for a study relevant to the New Zealand dairy industry. The heifers adapted to the cube diet and pen feeding facilities quickly, allowing consistent data collection over the whole study period. The feeding facility and diet enabled good rates of gain (ADG; 0.88 kg/d), slightly higher than the 0.77 kg/d reported for Holstein-Friesian animals of a similar age fed ad libitum on high quality pasture and silage (Macdonald et al., 2005). Average liveweights were similar to those reported for animals of the same age (Macdonald et al., 2005).
Most RFIs ranged from about -1.5 to +1.5 kg/d. This indicated that the most efficient individuals ate 1.5 kg less feed than predicted, and the least efficient individuals ate 1.5 kg more feed than predicted, leaving a difference of 3 kg feed between the most and least efficient individuals. This range in RFI is slightly smaller than those reported in studies with
animals were older and larger than the dairy heifers used in the present study and therefore had higher intakes and greater scope for variation in intakes. The large divergence in RFI in both this and other studies (Table 2.2) indicates that there is potential to improve individual efficiency of feed utilisation. The RFI trait is heritable (h2 = 0.38, Pryce et al., 2012), so selection will contribute to greater efficiency of the whole dairy system either through reduced feed requirements or increased stocking rates.
Large quantities of data were collected from the animals in the facility, making it important to screen data carefully to identify potential errors arising from automated collection of data from electronic ear tags and load cells under feed bins. Criteria for data screening can identify and remove errors, but there must be a balance between removing erroneous data and potentially removing accurate data. Most errors were associated with feed bin weights (e.g., problems with load cell malfunction) rather than animal identification, which has also been reported from similar electronic recording systems (Casey et al., 2005). The criteria used in the present study to screen and sort the data were developed to address these potential errors and were similar to some of the 16 criteria used by Casey et al. (2005) to identify and sort errors from automatically-recorded swine feeder data. Care was taken in this study to ensure accurate data were not removed in this process.
5.2 Feeding behaviour
Feeding behaviour can be affected by the diet, animals, feeding systems, and facilities where measurements are made. In general, the feeding behaviours measured from heifers in the feeding facility were similar to reports from other studies where animals were fed dry/conserved diets in confinement. The average intakes measured in this study (6.86-9.44 kg cubes/d; 5.83-8.02 kg DM/d) were similar to intakes measured in other studies on growing dairy and beef heifers (6.18-8.12 kg DM/d) fed total mixed ration (TMR) diets in confinement (Greter et al., 2008; Kelly et al., 2010). The animals in this study spent, on average, 2.79 h/d feeding, which is similar to other reported values in growing dairy heifers fed a lucerne cube diet (Williams et al., 2011) and also observations in both dairy cow and beef studies with TMR diets (2.83 h/d, Shabi et al., 2005; 2.59 h/d, Montanholi et al., 2010). Most of the animals measured here had 6-7 meals per day, which is similar to other reports (Tolkamp et al., 2000; DeVries et al., 2003b), although animals in Cohort 1 had an average of 12 meals per day. Cohort 1 spent much longer in the facility than the other cohorts and this may have affected their feeding behaviour.
Average meal size (1.4 kg cubes) and meal duration (32 min) in this study were similar to values for dairy heifers and cows fed silage or TMR diets (meal size: 0.9-1.6 kg; meal duration: 24-43 min) (Deswysen et al., 1993; Romney et al., 2000; Greter et al., 2008). The daily feeding rate of 49.4 g cubes/min measured in this study was in agreement with those reported for dairy heifers on a TMR and straw diet (Greter et al., 2008) and lower than the 67.0 g DM/min found in beef cattle (Montanholi et al., 2010), probably because these beef steers were older and larger than the heifers in the present study and thus capable of consuming more in the same period of time.
Feeding behaviour is likely to differ depending on the diet and feeding method, and the use of cubes as a sole diet in this study differs from other evaluations where silage/grain mixtures were fed (e.g., Greter et al., 2008; Kelly et al., 2010; Montanholi et al., 2010). Fibrous feeds are bulky and take longer to consume and digest than less fibrous concentrate-based feeds. For example, cows spent more time (463 vs. 348 min/d) eating long lucerne hay than silage (Brouk & Belyea, 1993). However, when fibrous feeds are chopped, as in this study and others with feeds of short fibre length, a rapid consumption of DM is possible.
The feeding system is likely to affect feeding behaviour, but the need to measure feed intake accurately precluded the use of either grazing or fresh forage feeding. In the current study, one feed bin was shared between eight animals, thus restricting access. Hosseinkhani et al. (2008) evaluated feeding systems with 36 non-lactating cows fed a TMR from either their own bin (one cow/bin) or a shared bin (two cows/bin). Cows that had to share and compete for feed access had an increased feeding rate and ate fewer meals (which tended to be larger and longer) than cows that did not have to share bins (Hosseinkhani et al., 2008). Dry matter intake was not different but daily distribution of that intake differed with competition (Hosseinkhani et al., 2008). Other studies also reported an increase in feeding rate from 43 to 71 g DM/min when cattle that had been fed from individual feeders were fed in groups or when number of feeders was reduced (Harb et al., 1985). The behaviour of animals in the present study was likely to be affected by the feeding system, with faster feeding rates and altered timing of meals due to sharing one feeder between eight animals.
individual animals. When given the choice, cattle often feed in synchrony (Tucker, 2009), so the feeding behaviours observed in systems where they must take turns at the feeder may not be the animal’s preferred behaviour, but rather an adaptation to suit the feeding system. Intake level is often consistent over time, but the feeding pattern to achieve that intake may differ between animals (Nielsen, 1999). For example, Friggens et al. (1998) found a five-fold range in meal size and frequency between cows, and this was even larger in the current study, with a 13-fold range in meal size and a 23-fold range in meal frequency between individuals. This variation in feeding behaviour between individuals allows investigation of relationships between behaviour and other variables, such as RFI and ADG.