Effect of allowed grazing time, inert rumen bulk and length of starvation before grazing on the weight, composition and dermentative end-products of the rumen contents of lactating dairy cows

The effect of length of the allowed grazing time (Experiment 1), length of starvation time and placement in the rumen of inert bulk material before grazing (Experiment 2) on liquid and particulate rumen pool sizes, composition and fermentability was investigated. In Experiment 1, four lengths of allowed grazing time (1.00, 1.75, 2.50 and 3.25 h) after overnight starvation were compared. The allowed grazing time had no significant effect on total and liquid rumen pool sizes after grazing but did affect (P < 0.05) dry-matter (DM) and organic matter (OM) rumen pool sizes. The non-significant diferences between the volatile fatty acid (VFA) rumen pool sizes before and after 1 h of grazing may indicate a delay in the availability of the more rapidly fermentable substrate for the microorganisms. The total VFA remen pool sizes increased significantly (P < 0.01) with the allowed grazing time, which suggests that these fermentation products may be involved in the control of the grazing time in later stages during the day. Experiment 2 consisted of a factorial combination of two lengths of starvation before grazing (16.5 and 2.5 h) and the presence or absence in the rummen of 12.5 kg of a synthetic indigestible material. The duration of starvation before grazing did not affect significantly the particulate, ammonia and VFA rumen pool sizes after grazing except for propionic acid, which was reduced (P < 0.09) by the longer starvation time. The inclusion of inert bulk material in the rumen before grazing significantly reduced (P < 0.05) the total, Liquid DM, OM, and ammonia rumen pool sizes but not the VFA rumen pool sizes after grazing. High levels of ammonia as well as total rumen contents may be involved in the control of the grazing time in this experiment.     

Effect of time of day on grazing behaviour by lactating dairy cows

An experiment was conducted to examine the effect of time of day on the rate of intake of herbage by grazing dairy cows. Eight unsupplemented Holstein Friesian cows in their fourth month of lactation grazed grass swards maintained at a sward surface height of 6·5 cm. Commencing at 07.00, 11.30, 16.00 and 19.00 h, intake rates were estimated by measuring the liveweight change, corrected for insensible weight loss, over a period of 1 h while grazing. During the period of grazing, recordings of jaw movement activity were made to determine total eating time, number of grazing jaw movements (GJMs) and bites. Total eating time over 24 h was measured: once before and once after determination of intake rate.
Although time of day did not affect GJM rate, it had a quadratic effect on the proportion of GJMs represented by biting and non-biting jaw movements, resulting in a significant effect on bite rate. Bite rate showed a quadratic effect of time, decreasing between 07.00 and 11.30 h, and then increasing by 16.00 h to reach a maximum at 19.00 h (52·6, 47·5, 51·6 and 59·4 bites min⁻¹ respectively). Bite mass (mg fresh matter bite⁻¹) was greatest at 07.00 h because of the lower dry-matter (DM) content of the herbage and the presence of surface moisture at that time, but the effect of time of day was not significant. Mean bite mass measured as DM or organic matter (OM) differed significantly between the different times of day (332, 384, 481 and 402 mg DM and 302, 348, 438 and 367 mg OM bite⁻¹ respectively). The net result of these differences in bite rate and bite mass was a linear increase in DM and OM intake rate over the day. The magnitude of such differences will have profound effects on mean daily intakes when calculated as the product of total eating time and intake rate.     

Effect of stocking rate on the grazing behaviour and faecal output of lactating dairy cows

Information about the grazing behaviour and the return of dung to pasture by lactating dairy cows was collected from stocking rate experiments in northern Victoria. Grazing behaviour was observed for 24-h periods in mid-summer in two years. Grazing time increased as herbage allowance decreased to about 32 kg DM cow⁻¹ d⁻¹ but as herbage allowance decreased further grazing time also decreased. A herbage allowance of 32 kg DM cow⁻¹ d⁻¹ corresponded to a stocking rate of about 5.5 cows ha⁻¹. This effect of herbage allowance on grazing time may have been confounded by herbage mass, however. Rumination time of the cows increased by 003 h for each kg increase in herbage allowance while resting time was not affected by treatment.
The effects of stocking rate on some of the characteristics of faecal output were measured for a 3-d period in mid-summer. The number of pats deposited per cow daily declined by 0.66 for each unit increase in stocking rate. The fresh weight of dung also declined as stocking rate increased by 0.16 kg per unit of stocking rate. While the values for the amounts of dung deposited on the pasture by the cows at the lower stocking rates are similar to many of those reported in the literature, this study has quantified the way in which stocking rate may influence this in one instance. Furthermore, provided that some measure of herbage intake is made when measurements of dung excretion are performed, it is suggested that estimates of in vivo digestibility can be obtained.     

Effect of sward surface height on intake and grazing behaviour by lactating Holstein Friesian cows

The effect of sward surface height (SSH) on grazing behaviour and intake by lactating Holstein Friesian cows on continuously stocked grass pastures maintained at mean heights of 5, 7 and 9 cm was studied during the growing season. Intake rate was estimated over periods of 1 h by weighing animals before and after grazing, with a correction made for insensible weight loss. Grazing behaviour during that hour and over 24 h was recorded automatically using sensors to measure jaw movements. Although maintained at the overall mean SSH, swards had a patchy appearance with short, frequently grazed areas interspersed with taller, infrequently grazed areas, which is typical of pastures continuously stocked with cattle. Daily organic matter (OM) intake, calculated as the product of daily grazing time and intake rate, was greater at a SSH of 7 cm than at 5 or 9 cm (14·1 vs. 10·5 and 12·1 kg respectively). On the 5-cm sward, OM intake per grazing jaw movement (GJM) was reduced compared with that on the 7-cm sward (0·182 vs. 0·264 g respectively), and because cows were unable either to increase significantly GJM rate (95·8 vs. 90·1 GJM min^?1) or the proportion of GJM that were bites (0·80 vs. 0·81) OM intake rate was reduced (16·9 vs. 23·5 g min^?1). Cows were unable to increase their grazing time significantly (628 vs. 604 min d^?1) to compensate for the reduction in intake rate, and as a result daily intakes were lower. Cows grazing the 9-cm sward also incurred a reduction in OM intake GJM^?1 compared with those on the 7-cm sward (0·237 vs. 0·264 g respectively) and therefore there was a reduction in OM intake rate (21·6 vs. 23·5 g min^?1). These animals did not compensate by increasing the time spent grazing (581 min d^?1), probably owing to an increased ruminating requirement per kg of herbage ingested compared with those on 7 cm SSH (2264 vs. 1780 ruminating jaw movements respectively). The results show that SSH can significantly influence intake rate, but, while the cow's only effective strategy to compensate for any reduction in intake rate is to increase grazing time, this may be limited by the requirement for ruminating and non-grazing, non-ruminating activities, which is influenced by qualitative and quantitative aspects of the herbage ingested, whereas the cows' only effective strategy to compensate for any reduction in intake rate is to increase grazing time.     

Effects of supplementation on the ingestive behaviour of grazing steers*

Herbage intake is usually depressed when beef cattle grazing abundant pastures are supplemented with energy-rich feedstuffs but relatively little is known about the effects of supplementation on the components of ingestive behaviour. An experiment was conducted to establish the effect of ground corn (Zea mays L.) on the ingestive behaviour of yearling Angus and Angus × Hereford steers (Bos taurus) (mean live weight (LW) of 323 kg) grazing autumn stockpiled Boone cocksfoot (Dactylis glomerata L.) using a tethered grazing system in which the experimental unit was the tethered steer and its grazing area (45 m²) for one grazing session. Herbage dry matter (DM) mass was 1662 kg ha^?1 and herbage DM allowance was 7–5 kg steer^?1 for each grazing session. Herbage DM intake was measured as the difference between herbage DM mass offered and refused. Grazing took place during two daily sessions each of about 2 h duration commencing at 08.00 and 14.00 h for 9 days. Ground corn (0, 1·5, 3·0 and 4·5 kg steer^?1) was fed each day at 12.00 h and had no significant (P < 0·05) effect on rate of DM intake, rate of biting or DM intake per bite. Mean DM intake was 6 2 kg steer^?1 d^?1 (87 mg (kg LW)^?1 min^?1). Steers averaged 4832 bites per grazing session, with a mean DM intake per bite of 644 mg (2·0 mg (kg LW)^?1) and a mean rate of 44 bites min^?1. Data obtained at the beginning and end of each grazing period on ingestive behaviour of one group of four steers (mean LW of 306 kg) fitted with oesophageal fistulae supported data for the two groups of normal steers and showed no response to supplementation. Mean values for rate of DM intake, DM intake per bite and rate of biting established for the fistulated cattle were 73 mg (kg LW)^?1 min^?1, 521 mg bite^?1 (1·7 mg (kg LW)^?1) and 39 bites min^?1, respectively.     

Effects of inoculant treatment on ryegrass silage fermentation, digestibility, rumen fementation, intake and performance of lactating dairy cattle

A randomized block experiment involving thirty-six lactating dairy cattle was carried out to evaluate a bacterial inoculant (Grazyme Grobac, Agritech), containing bacteria, enzymes and a rumen enhancer, as a silage additive. Herbage from the primary regrowth of predominantly perennial ryegrass swards was ensiled unwilted and precision-chopped after a 51-d growth interval on 4 and 5 August. Alternate loads of herbage were ensiled either untreated (C) or treated with formic acid at a rate of 2.65 1 (t herbage)^?1 (F) or the inoculant at a rate of 0.64 kg (t grass)^?1 (I). The treatments were harvested using the same harvester in the rotation of I, F and C treatments. Mean dry-matter (DM), water-soluble carbohydrate and nitrate nitrogen (N) concentrations and buffering capacity of the C herbages at ensiling were 198 g kg^?1, 18 2 g kg^?1, 290 mg (1 juice)^?1 and 379 mequiv. (kg DM)^?1 respectively. For silages C, F and I pH values were 3.7, 3.8 and 3.8 and ammonia N concentrations 61, 43 and 58 g (kg total N)^?1 respectively. Inoculant treatment did not alter aerobic stability of the silages, whereas formic acid treatment increased it. The silages were offered ad libitum and supplemented with 5 kg of concentrates per head daily. For treatments C, F and I silage DM intakes were 10.8, 11.2 and 10.8 (s.e. 0–33) kg d^?1, milk yields 21.3, 20.9 and 20.7 (s.e. 0.52) kg d^?1, fat concentrations 38.3, 40.3 and 37.2 (s.e. 0.83) g kg^?1 and protein concentrations 30.8, 32.6 and 32.6 (s.e. 0.49) g kg^?1 respectively. Inoculant treatment did not alter (P0.05) the digestibility coefficients of the total diets, whereas formic acid treatment decreased DM (P0.05), organic matter (P0.05), neutral detergent fibre (P0.01) and hemicellulose (P0.01) digestibilities. Formic acid treatment altered rumen fermentation patterns, whereas inoculant treatment had no effect. It is concluded that, relative to a well-preserved untreated silage, additive treatment did not alter DM intake, milk yield or fat plus protein yield. However, both additive treatments increased milk protein concentrations and formic acid treatment increased milk fat concentration relative to the well-preserved, untreated silage.     

Effects of conservation method and access time on silage intake and milk production in dairy cows

The effects of the time of access to feed (8 h or 24 h) with silage-based rations (unwilted or wilted silage) were studied for two years. In each year the experiment comprised 52 individually fed cows in a 2 × 2 factorial design and covered weeks 1-20 of the lactation. The cows were offered silage ad libitum , 1 kg of hay per day, and concentrate according to the predicted energy-corrected milk (ECM) yield.
Increasing the access time from 8 h to 24 h increased the total intake of dry matter (DM) and metabolizable energy (ME) by 6%. This resulted in increased yield of ECM by 5%. The eating rate of forage was significantly increased by restricted time of access. Wilting had no significant effect on total feed intake or milk yield. The importance of providing a sufficient length of time during which the cows have access to feed was confirmed. It was concluded that 8 h d⁻¹ of access to silage-based rations is not enough in early lactation.     

Effects of the amount of barley and time of access to grass silage on the voluntary intake, eating behaviour and production of dairy cows

Three separate changeover experiments were conducted to investigate the effect of the amount of rolled barley and time of access to silage on the voluntary intake, eating behaviour and production of dairy cows. In Experiment 1, twenty-four milking cows were used to compare the effect of 4 1 and 6 1 kg d⁻¹ rolled barley on voluntary intake and milk production. In Experiment 2, fourteen cows were used in a comparison of the effect on voluntary intake and milk production of 5- and 22-h access to silage. Experiment 3 measured the effects on intake of silage of 2 and 4 kg d⁻¹ rolled barley and of 5- and 22-h access to silage. In Experiment I, increasing the amount of barley eaten reduced intake of silage by 0–50 kg dry matter (DM) per kg barley DM but in Experiment 3 with 5-h access to silage there was no significant difference between the amounts of silage eaten with 2 and 4 kg d⁻¹ barley. However, in Experiment 3 when allowed 22-h access to silage, the replacement rate was 0–53 kg DM silage per kg DM barley. Increasing access from 5 to 22 h increased silage intake by 37% in Experiment 1 and by 27% in Experiment 3. Milk yield was significantly increased by 4% when extra barley was given in Experiment 1 but there was no significant effect in Experiment 3. Increasing the time of access to silage led to an 11% increase in milk yield in Experiment 2 but there was no significant effect in Experiment 3. There was much variation between cows in the depression of silage intake per kg change in barley DM eaten with coefficients of variation of 131% and 109% in Experiments 1 and 3, respectively. When allowed access to silage for 22 h daily, on average, each cow spent 180 min eating silage in ten meals, although there was appreciable variation between cows in eating behaviour. The amount of barley did not affect the cows' rate of eating silage nor the duration of eating.     

Effect of structure of a tropical pasture on ingestive behaviour, digestibility of diet and daily intake by grazing cattle

The effect of the structure of a tropical pasture, based on Dichanthium spp., on the ingestive behaviour, in vivo digestibility of the diet and herbage intake by eight Creole tethered heifers was studied. Two levels of nitrogen fertilizer (0 and 50 kg ha^?1) were applied to plots after each grazing cycle and there were 28 d between each of the three grazing cycles. Four heifers grazed individual subplots daily on each plot for 14 d in each of the successive grazing cycles. Simultaneous measurements of bite depth, bite mass, biting rate, short‐term intake rate and daily grazing time were made in two 4‐d periods at the end of each 14‐d period. The in vivo organic matter digestibility (OMD) and daily herbage organic matter intake (OMI, expressed on a kg LW^0·75 basis) were also measured at the same times. Relationships among pasture characteristics and ingestive behaviour were similar to those reported in other short‐term studies: pasture height was highly correlated with bite depth, bite mass and biting rate (r = 0·91, r =0·79 and r = ?0·68, respectively, P < 0·001). Pasture variables had lower correlations with grazing time and short‐term intake rate than with bite depth, bite mass and biting rate. Pasture structure was more highly correlated with OMD than OMI: leaf mass and length and also the extended tiller length were highly correlated with OMD (r = 0·77, r = 0·76 and r = 0·72, respectively, P < 0·001) whereas the crude protein concentration of the herbage was correlated with OMI and digestible OMI (r = 0·50 and r = 0·69, respectively, P < 0·001). Ingestive behaviour variables, as well as OMD, were correlated more with pasture characteristics than was OMI.     

The effects of ensiling on dry-matter intake and milk production by lactating dairy cattle given forage as the sole feed

An experiment involving forty-five British Friesian cows in mid-late lactation was carried out to evaluate the effects of ensiling on herbage digestibility, dry-matter intake and milk production. The herbage from the primary growth of a predominantly perennial ryegrass sward that had received 123 kg N ha^?1 was zero grazed (ZG) from 27 April to 24 May 1992. Before going onto the experimental diets all animals were offered a common silage as the sole diet and dry-matter intakes and milk yields were recorded. The herbage was mown, picked-up with a precision-chop harvester and offered as the sole diet, twice daily, 10 fifteen cows that were on average 176 days into lactation. On May 20 herbage from the same sward was harvested identically to the ZG herbage and ensiled, alternative loads being untreated (UT) or treated with formic acid (2.4 l^?1) (FA). For silages UT and FA respectively, pH values were 3.94 and 3.92 and ammonia nitrogen concentrations were 95 and 75 [g(kg total N^?1)]. Forty-two days after ensiling, the silages were fed twice daily as the sole diet to thirty cows which were on average 166 days into lactation. The feeding interval was 28 days and the last 7 days was the main recording period for each treatment. For diets ZG, UT and FA, dry-matter intakes (DMI) (kg d^?1), milk yields (kg d^?1), fat plus protein yields (kg d^?1). milk fat concentration (g kg^?1), milk protein concentration (g kg^?1)and fat plus protein yields [kg (kg DMI)^?1] were 12.70, 11.51 and 12.07 (Av s.e.d. = 0.458); 12.79, 10.01 and 10.18 (Av s.e.d. = 0.346); 0.900, 0.649 and 0.682 (Av s.e.d. = 0.026); 39.8, 33.7 and 36.7 (Av s.e.d. = 0.174); 32.9, 29.9 and 30.0 (Av s.e.d. = 0.83); 0.073, 0.055 and 0.055 (Av s.e.d. = 0.003). UT treatment significantly increased dry matter (DM), organic matter (OM). energy and crude fibre digestibilities and the digestible OM concentration. UT and FA compared with ZG altered rumen fermentation patterns, significantly decreasing butyrate and increasing valerate concentrations. FA treatment significantly decreased the non-glucogenic ratio. It is concluded that ensiling using formic acid had no effect on forage DMI relative to the parent fresh herbage. Ensiling either untreated or with formic acid significantly decreased milk yield and milk fat plus protein yield, resulting in a lower efficiency of conversion of DMI to milk fat plus protein.     

Effects of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritional quality and herbage intake of grazing dairy cows

Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m × 6 m) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 × 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral‐detergent fibre, acid‐detergent lignin, crude protein and water‐soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n‐alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseudostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water‐soluble carbohydrate concentration showing large variation (>0·35). Cultivars differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (>2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High‐yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.     

Effects of ruminal fill on short-term herbage intake rate and grazing dynamics of beef heifers

The impact of manipulating ruminal fill (RF) on intake rate of herbage and grazing dynamics was measured with three rumen‐cannulated beef heifers grazing Bermudagrass pastures individually. The treatments compared were removal of proportions of rumen contents of 0 (treatment RF0), 0·33 (treatment RF33), 0·66 (treatment RF66) and 1·00 (treatment RF100). Treatments were randomly applied in a 3 × 4 Youden‐square design. The rumens were emptied before and after planned grazing sessions (30 min) to set up the treatments, and to estimate intake rate and bite mass, respectively. Measurements were made of bite rate, bites per feeding station, feeding stations per minute, intake per feeding station, time per feeding station, eating and searching step rates and times. Apparent bite area and area grazed per feeding station were calculated. Ruminal fill affected short‐term intake rate and changed grazing dynamics. As RF increased, step rates, searching times, bite mass, apparent bite area, bites per feeding station, area grazed per feeding station, time per feeding station and intake per feeding station decreased (P < 0·01) while step times, eating step rates and bite depth increased (P < 0·01). The results of the present study indicate that RF is an important factor governing the intake characteristics and behaviour of grazing beef heifers.     

Effect of replacing time available for grazing with time available for eating maize silage and soyabean meal on milk yield and feeding behaviour in dairy cows

Low rates of herbage dry matter (DM) intake impose limits on total daily DM intake in grazing dairy cows. The objective of this study was to increase total daily DM intake and milk production by restricting daily time available for grazing (TAG) and replacing it with time available for eating a maize silage/soyabean meal (TAMS) diet indoors. The treatments (TAG + TAMS) were 20 + 0, 19 + 1, 10 + 10 and 5 + 15 h. Measurements were made of milk production, intake and feeding behaviour. The interactions of TAG + TAMS treatments with sward height (SH) and concentrate level (CL) were also examined. Two experiments, each lasting 42 days, were carried out in spring ( Experiment 1 ) and autumn ( Experiment 2 ) using forty‐eight and twenty‐four Holstein‐Friesian cows respectively. Treatments were arranged in a factorial design with TAG + TAMS treatments, SH ( Experiment 1 only) and CL as the independent variables and a TAG + TAMS of 20 h. Reducing TAG and increasing TAMS significantly reduced estimated herbage DM intake and significantly increased maize silage/soyabean meal intake in both experiments, but there were no significant main effects of TAG + TAMS treatments on milk yield (mean, 27·4 and 25·5 kg d^?1 for Experiments 1 and 2 respectively), and yield of milk constituents. Increasing SH ( Experiment 1 ) and CL ( Experiments 1 and 2 ) significantly increased milk yield. In Experiment 1 , there was a significant interaction between TAG + TAMS treatments and SH with the taller sward height of 8–10 cm and the 20 + 0 treatment having the highest milk yield (29·7 kg d^?1) and the 5 + 15 treatment the lowest (27·2 kg d^?1), whereas at the lower sward height of 4–6 cm, milk yield was lowest on the 20 + 0 treatment (25·5 kg d^?1) with the other three treatments being higher (mean, 26·9 kg d^?1). Replacing TAG with TAMS significantly increased liveweight gain in Experiment 1 but not in Experiment 2 . Estimated rates of intake of herbage were lower in the autumn experiment ( Experiment 2 , 9·6 g DM min ^?1) than in the spring experiment ( Experiment 1 , 29·4 g DM min ^?1) but rates of intake of maize silage were higher in the autumn (112·4 g DM min^?1) than in the spring (72·5 g DM min^?1). In conclusion, in spring the response to replacing TAG with TAMS was dependent on sward conditions with the highest milk fat plus protein yield being on the 20 + 0 treatment at the high sward height and on the 19 + 1 treatment at the low sward height. The high liveweight gain of the 5 + 15 treatment could be an important means of restoring body condition in grazing lactating cows. In autumn, intakes of herbage were low in spite of its high estimated nutritive value with all treatments having a similar level of performance.     

Herbage intake and milk production by grazing dairy cows. 3. The effect of grazing severity under continuous stocking

The effects of severity of grazing on the herbage intake and milk production of continuously stocked British Friesian cows calving in February–March were examined in three experiments conducted in the years 1976–78 (experiments 1–3 respectively) using a put-and-take technique. In experiment 1 four grazing severities were imposed by maintaining swards with different herbage masses (2500, 3000, 3500, 4000 kg OM ha^-1); in experiments 2 and 3 there were two severities of grazing maintained by keeping swards canopies at constant heights of 5 and 7 cm (experiment 2) and 5 and 7·2 cm (experiment 3). Cows were reallocated to treatment every 8 weeks in experiments 1 and 2 and there were three periods, whereas they all grazed throughout a 23-week period on the same treatment in the final trial.
A decrease in the quantity of herbage on offer or in sward height reduced herbage intake and milk production in all experiments. Mean daily herbage OM intakes were 11·2, 12·2, 12·2 and 12·2 kg respectively in experiment 1, 12·2 and 13·2 kg respectively in experiment 2 and 12·2 and 152 kg respectively in experiment 3. Mean daily solids–corrected milk yields were 14·2, 15·2, 15·2 and 16·2 kg respectively in experiment 1, 14·2 and 16·2 kg respectively in experiment 2 and 12·2 and 17·2 kg respectively in experiment 3. It was apparent from the data obtained in the first two trials that grazing at a sward canopy height of 7 rather than 9 cm had little effect, but that at 5 cm there were significant depressions in both herbage intake and milk production. Milk yield was depressed to a greater extent when cows were kept on the same treatment for the whole season.     

Performance,milk fatty acid composition and behaviour of high-yielding Holstein dairy cows given a limited grazing period

The effects of a limited grazing period on the performance, behaviour and milk composition of high-yielding dairy cows were examined. A total of 56 Holstein cows yielding 44.7 ± 0.42 kg/day were allocated to one of four treatments in one of two, 4-week periods. Treatments were as follows: control (C)—cows housed and offered TMR ad libitum; early grazing (EG)—cows grazed for 6 hr after morning milking then housed; delayed grazing (DG)—cows returned to housing for 1 hr after morning milking followed by grazing for 6 hr, then housed; restricted TMR (RT)—cows grazed for 6 hr after morning milking, then housed and fed TMR at 75% of ad libitum. Intake of TMR was highest in cows receiving C, intermediate in EG and DG, and lowest in RT at 26.9, 23.6, 24.7 and 20.3 kg DM/day respectively. Pasture intake was similar in cows receiving EG or DG, but was higher in RT at 2.4, 2.0 and 3.5 kg DM/day respectively. Milk yield was similar between cows receiving C, EG or DG, but lowest in RT at 45.7, 44.2, 44.9 and 41.7 kg/cow, respectively, while milk fat content of C18:3 n-3 was increased by grazing. Cows in C spent more than 55 min/day longer lying and had three additional lying bouts/day, while lying bouts were shorter than for cows receiving EG, RT or DG. It is concluded that high-yielding cows can be grazed for 6 hr/day with little impact on performance, provided TMR is available ad libitum when housed.     

The influence of strain of Holstein-Friesian dairy cow and pasture-based feeding system on grazing behaviour, intake and milk production

A comparative study of grazing behaviour, herbage intake and milk production of three strains of Holstein‐Friesian dairy cow was conducted using three grass‐based feeding systems over two years. The three strains of Holstein‐Friesian cows were: high production North American (HP), high durability North American (HD) and New Zealand (NZ). The three grass‐based feeding systems were: high grass allowance (MP), high concentrate (HC) and high stocking rate (HS). In each year seventy‐two pluriparous cows, divided equally between strains of Holstein‐Friesian and feeding systems were used. Strain of Holstein‐Friesian cow and feeding system had significant effects on grazing behaviour, dry matter (DM) intake and milk production. The NZ strain had the longest grazing time while the HD strain had the shortest. The grazing time of cows in the HC system was shorter than those in both the HS and MP systems. There was a significant strain of Holstein‐Friesian cow by feeding system interaction for DM intake of grass herbage and milk production. The NZ strain had the highest substitution rate with the HP strain having the lowest. Hence, response in milk production to concentrate was much greater with the HP than the NZ strain. Reduction in milk yield as a consequence of a higher stocking rate (MP vs. HS system) was, however, greater for the HP and HD strains compared with the NZ strain. The results suggest that differences in grazing behaviour are important in influencing DM intake and milk production.     

Effects of feeding clover silages on feed intake, milk production and digestion in dairy cows

Silages were made from pure crops of perennial ryegrass, red clover and white clover over 2 years. In all but one case the silage was stored as bales. A silage additive specially adapted for bales (Kofasil Ultra^TM) was used for all silages and they were all of good hygienic quality. The additive contained sodium nitrite, hexamethylene, tetraamine sodium bensoate and sodium propionate. The silages were offered ad libitum, either pure or mixed [grass/clover 0·50/0·50 on a dry‐matter (DM) basis] with a fixed amount (8 kg) of concentrate. Two experiments, one in each year, were performed with high‐yielding multiparous dairy cows in mid‐lactation, and both rumen‐cannulated and intact cows were used. The experiments were carried out using an incomplete changeover design with fifteen cows and five treatments each year. The cows consumed large quantities of these silages (12·7–16·3 kg DM per cow per day). The highest intakes were obtained when the red clover and the 0·50 red clover:0·50 perennial ryegrass silage diets were offered. However, there was a difference between years. In year 1, 0·50 red clover:0·50 perennial ryegrass and 0·50 white clover:0·50 perennial ryegrass silage diets showed the highest intakes while pure perennial ryegrass and white clover silage diets gave lower intakes. In year 2 the highest intake of silage was obtained when the diet containing silage from red clover from a second cut was offered, while the silage from red clover from a first cut gave the lowest intake. The voluntary intakes of silages from white clover and perennial ryegrass were intermediate. No cases of bloat or other digestive disturbances were observed. Milk yield was significantly lower for the perennial ryegrass silage diet compared with all other diets in year 1. In year 2 milk yield was highest for the white clover silage diets and lowest for the red clover silage diets from both cuts. In year 1 there were relatively small differences in milk composition while in year 2 milk fat content was significantly lower with white clover silage diet and milk protein content was significantly higher with the perennial ryegrass diet. The overall conclusion from these experiments was that cows were able to consume large quantities of pure legume silage without serious disturbance to their metabolism. Differences in measurements of rumen metabolism were found between diets and especially between years. Milk production differences appears to be coupled to both differences in rumen physical characteristics, such as passage rate and particle size as well as differences in volatile fatty acid production in the rumen.     

Variation among pregnant, non-lactating dairy cows in eating and ruminating behaviour, digestibility and voluntary intake of hay

The variation between non-lactating British Friesian cows in eating and ruminating pattern, digestibility and voluntary intake of hay were measured about 4 weeks before calving. Among fourteen of the cows the daily duration of eating ranged from 214 to 462 min and rumination from 410 to 599 min with CV of 20 and 14 respectively. Daily hay intake varied between cows from 5.93 to 11.18 kg dry matter (DM) with a CV of 14. The mean digestibility coefficient of organic matter measured in nineteen cows was 0.57 ± 0.014 s.d. and of cellulose 0.70 ± 0.013 s.d. Intake of hay and cellulose digestibility were correlated (r = 0.51, P <0.05). There was a positive correlation between hay intake and duration of eating (r=0.64, P <0.01) but not between intake of hay and rate of eating. Daily time spent ruminating per kg hay DM eaten was negatively correlated with hay intake (r = 0.66, P <0.01). It is concluded that variation between cows in chewing time and in digestibility of cellulose may be important factors related to variation between cows in voluntary intake of hay.     

GrazeIn: a model of herbage intake and milk production for grazing dairy cows. 2. Prediction of intake under rotational and continuously stocked grazing management

Decision support tools to help dairy farmers gain confidence in grazing management need to be able to predict performance of grazing animals with easy‐to‐obtain variables on farm. This paper, the second of a series of three, describes the GrazeIn model predicting herbage intake for grazing dairy cows. The model of voluntary intake described in the first paper is adapted to grazing situations taking account of sward characteristics and grazing management, which can potentially affect intake compared to indoor feeding. Rotational and continuously stocked grazing systems are considered separately. Specific effects of grazing management on intake were quantified from an extensive literature review, including the effect of daily herbage allowance and pre‐grazing herbage mass in rotational grazing systems, sward surface height in continuously stocked grazing systems, and daily time at pasture in both grazing systems. The model, based on iterative procedures, estimates many interactions between cows, supplements, sward characteristics and grazing management. The sensitivity of the prediction of herbage intake to sward and management characteristics, as well as the robustness of the simulations and an external validation of the GrazeIn model with an independent data set, is presented in a third paper.     

Concentrate supplementation of grazing dairy cows. 2. Effect of concentrate composition on herbage intake and milk production

The effect of feeding either traditional concentrates containing starch or high quality fibrous concentrates on the performance of grazing dairy cows was examined in a trial in which cows were given concentrates with either 350 g starch and sugars (kg dry matter (DM))^-1 (high-starch) or 100 g starch and sugars (kg DM)^-1 (high-fibre). The swards used consisted predominantly of perennial ryegrass and were usually aftermaths following cutting. Each area was grazed for 3 or 4 d at each grazing and a two-machine sward-cutting technique was used for estimating herbage intake.
The effect of concentrate composition on the herbage intake of grazing cows at a high daily herbage allowance of 28 kg OM above 4 cm cutting height was investigated in 1983 and 1984. With 54 kg OM d^-1 of high-starch concentrates the mean herbage intake was 11·5 kg OM d^-1 per cow while cows fed 5.3 kg d^-1 of high-fibre concentrates consumed on average 12–6 kg OM d^-1. The mean substitution rate of herbage by concentrates was reduced from 0·45 kg herbage OM (kg concentrate OM)^-1 with the high-starch concentrate to 0·21 with the high-fibre concentrates.
The effect of the treatments on milk production was studied in 1984. The cows consumed 5·5 kg OM d^-1 as concentrates and grazed at a lower herbage allowance of 19 kg OM above 4 cm cutting height. With high-fibre concentrates milk production and 4% fat-corrected milk production were 13 and 1·8 kg d^-1, respectively, higher than with the high-starch treatment. The daily live weight gain with the high-starch concentrates was 0·17 kg per cow more than with the high-fibre concentrates.