with a target DM at ensiling of 25–30%. Grass was ensiled in round bales with no additive applied at ensiling. Following a five-week storage period, silage was offered to a second similar group of 18 cows for 12 weeks. Cows in both groups were offered 8 kg concentrate per day via an out-of-parlour feeding system.
Study result The zero-grazed grass had an average DM content of 15.6%, while the grass silage had an average DM content of 27.3%. The silage had a slightly lower crude protein content than the zero-grazed grass, reflecting loss of protein during ensilage. However, both forages had a similar metabolisable energy and fibre content, indicating that both were harvested at a similar stage of maturity. Intakes of zero-grazed grass were higher than intakes of grass silage, with intakes of silage produced between 30 July and 3 September being especially low, reflecting the challenges of ensiling leafy herbage later in the season. Milk yields followed a similar trend to silage intakes, being relatively unaffected between treatments earlier in the sea- son, but then decreasing more rapidly with the silage treat- ment later in the season. While milk fat content was unaffected by the forage type offered, the types of fat in the milk differed. For example, cows offered zero-grazed grass produced milk with higher concentrations of “healthy” fats (monounsaturated and polyunsaturated fats) than those offered grass silage. In addition, the concentration of conjugated linoleic acid, a fat believed to have anticarcinogenic properties, was higher in milk from cows offered zero-grazed grass. Cows offered zero-grazed grass also produced milk with a higher protein content, likely reflecting improved supply of protein from the rumen bacteria. The fat plus protein yield was higher from cows offered the zero-grazed grass throughout the experiment. Cows offered zero-grazed grass had higher forage DM
intakes, milk yields, milk fat plus protein yields and a higher milk protein content compared to those offered grass silage prepared from the same sward. In addition, these cows produced milk containing “healthier” fats. The differences in intakes and milk yields were particularly apparent later in the season, during August and September, which is likely to reflect challenges of ensiling herbage at this time.
Conclusion Given the current cost of fuel and concentrate feeds, optimis- ing the inclusion of grazed grass in dairy cow diets offers the lowest cost strategy by which to produce milk. AFBI recognised that many farmers continue to demonstrate that well-managed grazing systems can sustain high levels of both physical and economic performance. However, it did say systems with a major focus on grazing are no longer practised on many farms. In these situations the current study has demonstrated that offering zero-grazed grass increased forage DM intakes, milk yield and milk fat plus protein yield, compared to grass silage prepared from the same sward at the same growth stage.
Figure 2 - Average weekly milk yield of cows offered zero grazed grass or grass silage produced from the same sward. 35
30 25 20 15 10
Date of harvest Zero-grazed grass Grass silage ▶ DAIRY GLOBAL | Volume 9, No. 3, 2022 17
Zero grazing could be a bet- ter option when other feed costs increase, de- pending on the cost of harvest- ing and hauling the grass.
18 June 25 June 2 July 8 July 16 July 21 July 29 July
8 Aug 12 Aug 19 Aug 26 Aug 3 Sept
Mil yield (kg/day)
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