Milk Urea Levels Research Articles

THE RELATION BETWEEN OXIDATIVE STATUS, MILK QUALITY AND CONCEPTION RATE IN DAIRY GOATS SUPPLEMENTED WITH VITAMIN C

Pregnant Agamy does were used in this experiment to evaluate the effects of Vitamin C (Vit C) supplementation as antioxidant agent to improve the performance of dairy goats during the evidence of oxidative stress (OS) in peri-parturient period. The does under experiment (n = 16) were assigned randomly into control and supplemented groups (n = 8 / group). The control group fed control diet without supplement and the supplemented group fed control diet plus Vit C 75mg/kg of body weight. Dietary supplementation began approximately one month before the expected kidding date till two months post-kidding. Compared to the control does, it was noticed that Vit C supplementation significantly increased (P<0.05) the conception rate (62.5 % vs. 25 %), the weaning weight (WW) (7.21 vs. 5.00 kg) as well as the average daily gain rate (DGR) (53.94 vs. 34.85 g/d) in the kids of the Vit C supplemented group. Vit C supplementation significantly (P<0.05) increased serum level of T3 from day 45 to day 60 and of T4 from day 30 to day 60 post-kidding. Meanwhile, serum cortisol level was significantly decreased (P<0.05) from day 30 to day 60 post-kidding in the Vit C supplemented group. Also, there was a significant increase (P<0.05) in serum total antioxidant capacity (TAC) from day 15 post-kidding and glutathione peroxidase (GPX) from day 30 post-kidding till the end of the experiment in the Vit C supplemented group as compared with the control one. Meanwhile, there was a significantly decrease (P<0.05) in serum Malondialdehyde (MDA) level from day 45 post-kidding and nitric oxide (NO) level from day 15 post-kidding till the end of the experiment. Concerning the effect of Vit C supplementation on milk quality, it was found that Vit C supplementation significantly (P<0.05) improved most of milk components especially fat, lactose, milk urea level (MUL), total solids (TS) and solid not fat (SNF); meanwhile there was a non-significant increase in protein % all over the experiment period. Moreover, both somatic cell counts (SCC) and the infection rates represented by the total bacterial count (TBC) were significantly (P<0.05) decreased in the Vit C supplemented group when compared with the control one. It was concluded that Vit C supplementation in dairy does around the peri-parturient period can improve the unfavorable effects of OS; this reflected on their milk quality and post-kidding conception rate and enhancement of growth rate as well as weaning weight of their kids.

Genetic and environmental determinants of the urea level in cow's milk

Abstract. This study was conducted on a sample of 2237 Polish Holstein-Friesian cows. The aim was to estimate the effect of selected environmental factors on the level of urea in cow's milk and on its genetic parameters, i.e. the heritability coefficients, and genetic correlation with other selected traits of milk production. The present study has revealed the existence of a highly significant influence of herd, year of calving, parity, lactation phase, and milk performance level on the urea content in cow's milk. A high urea level in milk was detected in samples collected from older animals, both during the winter season and the middle phase of lactation (101–200 days). The heritability estimates were generally at a low level, particularly in terms of milk yield (0.183) and urea content (0.152–0.159), which may indicate the dominant role of the environment in shaping them. Relatively low values of genetic correlation (−0.097–0.140) between the urea content and other traits suggest that improvement of milk yield and its composition modify the urea level in milk only to a small degree.

Vliv přídavku propylenglykolu na tělesnou kondici krav, jejich mléčnou užitkovost a kvalitu mleziva

The research was executed on 24 high yield dairy cows divided into three groups (n = 8). There was the control group (I) that the propylene glycol wasn’t given to cows, group II – the cows received 250 ml/day/per head of the propylene glycol, and the group III ─ the cows received 500 ml/day per head of the propylene glycol. The preparation was administered to cows per os beginning from 2 weeks before parturition to the end of the third week of lactation. During the research the condition of animals was estimated by BCS method, the daily yield was recorded, and analyses of the milk and colostrum composition were performed. The propylene glycol lightened the decrease of cows’ condition during entering at the peak of lactation. The higher dose (500 ml) was more profitable, because it had an influence on the content of the colostrum components, low urea level in milk as well as on daily yield, which was higher of about 3.64 kg while the preparation was given, in comparison to the control group. In the 3rd week of lactation the low level of somatic cells in milk of cows that received the preparation was stated. In conclusion, our study revealed a great positive effect of propylene glycol given to the cows shortly before and after parturition on their body condition and a less significant effect on colostrum quality and milk yield.

Relationship between milk urea level, protein feeding and urinary nitrogen excretion in high producing dairy goats

The aim of this study was to evaluate in high producing dairy goats the relationship between milk urea level (MUL) and diet composition, milk yield (MY), intestinal digestible protein (PDI) balance, milk N efficiency and urinary N (UN) excretion. Twenty-one mean treatment data, derived from thirteen diets tested in five experiments conducted on goats kept in metabolic cages to collect separately feces and urine, were used. Diets, orts and milk were analyzed for chemical composition; urine was analyzed for N content. PDI with N as limiting factor for rumen microbial growth (PDIN) was calculated according to the French system as well as PDI requirements. Relationships were developed using regression analysis based on mixed models that account for between-experiment variation. There were significant relationships between MUL (mg/dL) and dietary crude protein (CP) (g/kg DM): MUL=−45.3+0.484 CP (R2=0.914), and between MUL and PDIN balance (%): MUL=22.9+0.347 PDIN balance (R2=0.917). The relationship between MUL and MY was not significant. Milk N efficiency resulted negatively related with MUL and positively related with MY (kg/d): milk N efficiency=33.8–0.38MUL+2.58MY (R2=0.869). UN excretion (g/d) was positively related with MUL:UN excretion (g/d)=14.4+0.348MUL (R2=0.713).The urea concentration of goat's milk can be utilized for a finer tuning of protein feeding, in order to improve milk N efficiency and reduce urinary N excretion.

Effect of some factors on relationships between milk urea levels and cow fertility

Abstract. The effect of some factors on relationships between milk urea levels and fertility of 19 028 cows was analysed. The generalized linear model (GLM) of the SAS package (SAS 2004) was used in the statistical calculations. The increase in milk urea concentration was found to increase calving interval (r=0.05, P≤0.01), rest period (r=0.07, P≤0.01), service period (r=0.01, P≤0.01) and the number of services per conception (r=0.02, P≤0.01). Therefore, dairy breeders may find it advantageous to monitor urea concentrations, which could help to improve cow fertility. Herd milk production level, age of cow and lactation period were the factors that had the greatest effect on the relationship between milk urea levels and cow fertility parameters. The relationship between milk urea level and fertility was stronger in cows from herds with &gt;6 000 kg milk yield, in first-calf heifers and in cows at 3 months of lactation.

Effects of dietary changes on milk yield and quality and metabolic profile in dairy cattle

– Dietary changes can negatively affect digestive processes, particularly at ruminal level and mainly when rapid and associated with an increase of fermentable carbohydrates (Owens et al., 1998). Milk quality can also be affected by digestive functionality (Bertoni et al., 1992). Excesses of degradable N boost blood and milk urea levels but these latter parameters are also influenced by the amount of escape protein fed, the aminoacid profile of absorbed protein and the energy availability (Westwood et al., 1998). Some field experiences indicated increases of milk urea after reformulation of diets to change some ingredients,.......

Milk urea concentration as an indicator of ammonia emission from dairy cow barn under restricted grazing

Bulk milk urea concentration was evaluated to assess its potential as an indicator of ammonia emission from a dairy cow barn in a situation with restricted grazing. An experiment was carried out with a herd of, on average, 52 Holstein-Friesian dairy cows. The cows were housed in a naturally ventilated barn with cubicles and a slatted floor, were fed ensiled forages and feed supplements, and each day were allowed 8.5h of grazing. The experiment was a balanced randomized block design, replicated 3 times. The experimental factor was the bulk milk urea level, which was adjusted to levels of 15, 35, and 55mg of urea per 100g of milk, respectively, by changing the level of nitrogen fertilization of the pasture, the herbage mass and grass regrowth age, and the level and type of feed supplement. Ammonia emission from the barn was measured using sulfur hexafluoride as the tracer gas. Ammonia emission generally increased upon an increase in adjusted milk urea levels. A dynamic regression model was used to predict ammonia emission from bulk milk urea concentration, temperature, and a slurry mixing index. This model accounted for 66% of the total variance in ammonia emission and showed that emission increases exponentially with increasing milk urea concentration. At levels of 20 and 30mg of urea per 100g of milk, ammonia emission increased by about 2.5 and 3.5%, respectively, when milk urea concentration increased by 1mg/100g. Furthermore, emissions from the barn increased 2.6% when temperature increased by 1°C. The study showed that bulk milk urea concentration is a useful indicator for ammonia emissions from a dairy cow barn in a situation with restricted grazing.

Flow injection analysis biosensor for urea analysis in adulterated milk using enzyme thermistor

Urea in adulterated milk is one of the major health concern, it is especially harmful to pregnant women, children, and the sick. A sophisticated and reliable detection system is needed to replace current diagnostic tools for the urea in the milk. In this work, we report a flow injection analysis-enzyme thermistor (FIA-ET) bio-sensing system for monitoring of urea in adulterated milk. This biosensor was made of the covalently immobilized enzyme urease (Jack bean) on controlled pore glass (CPG) and packed into a column inside thermistor, which selectively hydrolysed the urea present in the sample. The specific heat registered from the hydrolysis of urea was found proportional to the concentration of urea present in the milk sample. The biosensor showed a linear range 1–200 mM, with % R.S.D. 0.96 for urea in 100 mM phosphate buffer, pH 7.2. Good recoveries were obtained (97.56–108.7%) for urea up to 200 mM in the spiked milk samples with % R.S.D. 0.95. In the adulterated milk, a simple filtration strategy and matrix matching technique was used to analyse urea. The response time of the sensor was evaluated for urea, which was 2 min, and it gives satisfactory output. A good comparison was observed between the urea concentrations measured through FIA-ET and the colorimetric method. These results indicate that utilizing this system could be very effective to detect low and high level of urea in adulterated milk. The immobilized urease column exhibited a good operational stability up to 180 days when used continuously at room temperature.

Effect of CSN1S1 genotype and its interaction with diet energy level on milk production and quality in Girgentana goats fed ad libitum

A study was carried out to evaluate how the energy level of the diet can affect milk production and quality in Girgentana lactating goats in relation to polymorphism at the alphas1-casein (CSN1S1) genotype locus. Twenty-seven goats, homogeneous for milk production (1.5+/-0.3 kg/d), days of lactation (90+/-10 d) and body weight (35.8+/-5.5 kg) were selected on the basis of their CSN1S1 genotype, as follows: nine goats homozygous for strong (AA) alleles, nine goats homozygous for weak alleles (FF) and nine goats heterozygous (AF). The goats were used in a 3x3 factorial arrangement of treatments, with three genotypes (AA, FF, AF) and three diets at different energy levels (100%, 65% and 30% of hay inclusion). The experiment consisted of three simultaneous 3x3 Latin squares for the three genotypes, with one square for each level of hay inclusion in the diet. All the animals were housed in individual pens. Each experimental period lasted 23 d and consisted of 15 d for adaptation and 8 d for data and sample collection, during which the goats received the scheduled diet ad libitum. The animals were fed three different diets designed to have the same crude protein content (about 15%) but different energy levels: a pelleted alfalfa hay (H100) and two feeds including 65% (H65) and 30% (H30) of alfalfa hay (respectively 1099, 1386 and 1590 kcal NE for lactation/kg DM). All the diets were ground and pelleted (6 mm diameter). AA goats were more productive than AF and FF goats (respectively: 1419 v. 1145 and 1014 g/d; P=0.002). Indeed the interaction energy levelxgenotype was significant (P=0.018): in fact AA goats showed their milk increase only when fed with concentrates. Differences in protein and in casein levels between the three genotypes were in line with results expected from the different allele contribution to alphas1-casein synthesis. Milk urea levels were significantly lower in AA goats compared with AF and FF genotypes (respectively 32.7 v. 40.4 and 40.4 mg/dl; P=0.049) and significantly lower when goats were fed with 65H and 30H diets than with 100H diet (respectively 37.4 and 34.3 v. 41.7 mg/dl; P<0.001). Indeed, a significant interaction genotypexdiet (P=0.043) occurred for milk urea, which was significantly lower in AA goats but only when fed with concentrates (65H and 30H). Blood concentrations of energy indicators (glucose, non-esterified fatty acids and beta-hydroxybutyric acid) were not influenced by genotype. The results confirm that strong alleles are associated with a greater efficiency of feed utilization and seem to show that a high energy level of the diet can further improve this efficiency.

WPŁYW POZIOMU MOCZNIKA I BIAŁKA W MLEKU NA WSKAŹNIKI PŁODNOŚCI KRÓW

An analysis of the effect of milk urea and protein levels in four consecutive lactations on fertility indices of Blackand- White Polish Holstein-Friesian cows, milk recorded in the Kujawsko-Pomorskie province has been made. Poorer fertility indices were found in first-calf heifers and second lactation cows receiving energy-deficient diets and in older (third and fourth lactation) cows receiving excess dietary protein and energy. Best fertility was found in young cows fed excess protein (>3.60%) regardless of milk urea levels, and in older cows having lower and optimum levels regardless of protein levels. Cow fertility is differentiated more by milk protein levels than by urea content. Fertility parameters were poorer in first and second lactation cows than in older cows. The coefficients of correlation between milk urea and protein levels and fertility indices were very low, with the only significant differences between protein content vs. calving interval and reproductive rest period.

UREA LEVEL IN COWS’ MILK FED ON TOTAL MIXED RATION (TMR) AND TRADITIONAL SYSTEM IN SUMMER AND WINTER SEASON

In the research urea content in milk and frequency of the occurrence of samples with different urea level in milk of cows fed on total mixed ration (TMR) and traditional system in summer and winter season were analyzed. Analysis covered 14272 of milk samples. On account of urea level they were divided on three groups: to 140, 141-250 and above 250 mg of urea in 1 liter of milk. It was found that average urea content in milk of cows fed on total mixed rations (TMR) amounted to 196 mg.l-1. Milk of cows from farm applying traditional feeding system included 184 mg.l-1 of that constituent average. Both these values therefore could have been recognized as optimal. Urea level pointed out to the energy-protein unbalancing of feed rations in 55.6% (TMR) and 57.7% (traditional) of milk samples. Urea level in milk of cows fed in traditional system was at p≤0.01 higher (196 mg.l-1) in summer than in winter season (166 mg.l-1). In winter feeding season the frequency of the occurrence of milk samples indicating the lack of protein in feed rations (to 140 mg of urea in 1 liter) was 11.9% higher than in summer season.

Fertility parameters in lactating Mediterranean buffaloes fed two different diets

The aim of this study was to evaluate the effects of two different diets on fertility rate in 64 Mediterranean buffalo cows. The animals were divided in two groups: Group S (n=32) received a total mixed ration based on haysilage of Italian ryegrass (Lolium multiflorum), hay and concentrates, whereas group H (n=32) was fed only hay and concentrates. Both diets consisted of 50-55 % forages and 45-50 % concentrates and contained 0.91 MFU/kg dry matter (DM) and 16% crude protein/DM. From February until September the cows were located together with bulls and pregnancy diagnosis was performed monthly. Furthermore, blood and milk samples were monthly collected on 20 animals in each group. Statistical analysis was performed by χ2 and t Student tests. A higher fertility rate was recorded in group H vs. group S (100 vs. 78.1%, respectively; P<0.05). Furthermore, higher blood and milk urea levels were recorded in group S during the first months of the trial (respectively 10.8 vs. 9.6 mmol L-1; P<0.01 and 55.4 vs. 50.6 mg/dl; P<0.05). It can be hypothesized that the higher levels of urea in group S may have affected the reproductive performances of the animals, increasing the nitrogen concentration in the uterus.

Usefulness of Milk Urea Concentration to Monitor the Herd Reproductive Performances in Crossbred Karan-fries Cowsp

The study was undertaken to investigate the validity of milk urea concentration as an index of the reproductive performances in crossbred Karan-Fries (Holstein FriesianxTharparkar) cows under farm condition. Milk urea wasanalysed in noon milk samples (1200 to 1300 h) to interrelate with the interval from parturition to first service, number of insemination per conception, first service conception rate and service period. Milk progesterone (P4) was analysed in noon milk samples on the day 1, 10, 20 and 30 post insemination to study the effect of milk urea concentration on early embryonic mortality. The interval from parturition to first service was found significantly (p<0.01) higher (77.2′5.5 days) when milk urea concentration was ≥63.4 mg/dl. The average milk urea concentrations (mg/dl) were found 42.1′2.5, 47.9′1.5 and 50.3′3.1, respectively in cows that conceived at 1 s t , 2 n d and 3 r d insemination. However, the variation was not statistically significant. The first insemination conception rate was found significantly (p<0.05) higher (68.8%) when milk urea level was ≤32.4 mg/dl. The service period was found significantly (p<0.05) higher (125.4′8.8 days) when milk urea concentration was ≥45.1 mg/dl. The milk P4 level indicated that the cows, those were detected as non-pregnant on day 60 post insemination were initially pregnant but the pregnancy was terminated sometime during the day 30 to 60 post insemination. The study indicates that the milk urea values may be used as an index of reproductive performances in dairy herd when individual animals are not being monitored for nutritional status. The altered milk urea values may be utilised by the farmers as ready reference to rectify the protein and energy nutrition in cows to achieve the better reproductive performances in herd.

Relationships between milk urea and production, nutrition, and fertility traits in Israeli dairy herds.

The objectives of this study were to identify and evaluate production and environmental factors that influence milk urea (MU) in Israeli dairy herds, to analyze the relationships between MU concentration and nutritional variables, and to examine a possible association between MU and pregnancy rate (PR). Production and environmental data were obtained from the Israeli Dairy Herd Improvement (DHI) Center (n = 1,279,600). Programmed total mixed rations (feeds and quantities) on milk-test day were collected from 42 dairy herds. Data on 36,073 cows that were inseminated close to milk-test day and pregnancy diagnosis results were obtained from the DHI data bank. Highly significant positive relationships were found between MU concentration and milk yield and fat percentage; relationships between MU and milk total protein percentage and somatic cell count were negative. Milk urea levels were higher during the summer months and were higher for adult cows. These levels increased as lactation progressed. Milk urea was positively associated with dietary levels of crude protein, ruminal digestible protein, and neutral detergent fiber contents; it was negatively associated with ration energy and nonstructural carbohydrate contents. Significant influences of specific feeds on MU were detected. A significant negative association was found between MU level and PR. Least squares means for PR for cows in the lowest and highest MU quartiles were 38.4 and 36.1%, respectively. Increasing levels of MU were negatively related to reproductive performance of dairy cows, but the risk of nonpregnancy caused by high levels of MU was lower than reported in previous studies.

Does spring application of fertiliser urea reduce dairy cow performance?

This paper reports a field experiment and a farm survey, which aimed to find out if there is evidence that elevated herbage crude protein (CP):sugar levels have negative effects on dairy cow performance. Differences in herbage CP levels were induced by using nitrogen (+N) or withholding (-N) applied as fertiliser urea for two groups of 20 dairy cows in early lactation (August to November 2003). Cows fed urea-fertilised herbage had elevated milk urea levels (-N = 5.4 mmol/l, +N = 8.3 mmol/l, P

Effects of Feeding Time on Nitrogen Capture by Lactating Dairy Cows Grazing Rye Pasture

The objective of this experiment was to determine whether varying times at which a partial mixed ration was fed, either before or after grazing, affected N utilization from rye pasture and thus affected milk yield and components. Sixteen Holstein cows were fed a partial mixed ration (PMR) either at 0700, 0830, or 1100h. Cows were milked at 0900h and turned out to graze at 0930h. Treatments represented feeding times 2.5h and 1h before grazing and immediately after grazing. The study was conducted as a 3×3 Latin square with three 17-d periods. There were no significant differences among treatments for pasture intake or yield of milk or milk components. Milk yield, fat %, and protein % were 29.4, 29.6, and 29.3kg, 3.5, 3.5, and 3.4%, and 3.4, 3.5, and 3.4% for treatments, respectively. The milk urea levels were 15.6, 15.1, and 15.5 mg/dl, and were not different among treatments. Blood samples were collected on the last day of each period at 0645, 0845, 1045, 1200, and 1400h. Blood urea nitrogen (BUN) was measured as an indicator of ruminal N capture. Concentrations were not significantly different among diets before grazing; however, they were significantly different among all treatments approximately 1h after cows were removed from pasture. Cows fed at 0700h, 2h before grazing, maintained lower BUN levels across the 7h during which the blood samples were collected. Cows that ate the PMR immediately after grazing maintained the highest BUN. Feeding a PMR to cows that graze at different times before and after grazing affected the capture of ruminal N, as indicated by differences in the levels of BUN, but there was no effect on yield of milk or milk components.

Production performance of dairy cows after the dietary addition of clinoptilolite

Clays are frequently proposed for the addition to dairy cattle diets to reduce the transfer of mycotoxins in milk. This study examined the effect of the addition of Clinoptilolite to the diet of lactating dairy cows on milk production and milk composition. Thirty-two lactating Holstein cows (average lactation length: 142 d) were blocked according to milk production, parity, and days of lactation for assignment to one of two dietary treatments: control diet; control diet + Clinoptilolite, 200g/d. The control diet was based on corn and alfalfa silages, hay and concentrates, and did not contain aflatoxins above the safe level. The experimental period lasted 76 days. The Clinoptilolite supplementation did not affect milk yield and milk composition other than urea contents. The urea level in milk was negatively affected by Clinoptilolite addition (control group 29.7 mg/100 ml vs Clinoptilolite group 31.3 mg/100ml). The dietary addition of Clinoptilolite did not change pH, ammonia content and VFA molar percentages in the rumen. No dietary effect on mineral contents of blood plasma (Na, K, Zn, and Ca) was observed. In case of clinoptilolite use in dairy cattle feeding, scarce negative effect on milk production and quality are expected.

The relationship between various animal and management factors and milk urea, and its association with reproductive performance of dairy cows grazing pasture

This study was designed to determine the use of milk urea to diagnose nutrient imbalances in diets of dairy cattle grazing pasture and infertility problems associated with excess dietary nitrogen (N). A first experiment investigated the influence of the ratio of N/water soluble carbohydrate (WSC) (g/g) and N/metabolisable energy (ME) (g/MJ) (% of estimated intake) in the diet, and animal and management factors, on urea concentrations of individual cow or bulk milk samples collected at monthly intervals over a 2-year period from a herd of 108 Friesian dairy cows grazing pasture. Mean±S.E. daily milk yield was 18.4±0.11 l milk/cow with 40.3±0.25 mg urea/dl of milk. This relatively high milk urea value is in line with the high estimated N/WSC ratio, which was three times the recommended ratio for that level of production. The ratio of N/WSC in the diet alone explained 8.8% of the variation in milk urea from individual cows, and this was increased to 21.5% when genetic merit, cow age, milk yield and milk protein content were included in the model. Level of feeding and cow live-weight had no significant effect on milk urea. Milk urea levels were lowest (at 32 mg/dl) when cows were between 40 and 60 days in lactation. Cows had higher ( P<0.001) levels of urea in their milk from January to June, when they grazed kikuyu grass pasture, than for the rest of the year when they grazed ryegrass pasture (43 vs. 35 mg/dl). There was a stronger relationship between N/WSC and the urea content of bulk milk ( r 2=30%) than individual cow milk ( r 2=11%), and this relationship was curvilinear. Substituting ME for WSC explained a further 2% and 2.7% of variation in bulk and individual milk urea, respectively. In a second experiment, the relationship between milk urea and the rates of non-return to service of Friesian cows grazing pasture was investigated. Milk samples were collected from 556 cows on four farms on the day of artificial insemination. The urea content of milk was not related ( P<0.05) to the chances of not returning to service. From the results of this study, it may be concluded that the urea content of bulk, but not individual cow, milk is a useful tool for assessing the appropriateness of the N/WSC ratio in the diet of dairy cows grazing pasture. There was no evidence that high milk urea levels are associated with poor reproductive performance in dairy cows grazing pasture.

The relationship between milk urea content and fertility in dairy cows

A number of studies have shown that milk urea levels above about 350 mg/l are associated with reduced fertility in dairy cows (Ropstad and Refsdal, 1987; Gustafsson and Carlsson, 1993). A significant and increasing proportion of UK milk producers receive regular information on the urea content of bulk milk as part of routine milk testing. Two studies were undertaken to examine whether the urea content in bulk milk (Study 1) or in milk from individual cows at about the time of service (Study 2) could be used as a management aid to improve fertility status.In Study 1, the milk urea (MU) contents in bulk milk samples from 475 farms in England and Wales were determined by NIRS. Fertility data for each farm was obtained from National Milk Records. Analysis of the data for each month of the study was restricted to those herds in which ≥15 cows were served.

Effect of altering the non-structural: structural carbohydrate ratio in a pasture diet on milk production and ruminal metabolites in cows in early and late lactation

AbstractThe effect on digestibility, ruminal metabolites, microbial protein synthesis and milk production of manipulating the non-structural (NSC): structural (SO carbohydrate ratio in a predominantly pasture diet was investigated in cows in early (trial 1) and late (trial 2) lactation. Twenty-four cows in trial 1 and 15 cows in trial 2 were offered pasture only (P), 0·85 P plus 0·15 NSC/protein mixture (PR), and P plus an additional 0·1 (trial 1) or 0·15 (trial 2) NSC (PE) in a Latin-square arrangement. All diets were isonitrogenous and P and PR were isoenergetic. PE but not PR increased microbial protein synthesis and decreased ruminal ammonia and milk urea levels, compared with P. Efficiency of microbial synthesis (g N per kg digestible organic matter intake) was not altered by treatment. Treatments had minor effects on ruminal pH and no effect on volatile fatty acid concentrations. PE and PR did not affect milk yield or protein yield and decreased fat yield compared with P in trial 1. Milk yield was increased on PE and PR compared with P and was greater on PE than PR, in trial 2. Yields of fat and protein were higher on PE than on P and yield of protein was higher on PR than on P. The results suggest that increasing the ratio of NSC: protein by increasing total carbohydrate intake was more effective in improving nitrogen utilization in the rumen than was increasing the NSC: SC ratio without increasing carbohydrate intake.