21 November 1997


By Jessica Buss

HIGH genetic merit cows need more feed than their lower merit contemporaries to maximise milk production potential, but this can be provided adequately by forage or concentrates without detrimental effects on condition or fertility.

According to Conrad Ferris a researcher at the Agricultural Research Institute of Northern Ireland, Hillsborough, high merit cows on a high forage system gave only 850kg less milk on 1t of concentrates than high merit cows fed 2.9t of concentrates.

Average 305-day lactations were 7950 litres and 8800 litres respectively, with high concentrate fed cows having slightly higher milk quality, supplying an extra 0.16% fat at 4.31% and 0.3% more protein at 3.53%, so increasing milk value.

There were no fertility differences between the two groups, but all high genetic merit cows suffered poor fertility compared with lower merit contemporaries in previous Hillsborough studies, he adds.

Early indications of body condition scores suggest that cows on the high forage diet will finish lactation at 2.4, about 0.3 points lower than high concentrate fed cows. But Dr Ferris believes this is within acceptable levels for high genetic merit cows. Some individuals, however, are below average. These will need to increase condition during the dry period to ensure they are in adequate condition at calving and performance does not suffer in the next lactation.

Although the high concentrate fed cows needed an additional 1.9t of concentrates to provide an extra 850kg of milk, Dr Ferris expects little difference in gross margin a litre for the two groups. The extra forage costs for grazing and silage may prove to equal the extra concentrate costs.

"To provide the high quality silage needed for cows on the high forage system, four cuts were taken, increasing silage costs above those for a two cut system achieving moderate quality silage." And high forage cows were grazed on almost 50% more land to provide a higher grass allowance, says Dr Ferris.

"Cows offered 23kg dry matter of grass leave a lot more behind them – after every second grazing we had to top what was left." They also ate more forage in winter.

"We looked at the two extremes. For some producers with little land it may be more economic to go for a high concentrate system, while for others with a low stocking rate, a high forage system may be more efficient." &#42

Conrad Ferris… forage or concentrate will support the production of high genetic merit cows without adversely affecting body condition or fertility.

Cows were fed…

High forage cows received very high quality silage at 78 D-value in winter and large summer grazing allowances of 23kg dry matter above 4cm (2in). Concentrates were flat rate fed at 5.5kg in winter, and at just 0.5kg at grass to carry a magnesium supplement. Spring grazing started at two hours a day from early April.

High concentrate cows received moderate quality silage in winter at 70 D-value, with 14kg of concentrates and a grass allowance averaging 16kg DM above 4cm (2in) in the grazing season with 4.5kg of concentrate. Turn out by day was later on April 10.

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