Genetic variation in milk urea nitrogen concentration of dairy cattle and its implications for reducing urinary nitrogen excretion

Nitrogen (N) leached into groundwater from urine patches of cattle grazing in situ is an environmental problem in pasture-based dairy industries. One potential mitigation is to breed cattle for lower urinary nitrogen (UN) excretion. Urinary nitrogen is difficult to measure, while milk urea nitrogen concentration (MUN) is relatively easy to measure. For animals fed diets of differing N content in confinement, MUN is moderately heritable and is positively related to UN. However, there is little information on the heritability of MUN, and its relationship with other traits such as milk yield and composition, for animals grazing fresh pasture. Milk urea nitrogen concentration data together with milk yield, fat, protein and lactose composition and somatic cell count was collected from 133 624 Holstein-Friesian (HF), Jersey (J) and HF×J (XBd) cows fed predominantly pasture over three full lactations and one part lactation. Mean MUN was 14.0; and 14.4, 13.2 and 13.9 mg/dl for HF, J and XBd cows, respectively. Estimates of heritability of MUN were 0.22 using a repeatability model that fitted year-of-lactation by month-of-lactation by cow-age with days-in-milk within month-of-lactation and cow-age, and 0.28 using a test-day model analysis with Gibbs sampling methods. Sire breeding values (BVs) ranged from −2.8 to +3.2 indicating that MUN could be changed by selection. The genetic correlation between MUN and percent true protein in milk was −0.22; −0.29 for J cows and −0.16 for HF cows. Should the relationship between MUN and UN observed in dietary manipulation studies hold similarly when MUN is manipulated by genetic selection, UN excretion could be reduced by 6.6 kg/cow per year in one generation of selection using sires with low MUN BVs. Although J cows had lower MUN than HF, total herd UN excretion may be similar for the same fixed feed supply because more J cows are required to utilise the available feed. The close relationship between blood plasma urea N concentration and MUN may enable early selection of bulls to breed progeny that excrete less UN.     

Dietary carbohydrate composition modifies the milk N efficiency in late lactation cows fed low crude protein diets

Nitrogen emissions from dairy cows can be readily decreased by lowering the dietary CP concentration. The main objective of this work was to test whether the milk protein yield reduction associated with low N intakes could be partially compensated for by modifying the dietary carbohydrate composition (CHO). The effects of CHO on digestion, milk N efficiency (milk N/N intake; MNE) and animal performance were studied in four Jersey cows fed 100% or 80% of the recommended protein requirements using a 4×4 Latin square design. Four iso-energetic diets were formulated to two different CHO sources (starch diets with starch content of 34.3% and NDF at 32.5%, and fiber diets with starch content of 5.5% and NDF at 49.1%) and two CP levels (Low=12.0% and Normal=16.5%). The apparent digestible organic matter intake (DOMI) and the protein supply (protein digestible in the small intestine; PDIE) were similar between starch and fiber diets. As planned, microbial N flow (MNF) to the duodenum, estimated from the urinary purine derivatives (PD) excretion, was similar between Low and Normal CP diets. However, the MNF and the efficiency of microbial synthesis (g of microbial N/kg apparently DOMI) were higher for starch v. fiber diets. Milk and milk N fractions (CP, true protein, non-protein N (NPN)) yield were higher for starch compared with fiber diets and for Normal v. Low CP diets. Fecal N excretion was similar across dietary treatments. Despite a higher milk N ouput with starch v. fiber diets, the CHO modified neither the urinary N excretion nor the milk urea-N (MUN) concentration. The milk protein yield relative to both N and PDIE intakes was improved with starch compared with fiber diets. Concentrations of β-hydroxybutyrate, urea and Glu increased and those of glucose and Ala decreased in plasma of cows fed starch v. fiber diets. On the other hand, plasma concentration of albumin, urea, insulin and His increased in cows fed Normal compared with Low CP diets. This study showed that decreasing the dietary CP proportion from 16.5% to 12.0% increases and decreases considerably the MNE and the urinary N excretion, respectively. Moreover, present results show that at similar digestible OM and PDIE intakes, diets rich in starch improves the MNE and could partially compensate for the negative effects of Low CP diets on milk protein yield.     

On the effects of the concentrate proportion of dairy cow rations in the presence and absence of a fusarium toxin-contaminated triticale on cow performance

The aim of the present study was to investigate the effects of a deoxynivalenol (DON) contaminated ration with a concentrate proportion of 50%, on the performance of dairy cows (Period 1), and to examine the effects when the concentrate proportion was elevated to 60% compared to a ration with 30% concentrates (Period 2). In Period 1, 13 lactating German Holstein cows (Myco group, on average 29 days in milk) were fed the experimental diet (on average 5.3 mg DON/kg DM) as total mixed ration over 11 weeks, while another 14 cows (on average 33 days in milk) received a control diet. Both rations contained 50% concentrates (on DM basis). In Period 2 (18 weeks), the same 27 cows plus five additional cows were divided into four groups: Control-30 (30% concentrates), Myco-30 (30% concentrates, 4.4 mg DON/kg DM), Control-60 (60% concentrates), Myco-60 (60% concentrates, 4.6 mg DON/kg DM). The overall performance level was characterised by a mean daily DM intake of 17.9 kg and a mean daily milk production of 26.7 kg fat corrected milk (FCM) in Period 1 and 17.3 kg DM intake and 24.5 kg FCM in Period 2, respectively. In both periods cows fed the Fusarium toxin-contaminated diets consumed more DM (in Period 2 only significant for group Myco-30) resulting from stimulating effects on the ingesta passage rate of the natural contaminated Fusarium-infected triticale. In Period 1, cows fed the Fusarium toxin-contaminated diet had a significantly higher milk yield, milk urea and somatic cell count, whereas milk fat and protein concentration and fat-to-protein-ratio (FPR) were significantly lower. In Period 2, on a low concentrate level, FCM was significantly higher in group Myco-30. On a high concentrate level, group Myco-60 produced significantly more milk, but milk fat and protein concentration, FPR and milk urea were significantly lower. A concentrate proportion of 60% had a depressing effect on milk fat concentration but was significantly more pronounced in the presence of Fusarium toxin-contaminated and Fusarium damaged-triticale.     

Über die Gewöhnung von Ziegen an eiskaltes Tränkwasser

90 urine samples obtained in three lamb trials and one experiment using adult wethers were analyzed for their contents of orotic acid and creatinine. The average daily excretion of orotic acid accounted for 0.5 mg to 1.5 mg (35 μg to 130 μg/W^0.75) with a high individual variation. Correlation coefficients between orotic acid and other urinary constituents were low indicating an entirely different response to metabolic variations. There was only a weak relationship to live weight, protein retention and rumen fluid traits. Defaunation reduced the orotic acid excretion (significant in the adult wethers) whereas the addition of rumen‐protected lysine as well as the use of different dietary carbohydrate sources were without effect. The urinary excretion of creatinine increased with live weight and age from 0.4 g/d in the 20 kg lambs to 1.7 g/d in the adult 53 kg wethers. The correlations with live weight were close whereas the apparently negative correlation with protein retention was not real as could be evaluated by calculation of the partial correlations. There was a close correlation of creatinine with total N, urea and allantoin. Neither defaunation nor rumen‐protected lysine and the kind of carbohydrate source had significant effects on creatinine. The use of orotic acid and creatinine as indicators of metabolic disorders were discussed. Easy application in practical diagnosis without quantitative urine collection might be possible by the determination of orotic acid in the milk of cows and of the creatinine/N ratio in urine.     

Metabolic and endocrine responses to short-term nutrient imbalances in the feed ration of mid-lactation dairy cows

Short-term imbalances of dietary nutrients occur during natural fluctuations in roughage quality (e.g. on pasture) or temporal shortages of supplementary feed components. In contrast to a deficiency, macronutrients (i.e. carbohydrates, proteins, lipids) beyond the adequate supply with other nutrients may, for instance, alter milk composition, increase BW or result in a greater excretion of nitrogen. Especially dairy cows with a moderate performance, in mid- or late lactation, or in extensive farming systems may be exposed to imbalanced rations. A better understanding of metabolic and endocrine responses depending on macronutrient supply may help to precisely feed dairy cows. The present study investigated short-term metabolic and endocrine responses to different levels of concentrates formulated to particularly provide one major macronutrient source (carbohydrates, proteins or lipids). Based on parity number, lactational stage, milk yield and BW, nine mid-lactating cows (211 ± 19 days in milk) were grouped into three blocks of three animals each. Concentrates (aminogenic: rich in CP and nitrogen sources; glucogenic: high content of carbohydrates and glucogenic precursors; lipogenic: high lipid content) were fed in addition to hay in a factorial arrangement at increasing levels from 2.5 to 7.5 kg/d during 9 d. Milk yield, BW and feed intake were recorded daily. Blood and milk were sampled every 3 d at the end of each concentrate level. Milk fat, protein, lactose and urea contents were determined. In blood, concentrations of various metabolites, endocrine factors and enzyme activities (e.g. glucose, non-esterified fatty acids (NEFAs), β-hydroxybutyrate, urea, cholesterol, triglycerides, insulin, glucagon, aspartate aminotransferase (ASAT), gamma-glutamyltransferase (GGT) and glutamate dehydrogenase activity (GLDH)) were measured. Milk yield, milk composition and BW were not affected by type and level of concentrates. Feed intake increased in cows with greater amounts of the aminogenic and lipogenic concentrate compared with the glucogenic concentrate. Milk and plasma urea concentrations were elevated in the aminogenic and to a lesser extent in the lipogenic treatment compared with the glucogenic treatment. Glucose concentrations in plasma were not affected by treatments, whereas insulin and glucagon increased, and NEFA concentrations decreased only in cows fed 7.5 kg/d aminogenic concentrate compared with the glucogenic and lipogenic treatment. Activities of ASAT, GGT and GLDH as well as the total antioxidant capacity were not affected by diets. In conclusion, immediate metabolic and endocrine responses were observed due to the short-term dietary changes. Particularly, a surplus of nitrogen supply via the aminogenic diet affected metabolic responses and stimulated insulin and glucagon secretion.     

Effect of substituting wet corn gluten feed and corn stover for alfalfa hay in total mixed ration silage on lactation performance in dairy cows

Wet corn gluten feed (WCGF) is a high moisture feed containing rapidly digestible, non-forage fiber and protein. The objective of this study was to investigate the effect of substituting WCGF and corn stover for alfalfa hay in total mixed ration (TMR) silage on lactation performance and nitrogen balance in dairy cows. Nine multiparous Holstein dairy cows (BW = 532 ± 28.9 kg and day in milk = 136 ± 5.6 d; mean ± SD) were used in a replicated 3 × 3 Latin square design with 21-d periods (14 d of diet adaption and 7 d of sample collection). Groups were balanced for parity, day in milk, and milk production and consumed one of three treatment diets during each period. The treatment diets were fed as TMR and contained similar concentrate mixtures and corn silage but different proportions of roughage and WCGF. The three treatments were: (1) 0% WCGF, 0% corn stover, and 22.1% alfalfa hay (0% WCGF); (2) 6.9% WCGF, 3.4% corn stover, and 11.8% alfalfa hay (7% WCGF); and (3) 13.3% WCGF, 4.9% corn stover, and 3.9% alfalfa hay (13.3% WCGF). Compared to the 0% WCGF diet, the cows fed the 7% and 13.3% WCGF diets had a higher milk yield and concentration of milk fat, protein, lactose, and total solids. Effective degradability of DM was higher in the cows fed the 7% and 13.3% WCGF diets than it was with the 0% WCGF diet. Cows fed the 13.3% WCGF had a higher CP effective degradability and a lower rumen undegraded protein than cows fed the 0% WCGF diet. The concentration of ruminal volatile fatty acids and ammonia-N was higher in cows fed the 7% and 13.3% WCGF diets than cows fed the 0% WCGF diet. The fecal N was lower in cows fed the 7% and 13.3% WCGF diets than it was in cows fed the 0% WCGF diet. Milk N secretion and milk N as a percent of N intake were higher in cows fed the 13.3% WCGF diet than cows fed the 0% and 7% WCGF diets. In conclusion, it appears that feeding a TMR silage containing WCGF and corn stover in combination, replacing a portion of alfalfa hay, may improve lactation performance and nitrogen utilization for lactating dairy cows.     

Lactational and metabolic effects in cows of lysine and methionine added to a ration deficient according to the I.N.R.A. method

The effects of adding lysine and/or methionine to a ration of calculated deficiency in these amino acids of 10% and 20%, respectively, were studied in 24 Brown Swiss cows. The mixed rations (27% grass silage, 19% maize silage, 5% hay and 49% concentrate on DM basis) contained 14.5% CP on average. Lysine supply was selectively elevated by adding fish meal in exchange for other concentrate ingredients. Methionine was supplied in a rumen‐protected form. Milk protein content was elevated whereas fat amount decreased by adding both amino acids. Lactose content increased without additional lysine from fish meal. Live weight, milk yield, milk fat content and protein amount remained unaffected by any variation of amino acids supply. Also nutrient digestibility and nitrogen balance were not changed by the treatments. Blood plasma concentrations confirmed the assumed variation in metabolic lysine and, less clear, methionine supply. Effects on plasma concentrations of other amino acids were relatively small. Most plasma hormones and enzymes, and metabolites in plasma, urine and milk did not respond to the variation in amino acid supply. Lysine addition via fish meal increased aspartate amino transferase and decreased urinary allantoin concentration. Additional methionine elevated plasma ornithine. Overall lysine and methionine appear to have been only marginally deficient in the unsupplemented ration fed for 3 weeks despite the deficiency of 10% to 20% as calculated by the I.N.R.A. method.     

Effect of dietary Quebracho tannin extract on feed intake,digestibility, excretion of urinary purine derivatives and milk production in dairy cows

The aim of this study was to evaluate the effects of dietary Quebracho tannin extract (QTE) on feed intake, apparent total tract digestibility (ATTD), excretion of urinary purine derivatives (PD) and milk composition and yield in dairy cows. Fifty Holstein cows were divided into two groups. To reach a similar performance of both groups, cows were divided according to their milk yield, body weight, days in milk and number of lactations at the start of the experiment averaging 33.2 ± 8.2 kg/d, 637 ± 58 kg, 114 ± 73 d and 2.3 ± 1.6 lactations, respectively. The cows were fed a basal diet as total mixed ration containing on dry matter (DM) basis 34% grass silage, 32% maize silage and 34% concentrate feeds. Three dietary treatments were tested, the control (CON, basal diet without QTE), QTE₁₅ (basal diet with QTE at 15 g/kg DM) and QTE₃₀ (basal diet with QTE at 30 g/kg DM). Two treatments were arranged along six periods each 21 d (13 d adaptation phase and 8 d sampling phase). The ATTD of DM and organic matter were reduced only in Diet QTE₃₀, whereas both QTE treatments reduced ATTD of fibre and nitrogen (N), indicating that QTE impaired rumen fermentation. Nevertheless, feed intake was unaffected by QTE. In Diet CON, urinary N excretion accounted for 29.8% of N intake and decreased in treatments QTE₁₅ and QTE₃₀ to 27.5% and 17.9%, respectively. Daily faecal N excretion increased in treatments CON, QTE₁₅ and QTE₃₀ from 211 to 237 and 273 g/d, respectively, which amounted to 39.0%, 42.4% and 51.7% of the N intake, respectively. Hence, QTE shifted N excretion from urine to faeces, whereas the proportion of ingested N appearing in milk was not affected by QTE (average 30.7% of N intake). Daily PD excretion as indicator for microbial crude protein (CP) flow at the duodenum decreased in treatment QTE₃₀ compared with Diet CON from 413 to 280 mmol/d. The ratios of total PD to creatinine suggest that urinary PD excretion was already lower when feeding Diet QTE₁₅. While there was no effect of Diet QTE₁₅, treatment QTE₃₀ reduced milk yield, milk fat and protein. Both QTE treatments reduced milk urea concentration, which suggest that ruminal degradation of dietary CP was reduced. In summary, adding QTE at dosages of 15 and 30 g/kg DM to diets of lactating dairy cows to improve feed and protein use efficiency is not recommended.     

Effects of mixtures of red clover and maize silages on the partitioning of dietary nitrogen between milk and urine by dairy cows

Eight multiparous lactating Holstein-Friesian cows were used to evaluate the partitioning of dietary nitrogen (N) from diets based on mixtures of red clover and maize silages in comparison with diets based on ryegrass silage. All cows received 4 kg/day of a standard dairy concentrate with one of four forage treatments in an incomplete changeover design with three 4-week periods. Three treatments were based on mixtures of red clover and maize silage. N intake was altered both by varying the ratio of these silages (40/60 and 25/75 on a dry matter (DM) basis) and by an additional treatment for which the DM intake of the 40/60 mixture was restricted to the level achieved with grass silage. Rumen passage rates were estimated from faecal excretion curves following a pulse oral dose of Dysprosium-labeled silage and urinary excretion of purine derivatives (PD) was used as an index of rumen microbial protein synthesis. Red clover silage mixtures led to significantly increased feed intake (21.5, 20.7 and 15.2 kg DM/day for 40/60 and 25/75 red clover/maize silage mixtures and grass silage, respectively), milk production (25.8, 27.8 and 20.0 kg/day for the same treatments, respectively) and milk component yields, but were without effect on milk fat and protein concentrations. The large increase in the yield of milk (24.5 kg/day) and milk components for the restricted red clover/maize silage treatment, in comparison with the grass silage treatment, was proportionately greater than the increase in DM intake (16.6 kg DM/day). There were no significant treatment effects on diet digestibility, while the higher intakes of red clover silage mixtures were associated with higher rumen passage rates (5.82%, 6.24% and 4.55%/h, respectively). There were significant effects of both N intake and forage source on the partitioning of dietary N between milk and urine. When dietary protein was diluted by the inclusion of maize silage, red clover silage led to increased milk N and reduced urinary N in comparison with grass silage. Improvements in N utilisation may be related to increased dietary starch and/or rumen passage rates leading to increased microbial protein synthesis for these treatments. Urinary excretion of PD was significantly higher for all diets based on mixtures of red clover and maize silages, in comparison with grass silage. Urinary N output was close to literature predictions based on N intake for the diet based on ryegrass silage, but 40 to 80 g/day (25% to 30%) less than predicted for the diets based on the mixtures of red clover and maize silages.     

Milk yield response of dairy cows fed fat along with protein

The influence of a fat-coated protein on milk production of Holstein dairy cows was determined using a 4×4 Latin square experiment. Twelve cows were fed a control diet or test diets supplemented with fat, fat plus ruminally undegraded protein (RUP), or a fat-coated protein (Duets™). Cows fed test diets received 0.55 kg of more fat per day than cows in the control treatment. Daily intakes of feed, energy, and protein were the same in all treatments. Cows produced 36.5, 37.3, 37.9, and 39.3 kg of energy-corrected milk per day in control, fat, fat plus RUP, and fat-coated protein treatments, respectively. Cows fed fat-supplemented diets produced an average 1.7 kg more milk daily compared with cows in the control treatment. Feeding RUP along with fat or fat-coated protein provided no further improvement in milk yield compared with fat alone, but partially alleviated the depression in protein content caused by supplemental fat and increased the daily yield of milk protein. In the present experiment, cows fed fat-coated protein produced daily an average 60 g of milk protein more than cows fed fat alone. Since, there was no advantage in milk yield, the decision to include fat-coated protein in dairy rations should be based on its price compared to fat alone and the return in terms of milk protein yield.     

Effect of condensed tannins in rations of lactating dairy cows on production variables and nitrogen use efficiency

The objective of this study was to evaluate the effect of supplemented condensed tannins (CT) from the bark of the Black Wattle tree (Acacia mearnsii) on production variables and N use efficiency in high yielding dairy cows. A feeding trial with 96 lactating German Holstein cows was conducted for a total of 169 days, divided into four periods. The animals were allotted to two groups (control (CON) and experimental (EXP) group) according to milk yield in previous lactation, days in milk (98), number of lactations and BW. The trial started and finished with a period (period 1 and 4) where both groups received the same ration (total-mixed ration based on grass and maize silage, ensiled sugar beet pulp, lucerne hay, mineral premix and concentrate, calculated for 37 kg energy-corrected milk). In between, the ration of EXP cows was supplemented with 1% (CT1, period 2) and 3% of dry matter (DM) (CT3, period 3) of a commercial A. mearnsii extract (containing 0.203 g CT/g DM) which was mixed into the concentrate. In period 3, samples of urine and faeces were collected from 10 cows of each group and analyzed to estimate N excretion. Except for a tendency for a reduced milk urea concentration with CT1, there was no difference between groups in period 2 (CON v. CT1; P>0.05). The CT3 significantly reduced (P<0.05) milk protein yield, the apparent N efficiency (kg milk N/k feed N) and milk urea concentration; but total milk yield and energy-corrected milk yield were not affected by treatment. Furthermore, as estimated from 10 cows per group and using urinary K as a marker to estimate the daily amount of urine voided, CT3 caused a minor shift of N compounds from urine to faeces, as urea-N in urine was reduced, whereas the N concentration in faeces increased. As an improvement in productivity was not achieved and N use efficiency was decreased by adding the CT product it can be concluded that under current circumstances the use in high yielding dairy cows is not advantageous.     

Influence of roughage/concentrate ratio and linseed oil on the concentration of trans-fatty acids and conjugated linoleic acid in duodenal chyme and milk fat of late lactating cows

The objective of the study was to investigate the influence of two roughage-to-concentrate ratios, with or without linseed oil supplementation, on the flow of fatty acids in the intestinal chyme and the secretion in milk fat in late lactating cows. Seven late lactating cows fitted with cannulae in the dorsal rumen and simple T-shaped cannulae in the proximal duodenum were randomly assigned to four experimental periods applying an incomplete replicated 2 x 2 Latin square design. The rations consisted of meadow hay and a concentrate mixture given in a ratio of 70:30 or 30:70 on dry matter basis. The basal rations were fed without or with 200 g linseed oil daily. After three weeks of adaptation, samples from the duodenal chyme were taken to study the flow of fatty acids. Additionally, milk samples were analysed for their milk fat composition. Decreasing roughage/concentrate ratio and linseed oil supplementation significantly increased the flow of monounsaturated fatty acids (MUFA), trans-fatty acids (tFA) and conjugated linoleic acids (CLA) in the duodenum. Furthermore, linseed oil increased the flow of saturated fatty acids (SFA) in the duodenum. Higher concentrate portion (H 30) and linseed oil supplementation significantly decreased the milk fat content. SFA were lower (p < 0.05) and MUFA were higher (p < 0.05) in milk fat after linseed oil supplementation; H 30 resulted in more polyunsaturated fatty acids (PUFA, p < 0.05) in the milk. Linseed oil supplementation significantly increased tFA and CLA in milk fat. The higher CLA content in milk fat as compared to that in the digesta suggests that a substantial endogenous synthesis of CLA in the mammary gland tissue through A9-desaturase took place. Between 21% and 48% of duodenal t11-C(18:1) were converted into c9, t11-CLA in milk fat.     

Diet-induced nephrocalcinosis and urinary excretion of albumin in female rats

This study was carried out to test the hypothesis that diet-induced nephrocalcinosis causes enhanced loss of albumin in urine, irrespective of the composition of the nephrocalcinogenic diet. Female rats were fed various purified diets for 28 days. There was a control diet (0.5% Ca, 0.04% Mg, 0.4% P, 15.1% protein, wt/wt), a low Mg (0.01% Mg), a high protein (30.2% protein) and a high P diet (0.6% P). The low Mg and high P diet induced nephrocalcinosis as demonstrated histologically and by markedly increased concentrations of kidney Ca. In rats fed the high protein diet, nephrocalcinosis was essentially absent. Group mean values of urinary excretion of albumin and plasma concentrations of urea were increased in rats fed either the low Mg or high P diet. The high protein diet did not affect urinary albumin but caused lysozymuria which was not seen in the other groups. Plasma urea was increased in rats fed the high protein diet. In individual rats, the concentration of Ca in kidney and urinary albumin excretion were positively correlated. It is suggested that nephrocalcinosis in female rats induced by either low Mg or high P intake causes kidney damage which in turn leads to increased concentrations of albumin in urine and urea in plasma.     

Preconditioning with hydrogen peroxide (H2O2) or ischemia in H2O2-induced cardiac dysfunction

To assess whether allantoin levels in serum and urine are influenced by exhaustive and moderate exercise and whether allantoin is a useful indicator of exercise-induced oxidative stress in humans, we made subjects perform exhaustive and moderate (100% and 40% VO₂max) cycling exercise and examined the levels of allantoin, thiobarbituric acid reactive substances (TBARS) and urate in serum and urine. Immediately after exercise at 100% VO₂max, the serum allantoin/urate ratio was significantly elevated compared with the resting levels while the serum urate levels was significantly elevated 30 min after exercise. The serum TBARS levels did not increase significantly compared with the resting levels. Urinary allantoin excretion significantly increased during 60 min of recovery after exercise, however, urinary urate excretion decreased significantly during the same period. The urinary allantoin/urate ratio also rapidly increased during 60 min of recovery after exercise. Urinary TBARS excretion decreased during the first 60 min of the recovery period and thereafter significantly increased during the latter half of the recovery period. On the contrary, after 40% VO₂max of exercise, no significant changes in the levels of urate, allantoin and TBARS in serum or urine were observed. These findings suggest that allantoin levels in serum and urine may reflect the extent of oxidative stress in vivo and that the allantoin which appeared following exercise may have originated not from urate formed as a result of exercise but from urate that previously existed in the body. Furthermore, these findings support the view that allantoin in serum and urine is a more sensitive and reliable indicator of in vivo oxidative stress than lipid peroxidation products measured as TBARS.     

The effect of dietary protein on the mineral status of vervet monkeys with special reference to the impact of milk solids on calcium excretion

This study assessed the impact of Westernised and traditional African diets on mineral metabolism in general and calcium status in particular in vervet monkeys. Twelve adult male vervet monkeys (Cercopithecus aethiops), with an average weight of 5+/-0.58 kg each, were divided into two groups of six individuals each and fed traditional diets containing largely maize + legumes (17.4%) or Westernised diets containing milk solids (17.2%) as the source of high crude protein for 8 weeks. Blood was taken at 2-week intervals, the animals were weighed, while urine and stool samples were collected over 24 hours. The monkeys on the milk solids diet had diarrhoea for 6 weeks post-dietary intervention, and produced significantly greater quantities (P<0.02) of stool. These animals also produced significantly more urine (P<0.02). There was no difference in the degree of calciuresis of the two groups, but the monkeys on maize + legume proteins absorbed significantly more calcium during weeks two and six (P<0.04). Furthermore, both groups of monkeys showed a significant decline in plasma calcium levels over the experimental period (P<0.001). The diets had no effect on phosphate levels in the plasma or urine. However, both groups of animals absorbed less phosphate (P<0.09). There was an increasing loss of urinary magnesium (P = 0.03) in both groups, with the milk solids group showing lower plasma levels of this element (P = 0.09). However, the milk solids group lost less magnesium through the stool (P<0.03). In addition, the animals on milk solids showed significant natriuresis (P<0.05), while plasma sodium levels in both groups declined over time (P<0.03). Both diets induced a state of urinary potassium loss (P = 0.0003) and decrease in plasma potassium (P<0.0002). Urinary pH and plasma urea were unaffected by the diets, but the monkeys on maize + legumes excreted significantly less (P<0.001) urinary urea. This study indicates that the milk solids diet compromised mineral homeostasis by interfering with gut and renal functioning, while the traditional African diet did not induce these effects.     

Effects of feeding propylene glycol on dry matter intake, lactation performance, energy balance and blood metabolites in early lactation dairy cows

The objectives of this study were to evaluate effects of feeding propylene glycol (PG) on feed intake, milk yield and milk composition, blood metabolites and energy balance in Holstein dairy cows from 1 to 63 days in milk. Thirty-two multiparous cows, blocked by lactation number, previous 305-day milk production and expected calving date, were arranged into four groups in a randomized block design. Treatments were: control, low PG, medium PG and high PG with 0, 150, 300 and 450 ml PG per cow per day, respectively. The supplement of food grade PG (0.998 g/g PG) was hand-mixed into the top one-third of the daily ration. Cows were fed ad libitum a total mixed ration consisting of forage and concentrate (50 : 50, dry matter basis). Feed intake, milk yield and milk components were not affected (P > 0.05) by PG supplementation. Overall, body weight (BW) loss tended (P < 0.08) to be linearly reduced, and energy status was linearly improved with increasing PG supplementation. Concentrations of glucose in plasma were higher for cows fed PG relative to control (55.6 v. 58.9 mg/dl) and linearly increased (P < 0.01) with increasing PG supplementation. Plasma concentrations of non-esterified fatty acids and beta-hydroxybutyrate were linearly increased, but urine acetoacetate concentration was quadratically changed with the highest for control diet and the lowest for 450 ml/day of PG. These results indicated that supplementation of PG in the early lactating cow diets had minimal effects on feed intake and milk production, but may potentially reduce contents of milk fat and milk protein. Supplementation of early lactating dairy cow diets with PG is beneficial in terms of improving energy status and reducing BW loss.     

Effects of niacin on milk yield,milk composition,and blood components of dairy cows in hot weather

Twenty multiparous Friesian cows, 90 ± 30 days postpartum, were allocated to two groups of ten cows according to calving date, lactation number and daily milk yield, and assigned randomly to one of two diets in a cross-over experiment. The experimental diet consisted of concentrate and maize silage in the proportions 1:1 (dry matter basis) containing either 0 or 10 g niacin per cow per day, which was handmixed into the concentrate. The diets were offered individually as total mixed rations in two equal proportions at 09:00 and 20:00 h in amounts sufficient to ensure 10% refusals. Dry matter, metabolisable energy and crude protein intakes, as well as milk yield, milk protein proportion and yield, milk lactose, total solids and solids-not-fat proportions were not affected by niacin supplementation. In contrast, niacin supplementation increased milk fat proportion and yield. No differences were observed in blood serum concentrations of glucose, total protein, triglycerides, cholesterol, Na, K, Ca, P or Mg. However, the serum concentration of urea was lower when the cows were supplemented with niacin.     

The role of energy,serine, glycine,and 1-carbon units in the cost of nitrogen excretion in mammals and birds

The efficiency with which dietary protein is used affects the nitrogen excretion by the animal and the environmental impact of animal production. Urea and uric acid are the main nitrogen excretion products resulting from amino acid catabolism in mammals and birds, respectively. Nitrogen excretion can be reduced by using low-protein diets supplemented with free amino acids to ensure that essential amino acids are not limiting performance. However, there are questions whether the capacity to synthesize certain nonessential amino acids is sufficient when low-protein diets are used. This includes glycine, which is used for uric acid synthesis. Nitrogen excretion not only implies a nitrogen and energy loss in the urine, but energy is also required to synthesize the excretion products. The objective of this study was to quantify the energy and metabolic requirements for nitrogen excretion products in the urine. The stoichiometry of reactions to synthesize urea, uric acid, allantoin, and creatinine was established using information from a publicly available database. The energy cost was at least 40.3, 60.7, 64.7, and 65.4 kJ/g excreted N for urea, uric acid, allantoin, and creatinine, respectively, of which 56, 56, 47, and 85% were retained in the excretion product. Data from a broiler study were used to carry out a flux balance analysis for nitrogen, serine, glycine, and so-called 1-carbon units. The flux balance indicated that the glycine intake was insufficient to cover the requirements for growth and uric acid excretion. The serine intake was also insufficient to cover the glycine deficiency, underlining the importance of the de novo synthesis of serine and glycine. One-carbon units are also a component of uric acid and can be synthesized from serine and glycine. There are indications that the de novo synthesis of 1-carbon units may be a “weak link” in metabolism, because of the stoichiometric dependency between the synthesized 1-carbon units and glycine. The capacity to catabolize excess 1-carbon units may be limited, especially in birds fed low-protein diets. Therefore, there may be an upper limit to the 1-carbon-to-glycine requirement ratio in relation to nutrients that supply 1-carbon units and glycine. The ratio can be reduced by increasing uric acid excretion (i.e., reducing protein deposition) or by dietary supplementation with glycine. The hypothesis that the 1-carbon-to-glycine requirement ratio should be lower than the supply ratio provides a plausible explanation for the growth reduction in low-protein diets and the positive response to the dietary glycine supply.     

Feeding a High Concentrate Diet Down-Regulates Expression of ACACA,LPL and SCD and Modifies Milk Composition in Lactating Goats

High concentrate diets are fed to early and mid-lactation stages dairy ruminants to meet the energy demands for high milk production in modern milk industry. The present study evaluated the effects of a high concentrate diet on milk fat and milk composition, especially, cis-9, trans-11 CLA content in milk and gene expression of lactating goats. Eight mid-lactating goats with rumen fistula were randomly assigned into a high concentrate diet (HCD) group and low concentrate diet (LCD) group. High concentrate diet feeding significantly increased lipopolysaccharides (LPS) in plasma and decreased milk fat content, vaccenic acid (VA) and cis-9, trans-11 CLA in milk of the lactating goats. The mRNA expression levels of sterol regulatory element binding protein B 1c (SREBP1c), lipoprotein lipase (LPL), fatty acid synthetase (FASN) and acetyl-CoA carboxylase α (ACACA, ACCα) involving in lipid metabolism were analyzed, and ACACA and LPL all decreased in their expression level in the mammary glands of goats fed a high concentrate diet. DNA methylation rate of stearoyl-CoA desaturase (SCD) was elevated and decreased, and SCD mRNA and protein expression was reduced significantly in the mammary glands of goats fed a high concentrate diet. In conclusion, feeding a high concentrate diet to lactating goats decreases milk fat and reduced expression of SCD in the mammary gland, which finally induced cis-9, trans-11 CLA content in milk.     

Is allantoin in serum and urine a useful indicator of exercise-induced oxidative stress in humans?

To assess whether allantoin levels in serum and urine are influenced by exhaustive and moderate exercise and whether allantoin is a useful indicator of exercise-induced oxidative stress in humans, we made subjects perform exhaustive and moderate (100% and 40% VO₂max) cycling exercise and examined the levels of allantoin, thiobarbituric acid reactive substances (TBARS) and urate in serum and urine. Immediately after exercise at 100% VO₂max, the serum allantoin/urate ratio was significantly elevated compared with the resting levels while the serum urate levels was significantly elevated 30 min after exercise. The serum TBARS levels did not increase significantly compared with the resting levels. Urinary allantoin excretion significantly increased during 60 min of recovery after exercise, however, urinary urate excretion decreased significantly during the same period. The urinary allantoin/urate ratio also rapidly increased during 60 min of recovery after exercise. Urinary TBARS excretion decreased during the first 60 min of the recovery period and thereafter significantly increased during the latter half of the recovery period. On the contrary, after 40% VO₂max of exercise, no significant changes in the levels of urate, allantoin and TBARS in serum or urine were observed. These findings suggest that allantoin levels in serum and urine may reflect the extent of oxidative stress in vivo and that the allantoin which appeared following exercise may have originated not from urate formed as a result of exercise but from urate that previously existed in the body. Furthermore, these findings support the view that allantoin in serum and urine is a more sensitive and reliable indicator of in vivo oxidative stress than lipid peroxidation products measured as TBARS.