Influence of previous plane of nutrition on molecular mechanisms regulating the expression of urea and water metabolism related genes in the rumen and kidney of finishing crossbred Angus steers

This study aimed to understand how molecular mechanisms controlling water and urea metabolism at the finishing phase can be affected by previous plane of nutrition of crossbred Angus beef steers. Twenty-four (n = 24) animals were randomly distributed into either a moderate (MP) or high plane of nutrition during the background phase for 85 d. Animals were then blocked by their previous plane and were moved onto a 105-d finishing phase in a 2 × 2 factorial arrangement. The forage-finished group received only high-quality alfalfa hay, whereas the grain-fed group received a high grain diet (80% whole corn and 20% alfalfa hay). By the end of the finishing phase, animals were harvested and tissue samples from the rumen and kidney were collected. Changes in gene expression of aquaporins (AQP)-2, -3, -4, -7, ATP1A1, ATP1B1, SGK1, CLIC1 (kidney and rumen), UT-A1 (kidney only) and UT-B (rumen only), were assayed via real-time qPCR; 18S rRNA was used as an endogenous control. One-way ANOVA followed by Tukey's post hoc analysis was conducted. When animals were from MP, forage-finishing increased the relative abundance of AQP3 (P ≤ 0.05), AQP7 (P ≤ 0.05), ATP1B1 (P ≤ 0.05), and SGK1 (P ≤ 0.05) in the kidney when compared to grain-fed animals. In the rumen, for the MP group, AQP7 was differentially expressed in both treatments at the finishing phase (P ≤ 0.01), with forage-finished steers having the highest expression of AQP7. For the MP group, UT-B had a tendency of presenting a higher expression on grain-fed animals (P = 0.075). Overall, these results suggest that previous plane can impact expression of genes associated with water and urea metabolism during the finishing phase, namely AQP3, AQP7, ATP1B1, and SGK1 in the kidney, and AQP7 and UT-B in the rumen. The greatest impact observed on gene expression changes of investigated genes at the finishing phase was reflective of animals backgrounded on the moderate previous plane.

Evaluation of Urine Nitrogen Excretion as the Measure of the Environmental Load and the Efficiency of Nitrogen Utilization

The aim of this study was to evaluate the relationship between nutrition, the concentration of milk urea nitrogen (MUN) and the urinary nitrogen excretion in farm conditions and to use the MUN concentration as a tool to control protein nutrition and environmental load in dairy farming. Urinary N excretion was evaluated by an empirical model according to the intake and metabolic transformation of N to milk protein in selected farms was on average 208.8 ± 34.8 g with a range of values from 127.7 to 277.8 g N.day−1. The evaluated proportion of excreted N in relation to crude protein (CP) intake in the total mix ration (TMR) was statistically significant (R2 = 0.504; P < 0.0001). Urinary N excretion, evaluated according to the analysis of the MUN content, using selected regression equations, was on average 211.8 ± 24.3 g.day−1 with an individual variation of 157.2‒274.7 g.day−1 with a significantly higher positive correlation to the received CP in the TMR (R2 = 0.693; P < 0.0001). The evaluated effect of CP concentration in the TMR on urine N excretion confirmed the higher nitrogen excretion in the urine by 25.6 g per day with an increased CP in the TMR by 1 %. The proportion of urea nitrogen in the total N excreted in the urine was on average 80.5 %. The validation of the models for the prediction of nitrogen excretion, according to the MUN for the practical application on farms, was determined the best equation by Kaufmann a St-Pierre, which used available data from routine analysis of milk composition by the Breeding service of Slovakia. The MUN analysis offered a simple and non-invasive approach to the evaluation of the urinary N excretion, as well as, the efficiency of N utilization from feed to milk.

Prediction of nitrogen excretion from data on dairy cows fed a wide range of diets compiled in an intercontinental database: A meta-analysis

Manure nitrogen (N) from cattle contributes to nitrous oxide and ammonia emissions and nitrate leaching. Measurement of manure N outputs on dairy farms is laborious, expensive, and impractical at large scales; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were (1) to collate an international database of N excretion in feces and urine based on individual lactating dairy cow data from different continents; (2) to determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; and (3) to develop robust and reliable N excretion prediction models based on individual data from lactating dairy cows consuming various diets. A raw data set was created based on 5,483 individual cow observations, with 5,420 fecal N excretion and 3,621 urine N excretion measurements collected from 162 in vivo experiments conducted by 22 research institutes mostly located in Europe (n = 14) and North America (n = 5). A sequential approach was taken in developing models with increasing complexity by incrementally adding variables that had a significant individual effect on fecal, urinary, or total manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models including experiment as a random effect. Simple models requiring dry matter intake (DMI) or N intake performed better for predicting fecal N excretion than simple models using diet nutrient composition or milk performance parameters. Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI, but simple models using milk urea N (MUN) and N intake performed even better for urinary N excretion. The full model predicting fecal N excretion had similar performance to simple models based on DMI but included several independent variables (DMI, diet crude protein content, diet neutral detergent fiber content, milk protein), depending on the location, and had root mean square prediction errors as a fraction of the observed mean values of 19.1% for intercontinental, 19.8% for European, and 17.7% for North American data sets. Complex total manure N excretion models based on N intake and MUN led to prediction errors of about 13.0% to 14.0%, which were comparable to models based on N intake alone. Intercepts and slopes of variables in optimal prediction equations developed on intercontinental, European, and North American bases differed from each other, and therefore region-specific models are preferred to predict N excretion. In conclusion, region-specific models that include information on DMI or N intake and MUN are required for good prediction of fecal, urinary, and total manure N excretion. In absence of intake data, region-specific complex equations using easily and routinely measured variables to predict fecal, urinary, or total manure N excretion may be used, but these equations have lower performance than equations based on intake.

Milk Composition and Production Efficiency within Feed-To-Yield Systems on Commercial Dairy Farms in Northern Ireland

Simple Summary

Feed-to-yield concentrate allocation systems seek to improve precision by targeting more nutrients to dairy cows with the greatest nutrient requirements. This study investigated the effect of offering concentrates on a feed-to-yield basis to housed cows on the relationships between milk yield, intake, milk composition and production efficiency during the first five months of lactation. Performance data for individual cows were collected from 26 farms in Northern Ireland, and intakes were subsequently calculated. Total dry matter intake increased with increasing milk yield. Cows with higher milk yields produced milk with a lower fat and protein concentration, likely due to a combination of cow genetics, diet, and a ‘dilution’ effect associated with yield. The reduction in milk fat and milk protein concentration with increasing milk yield is particularly important for farmers supplying milk for processing, as milk pricing mechanisms within these supply contracts normally include bonuses or deductions determined by milk composition. Cows with greater milk yields had improved nitrogen and energy use efficiency but were offered more concentrates per kilogram of energy-corrected milk produced.

Abstract

This study examined the relationships between milk yield and diet composition, nutrient intakes, milk composition, and feed use efficiency when concentrates were offered using a feed-to-yield (FTY) approach. The study was conducted on 26 dairy farms in Northern Ireland. Cows (n = 3471) were fully housed and were offered concentrates on an FTY basis. Individual cow genetic information was obtained for 18 herds. Concentrate intakes of individual cows were either obtained from the farms or calculated, while milk yield and milk composition data were obtained from test-day milk recording. Mean test-day milk yields during months 2 to 5 post-calving were calculated for each cow, and cows within each lactation were placed into one of six equal-sized milk yield (kg/cow/day) groups. Diet effects and performance responses to milk yield groups were tested for linear and quadratic effects. Total dry matter intakes increased with increasing milk yield. Milk fat and milk protein concentration declined as milk yield increased, which could be attributed in part to genetics and diet. As milk yield increased, nitrogen and energy use efficiency was improved. However, concentrates offered per kg of energy-corrected milk also increased at higher milk yields, indicating an increased reliance on concentrates for these cows.

Nitrogen excretion from beef cattle fed a wide range of diets compiled in an intercontinental dataset: a meta-analysis

Manure N from cattle contributes to nitrate leaching, nitrous oxide and ammonia emissions. Measurement of manure N outputs on commercial beef cattle operations is laborious, expensive, and impractical; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were to (1) collate an international dataset of N excretion in feces and urine based on individual observations from beef cattle; (2) determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; (3) develop robust and reliable N excretion prediction models based on individual observation from beef cattle consuming various diets. A meta-analysis based on individual beef data from different experiments was carried from a raw dataset including 1,004 observations from 33 experiments collected from 5 research institutes in Europe (n = 3), North America (n = 1), and South America (n = 1). A sequential approach was taken in developing models of increasing complexity by incrementally adding significant variables that effected fecal, urinary, or total manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models with experiment as a random effect. Simple models including dry matter intake (DMI) were better at predicting fecal N excretion, than those using only dietary nutrient composition or BW. Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI. A model including DMI and dietary component concentrations led to the most robust prediction of fecal and urinary N excretion, generating root mean square prediction errors as a percentage of the observed mean values of 25.0% for feces and 25.6% for urine. Complex total manure N excretion models based on BW and dietary component concentrations led to the lowest prediction errors of about 14.6%. In conclusion, several models to predict N excretion already exist, but the ones developed in this study are based on individual observations encompassing larger variability than the previous developed models. In addition, models that include information on DMI or N intake are required for accurate prediction of fecal, urinary and total manure N excretion. In the absence of intake data, equations have poor performance as compared to equations based on intake and dietary component concentrations.

Effect of decreasing dietary crude protein in fattening calves on the emission of ammonia and greenhouse gases from manure stored under aerobic and anaerobic conditions

Dietary strategies can potentially help to reduce nitrogen (N) emissions and decrease the environmental impact of beef production. This study aimed to evaluate the effects of dietary crude protein (CP) concentration on animal performance, N excretion, and manure N volatilisation of finishing Holstein animals. In a first study, 105 Holstein bulls (BW 344 ± 2.6 kg; age 252 ± 0.9 days) were allocated to eight pens to evaluate the effect of two treatments (medium (M) and low (L), which contained CP 14.5% and 12% on a DM basis, respectively) on performance, and results confirmed that dietary CP decrease did not impair animal growth. In a second study, N excretion study, 24 Holstein heifers (BW 310 ± 5.3 kg; age 251 ± 1.4 days) were distributed randomly depending on the initial BW to three treatments (high (H), M, and L, which contained CP 17%, 14.5% and 12% on a DM basis, respectively). Based on N excretion, urinary N excretion was greater (P < 0.001) in H than in M and L diets, but no differences in faecal N excretion were observed among treatments. A third study with in vitro assays under aerobic and anaerobic conditions was designed to analyse gaseous emissions (volatilisation of N and carbon, C) during the storage stage of manure. Manure, faecal and urine samples, mixed at a ratio of 1:1 (wet weight), were collected during the N excretion study (manure-H, manure-M, manure-L). Under aerobic conditions, manure-M and manure-L showed a delay of 4-5 days in manure ammonia emission compared with manure-H (P < 0.01). Total N content was lower (P < 0.01) in manure-L compared with manure-M and manure-H, but N volatilisation (percentage relative to initial N) in manure-L and manure-M was greater (P < 0.01) than in manure-H. In contrast, the anaerobic N volatilisation was 20 times greater in manure-M and 10 times greater in manure-H compared with manure-L. Under aerobic and anaerobic conditions, the emission of C, as C-CO₂ and C-CH₄, was greater in manure-L than in manure-H and manure-M. Therefore, the decrease of dietary CP concentration from 17% to 14.5% and 12% is an efficient strategy to reduce urinary N excretion by 40%, without impairing performance, and also to reduce manure N losses through ammonia volatilisation under anaerobic conditions. However, a dietary CP content of 14.5% resulted in less environmental impact than a CP content of 12.8% when also considering manure emissions under aerobic or anaerobic conditions.

Evaluation of nitrogen excretion equations for ryegrass pasture-fed dairy cows

Accurate and precise estimates of nitrogen (N) excretion in faeces and urine of dairy cattle may provide direct tools to improve N management and thus, to mitigate environmental pollution from dairy production. Empirical equations of N excretion have been evaluated for indoor dairy cattle but there is no evaluation for cows fed high proportions of fresh forage. Therefore, the objective of the current study was to evaluate N excretion equations with a unique data set of zero-grazing experiments. Through literature searches, 89 predictive equations were identified from 13 studies. An independent data set was developed from seven zero-grazing experiments with, in total, 55 dairy Holstein-Friesian cows. Models' performance was evaluated with statistics derived from a mixed-effect model and a simple regression analysis model. Squared sample correlation coefficients were used as indicators of precision and based on either the best linear unbiased predictions (R²_BLUP) or model-predicted estimates (R²_MDP) derived from the mixed model and simple regression analysis, respectively. The slope (β₀), the intercept (β₁) and the root mean square prediction error (RMSPE_m%) were calculated with the mixed-effect model and used to assess accuracy. The root mean square prediction error (RMSPE_sr%) and the decomposition of the mean square prediction error were calculated with the simple regression analysis and were used to estimate the error due to central tendency (mean bias), regression (systematic bias), and random variation. Concordance correlation coefficient (CCC) were also calculated with the simple regression analysis model and were used to simultaneously assess accuracy and precision. Considering both analysis models, results suggested that urinary N excretion (UN; R²_MDP = 0.76, R²_BLUP = 0.89, RMSPE_m% = 17.2, CCC = 0.82), total manure N excretion (ManN; R²_MDP = 0.83, R²_BLUP = 0.90, RMSPE_m% = 11.0, CCC = 0.84) and N apparently digested (NAD; R²_MDP = 0.97, R²_BLUP = 0.97, RMSPE_m% = 5.3, CCC = 0.95) were closely related to N intake. Milk N secretion was better predicted using milk yield as a single independent variable (MilkN; R²_MDP = 0.77, R²_BLUP = 0.97, RMSPE_m% = 6.0, CCC = 0.74). Additionally, DM intake was a good predictor of UN and ManN and dietary CP concentration of UN and ManN. Consequently, results suggest that several evaluated empirical equations can be used to make accurate and precise predictions concerning N excretion from dairy cows being fed on fresh forage.

Effects of faba bean, blue lupin and rapeseed meal supplementation on nitrogen digestion and utilization of dairy cows fed grass silage-based diets

There is increasing interest in using locally produced protein supplements in dairy cow feeding. The objective of this experiment was to compare rapeseed meal (RSM), faba beans (FBs) and blue lupin seeds (BL) at isonitrogenous amounts as supplements of grass silage and cereal based diets. A control diet (CON) without protein supplement was included in the experiment. Four lactating Nordic Red cows were used in a 4 × 4 Latin Square design with four 21 d periods. The milk production increased with protein supplementation but when expressed as energy corrected milk, the response disappeared due to substantially higher milk fat concentration with CON compared to protein supplemented diets. Milk protein output increased by 8.5, 4.4 and 2.7% when RSM, FB and BL were compared to CON. The main changes in rumen fermentation were the higher propionate and lower butyrate proportion of total rumen volatile fatty acids when the protein supplemented diets were compared to CON. Protein supplementation also clearly increased the ruminal ammonia N concentration. Protein supplementation improved diet organic matter and NDF digestibility but efficiency of microbial protein synthesis per kg organic matter truly digested was not affected. Flow of microbial N was greater when FB compared to BL was fed. All protein supplements decreased the efficiency of nitrogen use in milk production. The marginal efficiency (amount of additional feed protein captured in milk protein) was 0.110, 0.062 and 0.045 for RSM, FB and BL, respectively. The current study supports the evidence that RSM is a good protein supplement for dairy cows, and this effect was at least partly mediated by the lower rumen degradability of RSM protein compared to FB and BL. The relatively small production responses to protein supplementation with simultaneous decrease in nitrogen use efficiency in milk production suggest that economic and environmental consequences of protein feeding need to be carefully considered.

Effect of Potato By-Product on Production Responses of Dairy Cows and Total Mixed Ration Stability

Vegetable by-products have great potential for use as animal feeds and thus could improve the sustainability of the food system. The objective was to evaluate the milk production potential of potato by-product (PBP) replacing cereal grains in grass silage-based total mixed ration (TMR). Additionally, a laboratory scale experiment was conducted to assess the effect of PBP and chemical preservatives on the aerobic stability of TMRs. A change-over dairy cow feeding experiment was conducted to evaluate the inclusion of 135 g/kg (on a dry matter (DM) basis) of PBP in TMR. Additionally, the aerobic stability of TMR was evaluated by preparing TMRs with increasing levels of PBP and treated with different doses of formic and propionic acid or salt-based preservatives. The inclusion of PBP in dairy cow diets decreased feed intake, but organic matter digestibility was greater in the PBP diet, resulting in only slightly decreased production (milk protein 1435 vs. 1363 g/day, p < 0.05; milk lactose 1716 vs. 1606 g/day, p < 0.05). The aerobic stability of TMR was negatively affected by the inclusion of PBP, but it could to a limited extent be prolonged using chemical preservatives. The inclusion of PBP decreased feed intake and milk production to some extent when included in the diet of high-producing dairy cows. The utilization of PBP may, however, be justified from a sustainability point of view, as it provides a way to circulate the nutrients of a non-human edible feed material back into the food chain.

Identification of Genomic Regions Associated with Concentrations of Milk Fat, Protein, Urea and Efficiency of Crude Protein Utilization in Grazing Dairy Cows

The objective of this study was to identify genomic regions associated with milk fat percentage (FP), crude protein percentage (CPP), urea concentration (MU) and efficiency of crude protein utilization (ECPU: ratio between crude protein yield in milk and dietary crude protein intake) using grazing, mixed-breed, dairy cows in New Zealand. Phenotypes from 634 Holstein Friesian, Jersey or crossbred cows were obtained from two herds at Massey University. A subset of 490 of these cows was genotyped using Bovine Illumina 50K SNP-chips. Two genome-wise association approaches were used, a single-locus model fitted to data from 490 cows and a single-step Bayes C model fitted to data from all 634 cows. The single-locus analysis was performed with the Efficient Mixed-Model Association eXpedited model as implemented in the SVS package. Single nucleotide polymorphisms (SNPs) with genome-wide association p-values ≤ 1.11 × 10⁻⁶ were considered as putative quantitative trait loci (QTL). The Bayes C analysis was performed with the JWAS package and 1-Mb genomic windows containing SNPs that explained > 0.37% of the genetic variance were considered as putative QTL. Candidate genes within 100 kb from the identified SNPs in single-locus GWAS or the 1-Mb windows were identified using gene ontology, as implemented in the Ensembl Genome Browser. The genes detected in association with FP (MGST1, DGAT1, CEBPD, SLC52A2, GPAT4, and ACOX3) and CPP (DGAT1, CSN1S1, GOSR2, HERC6, and IGF1R) were identified as candidates. Gene ontology revealed six novel candidate genes (GMDS, E2F7, SIAH1, SLC24A4, LGMN, and ASS1) significantly associated with MU whose functions were in protein catabolism, urea cycle, ion transportation and N excretion. One novel candidate gene was identified in association with ECPU (MAP3K1) that is involved in post-transcriptional modification of proteins. The findings should be validated using a larger population of New Zealand grazing dairy cows.

The effects of gradual replacement of barley with oats on enteric methane emissions, rumen fermentation, milk production, and energy utilization in dairy cows

This study evaluated the effects of gradual replacement of barley with oats on enteric CH₄ emissions, rumen fermentation, diet digestibility, milk production, and energy utilization in dairy cows fed a grass silage-based diet. Sixteen lactating Nordic Red dairy cows received a total mixed ration [58:42 forage:concentrate on dry matter (DM) basis]. Grass silage (Phleum pratense) was the sole forage with canola meal (10% of diet DM) as a protein supplement. The effects of gradual replacement of barley with oats on DM basis were evaluated using a replicated 4 × 4 Latin square design with 21 d periods. The grain supplements (30% of diet DM) consisted of 100% barley, 67% barley and 33% oats, 33% barley and 67% oats, and 100% oats. In addition to intake, milk production, and digestibility measurements, CH₄ emissions were measured by the GreenFeed system (C-Lock Inc.). The energy metabolism was estimated from the gas exchange measurements recorded by the GreenFeed unit. The last 10 d of each period were used for recordings of gas exchanges, feed intake and milk production. Dry matter intake, body weight, milk yield, and energy-corrected milk yield were not affected by gradual replacement of barley with oats in the diet. Increased inclusion of oats linearly decreased CH₄ emissions from 467 to 445 g/d, and CH₄ intensity from 14.7 to 14.0 g/kg energy-corrected milk. In addition, the ratio of CH₄ to CO₂ decreased with increasing inclusion of oats in the diet. Digestibility of organic matter, neutral detergent fiber, and potentially digestible neutral detergent fiber decreased linearly with increasing inclusion of oats. Increased inclusion of oats linearly increased fecal energy from 121 to 133 MJ/d, whereas urinary energy and heat production were not affected by dietary treatment. This resulted in a linear decrease in metabolizable energy intake. However, increased levels of oat in the diet did not significantly affect energy balance or efficiency of metabolizable energy utilization for lactation. This study concludes that barley could be replaced with oats in the diet of dairy cows fed a grass silage-based diet to mitigate CH₄ emissions without having any adverse effects on productivity or energy balance. However, the effect of replacing barley with oats on CH₄ emissions is dependent on the differences between barley and oats in the concentrations of indigestible neutral detergent fiber and fat.

The use of an upgraded GreenFeed system and milk fatty acids to estimate energy balance in early-lactation cows

Measurements of energy balance (EB) require the use of respiration chambers, which are quite expensive and laborious. The GreenFeed (GF) system (C-Lock Inc.) has been developed to offer a less expensive, user friendly alternative. In this study, we used the GF system to estimate the EB of cows in early lactation and compared it with EB predicted from energy requirements for dairy cows in the Finnish feeding standards. We also evaluated the association between milk fatty acids and the GF estimated EB. The cows were fed the same grass silage but supplemented with either cereal grain or fibrous by-product concentrate. Cows were followed from 1 to 18 wk of lactation, and measurements of energy metabolism variables were taken. Data were subjected to ANOVA using the mixed model procedure of SAS (SAS Institute Inc.). The repeatability estimates of the gaseous exchanges from the GF were moderate to high, presenting an opportunity to use it for indirect calorimetry in EB estimates. Energy metabolism variables were not different between cows fed different concentrates. However, cows fed the grain concentrate produced more methane (24.0 MJ/d or 62.9 kJ/MJ of gross energy) from increased digestibility than cows fed the by-product concentrate (21.3 MJ/d or 56.5 kJ/MJ of gross energy). Nitrogen metabolism was also not different between the diets. Milk long-chain fatty acids displayed an inverse time course with EB and de novo fatty acids. There was good concordance (0.85) between EB predicted using energy requirements derived from the Finnish feed table and EB estimated by the GF system. In conclusion, the GF can accurately estimate EB in early-lactating dairy cows. However, more data are needed to further validate the system for a wide range of dietary conditions.

Interactions of amino acids and hormones regulate the balance between growth and milk protein synthesis in lactating rats fed diets differing in protein content

Insulin-like growth factor-I (IGF-I), growth hormone (GH), and prolactin (PRL) play important roles in milk protein synthesis, and their plasma concentrations were reported to be affected by dietary protein intake. To investigate the relationship between circulating amino acid (AA) and concentrations of these hormones, 18 Wistar rats aged 14 wk were assigned to a low (LP; 9% protein), standard (SP; 21% protein), or high-protein (HP; 35% protein) diet from parturition through day 15 of lactation. Plasma, liver, pituitary gland, skeletal muscle, and mammary gland samples were collected at the end of treatment. Circulating and hepatic IGF-I concentrations increased linearly with elevated dietary protein concentrations (P < 0.0001). Rats receiving the HP diet had higher circulating GH (P < 0.01) and pituitary PRL concentrations (P < 0.0001) but lower pituitary GH concentration (P < 0.0001) relative to those in rats receiving the LP and SP diets. Pearson correlation test performed on composed data across treatments showed that several circulating AAs were correlated with circulating and tissue concentrations of IGF-I, GH, and PRL. Multiple linear regression analyses identified Leu, Gln, Ala, Gly, and Arg as the main AAs associated with hormone responses (R2 = 0.37 ~ 0.80; P < 0.05). Rats fed the LP and HP diets had greater Igf1 and Ghr gene expression in skeletal muscle than those fed the SP diets (P < 0.01). However, LP treatment decreased Prlr mRNA abundance in mammary glands as compared with the SP and HP treatments (P < 0.05). The HP diets increased AA transporter expression (P < 0.01) but decreased mammalian target of rapamycin (P < 0.05) and 70 kDa ribosomal protein S6 kinase 1 (P < 0.01) phosphorylation in mammary glands as compared with the LP and SP diets. The results of the present study suggested that several circulating AAs mediated the effects of dietary protein supply on concentrations of IGF-I, GH, and PRL, which in turn altered the metabolism status in peripheral tissues including the lactating mammary glands.

The effects of rumen nitrogen balance on nutrient intake, nitrogen partitioning, and microbial protein synthesis in lactating dairy cows offered different dietary protein sources

The aim was to study the effects of rumen N balance (RNB), dietary protein source, and their interaction on feed intake, N partitioning, and rumen microbial crude protein (MCP) synthesis in lactating dairy cows. Twenty-four lactating Holstein cows were included in a replicated 4 × 4 Latin square experimental design comprising four 20-d periods, each with 12 d of adaptation to the experimental diets and 8 d of sampling. The dietary treatments followed a 2 × 2 factorial arrangement (i.e., 4 treatments) with 2 main protein sources [faba bean grain (FB) and SoyPass (SP; Beweka Kraftfutterwerk GmbH, Heilbronn, Germany)] offered at 2 dietary RNB levels each [0 g/kg of dry matter, DM (RNB0) and -3.2 g/kg of DM (RNB-)]. The RNB was calculated as the difference between dietary crude protein (CP) intake and the rumen outflow of undegraded feed CP and MCP and divided by 6.25. Composition of concentrate mixtures was adjusted to create diets with desired RNB levels. Each of these protein sources supplied ≥35% of total dietary CP. Both diets for each protein source were isoenergetic but differed in CP concentrations. The DM intake (kg/d) was lower for RNB- than for RNB0 in diets containing FB, whereas no differences were seen between the RNB levels for SP diets. The RNB- decreased N intake and urinary N excretion but increased milk N use efficiency in both FB and SP diets, with greater differences between the RNB levels for FB diets than for SP diets. Similarly, duodenal MCP synthesis (g/kg of digestible organic matter intake) estimated from purine derivatives in the urine was lower for RNB- than for RNB0 in FB diets but similar between the RNB levels in diets containing SP. Low RNB of approximately -65 g/d (approximately -3.2 g/kg of DM) in diets reduced feed intake, N balance, and performance in high-yielding dairy cows with possibly more pronounced effects in diets containing rapidly degradable protein sources.

Low dietary protein resilience is an indicator of the relative protein efficiency of individual dairy cows

Our objectives were to determine (1) the sources of variation in cow responses to dietary protein reduction, and (2) the association of low dietary protein resilience (LPR) with protein efficiency. Lactating Holstein cows in peak lactation (n = 166; 92 primiparous, 77 multiparous) with initial milk yield 41 ± 9.8 kg/d were fed high-protein (HP) or low-protein (LP) diets in 4-wk periods in a crossover design with half the cows fed LP first and half fed HP first. The study was repeated for 69 of these cows (42 primiparous, 27 multiparous) in late lactation. Low-protein diets were 14% crude protein (CP) in peak lactation and 13% CP in late lactation and were formulated to contain adequate rumen-degradable protein to maintain rumen function but inadequate rumen-undegradable protein for cows with average production in this study to maintain their production. High-protein diets were 18% CP in peak lactation and 16% CP in late lactation and contained extra expeller soybean meal to meet metabolizable protein requirements. Protein efficiency was defined as the protein captured in milk or in both milk and body tissues per unit of consumed protein. Low dietary protein resilience was calculated for each cow in peak and late lactation based on actual intake, production, and body weight measures. The ability of a cow to maintain total protein captured in milk and body gain when fed less protein varied considerably and the variation was mostly explained by a cow's captured protein per kilogram of metabolic body weight when fed HP, her parity, treatment sequence, and experiment. Protein efficiency was moderately repeatable across diets within lactation stage. Milk urea nitrogen was not associated with protein efficiency in individual cows within a diet and lactation stage. Cows with greater dietary protein resiliency (higher LPR) had similar protein efficiency on the HP diet as cows with lower LPR, but higher protein efficiency on the LP diet. In conclusion, cows generally maintained their protein efficiency rankings when switching diets between sufficient or insufficient protein; however, some high-producing cows are better able to maintain high production when fed less protein. We define this ability as LPR and suggest it might be useful for identifying cows that use protein more efficiently to enhance dairy sustainability.

The market for amino acids: understanding supply and demand of substrate for more efficient milk protein synthesis

For dairy production systems, nitrogen is an expensive nutrient and potentially harmful waste product. With three quarters of fed nitrogen ending up in the manure, significant research efforts have focused on understanding and mitigating lactating dairy cows’ nitrogen losses. Recent changes proposed to the Nutrient Requirement System for Dairy Cattle in the US include variable efficiencies of absorbed essential AA for milk protein production. This first separation from a purely substrate-based system, standing on the old limiting AA theory, recognizes the ability of the cow to alter the metabolism of AA. In this review we summarize a compelling amount of evidence suggesting that AA requirements for milk protein synthesis are based on a demand-driven system. Milk protein synthesis is governed at mammary level by a set of transduction pathways, including the mechanistic target of rapamycin complex 1 (mTORC1), the integrated stress response (ISR), and the unfolded protein response (UPR). In tight coordination, these pathways not only control the rate of milk protein synthesis, setting the demand for AA, but also manipulate cellular AA transport and even blood flow to the mammary glands, securing the supply of those needed nutrients. These transduction pathways, specifically mTORC1, sense specific AA, as well as other physiological signals, including insulin, the canonical indicator of energy status. Insulin plays a key role on mTORC1 signaling, controlling its activation, once AA have determined mTORC1 localization to the lysosomal membrane. Based on this molecular model, AA and insulin signals need to be tightly coordinated to maximize milk protein synthesis rate. The evidence in lactating dairy cows supports this model, in which insulin and glucogenic energy potentiate the effect of AA on milk protein synthesis. Incorporating the effect of specific signaling AA and the differential role of energy sources on utilization of absorbed AA for milk protein synthesis seems like the evident following step in nutrient requirement systems to further improve N efficiency in lactating dairy cow rations.

Effect of strategy for harvesting regrowth grass silage on performance in dairy cows

The objective of this study was to evaluate the effects of feeding lactating dairy cows with regrowth silages from different 2- and 3-cut harvesting systems on milk production, efficiency of N, and energy utilization. Thirty Nordic Red cows were offered 5 experimental diets containing regrowth silages, crimped barley, and canola meal in replicated incomplete 5 × 4 Latin squares with four 21-d periods consisting of 14 d of feed adaptation and 7 d of sampling. Four second-cut silage diets were examined in a 2 × 2 factorial arrangement, enabling evaluation of effect of harvest time of the early or late first cut on second-cut silages, short or long regrowth interval within second cut, and their interaction on dairy cow performance. The third-cut silage diet harvested from early first cut and short regrowth interval of second-cut ley was compared with the second-cut silage diets to evaluate the difference in dairy cow performance between second- and third-cut silages. Postponing the first cut and extending the regrowth interval decreased dry matter intake (DMI), energy-corrected milk (ECM) yield, nutrient digestibility, and urinary energy output, but improved N efficiency (milk N/N intake). Postponing the first cut also decreased the efficiency of metabolizable energy use for lactation, but increased CH₄ yield (CH₄/DMI). Extending the regrowth interval decreased feed efficiency (ECM/DMI) and increased CH₄ intensity (CH₄/ECM). Thus, feeding regrowth silages in 2- or 3-cut systems harvested after an early first cut and short regrowth interval promoted better dairy performance and feed intake, and higher efficiency of feed and energy utilization, but with poorer N efficiency. Feeding third-cut silage improve milk yield and feed efficiency compared with second-cut silages.

Grass silage pulp as a dietary component for high-yielding dairy cows

Green biorefineries provide novel opportunities to use the green biomass efficiently and utilize the ecosystem services provided by grasslands more widely. The effects of the inclusion of fractionated grass silage solid fraction (pulp) on feed intake, rumen fermentation, diet digestion and milk production in dairy cows were investigated. Pulp was separated from grass silage using a screw press simulating a green biorefinery. Partial removal of liquid from forage increased DM concentration from 220 to 432 g/kg and NDF from 589 to 709 g/kg DM while CP decreased from 144 to 107 g/kg DM. A feeding trial using an incomplete changeover design with 24 Nordic Red cows and two 3-week periods was conducted. The pulp replaced grass silage in the diet at 0 (P0), 25 (P25) and 50 (P50) percentage of total forage, which was fed ad libitum with 13 kg of concentrate for all treatments. The forage DM intake was highest on P25 (14.1 kg/day) while P0 and P50 did not differ from each other (13.2 and 13.0 kg/day, respectively). There were no differences between the treatments in rumen pH or ammonia N, but the proportion of acetate increased with increasing pulp inclusion. The digestibility was measured using acid insoluble ash and indigestible NDF (iNDF) as internal markers. Neither of the markers detected differences in NDF digestibility, but according to iNDF, apparent total tract organic matter digestibility decreased with increasing pulp inclusion. The cows maintained milk production at P25, but it showed some decline at P50 (energy-corrected milk at P0 and P25 was 39.8 kg/day while for P50, it was 38.5 kg/day, P = 0.056) and the milk protein yield significantly declined with higher pulp inclusion. Simultaneously, the nitrogen use efficiency in milk production increased. It seems that the fibrous grass-based fraction from a biorefinery process has potential to be used as a feed for ruminants.

Intake and feed utilization in two breeds of pregnant beef cows fed forages with high-fiber concentrations

Hereford and Charolais beef cows (n = 24 per breed) were used to study the effect of breed and to evaluate late-cut reed canarygrass (RC) and whole-crop oats plus urea (WCO) compared with late-cut timothy (TG) with respect to feed intake and digestibility, rumination time, fecal particle size (PS) distribution, N excretion, and ruminal microbial CP production (MCP). The TG and RC were cut at flowering and WCO at hard dough stage of maturity. Cows were group-housed, 6 groups per breed, and fed 3 diets ad libitum in 3 periods. The study was designed as two 3 × 3 Latin squares amalgamated to form a 3 × 6 rectangle for each breed. All data were statistically analyzed on group level. Indigestible NDF (iNDF) and urinary creatinine excretion were used as markers to estimate apparent diet digestibility and daily urine volume, respectively. Fecal PS distribution was determined by dry sieving, and ruminal MCP synthesis was estimated based on urinary output of purine derivatives. The TG diet had a higher apparent digestibility of OM and NDF (P < 0.001) than RC and WCO, which did not differ. The TG diet resulted in the greatest daily DMI, followed by WCO and RC (P < 0.001). Intake of NDF (NDFI, kg/d and % of BW) was greatest for TG, followed by RC and WCO (P < 0.001). Rumination time per kg DMI was longest for RC (P < 0.001), and RC and WCO resulted in longest rumination time per kg NDFI (P < 0.001). The WCO diet resulted in the largest geometric mean fecal PS and proportion of large particles and in the smallest proportion of small particles, whereas the opposite was found for RC, with TG being intermediate (P < 0.001). Intakes in kg per day were higher for Charolais than for Hereford (P = 0.002), but no breed effect was detected when intake was expressed in relation to BW. Charolais ruminated longer per kg NDFI corrected for BW (P = 0.02) and had smaller mean fecal PS (P = 0.049) than Hereford. Total N excretion was highest for RC and lowest for WCO (P < 0.001). The TG diet stimulated MCP production to a greater extent than RC and WCO (P < 0.001). The results indicate that late-cut RC and WCO could be suitable alternatives to late-cut TG for ad libitum feeding of early pregnant beef cows, and that intake was associated with cow BW, but not with breed. The variations in NDF and iNDF concentrations between forage diets were reflected in their effects on intake, rumination, apparent digestibility, and fecal PS.

Review: Alternative and novel feeds for ruminants: nutritive value, product quality and environmental aspects

Ruminant-based food production faces currently multiple challenges such as environmental emissions, climate change and accelerating food-feed-fuel competition for arable land. Therefore, more sustainable feed production is needed together with the exploitation of novel resources. In addition to numerous food industry (milling, sugar, starch, alcohol or plant oil) side streams already in use, new ones such as vegetable and fruit residues are explored, but their conservation is challenging and production often seasonal. In the temperate zones, lipid-rich camelina (Camelina sativa) expeller as an example of oilseed by-products has potential to enrich ruminant milk and meat fat with bioactive trans-11 18:1 and cis-9,trans-11 18:2 fatty acids and mitigate methane emissions. Regardless of the lower methionine content of alternative grain legume protein relative to soya bean meal (Glycine max), the lactation performance or the growth of ruminants fed faba beans (Vicia faba), peas (Pisum sativum) and lupins (Lupinus sp.) are comparable. Wood is the most abundant carbohydrate worldwide, but agroforestry approaches in ruminant nutrition are not common in the temperate areas. Untreated wood is poorly utilised by ruminants because of linkages between cellulose and lignin, but the utilisability can be improved by various processing methods. In the tropics, the leaves of fodder trees and shrubs (e.g. cassava (Manihot esculenta), Leucaena sp., Flemingia sp.) are good protein supplements for ruminants. A food-feed production system integrates the leaves and the by-products of on-farm food production to grass production in ruminant feeding. It can improve animal performance sustainably at smallholder farms. For larger-scale animal production, detoxified jatropha (Jatropha sp.) meal is a noteworthy alternative protein source. Globally, the advantages of single-cell protein (bacteria, yeast, fungi, microalgae) and aquatic biomass (seaweed, duckweed) over land crops are the independence of production from arable land and weather. The chemical composition of these feeds varies widely depending on the species and growth conditions. Microalgae have shown good potential both as lipid (e.g. Schizochytrium sp.) and protein supplements (e.g. Spirulina platensis) for ruminants. To conclude, various novel or underexploited feeds have potential to replace or supplement the traditional crops in ruminant rations. In the short-term, N-fixing grain legumes, oilseeds such as camelina and increased use of food and/or fuel industry by-products have the greatest potential to replace or supplement the traditional crops especially in the temperate zones. In the long-term, microalgae and duckweed of high-yield potential as well as wood industry by-products may become economically competitive feed options worldwide.

Effects of forage types on digestibility, methane emissions, and nitrogen utilization efficiency in two genotypes of hill ewes

Thirty-six nonpregnant hill ewes (18 pure Scottish Blackface and 18 Swaledale × Scottish Blackface) aged 18 mo and weighing 48 ± 4.8 kg were allocated to 3 forage treatments balanced for genotype and BW. Each genotype was offered 3 forages (pelleted ryegrass, fresh lowland grass, and fresh hill grass) ad libitum with 6 ewes for each of the 6 genotype × diet combination treatments. Pelleted ryegrass was sourced from a commercial supplier (Drygrass South Western Ltd, Burrington, UK). Fresh lowland grass was harvested daily in the morning from a third regrowth perennial ryegrass () sward. Fresh hill grass was harvested from a seminatural hill grassland every 2 d and stored in plastic bags at 4 to 5°C until offered. The animals were individually housed in pens and offered experimental diets for 14 d before being transferred to 6 individual respiration chambers for a further 4 d, during which feed intake, fecal and urine outputs, and CH emissions were measured. There was no interaction between genotype and forage types on any variable measured. In a comparison of effects of the 3 forages, pelleted ryegrass had the greatest ( < 0.001) values in DMI, GE intake, CH emissions, N intake (NI), and fecal N (FN), urine N (UN), and manure N (MN) outputs, whereas hill grass had the lowest ( < 0.001) values in DMI, energy (GE, DE, and ME) intake, CH emissions, NI, UN, and MN. However, pelleted ryegrass had the lowest ratio in CH emissions per unit DMI ( = 0.022) or GE intake ( = 0.026) or UN excretion as a proportion of NI or MN ( < 0.001). Lowland grass had a greater ( < 0.001) digestibility of DM, OM, CP, NDF, ADF, and GE and a greater ( < 0.001) ME:GE ratio or retained N:NI ratio than pelleted ryegrass and hill grass. Genotypes of sheep had no effect on any variable in feed intake, digestibility, CH emissions, or N utilization. The CH conversion factors (CH energy/GE) for pelleted ryegrass, lowland grass, and hill grass were 4.4, 5.7, and 5.6%, respectively. All data were then pooled to develop regression equations between CH and DMI or between N excretions (FN, UN, and MN) and NI. Methane emissions and N excretions were positively related to DMI and NI ( < 0.001), respectively. However, increasing DMI could reduce CH emissions per kilogram DMI. These equations add new information in predicting enteric CH emissions and N utilization efficiency and can be used to quantify the environmental footprint of hill sheep production systems.

Prediction of fecal nitrogen and phosphorus excretion for Chinese Holstein lactating dairy cows

Mathematical models for predicting nitrogen and phosphorus excretion play a key role in manure application and environment monitoring. An analysis for prediction of fecal nitrogen (FN, g/d) and fecal phosphorus (FP, g/d) excretion for Chinese Holstein lactating dairy cows was conducted using a data set from 15 dairy farms in northern China. The whole independent-variable data set, obtained with questionnaires, consisted of 110 sets of average diet nutrient compositions, including DMI (kg/d), CP content (% DM), OM intake (OMI, kg/d), nitrogen intake (NI, g/d), and phosphorus intake (PI, g/d), and animal characteristics, including average days in milk (DIM, d), average milk yield (MY, kg/d), and average BW (kg). In addition, 110 fecal samples in total were collected to analyze FN and FP excretions, which were considered dependent variables of prediction equations. Correlations between diet and animal variables were examined, and several variable subpools were derived that were used to develop equations to predict FN and FP excretions by stepwise regression analysis. The results showed that among all variables, OMI was the best predictor for FN excretion (root-mean-square prediction error [RMSPE] = 9.58%, = 0.70), followed by NI (RMSPE = 10.19%, = 0.67). However, when both DMI and CP were used as independent variables, the equation showed more accurate prediction for FN excretion (RMSPE = 8.55%, = 0.77) in comparison with univariate prediction equations. Simultaneously, PI was the best predictor of FP excretion (RMSPE = 10.28%, = 0.67). Evaluation results using 3-fold cross validation and comparison with extant equations indicated that the proposed equations were accurate with low prediction errors, which could be recommended for use to estimate FN and FP excretions from Chinese Holstein lactating dairy cows.

Partitioning of dietary nitrogen in response to feeding cereal grain supplements to dairy cows during four periods of an extended lactation

Holstein–Friesian dairy cows managed in pasture-based systems are capable of lactating for considerably longer than the traditional 300 days. However, the partitioning of dietary nutrients in the second 300 days of an extended lactation has been shown to be different from that in the first 300 days. The partitioning of dietary nitrogen (N) was investigated using two groups of eight Holstein cows in four experimental periods of 6 days, at 110, 270, 450 and 560 days in milk (DIM). During each period, cows were housed in individual stalls where N intake and output were measured. Cows in a control group received a forage-based diet ad libitum, whereas cows in a second group received 5 kg DM of cereal grain and the basal forage diet ad libitum. N intake was positively related to outputs of milk N, urinary N and faecal N, and negatively to N-use efficiency (NUE). DIM was positively related to output of urinary N and negatively related to NUE and outputs of milk N and faecal N. The partitioning of N in the second year of an extended lactation was different from that in the first year, meaning that the partitioning of N reported for cows up to 300 DIM cannot be used to accurately predict the partitioning of N in cows beyond 300 DIM. Adding grain to the diet increased total nitrogen intake but decreased NUE. However, it is plausible for the addition of cereal grain to the diet of dairy cows to increase NUE, but only when the concentration of dietary crude protein decreases and any increase in dry-matter intake is small, such that total nitrogen intake is decreased.

Effects of concentrate crude protein content on nutrient digestibility, energy utilization, and methane emissions in lactating dairy cows fed fresh-cut perennial grass

Although many studies have investigated mitigation strategies for methane (CH₄) output from dairy cows fed a wide variety of diets, research on the effects of concentrate crude protein (CP) content on CH₄ emissions from dairy cows offered fresh grass is limited. The present study was designed to evaluate the effects of cow genotype and concentrate CP level on nutrient digestibility, energy utilization, and CH₄ emissions in dairy cows offered fresh-grass diets. Twelve multiparous lactating dairy cows (6 Holstein and 6 Holstein × Swedish Red) were blocked into 3 groups for each breed and assigned to a low-, medium-, or high-CP concentrate diet [14.1, 16.1, and 18.1% CP on a dry matter (DM) basis, respectively], in a 3-period changeover study (25d per period). Total diets contained (DM basis) 32.8% concentrates and 67.2% perennial ryegrass, which was harvested daily. All measurements were undertaken during the final 6d of each period: digestibility measurements for 6d and calorimetric measurements in respiration chambers for 3d. Feed intake and milk production data were reported in a previous paper. We observed no significant interaction between concentrate CP level and cow genotype on any parameter. Concentrate CP level had no significant effect on any energy utilization parameter, except for urinary energy output, which was positively related to concentrate CP level. Similarly, concentrate CP content had no effect on CH₄ emission (g/d), CH₄ per kg feed intake, or nutrient digestibility. Cross breeding of Holstein cows significantly reduced gross energy, digestible energy, and metabolizable energy intake, heat production, and milk energy output. However, cow genotype had no significant effect on energy utilization efficiency or CH₄ parameters. Furthermore, the present study yielded a value for gross energy lost as CH₄ (5.6%) on fresh grass-based diets that was lower than the widely accepted value of 6.5%. The present findings indicate that reducing concentrate CP content from 18.1 to 14.1% may not be a successful way of alleviating CH₄ emissions from lactating dairy cows offered good-quality fresh grass, but grazing cows could be offered a low-CP concentrate without compromising energy utilization efficiency. Further research is needed to investigate whether larger differences in dietary CP content may yield positive results.

Short communication: Evaluation of nitrogen excretion equations from cattle

Nitrogen excretion in dairy manure is a precursor for N2O and NH3 formation in livestock housing, manure storage facilities, and after manure is applied to land. Nitrous oxide is a major contributor to greenhouse gas emissions, and reducing N output from dairy production facilities can reduce the amount of anthropogenic N2O entering the atmosphere. The objective of the study was to conduct a comprehensive evaluation of extant prediction models for N excretion in feces and urine using extensive literature data. A total of 45 N excretion equations were evaluated for lactating cows, heifers, and nonlactating cows and steers. These equations were evaluated with 215 treatment means from 69 published studies collected over 20 yr from 1995 to 2015. Two evaluation methods were used: the root mean square prediction error and the concordance correlation coefficient. Equations constructed using a more rigorous development process fared better than older extant equations. Equations for heifers and nonlactating cows had greater error of prediction compared with equations used for lactating cows. This could be due to limited amount of data available for construction and evaluation of the equations. Urinary N equations had greater prediction errors than other forms of excretion, possibly due to high variability in urinary N excretion and challenges in urine collection. Fecal N equations had low error bias and reached an acceptable level of precision and accuracy.

Dairy cow responses to graded levels of rapeseed and soya bean expeller supplementation on a red clover/grass silage-based diet

The effects of rapeseed and soya bean expeller (SBE) supplementation on digestion and milk production responses in dairy cows were investigated in an incomplete Latin square design using five cows and four 3-week periods. The experimental diets consisted of five concentrate treatments fed at a rate of 9 kg/day: a mixture of barley and oats, which was replaced with rapeseed or SBE at two levels (CP concentration (g/kg dry matter (DM)) of 130 for the control concentrate and 180 and 230 for the two protein supplemented levels). A mixture of grass and red clover silage (1:1) was fed ad libitum and it had a CP concentration of 157 g/kg DM. Supply of nutrients to the lower tract was measured using the omasal canal sampling technique, and total digestion from total faecal collection. Protein supplementation increased omasal canal amino acid (AA) flows and plasma concentrations of AA, and was also reflected as increased milk production. However, N use efficiency (NUE) decreased with increased protein supplementation. Rapeseed expeller (RSE) tended to increase silage DM intake and elicited higher milk production responses compared with SBE and also resulted in a higher NUE. The differences between the protein supplements in nitrogen metabolism were relatively small, for example, there were no differences in the efficiency of microbial protein synthesis or omasal canal flows of nitrogenous components between them, but plasma methionine concentration was lower for soya bean-fed cows at the high CP level in particular. The lower milk protein production responses to SBE than to RSE supplementation were at least partly caused by increased silage DM and by the lower methionine supply, which may further have been amplified by the use of red clover in the basal diet. Although feed intake, diet digestion, AA supply and milk production were all consistently improved by protein supplementation, there was a simultaneous decrease in NUE. In the current study, the milk protein production increased only 9% and energy-corrected milk production by 7% when high level of protein supplementation (on average 2.9 kg DM/day) was compared with the control diet without protein supplementation showing that dairy production could be sustained at a high level even without external protein supplements, at least in the short term. The economic and environmental aspects need to be carefully evaluated when decisions about protein supplementation for dairy cows are taken.

Evaluation of between-cow variation in milk urea and rumen ammonia nitrogen concentrations and the association with nitrogen utilization and diet digestibility in lactating cows

Concentrations of milk urea N (MUN) are influenced by dietary crude protein concentration and intake and could therefore be used as a biomarker of the efficiency of N utilization for milk production (milk N/N intake; MNE) in lactating cows. In the present investigation, data from milk-production trials (production data set; n=1,804 cow/period observations from 21 change-over studies) and metabolic studies involving measurements of nutrient flow at the omasum in lactating cows (flow data set; n=450 cow/period observations from 29 studies) were used to evaluate the influence of between-cow variation on the relationship of MUN with MNE, urinary N (UN) output, and diet digestibility. All measurements were made on cows fed diets based on grass silage supplemented with a range of protein supplements. Data were analyzed by mixed-model regression analysis with diet within experiment and period within experiment as random effects, allowing the effect of diet and period to be excluded. Between-cow coefficient of variation in MUN concentration and MNE was 0.13 and 0.07 in the production data set and 0.11 and 0.08 in the flow data set, respectively. Based on residual variance, the best model for predicting MNE developed from the production data set was MNE (g/kg)=238 + 7.0 × milk yield (MY; kg/d) - 0.064 × MY(2) - 2.7 × MUN (mg/dL) - 0.10 body weight (kg). For the flow data set, including both MUN and rumen ammonia N concentration with MY in the model accounted for more variation in MNE than when either term was used with MY alone. The best model for predicting UN excretion developed from the production data set (n=443) was UN (g/d)=-29 + 4.3 × dry matter intake (kg/d) + 4.3 × MUN + 0.14 × body weight. Between-cow variation had a smaller influence on the association of MUN with MNE and UN output than published estimates of these relationships based on treatment means, in which differences in MUN generally arise from variation in dietary crude protein concentration. For the flow data set, between-cow variation in MUN and rumen ammonia N concentrations was positively associated with total-tract organic matter digestibility. In conclusion, evaluation of phenotypic variation in MUN indicated that between-cow variation in MUN had a smaller effect on MNE compared with published responses of MUN to dietary crude protein concentration, suggesting that a closer control over diet composition relative to requirements has greater potential to improve MNE and lower UN on farm than genetic selection.

Predicting nitrogen excretion from cattle

Manure nitrogen (N) from cattle production facilities can lead to negative environmental effects, such as contribution to greenhouse gas emissions, leaching and runoff to aqueous ecosystems leading to eutrophication, and acid rain. To mitigate these effects and to improve the efficiency of N use, accurate prediction of N excretion and secretions are required. A genetic algorithm was implemented to select models to predict fecal, urinary, and total manure N excretions, and milk N secretions from 3 classes of animals: lactating dairy cows, heifers and dry cows, and steers. Two tiers of model classes were developed for each category of animals based on model input requirements. A total of 6 models for heifers and dry cows and steers and an additional 2 models for lactating dairy cattle were developed. Evaluation of the models using K-fold cross validation based on all data and using the most recent 6 yr of data showed better prediction for total manure N and fecal N compared with urinary N excretion, which was the most variable response in the database. Compared with extant models from the literature, the models developed in this study resulted in a significant improvement in prediction error for fecal and urinary N excretions from lactating cows. For total manure production by lactating cows, extant and new models were comparable in their prediction ability. Both proposed and extant models performed better than the prediction methods used by the US Environmental Protection Agency for the national inventory of greenhouse gases. Therefore, the proposed models are recommended for use in estimation of manure N from various classes of animals.

Effects of alfalfa silage storage structure and roasting corn on ruminal digestion and microbial CP synthesis in lactating dairy cows

The objective of this experiment was to quantify the effects of unroasted or roasted ground-shelled corn (GSC), when fed with alfalfa ensiled in bag, bunker, or O2-limiting tower silos on ruminal digestion and microbial CP synthesis in lactating dairy cows. The roasted corn was heat-treated in a propane-fired roasting system. Alfalfa was harvested as second cutting from fields with regrowth of the same maturity. A portion of each field was allotted to each silo. The diets with 3 × 2 factorial arrangement of treatments were fed to six multiparous rumen-cannulated Holstein cows in a cyclic change-over design with five 21-day periods. Experimental diets were comparable and averaged (on dry matter (DM) basis): 410 g/kg alfalfa silage (AS), 150 g/kg corn silage, 350 g/kg GSC, 50 g/kg soybean meal, 40 g/kg roasted soybeans, 177 g/kg CP, 264 g/kg NDF and 250 g/kg starch. Nutrient flow was quantified by the omasal sampling technique with use of three markers (Co, Yb and indigestible NDF). Continuous infusion of 10% atom excess (15NH4)2SO4 was used to label microbial CP. None of the interactions between storage structure of dietary AS and corn type were significant. DM intake was not different among dietary treatments, averaging 24.5 kg/day across diets. Means of ADF digested in the rumen for cows fed diets with AS from bag, bunker and O2-limiting tower silo were 2.1, 1.7 and 2.1 kg/day, respectively, and was lower in cows fed AS from the bunker silo. This response may partly be a reflection of the higher intake of ADF by cows fed AS ensiled in the O2-limiting tower silo compared with the bunker. There was a slightly greater supply of fermentable substrates for cows fed diets with roasted compared with unroasted GSC. The small increases in yield of milk protein and lactose observed in the previous production trial in cows fed diets containing roasted corn may have occurred because of greater supply of fermentable substrates.

Effect of niacin supplementation on digestibility, nitrogen utilisation and milk and blood variables in lactating dairy cows fed a diet with a negative rumen nitrogen balance

The aim of the present experiment was to determine if a niacin supplementation of 6 g/d to lactating dairy cow diets can compensate negative effects of a rumen nitrogen balance (RNB) deficit. A total of nine ruminally and duodenally fistulated lactating multiparous German Holstein cows were successively assigned to one of three diets consisting of 10 kg maize silage (dry matter [DM] basis) and 7 kg DM concentrate: Diet RNB- (n = 6) with energy and utilisable crude protein at the duodenum (uCP) according to the average requirement of the animals but with a negative RNB (-0.41 g N/MJ metabolisable energy [ME]); Diet RNB0 (n = 7) with energy, uCP and a RNB (0.08 g N/MJ ME) according to the average requirement of the animals and, finally, Diet NA (n = 5), which was the same diet as RNB-, but supplemented with 6 g niacin/d. Samples of milk were taken on two consecutive days, blood samples were taken on one day pre- and post-feeding and faeces and urine were collected completely over five consecutive days. The negative RNB reduced milk and blood urea content and apparent total tract digestibility of DM, organic matter (OM) and neutral detergent fibre (NDF). Also N excretion with urine, the total N excreted with urine and faeces and the N balance were reduced when the RNB was negative. Supplementation of niacin elevated plasma glucose concentration after feeding and the N balance increased. Supplementing the diet with a negative RNB with niacin led to a more efficient use of dietary N thereby avoiding the negative effects of the negative RNB on the digestibility of DM, OM and NDF.