### INTRODUCTION

*Zea mays*L), forage rape (

*Brassica napus*L) and a legume, field peas (

*Pisum sativum*L) or Persian clover (

*Trifolium repesinatum*L.) for conservation and grazing. Cost per kg DM of HGF was reportedly lower than the cost of purchased feeds (Chapman et al., 2008a, b). Farina et al. (2013) reported that pasture in association with grazeable plus conserved CFR was more profitable compared to the pasture only system in conventional milking. Farina et al. (2013) defined this system as a complementary forage system (CFS), which combined an area of CFR crop with an area of pasture in 35% and 65% of the farm area. Thus, this grazeable CFS has the potential to increase profitability of a large herd AMS farm compared to pasture-based AMS.

### MATERIALS AND METHODS

*ad hoc*in MS Excel to determine the effect of herd sizes, pasture utilisation and rates of replacement CFR by pasture (i.e. 12 scenarios) on walking distances, MI, MY, and economic losses. Walking distances, estimation of energy loss due to walking, MI, MY and profit/loss due to increased herd sizes are calculated based on information in the literature as follows:

### Calculation of milking interval and walking distances

### Calculation of milk yield loss due to milking interval

### Calculation of milk yield loss due to walking distances and grazing

W = live weight of cows assumed as 600 kg (Farina et al., 2011);

C = 0.0025 constant for cattle;

DMI = dry mater intake from pasture (10 kg/d) excluding supplementary DM assumed as 10 kg (i.e. 50% of the total diet is pasture or CFR; Garcia and Fulkerson, 2005);

D = digestibility of DM (decimal) assumed as 0.7;

H = horizontal equivalent of the distance walked (km) computed as:

T = taken as average of 1.5 in the present study where values can range from 1.0 to 2.0 as terrain varies from level to steep;

SR = current grazing density (cows/ha) which was assumed as 4 and 5 for moderate and high pasture respectively and 5 and 5.7 for 30% CFR in moderate and high pasture respectively (Islam et al., 2013a);

SD = threshold for grazing density (cows/ha) considered the same as SR;

GF = availability of green forage (t DM/ha) assumed as 15.0 (Islam et al., 2013a, b) and 19.7 (Farina et al., 2011) t DM/ha in moderate and high pasture utilisation in AMS. In addition 70:30 pasture:CFR forage availability was calculated based on yield of moderate and high pasture as above and CFR yield of 28.2 t DM/ha (Islam et al., 2012);

M = total distances walked (km) each day from the milking parlour to the paddock and return to the parlour based on average 2 visits/d.

K

_{m}= net efficiency of use of ME, which was calculated from the following equation:

M/D usually referred to as ME content (MJ/kg DM) of a diet or pasture and was calculated from the following equation;

DMD = DM digestibility of pasture assumed as being constant at 70% resulting in M/D being held constant at 10.3 (CSIRO, 2007).

### Relationship between land areas and milk yield or economic loss

### RESULTS

### Effect of herd size on walking distances and milking interval

### Effect of herd size on energy loss attributed to walking and grazing

### Effect of herd size on milk yield and economic loss

### DISCUSSION

### Effect of herd size on walking distances and milk yield

*Bos taurus*cattle use 2 J/m per kg liveweight (speed 0.5 to 1.4 m/s; weight 383 to 430 kg) for walking. According to this calculation, energy cost (per km) for walking only (between the paddock and the parlour) in our study would be 1.2 MJ ME/cow out of total 3.5 MJ ME/cow energy cost. Thus, energy cost for simultaneous grazing and walking per km would be twice (2.3 MJ/cow/km; i.e. 3.5 minus 1.2 MJ ME/cow) the rate of walking only. If it were assumed that the energy required for walking whilst grazing was equivalent to the energy expended for walking (to traffic somewhere as opposed to harvesting), it is likely that the energy expended during foraging would be partitioned equally between the distinct activities of grazing and walking at the rate of ~1.2 MJ/cow/km. Double energy loss in simultaneous grazing and walking compared to walking only can be explained by the energy cost due to biting during grazing. di Marco et al. (1996) reported an increased energy cost with increased biting rate. These energy costs due to simultaneous walking and grazing during foraging as well as due to walking only were instrumental in reductions in MY of cows with increased herd size in AMS.