Improving dry-matter intake of perennial-ryegrass pasture by dairy cows

Dairy cows fed on perennial-ryegrass pasture produce higher-quality milk in terms of fatty-acid composition; however, they produce much less milk compared to dairy cows under other systems. The low dry-matter intake (DMI) has been identified as the main factor responsible for the lower milk production in pasture-based systems. To maximize milk production from those systems it is important to maximize DMI from pasture. Many interventions have been studied, such as: manipulating herbage allowance, feeding frequency, time of allocating the new pasture, pasture maturity, fertilization rate and the choice of perennial-ryegrass variety. The results have shown that pasture DMI increases in a curvilinear asymptotic manner as herbage allowance increases. However, increasing herbage allowance decreases milk production per hectare and increases production cost due to the increased need for pasture and land. More frequent allocation of pasture has shown no effect on pasture DMI. Allocating the new pasture after the evening milking has sometimes shown to increase pasture DMI without any negative effect in terms of productivity per hectare. Allocating a young and leafy grass has shown to increase DMI, but at the same time pasture holding capacity was reduced and milk production per hectare decreased. Using high-sugar grass was advocated as a way to improve DMI of dairy cows on pasture. Research findings with regard to the effect of high-sugar grass on DMI are very inconsistent. Some experiments reported a positive effect of high-sugar grass on DMI, but that was due to the confounded effect of high sugar and digestibility. Whereas, other experiments reported no effect, as in those experiments the high- and low-sugar grasses had a similar digestibility. This indicated that high sugar is not always associated with higher digestibility especially in young and leafy perennial ryegrass. It also indicated that grass digestibility exerts a stronger effect on DMI than its sugar content does. It was hypothesized that feeding grass that has a fast clearing or degrading fibre would improve DMI. The results of several experiments that screened different perennial-ryegrass varieties for their fibre clearance and degradation rates under grazing indicated that variation in these traits between perennial-ryegrass varieties is very limited under the chosen conditions. This suggested that choosing varieties with fast degrading fibre, as a means to improve pasture DMI, is very limite

Perennial ryegrass for dairy cows: Grazing behaviour, intake, rumen function and performance

Keywords: Dairy cows, Perennial ryegrass, Rumen fill, Clearance, Degradation, Grazing behaviour.In temperate environments, perennial ryegrass is the most widely used species for feeding dairy cows. That is because of its high productivity, palatability, digestibility and nutritive value. However, perennial ryegrass suffers from two main disadvantages: firstly, its unbalanced nutrient content in terms of crude protein (CP) and energy availability at rumen level and secondly, its low dry matter intake (DMI) by high producing dairy cows. In ruminant animals, DMI is a function of the balance between eating motivation, which is strongly related to palatability, on one hand and rumen capacity on the other. This thesis was divided into three parts: the first part aimed to investigate the possibility of improving pasture DMI by increasing rumen capacity. Rumen capacity is related to the rate of clearance (Kcl) of material from the rumen, which is the summation of both rates of degradation (kd) and passage (kp). Six varieties of perennial ryegrass were screened for their clearance and degradation rates using in vitro , in vivo and in situ techniques. The results suggested that there is a narrow range for selection with respect to clearance and degradation rate. The second part of this thesis aimed at investigating the possibility of improving pasture DMI by improving its palatability. Palatability is mainly a function of flavour and taste, which arise from certain compounds in the grass, especially water-soluble carbohydrates (WSC). High sugar grass varieties were fed to dairy cows in mid lactation. The results showed that feeding high sugar grass did not lead to an improved DMI and milk yield under both stall-feeding and grazing conditions. Moreover, milk composition in terms of fat, protein and lactose, rumen pH, fibre clearance and degradation rates were not influenced. However, rumen ammonia and milk urea concentrations were significantly reduced when feeding high sugar grass. The third part of this thesis aimed to investigate the role rumen fill and fermentation end products may play in signalling the termination of a grazing bout, especially the dusk grazing bout of dairy cows under continuous stocking. It was found that dairy cows interrupted the first two main grazing bouts at the morning and afternoon long before their maximal rumen capacity was reached. Moreover, rumen fill was always maximal at the time when the dusk grazing bout ceased indicating that rumen fill is more likely to play a major role in signalling the termination of the dusk grazing bout

Sward characteristics important for intake in six Lolium perenne varieties

An experiment was conducted to determine the genetic variation among diploid perennial ryegrass (Lolium perenne L.) varieties for sward structural characteristics considered to be important for intake by cattle. Assessments were made between June and September in 2000 and 2001. Six varieties (Abergold, Respect, Agri, Herbie, Barezane and Barnhem) were subjected to a cutting experiment where swards were cut after 3 to 4 weeks of regrowth during the growing season. The variables, measured in three 2-week periods, were herbage mass of dry matter (DM), sward surface height (SSH), bulk density, proportion of green leaf, tiller density, tiller weight, extended tiller height, length of sheath and length of leaf blade. Significant differences among varieties were found in both years for herbage mass of DM, SSH, bulk density, proportion of green leaf, tiller density, tiller weight and length of sheath. The results show that there is significant genetic variation among diploid perennial ryegrass varieties for sward characteristics important for intake during grazing

The role of rumen fill in terminating grazing bouts of dairy cows under continuous stocking

This experiment was aimed at studying the role of rumen fill in signalling the termination of grazing bouts of dairy cows using a combination of experimental and modelling approaches. The day was divided into three main periods (06:00-12:00 h, 12:00-18:00 h and 18:00-24:00 h) during which the three main grazing bouts (dawn, afternoon and dusk) of dairy cows usually occur. Four rumen-cannulated dairy cows were used in a repeated measurements design, with time of day as the within subjects factor. The cows were rumen-evacuated at 6:00, 12:00, 18:00 and 23:30 h. Data on grazing behaviour of the cows were obtained using jaw recorders fitted to the cows. Fractional clearance rate (Kcl) was estimated from the difference in rumen fill between 23:30 and 8:00 h next morning, during which period cows were deprived of feed. Because rumen evacuations were performed at fixed times during the day and not immediately when grazing ceased, the fluctuation in rumen fill between the measured points had to be estimated in order to draw valid conclusions concerning its role in regulating the cessation of grazing. To estimate rumen fill fluctuation, a simple dynamic model was constructed. There is one state variable, the rumen neutral detergent fibre (NDF) pool. The model was based on the measured total eating time, the exact timing of each individual grazing event, bite rate, bite mass and Kcl. The diurnal fluctuation in rumen pool sizes of dairy cows was predicted satisfactorily. The mean squared prediction error (MSPE) was small (5.1% of observed mean), and the major part of the error was due to random variation. The simulated pool sizes indicated that cows stopped grazing during the morning and afternoon at a point where rumen pool size was much lower than what the rumen could hold at 23:30 h. This illustrated that dairy cows interrupted grazing bouts at dawn and in the afternoon long before reaching their maximum rumen fill capacity

A note on eating behaviour of dairy cows at different stocking systems - diurnal rhythm and effects of ambient temperature

This experiment was aimed at studying the diurnal rhythm of dairy cows eating behaviour at different stocking systems, and quantifying the effect of daily ambient temperature on this diurnal rhythm. In two experiments carried out in the summer of 2003 in The Netherlands, eight dairy cows were offered fresh pasture of perennial ryegrass. In the first experiment, four cows were given access to 1 ha pasture under a continuous stocking system (CSS), whereas, in the second experiment, four cows were given access to 528 m2 of a pasture daily, under a 1-day strip grazing system (SGS). In both experiments, grazing behaviour was measured repeatedly using jaw recorders. Under CSS, dairy cows had the longest meal at the evening, whereas under SGS, they had the longest meal in the afternoon. Under both systems, bite rate was maximal and chewing rate minimal during the evening bout. Dairy cows reduced their daylight eating time when maximum daily ambient temperature exceeded 25 °C. Bite rate and chewing rate were not influenced by management or ambient temperature. It appears to be possible to influence the timing and length (duration) of grazing bouts by management, mainly by changing the timing of allocating the new plot. However, it seems to be harder to influence the daily rhythm in bite rate and chewing rate, as both appeared not be influenced by ambient temperature or managemen