Extended grazing delivers feed savings on marginal soils

A study completed in Ballyhaise College examined the impact of extending the grazing season on marginal soil types at two varying stocking rates to quantify the impact on pasture and animal performance, along with the input requirements of a grass-based dairy farming system.

The study, which took place over four grazing years (2017-2020 inclusive), consisted of two grazing season lengths – extended (270 days) and average (205 days) and two stocking rates, which were medium (2.5 cows/ha) and high (2.9 cows/ha). Operating under best practice grazing management, the study was designed to achieve 500, 600, 700 and 800 cow grazing days per hectare per year.

The study revealed that extending the grazing season on marginal soil types can maintain high levels of milk production per hectare across a range of stocking rates, while reducing the requirement for supplementary feedstuffs - such as silage and concentrates - during the lactation period, thus showing the importance of additional efforts to increase grazing days for spring-calving herds operating on poorly-draining and marginal soil types.

Under the study, cows were assigned to one of four treatments; each group had their own farmlet and were managed separately depending on grazing season length and stocking rate over the entire duration of the study. Fertiliser application rates across the four separate farmlets also remained constant over the duration at 250kg N/ha, with slurries evenly applied back based on the grazing season length.

Cows grazing under extended grazing season conditions were turned out to pasture as the calved from mid-February and remained at grass full time until mid-November. On-off grazing was utilised and the number of grazing days was recorded. The only periods when this group was not given access to grass was during periods of inclement weather when on-off grazing could not be practiced. Meanwhile, the average grazing group remained indoors until mid-March and were re-housed again in mid-October.

In terms of meal feeding rates, cows under extended grazing conditions were offered 3kg/head/day of concentrate initially post-calving, until grass supply was sufficient and then it was reduced and removed. Cows on the average grazing season length treatment were offered 5kg/head/day of concentrate at the start of lactation, supplemented with soyabean meal, while indoors on a grass silage diet.

Key results – grazing and supplementary feeding

• Total average annual grass production over the four-year period was 14,133kg +/-538 DM/ha; this was unaffected by grazing season length or stocking rate;
• More grass was grazed under the extended grazing treatment (+758kg DM/ha) when compared to the average;
• More silage was preserved under the average grazing season treatment (+716kg DM/ha) when compared to the extended;
• Less silage (-726kg DM/ha) was preserved under the high stocking rate treatment versus the medium stocking rate treatment;
• Extended grazing cows grazed for 30 days/cow longer when compared to the average – split almost evenly between spring and autumn. On a hectare basis, this is 79 days extra;
• Extended grazing cows consumed less parlour concentrate than the average grazing season cows (597kg versus 646kg). This extra concentrate was consumed during the early spring (+20kg) and early mid-season (+29kg);
• Average grazing season cows also received an additional 47kg DM of soyabean during the period between calving and turnout;
• The average grazing season cows consumed more silage during lactation than the extended grazing season treatment (896kg DM/cow versus 555kg DM/cow);
• Over the entire year, the average treatment consumed 1,859kg DM/cow of silage compared to 1,436kg DM/cow for the extended grazing treatment (includes both dry and lactation periods).

Milk production

In addition to the differences noted in grass, silage and concentrate consumption, the authors also unearthed a number of differences in terms of milk production.

Although the average lactation length (278 days), daily milk yield (17.0kg), fat content (5.15%) and fat yield (0.87kg/cow) were similar across the grazing season lengths and stocking rates, cows turned out to pasture from mid-February (extended) produced milk of higher protein content than those turned out in March (average) (3.93% versus 3.88%), with these higher protein contents maintained throughout the entire lactation. However, no difference was recorded in lactose content (4.06%) or lactation persistency between the extended or average groups. In terms of stocking rate, cows on the higher stocking rate treatment produced milk that was lower in both milk protein and lactose (-0.03% in each case) compared to the medium stocking rate.

The researchers also examined the effects of grazing season length and stocking rate on milk production, with neither having a significant impact on cumulative lactation milk and fat plus protein production per cow, which was 5,039kg and 440kg, respectively. No significant difference was observed in terms of the grazing season length on milk and fat plus protein production per hectare at 13,755kg/ha and 1,188kg/ha, respectively, but the high stocking rate group did produce 1,853kg/ha more milk and 190kg/ha more solids that the medium stocking rate group, which produced 12,828kg/ha of milk and 1,093kg/ha of milk solids.

For full access of the paper titled: Grazing season length and stocking rate affect milk production and supplementary feed requirements of spring-calving dairy cows on marginal soils, co-written by L. Cahill, D. Patton, B. Reilly, K. M. Pierce and B. Horan, click here.