Post-grazing Herbage Mass Research Articles

Grazing management practices on Waikato and Canterbury dairy farms diverging in bulk milk urea content

New Zealand dairy farmers have little realtime information on surplus nitrogen (N) in their herd’s diet to help manage farm-scale N loss. By understanding the influence of management on bulk milk urea (BMU), farmers could potentially use milk components to identify changes in dietary N surplus. Our study examined the relationships between grazing management and BMU concentration on 38 dairy farms selected for low or high BMU in Canterbury and Waikato. Measurements included pre- and post-grazing herbage mass, perennial ryegrass leaf stage at grazing, and botanical and chemical composition (crude protein (CP) and metabolisable energy (ME) content) of herbage on four occasions over a year. Herds with Low BMU tended to graze pastures with a greater pre-grazing herbage mass (+153 kg DM/ha), a more advanced leaf stage (+0.13 number of leaves), and longer grazing intervals (+11 days). Consistent with this, herbage on Low BMU farms had lower CP (-2.7%) compared with High BMU farms. We identified grazing management differences between Low and High BMU groups, which could be linked to reductions in N surplus in the herd’s diet through the lower CP% of pasture offered. Future work should determine the importance of this in relation to other farm management factors such assupplement and N fertiliser use.

112 Herbage Mass, Nutritive Value, and Grain Yield of four Wheat Varieties Managed as a Dual-Purpose Crop

Abstract Dual-purpose wheat (Triticum aestivum L.) systems increase farm sustainability by diversifying on-farm income. While these systems are common in the Southern Great Plains of the U.S., they are not often utilized in the Southeast. This study aimed to evaluate pre- and post-grazing herbage mass (HM) of four winter wheat varieties managed under a dual-purpose grazing and grain production system. The wheat varieties evaluated were generic feed-type wheat (unknown variety blend, Feed), seed-type wheat ‘GA Gore’ (Seed) and two forage-type varieties, ‘AGS 2024’ (AGS) and ‘Pioneer 26R41’ (Pioneer). The experiment was a randomized complete block design (n = 4) conducted during the winter of 2021 and 2022. Three grazing frequencies were utilized: an ungrazed control (NG), low frequency (LF) and high frequency (HF) grazing schedule. Low frequency plots received monthly grazing in January and February while HF treatments received a third grazing in March. Plots were grazed with 20 cow-calf pairs (Bos taurus) until an even defoliation height of 10 cm was achieved. Herbage mass was determined using three 0.1m2-quadrats per plot and clipped to a 10 cm stubble height before (PreG) and after (PostG) each grazing event. Forage samples were then dried at 45°C for 72 h. Data were analyzed using PROC GLIMMIX of SAS (SAS Inst., Cary, NC) with forage sample date as a repeated measure. Differences were declared at P < 0.05. Final biomass, including stems, chaff, and grain, was greatest for Pioneer but was not different from AGS or Feed (4,112 kg/ha and 4,003 kg/ha; P ≤ 0.94). Before grazing, AGS herbage mass (2,646 kg/ha) was greater (P ≤ 0.03) than all other varieties. There was an interaction (P ≤ 0.01) of variety and grazing frequency for Pre-G herbage mass. Compared with all other varieties, AGS had greater ADF (24.93%; P < 0.01) and least TDN (72.49%: P < 0.01). Forage nitrate-nitrogen was not different (P ≥ 0.49) among all varieties or grazing frequencies (157.73 ppm). Across grazing frequencies, Pioneer had greater final grain yield (3,619.43 kg/ha; P < 0.01) with Seed having the least (1,272.12 kg/ha; P < 0.01). These results indicate that common Southeastern wheat varieties can be successfully utilized in a dual-purpose management system; however, grazing frequency should be monitored to prevent grain yield losses.

Grazing management effects on cover crop responses and cotton lint yield

AbstractGrazing cover crops can improve land‐use efficiency and diversification, making agricultural enterprises more resilient to market fluctuations. We investigated how grazing intensity affects cover crop forage responses and cotton (Gossypium hirsutum L.) lint yield. Cover crops were a rye (Secale cereale L.)–oat (Avena sativa L.) mixture managed as follows: no grazing + 34 kg N ha–1 (NG34), no grazing + 90 kg N ha–1 (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG), compared with a no cover crop control. All grazed treatments received 90 kg N ha–1. Average postgrazing herbage mass (HM) for HG, MG, and LG was 520, 1,350, and 2,120 kg dry matter ha–1, respectively. Herbage accumulation (HA) rate was greater for LG than HG, with MG being intermediate. Forage crude protein (CP) and in vitro digestible organic matter (IVDOM) concentrations decreased as the season progressed and were usually greater for HG than MG and LG. Stubble residue before cover crop termination was greatest for NG34 and NG90 in 2018 and 2020, however, in 2019 NG90 had greater stubble residue before termination than NG34 (7540 vs. 6650 kg dry matter ha–1). Heavy grazing resulted in greater weed proportion (17 vs. 6.5%) and lesser soil cover (49 vs. 70%) than nongrazed cover crops. Cotton lint yield was low and unaffected by treatment, reaching a maximum of 520 kg ha–1 in 2019. Although lint yield was not affected by cover crop fertilization or grazing during 3 yr, HG reduced soil cover and increased weed presence.

Effects of liveweight and incisor arcade breadth on bite mass of grazing Holstein-Friesian dairy cows

Bite mass is the dry matter ingested per prehension bite. It has previously been reported that sward characteristics such as herbage height, density and allowance can affect bite mass in grazing cows. Animal characteristics such as liveweight and incisor arcade breadth may also affect bite mass. Understanding factors that influence bite mass can lead to an improvement in the estimate of dry matter intake of grazed herbage. The aim of this study was to determine the effects of liveweight and incisor arcade breadth on average daily bite mass of grazing dairy cows. The research consisted of two parts. In Part I, 113 multiparous lactating Holstein-Friesian cows were assessed for their 7-d average liveweight and incisor arcade breadth. In Part II, from the 113 cows screened in Part I, 32 cows were selected for use in a grazing experiment. The 32 cows were allocated to one of four groups of 8 cows based on the following factors: light cows (mean liveweight of 542 kg) with narrow incisor arcade (mean of 8.2 cm) (L-N), light cows (mean liveweight of 581 kg) with wide incisor arcade (mean of 9.5 cm) (L-W), heavy cows (mean liveweight of 658 kg) with narrow incisor arcade (mean of 8.2 cm) (H-N) and heavy cows (mean liveweight of 660 kg) with wide incisor arcade (mean of 9.5 cm) (H-W). Each cow grazed in an individual plot and herbage intake was calculated as the difference between estimated pre-and post-grazing herbage mass in each plot, as measured with a rising plate metre. Prehension bites were counted using jaw movement sensors. In Part I, incisor arcade breadth of the cows was between 7.0 and 9.8 cm and liveweight was between 490 and 745 kg. There was no relationship (P = 0.30) between liveweight and incisor arcade breadth of these cows. In Part II, mean bite masses were 0.46, 0.50, 0.50 and 0.49 g DM/bite for LN, LW, HN and HW, respectively and the differences between them were not significant (P = 0.30, SED = 0.03). There was also no effect of liveweight category (P ≥ 0.68) or incisor arcade breadth category (P ≥ 0.72) or their interaction (P ≥ 0.78) on prehension bites, mastication chews or total eating bites. These findings suggest that mechanistic models for estimating bite mass and herbage intake may not need to include liveweight or incisor arcade breadth.

Biological and economic responses to increasing nitrogen rates in Momba\xe7a guinea grass pastures

Nitrogen fertilization has been recognized as an essential tool towards the establishment of sustainable intensification of pasture-based livestock systems using tropical perennial grasses if, for a given ecosystem it is capable of increasing forage growth, stocking rates and animal performance. This study assessed pasture growth traits, nutritive value, animal and economic responses of Panicum maximum cv. Mombaça guinea grass pastures subjected to different levels of N fertilization (100 (N100), 200 (N200), and 300 (N300) kg N ha−1 yr−1). Pastures were managed under rotational stocking to maintain similar pre (80–90 cm) and post-grazing (45 cm) canopy heights. A partial budget and a Benefit–Cost Analysis were used to assess the economic returns on increasing N fertilization. N300 resulted in greater post-grazing herbage mass. A slightly higher neutral fiber and acid lignin detergent was observed at N100 (P < 0.05); crude protein increased linearly, and in vitro digestible organic matter reached maximum value at 265.4 kg N ha−1 yr−1. Annual averages of animal weight gain were 515, 590 and 660 g d−1, respectively, for N100, N200 and N300. There was a decrease from 3.7 to 1.9 kg of body weight gain per kg of additional N applied when increasing N rates from 100 to 200 and from 100 to 300 kg ha−1. The net profit improved with increasing N levels, but at reducing rates, reaching its maximum at the N300 level. The change from 100 to 200 kg N ha−1 presented the best return, with USD 3.73 for each additional dollar invested, while the change from 200 kg N ha−1 to 300 kg N ha−1 was economically less than optimal, recouping only USD 1.60 for each dollar. The N300 rate presented the highest net profit per hectare (accounting profit), even in a pessimist scenario (25% reduction in production). Despite being profitable, the N300 rate was less than optimal from an economic standpoint, since an additional 100 kg of Nitrogen ha−1 to change from N200 to N300 level reduced both the net returns and the Benefit–Cost ratio. Our results suggest that the economically optimal level of N fertilization for Mombaça guinea grass pasture should be between 200 and 300 kg ha−1.

176 Evaluating Dual-purpose Wheat Varieties in the Southeastern U.S

Abstract Dual-purpose wheat (Triticum aestivum L.) systems increase farm sustainability by diversifying on-farm income. While these systems are common in the Southern Great Plains of the United States, they are not often utilized in the Southeast. This study aimed to evaluate pre- and post-grazing herbage mass (HM) of four winter wheat varieties managed under a dual-purpose grazing and grain production system. The winter wheat varieties evaluated were generic feed-type wheat (mixed variety, Feed), seed-type wheat (‘GA Gore’) and two forage-type varieties, ‘AGS 2024’ (AGS) and ‘Pioneer 26R41’ (Pioneer). The experiment was a completely randomized block design with n = 4. Each plot was randomly assigned either as no-grazing (CON) or grazing (GF2). Plots were grazed with cow-calf pairs that were fasted 24 h before each grazing event. Grazing was considered complete when the average stubble height was 10 cm. Herbage mass was determined using three 0.1m2-quadrats per plot and clipping to a 10 cm stubble height before (PreG) and after (PostG) each grazing event. Forage samples were then dried at 45°C for 72 h. Data were analyzed using PROC GLIMMIX of SAS (SAS Inst., Cary, NC). Differences were declared at P &amp;lt; 0.05. Initial HM was greater for PreG than PostG (883 and 615 kg/ha, respectively; P &amp;lt; 0.01). Prior to grazing, AGS (1204 kg/ha) was greater (P &amp;lt; 0.02) than all other varieties. Pre-grazing, there were no differences among the other varieties (776 kg/ha; P &amp;gt; 0.14). Post-grazing, AGS had a greater HM than Seed (788 and 391 ka/ha, respectively; P = 0.04), while all other varieties were intermediate (642 kg/ha). Herbage mass was affected by grazing frequency with CON being greater (P &amp;lt; 0.01) than GF2 (993 and 691 kg/ha, respectively). These results indicate that both wheat variety and grazing treatment had an effect on dual-purpose wheat herbage mass.

Grazed rain-fed small-grain cereals as a forage option for small-scale dairy systems in central Mexico.

Small-scale dairy systems face reduced availability of water for irrigation of pastures and disruption in the amount or pattern of rains due to climate change, so research on alternative short-cycle rain-fed forages is needed. Grazing reduces feeding costs and small-grain cereals may be an option. The objective was to assess on-farm the performance of dairy cows grazing 6h/day of three small-grain cereals: rye (RYE), wheat (WHT), and triticale (TRT), and supplemented 4.5kg dry matter (DM)/cow/day of concentrate. Twelve Holstein cows were used in repeated 3 × 3 Latin squares with 14-day experimental periods. Pasture variables were analysed with a split-plot design, and economic analysis was performed with partial budgets. Sampling of forage (sward height, net herbage accumulation, botanical and chemical composition of herbage) and animal variables (milk yield and composition, live weight, and body condition score) were at the end of each period. The RYE showed a trend (P > 0.05) for higher net herbage accumulation (NHA) with highly significant differences (P < 0.001) among periods. The RYE had higher DM, a lower crude protein (CP) content (P < 0.05), and no differences for other chemical components between treatments (P > 0.05). The RYE proportion in pasture was consistently higher, whilst the lowest cereal proportion was in WHT. There were no differences (P > 0.05) for any animal variable. The RYE and TRT treatments proved useful as rain-fed forage alternatives under grazing. WHT showed lower crop and economic performance. However, given the higher cereal component in pastures, regrowth potential, and post-grazing herbage mass, as well as better economic performance, the RYE treatment was better ranked by the participating farmer.

Short-Term Effect of Daily Herbage Allowance Restriction on Pasture Condition and the Performance of Grazing Dairy Cows during Autumn.

Simple SummaryDaily herbage allowance (defined as herbage mass × daily offered area) is recognized as the main grazing management factor to improve pasture utilization and milk output per hectare. Daily herbage allowances should balance the dual objectives of high milk output per hectare while maintaining the quality of the pasture to optimize the profitability of grazing-based dairy production systems. We tested two contrasting herbage allowances (17 and 25 kg dry matter (DM)/cow.day) and two levels of maize silage supplementation (4.5 and 9 kg DM/cow.day) in grazing dairy cows and measured a set of variables related to pasture management, sward characteristics, dynamic of herbage depletion throughout the grazing sessions, and cows grazing behavior, among others. Our results suggest that a more intensive grazing regime of 17 kg DM/cow per day of daily herbage allowance rather than a high level of supplementation with maize silage is appropriate to improve milk production and solids yield per hectare without affecting pasture quality or sward characteristics over the short-term.The aim of this study was to evaluate the short-term effects of daily herbage allowance (DHA, defined as the product of pre-grazing herbage mass and offered area per animal) on pasture conditions and milk production of Holstein-Friesian dairy cows. Forty-four early lactation dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design that tested two levels of DHA (17 and 25 kg DM/cow.day) and two levels of maize silage supplementation (MSS, 4.5 and 9 kg DM/cow.day) over a 77-day period. Low DHA decreased the post-grazing herbage mass from 1546 to 1430 kg DM/ha and the compressed sward height from 5 to 4.4 cm, while the grazing efficiency remained unaffected. Low DHA induced a faster herbage mass reduction, while the sward-height and pasture characteristics did not differ from the high DHA regime. Low DHA decreased the tiller production rates and daily lamina growth, while the leaf-production rate was not affected by the DHA. Daily increases of herbage mass were greater in the high DHA than in the low DHA treatments. Individual milk production and milk protein concentration decreased at a low DHA compared to high DHA, while the milk fat concentration was greater and the milk output per hectare increased by 1510 kg. Neither the MSS level nor the interaction DHA by the MSS level had any effect on the sward characteristics or the productivity of the cows. From these results, it is suggested that, in a high-quality pasture, using 17 kg DM/cow.day was appropriate for improving both herbage utilization and milk production per hectare while maintaining the short-term conditions of a pasture grazed by dairy cows in the autumn.

Herbage dry matter intake estimation of grazing dairy cows based on animal, behavioral, environmental, and feed variables

Information about the individual herbage DMI (HDMI) of grazing dairy cows is important for an efficient use of pasture herbage as an animal feed with a range of benefits. Estimating HDMI, with its multifaceted influencing variables, is difficult but may be attempted using animal, performance, behavior, and feed variables. In our study, 2 types of approaches were explored: 1 for HDMI estimation under a global approach (GA), where all variables measured in the 4 underlying experiments were used for model development, and 1 for HDMI estimation in an approach without information about the amount of supplements fed in the barn (WSB). The accuracy of these models was assessed. The underlying data set was developed from 4 experiments with 52 GA and 50 WSB variables and one hundred thirty 7-d measurements. The experiments differed in pasture size, herbage allowance, pregrazing herbage mass, supplements fed in the barn, and sward composition. In all the experiments, cow behavioral characteristics were recorded using the RumiWatch system (Itin and Hoch GmbH, Liestal, Switzerland). Herbage intake was estimated by applying the n-alkane method. Finally, HDMI estimation models with a minimal relative prediction error of 11.1% for use under GA and 13.2% for use under WSB were developed. The variables retained for the GA model with the highest accuracy, determined through various selection steps, were herbage crude protein, chopped whole-plant corn silage intake in the barn, protein supplement or concentrate intake in the barn, body weight, milk yield, milk protein, milk lactose, lactation number, postgrazing herbage mass, and bite rate performed at pasture. Instead of the omitted amounts of feed intake in the barn and, due to the statistical procedure for model reduction, the unconsidered variables postgrazing herbage mass and bite rate performed at pasture, the WSB model with the highest accuracy retained additional variables. The additional variables were total eating chews performed at pasture and in the barn, total eating time performed at pasture, number of total prehension bites, number of prehension bites performed at pasture, and herbage ash concentration. Even though behavioral characteristics alone did not allow a sufficiently accurate individual HDMI estimation, their inclusion under WSB improved estimation accuracy and represented the most valid variables for the HDMI estimation under WSB. Under GA, the inclusion of behavioral characteristics in the HDMI estimation models did not reduce the root mean squared prediction error. Finally, further adaptation, as well as validation on a more comprehensive data set and the inclusion of variables excluded in this study such as body condition score or gestation, should be considered in the development of HDMI estimation models.

Pasture condition and milk production by grazing dairy cows as affected by daily herbage-allowance restriction

Daily herbage allowance is recognised as the main tool to control pasture utilisation and milk production per cow. The aim of the present study was to evaluate the long-term effects of daily herbage allowance (DHA) on pasture characteristics and milk production of dairy cows. Forty-four dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design by considering two levels of DHA (20 and 30 kg DM/cow.day) and two types of supplements (high-moisture maize and maize silage) over a 77-day period. Pre- and post-grazing herbage masses, vertical distribution of herbage mass, species density, botanical and chemical composition, sward depletion and changes in morphological components of the pasture were measured. The effect of DHA on soil compaction was evaluated on the basis of the penetration resistance. Milk production and composition levels, bodyweights and body condition scores were recorded. Post-grazing residual declined as the level of DHA decreased, while grazing efficiency increased from 39.8% to 44.8%. We found no effects of DHA on any pasture characteristics, pasture regrowth or soil compaction. Low-DHA conditions induced a faster sward-height reduction, while the herbage mass remained unaffected. Individual milk production decreased with DHA. However, milk outputs per hectare increased by 2772 L/ha. Milk composition, bodyweight and body condition score were not affected by DHA. The results showed that DHA restriction decreases milk production per cow while increasing both herbage utilisation and milk production per hectare, without affecting long-term pasture condition.

An on-farm study of the herbage quality and sward characteristics of plantain-clover mixes during late summer and autumn and resulting lamb growth rates

An on-farm study investigated the herbage quality and sward characteristics of plantain-clover mixes and resulting lamb growth rates during late summer and autumn. Three farms were chosen, each with a minimum of 10 ha of plantain-clover mix (Plantago lanceolata ‘Ceres Tonic’, Trifolium pratense, Trifolium repens) used for lamb finishing. Each farm managed the plantain-clover mix area using their routine management without advice or comment from research staff. Throughout autumn, at approximately monthly intervals on the three farms, the pre- and post-grazing herbage masses, botanical composition, herbage quality, plantain dry matter content, secondary chemical composition and lamb growth rates were monitored. A low percentage of clover in the sward, a high percentage of dead stem material and a low crude protein concentration in plantain during dry periods, were identified as the most likely causes of low lamb liveweight gains during autumn. Grazing management during spring that maintains control of plantain stems and encourages the presence of clover, appears to be a key management technique for ensuring high lamb liveweight gains on plantain-clover mixes in late summer and autumn.

Effect of daily herbage allowance restriction on pasture characteristics and milk production by grazing dairy cows in spring

The cumulative effects of daily herbage allowance (DHA) restriction on pasture characteristics and the sustainability of pasture-based dairy systems were evaluated. Sixty-four dairy cows were randomly assigned to one of two grazing treatments (20 and 30 kg DM cow-1 day-1). Milk yield and pre- and post-grazing herbage mass were recorded for every grazing event. Botanical and chemical compositions of the pasture were evaluated. Low DHA increased the stocking rate by 0.7 cows ha-1 and consequently increased grazing efficiency from 41 to 47%. Daily herbage allowance restriction did not affect pasture characteristics or milk production per cow, but DHA restriction increased milk production per hectare (+27%). The results suggest that restriction on daily herbage allowance ensures a higher level of herbage utilization and milk output per ha than high DHA, without affecting pasture characteristics. Therefore, DHA might be a useful grazing management tool for improving the profitability and sustainability of grazing-based dairy systems.

Ad libitum Pasture Feeding in Late Pregnancy Does Not Improve the Performance of Twin-bearing Ewes and Their Lambs.

The present study evaluated the effect of controlled ryegrass-white clover herbage availability from day 128 until day 142 of pregnancy in comparison to unrestricted availability, on the performance of twin-bearing ewes of varying body condition score (BCS; 2.0, 2.5, or 3.0) and their lambs. It was hypothesised that under conditions of controlled herbage availability, the performance of lambs born to ewes with a greater BCS would be greater than those born to ewes with a lower BCS. During the period that the nutritional regimens were imposed, the pre- and post-grazing herbage masses of the Control regimen (1,070±69 and 801±30 kg dry matter [DM]/ha) were lower than the ad libitum regimen (1,784±69 and 1,333±33 kg DM/ha; p<0.05). The average herbage masses during lactation were 1,410±31 kg DM/ha. Nutritional regimen had no effect on ewe live weight, BCS and back fat depth or on lamb live weight, indices of colostrum uptake, maximal heat production, total litter weight weaned or survival to weaning (p>0.05). The difference in ewe BCSs and back fats observed among body condition groups was maintained throughout pregnancy (p<0.05). At weaning, ewes from the BCS2.0 group had lower BCS and live weight (2.4±0.2, 74.3±2.6 kg) than both the BCS2.5 (2.6±0.2, 78.6±2.4 kg) and BCS3.0 ewes (2.7±0.2, 79.0±2.6 kg; p<0.05), which did not differ (p>0.05). Ewe BCS group had no effect on lamb live weight at birth or weaning or on maximal heat production (p>0.05). Serum gamma glutamyl transferase concentrations of lambs born to BCS3.0 ewes were higher within 36 hours of birth than lambs born to BCS2.0 ewes and BCS2.5 ewes (51.8±1.9 vs 46.5±1.9 and 45.6±1.9 IU/mL, respectively [p<0.05]). There was, however, no effect of ewe body condition on lamb plasma glucose concentration (p>0.05). Lamb survival was the only lamb parameter that showed an interaction between ewe nutritional regimen and ewe BCS whereby survival of lambs born to BCS2.5 and BCS3.0 ewes differed but only within the Control nutritional regimen ewes (p<0.05). These results indicate farmers can provide twin-bearing ewes with pre- and post-grazing ryegrass-white clover herbage covers of approximately 1,100 and 800 kg DM/ha in late pregnancy, provided that herbage covers are 1400 in lactation, without affecting lamb performance to weaning. The present results also indicate that under these grazing conditions, there is little difference in ewe performance within the BCS range of 2.0 to 3.0 and therefore they do not need to be managed separately.

Differential response to stocking rates and feeding by two genotypes of Holstein-Friesian cows in a pasture-based automatic milking system

The throughput of automatic milking systems (AMS) is likely affected by differential traffic behavior and subsequent effects on the milking frequency and milk production of cows. This study investigated the effect of increasing stocking rate and partial mixed ration (PMR) on the milk production, dry matter intake (DMI), feed conversion efficiency (FCE) and use of AMS by two genotypes of Holstein-Friesian cows in mid-lactation. The study lasted 8 weeks and consisted in a factorial arrangement of two genotypes of dairy cattle, United States Holstein (USH) or New Zealand Friesian (NZF), and two pasture-based feeding treatments, a low stocking rate system (2 cows/ha) fed temperate pasture and concentrate, or a high stocking rate system (HSR; 3 cows/ha) fed same pasture and concentrate plus PMR. A total of 28 cows, 14 USH and 14 NZF, were used for comparisons, with 12 cows, six USH and six NZF, also used for tracking of animal movements. Data were analyzed by repeated measure mixed models for a completely randomized design. No differences (P>0.05) in pre- or post-grazing herbage mass, DMI and FCE were detected in response to increases in stocking rate and PMR feeding in HSR. However, there was a significant (P<0.05) grazing treatment×genotype×week interaction on milk production, explained by differential responses of genotypes to changes in herbage mass over time (P<0.001). A reduction (P<0.01) in hours spent on pasture was detected in response to PMR supplementation in HSR; this reduction was greater (P=0.01) for USH than NZF cows (6 v. 2 h, respectively). Regardless of the grazing treatment, USH cows had greater (P=0.02) milking frequency (2.51 v. 2.26±0.08 milkings/day) and greater (P<0.01) milk yield (27.3 v. 16.0±1.2 kg/day), energy-corrected milk (24.8 v. 16.5±1.0 kg/day), DMI (22.1 v. 16.6±0.8 kg/day) and FCE (1.25 v. 1.01±0.06 kg/kg) than NZF cows. There was also a different distribution of milkings/h between genotypes (P<0.001), with patterns of milkings/h shifting (P<0.001) as a consequence of PMR feeding in HSR. Results confirmed the improved FCE of grazing dairy cows with greater milk production and suggested the potential use of PMR feeding as a tactical decision to managing HSR and milkings/day in AMS farms.

Enteric methane from lactating beef cows managed with high- and low-input grazing systems.

The objective of this study was to compare methane (CH) emissions from lactating beef cows grazed with different combinations of stocking rate and density. We hypothesized that a low stocking rate coupled with high-stocking-density grazing management would result in poorer forage quality, thereby increasing enteric CH emissions. System A (SysA) consisted of 120 cow-calf pairs rotating on a total of 120 ha divided into 2-ha pastures (stocking rate 1 cow/ha, stocking density 112,000 kg BW/ha, rest period of 60 to 90 d). System B (SysB) consisted of 16 groups of 4 cow-calf pairs each rotating on a 1.6-ha pasture (stocking rate 2.5 cows/ha, stocking density 32,000 kg BW/ha, rest period of 18 to 30 d). Enteric CH measurements were collected using a sulfur hexafluoride (SF) tracer gas method. Sampling occurred during 2012 and 2013 in 2 periods: the beginning (P1) and end of the grazing season (P2). Cannulated Angus cows were stratified by weight, age, and parity and were assigned to each treatment ( = 6) in a crossover design with a doubly repeated measures design, with period and day as repeated measures (α = 0.05). Dry matter intake was determined using chromic oxide (CrO) as a marker. Forage samples were collected ( = 3) for nutrient composition analyses and total forage mass determination. Forage botanical composition was determined using the dry-weight-rank method. Postgrazing herbage mass was greater for SysA during P2 in 2012 ( < 0.01) and 2013 ( = 0.01). Grasses were predominant and represented 67% to 96% of pastures; legumes contributed 3% to 21% of pastures across periods and treatments. The proportion of legumes tended to be higher in SysB pasture sites in P2 than in P1. There were no treatment effects on DMI. There was a period effect on DMI ( < 0.01); DMI of SysA and SysB cows increased from P1 to P2 (4 and 1.1 kg DMI/d increase, respectively). Cows ingested, on average, 2.6% (SysA) and 2.8% (SysB) of their BW. There was no year effect on CH emissions ( = 0.16). Daily enteric CH emissions did not vary with treatment and ranged from 195 to 249 g CH/d across treatment. Enteric CH emissions per unit GE intake varied with treatment during P1 (6.4% and 3.8% for SysA and SysB, respectively; < 0.01). Across treatments and periods, enteric CH emission per unit GE intake was 4.6%, which could be considered low for grazing lactating beef cows. It is likely that cows in the present study were selecting high-quality forage and produced comparatively lower CH emissions.

Frequency and intensity of grazing in winter: their effects on herbage accumulation and nutritive value of Lolium perenne L. dominant swards

A study was conducted in southern Chile with the objective of determining the effect of two frequencies and two intensities of grazing, measured as herbage mass, on production and nutritive value of a permanent sward dominated by Lolium perenne L. during winter season. Additionally the residual effect of the treatments applied in winter was evaluated on the same variables in the following spring. Two pre-grazing herbage mass (kg DM ha-1): low frequency (1,800), high frequency (1,500) and two post-grazing herbage mass: low intensity (1,300), high intensity (1,000), were evaluated. Plots of 145.7 m2 were grazed by dairy cows. The same plots were grazed in the subsequent spring to a frequency of 2,400 kg DM ha-1 and intensity of 1,400 kg DM ha-1. There was no significant effect of the frequency of grazing on herbage mass and growth rate during the first winter. However, in the second winter a greater production with low frequency was obtained. In the two winter seasons, a significant effect of the intensity was obtained, with greater production in high intensity. The most frequently grazed treatments showed higher crude protein and lower soluble carbohydrates. Also, there was a residual effect in the spring generated by frequency and intensity of grazing in the first year, and only for the intensity the second year. It can be concluded that frequency and intensity of grazing applied in winter generate changes in herbage mass production and nutritive value of the sward and also a residual effect in the following spring.

Incorporating a prediction of postgrazing herbage mass into a whole-farm model for pasture-based dairy systems

The DairyNZ whole-farm model (WFM; DairyNZ, Hamilton, New Zealand) consists of a framework that links component models for animal, pastures, crops, and soils. The model was developed to assist with analysis and design of pasture-based farm systems. New (this work) and revised (e.g., cow, pasture, crops) component models can be added to the WFM, keeping the model flexible and up to date. Nevertheless, the WFM does not account for plant-animal relationships determining herbage-depletion dynamics. The user has to preset the maximum allowable level of herbage depletion [i.e., postgrazing herbage mass (residuals)] throughout the year. Because residuals have a direct effect on herbage regrowth, the WFM in its current form does not dynamically simulate the effect of grazing pressure on herbage depletion and consequent effect on herbage regrowth. The management of grazing pressure is a key component of pasture-based dairy systems. Thus, the main objective of the present work was to develop a new version of the WFM able to predict residuals, and thereby simulate related effects of grazing pressure dynamically at the farm scale. This objective was accomplished by incorporating a new component model into the WFM. This model represents plant-animal relationships, for example sward structure and herbage intake rate, and resulting level of herbage depletion. The sensitivity of the new version of the WFM was evaluated and then the new WFM was tested against an experimental data set previously used to evaluate the WFM and to illustrate the adequacy and improvement of the model development. Key outputs variables of the new version pertinent to this work (milk production, herbage dry matter intake, intake rate, harvesting efficiency, and residuals) responded acceptably to a range of input variables. The relative prediction errors for monthly and mean annual residual predictions were 20 and 5%, respectively. Monthly predictions of residuals had a line bias (1.5%), with a proportion of square root of mean square prediction error (RMSPE) due to random error of 97.5%. Predicted monthly herbage growth rates had a line bias of 2%, a proportion of RMSPE due to random error of 96%, and a concordance correlation coefficient of 0.87. Annual herbage production was predicted with an RMSPE of 531 (kg of herbage dry matter/ha per year), a line bias of 11%, a proportion of RMSPE due to random error of 80%, and relative prediction errors of 2%. Annual herbage dry matter intake per cow and hectare, both per year, were predicted with RMSPE, relative prediction error, and concordance correlation coefficient of 169 and 692kg of dry matter, 3 and 4%, and 0.91 and 0.87, respectively. These results indicate that predictions of the new WFM are relatively accurate and precise, with a conclusion that incorporating a plant-animal relationship model into the WFM allows for dynamic predictions of residuals and more realistic simulations of the effect of grazing pressure on herbage production and intake at the farm level without the intervention from the user.

E-Dairy: a dynamic and stochastic whole-farm model that predicts biophysical and economic performance of grazing dairy systems

A whole-farm, stochastic and dynamic simulation model was developed to predict biophysical and economic performance of grazing dairy systems. Several whole-farm models simulate grazing dairy systems, but most of them work at a herd level. This model, named e-Dairy, differs from the few models that work at an animal level, because it allows stochastic behaviour of the genetic merit of individual cows for several traits, namely, yields of milk, fat and protein, live weight (LW) and body condition score (BCS) within a whole-farm model. This model accounts for genetic differences between cows, is sensitive to genotype × environment interactions at an animal level and allows pasture growth, milk and supplements price to behave stochastically. The model includes an energy-based animal module that predicts intake at grazing, mammary gland functioning and body lipid change. This whole-farm model simulates a 365-day period for individual cows within a herd, with cow parameters randomly generated on the basis of the mean parameter values, defined as input and variance and co-variances from experimental data sets. The main inputs of e-Dairy are farm area, use of land, type of pasture, type of crops, monthly pasture growth rate, supplements offered, nutritional quality of feeds, herd description including herd size, age structure, calving pattern, BCS and LW at calving, probabilities of pregnancy, average genetic merit and economic values for items of income and costs. The model allows to set management policies to define: dry-off cows (ceasing of lactation), target pre- and post-grazing herbage mass and feed supplementation. The main outputs are herbage dry matter intake, annual pasture utilisation, milk yield, changes in BCS and LW, economic farm profit and return on assets. The model showed satisfactory accuracy of prediction when validated against two data sets from farmlet system experiments. Relative prediction errors were <10% for all variables, and concordance correlation coefficients over 0.80 for annual pasture utilisation, yields of milk and milk solids (MS; fat plus protein), and of 0.69 and 0.48 for LW and BCS, respectively. A simulation of two contrasting dairy systems is presented to show the practical use of the model. The model can be used to explore the effects of feeding level and genetic merit and their interactions for grazing dairy systems, evaluating the trade-offs between profit and the associated risk.

Management targets for maximising the short-term herbage intake rate of cattle grazing in Sorghum bicolor

One of the variables in the structure of the sward with the most influence on the short-term herbage intake rate by grazing ruminants is the canopy height. The objective of this study was therefore to characterise the effect of the canopy height on short-term herbage intake rate using Sorghum bicolor cv BR 501. as a reference. Two experiments were conducted at Research Station of the Federal University of Rio Grande do Sul, Brazil, between December 2009 and April 2010. The treatments in experiment 1 were used to determine the influence of the pre-grazing canopy height on the short-term herbage intake and consisted of six canopy heights (30, 40, 50, 60, 70 and 80cm). The treatments in experiment 2 used the pre-grazing canopy height from experiment 1 that maximised the short-term herbage intake rate to evaluate the influence of the severity of grazing down (16, 33, 50, 67 and 84%) on the herbage intake. Both experiments used a completely randomised block design, with two replicates in experiment 1 and three replicates in experiment 2. Four heifers (24±2months and 306±56.7kg) were used in experiment 1. Three of these animals were used in experiment 2, which were then 26±2months and 339±45.5kg. The short-term herbage intake rate was measured by weighing the heifers pre- and post-grazing, corrected for insensible weight losses. The number of grazing jaw movements (biting and non-biting) was counted automatically using an IGER Behaviour Recorder. In both experiments, the sward measurements included the pre- and post-grazing canopy height, the pre-grazing herbage mass and the vertical distribution of morphological components. In experiment 2, the post-grazing herbage mass was also measured. The results showed that the grazing canopy height that maximised the short-term herbage intake rate was approximately 50cm. The grazing down protocol showed that the short-term herbage intake rate was constant until the depletion of 40% of the optimal pre-grazing canopy height. After this level of depletion, there was a marked reduction in the short-term herbage intake rate. The results show that the best target management height in a Sorghum cv. BR 501 pasture, allowing for high levels of the short-term herbage intake rate, is 50cm. With intermittent stocking, this level should be considered as the pre-grazing canopy height, and the level of herbage depletion should not exceed 40%.

Effects of feeding strategy on milk production, reproduction, pasture utilization, and economics of autumn-calving dairy cows in eastern North Carolina

A balance among stocking rate (SR), pasture management, and supplementary feeding is required to optimize overall farm performance and profitability in pasture-based dairying. Beginning in September 2003, a seasonal, autumn-calving, pasture-based farming system was established to address the effects of feeding strategy (FS; i.e., a unique combination of stocking and supplementation rate) on productive, reproductive, and economic performance of lactating herds over 3 yr. Eighty lactating cows (1/3 Holsteins, 1/3 Jerseys, and 1/3 crosses of those breeds) were randomly assigned to either a lesser stocking, lesser supplementation group [LSR; 2.2 cows/ha, 6.3kg of dry matter (DM) of a corn-based concentrate consumed daily, n=40] or a greater stocking, greater supplementation group (HSR; 3.3 cows/ha, 9.2kg of DM of a corn-based concentrate consumed daily, n=40). Pasture/forage crop rotations included annual ryegrass and sorghum-Sudan (50%), annual ryegrass and bermudagrass (20%), and a tall fescue–white clover pasture (30%). Pre- and postgrazing herbage mass values and grazing intervals (3,347±255.8kg of DM/ha, 1,861±160.6kg of DM/ha, 23.6±1.9 d) did not differ between FS. The nutritive value of fresh and conserved forages was similar between feeding strategies, except for acid detergent fiber in freshly grazed bermudagrass (29.6 vs. 26.3% of DM for LSR and HSR, respectively). Cows on HSR tended to spend more time on an adjacent feeding area where conserved forages were offered (85 vs. 61 d/yr) as opposed to grazing paddocks (204 vs. 228 d/yr). Lactation performance was greater for HSR; cows on HSR produced 10.8% more milk fat and 6.3% more milk protein than cows on LSR. Holstein cows produced the greatest amounts of mature-equivalent milk, but did not differ from crossbred cows in terms of energy-corrected milk, and mature-equivalent fat and protein yields. Reproductive efficiency did not differ among feeding strategy, but breed differences were observed; conception rates at first and all services, as well as pregnancy rates, were greater for Jersey and crossbred cows compared with Holsteins. The greater stocking rate required additional supplemental concentrate and time away from grazing paddocks, but reproductive efficiency was similar and overall lactation performance was greater. The greater stocking rate resulted in increased productivity and greater income over feed costs per unit of land.