Motivation for additional water use of growing-finishing pigs

Liquid fed growing-finishing pigs receive an amount of water in their ration that is more than their physiological requirement. For welfare reasons it can be argued that in addition to this diet, pigs may be motivated to obtain additional fresh water. The aim of the present experiment was to test the hypotheses that liquid fed pigs will work harder to obtain extra fresh water, compared to dry fed pigs which receive water in a conventional way. A consumer-demand technique was used, in which flow rate from an extra (test) drinker determined the ease with which pigs could obtain the water. The more persistent pigs were to obtain water from the test drinker (with declining flow rates), the harder they were assumed to work for it. Four treatments were divided over 48 pens of 12 finishing pigs in 2 batches (566 pigs). There was one Dry Feed treatment (D, with standard drinking nipple in a single space trough) and three liquid feeding systems: Long trough (LT); Sensor Feeding (S) and Variomix (V). Each pen had an additional drinker with a weekly randomly changing flow rate of 134, 356, 733 or 1041 ml/min. From the extra drinker pigs used on average 3.39a (D), 0.76b (LT), 0.58bc (S) and 0.44c (V) litre per day (different superscripts indicate differences P < 0.05). The persistence to obtain water differed between the four treatments. This was indicated by the rate of decline (ρi) of the asymptotic curve depicting water disappearance at decreasing flow rates: ρi = 0.00378a, 0.00274ab, 0.00122b and 0.00275ab for D, LT, S and V, respectively. This suggests that liquid fed pigs work equally hard (LT and V) or less hard (S) to obtain water from an extra drinking nipple, compared to dry fed pigs (D).