NEWS
Table 1 . The results of this Mann-Whitney U test comparison contrasting the farms with a higher stocking rate to the lower stocking rate farms ( see Table 7 for actual results ).
Table 2 . Significant differences in sustainability parameters between top performing farms and rest of farms .
in milk per litre of milk ( g / l )
• lower pasture utilisation ( tons req ./ tons grown )
• higher proportion of pasture in the overall farm diet and lower proportion of bought and home-grown feed (% contribution )
• lower N application rate ( kg N / ha )
• lower cost of feed ( R / l )
• higher cost of fertiliser ( R / l )
• higher gross margin per litre ( R / l )
• lower gross margin per hectare ( R / ha )
These results are the epitome of why this conversation is so complex . Having a higher amount of pasture available per cow has obvious advantages . Especially in terms of limiting the total cost of production . But two of the results – lower pasture utilisation and lower gross margin per hectare are problematic .
The relationship with stocking rate can be seen here . A higher stocking rate gives you less pasture per animal , but it results in better pasture utilisation . In other words , although there is a lot of pasture available at a lower stocking rate , a lot of this pasture is wasted . The higher stocking rate also means more feed must be brought onto the farm , at a cost , but it results in a higher gross margin per hectare .
Table 3 . Other notable differences in sustainability parameters between top performing farms and rest of farms .
Table 4 . Correlations between stocking rate and various profitability , productivity , and sustainability indicators using data from the Trace & Save research database on all the farms which raise heifers on the farm ( n = 316 ).
Is there an ideal stocking rate ?
Although correlations using a large dataset are insightful and can teach us a lot about the relationship between various factors making up a farm system , it does not always provide absolute clarity on what the best system is . The data we have looked at so far points towards a higher stocking rate being better across most measures , but is there a specific stocking rate which is ideal ?
To further explore this question , let ’ s look at specific farm systems . Since the data so far has indicated that a higher stocking rate is better , I thought to compare all the parameters we have been looking at between the observations with the highest stocking rate ( top 33 % or top 58 farms ) with the rest of the farms with a lower stocking rate . I used the smaller , 176 farm dataset , since these farms are more directly comparable to each other .
These results follow a very similar trend to those shown by the correlation data , but it is interesting to see the actual numbers for each parameter . The advantage of higher stocking rate is re-emphasised here with the higher pasture utilisation , but there is still the disadvantage of lower pasture per cow and lower pasture in the diet . There is also the disadvantage of a higher nitrogen application rate , but the overall cost of
Grassroots Vol 22 No 2 July 2022 16