Definiciones Conceptuales

Preference testing and demand testing have been used in a limited number of studies directly assessing cattle preference between indoor housing and pasture. These studies have yielded complex results: in general, dairy cows prefer to be at pasture when given free-choice, but a number of factors appear to influence this preference.

1.5.1 Overall preference to be indoors or at pasture

Krohn et al. (1992) reported that when given free access between deeply bedded (long straw) free-stalls and a yard or pasture, cows spent the majority of their time at pasture (17.2 h/day) during the summer. This is in agreement with both Charlton et al. (2011b) and Charlton et al. (2013) who reported that when given free choice between free-stall housing with rubber mattresses or pasture, cows expressed a partial preference to be at pasture (71 % and 58 % respectively). Additionally, when given a choice between an open feedlot environment (gravel base with 250 mm thick feedlot compost) and pasture, beef cattle also preferred to be at pasture, spending 75 % of their time there (Lee et al., 2013). Some studies have not reported an overall preference for pasture, but rather a preference for pasture during the night-time (20:00 – 06:00 h) when given the choice between free- stalls with geotextile mattresses deeply bedded with washed river sand and pasture (0.1 m depth) (Legrand et al., 2009, Falk et al., 2012). It appears that only one study to date that directly assessed preference between pasture and free stall housing (with rubber

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spending about 92 % of their time there (Charlton et al., 2011a). Charlton et al. (2011a) speculated that this result may have been due to the cows’ limited prior experience of pasture.

Additionally, a few studies have quantified time spent in cubicle housing vs. pasture when given 24 h access to both locations while not directly assessing preference. Ketelaar-de Lauwere et al. (1999), Ketelaar-de Lauwere et al. (2000), and Spörndly and Wredle (2004) reported that dairy cows spend approximately 76 %, 85 %, and 68 % of their time

respectively at pasture over indoor cubicle housing.

Finally, it appears only a single study has attempted to quantify dairy cow motivation for access to pasture using motivation testing. Charlton et al. (2013) reported that when cows were asked to walk 60, 140, or 260 m to gain access to pasture, the cows reduced pasture use as the “price” to gain access to pasture increased. Cows were willing to walk up to 260 m to gain access to pasture during the night however, and overall pasture use (24 h) was not influenced by distance.

Although the majority of these studies reported that dairy cows express a partial preference to be at pasture and there is emerging evidence that cows are motivated to gain access to pasture at night, this preference is conditional on a number of factors. As this preference is not straightforward, it is important to try and understand which factors influence

preference for pasture rather than purely quantifying where they spend their time. To date, the studies assessing preference have directly shown that the following factors influence dairy cow preference for pasture.

1.5.2 Season

Two of the previously conducted preference experiments assessed seasonal differences in preference for pasture. Krohn et al. (1992) reported that in Denmark during May-

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September cows expressed a preference for pasture, while during November-March cows spent only about 5 h /day outdoors. This is in agreement with Charlton et al (2011b) who also reported that as the season progressed in the UK, pasture use decreased with cows spending 86.7 % of their time at pasture during August-September, 68.3 % during September-October, and 58.3 % from October-November. It can be argued that this change in pasture may be due to weather conditions (including ground conditions) as discussed in the following section, but it may also be due to the change in grass quality and

quantity as discussed in section 1.6.1.

1.5.3 Weather

Previous research indicates that cattle behaviour is affected by weather conditions and availability of shelter (Redbo et al., 2001, Tucker et al., 2008). In hot weather, cattle

actively seek shade (Blackshaw and Blackshaw, 1994) and Bos taurus breeds tend to be

more sensitive to heat rather than cold (Hemsworth et al., 1995). Several studies

mentioned in section 1.5.1 indicated that dairy cows changed their location in response to

both humidity and rainfall. Legrand et al. (2009) and Falk et al. (2012) both observed a

decrease in pasture use as the temperature humidity index (THI) increased at pasture

(range: 49.9-74.6 and 54-68 respectively) during the day-time and as rainfall increased during the night-time (range: 0-65.4 and 0-25 mm/d respectively). Charlton et al. (2011a) and Charlton et al. (2013) did not find an effect of humidity on preference for pasture, but reported that on days with greater than average rainfall cows spent less time at pasture. Charlton et al. (2011b) found that when the THI increased indoors, cows spent more time at pasture. The apparent inconsistencies in the literature with respect to THI are likely to be due to the comparatively low mean THI values reported in both Charlton et al. (2011a) and Charlton et al. (2013) of 59.9 and 59.6 respectively at pasture as the upper critical THI limit for dairy cows (the point at which milk production levels are compromised) is

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reported to be 72 (Tucker et al., 2008). The decline in pasture use during the day due to heat (using the black globe humidity index as a measure of heat stress) as well as heavy rain overall was also reported by Ketelaar-de Lauwere et al. (1999) and Ketelaar-de Lauwere et al. (2000). Finally, Krohn et al. (1992) observed that when the ground was frozen at pasture, cows stayed exclusively indoors.

1.5.4 Time of day

Cows used in preference studies spent more time at pasture during the night (after evening milking). Legrand et al. (2009) reported that between morning and evening milking (08:00 to16:00 h) cows were outside for less than 3 h. In contrast, after 16:00 h cows spent the majority of their time at pasture, and most cows were exclusively on pasture between 00:00 to 04:00 h. This is in agreement with Krohn et al. (1992) who reported that during the summer cows spent all their time at pasture from dusk until dawn. Falk et al. (2012) also reported similar results with cows spending 78 % of their time at pasture between 20:00 to 06:00 h and only 41 % of their time at pasture between 08:35 to 15:00 h. Finally, Charlton et al. (2013) reported that dairy cows spent about 80 % of their time at pasture during the night.

1.5.5 Performance

Three of the preference studies examined the effect of performance factors (body condition score, milk yield, lactation number, lameness, and weight) on preference to be at pasture with differing results. Charlton et al. (2011a) and Charlton et al. (2011b) reported that

cows with a body condition score (BCS) greater than 2.7 and 3 respectively had a tendency

to spend less time at pasture while Charlton et al. (2013) found no effect of BCS. Charlton et al. (2011a) also reported that cows producing greater than 26.9 kg of milk per day spent less time at pasture while (Charlton et al., 2011b) and (Charlton et al., 2013) reported no

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effect of milk yield on preference to be at pasture. Mean lactation number, reported to be 1.8 (Charlton et al., 2011a), 2.3 (Charlton et al., 2011b), and 2.6 (Charlton et al., 2013) had no impact on time spent at pasture. Lameness score (1.5) and live-weight (644 kg) did not influence preference according to Charlton et al. (2011a), but cows with a lameness score greater than 1.5 spent less time at pasture (Charlton et al., 2011b).

1.6 GAPS EMERGING FROM PREVIOUS RESEARCH INVESTIGATING