5. Discussion
On average beef cattle, on hill country defecated at a rate of 0.2 faeces per cow per day, in the riparian zone. In this study, the numbers of defecations in the riparian zone, the total numbers of defecations in the field and the percent of defecation in the riparian zone were unaffected by factors such as the presence or absence of a trough, the availability of a shade structure, the size of the field, or pasture availability in the riparian zone.
Hafez & Bouissou (1975) reported that cattle at pasture defecate 12 to 18 times in a 24-hour period, and Wagnon (1963) observed grazing cattle defecating between 9 to 12 times over 24 hours. In a more recent study Sahara et al. (1990) found that Holestein cows indoors, average defecation frequencies were about half (9 +/- 2.5) that observed by Hafez & Bouissou (1975). Over these studies, the average rate of defecation for cattle was 11.5, therefore, it is reasonable to expect approximately half the number of excreta in a 12 hour period (5.75).
Cattle in this study spent on average 4 percent of the day (12 hours) in the riparian zone. If cows defecate at an average rate of 5.75 faeces per 12 hours, then in 4 percent of the day cows would deposit on average 0.23 faeces, which is similar to the average number of faeces deposited in the riparian zone in this study (0.2 faeces). Consequently, it may be suggested that the number of faeces deposited by a cow in the riparian zone may be related to the amount of time the individual spends in that area.
In a recent study, Davies-Colley et al. (in prep.) observed cows travelling down a 200m raceway and across a 20m river. Despite the difficulty in estimating the numbers of defecations in the water (e.g. due to cattle bunching together) they suggested that cows were about 50 times more likely to defecate in the river (on the ford) than elsewhere on the raceway. This might have been due to the longer periods of time the cows spent in the river, rather than the presence of water per se. Unfortunately, this study does not indicate the length of time cows spent on the raceway, however, Davies-Colley et al. (in prep.) report that cows tended to linger in the water much longer than elsewhere on the raceway. Thus, it appears that Davies-Colley et al. (in prep.) data may support the notion that defecation in an area is in proportion to the time spent in that area.
Individual cows in this study were observed defecating on average 1.2 times in the non-riparian parts of the field in (approximately) a 12-hour period, which is much lower than would be expected from information in the literature. A possible reason for the low numbers of defecations observed in the field was as a result of the particular recording protocol used (as required in another associated study); the behaviour and location of cattle in the field were recorded every 10-minutes. Excretion behaviour is relatively infrequent and short duration behaviour, therefore, it is perhaps not surprising that relatively few instances of defecation were recorded in the 10 minute scan sampling. However, when the cows were in the riparian zone, the behaviour of individual animals was recorded every minute. Therefore, there is confidence that the numbers of defecations recorded in this area would be close to the actual numbers of defecations deposited in this area (during daylight hours).
Despite the low numbers of defecations recorded at pasture, cows were found to defecate more (in the entire field) during the summer and autumn compared with the spring and winter. The most likely explanation for this is higher feed availability during the summer and autumn compared with the spring and winter.
In the three experiments of this study, it appears that cows spent relatively little time in the riparian zone, with a small number of faeces per cow deposited each day in this area. Despite this, the impact of even small amounts of faecal material on water pathogen levels may be quite high (Davies-Colley et al., in prep.). Further studies are required to quantify the precise risks to New Zealand waterways from the proximity of cattle to streams.
Reducing the time cows spend in the riparian zone may be one method of minimising the bacterial contamination of streams by faecal material. To assess the possibility of decreasing cattle stream use, firstly, it is essential to understand where cattle spend their day, and, secondly, it is important to establish what attracts cattle to the riparian area. Both aspects are likely to influence the use of streams and the surrounding area.
Bagshaw (2001) described the diurnal behaviour pattern of beef cattle on hill country in New Zealand. Bagshaw (2001) found that cattle on hill country in New Zealand have strong diurnal behaviour patterns. They graze mostly in early morning and evening, and rest mostly in the middle of the day (Martin, 1978; Sneva, 1970; Hafez & Bouissou, 1975; Bagshaw, 2001). Typically, at 8 am (Experiment 1), cows graze on the flattest land near the top of the field. Cows would weave their way back and forth across the field grazing for about 3 hours. Cows grazed longer on the upper slopes of the field in the Morning and Midday time intervals as the days of the trial progressed. Occasionally, animals would drink from the trough when they were at the top of the field, during the Morning and Midday time intervals. Often, the animals would rest between 11 am and midday. They would stand or lie down, ruminating, for approximately 2 to 3 hours on flat areas either at the top or middle of the field. In field 3, there was a large flat area at the top of the field next to a trough, cattle would spend the majority of their resting time in this area, and there was an increase in trough use. This resting bout appeared to be reduced if there was low pasture availability, which was also found by Hafez & Bouissou (1975).
The behaviour of cattle near the stream also showed a diurnal pattern. Bagshaw (2001) and Duncan (1996) observed cattle drinking from the stream mostly in the afternoon. Bagshaw (2001) typically observed that at approximately 2 pm, one or two individuals would move towards the stream. Within half an hour of this the rest of the group was often observed running down the slope to the stream. Dominant animals would push others out of the way, and there was often much bunting, as animals tried to get first access to the water through one of the two common stream access points. Some individuals would move into the stream while others would queue on the stream bank.
Cattle may defecate on the stream bank while waiting to get into the stream or in the stream itself. Once an animal was next to the water it would drink, then stand for several minutes before either walking into the stream, or on to the stream bank where they would graze or rest. By late afternoon, most animals had drunk from the stream. Cows would then drift away from the stream, grazing up the slope to their night-time resting sites near the top of the hill. The cows, in this present study behaved in a manner similar to cattle grazing a variety of pasture types in other studies (Sneva et al., 1973; Hafez & Bouissou, 1975). The diurnal behaviour of cattle appears to be robust in nature. Consequently, it may be difficult to change.
Researchers have suggested that cattle congregate in riparian habitats to gain access to numerous factors such as shade (Garrett et al., 1960), particularly succulent vegetation, proximity to water and gentle terrain (Platts, 1978; Armour et al., 1991; Kie & Boroski, 1996; Bryant, 1982; Roath & Krueger, 1982; Smith et al., 1992). External factors in the stream environment which may influence the time cattle spend in an area have been discussed in detail by Bagshaw (2001). In Experiment 3, (Bagshaw, 2001) the importance of water for drinking, water for cooling, shade and forage specific to the riparian area on use of the riparian habitat was investigated. In relation to the frequency and distribution of defecation, the resources available in an area may be important if they alter the amount of time cattle spend in an area. Bagshaw (2001) suggested that the stream area (riparian zone) was relatively attractive to cattle. It was found that pasture availability was one factor which may influence the time cattle spend near streams.
When there was an abundance of good-quality pasture elsewhere in the field, cattle spent less time drinking from the stream compared to later in the trial (when there was less forage available). Thus, when pasture availability is low, there is a potential for a greater impact on streams. In addition, the opportunity to cool was possibly an important feature of the stream. When cattle were unable to paddle in the water they spent more time under the shade structure compared to when they had complete stream access.
The role of the other factors investigated remains unclear, but because all of the resources that were made available were used, it would appear that factors such as shade, food and access to water are important. As yet, it is not possible to ascertain the relative importance of the various streamside factors to cattle. If important features could be identified, then such factors might be able to be manipulated to reduce the use of riparian areas by cattle and defecation in these areas (Bagshaw, 2001).
Further studies are required to ascertain the influence of different combinations of resources to alter the time cattle spend in an area.
Management Implications
There is an indication from this study that the length of time cattle spend in a particular area may influence the number of faeces deposited in that area. Obviously, if this were true, it should be possible to reduce the numbers of defecations in the riparian zone by reducing stream use. Cattle have a particularly strong diurnal pattern of behaviour, which is likely to be quite difficult to change. In addition, they are highly likely to be attracted the riparian area, which is rich in resources. Bagshaw (2001) suggested a number of ways which might reduce the amount of time cattle spend in the riparian zone:
- the manipulation of the availability of the factors near the stream (such as shade, water for cooling, water to drink or forage specific to the riparian area);
- reducing the availability of resting sites;
- presenting combinations of attractive resources distant from the stream to reduce the time spent in the riparian area;
- perhaps also block access into the stream, as in hill country there are usually few convenient and easy access points to the stream;
- further studies are required to test amelioration methods to reduce defecation by cattle in sensitive ecological areas.
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