequences of changing to a TMR system.Reviewed October 1993 -- Extension website

Thermal status for different breeds of dairy cattle exposed to summer heat stress in a grazing environment [abstract]

Abstract only availableA study was conducted to investigate thermal balance of lactating dairy cattle managed in an intensive managed rotational grazing system. The farm was located at the University of Missouri Southwest Research Center in Vernon County, MO. Thirty six lactating dairy cows were blocked by parity, days in milk, milk production and breed. Cows were grouped by breed with 100% Holstein (H, n=8), 75%H:25% Jersey (J) (75H, n=5), 50%H:50%J (50H, n=8), 25%H:75%J (75J, n=7), and 100% J (J, n=8), and maintained on the same pastures from June 15 through August 1, 2006. Cows were rotated to paddocks to maintain ad libitum access to pasture. Ambient variables, including air temperature (Ta) and relative humidity, were measured continuously. Ranges of Ta and calculated THI were 12 to 38C and 55 to 87, respectively. Thermal balance was evaluated prior to morning (0500) and afternoon (1600) milkings by measuring rectal temperature (Tre) and respiration rate (RR) on 16 days throughout the study during periods of maximum and minimum heat stress. Breed groups had different body weights (p < 0.0001) ranging from 530 kg (H) to 378 (J). However, body weight was similar for 75J and 75H (460 kg versus 501 kg, respectively). Although body weights were different across breed, combined change in rectal temperature with Ta (r = 0.89) and THI (r = 0.92) was predictable (p < 0.0001). Change in Tre with increasing Ta and THI was slowest for J and 75J, and highest for H and 75H. Change in Tre was influenced more by breed more than body weight. Respiration rate was correlated with Ta (r = 0.88) and THI (r = 0.89) (p < 0.0001), with 75J being more responsive than 75H. These results suggest that breed selection can be used to improve thermal balance of cows in intensively managed rotational grazing systems.CAFNR On Campus Research Internshi