An experiment was conducted with dairy cows to study the partitioning of excreted purine derivatives between urine and milk and to quantify the endogenous contribution following the isotopic labeling of microbial purine bases. Three lactating cows in their second lactation that had been cannulated in the rumen and the duodenum were fed a mixed diet (48:52, roughage/concentrate ratio) distributed in equal fractions every 2 h, and duodenal flow of purine bases was determined by the dual-phase marker system. Nitrogen-15 was infused continuously into the rumen to label microbial purine bases, and the endogenous fraction was determined from the isotopic dilution in urinary purine derivatives. Urinary and milk recovery of duodenal purine bases were estimated at early (wk 10) and late (wk 33) lactation by the duodenal infusion of incremental doses (75 and 150 mmol purine bases/d) of RNA from Torula yeast. Each period was 6 d, with RNA being infused during the last 4 d, followed by measurement of the flow of purine bases to the duodenum. The isotope dilution of purine derivatives in urine samples confirmed the presence of an endogenous fraction (512 +/- 36.43 micromol/W0.75 or 56.86 mmol/d) amounting to 26 +/- 3.8% of total renal excretion. Total excretion of purine derivatives in urine plus milk was linearly related to the duodenal input of purine bases, but the slopes differed (P < 0.005) between lactation stages resulting in a lower equimolar recovery in early (y = 58.86 (+/-3.89) +0.56 (+/-0.0164) x; r = 0.90) than late lactation (y = 58.86 (+/-3.89) + 0.70 (+/-0.046) x; r = 0.80). Excretion of purine derivatives through milk represented a minimum fraction of total excretion but responded significantly to the duodenal input of purine bases. No differences between lactation stages were detected, and variations in milk yield did modify significantly the amount of purine derivatives excreted through the milk.

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Three multiparous, ruminally and duodenally cannulated Holstein-Friesian milking cows (558 +/- 14 kg BW) with a mean milk yield of 19.9 +/- 1.4 kg/d in their 4th mo of lactation were fed a mixed diet of forage and concentrate at 100, 85, and 75% of ad libitum intake in a 3 x 3 Latin square design. Duodenal digesta flow was estimated using the dual-phase technique in which Cr-EDTA and Yb-acetate were used as liquid and solid markers, respectively. Microbial N (MN) was estimated using the duodenal flow of purine bases (PB); bacterial isolates from the rumen liquid and solid phases were used as references. Additionally, duodenal flow of PB and MN were estimated indirectly using the excretion of purine derivatives (PD) in urine and milk. Duodenal flow of PB and derived MN tended to decrease with feed restriction (from 258 to 154 mmol/d and 123.5 to 74.4 g/d, respectively). Estimates of PB and MN based on urinary PD showed the same trend, and decreases in PB (from 314 to 266 mmol/d, using LAB) were statistically significant. Using LAB, efficiencies of microbial protein synthesis in the ad libitum treatment were 12.9 and 17.0 g of MN/g of organic matter apparently digested in the rumen when estimated using duodenal PB and urinary excretion of PD, respectively. Urinary excretion of PD closely reflected changes in duodenal flow of PB as a result of feed restriction.

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Chia seed (Salvia hispanica L.) is the greatest known plant source of n-3 α-linolenic acid. The present study evaluated the effects of 3 inclusion levels of chia seed [zero (control); low, 2.7% (CLow); and high, 5.5% (CHigh)] in diets of dairy goats on milk yield and fatty acid profile. Nine Saanen dairy goats in the last third of lactation period, live weight 38 ± 8.7 kg, housed in metabolic cages, were fed iso-proteic and iso-energetic (160 g of crude protein/d and 11 MJ of metabolizable energy/d) diets. Gas chromatography was used to analyze fatty acid profile and total conjugated linoleic acid (CLA). Silver ion HPLC was used to analyze the isomeric profile of CLA. The results were subjected to variance analysis using a Latin square design repeated 3 × 3. The CHigh treatment was higher for dry matter, neutral detergent fiber, and acid detergent fiber intake compared with CLow and control diets. Digestibility was not affected by the inclusion of chia seeds. The CHigh diet improved N intake with respect to the control and CLow diet. Milk yield and chemical composition were not affected by the treatment. The milk fatty acid profile of C18:0, C18:1, C18:2, and C:20 was higher for CHigh than the other treatments. The in vitro gas production (mL of gas/g of dry matter) was lower in CHigh than the control diet. In conclusion, the addition of chia seeds at the CHigh level in dairy goat diets negatively affected in vitro rumen fermentation, but increased the milk fatty acid profile of C18:0, C18:1n-9 cis, and C:20, monounsaturated fatty acids, and polyunsaturated fatty acids. The total CLA content increased from 0.33 to 0.73% with the supplementation of chia to the diet, as well as the isomers cis-9,trans-11, trans-7,cis-9, trans-11,cis-13, and trans-12,trans-14.

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The limited availability of food, together with the constraints that traditional management systems impose on the natural foraging behaviour of donkeys, often results in severe under-nutrition. Few studies have been conducted into the digestibility of different forages and little information exists on nutritional requirements of donkeys. In order to measure digestible energy requirements of donkeys under tropical conditions, an experiment was carried out at the Centre for Research in Agricultural Science (CICA) and the Faculty of Veterinary Medicine of the Universidad Aut6noma del Estado de México located in the Toluca valley, Central Mexico. Thirty-two donkeys of a body condition typical for Central Mexico were divided into four groups of 8 animals each according to their sex and live weight: group 1 (G1) comprised male donkeys below the average body weight (102+/-5 kg); group 2 (G2) comprised male donkeys of average body weight (121.5+/-4 kg); group 3 (G3) comprised female donkeys below average weight (111.8 +/- 5 kg); and group 4 (G4) comprised female donkeys of average weight (127.6 +/- 5 kg). A diet of oat straw or maize stover and 15% alfalfa hay was offered to meet exact maintenance requirements. The donkeys were monitored for 13 months. The live weight of all animals was recorded daily in order to monitor whether maintenance requirements were being met. Mean daily digestible energy (DE) requirements were measured during the winter, spring, summer and autumn of 2003-2004. Digestible energy requirements of all four sex and liveweight groups were significantly (p > 0.05) higher during the spring than during the other seasons of the year (13.5, 18.0, 10.4 and 14.3 MJ DE per day during winter, spring, summer and autumn, respectively). Predicted DE requirements of donkeys with a live weight range betweenn 90 and 150 kg using the data from the present study were less than those predicted using scaled-down horse feeding standards.