W. Pittroff

Quantitative prediction of feed intake in ruminants: I. Conceptual and mathematical analysis of models for sheep

Abstract A comparative mathematical and conceptual analysis of quantitative feed intake prediction models for cattle was conducted. The objective was to analyse the theoretical basis of current cattle intake models and provide directions for experimental research. Results for the models analysed indicated (1) weak conceptual basis of models in the sense of ability to accommodate experimental data; (2) frequently problematic implementation in terms of mathematical properties of models; (3) absence of new hypotheses for experimental research provided by reviewed models. These findings agree with similar results obtained in an analysis of sheep models. Suggestions for improved model development, implementation and documentation are provided.

Quantitative prediction of feed intake in ruminants III. Comparative example calculations and discussion

Abstract A comparison of feed intake prediction models for sheep and cattle was conducted for identical data sets. The objective was to determine the degree of agreement between model predictions. This exercise concludes a series of papers on current quantitative concepts in the prediction of feed intake in cattle and sheep. A discussion of mathematical, conceptual and implementation properties of these models is provided. The central result of the study is the conclusion that quantitative models for the prediction of feed intake seem to be inadequate not only for robust prediction of intake levels, but also in conceptual and often mathematical terms. More importantly, the analysis provides disturbing evidence of the failure of model developers to thoroughly examine the theoretical basis of key assumptions upon which their models rest. Although it would be clearly more appropriate to formulate models as researchable hypotheses, given the current state of knowledge of intake regulation in ruminants, this is generally not done. Conflict of experimental evidence with model concepts was never found to be a stated incentive for experimental research.

Sphaeralcea Angustifolia as a Substitute for Alfalfa for Growing Goats

Abstract Narrowleaf globemallow (Sphaeralcea angustifolia [Cav.] G. Don) occurs on millions of hectares of rangeland in the United States and Mexico, and it constitutes an important forage for herbivores. Forty 2-mo-old crossbred female goats (native×dairy goats; 9.4 ± 2.2 kg) were randomly allotted to five dietary groups (two] goats per pen, four replications per ration) to evaluate the effects of feeding different levels of S. angustifolia in a complete ration on growth performance and diet digestibility. The rations were a total mixed control ration containing 0% S. angustifolia (T0) and four rations in which S. angustifolia progressively replaced alfalfa (25% [T25], 50% [T50], 75% [T75], and 100% [T100]). Grains and forage made up 70% and 30% of the dietary dry matter (DM) in all rations. Differences (P < 0.05) were observed between treatments in average daily gain (ADG; range 88–124 g·d−1) and DM intake (DMI; range 3.3–4.0% body weight). Feed conversion ratio (DMI/ADG; range 4.0–4.8) was similar (P>0.20) among treatments. Goats fed diets with any of the S. angustifolia levels had similar apparent nitrogen (N) digestion (range 67.6–69.8%) as those fed only alfalfa, but N retention was greater (P < 0.05) in goats on T25 and T50 diets compared to other diets. The apparent digestibilities of DM, neutral detergent fiber, and acid detergent fiber were greater (P < 0.05) for T25 and T50 than for other diets. Results indicate that S. angustifolia at the flowering stage was a savory and nutritious roughage, which could fully replace alfalfa hay in diets of growing goats. Considering that S. angustifolia is readily consumed by foraging animals, it is abundant enough that it is a significant source of forage, and has a sufficient quality to nutritionally satisfy herbivores, this forb is a potentially useful forage for pen-fed goats.

Performance of Sheep and Goats Fed Arctostaphylos canescens With and Without Polyethylene Glycol Supplementation

Abstract Arctostaphylos canescens Eastw. is considered an important element in the chaparral fire matrix and an invasive plant in coniferous forest plantations in California. Previous studies reported that dry matter intake of Arctostaphylos was low, presumably because of its low nutritional quality and high condensed tannin (CT) content. We hypothesized that intake and digestibility of Arctostaphylos could be increased by the provision of a tannin-complexing agent polyethylene glycol (PEG). This study determined the effects of PEG (MW 4000) supplementation on intake (I) and digestibility (D) of Arctostaphylos in goats and sheep. Polyethylene glycol was added to drinking water at four levels (0.3%, 0.15%, 0.05%, and 0%) of body weight (BW). Alfalfa pellets were used as diet supplement at 1.5% of BW. Nutritional quality of Arctostaphylos was low as compared with alfalfa pellets. Arctostaphylos crude protein (CP) levels were low (4.5% vs. 17.9%) and CT concentration was high (23.1% vs. 0%), whereas estimates of in vitro organic matter digestibility (OMD, 36.6%) and metabolizable energy (5.1 MJ · kg−1 dry matter [DM]) in Arctostaphylos were almost half of those found for alfalfa pellets (70.3% and 9.5 MJ · kg−1 DM). A curvilinear increase (P < 0.05) in nutrient intake (per g · d−1 and per kg BW0.75) was observed in goats and sheep as PEG levels increased, although a linear increase (P < 0.001) was observed in CP intake (g · d−1) of Arctostaphylos by goats. Addition of PEG curvilinearly increased (P < 0.05) digestibility of DM, CP, and neutral and acid detergent fiber, but quadratically increased (P < 0.05) that of OM in goats and sheep. Incorporation of PEG in drinking water at the level of 0.15% BW in sheep and goats was effective to maximize inactivation of CT in Arctostaphylos. However, the success in adopting this practice as a useful tool in vegetation management programs will depend on the cost–benefit ratio.

Rough Agave Flowers as a Potential Feed Resource for Growing Goats

Abstract The objective of this study was to evaluate the effect of different levels of rough agave (Agave scabra Ortega) flowers on dry matter intake (DMI), average daily gain (ADG), volatile fatty acid (VFA) production in the rumen, and particular serum metabolites and minerals of native × dairy growing goats (Capra hircus L.). Forty female goats with an initial weight of 11.1 ± 1.9 kg (mean ± SD) were used in a completely randomized design experiment that lasted for 84 d. Goats were fed a completely mixed ration (30% roughage, 70% ground corn [Zea mays L.] and soybean [Glycine max {L.} Merr] meal). Treatments consisted of offering goats (4 pens · group−1, 2 goats · pen−1) air-dry rough agave flowers, which replaced alfalfa (Medicago sativa L.) hay at 0% (control; T0), 25% (T25), 50% (T50), 75% (T75), and 100% (T100) of the of the roughage portion of the diet. Values of nutritional parameters for rough agave flowers were in vitro organic matter digestibility, 493 g · kg−1; crude protein, 115 g · kg−1; and metabolizable energy, 6.29 MJ · kg−1 DMI. There were differences (P < 0.05) in ADG (range, 108–155 g · d−1) between diets. Goats fed T0 had higher (P < 0.05) gains than goats fed T50 and T100. DMI was not affected by dietary treatments (range, 3.4% to 3.6% of body weight). Feed conversion ratio (FCR, defined as DMI/ADG) increased (P < 0.05) 27% with total substitution of alfalfa by rough agave flowers, in comparison with T0. Lower (P < 0.05) values of total VFA were obtained with T100, in comparison with all other dietary treatments. These results demonstrated that totally replacing alfalfa with rough agave flowers in diets did not affect DMI but decreased AGD and compromised FCR. Thus, rough agave flowers have the potential to partially replace alfalfa in diets for growing goats.

Degradación in vitro de Bouteloua repens por cultivos de R. flavefaciens y F. succinogenes aislados de ganado alimentado con pastos tropicales en Colombia

I N T R O D U C C I Ó N THE ADAPTATION of cattle to nutritional environments characterized by poorquality feed resources is the result of genetic selection in the host animal and of symbiosis with microbial species, especially those adapted to feeds characterized by high cell wall content and low digestibility. The total digestion of forages results from the capacity of microbial species to colonizate the particule and its celulollityc activity. This evolutionary interaction is still poorly understood, and efforts to manipulate the composition of microbial species reviewed by Jouany et al. (2000), or the application of biotechnology (enzyme characterization, construction of transgenics review by Forsberg et al., (1999), have had variable success.The ruminal microorganims can work eficientily in consorcios, as mixed systems. (Arcos y Díaz, 2000). For this reason, the problems of intraespecific competitivity and sintropism it should look to try strategies of manipulation or genetic manipulation (Díaz, 2002). The ability to increase the digestion of low quality feedstuffs by sustainable manipulation of the rumen ecosystem is a goal for tropical cattle production systems, currently with low levels of productivity. The studies reported in this work were designed to isolate and identify rumen bacteria, with high capacity to digest native tropical forages in Colombia, where cattle are mainly fed on forage. The Llanos Orientales, a tropical savannah ecosystem located at the East of the Andes, is one of the most important cattle production regions of the country. Most of its area is Cell wall degradation of Bouteloua repens in vitro by pure cultures of R. flavefaciens and F. succinogenes isolate from cattle grazing tropical lowland pastures in Colombia