Birte L. Nielsen

On the interpretation of feeding behaviour measures and the use of feeding rate as an indicator of social constraint

Abstract This paper highlights a number of issues associated with the use and interpretation of feeding behaviour measures using examples from the literature on rats, cows and pigs. The inter-relatedness of six feeding behaviour variables is illustrated. Different meal patterns adopted to achieve similar intakes are briefly discussed in the context of flexibility of feeding behaviour. The relative constancy of feeding rate of an individual in a given environment is described, and the notion of a preferred rate of eating is introduced. It is suggested that an animal kept individually will eat a given amount of food at a preferred rate of eating. Changes in feeding rate by individuals are examined and different causes discussed. These include increased feeding motivation (hunger), and influences from the social environment. It is proposed that changes in the feeding rate of individual group housed animals may reflect concomitant changes in the social environment, and could thus be used as an indicator of social constraint. In addition, it is proposed that the depression in daily food intake seen in group housed animals compared to single kept individuals may reflect a shift in behavioural priorities.

Effect of group size on feeding behaviour, social behaviour, and performance of growing pigs using single-space feeders

Use of computerized feed intake recording (CFIR) equipment allows automatic recording of individual feed intake of animals kept in groups. However, current CFIR systems have only one feeding space per social group which may lead to increased competition for access to the feeder. The present experiment examined the effect of increased competition around a single-space feeder on individual performance and behaviour by manipulating the number of pigs per feeder. 150 male crossbred pigs were penned at 34 ± 0.3 kg (mean ± SE) in groups of 5, 10, 15, or 20 for 29 days with one single-space computerized feeder per pen and 1.06 m2/pig. Pigs kept in groups of 20 made fewer but longer visits to the feeder and ate more and faster than pigs kept in the smaller groups (7.1 vs. 14.3 visits/day, P < 0.01; 6.91 vs. 4.64 min/visit, P < 0.05; 214 vs. 119 g/visit, P < 0.05; 31.6 vs. 25.9 g/min, P < 0.05; means of group size 20 vs. means of group size 5, 10, and 15, respectively). No differences were found between group sizes in daily feed intake, daily live-weight gain and feed conversion ratio (overall means: 1490 g/day, 725 g/ day and 2.09 g/g, respectively). Mean number of aggressive interactions initiated and won were significantly lower for the two largest group sizes on the day of grouping. A rank index based on pairwise aggressive interactions was not correlated to any of the production or feeding behaviour variables. No significant effect of group size was found on mean number of attempts to displace other pigs from the feeder. The change in feeding pattern in the largest groups appears to represent an adaptation to the constraint placed on their feeding behaviour and they succeed in adjusting to the lack of feeding space as there were no significant differences between groups in production variables. A correlation between performance and social behaviour may have been disguised by environmental factors such as space allowance and straw provision or, alternatively, aggression and growth may be independent characteristics.

Feeding behaviour of growing pigs using single or multi-space feeders

Most studies of the feeding behaviour of group housed growing pigs have used computerized single-space feeders, which result in a pig:trough ratio which differs from that found on commercial pig farms, where multi-space feeding troughs are used. The present experiment compared the feeding patterns of group housed, growing pigs given access to either a computerized single-space feeder or a four-space feeding trough. Eighty cross-bred entire male pigs (initial live-weight 32.3 ± 0.62 kg; mean ± s.e.) were allocated to groups of ten, and each group given access to one of the two feeder types. The feeding behaviour was measured automatically fro the single-space feeders, and determined for the four-space trough treatment from video tapes, where feeder visits were counted and timed, combined with daily weights of the food eaten per group. Pigs given access to a four-space trough visited the feeder much more frequently (84.5 vs. 14.3 visits day−1; s.e.d. = 5.3; P < 0.001), and for shorter durations (0.67 vs. 4.67 min per visit; s.e.d. = 0.36; P < 0.001), eating only a little per visit (24 vs. 149 g per visit; s.e.d. = 14; P < 0.001) compared with pigs kept in the groups given access to a computerized single-space feeder. High levels of allelomimetic feeding were shown by pigs using the four-space trough, with 61% of all visits initiated whilst one or more pigs were already feeding. Also, a higher proportion of visits were made adjacent to a feeding pig than would have been expected by change (0.59 vs. 0.50; P < 0.001). No significant differences were found between treatment in the rate of feeding or daily feeder occupation. The differences in feeding pattern did not result in differences in production variables in terms of daily feed intake, daily live-weight gain, and feed conversion ratio. A bout analysis was applied to the data using frequency distributions of length of intervals between visits. For pigs using the four-space trough visits could justifiably be collapsed into feeding bouts, whereas this was not the case for visits displayed by pigs using the single-space feeder. Pigs using the four-space trough showed a high frequency (0.64) of changes between spaces within each feeding bout. This may represent exploratory or sampling behaviour, which may aid the pig in obtaining a nutrient-sufficient diet should many different food items be available. Comparing feeding bouts from the four-space feeders to visits from the single-space feeders revealed no differences between the two types of feeders, indicating that single-space feeders constrain the feeding pattern mainly in terms of preventing changes between trough-spaces within bursts of feeding.

Effects of single-space feeder design on feeding behaviour and performance of growing pigs

Computerized food intake recording systems of various designs are used by research, centres and breeding companies to monitor the individual food intake of pigs kept in groups. In the present experiment, three feeder designs are compared in order to estimate the effect on performance and feeding behaviour. Ninety entire male pigs (34 (s.e. 0·6) kg) were allocated in three replicates to pens of 10 pigs; each pen containing one of three different feeder entrance designs: low (head-guard), medium (full-length standard race), and high (enclosed pneumatic race) protection against disturbance of the feeding pig. No significant differences were found between treatments in daily food intake, daily live-weight gain, food conversion ratio, number of visits per day and daily feeder occupation. Pigs with access to an enclosed race had longer visits than pigs on the two other treatments, and they also ate more per visit (4·8, 4·8 and 6·2 (s.e.d. = 0·37) min per visit; 172, 157, and 202 (s.e.d. = 11·1) g per visit; means of low, medium and high protection, respectively). The enclosed race was not only the most protective, it was also the most difficult to enter, and this decreased accessibility of the food may have given rise to the changed feeding pattern displayed by pigs using this type of race. Access to a feeder with low protection resulted in a faster rate of eating (36·9, 33·2, and 32·8 (s.e.d. = 0·82) g/min; means of low, medium and high protection, respectively) indicative of a more forced feeding behaviour.

Effect of individual housing on the feeding behaviour of previously group housed growing pigs

The feeding behaviour of individually housed growing pigs differs significantly from that of group housed animals, with individual penning resulting in shorter, more frequent visits to the feeding trough (De Haer and Merks, 1992. Anim. Prod., 54: 95–104). Substituting group housing by a single housing environments was therefore expected to increase substantially the number of visits to the feeding trough. Three groups of ten cross-bred entire male pigs (initial live-weight 29.3 ± 0.6 kg; mean ± SE) were housed for 14 days (Period 1) with ad libitum access to one computerized single-space feeder per group. Four pigs were chosen from each group; two pigs showing a high feeding frequency (H pigs: 18.9 ± 2.0 visits day−1; mean ± SE; n = 6) and two pigs showing a low feeding frequency (L pigs: 9.5 ± 0.8 visits day−1; mean ± s.e.; n = 6). The L pigs had a higher feed intake per visit (137 vs 82 g per visit; SED = 8; P < 0.001), and a lower daily feed intake (1246 vs 1477 g day−1; SED = 84; P < 0.05) than H pigs. On Day 15, H and L pigs were moved to individual pens identical to the group pens for a period of 14 days (Period 2). This individual housing resulted in only a small increase in the frequency of feeder visits (2.8 ± 0.8 visits day−1, irrespective of the feeding frequency displayed by the pigs during Period 1. The relatively small increase in number of daily feeder visits resulted in a significant increase (P < 0.05) in daily feed intake, leading to no differences between pigs in daily feed intake once individually penned. Pigs showing a low number of daily feeder visits when group housed may have been constrained in terms of daily feed intake as a result of the displayed feeding pattern. In addition, the feeding pattern of growing pigs may be less flexible than expected, and pigs, which have been constrained in their food intake, will make only small modifications to their feeding pattern, sufficient to compensate for the previous constraint. It is likely that growing pigs will adhere to a feeding pattern that has provided them with sufficient food in the past, even when a change in the environment allows for more extreme modifications to occur.

Effects of genotype, feed type and lactational stage on the time budget of dairy cows

The effects of genetic merit, feeding system and stage of lactation on the time budget of dairy cows were studied. Sixteen loose-housed Holstein Friesian cows (parity=1) of either high or UK average genetic merit were fed one of two complete mixed silage-based diets (high and low concentrate inclusion). Five-minute time samples were carried out on 11 days across lactation between morning feeding and afternoon milking. Cows fed the low concentrate diet spent more time eating, more time ruminating whilst standing, and less time lying, especially inactive. Genetic line did not affect the time budget of the cows. Standing and rumination decreased with time from calving, whereas the duration of lying bouts increased during the first 3 months of lactation. In this study the time budget of dairy cows was influenced by food roughage inclusion, and not by the production level of the animal.

Investigation of the relationship between farrowing environment, sex steroid concentrations and maternal aggression in gilts

Maternal oestrogen and progesterone have been shown to be important in the initiation of maternal behaviour. Thirty-three Large White x Landrace gilts, housed in groups during pregnancy, were observed and aggressive interactions recorded. Individuals had jugular catheters implanted 14.5 (s.e. 0.34) days before their expected parturition date (EPD). Five days before EPD gilts were randomly allocated and moved to either a conventional farrowing crate (C; without straw, 16 gilts) or a pen (P; 2.1 x 3.1 m2; with straw bedding, 17 gilts). Blood samples were taken at frequencies determined by the proximity to farrowing onset. Piglets were removed at birth and returned 2 h after placental expulsion. The reaction of each gilt to her piglets was monitored. Gilts savaging piglets were sedated with azaperone (n = 8). There was no overall effect of farrowing environment on oestradiol and progesterone concentrations. The pre-farrowing ratio of progesterone to oestradiol was higher for (P) gilts (0.45 vs. 0.25, (P) vs. (C); S.E.D. 0.085, P < 0.05) as was their overall maximum oestradiol level (3.39 vs. 2.29 ng/ml, (P) vs. (C); S.E.D. 0.39, P < 0.01). In contrast to progesterone, oestradiol patterns varied considerably between individuals. Dominance rank value during pregnancy, but not levels of aggression, correlated positively to pre-farrowing oestradiol concentrations. Treatment with azaperone was not related to farrowing environment, piglet weight or litter size. Azaperone treated gilts showed a higher pre-farrowing oestradiol to progesterone ratio (0.55 vs. 0.29, +/- azaperone; S.E.D. 0.10, P < 0.05), significantly higher levels of oestradiol post-partum (0.7 vs. 0.19 ng/ml, +/- azaperone; S.E.D. 0.20, P < 0.001) and significantly lower levels of aggression during pregnancy (1.68 vs. 2.23 aggressive interactions/h, +/- azaperone; S.E.D. 0.15, P < 0.001). The results indicate that there are no major effects of farrowing environment on sex steroid concentrations. Maternal aggression under these conditions appears to be negatively related to aggression during pregnancy, but this is not reflected in plasma concentrations of sex steroids around parturition.

Effects of calcium deficiency in broilers on the use of outdoor areas, foraging activity and production parameters

The present experiment investigated the effects of a calcium deficient diet on the use of outdoor areas, foraging activity and production parameters in two strains of slow-growing broilers (i657 and a Labresse cross). The birds were housed as day-old in an indoor system of 2 × 8 groups of each 111 birds (11.8 birds/m 2 ). After 6 weeks, the groups were moved to an outdoor housing system of 2 × 8 houses (3 m × 5 m) with free access to outdoor grass-covered areas (9 m × 22 m). The outdoor areas were equipped with two supported sloping roofs and a sandpit. In the outdoor system, the birds were fed one of the two feeds; high (1.1%) or low (0.3%) calcium, ad libitum in a 2 × 2 factorial design with four replicates. In each group, number and behaviour of birds outside were recorded 1 day per week between sunrise and sunset (15 scan samples per group per day) during a 6-week period until slaughter at 84 days of age. The number of birds in the outdoor area and the proportion of these being inactive was unaffected by the treatment. Surprisingly, birds on the high calcium diet showed more foraging activity when outside (P = 0.04), and these birds also consumed more pelleted feed (P = 0.01) and consequently had a larger body weight at slaughter (P = 0.01). Birds on both treatments showed a diurnal activity rhythm and stayed more in the zones closest to and furthest from the house. In conclusion, the deprivation of calcium diminished foraging activity, feed intake and growth rate of the broilers.