Are lower milk fat levels a problem?

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The adoption of feed-to-yield systems in which concentrates are offered to individual cows according to their milk yield is now common practice. This often involves farms offering a ‘basal diet’ of silage and concentrates, to support the energy requirements of the cow for maintenance, plus a certain milk yield.

Additional concentrates are then offered to individual cows to support milk yields above those supported by the basal diet. These additional concentrates are often offered at a feed-rate of 0.45 kg of concentrate per litre of milk.

Recent research by Dr Conrad Ferris at AFBI, Hillsborough, examined the impact of ‘feed-rate’ on dairy cow performance. Cows were offered a ‘basal’ ration comprising silage (70% grass silage, 30% maize silage: DM basis) and concentrates (included in the mix to provide an intake of 6.0 kg/cow/day).

In addition, cows were offered further concentrates using out-of-parlour feeders on a ‘feed-to-yield’ basis to support milk yields in excess of those supported by the basal diet. Three feed rates were used, namely 0.35, 0.45 or 0.55 kg of concentrate per kg of milk.

A key finding from the study was that when concentrate feed rate increased from 0.45 to 0.55, there was an unexpectedly large increase in concentrate intakes, and a reduction in silage intake (Table 1). This increase in concentrate intake was accompanied by an increase in milk yield (although not significant), and by a large fall in the fat percentage of the milk.

The impact of higher concentrate feed levels on milk fat content is well known, with Figure 1 highlighting that the milk fat percentage decreased with increasing concentrate level, with this effect being particularly dramatic with concentrate levels above 13 - 14 kg/cow/day. As a consequence, some of the potential economic benefits of these higher yielding cows are lost. Nevertheless, there is currently no ‘farm data’ to support this important finding, nor is there evidence of the impact of these feed levels on cow fertility and health.

To help address this important issue, AgriSearch, in partnership with AFBI, are currently seeking to recruit 30 dairy farmers from across Northern Ireland to participate in a new project to identify factors driving efficiency within feed-to-yield systems.

It is expected that many factors will influence the performance and profitability of cows within feed-to-yield systems. These include silage quality, concentrate composition, concentrate intakes, feeding assumptions adopted, and cow genetics. This project aims to examine how these factors affect the performance of individual cows within feed-to-yield systems, and in particular their effects on milk yield, milk composition, fertility and health.

Farmers interested in participating in this exciting new project can download an application form from the AgriSearch website www.agrisearch.org and return it via email to elizabeth@agrisearch.org or by post to: AgriSearch, Innovation Centre, Large Park, Hillsborough, County Down, BT26 6DR.

If you have any specific queries then contact Elizabeth Earle (AgriSearch) on 028 9268 1514.