Part-time grazing is a good alternative to full-time silage diet of dairy cows. Grazing is also a visible part of ethical milk production. When planned properly, the milk yields of rotationally-grazed dairy cows remain as high at pasture as in indoor feeding.
Auvo Sairanen, M.Sc. (Agriculture & Forestry), Senior Researcher at the MTT Agrifood Research Finland, detected in his doctoral dissertation study that the principles of feeding planning normally used for silage feeding also apply to grazing.
"No particular factor was found in grazing that would significantly differ from silage feeding, as long as the pasture rotation is in order, and the forage value of the pasture is taken into account," he points out.
Dietary experiments provide information of forage digestibility
The objective of the doctoral dissertation was to seek dietary factors that limit the milk yield of grazing cows.
The study included nine different dietary experiments, with concentrate supplement varying from zero to 12 kg provided twice a day as the cows were milked. With the exception of two experiments, the concentrate was of industrial origin. In addition to changing the amount of concentrate supplement, the cows had free access to forage at pasture or an herbage allowance between 19 and 25 kg of dry matter/cow per day. In milk yield experiments, the yield responses to concentrate supplementation were defined, facilitating economic comparison between grazing and concentrate feeding.
One of the experiments looked into the physiological factors of a diet of freshly cut grass in tie-stall conditions. The flow of nutrients was defined by taking samples from the cow's rumen and omasum. By means of nutrient flow it is possible to study the processes inside the cow's rumen in the first place, when the feed contains digestible forage from pasture and a varying amount of concentrate supplement.
In addition to these, the use of part-time grazing was studied as a summer feeding strategy. The control group was in full-time silage feeding indoors.
Sufficient amount of pasture and flat-rate concentrate feeding
The responses to concentrate at pasture were quite similar to those reported in the reference material for concentrate feeding. In numerical terms, the response to silage seems to be somewhat higher at pasture than with exclusive silage feeding, considering the high forage value of the grass from pasture.
"This can only be explained by the fact that, for some reason or another, a cow cannot intake unlimited amounts of forage from pasture. The physiology of the rumen did not limit the intake of forage, so the limitation must derive from pasture management factors. One example of such factors is that cows have to collect their forage from a large area, whereas in indoor feeding forage is served in one point," Auvo Sairanen points out.
Judging by changes in the milk production and live weight of cows, 20 kg of dry matter per day per hectare at pasture is not enough for per cow if the amount of concentrate supplementation is low. However, this low amount of herbage allowance did not cause any health problems. It is therefore economically sensible to increase concentrate feeding and ensure availability of a sufficient amount of forage from pasture. On the basis of the study, 25 kg of dry matter is a sufficient amount of pasture, but to avoid any risks, the amount of forage from pasture can be even higher.
The responses to concentrate remained the same throughout the lactation period, with the exception of the very end of the period. This means that the proportion of concentrate in the diet can be the same during the most part of lactation. At the end of the lactation the percentage of concentrate can be reduced to avoid unnecessary increase in body condition score.
The dissertation is available in electronic format at http://urn.fi/URN:ISBN:978-952-487-525-7.
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