IntroductionTop
As in most temperate climates, the predominant dairy systems are those that base their feeding on permanent pastures used mainly by grazing during the spring, summer, and autumn, because they are more cost effective than indoor system based on concentrate feeding (Dillon et al., 2005). However, during autumn, the low dry matter (DM), low water-soluble carbohydrates (WSC) and high crude protein (CP) content limit milk production of autumn calving dairy cows due to low pasture DM intake (Pulido et al., 2010; Ruiz-Albarrán et al., 2016). In addition, environmental pollution occurs as a consequence of N intake from pasture exceeding N cow requirements. Therefore, all N that is not used for maintenance and production purposes is excreted through urine and feces, contributing to environmental pollution by emissions of nitrous oxide and ammonia (Selbie et al., 2015).
Supplementation of dairy cows on pasture is a strategy to improve milk production in response to increasing total DM intake (DMI), supplying energy and protein at appropriate concentrations to cover animal requirements (Bargo et al., 2003). Grass silage supplementation is amply used during the autumn season in Southern Chile to cover pasture deficit and maintain a high DMI and milk production (Morales et al., 2014; Ruiz-Albarrán et al., 2016). However, effects of supplementation on DMI and milk production not only depend on composition and amount of supplement offered, but also on the timing of supplementation (Chilibroste et al., 2008). The most important grazing bout in the day (morning and afternoon) can be modified by strategic supplementation at these times and thereby, pasture DMI, milk production (Sheahan et al., 2013; Al-Marashdeh et al., 2016b) and nutrient flow throughout day can be modified (Gregorini et al., 2010). However, there is not a consensus as to its effect on pasture DMI, grazing behavior and milk production (Sheahan et al., 2013; Al-Marashdeh et al., 2016a; Mattiauda et al., 2018).
Time of pasture allocation is another strategy to modify pasture DMI, milk production and N excretion: In comparison to pasture allocation in the morning, afternoon allocation is characterized by a greater WSC and DM and lower CP content of the pasture in response to sugar accumulation during photosynthesis and losses of moisture during the day (Delagarde et al., 2000; Pulido et al., 2015). This better chemical composition of afternoon pasture has been associated with greater WSC/CP intake and changes in rumen fermentation and grazing behavior (Abrahamse et al., 2009; Pulido et al., 2015). However, studies evaluating the time of pasture allocation have found that cows receiving a new pasture strip in the afternoon had similar (Abrahamse et al., 2009) or tended to have greater milk production (Pulido et al., 2015; Vibart et al., 2017) and similar urine N excretion than cows receiving a morning new pasture strip (Vibart et al., 2017).
Combining time of fresh pasture and supplementation allocation could be used as a strategy to alter milk production and N excretion due to their individual effects on pasture DMI, nutrient intake and rumen fermentation. Thus, it is possible to hypothesize that morning allocation of grass silage could reduce morning pasture DMI and increase afternoon DMI, where pasture is characterized by a better nutritional composition than that in the morning. The aim of this study was to evaluate the effect of time of fresh pasture and grass silage allocations on DMI, grazing behavior, milk production, rumen function and N partitioning of grazing dairy cows during autumn.
Material and methodsTop
This experiment was carried out at the Austral Agricultural Research Station of the Universidad Austral de Chile (39°47ʹS, 73°13ʹW, Valdivia, Chile) over a period of 71 days (20th April to 30th June 2014), with 14 days of adaptation to the treatments and a 57-day measurement period. The climate is a typical cold weather Mediterranean, with a mean air temperature of 9.6° C (5.9° C - 13.3° C) and total precipitation of 830 mm during the experiment. The experimental procedures used in this study were approved by the Animal Welfare Committee of Universidad Austral de Chile.
Experimental design
Forty-five multiparous autumn calving Holstein-Friesian cows, including three rumen cannulated cows (milk production 24.5 ± 3.5 kg/d, body weight (BW) 516 ± 71 kg and days in milk 57.3 ± 10.4) were randomly allocated to one of three treatments: 1) MPA: 75% of the daily strip-pasture and 25% of the silage allowance were assigned in the morning; 2) BPA: 50% of the daily strip-pasture and 50% of the daily allowance were assigned in the morning; 3) APA: 25% of the daily strip-pasture and 75% of the daily silage allowance were assigned in the morning. All treatments received their remaining pasture-strip of fresh pasture and grass silage in the afternoon (Fig. 1).
The cows were strip-grazed with a daily fresh pasture allowance of 21 kg DM/cow (measured above ground level) offered after morning and afternoon milking according to the requirements of the respective treatments. All cows were offered 3.5 kg DM of cereal-based concentrate in two meals, 1.75 kg DM at each milking (07:00 and 14:00 h). All cows received a total of 3.0 kg DM of grass silage offered in feeding pens after milking times (08:00 h and 15:00 h) with the amount offered to each treatment differing in the morning and afternoon according to the requirements of the respective treatments. Concentrate was comprised of (on a % on DM basis) 49.3 maize, 11.5 soybean meal, 30.0 beet pulp, 4.6 beet molasses and 4.5 mineral mix.
The three rumen cannulated cows were allocated to one of three treatments in a Latin Square Design, staying on each treatment for 14 days, comprising a 13day diet adaptation period and a 1-day recording period to allow for measurement of rumen fermentation parameters. Once each period finished, the cannulated cows changed treatment.
Figure 1. Pasture, grass silage and concentrate allocation of treatments. 1MPA= 75% of the fresh pasture and 25% of the silage allowance were assigned in the morning; 2BPA= 50% of the fresh pasture and silage allowance were assigned in the morning; 3APA= 25% of the fresh pasture and 75% of the silage allowance were assigned in the morning.
Grazing management
The study was run on 12 ha of Lolium perenne L. dominated sward (55% L. perenne, 33% Bromus valdivianus, 5% Trifolium repens and 7% of other species), subdivided in 9 paddocks, which were not fertilized during experiment. All treatments were allocated within the same paddock, separated by an electric fence. The cows had access to new fresh pasture allowances at 10:00 h or 16:00 h according to the treatment.
Pre- and post-grazing pasture mass (kg DM/ha, ground level) were estimated three times per week from 100 compressed sward height measurements using a rising plate meter (Ashgrove Plate Meter, Hamilton, New Zealand).
Pasture and supplement sampling and analyses
Pre-grazing pasture samples were collected once a week at 10:00 h (MPA and BPA) and 16:00 h (APA and BPA) before cows had access to the new daily strip, cutting at 4 cm height. Samples of grass silage and concentrate were collected on days 17, 40 and 59 of the experiment. All samples were immediately frozen at -20°C and then freeze-dried for chemical analysis. Before chemical analysis, pasture and supplement samples were ground through a 1-mm screen (Willey Mill, 158 Arthur H, Thomas, Philadelphia, PA, USA), and analyzed for DM, CP, acid detergent fiber (ADF), ash (AOAC, 1996), neutral detergent fiber (NDF) (Van Soest et al., 1991) and metabolizable energy (ME) (Tilley & Terry, 1963; Goering & Van Soest, 1970). Soluble carbohydrates were determined using near-infrared spectroscopy (R2 of equation = 0.97). D-value was estimated using in-vitro digestibility (Tilley & Terry, 1963). The pH and N ammonia in silage samples were derived by the method of AOAC (1996).
Dry matter intake and grazing behavior
Daily DMI was estimated using the indigestible marker technique (Penning, 2004) during days 49 and 62 of the trial. All cows were given paper capsules containing chromium oxide (6 g/d, 68% wt/wt) after each milking, using an oral dispenser. Over the last 6 days, feces samples were collected twice per day from the rectum of each cow at the time of dosing. Fecal concentration of Cr was later determined by atomic absorption spectroscopy (Spectronic Genesys 5 spectrophotometer, Milton Roy, Ivyland, PA, USA). Total and pasture DMI from chromium oxide excretion were calculated as described by Pulido et al. (2015).
Individual grazing behavior was recorded over a 24-h period during days 18 and 45 of the experiment. Grazing activities (grazing, ruminating and idling) were observed by three experienced observers (one for each treatment) every 10 min during daylight hours and every 15 min during evening hours.
Milk yield, BW and body condition score
Milk yield was measured daily during each milking with an automated system (MPC580 DeLaval). Milk samples were collected once a week throughout the experiment during a morning and afternoon milking. These samples were used to estimate protein, fat and urea in milk by infrared spectroscopy (Milko-scan, System 4300, Foss Electric, Denmark).
Daily BW was recorded after each milking events with an automated system in the milking parlor. Body condition score (BCS) was evaluated once a week after morning milking by an experienced observer using a 5-point scale (Ferguson et al., 1994).
Ruminal concentration of volatile fatty acids
Ruminal concentration of volatile fatty acids (VFA) were evaluated using the rumen cannulated cows. Individual rumen samples were collected from three locations in the rumen (cranial, ventral and caudal) at 08:00, 10:00, 13:00, 16:00, 20:00, 00:00 and 03:00 hours during days 14, 28 and 42 of the experiment. Immediately after collection of rumen fluid, the samples (from each ruminal site) were bulked and frozen for chemical analysis. Samples were thawed and a subsample of 4 mL was diluted with formic acid (4:1 ratio) and rumen concentration of VFA was determined by gas chromatography (Shimadzu GC-2010 plus High-end GC, equipped with GC Capillary Column, SGE, BP21) (Bal et al., 2000).
Nitrogen partitioning
N partitioning was carried out between weeks 7 and 8 of the experiment. The same bulked fecal samples used to estimate pasture DMI were used to quantify N concentration by a N autoanalyzer LECO FP528 based on DUMAS method (AOAC, 1996). N partitioning was calculated using the equations proposed by Whelan et al. (2012):
N intake = [(pasture DMI × % N in pasture ÷ 100) + (concentrate DMI × % N in concentrate ÷ 100) + (grass silage DMI × % N in grass silage ÷ 100)];
Fecal N = (fecal DM excretion × % N in feces ÷ 100), where fecal DM excretion = Total DMI (1−dietary DM digestibility) (Burke et al., 2008);
Milk N = (milk yield × % N in milk ÷ 100);
Urine N = (N intake – fecal N – milk N).
Statistical analysis
Chemical composition of pasture and pasture mass (pre- and post-grazing) were analyzed using a mixed model procedure (PROC MIXED; SAS, v9.4). The model included the fixed effects of treatment, day of sampling, and their interaction, and the random effect of paddock. As day of sampling and interaction were not significant, they were dropped from the model.
Dry matter intake, N partitioning, change in BW and change in BCS were analyzed using a mixed model procedure (PROC MIXED; SAS, v9.4). The model included the fixed effects of treatment and the random effect of cows.
Milk production, milk composition, grazing behavior and rumen parameters were analyzed as repeated measures in time using the mixed model procedure (PROC MIXED; SAS, v9.4). Statistical model included the fixed effects of treatment, random effect of cows, time of sampling as repeated measurement and interaction between treatment and day of sampling. Milk production and body condition score were analyzed including the pre-experimental period as a covariate.
Comparison between treatments was carried out using the Tukey test. Results were considered significant at p<0.05 and tendency at p<0.1.
ResultsTop
Chemical composition of pasture
Results of chemical composition of pasture are presented in Table 1. Dry matter content was greater for afternoon pasture than morning pasture (p=0.03) and WSC and WSC/CP ratio tended to be greater in the afternoon pasture (p=0.07 and p=0.09, respectively). Other parameters of chemical composition of pasture were not modified by treatments (p>0.05).
Dry matter intake and grazing behavior
Results of DMI and grazing behavior are presented in Table 2. Treatments did not modify total and pasture DMI, which averaged 15.6 and 9.1 kg DM/cow, respectively (p>0.05). However, pasture WSC intake tended to be greater for APA than other treatments (p=0.1). Grazing time between morning and afternoon milking was longer for MPA (p<0.01), while grazing time between afternoon and morning milking was longer for APA compared to other treatments (p<0.01). Treatments did not modify total grazing, ruminating and idling time (p>0.05).
Milk production and change in BW and BCS
Results of milk production and change in BW and BCS are presented in Table 3. Milk production was unaffected by treatment (p=0.99), averaging 22.8 kg/d. Fat, protein and urea in milk were similar between treatments (p>0.05) (4.4%, 3.2% and 6.7 mmol/L, respectively).
Table 1. Chemical composition of morning and afternoon pasture and supplements offered to dairy cows under autumn grazing conditions.
1 DM, dry matter (% DM); CP, crude protein (% DM); NDF, neutral detergent fiber (% DM); ADF, acid detergent fiber (% DM); ME, metabolizable energy (MJ ME kg/DM); WSC, water soluble carbohydrates (% DM); VD: digestibility value; N-NH3, ammonia-N (% DM). 2 Standard error of the mean. Means within a row with different letter differ (p<0.05).
Table 2. Pasture mass, dry matter intake and grazing behavior of grazing dairy cows under autumn conditions.
1 MPA= 75% of the fresh pasture and 25% of the silage allowance were assigned in the morning; BPA= 50% of the fresh pasture and silage allowance were assigned in the morning; APA= 25% of the fresh pasture and 75% of the silage allowance were assigned in the morning. 2 Standard error of the mean. 3 Water soluble carbohydrates. 4 Metabolizable energy intake = MJ ME/animal/d. Means within a row with different letter differ (p<0.05)
Table 3. Milk production, milk solids and change in body weight and body condition score of grazing dairy cows under autumn conditions.
1 MPA= 75% of the fresh pasture and 25% of the silage allowance were assigned in the morning; BPA= 50% of the fresh pasture and silage allowance were assigned in the morning; APA= 25% of the fresh pasture and 75% of the silage allowance were assigned in the morning. 2 Standard error of the mean. 3 Body weight. 4 Body condition score. Means within a row with different letter differ (p<0.05)
Ruminal concentration of VFA
Results of rumen fluid concentrations of VFA are presented in Table 4 and Figure 2. Propionate molar propor-tion was greater (p=0.03) for BPA than APA, but similar between BPA and MPA. No differences were observed for acetate, butyrate and concentration of total VFA (p>0.05). It was not observed interaction between treatment and time of the day (hour) (p>0.05).
Nitrogen partitioning
Results of N partitioning are presented in Table 4. Treatments did not modify N intake and its partitioning into milk, urine and feces (p>0.05), averaging 458, 119, 195 and 144g N/d. Treatments did not modify N use effi-ciency (milk N/N intake), which ranged between 25-27% (p=0.09).
Table 4. Parameters of rumen fermentation and N partitioning of grazing dairy cows under autumn conditions.
1 MPA= 75% of the fresh pasture and 25% of the silage allowance were assigned in the morning; BPA= 50% of the fresh pasture and silage allowance were assigned in the morning; APA= 25% of the fresh pasture and 75% of the silage allowance were assigned in the morning. 2 Standard error of the mean. 3 Body weight. 4 Body condition score. Means within a row with different letter differ (p<0.05)
DiscussionTop
Times of pasture allocation (Abrahamse et al., 2009; Pulido et al., 2015; Vibart et al., 2017) has been evaluated separately with positive (Pulido et al., 2015) or no effects (Abrahamse et al., 2009; Vibart et al., 2017) on milk pro-duction, with no effect on N partitioning (Vibart et al., 2017) in grazing dairy cows. On the other hand, time of silage allocation have had a positive (Al-Marashdeh et al., 2016b; Ueda et al., 2017) or non-effects (Al-Marashdeh et al., 2015, 2016a; Mattiauda et al., 2019) on milk production. Similarly, time of silage allocation had a positive (Al-Marashdeh et al., 2015) or non-effects (Al-Marashdeh et al., 2016a,b) on N partitioning, suggesting that profitability goes against the environmental goals (reduction in the urinary N excretion goals, similar than reported by Beltran et al. (2019a).
All these studies have evaluated the timing of energy supplements, but there is a lack of information on the literature about the effect of time of grass silage allocation, the most common supplement offered to autumn calving cows during autumn-winter where pasture is limited (Ruiz-Albarran et al., 2016). Therefore, there are no studies evaluating the combination of time of fresh pasture and grass silage allocation as nutritional strategies at the same time.
Figure 2. MEffect of time of pasture and grass silage allocation of ruminal concentration of a) acetate, b) butyrate and c) propionate of grazing dairy cows. MPA= 75% of the fresh pasture and 25% of the silage allowance were assigned in the morning; BPA= 50% of the fresh pasture and silage allowance were assigned in the morning; APA= 25% of the fresh pasture and 75% of the silage allowance were assigned in the morning.
Chemical composition of pasture
Afternoon pasture showed a greater DM content and tended to have greater WSC content than morning pasture, which could be related to the loss of surface moisture and accumulation of simple sugars from the process of photosynthesis in the plant (Delagarde et al., 2000). The tendency to greater WSC content in the afternoon pasture could be explained by the lower day-length for autumn compared to spring (Delagarde et al., 2000), suggesting that the degree of sugar accumulation in the afternoon may vary depending on the season of the year. Similar results were found in other experiments evaluating time of pasture allocation (Pulido et al., 2015; Vibart et al., 2017).
Grazing behavior and DMI
The time that cows spent grazing after morning and afternoon milking were longer depending on when cows received most of their fresh pasture allowance – cows receiving 75% of fresh pasture in the morning (MPA) grazed for longer in the morning and less in the afternoon than the cows receiving 75% of their fresh pasture allowance in the afternoon (APA), and vice versa. These results were expected, considering that cows tend to spend more time grazing when a new fresh pasture is allocated (Vibart et al., 2017). In this sense, time of pasture allocation allowed for a change in the intensity of the most important grazing bouts throughout the day (dawn and dusk bouts) (Gregorini, 2012), independently of time of grass silage allocation. Despite the lack of effect of time of grass silage allocation on intake and milk production, grass silage should be used during autumn season to maintain a high DMI and thereby, satisfy the milk production requirements of autumn-calving cows (Morales et al., 2014; Ruiz-Albarran et al., 2016).
Despite these changes in grazing intensity in the most important grazing bout, total grazing time and pasture DMI were similar among treatments. A greater DMI for APA than other treatments was expected; however, pasture and total DMI were similar among treatments, suggesting that shorter grazing time in the morning and longer grazing time in the afternoon for APA were not enough to increase pasture DMI. This could be associated to the lower daylight hours available for grazing in autumn compared to spring (Pulido et al., 2015), which can limit the afternoon grazing time for APA, minimizing any effects of time of silage allocation on pasture intake. Similar results were reported by Sheahan et al. (2013), where morning or afternoon allocation of energy supplement did not modify pasture intake.
The cows in all treatments spent more time grazing after afternoon milking. This agreement between treatments occurs in response to diurnal grazing patterns in ruminants, with a daily frequency of three to five grazing bouts with the dusk grazing being the longest and most intense (Gregorini, 2012). The longer grazing time in the afternoon is supported by Gregorini (2012), who hypothesized that ruminant animals aim to maximize rumen f ill before the time when predation risk and vigilance increase (night), allowing a stable release of nutrients during this time. Similar results have been reported in other experiments evaluating the time of pasture allocation in grazing dairy cows (Abrahamse et al., 2009; Pulido et al., 2015; Vibart et al., 2017).
Milk production and composition
A greater milk production was expected for cows receiving 75% of their fresh pasture allowance in the afternoon (APA), since longer and most intense grazing events occur at this time (Gregorini, 2012), as pasture has higher WSC/CP ratio compared to morning pasture (Gregorini, 2012; Vibart et al., 2017). However, in our experiment milk production was not affected by treatments, which can be associated with the similar DMI among treatments. Therefore, the tendency for greater WSC intake for APA was not enough to improve the energy intake, which is the main nutrient limiting milk production.
Protein in milk was not affected by treatments, in response to similar energy supply (Pérez-Prieto & Delagarde, 2012), while similar milk fat between treatments can be associated with the similar rumen acetate:propionate ratios (Abrahamse et al., 2009). In contrast with our findings, Pulido et al. (2015) reported an increased milk protein concentration for cows allocated to a pasture strip in the afternoon.
Rumen fermentation
Rumen fluid concentration of propionate was greater for MPA than APA, indicating a change in the diurnal energy flow among treatments, which is supported by the numerically greater propionate concentration by MPA compared to APA in the evening-night (see Fig. 2). In this way, it is possible that morning grass silage allocation (APA) after a longer fasting period did not improve ruminal propionate as a consequence for low WSC content from grass silage (Ueda et al., 2016), while morning allocation of pasture improve the ruminal ratio of WSC:CP at the time of 75% of pasture allocation in the afternoon, supporting the numerical peak at 20:00 h. This is supported by Beltran et al. (2019b), who found that ruminal concentration of N-NH3 was greater two hours after morning allocation of grass silage for cows receiving a new pasture allocation in the afternoon, suggesting that high protein degradability of grass silage and its low WSC content reduced the N utilization by microorganism. The tendency for greater pasture WSC intake for APA was insufficient to compensate the energy imbalance from morning silage allocation, which is supported by the similar ME intake among treatments. Rumen fluid concentration of acetate was not affected by treatments, in response to similar NDF intake (Abrahamse et al., 2009), which is the main precursor for acetate synthesis.
Nitrogen partitioning
The lack of effect of timing of pasture and silage allocation on N intake can be attributed to insufficient increase of WSC/CP ratio in the afternoon pasture (Bryant et al., 2014). This result suggests that longer afternoon grazing time for APA was unable to modify CP intake in response to similar CP content compared with MPA. Similar results have been reported for autumn (Vibart et al., 2017) and spring (Bryant et al., 2014) conditions, where grazing dairy cows receiving a morning or afternoon pasture allocation had similar N intakes. Moreover, similar N intake between treatments would explain the lack of effect on urinary N excretion, in response to a positive relationship between N intake and its excretion through urine (Pacheco & Waghorn, 2008).
According to Keim & Anrique (2011), an increase in WSC and a reduction in CP concentrations respectively are required to enhance nitrogen use efficiency (NUE), suggesting that a greater WSC/CP in in the afternoon pasture was not enough to improve NUE as a consequence to a similar CP content between morning and afternoon pasture. The mean NUE value observed in this study (27%) was greater than those previously reported (Al-Marashdeh et al., 2016a; Trevaskis et al., 2004), who evaluated the timing of energy supplements such as maize silage or cereal based-concentrate, that it could be associated with the amount of pasture in the diet and the stage of lactation of the cows. In the current study, pasture represented 58% of the diet, a considerably lower amount than the 85% and 77% described by Al-Marashdeh et al. (2016a) and Trevaskis et al. (2004) respectively, suggesting that the lower proportion of pasture in the diet allowed to reduce N intake increasing the NUE. In addition, the use of cows in early lactation in the current study in contrast with those with cows in middle and late lactation (Trevaskis et al., 2004; Al-Marashdeh et al., 2016a, respectively) indicate that N partitioning into milk protein is greater in early lactation than late lactation, as previously reported (Miller et al., 2001; Moorby et al., 2006).
The lack of effect of time of pasture and grass silage allocation on NUE and urinary N excretion can be related to the similar urea in milk between treatments. Urea in milk have been suggested as a farm tool to estimate the urinary N excretion (Spek et al., 2016) and protein utilization in the gastrointestinal tract of dairy cows (Guliński et al., 2016). When the supply of amino acids in the rumen are in excess and rumen energy is limited, amino acids are deaminated and excreted by ruminal bacteria as NH3, which is transported into the liver to be converted to urea, then flowing into the milk, recycled into the rumen via saliva, and then excreted via urine (Pacheco & Waghorn, 2008; Beltran et al., 2019a). Similar rumen degradation of protein (87% and 89%, data unpublished) and organic matter (74% ad 78%) between morning and afternoon pasture supports the idea of similar N utilization by ruminal microorganisms, explaining the lack of effect on urea in milk, NUE and urinary N excretion.
More research is needed to evaluate the effect of the time of pasture and supplement allocations on milk production, rumen function and N partitioning, using high WSC and low CP content supplements which could promote bigger changes in grazing behavior and flow of energy and N throughout the day.
In summary, time of fresh pasture and grass silage allocation had a minimal effect on the chemical composition of pasture (DM and WSC content of pasture), grazing time and ruminal fermentation. However, milk production and N excretion were similar among treatments, possibly associated with the similar pasture and nutrient intake among treatments.
ReferencesTop
| ○ | Abrahamse PA, Tamminga S, Dijkstra J, 2009. Effect of daily movement of dairy cattle to fresh grass in morning or afternoon on intake, grazing behaviour, rumen fermentation and milk production. J Agr Sci 147: 721-730. https://doi.org/10.1017/S0021859609990153 |
| ○ | Al-Marashdeh O, Greenwood S, Hodge S, Edwards G, 2015. The effects of feeding maize silage at different times prior to a herbage meal on dry matter intake, milksolids production and nitrogen excretion in late-lactation dairy cows. Proc New Zeal Soc Anim Prod 75: 140-144. |
| ○ | Al-Marashdeh O, Gregorini P, Edwards GR, 2016a. Effect of time of maize silage supplementation on herbage intake, milk production, and nitrogen excretion of grazing dairy cows. J. Dairy Sci 99: 7123-7132. https://doi.org/10.3168/jds.2015-10681 |
| ○ | Al-Marashdeh O, Gregorini P, Greenwood SL, Edwards G, 2016b. The effect of feeding maize silage 1 h or 9 h before the herbage meal on dry matter intake, milk production, nitrogen partitioning and rumen function of lactating dairy cows. Anim Prod Sci 56: 2004-2013. https://doi.org/10.1071/AN14790 |
| ○ | AOAC, 1996. Official methods of analysis, 16th ed. AOAC Int, Gaithersburg, MD, USA. |
| ○ | Bal MA, Shaver RD, Jirovec AG, Shinners KJ, Coors JG, 2000. Crop processing and chop length of corn silage: Effects on intake, digestion, and milk production by dairy cows. J Dairy Sci 83: 1264-1273. https://doi.org/10.3168/jds.S0022-0302(00)74993-9 |
| ○ | Bargo F, Muller LD, Kolver ES, Delahoy JE, 2003, Invited review: Production and digestion of supplemented dairy cows on pasture. J Dairy Sci 86: 1-42. https://doi.org/10.3168/jds.S0022-0302(03)73581-4 |
| ○ | Beltrán IE, Al-Marashdeh O, Burgos AR, Gregorini P, Balocchi OA, Wittwer F, Pulido RG, 2019a. The order of grass and maize silage supplementation modifies milk yield, grazing behavior and nitrogen partitioning of lactating dairy cows. Animals 9 (6): 373. https://doi.org/10.3390/ani9060373 |
| ○ | Beltrán IE, Gregorini P, Daza J, Balocchi OA, Morales A, Pulido RG, 2019b. Diurnal concentration of urinary nitrogen and rumen ammonia are modified by timing and mass of herbage allocation. Animals 9 (11): 961. https://doi.org/10.3390/ani9110961 |
| ○ | Bryant RH, Dalley DE, Gibbs J, Edwards GR, 2014. Effect of grazing management on herbage protein concentration, milk production and nitrogen excretion of dairy cows in mid-lactation. Grass Forage Sci 69: 644-654. https://doi.org/10.1111/gfs.12088 |
| ○ | Burke F, O'Donovan MA, Murphy JJ, O'Mara FP, Mulligan FJ, 2008. Effect of pasture allowance and supplementation with maize silage and concentrates differing in crude protein concentration on milk production and nitrogen excretion by dairy cows. Livest Sci 114: 325-335. https://doi.org/10.1016/j.livsci.2007.05.019 |
| ○ | Chilibroste P, Dijkstra J, Robinson PH, Tamminga S, 2008. A simulation model "CTR Dairy" to predict the supply of nutrients in dairy cows managed under discontinuous feeding patterns. Anim Feed Sci Tech 143: 148-173. https://doi.org/10.1016/j.anifeedsci.2007.05.009 |
| ○ | Delagarde R, Peyraud JL, Delaby L, Faverdin P, 2000. Vertical distribution of biomass, chemical composition and pepsin-cellulase digestibility in a perennial ryegrass sward: Interaction with month of year, regrowth age and time of day. Anim Feed Sci Tech 84: 49-68. https://doi.org/10.1016/S0377-8401(00)00114-0 |
| ○ | Dillon P, Roche JR, Shalloo L, Horan B, 2005. Optimizing financial return from grazing in temperate pastures. Utilization of grazed grass in temperate animal systems. Proc of a Satellite Workshop, XXth Int Grassland Congr, Cork (Ireland). pp: 31-147. |
| ○ | Ferguson JD, Galligan DT, Thomsen N, 1994. Principal descriptors of body condition score in Holstein cows. J Dairy Sci 77: 2695-2703. https://doi.org/10.3168/jds.S0022-0302(94)77212-X |
| ○ | Goering H, Van Soest PJ, 1970. Forage fiber analysis (apparatus, reagents, procedures, and some applications). USDA, Washington. |
| ○ | Gregorini P, 2012. Diurnal grazing pattern: Its physiological basis and strategic management. Anim Prod Sci 52: 416-430. https://doi.org/10.1071/AN11250 |
| ○ | Gregorini P, Soder KJ, Waghorn G, 2010. Effects of timing of corn silage supplementation on digestion, fermentation pattern, and nutrient flow during continuous culture fermentation of a short and intensive orchardgrass meal. J Dairy Sci 93: 3722-3729. https://doi.org/10.3168/jds.2009-2950 |
| ○ | Guliński P, Salamończyk E, Młynek K, 2016. Improving nitrogen use efficiency of dairy cows in relation to urea in milk - A review. Anim Sci Pap Rep 34 (1):5-24. |
| ○ | Keim JP, Anrique R, 2011. Nutritional strategies to improve nitrogen use efficiency by grazing dairy cows. Chil J Agr Res 71: 623-633. https://doi.org/10.4067/S0718-58392011000400019 |
| ○ | Mattiauda DA, Gibb MJ, Carriquiry M, Tamminga S, Chilibroste P, 2019. Effect of timing of corn silage supplementation to Holstein dairy cows given limited daily access to pasture: intake and performance. Animal: 127-135. https://doi.org/10.1017/S1751731118000794 |
| ○ | Miller LA, Moorby JM, Davies DR, Humpherys MO, Scollan ND, MacRae JC, Theodorou MK, 2001. Increased concentration of water-soluble carbohydrate in perennial ryegrass (Lolium perenne L.): Milk production from late-lactation dairy cows. Grass Forage Sci 56: 383-394. https://doi.org/10.1046/j.1365-2494.2001.00288.x |
| ○ | Moorby JM, Evans RT, Scollan ND, MacRae JC, Theodorou MK, 2006. Increased concentration of water-soluble carbohydrate in perennial ryegrass (Lolium perenne L.). Evaluation in dairy cows in early lactation. Grass Forage Sci 61: 52-59. https://doi.org/10.1111/j.1365-2494.2006.00507.x |
| ○ | Morales A, Grob D, Balocchi OA, Pulido RG, 2014. Productive and metabolic response to two levels of corn silage supplementation in grazing dairy cows in early lactation during autumn. Chil J Agr Res 74: 205-212. https://doi.org/10.4067/S0718-58392014000200012 |
| ○ | Pacheco D, Waghorn G, 2008. Dietary nitrogen-definitions, digestion, excretion and consequences of excess for grazing ruminants. Proc New Zeal Grassl Assoc 70: 107-116. https://doi.org/10.33584/jnzg.2008.70.2738 |
| ○ | Penning PD, 2004. Animal-based techniques for estimating herbage intake. In: Herbage intake handbook; Penning PD (eds). pp: 53-94. Reading, UK. |
| ○ | Pérez-Prieto LA, Delagarde R, 2012. Meta-analysis of the effect of pregrazing pasture mass on pasture intake, milk production, and grazing behavior of dairy cows strip-grazing temperate grasslands. J Dairy Sci 95: 5317-5330. https://doi.org/10.3168/jds.2012-5609 |
| ○ | Pulido RG, Muñoz R, Jara C, Balocchi OA, Smulders JP, Wittwer F, Orellana P, O'Donovan M, 2010. The effect of pasture allowance and concentrate supplementation type on milk production performance and dry matter intake of autumn-calving dairy cows in early lactation. Livest Sci 132: 119-125. https://doi.org/10.1016/j.livsci.2010.05.010 |
| ○ | Pulido RG, Ruiz-Albarrán M, Balocchi OA, Nannig P, Wittwer F, 2015. Effect of timing of pasture allocation on production, behavior, rumen function, and metabolism of early lactating dairy cows during autumn. Livest Sci 177: 43-51. https://doi.org/10.1016/j.livsci.2015.04.002 |
| ○ | Ruiz-Albarrán M, Balocchi OA, Noro M, Wittwer F, Pulido RG, 2016. Effect of the type of silage on milk yield, intake and rumen metabolism of dairy cows grazing swards with low herbage mass. Anim Sci J 87: 878-884. https://doi.org/10.1111/asj.12513 |
| ○ | Selbie DR, Buckthought LE, Shepherd MA, 2015. The challenge of the urine patch for managing nitrogen in grazed pasture systems. Adv Agron 129: 229-292. https://doi.org/10.1016/bs.agron.2014.09.004 |
| ○ | Sheahan AJ, Gibbs SJ, Roche JR, 2013. Timing of supplementation alters grazing behavior and milk production response in dairy cows. J Dairy Sci 96: 477-483. https://doi.org/10.3168/jds.2012-5781 |
| ○ | Spek JW, Dijkstra J, Bannink A, 2016. Influence of milk urea concentration on fractional urea disappearance rate from milk to blood plasma in dairy cows. J Dairy Sci 99 (5): 3880-3888. https://doi.org/10.3168/jds.2015-9421 |
| ○ | Tilley JMA, Terry RA, 1963. A two-stage technique for the in vitro digestion of forage crops. Grass Forage Sci 18: 104-111. https://doi.org/10.1111/j.1365-2494.1963.tb00335.x |
| ○ | Trevaskis LM, Fulkerson WJ, Nandra KS, 2004. Effect of time of feeding carbohydrate supplements and pasture on production of dairy cows. Livest Prod Sci 85: 275-285. https://doi.org/10.1016/S0301-6226(03)00122-2 |
| ○ | Ueda K, Mitani T, Kondo S, 2016. Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening. Anim Sci J 87: 997-1004. https://doi.org/10.1111/asj.12527 |
| ○ | Ueda K, Mitani T, Kondo S, 2017. Effect of timing and type of supplementary grain on herbage intake, nitrogen utilization and milk production in dairy cows grazed on perennial ryegrass pasture from evening to morning. Anim Sci J 88: 107-118. https://doi.org/10.1111/asj.12605 |
| ○ | Van Soest PJ, Robertson JB, Lewis BA, 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J Dairy Sci 74: 3583-3597. https://doi.org/10.3168/jds.S0022-0302(91)78551-2 |
| ○ | Vibart RE, Tavendale M, Otter D, Schwendel BH, Lowe K, Gregorini P, Pacheco, D, 2017. Milk production and composition, nitrogen utilization, and grazing behavior of late-lactation dairy cows as affected by time of allocation of a fresh strip of pasture. J Dairy Sci 100: 5305-5318. https://doi.org/10.3168/jds.2016-12413 |
| ○ | Whelan SJ, Pierce KM, McCarney C, Flynn B, Mulligan FJ, 2012. Effect of supplementary concentrate type on nitrogen partitioning in early lactation dairy cows offered perennial ryegrass-based pasture. J Dairy Sci 95: 4468-4477. https://doi.org/10.3168/jds.2011-4689 |