Pasture Allowance Research Articles

Responses to supplementation by dairy cows given low pasture allowances in different seasons 1. Pasture intake and substitution

AbstractTwo factorial experiments were designed to determine the effects of stage of lactation, and season of the year, on cow responses to supplementary feeding. These experiments were conducted over consecutive years with 128 high genetic merit multiparous Holstein-Friesian cows in early, mid and late lactation in spring, summer, autumn and winter. At each stage of lactation, and in each season of the year, cows were offered a restricted pasture allowance (25 to 35 kg dry matter (DM) per cow per day), either unsupplemented (control) or supplemented with 50 MJ metabolizable energy (ME) per cow per day in experiment 1 and 80 MJ ME per cow per day in experiment 2. Two different supplements were offered, namely, rolled maize grain (MG) and a mixture of foods (BR) formulated to nutritionally balance the diet. In experiment 2, a fourth treatment consisting solely of a generous pasture allowance (60 to 75 kg DM per cow per day, AP) was introduced. Offering MG and BR increased DM intake (DMI). At the restricted pasture allowance, increasing total ME allowance (MEA) by offering supplementary foods increased ME intake (MEI) by 0·68 (s.e. 0·047) MJ per extra MJ ME offered. This highly significant (P<0·001) linear relationship was consistent across seasons, and did not diminish at higher MEA. In experiment 2, cows in early lactation had lower substitution rates than mid and late lactation cows irrespective of season. Substitution rate was higher when higher pasture allowance or quality of pasture on offer enabled the unsupplemented cows to achieve higher DMI from pasture than at other times of the year. These results suggest that one of the key factors determining the intake response to supplementary foods is pasture allowance. Within spring calving dairying systems, the largest increases in total DMI per kg of supplement offered is likely when offering supplements to early lactation cows grazing restricted allowances of high quality pasture.

Responses to supplementation by dairy cows given low pasture allowances in different seasons 2. Milk production

AbstractTwo factorial experiments were designed to determine the effects of stage of lactation, and season of the year, on cow responses to supplementary feeding. These experiments were conducted over consecutive years with 128 high genetic merit multiparous Holstein-Friesian cows in early, mid and late lactation in spring, summer, autumn and winter. At each stage of lactation, and in each season of the year, cows were offered a restricted pasture allowance (25 to 35 kg dry matter (DM) per cow per day), either unsupplemented (control) or with supplement at 50 MJ metabolizable energy (ME) per cow per day in experiment 1 and 80 MJ ME per cow per day in experiment 2. The two supplements given in both years were rolled maize grain (MG) and a mixture of foods formulated to nutritionally balance the diet (BR). In experiment 2, another treatment, of a generous pasture allowance (60 to 75 kg DM per cow per day) (AP), was imposed on an additional group of early lactation cows during each season. Direct milk solids (MS) (milk fat plus milk protein) responses in experiment 1 to MG were 169, 279, 195 and 251 g MS per cow per day in spring, summer, autumn and winter, respectively, while those to BR were 107, 250, 192, 289 g MS per cow per day. In experiment 2, however, milk solids responses to both supplements during spring were slightly below the control treatment, with values similar to those in experiment 1 in summer and autumn for cows on the BR but not the MG supplement. Milk solids responses to supplementary foods were largest during seasons of the year when the quantity and quality of pasture on offer resulted in the lowest milk solids yield from unsupplemented cows. When carry-over effects of feeding MG and BR on milk solids production were detected, they were only about half the magnitude of the direct effects. Serum urea concentrations were higher in control cows than those offered MG with a similar effect for BR in all but summer in experiment 1, while serum glucose concentrations were highest in winter and lowest in summer. The most important factor influencing milk solids responses was the relative food deficit (RFD) represented by the decline in milk solids yield of the respective control groups after changing from a generous pasture allowance to restricted allowance when the feeding treatments were imposed. Total milk solids responses (direct and carry-over) to supplements were greatest when severe food restrictions, relative to the cows' current food demand, resulted in large reductions in milk solids yield of the control groups. The RFD was the best predictor of milk solids response to supplementary foods. Therefore, it is likely that cows are most responsive to supplementary foods during or immediately after the imposition of a severe food restriction.

Effects of melatonin on the yield and composition of milk from grazing dairy cows in New Zealand

The aim was to determine whether administration of melatonin would alter the yield and composition of milk from grazing dairy cows in summer. Twelve sets of spring-calving identical twin Friesian cows were used in the experiment. In late-November (late spring), one twin from each set was given slow-release melatonin implants behind the ears (108 mg melatonin/cow). Two further implantations occurred at 4-weekly intervals to maintain increased circulating concentrations of melatonin for 12 weeks. The other twin served as a control. Milk yield and composition were measured twice prior to treatment and then four times over the following 12 weeks. Concentrations of melatonin, prolactin and insulin-like growth factor 1 (IGF-1) were measured in blood plasma twice before treatment and then either seven (melatonin and prolactin) or three (IGF-1) further times during the experiment. Management procedures for all cows were similar and cows grazed a daily pasture allowance of approximately 30 kg DM/cow as their sole feed source. In melatonin-treated cows there was a decrease in mean concentrations of prolactin in plasma, but concentrations of IGF-1 did not change. Melatonin reduced milk yield by 6 weeks after treatment and by the end of the 12-week experimental period milk yield in melatonin-treated cows had fallen by 23%. Melatonin also reduced concentrations of lactose in milk, but increased concentrations of fat, protein and casein, changes that were broadly similar to those that occur in late lactation in seasonally calving dairy cows. Thus, the results suggest that some of the variation in the volume and quality of milk throughout the season in New Zealand dairy systems may be due to changes in photoperiod mediated by increased concentrations of plasma melatonin in association with decreased concentrations of plasma prolactin.

Effect of pasture allowance and energy supplementation upon dairy cows milk yield.

The effect of different levels of daily allowance and supplementation on intake, milk production and composition and per hectare productivity was studied. Pasture consisted of an association of alfalfa (Medicago sativa), tall fescue (Festuca arundinacea) and prairie grass (Bromus wildenowii) and high moisture corn was used as supplement. 32 cows were allocated to four levels of pasture allowance (NA) and two levels of energy supplementation (SE). Pasture intake and individual and per hectare production were affected by NA, but SE had no signifi cant effect. No interactions were detected between any of the variables. Milk composition were not affected by NA, whereas only non fat solids were affected by SE. Liveweight change and condition score did not show differences among treatments. Urea level in both, plasma and milk, was not affected by NA, whereas the level of urea in plasma showed a trend to be different and the level of urea in milk was signifi cantly different for SE. Critical levels of pasture allowance which directly affect the productivity per hectare, need to be reached in order to perform a signifi cant increase of individual production. Milk fat and protein concentration did not appear to be responsive variables to different levels of supplementation and allowance, whereas the little variation in urea levels, as a response to a greater level of supplementation, did not make this a valuable tool to improve the milk protein constituents. Se estudio el efecto que distintos niveles de asignacion diaria y suplementacion producen sobre el consumo, la produccion y composicion de la leche y la productividad por hectarea. La pastura utilizada fue una asociacion de alfalfa (Medicago sativa), festuca (Festuca arundinacea) y cebadilla criolla (Bromus wildenowii) y el suplemento fue grano de maiz humedo. Se utilizaron 32 vacas y se establecieron cuatro niveles de asignacion de pastura (NA) y dos niveles de suplementacion energetica (SE). El consumo de pastura y la produccion individual y por hectarea fueron afectados por NA y no por SE. Al igual que para el resto de las variables, no se detectaron interacciones entre NA y SE. La composicion de la leche no fue afectada por NA, mientras que SE solo tuvo efecto sobre los solidos no grasos. La evolucion del peso vivo y del estado corporal no mostraron diferencias entre tratamientos. Los niveles de urea en plasma y leche no difi rieron signifi cativamente para NA, no ocurriendo lo mismo para SE, donde el nivel de urea en plasma tendio a diferir y el nivel de urea en leche difi rio signifi cativamente. Se concluyo que para conseguir aumentos signifi cativos en la produccion individual es necesario ofrecer niveles de asignacion que afectan negativamente la produccion por hectarea. La concentracion de grasa y proteina de la leche no parecieron ser variables sensibles a distintos niveles de suplementacion y asignacion, mientras que la escasa variacion en los niveles de urea, debida al mayor nivel de suplementacion, relativizo el valor de esta herramienta para mejorar la composicion de la proteina lactea.

Effects on Performance of Sulla and/or Maize Silages Supplements for Grazing Dairy Cow

The objective of this study was to investigate the effects of either maize or sulla silage supplementation to grazing dairy cows in summer. Forage mixtures used in the four week trial were based on previous experimental results but inclusion of rumen fistulated cows in five treatments enabled rumen sampling and use of in sacco incubations to determine the diet effects on digestion kinetics. Sulla and maize silages were used to supplement pasture and to meet minimum requirements for dietary protein concentration. Five groups often cows were grazed on a restricted daily allowance of 18 kg dry matter (DM) pasture/cow to simulate a summer pasture deficit, and four of these five groups received an additional 6 kg DM cow -1 d -1 of silage (sulla, maize, or sulla and maize silages). A sixth group was given a relatively unrestricted (38 kg DM cow -1 d -1 ) pasture allowance. The silage mixtures and pasture were incubated in sacco during the final week of the trial. The pasture was of high nutritive value and not typical of usual summer conditions, which favoured a response to quantity rather than quality of silage supplements. There was no difference in cow performance with the four silage supplements and the low milk solids (MS) production (about 1.0 kg MS d -1 ) relative to full pasture (1.3 kg MS d -1 ) showed the principal limitation to performance was dry matter intake. Milk composition was not affected by silage type and the low level of pasture substitution (0.29) suggested metabolizable energy (ME) was the principal limitation to performance. Samples of rumen liquor and in sacco data demonstrated significant effects of supplement; DM degradation rates (k) was highest (0.084 h-') when cows were fed 6 kg sulla silage whereas diets with a high proportion of maize silage were slowly degraded (p<0.01).

Rate of feed degradation in strip-grazing dairy cows

Nylon bags containing Persian clover, perennial ryegrass or perennial pasture hay were incubated for 12-h periods in lactating dairy cows grazing Persian clover pasture. The hypothesis was that the rate of dry matter disappearance over the first 12 h of incubation in the rumen would be lower when bags were inserted at a time when the rumen pH was at its lowest point for the day compared with a time when it was at its highest. It was also hypothesised that the reduction in rate of DM loss over 12 h at the initially low and then fluctuating rumen pH would be lower for Persian clover than for perennial ryegrass and the hay. Rumen fistulated cows grazing at 4 different pasture allowances (9, 16, 32 and 53 kg DM/day; 4 cows per treatment) were used in a completely randomised, split-plot design. The nylon bag incubation periods were 0700 to 1900 hours (period 1) and 1900 to 0700 hours (period 2) and rumen fluid pH was measured every 3 h during these periods. The ruminal fluid pH at the time of insertion of the nylon bags was higher (6.3 v. 5.7; P&lt;0.001) in incubation period 1 than in period 2, and there was an interaction between the effects of incubation period and pasture allowance on the average rumen fluid pH in each period. Rate of DM loss was higher (3.47 v. 3.28%/h; P = 0.019) in incubation period 1 than in incubation period 2, highest (P&lt;0.001) for clover, followed by ryegrass and then hay (5.05 v. 3.15 v. 1.93%/h) and higher (P&lt;0.001) in cows grazing at the low (9 and 16 kg DM/cow) compared with high (32 and 53 kg DM/cow) allowances. There was a significant linear relationship (P&lt;0.05) between DM loss rate calculated over 12 h and rumen fluid pH for grass and hay, but for clover this relationship only occurred in incubation period 2. These results suggest that more than 1 factor is important for determining feed degradation rates in the rumen at any particular time and that only using rates of forage DM loss that are obtained from nylon bags inserted prior to the morning feed, may overestimate the extent of rumen degradation of the feed eaten over the whole day in cows strip-grazing highly digestible pastures.

Dietary preferences of cows offered choices between white clover and 'high sugar' and 'typical' perennial ryegrass cultivars

An experiment was conducted to compare dietary preferences of cows offered simple choices between spatially separated monocultures of perennial ryegrass cvv. AberDawn (AD) and AberElan (AE), and white clover (WC) under strip grazing. AberDawn was bred to express high water soluble carbohydrate concentrations, whereas AE has typical levels. The proposed hypotheses were that cows would exhibit a partial preference for the ryegrass cultivar with a higher concentration of non-structural carbohydrates, and that there would be an interaction between the non-structural carbohydrate concentration of the ryegrass and strength of preference for WC. Non-lactating cows were offered a pasture allowance of about 20 kg DM each day for 9 days in 3 ‘choice’ treatments: AD + WC, AE + WC and AD + AE. All pastures had similar estimated metabolisable energy contents, but AD had a higher crude protein (136 v. 118 g/kg DM) and slightly lower neutral detergent fibre (480 v. 497 g/kg DM) concentration than AE, and non-structural carbohydrate concentrations were similar in both grasses. White clover had higher crude protein (236 v. 127 g/kg DM), and lower neutral detergent fibre (317 v. 489 g/kg DM) and non-structural carbohydrate concentrations (140 v. 183 g/kg DM), and contained less dead material (60 v. 242 g/kg DM) than the grasses. AberDawn contained less (P&lt;0.05; 578 v. 698 g/kg DM) green ryegrass than AE. Pre-grazing pasture mass (1870 v. 2010 kg DM/ha), pasture allowance (23 v. 25 kg DM/cow), and residual pasture mass (1610 v. 1710 kg DM/ha) were lower for AD than AE, and for WC were lower (P&lt;0.05) than for both grasses. Dry matter intake, intake rate and bite size were lower (P&lt;0.05) on AD + AE than on treatments containing WC. Cows grazing AD + AE ruminated longer (P&lt;0.05), ruminated more (P&lt;0.05) boli, and had more (P&lt;0.05) ruminating chews than those on treatments including WC. The cows on AD + AE had more (P&lt;0.05) total chews than those on AD + WC or AE + WC, but grazing time was not always significantly different between choice treatments. It is suggested that the longer ruminating times and greater number of boli processed in cows grazing only grass may reflect the slower digestion rates of ryegrass compared with clover. Cows grazing the AD + WC or AE + WC choice treatments showed a partial preference for WC, spending more (P&lt;0.001) time grazing and consuming more (P&lt;0.001) WC than ryegrass. Within the AD + AE choice treatment, cows spent more (P&lt;0.05) time grazing and consumed more (P&lt;0.05) AE than AD. Using the mean of 2 methods of estimation, the partial preferences for AD + WC, AE + WC and AD + AE were 39 : 61, 41 : 59 and 45 : 55, respectively.

Effect of cow diet on free fatty acid concentrations in milk

Two experiments were conducted: one during summer 1999 (Experiment 1, 180–200 days in milk (DIM)) and one in autumn 1999 (Experiment 2, 220–250 DIM), to examine the effect of pasture allowance on the formation of free fatty acids (FFA) in milk from multiparous Jersey cows. In Experiment 1, three treatments were investigated (n = 15): fully fed on pasture (FFP) (pasture allowance 36 kg DM/cow per day), restricted pasture (RP) (pasture allowance 23 kg DM/cow per day), and RP plus 5 kg DM/cow per day of pasture silage (RP+S). Treatments were applied for 21 days. Experiment 2 ran for 14 days and comprised two treatments, (n = 15) FFP (pasture allowance 38 kg DM/cow per day) and a more restricted pasture allowance (RP), of 16 kg DM/cow per day. Milk samples for FFA analyses were collected by hand milking each cow during the morning milking. The sample was split into three subsamples: Sample 1 was fixed to prevent any further lipolysis (L0), Sample 2 had no additive (L24), and for Sample 3 air was drawn through the sample for 4 min (D24). All samples were stored at 4°C for 24 h before being analysed for FFA concentrations by the Bureau of Dairy Industries (BDI) method. A restricted pasture allowance (RP) reduced milk yield by 14 and 36% in Experiments 1 and 2, respectively. The feeding of silage to cows on a restricted pasture allowance had no effect on milk yield. Pasture allowance or supplementary feeding in Experiment 1 had no effect on total FFA concentrations in L0, L24, or D24 samples. However, the increase in FFA during 24 h, storage (L24‐L0) was greater (P < 0.001) for the RP and RP+S than the FFP treatments. The restricted pasture allowance in Experiment 2 caused an increase in total FFA concentrations in the L24 (P < 0.001) and D24 (P < 0.05) samples. The increase in FFA concentration during storage (L24‐L0) was greater (P < 0.001) in milk from the RP treatment. In both trials, the increase in FFA concentrations over 24 h between damaged and undamaged milk (D24‐L24) was similar for each treatment. The greater increase in FFA concentration was in undamaged milk (L24‐L0) from the RP treatments. From this observation it is hypothesised that the increase in FFA concentrations in milk due to underfeeding resulted from an increase in the activity of lipoprotein lipase and not from an increased susceptibility of the milk fat globule membrane to damage. Overcoming a restricted pasture allowance by supplementary feeding of silage had little effect on reducing the impact of arestricted availability of summer pasture on milk yield or FFA concentrations.

The effect of pasture allowance fed to twin- and triplet-bearing ewes in late pregnancy on ewe and lamb behaviour and performance to weaning

This paper investigates whether pasture allowance before and at lambing affects ewe behaviour, lamb behaviour and subsequent twin and triplet lamb performance to weaning. The trial was carried out at Massey University Keeble Farm in New Zealand. At pregnancy scanning, 186 first cycle-mated ewes were identified as carrying twins ( n = 96) or triplets ( n = 90). The ewes were randomly divided into four nutritional treatments (2, 4, 6 and 8 cm post-grazing sward heights). Each treatment was replicated ( n = 12 ewes in each replicate during pregnancy) on two separate blocks. The trial ewes remained on the four nutritional treatments during pregnancy and parturition. The mean lambing date was the 9 September 2002. Within 12 h of birth lambs were weighed, their sex recorded and identified to the ewe. Maternal and lamb behaviours were then recorded for a period of 5 min. Twin litter weight at birth was similar for ewes grazing 2-, 4- and 6-cm sward heights. Increasing pasture allowance from just 2 cm to 4 cm to ewes with triplet litters increased litter weight at birth by 2 kg, increased weight of lamb weaned by 8 kg and improved litter survival to tagging by 4%. Triplet lamb survival to tagging increased by 15% from the lowest pasture allowance to the highest (from 2 cm to 8 cm). Triplet litter survival was similar to twin litter survival at the highest pasture allowance (8 cm; 2000 kg DM/ha). Pasture allowance had a greater effect on lamb behaviour than ewe behaviour and triplets were more affected than twins. Feeding level did not affect Maternal Behaviour Score (MBS); however, MBS was related to a number of lamb behaviours. Ewes on higher pasture allowances were more likely to stay with their litter at the tagging site. Ewes with triplet litters on the 2-cm sward height were further from their litter 5 min after tagging and high-pitch bleated significantly more than ewes on higher swards. These ewes were less likely to make contact with their lamb after tagging. Triplets born on lower pasture allowances were less likely to stand, locate their dam's udder and follow their moving dam. Fewer triplet lambs bleated following tagging and this might be why fewer ewes made contact. Ewes with triplets grazing high pasture allowances in late pregnancy can achieve litter survival rates similar to those with twins. Ewes with triplets require higher pasture allowances to achieve similar production as ewes with twin litters.

Milk fatty acid composition of dairy cows grazing at two pasture allowances and supplemented with different levels and sources of concentrate

Milk fatty acid (FA) composition of dairy cows from two grazing studies was examined. In the first study, effects of concentrate supplementation and pasture allowance were evaluated using 20 multiparous Holstein cows in five 4 × 4 Latin squares. The four treatments resulted from the combination of two pasture allowances (i.e., low, 25 versus high, 40 kg dry matter/cow/day) and two concentrate supplementation levels (i.e., 0 versus 1 kg concentrate/4 kg milk). No interactions occurred between concentrate supplementation and pasture allowance for milk FA composition. Concentrate supplementation increased short-chain FA content, and reduced the content of long-chain FA, trans11 C18:1, and cis9, trans11 conjugated linoleic acid (CLA) (1.36 versus 1.18 g/100 g). Concentrate supplementation increased saturated FA (58.6 versus 54.0 g/100 g) and reduced unsaturated FA content (39.9 versus 43.8 g/100 g). Grazing at high pasture allowance increased short-, medium-, and long-chain FA content, without affecting cis9, trans11 CLA content. Saturated FA content was higher (57.1 versus 55.6 g/100 g), and unsaturated FA content was lower (41.3 versus 42.5 g/100 g), when cows grazed at high pasture allowance. Concentrate supplementation reduced unsaturated FA and cis9, trans11 CLA in milk of dairy cows grazing at two pasture allowances. In the second study, two experiments evaluated effects of different energy supplements in grazing dairy cows. In Experiment 1, 25 multiparous Holstein cows were assigned to a cracked corn (CC) or a steam flaked corn (SFC) supplement containing 667 g/kg of corn grain plus a pelleted protein/mineral supplement. In Experiment 2, 22 multiparous Holstein cows were assigned to a ground corn grain (GC) or a non-forage fiber (NFF) supplement. The GC supplement contained 850 g/kg of corn grain, and the NFF supplement contained 440 g/kg of non-forage fiber sources (i.e., beet pulp, soyhulls, wheat middlings) that partially replaced corn grain. Milk FA composition was not affected by corn processing or carbohydrate source. The content of short-, medium-, long-chain FA, and cis9, trans11 CLA (2.5 g/100 g in Experiment 1; 2.1 g/100 g in Experiment 2) was similar between supplements in both experiments. The type of supplement did not affect the content of saturated (62.6 g/100 g in Experiment 1; 65.4 g/100 g in Experiment 2) and unsaturated FA (37.5 g/100 g in Experiment 1; 34.6 g/100 g in Experiment 2). Supplementation with supplements differing in the rate and extent of ruminal carbohydrate digestion did not affect the milk FA composition of grazing dairy cows.

Increasing the intake of highly digestible Persian clover herbage reduces rumen fluid pH and the rate of degradation of neutral detergent fibre in grazing dairy cows

An experiment was conducted to investigate the hypothesis that increasing the intake of Persian clover (Trifolium resupinatum L.) would decrease rumen fluid pH and the rate of loss of neutral detergent fibre from nylon bags. It was further hypothesised that the reduction in the rate of disappearance of neutral detergent fibre with increased intake would be less in highly digestible clover than in highly digestible ryegrass or pasture hay. Sixteen rumen fistulated cows, in late lactation, were used in a completely randomised, split-plot design for 33 days. There were 4 pasture allowance treatments (9, 16, 32 and 53 kg dry matter (DM)/cow.day of Persian clover) with 4 cows per treatment. Cows grazed in individual plots, pasture intakes were measured, and rumen fluid and in sacco measurements were undertaken. Pasture DM intake increased asymptotically as pasture allowance increased from 9 to 53 kg DM. Cows grazing at the 9 kg pasture allowance spent less time grazing than cows at higher allowances (294 v. 368, 421 and 414 min, P&lt;0.05). Cows grazing at the 2 lower allowances spent less time grazing at night than cows at the 2 higher allowances. There was no effect (P&gt;0.05) of pasture allowance on time spent ruminating, which averaged 236 min. Estimated rates of intake increased (P&lt;0.05) with pasture allowance. Average daily rumen fluid pH decreased linearly (P&lt;0.05) with pasture intake, with the averages for the pasture allowance treatments being 6.03, 5.95, 5.83 and 5.79 as pasture allowance increased. The patterns of rumen fluid pH over 24 h indicated that it was only late in the night that treatment differences were detected, with the lower pasture allowance treatments recording higher rumen fluid pH values than the higher pasture allowance treatments. There was no effect of pasture allowance on average daily rumen fluid ammonia-N concentrations (25 mg/100 mL). Total volatile fatty acids concentrations averaged 139, 152, 163 and 168 mmol/L as pasture allowance increased from 9 to 53 kg DM/cow.day. The proportion of acetate in total volatile fatty acids generally declined (71.4, 70.4, 67.4 and 69.2%; s.e.d. = 1.14) and the proportion of propionate generally increased (15.2, 15.5, 17.6 and 17.0%; s.e.d. = 0.77) as pasture allowance increased from 9 to 53 kg DM/cow, respectively. Rate of neutral detergent fibre loss from nylon bags was highest in clover, and lowest in hay, and was higher in cows grazing at 9 and 16 kg allowances compared with cows at 32 and 53 kg (P&lt;0.05). There was a linear relationship (P&lt;0.05) between rate of neutral detergent fibre loss and rumen fluid pH for clover and ryegrass, but not hay (P&gt;0.05). There were no differences (P&gt;0.05) in total rumen contents (75.6 kg; s.e.d. = 6.95), or DM (7.3 kg; s.e.d. = 0.73) and neutral detergent fibre (2.7 kg; s.e.d. = 0.32) pools, of cows grazing at different allowances. Offering cows increasing allowances of Persian clover pasture reduced rumen digesta retention times, as rumen pool sizes did not change. Average daily pH fell with increasing allowance due to differences in daily intake and pH patterns, and increasing pasture allowance decreased the rate of disappearance of neutral detergent fibre. It is suggested that increased outflow rates, driven by differences in daily pH patterns and changes in substrate composition, were responsible for the decline in disappearance of neutral detergent fibre from nylon bags, but the effects of the factors cannot be separated.

Grazing Behavior Affects Daily Ruminal pH and NH3 Oscillations of Dairy Cows on Pasture

Grazing behavior of Holstein cows in late lactation at 2 pasture allowances without or with supplementation was studied in a single reversal design. Twenty multiparous cows (4 ruminally cannulated) grazed a bromegrass/orchardgrass pasture offered at 2 pasture allowances: 1) low, and 2) high, with 25 and 40kg/d of DM per cow, respectively. Half of the cows were supplemented with a mineral/vitamin mixture (1kg/ d of the mix in a corn/molasses carrier) and the other half supplemented with a corn-based concentrate (1kg of concentrate per 4kg of milk). Automatic behavior recorders were used to measure grazing time and number of bites. For the mineral/vitamin mixture-supplemented cows, grazing time and number of bites after the p.m. milking was greater and ruminal pH was numerically lower at the high pasture allowance. For the concentrate-supplemented cows, grazing behavior and ruminal pH did not differ between the 2 pasture allowances. Pattern of grazing time of mineral/vitamin mixture-supplemented and concentrate-supplemented cows influenced daily oscillations of ruminal pH and NH3-N concentration. Pasture allowance affected grazing behavior of mineral/vitamin mixture-supplemented cows; however grazing behavior of concentrate-supplemented cows was not affected by pasture allowance.

Rumen fermentation characteristics of dairy cows grazing different allowances of Persian clover- or perennial ryegrass-dominant swards in spring

An experiment was conducted in which cows in early lactation grazed Persian clover (Trifolium resupinatum L.) or perennial ryegrass (Lolium perenne L.)-dominant pastures at low or high pasture allowances in order to determine the effects of pasture type and level of feeding on rumen fermentation patterns. The hypotheses for grazing dairy cows were: (i) the consumption of Persian clover would result in a more rapid rate of degradation and less stable rumen fermentation patterns compared with perennial ryegrass; and (ii) the greater intake of cows grazing at high compared with low pasture allowances would also cause less stable rumen fermentation patterns. Stability of rumen fermentation refers to the level to which rumen fluid pH declines, especially for long periods of a day, indicating that the rumen is not coping with neutralising and/or removing acids. Cows grazing Persian clover had lower (P&lt;0.05) average daily rumen fluid pH (5.7 v. 5.9), molar proportions of acetic acid (68.3 v. 70.6%) and ratios of lipogenic to glucogenic volatile fatty acid (4.6 v. 5.1) in the rumen than those grazing perennial ryegrass. They had higher (P&lt;0.05) rumen fluid ammonia-N (26.3 v. 13.0 mg/100 mL) and total volatile fatty acid (165 v. 134 mmol/L) concentrations and molar proportions of butyric (11.3 v. 10.7%) and propionic (17.2 v. 16.1%) acids than cows grazing perennial ryegrass. Cows grazing at low pasture allowances had a higher (P&lt;0.05) average daily rumen fluid pH (5.9 v. 5.7) and lower rumen fluid ammonia-N (18.6 v. 20.7 mg/100 mL) and total volatile fatty acid (143 v. 156 mmol/L) concentrations than cows grazing at high pasture allowances. Cows given Persian clover at the high allowance had a rumen fluid pH less than 6.0 for the entire day while rumen fluid pH was below 6.0 for at least 15 h of the day on all the other treatments. There was no effect (P&gt;0.05) of pasture allowance on the degradation rate of perennial ryegrass dry matter, but the higher allowance of Persian clover resulted in the highest (P&lt;0.05) rate of degradation of dry matter compared with either ryegrass treatment or the low allowance of Persian clover. The effective dry matter degradability of Persian clover was greater (P&lt;0.05) than that of perennial ryegrass, and the effective dry matter degradability of herbage in cows grazing at low allowances was greater (P&lt;0.05) than at higher allowances. However, future research should consider neutral detergent fibre degradation in grazing dairy cows with low rumen fluid pH levels.

Effects of grain or hay supplementation on the chewing behaviour and stability of rumen fermentation of dairy cows grazing perennial ryegrass-based pasture in spring

Cows grazing highly digestible pasture in early spring can have very low rumen fluid pH that can negatively impact on the efficiency of microbial digestion. In this experiment, cows in early lactation grazed perennial ryegrass (Lolium perenne L.)-based pasture alone at low or high allowances, or at a low allowance supplemented with either a cereal grain pellet, a chopped hay cube or a cube containing cereal grain and chopped hay to determine the effects of the addition of neutral detergent fibre as hay on chewing behaviour and stability of rumen fermentation. The hypotheses tested were that: (i) supplementing high digestibility ryegrass pasture with pelleted cereal grain would increase the proportion of the day that the pH of rumen fluid was below 6.0 and would decrease the rate of degradation of neutral detergent fibre in pasture and hay; and (ii) the inclusion of chopped hay with the cereal grain supplement in cubes would reduce the proportion of the day that the rumen fluid pH was below 6.0 and restore the rate of degradation of neutral detergent fibre in pasture and hay to that in unsupplemented cows. Rumen fluid pH was highest (P&lt;0.05) in cows fed a chopped hay cube and lowest (P&lt;0.05) in cows fed a cube containing cereal grain and chopped hay, with no significant (P&gt;0.05) difference between those fed pasture only or cereal grain pellets. The introduction of grain, with or without hay, did not substantially alter the pattern or magnitude of changes in rumen fluid pH, but did reduce (P&lt;0.05) the rate of degradation of neutral detergent fibre in pasture (5.3 v. 7.6%/h) and hay (2.7 v. 5.0%/h) in the rumen. Rumen degradation rates of pasture dry matter and neutral detergent fibre were not improved by adding chopped hay. Total volatile fatty acid concentrations in rumen fluid were highest (P&lt;0.05) on the high pasture allowance treatment and lowest (P&lt;0.05) on the low pasture allowance and the chopped hay cube treatments. Supplementation with grain reduced (P&lt;0.05) the proportion of acetate and increased (P&lt;0.05) the proportion of propionate in total volatile fatty acids. There were no significant (P&gt;0.05) effects of dietary treatment on time spent grazing or on rate of biting while grazing. Cows in treatments receiving grain supplements (532 min) and those in the high pasture allowance treatment (566 min) spent more (P&lt;0.05) time ruminating than those in the low pasture allowance (415 min) and chopped hay cube (465 min) treatments. The relative contributions of low pH and of starch to the reduction in rates of dry matter and neutral detergent fibre degradation in the rumen cannot be determined from this experiment, however, it is likely that both factors contribute to a relative increase in the metabolic activity of non-cellulolytic microorganisms.

Manipulating the Dietary Cation-Anion Difference via Drenching to Early-Lactation Dairy Cows Grazing Pasture

Diets offered to grazing dairy cows can vary considerably in their dietary cation-anion difference (DCAD) and are often well in excess of what has been considered optimal. The effects of a range of DCAD on the health and production of pasture-based dairy cows in early lactation was examined in a randomized block design. Four groups of 8 cows were offered a generous allowance of pasture (45±6 kg/d of dry matter (DM) per cow) for 35 d and achieved mean pasture intakes of approximately 17 kg/d of DM per cow. Cows were drenched twice daily with varying combinations of mineral compounds to alter the DCAD. Dietary cation-anion difference ranged from +23 to +88 mEq/100g of DM. A linear increase in blood pH and HCO3− concentration and blood base excess, and a curvilinear increase in the pH of urine with increasing DCAD indicated a nonrespiratory effect of DCAD on metabolic acid-base balance. Plasma concentrations of Mg, K, and Cl declined as DCAD increased, whereas Na concentration increased. Urinary excretion of Ca decreased linearly as DCAD increased, although the data suggest that the decline may be curvilinear. These results in conjunction with the increased concentrations of ionized Ca suggest that intestinal absorption of Ca or bone resorption, or both, increased as DCAD declined. Dry matter intake, as measured using indigestible markers, was not significantly affected by DCAD. However, the linear increase in the yield of linolenic acid, vaccenic acid, and cis-9, trans-11 conjugated linoleic acid in milk, as DCAD increased is consistent with a positive effect of DCAD on DM intake. Increasing DCAD did not significantly affect milk yield or milk protein, but the concentration and yield of milk fat linearly increased with increasing DCAD. The increased milk fat yield was predominantly a result of increased de novo synthesis in the mammary epithelial cells, although an increase in the yield of preformed fatty acids also occurred. Milk production results suggest that DCAD for optimal production on pasture diets may be higher than the +20 mEq/100g of DM previously identified for total mixed rations.

Investigating the interaction between body condition at calving and pre-calving energy and protein nutrition on the early lactation performance of dairy cows

The experiment was an investigation into the interaction between body condition at calving and the provision of additional dietary energy or protein to a total mixed ration (TMR) in late gestation on milk production and indices of reproductive performance. Seventy-two Holstein–Friesian multiparous cows (12 per treatment) were fed to achieve target body condition scores (BCS) of either 4 (3.5–4.5) or 6 (5.5–6.5) units by 1 month before they calved (July). They were individually fed 1 of 3 diets during the last 26 (s.d. ± 7.4) days before calving date (mean of 19 August; s.d. ± 9.7). The 3 diets were (1) a TMR containing maize silage, barley grain, canola meal and hay, fed at 1.5% of liveweight (control diet), (2) the TMR plus 3.5 kg DM of wheat-based pellets (energy diet), and (3) the TMR plus 3.1 kg DM of soyabean meal (protein diet). Cows grazed highly digestible pasture after calving at pasture allowances of about 35 kg DM/cow.day, and were supplemented with 6 kg DM of cereal grain-based pellets per day. Cows were fed this diet for an average of about 10 weeks, from calving until the start of mating at the end of October. The provision of additional dietary energy and protein before calving did not affect post-partum production, and there were no interactions with body condition. On average, the BCS 6 cows were 111 kg heavier (P&lt;0.05), and were 1.8 units of body condition higher (P&lt;0.05), than the BCS 4 cows. The thin cows maintained body condition during the month before parturition while the fat cows lost condition. The cows offered additional protein improved their body condition (+0.07 units) during this time, while the cows in the other 2 dietary treatments lost condition (–0.10 units). Average daily rumen fluid pH was lowest in the cows fed the additional energy. Blood urea and rumen fluid ammonia concentrations were increased markedly by feeding the protein diet. In comparison with cows offered the control and energy diets, the cows offered additional protein had the highest (P&lt;0.05) urine pH levels (6.24 v. 5.64 and 5.59 for the protein, control and energy diets, respectively), the lowest (P&lt;0.05) blood serum concentrations of calcium at calving (1.74 v. 2.06 and 1.99 mmol/L for the protein, control and energy diets, respectively), and tended to have more milk fever and retained foetal membranes. Regression analysis indicated that the response to improving BCS at calving was 1.1 kg milk per additional BCS at calving (P&lt;0.05), and the fatter cows produced milk with a higher (P&lt;0.05) milk fat concentration (3.46 v. 3.07%) than the thinner cows. There was no effect (P&gt;0.05) of treatment on days to first ovulation or in-calf rates although only about 80% of cows conceived during the 12-week mating period.

The Effect of Pasture Allowance and Supplementation on Feed Efficiency and Profitability of Dairy Systems

Partial budgeting was used to compare income over feed costs of high-yielding Holstein cows based on data from an experiment with 4 dietary treatments arranged in a 2×2 factorial. The factors were low (25kg DM/cow per day) and high (40kg DM/cow per day) pasture allowance (PA) and supplemental grain fed at 1kg/4kg of milk or no supplemental grain fed. The 4 treatments were low PA unsupplemented (LPAU), low PA concentrate supplementation (LPAC), high PA unsupplemented (HPAU), and high PA concentrate supplementation (HPAC). Two management systems were modeled. The first, a fixed herd size flexible rotation length model, and the second, a flexible herd size model where rotation length was fixed. The LPAC treatment yielded the highest income over feed costs, followed by the HPAC treatment. The treatment generating the lowest income was the HPAU system. The low PA systems generated more income than did the high PA systems for equivalent supplemental feeding strategies. The results also showed that feeding supplemental grain increased the income-over-feed costs compared with systems that did not feed supplemental grain. In most treatments, comparing the fixed herd against the flexible herd models, the flexible herd size model generated higher income due to the substitution of relatively low income per hectare of hay production for higher income from milk production. There were also differences in feed conversion efficiencies for milk production due to concentrate supplementation (1.04 unsupplemented vs. 1.21 supplemented), but PA did not affect the efficiency of milk production. Neither supplementation nor PA affected the feed conversion efficiency of milk fat yield. However, the efficiency of milk protein yield was affected by concentrate supplementation (0.028 unsupplemented vs. 0.034 supplemented) but not by pasture allowance.

Relação entre variáveis na regulação do consumo de vacas Holandês × Zebu em lactação sob pastejo em capim-elefante

A análise fatorial de componentes principais (CP) foi usada no exame do relacionamento entre variáveis de um banco de dados da Embrapa Gado de Leite. As variáveis disponíveis foram relacionadas às vacas (dias em lactação, teores lácteos de gordura e extrato seco total, produção de leite, ordem de lactação, peso vivo e grau de sangue), ao manejo (dia de pastejo, disponibilidade e períodos de descanso da pastagem), ao ambiente (estação do ano, precipitação pluviométrica) e ao alimento (consumo de nutrientes do concentrado e da cana × uréia, consumo de MS de pastagem de capim-elefante, composição química e digestibilidade in vitro da pastagem e concentração fecal de PB, FDN e FDA). O primeiro CP (33,7% da inércia dos dados) representou o uso da suplementação volumosa (cana × uréia) da pastagem em resposta à redução sazonal da disponibilidade e do consumo de capim-elefante. O segundo CP (15,3% da inércia) foi relacionado ao consumo de nutrientes do concentrado. O terceiro CP (8,5% da inércia) representou efeitos do manejo sobre a composição química da pastagem. A interpretação gráfica dos resultados favoreceu a percepção mais dinâmica da intensidade da associação e do antagonismo entre as variáveis contextualizadas no estudo.

The effects of cold exposure, food allowance and litter size on immunity of periparturient sheep toTeladorsagia circumcinctaand Trichostrongylus colubriformis

AbstractSixty twin- and 60 single-bearing ewes were used in a 2 ✕ 2 ✕ 2 factorial design incorporating nutritional and shearing-cold exposure treatment (no. = 15 per subgroup) to study the effects on periparturient immunity against nematode infection. From week –8 to week –4 relative to parturition, animals grazed ryegrass-white clover pastures at allowances designed to provide either 0·8 (low allowance) or 1·2 (high allowance) of estimated metabolizable energy requirement for a ewe carrying 1·5 lambs. During week –4, half the sheep from each reproductive effort and nutritional group were shorn and exposed to artificial wind and rain for 4 h on each of 4 days consecutively. During the same week, all animals were challenged twice with 1·5 ✕ 104Teladorsagia circumcincta and 1·5 ✕ 104Trichostrongylus colubriformis infective third stage larvae to supplement the natural infection from pasture. From week –3 to week + 5 relative to parturition the sheep were run together and offered pasture at rates estimated to enable them to meet their nutrient requirement.Shearing and cold stress reduced ewe body weight (by up to 4·66 kg per sheep), and temporarily reduced the levels of IgA against T. circumcincta (by proportionately 0·24) and T. colubriformis (0·34), and raised faecal egg count (1·6 to 4·4 fold) but did not affect the parasite-specific total antibody levels in the serum. The low allowance during pregnancy was associated with a 6·09-kg decrease in ewe body weight, decrease in the levels of total antibody and of IgA against both T. circumcincta and T. colubriformis, and increased faecal egg count (by 1·5 to 10·6 fold) during pregnancy and lactation. Faecal egg count was consistently higher (up to 8·8 fold) in twin-bearing and rearing ewes than in single-bearing and rearing ewes except during the first 4 weeks of the experiment. A significant effect of litter size on antibody levels was relatively small when compared with short-term changes (reductions) in antibody levels immediately around parturition. There were significant negative correlations between faecal egg count during late pregnancy and ewe body weight in lactation and significant negative correlations between the levels of total antibody against T. colubriformis and faecal egg counts near the end of the experiment. We conclude that litter size is likely to have greater influence on the resistance of ewes to nematode infections in the periparturient period than either pasture allowance or cold stress within the range of parameters used in this work.

Decision support tools to optimise conversion of pasture to milk

This paper examines the logic behind the efficient feeding of grazing dairy cows with the objective of improving on-farm productivity. Efficient utilisation of feeds by grazing dairy cows requires a detailed knowledge and understanding of feed budgeting principles, based on an understanding of seasonal pasture growth and pasture accumulation rates, nutritive characteristics of the pasture consumed, relationships between allowance of pasture and pasture intake, and interactions between pasture and supplementary feeds. Decision support tools that assist in making complex operational decisions to more efficiently feed grazing dairy cows have been briefly reviewed.