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Nitrogen (N) excretion from livestock production systems is of significant environmental concern; however, few studies have investigated the effect of dietary CP concentration on N utilisation efficiency at different stages of lactation, and the interaction between dietary CP levels and stages of lactation on N utilisation. Holstein-Friesian dairy cows (12 primiparous and 12 multiparous) used in the present study were selected from a larger group of cows involved in a whole-lactation study designed to examine the effect of dietary CP concentration on milk production and N excretion rates at different stages of lactation. The total diet CP concentrations evaluated were 114 (low CP), 144 (medium CP) and 173 (high CP) g/kg DM, with diets containing (g/kg DM) 550 concentrates, 270 grass silage and 180 maize silage. During early (70-80 days), mid- (150-160 days) and late (230-240 days) lactation, the same 24 animals were transferred from the main cow house to metabolism units for measurements of feed intake, milk production and faeces and urine outputs. Diet had no effect on BW, body condition score, or milk fat, protein or lactose concentration, but DM intake, milk yield and digestibilities of DM, energy and N increased with increasing diet CP concentration. The effect of diet on milk yield was largely due to differences between the low and medium CP diets. Increasing dietary CP concentration significantly increased urine N/N intake and urine N/manure N, and decreased faecal N/N intake, milk N/N intake and manure N/N intake. Although increasing dietary CP level significantly increased urine N/milk yield and manure N/milk yield, differences in these two variables between low and medium CP diets were not significant. There was no significant interaction between CP level and stage of lactation on any N utilisation variable, indicating that the effects of CP concentration on these variables were similar between stages of lactation. These results demonstrated that a decrease in dietary CP concentration from high (173 g/kg DM) to medium level (144 g/kg DM) may be appropriate for Holstein-Friesian dairy cow to maintain milk production efficiency, whilst reducing both urine N and manure N as a proportion of N intake or milk production.

Improving nitrogen use efficiency (NUE) at both the individual cow and the herd level has become a key target in dairy production systems, for both environmental and economic reasons. Cost-effective and large-scale phenotyping methods are required to improve NUE through genetic selection and by feeding and management strategies. The aim of this study was to evaluate the possibility of using mid-infrared (MIR) spectra of milk to predict individual dairy cow NUE during early lactation. Data were collected from 129 Holstein cows, from calving until 50 d in milk, in 3 research herds (Denmark, Ireland, and the UK). In 2 of the herds, diets were designed to challenge cows metabolically, whereas a diet reflecting local management practices was offered in the third herd. Nitrogen intake (kg/d) and nitrogen excreted in milk (kg/d) were calculated daily. Nitrogen use efficiency was calculated as the ratio between nitrogen in milk and nitrogen intake, and expressed as a percentage. Individual daily values for NUE ranged from 9.7 to 81.7%, with an average of 36.9% and standard deviation of 10.4%. Milk MIR spectra were recorded twice weekly and were standardized into a common format to avoid bias between apparatus or sampling periods. Regression models predicting NUE using milk MIR spectra were developed on 1,034 observations using partial least squares or support vector machines regression methods. The models were then evaluated through (1) a cross-validation using 10 subsets, (2) a cow validation excluding 25% of the cows to be used as a validation set, and (3) a diet validation excluding each of the diets one by one to be used as validation sets. The best statistical performances were obtained when using the support vector machines method. Inclusion of milk yield and lactation number as predictors, in combination with the spectra, also improved the calibration. In cross-validation, the best model predicted NUE with a coefficient of determination of cross-validation of 0.74 and a relative error of 14%, which is suitable to discriminate between low- and high-NUE cows. When performing the cow validation, the relative error remained at 14%, and during the diet validation the relative error ranged from 12 to 34%. In the diet validation, the models showed a lack of robustness, demonstrating difficulties in predicting NUE for diets and for samples that were not represented in the calibration data set. Hence, a need exists to integrate more data in the models to cover a maximum of variability regarding breeds, diets, lactation stages, management practices, seasons, MIR instruments, and geographic regions. Although the model needs to be validated and improved for use in routine conditions, these preliminary results showed that it was possible to obtain information on NUE through milk MIR spectra. This could potentially allow large-scale predictions to aid both further genetic and genomic studies, and the development of farm management tools.

Twenty 5-mo-old Holstein cattle (10 steers and 10 heifers) were selected from a dairy herd for a 28 d study of enteric methane emissions and energy utilization. The cattle were offered a completely mixed diet with grass silage and concentrates (0.45 and 0.55, DM basis, respectively). They were housed as a single group in cubicle accommodation for the fi rst 20 d, transferred to metabolism units for 3 d, and subsequently housed in indirect open-circuit respiration calorimeter chambers for next 5 d with measurements of feed intake, feces and urine outputs, and gaseous exchange. There were no signifi cant differences (P > 0.05) between the 2 groups in terms of animal performance (feed intake, BW, or BW gain), energy metabolism (energy intake, energy outputs, or energy use effi ciency), or methane emission rates (total methane emissions expressed on feed intake or energy intake basis). Therefore, the data from the 2 groups were pooled to develop a range of relationships between inputs and outputs. The regression of energy balance or heat production against ME intake (r 2 = 0.85; P < 0.001) indicated a NE m of 0.57MJ/kg BW 0.75 , which is greater than reported for adult dairy cattle. The methane energy output was found to be 0.068 of GE intake when the intercept was omitted from the linear equation (r 2 = 0.73; P < 0.001), which is greater than the commonly accepted value (0.065) for adult cattle used for development of methane emission inventories for dairy and beef production systems. These data can add useful information, as there is little information available on measurements of maintenance energy requirement or methane emissions in young stock (6 mo old) of the current high-yielding dairy cattle. The use of these data can potentially improve the accuracy of prediction of energy requirement and methane emissions for dairy and beef production systems in these dietary conditions.

Milk responses to dietary change are influenced by the relative production level, that is, the distance between observed production and potential production. The closer the animal is to its potential, the smaller the expected response is to extra nutrients. Therefore, the aim of this work was to provide a method to quantify cow potential, to estimate subsequent responses to changes in nutrient supply. The observed efficiencies in net energy for lactation (NEL) and metabolizable protein (MP) are proposed as a basis to estimate the relative production level of the animal. The rationale for using NEL and MP efficiency (ratios of milk energy yield/NEL above maintenance supply and milk protein yield/MP above maintenance supply) builds on the uniformity of the observed relationships between size of the milk responses and extra NEL, supply and MP supply, when centered on a given efficiency. From there, a pivot nutritional situation where MP and NEL efficiency are 0.67 and 1.00, respectively, was defined, from winch milk responses could be derived across animals varying in production potential. An implicit assumption of using response equations centered on reference efficiency pivots is that the size of the response to a fixed change in nutrient supply, relative to the pivot, is identical for animals with different production capacities. The proposed approach was evaluated with 2 independent data sets, where different dietary treatments were applied during the whole lactation. In these data sets, MP and NEL above maintenance supply were calculated weekly using the recently updated INRA Systali feed units system. Differences in NEL and MP supply above maintenance between the extreme dietary treatments were large, on average 667 g of MP/d and 13 MJ of NEL/d (3.11 Mcal/d) in the first data set. and 513 g of MP/d and 29 MJ of NEL/d (6.93 Mcal/d) for the second data set. Milk energy yield and milk component yields were predicted with root mean square prediction errors between 7.6 and 13.5% and concordance correlation coefficients between 0.784 and 0.934, respectively. Assessed by the Akaike's information criterion, significant: differences existed in the accuracy of prediction for milk energy yield and milk component yields between stages of lactation. However, the effects of stage of lactation were not consistent between data sets and, for most of the predicted variables, relatively small. We concluded that the pivot concept can be used to predict milk energy yield and milk component; yields responses to dietary change with a good accuracy for diets that are substantially different and across all stages of lactation.

There is increasing interest in the use of continuous housing systems for dairy cows, with various reasons put forward to advocate such systems. However, the welfare of dairy cows is typically perceived to be better within pasture-based systems, although such judgements are often not scientifically based. The aim of this review was to interrogate the existing scientific literature to compare the welfare, including health, of dairy cows in continuously housed and pasture-based systems. Although summarising existing work, knowledge gaps and directions for future research are also identified. The scope of the review is broad, examining relevant topics under three main headings; health, behaviour and physiology. Regarding health, cows on pasture-based systems had lower levels of lameness, hoof pathologies, hock lesions, mastitis, uterine disease and mortality compared with cows on continuously housed systems. Pasture access also had benefits for dairy cow behaviour, in terms of grazing, improved lying/resting times and lower levels of aggression. Moreover, when given the choice between pasture and indoor housing, cows showed an overall preference for pasture, particularly at night. However, the review highlighted the need for a deeper understanding of cow preference and behaviour. Potential areas for concern within pasture-based systems included physiological indicators of more severe negative energy balance, and in some situations, the potential for compromised welfare with exposure to unpredictable weather conditions. In summary, the results from this review highlight that there remain considerable animal welfare benefits from incorporating pasture access into dairy production systems.

In the UK, dairy cows are increasingly housed at night throughout the grazing season. However, there is limited information on cow performance and the impact on labour requirements when a forage supplement is offered during housing at night throughout the entire grazing season. The effects of housing at night were studied in two experiments, in which two treatments were compared. On treatment part-grazing (PG), dairy cows were given access to grazing by day and were offered grass silage while housed at night, and, on treatment continuous grazing (CG), dairy cows were given access to grazing both by day and by night. Experiments 1 (138-d duration) and 2 (127-d duration) involved sixty (primiparous) and seventy-six (primiparous and multiparous) Holstein-Friesian dairy cows respectively. Concentrates were offered during milking at 4·0 and 3·0 kg per cow per day in Experiments 1 and 2 respectively. In Experiment 1, total milk output was significantly higher with treatment PG than treatment CG (P

This review paper examines a number of the challenges of pasture-based dairy systems. Ensuring adequate nutrient intakes of highyielding dairy cows within grazing systems is one of the key challenges being faced by many dairy farmers. Options examined to increase nutrient intakes include: increasing herbage allowances, manipulating sward structure, modifying herbage composition, and the use of both forage and concentrate supplements. The potential to achieve high levels of animal performance with grazed grass combined with high levels of concentrate supplementation is examined, while forage supplements appear to offer much less scope by which to increase nutrient intakes. Low levels of herbage utilization provide another challenge on many farms, with options to extend the grazing season and to improve early-season forage utilization examined. The results of a whole systems approach to achieving high total nutrient intakes with grassland-based systems are highlighted. The potential to improve the sustainability of dairy systems through breed substitution and by identifying more appropriate strains of Holstein animals for use within grazing systems is also examined. A number of environmental challenges associated with grazing systems together with possible opportunities to reduce their impact are highlighted. These include reducing inputs of inorganic fertilizer nitrogen, reducing the crude protein content of concentrate feedstuffs offered during grazing, and reducing the phosphorus content of dairy cow diets. Key words: Dairy cows, grazing, herbage utilization, dairy breeds, environment

Two experiments were conducted to examine the effect of two winter feeding systems on the performance of dairy cows in early lactation. Experiments 1 (144 d duration) and 2 (146 d duration) involved sixty-four (primiparous) and eighty-six (primiparous and multiparous) Holstein Friesian dairy cows respectively. Rations offered comprised grass silage, maize silage [0·26–0·29 of forage dry matter (DM)] and concentrates (10–12 kg d−1). With the complete diet (treatment CD), the forage and concentrate components were mixed using a complete diet mixer wagon, and offered daily in the form of a ‘complete diet’. With the easy feed (treatment EF), the dairy cows were offered the forage component of the ration twice weekly in whole blocks, in quantities sufficient for the following 3- or 4-d period, while the concentrate component of the diet was offered via electronic out-of-parlour feeding stations. Total DM intakes were similar, namely 17·6 and 17·0 kg d−1 (Experiment 1) and 18·7 and 18·5 kg d−1 (Experiment 2), for treatments CD and EF respectively. Feeding system had no significant effect on milk yield, milk fat or milk protein content, or on end of study indices of body tissue reserves in either experiment (P > 0·05). Similarly, feeding system had no significant effect on the digestibility of the ration measured in Experiment 2 (P > 0·05). Feeding times associated with each component of the two feeding systems were measured, and these were then used to calculate total feeding time for a 97-cow dairy herd. Calculated feeding times for this herd were 209·3 and 156·0 min week−1 for treatments CD and EF respectively.

It is well established that the genetic merit of the Holstein-Friesian dairy cow for milk production has increased over the past 20 years. Previous studies have examined the effect of feeding system on indices of body tissue reserves of medium genetic merit Holstein-Friesian dairy cows. The aim of the current study was to examine the weight and concentration of body components in high genetic merit Holstein-Friesian dairy cows, managed on four different grassland-based feeding regimes, using direct measures of body composition. Results indicate that there was no significant effect of different grassland-based feeding regimes on the weight or composition of body components of high genetic merit cows. Therefore, high levels of cow performance can be sustained from very different grassland-based systems of milk production without having a detrimental effect on body tissue reserves.

The effects of level of concentrate supplementation on the response of dairy cows to grass silage-based diets containing a constant proportion of fodder beet were examined. Forty Holstein-Friesian dairy cows of mixed parity were used in a 2 × 5 factorial design experiment. Two basal diet types [grass silage alone or grass silage mixed with fodder beet in a 70:30 dry matter (DM) ratio] were offered ad libitum, and the effects of five levels of concentrate supplementation (mean = 3·0, 5·3, 7·5, 9·8 and 12·0 kg DM per cow d−1) were examined. Concentrate supplements were offered via an out-of-parlour feeding system. These treatments were examined in a three-period (period length = 4 weeks) partially balanced changeover design experiment. Fodder beet inclusion had no significant effect on the estimated metabolizable energy (ME) concentration of the ration (P > 0·001). Total DM intake, estimated ME intake, milk yield, milk protein content and milk energy output all showed significant linear increases with increasing level of concentrate inclusion (P 0·05), while increasing milk protein content and milk energy output (P ≤ 0·05). Milk energy output, as a proportion of estimated ME intake, was significantly (P

Two experiments were carried out in consecutive years to examine the influence of cutting date and restricting fermentation by carboxylic acid treatment on the nutrient intake from grass silage by beef cattle. In year 1, four cutting dates during July and August after a primary growth harvest and, in year 2, five cutting dates of primary growth between mid-May and early July were examined. Herbage was ensiled either untreated or treated with high levels of acid additive ('Maxgrass', mean 8.6 1 t(-1)). Ninety-six (year 1) or forty-eight (year 2) continental cross steers were used in partially balanced changeover design experiments with each silage type either unsupplemented or supplemented with 4.5 (year 1) or 5.5 (year 2) kg concentrates head(-1) d(-1). Silage digestibility declined significantly between initial and final harvest dates (P < 0.001), whereas silage dry-matter (DM) and digestible energy (DE) intakes were significantly higher in the initial compared with final harvest dates in both years of the study (P < 0.01). Similarly, silage DM and DE intakes, and total DM intakes, of acid-treated and unsupplemented silages were greater than those of untreated and concentrate supplemented silages, respectively (P < 0.001). The results indicate that earlier cutting dates, and addition of acid to herbage before ensiling, can increase silage DM intake by beef cattle.

The development of production systems, which allow increased nutrient intakes to be achieved, is a key issue in the management of high genetic merit dairy cows. Consequently, forty high genetic merit autumn calving dairy cows (PTA95fat + protein = 38.2 kg) were managed on either a ‘high forage (HF)’ or ‘high concentrate (HC)’ based system of milk production for the first 305 days of lactation, with the study encompassing both the indoor winter and outdoor summer grazing periods. System HF involved a high feed value silage, a lax grazing regime, and a low concentrate input (842 kg DM), while system HC involved a medium feed value silage, a tighter grazing regime and a higher concentrate input (2456 kg DM). Total milk outputs with each of systems HF and HC were 7854 and 8640 kg respectively (P0.05), although fertility with both systems was poor. There were no obvious reasons for the poor fertility noted in this trial.

Twenty-eight high genetic merit and 32 medium genetic merit Holstein/Friesian dairy cows with Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein) of 43·3 and 1·0 kg respectively, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment consisting of eight treatments. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), while the forage component of the diet was grass silage. Diets were offered ad libitum in the form of a complete diet. Animals remained on these concentrate regimes for a mean of 84·7 days before completing a standard 98-day grazing period. At pasture, cows received either 5·0 or 6·0 kg concentrate daily according to turnout date. There were no significant genotype×nutrition interactions for any of the variables examined during either the indoor feeding or post-turnout grazing periods (PPPPPPP>0·05), while high merit cows continued to have higher outputs of milk and milk constituents (P

Sixty Holstein/Friesian dairy cows, 28 of high genetic merit and 32 of medium genetic merit, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment. High and medium merit animals had Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 43·3 kg and 1·0 kg respectively. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), with the remainder of the diet being grass silage. During this milk production trial, 24 of these animals, 12 from each genetic merit, representing three animals from each concentrate treatment, were subject to ration digestibility, and nitrogen and energy utilization studies. In addition, the efficiency of energy utilization during the milk production trial was calculated.There were no genotype×concentrate level interactions for any of the variables measured (P>0·05). Neither genetic merit nor concentrate proportion in the diet influenced the digestibility of either the DM or energy components of the ration (P>0·05). When expressed as a proportion of nitrogen intake, medium merit cows exhibited a higher urinary nitrogen output and a lower milk nitrogen output than the high merit cows. Methane energy output, when expressed as a proportion of gross energy intake, was higher for the medium than high merit cows (PPl), were affected by either cow genotype or concentrate proportion in the diet (P>0·05). However when kl was calculated using the production data from the milk production trial the high merit cows were found to have significantly higher kl values than the medium merit cows (0·64 v. 0·59, Pl tended to fall with increasing proportion of concentrate in the ration (P

A two period, partially balanced change-over design study, using 12 steers (416 sd 34.1 kg), was set up to examine the effect of rapid wilting of perennial ryegrass herbage, and type of forage additive applied, prior to ensiling on energy utilisation by growing cattle. The forages used were either unwilted or wilted for 26 h (mean DM 193 and 450 g/kg respectively) each conserved using either a bacterial inoculant to stimulate, or formic acid to restrict, fermentation. Six feeding treatments, comprising the two unwilted silages (inoculated and acid treated) each offered ad libitum, the two wilted silages (inoculated and acid treated) each offered ad libitum and restricted to 0.7 of ad libitum intake were offered to two animals per period during a 19-day feeding period. Ration digestibility and data on energy exchange determined using indirect open-circuit respiration calorimetry, were recorded during the last 9 and 3 days of each period respectively. The data were analysed by analysis of variance according to the two silage types (wilted, unwilted), * 2 additive (inoculant, acid) factorial structure to test for the main effects of each factor and interactions. There were no significant interactions in any of the measurements. Regression analyses were used to compare the energy utilisation variables for the wilted and unwilted silages at equal ME intakes. At equal ME intakes heat production, energy retention and efficiency of ME utilisation for tissue gain kg were not influenced by wilting of the forage. Neither did additive type (stimulant, restrictor) influence these variables. Overall regression analysis of energy retention against ME intake indicated a maintenance ME requirement of 0.62 MJ kg W 0.75 and kg of 0.39. These values support the recent published figures from this Institute and add weight to the view that maintenance energy

Twenty 5-mo-old Holstein cattle (10 steers and 10 heifers) were selected from a dairy herd for a 28 d study of enteric methane emissions and energy utilization. The cattle were offered a completely mixed diet with grass silage and concentrates (0.45 and 0.55, DM basis, respectively). They were housed as a single group in cubicle accommodation for the first 20 d, transferred to metabolism units for 3 d, and subsequently housed in indirect open-circuit respiration calorimeter chambers for next 5 d with measurements of feed intake, feces and urine outputs, and gaseous exchange. There were no significant differences (P0.05) between the 2 groups in terms of animal performance (feed intake, BW, or BW gain), energy metabolism (energy intake, energy outputs, or energy use efficiency), or methane emission rates (total methane emissions expressed on feed intake or energy intake basis). Therefore, the data from the 2 groups were pooled to develop a range of relationships between inputs and outputs. The regression of energy balance or heat production against ME intake (r2=0.85; P0.001) indicated a NEm of 0.57 MJ/kg BW0.75, which is greater than reported for adult dairy cattle. The methane energy output was found to be 0.068 of GE intake when the intercept was omitted from the linear equation (r2=0.73; P0.001), which is greater than the commonly accepted value (0.065) for adult cattle used for development of methane emission inventories for dairy and beef production systems. These data can add useful information, as there is little information available on measurements of maintenance energy requirement or methane emissions in young stock (6 mo old) of the current high-yielding dairy cattle. The use of these data can potentially improve the accuracy of prediction of energy requirement and methane emissions for dairy and beef production systems in these dietary conditions.

Three studies were undertaken with the aim of examining in-silo losses associated with ensiling mixtures of beet pulp and herbage. In Experiment 1, first-regrowth perennial ryegrass was ensiled untreated or mixed with either 40 or 120 kg unmolassed beet pulp t−1 fresh grass prior to ensiling. In each of Experiments 2 and 3, second-regrowth ryegrass was ensiled untreated or mixed with either 40, 80 or 120 kg unmolassed beet pulp t−1 fresh grass prior to ensiling. Dry-matter concentrations of herbage ensiled in Experiments 1, 2 and 3 were 141, 157 and 139 g kg−1 respectively. Time-course studies indicated a more rapid fermentation with the untreated silages. Ensiling beet pulp with herbage resulted in significant improvements in silage fermentation, reflected in reductions in silage pH and ammonia nitrogen concentrations, with these effects being pronounced at beet pulp inclusion in excess of 80kg t−1. Beet pulp inclusion increased the dry-matter concentrations of the resulting silages while reducing crude protein, modified acid detergent fibre and gross energy concentrations. In Experiment 1 beet pulp retained 1·62 and 1·641 effluent kg−1 at the 40 and 120kg t−1 application rates respectively. In Experiments 2 and 3, effluent retentions were 1·40, 1·29 and 0·93 1 kg−1 and 2·87, 2·19 and 1·781 kg−1 at the 40, 80 and 120kg t−1 beet pulp inclusion rates respectively. In each of Experiments 1 and 3, in-silo losses were reduced with increasing level of beet pulp inclusion, while in Experiment 2 in-silo losses were relatively unaffected by treatment. Nutrient losses in effluent were reduced by the inclusion of beet pulp in all three experiments, while nutrient losses in surface waste and invisible nutrient losses tended to increase with higher levels of beet pulp inclusion. It is concluded that the inclusion of beet pulp with herbage at ensiling can result in an improved silage fermentation and a reduction in in-silo losses, while at the same time retaining considerable quantities of effluent within the silo. However, with herbage dry-matter concentrations below 160gkg−1, beet pulp inclusion in excess of 120 kg t−1 herbage would be required to eliminate effluent production totally.

Twenty-one British Friesian dairy cows, in mid-lactation, were used in a seven-treatment, partially balanced change-over design experiment consisting of three periods each of 4 weeks' duration. Treatments involved offering grass silage either without a sugar-beet pulp (beet pulp) supplement (US) or supplemented with beet pulp at silage/beet pulp dry matter ratios of 80:20 (C40), 65:35 (C80) and 55:45 (C120), and offered in the form of a mixed ration. A further three treatments consisted of offering ensiled blends of silage and beet pulp, produced by mixing 40 (E40), 80 (E80) and 120 (E120)kg beet pulp t−1 of grass at ensiling. Silage was offered ad libitum on all treatments, with cows receiving 1kg d−1 of a concentrate supplement containing 470 g crude protein kg−1 fresh weight. Dry matter intakes increased with increasing level of beet pulp inclusion in the diet, irrespective of method of beet pulp inclusion in the diet. Similarly, milk fat + protein yields increased with increasing level of beet pulp offered. However, when comparisons were made between the two methods of beet pulp inclusion in the diet with beet pulp requirements equivalent to those obtained in treatments C40, C80 and C120, namely 2·28, 4·53 and 6·21 kg d−1, offering beet pulp as a supplement to an untreated silage resulted in fat + protein yields of 32 (s.e.d. 9·8), 53 (s.e.d. 19·5) and 81 (s.e.d. 21·3)gd−1 greater than would have been achieved had equivalent quantities of beet pulp been included at ensiling as part of an ensiled blend. This effect can be attributed to the higher metabolizable energy intakes with the control silage supplemented with beet pulp at feeding, a consequence of the loss of nutrients from the beet pulp fraction during ensiling, in the case of treatments E40, E80 and E120. However, when account is taken of differences in the efficiency of recovery of edible silage dry matter between ensilage systems and differences in forage dry-matter intake between treatments, overall efficiency of feed use was not significantly different between the two systems of beet pulp inclusion in the diet.

Twenty early-lactation British Friesian dairy cows were used in a five-treatment, partially balanced change-over design experiment, consisting of four periods each of 4 weeks' duration. Three treatments consisted of offering ensiled blends of silage and sugar-beet pulp produced by mixing 40 (S40), 80 (S80) and 120 (S120)kg beet pulp t−1 herbage at ensiling. In two further treatments, an untreated silage was supplemented with 5 kg of beet pulp daily, either mixed with the silage prior to feeding (SM) or offered in two equal feeds each day (ST). Silage was offered ad libitum in all treatments, while in addition all cows received 1 kg d−1 of a concentrate supplement containing 470 g crude protein kg−1 fresh weight. Dry-matter intakes and milk fat + protein yields increased with increasing level of beet pulp inclusion in the diet, irrespective of whether it was offered in the form of an ensiled blend or as a supplement to an untreated silage. With the exception of D-value (digestible organic matter in the dry matter), which was significantly higher with treatments SM and ST than with the ensiled blend treatment (S80), no significant differences were identified in total ration digestibility or in the efficiency of nitrogen or energy utilization between methods of beet pulp inclusion in the diet. However, offering beet pulp in the form of an ensiled blend reduced the acetate/propionate ratio in rumen fluid compared with offering best pulp as a supplement to an untreated silage. When account is taken of differences in the efficiency of recovery of edible silage dry matter between ensilage systems and of differences in dry-matter intakes between treatments, total milk fat + protein outputs per 10000 kg herbage dry matter ensiled were 55 (s.e. 50·9) and 78 (s.e. 47·5) kg lower when equal quantities of beet pulp were offered as part of an ensiled blend rather than as a supplement to an untreated silage, as in treatments SM and ST respectively. However, these differences were non-significant. Alternatively, in order to produce an equal milk output from ensiling a given quantity of herbage, 12·5 and 16·2% more beet pulp would have been required if the beet pulp had been mixed with the herbage at ensiling, rather than offered as a supplement, as in treatments SM and ST respectively.

The increasing use of concentrate feedstuffs within Northern Ireland dairy systems has resulted in significant farm gate phosphorus (P) surpluses, and these have contributed to increased soil P levels and risk of P loss to overland flow. However, the P content of feed concentrates can be lowered without compromising animal performance. This study focuses on P losses from grassland and evaluates how adjusting the P content of manure impacts on the P composition and concentration in overland flow. Dairy cows were offered diets containing 5.3 to 3.0 g P kg(-1) dry matter (DM) and produced manures with a range of P contents. Manure was applied at a rate of 50 m3 ha(-1) to 0.5-m2 grassland plots, and simulated rainfall (40 mm h(-1)) was applied repeatedly 2, 9, 28, and 49 d after during the summer, winter, and spring. Decreasing the P content in the diet, from the highest to the lowest P treatment (43%), produced a proportionately greater reduction in manure TP content (63%), but reductions were not exclusively in the water-soluble fraction. Following surface applications of manure, P concentrations in overland flow increased in all seasons (P < or = 0.001), while the greatest impact of varying the manure P content was most evident during the first simulated overland flow event. When diet P content was reduced from 5.4 to 3.0 g P kg(-1) DM, a statistically significant reduction in runoff P concentration was observed in all seasons. Elevated P concentrations in overland flow were observed for 28 d in spring and 9 d in summer and winter. The large drop in P concentrations between simulated rainfall events on Day 2 and Day 9 suggests that increasing the time interval between manure application and the generation of overland flow has a greater impact on P losses than does varying the dietary P content.

Introduction The integration of dairy heifers into the main herd during the post calving period can have negative effects on the heifer’s welfare and productivity (Gonzalez et al, 2003). This appears to be related to the fact that heifers attain low social status when entering the milking herd and therefore are subjected to increased levels of bullying and aggression (Wierenga, 1990; Knierim, 1999). The aim of this study was to assess if the time of day (i.e. after ‘AM’ or ‘PM’ milking) when freshly-calved heifers are introduced to a group containing mature cows influences the heifers’ welfare and performance.

Incidence of fertilization failure and embryo loss in Holstein Friesian heifers and postpartum dairy cows R. A. Law, E. J. Williams, H. S. Gilmore, F. Carter, F. J. Young, P. Lonergan, M. A. Crowe, M. G. Diskin, C. P. Ferris, A. Evans Agri-Food & Biosciences Institute, Agriculture Branch, Hillsborough, County Down, United Kingdom, School of Agriculture, Food Science and Veterinary Medicine, UCD, Dublin, Ireland, Teagasc, Athenry, Co. Galway, Ireland Email: Ryan.Law@afbini.gov.uk

Norway has adopted a multi-trait selection programme within its Norwegian Red (NR) dairy cow population for over thirty years, in contrast to breeding programmes with the Holstein-Friesian (HF) breed, which have, until recently, focused primarily on milk production. As a result, evidence from Norway suggests a dairy cow population with high levels of fertility and a relatively low incidence of mastitis. Consequently, there is considerable international interest in the NR breed as a means of overcoming some of the fertility, health and longevity problems that currently exist within the HF breed. To examine the potential of the NR breed, an experiment was established on 19 commercial dairy farms to compare the production, fertility and longevity of animals of the NR and HF breed across a range of production systems.

Enteric fermentation in ruminants is an important source of methane (CH4) production. In the UK, ruminants contribute approximately 20% of all CH4 emission, with most arising from cattle. This presents a considerable challenge for the dairy industry in the battle against global warming, and reduced CH4 emission is likely to be a major target for government policy within the next few years. The objectives of the present study were to evaluate the effects of level of concentrate supplementation and cross-breeding of Holstein cows with Jersey sires on CH4 production.

Fertility traits have been included within breed selection programmes for the Norwegian Red (NR) dairy cow population in Norway for over thirty years. As a consequence, a 60 day non-return rate to first artificial insemination (AI) of 72.5% was recently calculated for NR cows in Norway (Garmo et al., 2008). In view of this long term breeding programme, and current fertility performance within Norway, there is considerable interest in the NR breed as a means of overcoming the high levels of infertility that currently exist within the Holstein-Friesian (HF) breed. However, farming systems within Norway are very different from those within the UK, with herd sizes in particular being much smaller. Thus an experiment was established on 19 commercial dairy farms to compare the fertility performance of cows of the NR and HF breeds.

Labour constitutes a major and increasing cost on dairy farms, while at the same time, the availability of skilled labour is decreasing. In addition, younger farmers are placing an increasing emphasis on lifestyle. Consequently, there is an increased interest in milk production systems involving reduced labour inputs. In view of the fact that approximately 33% (O’Brien et al., 2002) of the daily labour input on dairy farms is associated with the milking routine (herding, milking and washing), the adoption of once daily milking would appear to offer considerable potential to reduce labour inputs. This study examined the effect of once-daily milking, in late lactation, on animal performance.

While the milk yield response of spring calving dairy cows to concentrate supplementation during the main summer grazing period has been examined in a number of studies, there is little information available concerning the milk yield response to supplementation in late summer/early autumn. With milk yield at this stage of the lactation having declined considerably, supplementation might appear unnecessary. However, herbage quality and availability are also lower in late season, and as such, responses to concentrate supplementation might be expected. This study was conducted to examine the milk yield response to concentrate supplementation of dairy cows grazing late summer/autumn grass.

There is little information available in the literature on the validation of the currently adopted energy feeding systems developed from calorimetric data, using data obtained in production studies. The objective of the present study was to use production data from feeding studies to validate some metabolisable energy (ME) systems (AFRC, 1990 and 1993; SCA, 1990) and net energy (NE) systems (Van Es, 1978, INRA, 1989; NRC, 2001).

AFRC (1993) recommends a reduction of proportionately 0.018 in dietary metabolisble energy (ME) concentration with each unit increase in feeding level above maintenance in dairy cows (feeding level is calculated as total ME intake divided by ME requirement for maintenance). A similar value (0.016) was reported recently by Yan et al. (2001) using a number of linear and multiple regression techniques with lactating dairy cows offered grass silage-based diets. The objectives of the present study were to validate these two values and also to evaluate the effects of feeding level on nutrient digestibility and ME concentration in the mixed diets.

The energy feeding systems currently adopted for dairy cows in Western Europe and North America were developed from calorimetric data published 30 years ago. However, the calorimetric measurements were usually undertaken with a small number of trained animals, housed for a short period in respiration chambers. The objective of the present study was to use production data to develop the metabolisable energy (ME) requirement for maintenance (MEm) and the efficiency of ME use for lactation (kl) for dairy cows.

Wilting of grass prior to ensiling generally produces positive responses in dry matter (DM) intake of cattle, but the responses in animal performance are often small, or even negative. The primary objective of the present study was to compare energy utilization from heavily wilted and unwilted silages by growing cattle when given at equal metabolisable energy (ME) intakes. A secondary objective was to evaluate effects of silage additive type (inoculant v. formic acid) on energy utilization.Four silages were produced from unwilted and wilted grasses (DM 193 and 450 g/kg) obtained from a perennial ryegrass sward. The wilted grass was dried in the field for 26 hours using rapid wilting techniques involving crop conditioning and spreading. At ensiling both the unwilted and wilted grasses were each treated with two additives, a bacterial inoculant (Ecosyl, Zeneca Bioproducts Limited) and a formic acid additive (ADD-F, BP Chemicals Ltd.).

Wilting of grass prior to ensiling has been widely adopted as a means of improving the fermentation quality of silage. However, the effects on intake have been variable. For example, with growing cattle, Rohr and Thomas (1984) reported that wilting increased silage dry matter (DM) intake by 0.09, while Steen (1984) reported an increase of 0.18. Similarly with lactating cattle, Rohr and Thomas (1984) reported and increase in intake in response to wilting of 0.04, while Patterson, Yan, Gordon and Kilpatrick (1997) observed an increase of 0.20. However, a range of additives were used in these studies and it is suggested that this may have caused variation in the fermentation quality of the unwilted silages which in turn may have affected the response to wilting. Consequently an experiment was designed to determine if the variability in the intake responses to wilting could be explained by differences in the fermentation characteristics of the unwilted silage.

In recent years there has been an improvement in the genetic potential of dairy cattle through intensive breeding programs and of beef cattle through a shift from native beef breeds to Continental breeds. These potential improvements can only be realised if increased intakes can be achieved. If conserved forages are to meet these higher nutrient requirements then the intake of conserved forages should be maximised. Two potential methods by which silage intake can be increased are by increasing silage digestibility through more frequent harvesting of grass (Gordon, 1989) or by restricting fermentation of the resulting silage (Doherty and Mayne, 1996). The objective of the current study was to examine the relative effects of digestibility and restricting fermentation on the intake of silage with the aim of establishing the optimum approach to achieving higher nutrient intakes from ensiled forages.

In classical studies estimates of maintenance energy requirements for cattle have been derived from measurements of fasting heat production (FHP) and urinary energy output following a period of restricted nutrition. Using 8 such sets of data, ARC (1980) developed equations to calculate the metabolisable energy (ME) requirement for maintenance (MEm) for lactating dairy cattle. This approach was further supported by AFRC (1990). However, recent studies using regression techniques at this Institute would suggest that the MEm for lactating dairy cows with access ad libitum to high forage diets is considerably higher than that calculated from AFRC (1990). The objective of the present study was therefore to measure the FHP of dairy cows offered forage diets ad libitum prior to fasting and to establish if this would support the higher MEm for dairy cows obtained using regression techniques .

Including dry feed materials (absorbents) with grass at ensiling has been shown to reduce effluent output and improve silage fermentation (Offer and Al-Rwidah, 1989) although the effects of this practice on animal performance have been somewhat variable (Ferris and Mayne, 1990; Jones, Jones and Moseley, 1990). However little is known about the fate of these absorbents during ensilage or the effects of ensiling upon their chemical composition. The aim of this investigation, which was part of a large scale dairy cow production study was to examine the nutrient recovery and compositional changes occurring with unmolassed sugar-beet pulp (SBP) when ensiled with grass at three levels of inclusion.

There is increasing interest in the addition of dry feed materials to grass at ensiling, primarily as a means of reducing effluent production, although other benefits claimed include improvements in silage fermentation and animal performance.A large number of studies have demonstrated lower effluent outputs and improvements in silage fermentation due to the inclusion of materials such as cereals and sugar beet pulp, although experiments examining the effects on animal performance are limited.Recently, Jones and Jones (1988) observed higher liveweight gains from beef steers fed silage produced by ensiling grass with molassed beet feed compared to animals fed the same quantity of beet feed mixed with silage produced from untreated grass at the point of feeding. The major objectives of the present study were to evaluate the possible use of sugar beet pulp as an absorbent material in silage making and to examine the effects of its inclusion with grass at ensiling on animal performance.