The dip in butterfat levels seen around spring and early summer is associated with turnout onto lush fresh grass, due to a combination of both rumen shock, as cows move from a controlled ration to grazing, and the nutritional composition of fresh spring grass.
When compared to later season fresh grass and silage, spring grass has a different nutritional make up, with high levels of sugar and oils, and low levels of ﬁbre. This can put cows at risk of both depressed butterfats and acidosis.
The composition of spring grass means it is more rapidly fermentable, so it will pass through the rumen rapidly – risking a drop in both rumen pH and butterfat levels.
Butterfat is produced by cows in two ways. The ﬁrst is direct production from dietary sources, such as rumen protected fats.
The second is indirect production, where rumen fermentation of forages and sugars into volatile fatty acids (VFAs) fuels the production of milk fats in the udder. It is important that cow rations are able to support both butterfat production mechanisms.
The ﬁrst step in any plan to manage butterfats at turnout is a greater understanding of the grass in front of your cows. Assess both the quantity and nutrient quality of grazing and focus on supporting the production of butterfats by paying close attention to:
Oil – diets that are high in polyunsaturated fatty acids (PUFAs) can limit butterfat production by preventing rumen microbes breaking down dietary ﬁbre into butterfat precursors.
Fibre (NDF) – grass with low ﬁbre content will pass through the rumen quicker, reducing the opportunity for breakdown into butterfat precursors. This can be hindered further by low dry matter content.
Sugar – high levels of sugar in grass means that it will be rapidly fermented in the rumen, causing a drop in pH and a reduction in the breakdown of ﬁbre into butterfat precursors.
In order to reduce the risk of depressed butterfats following spring turnout, producers should aim to supply cows with a diet that promotes a healthy rumen and high levels of ﬁbre digestion.
This can be achieved by buffer feeding a high-ﬁbre feed source alongside a rumen-protected fat supplement. This will help to slow the digestive ﬂow, as well as optimise rumen conditions, and promote the production of butterfats.